biology AT1

KISS Resources for NSW Syllabuses & Australian Curriculum. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 1 KEEP IT SIMPLE SCIENCE OnScreen Format Biology Year 11 Module 1 Cells as the Basis of Life Usage & copying is permitted only according to the following Site Licence Conditions for Schools A school (or other recognised educational institution) may store the disk contents in multiple computers (or other data retrieval systems) to facilitate the following usages of the disk contents: 1. School staff may print and/or photocopy unlimited copies at one school and campus only, for use by students enrolled at that school and campus only, for non-profit, educational use only. 2. School staff may display the disk contents via computer networks, or using projectors or other display devices, at one school and campus only, for viewing by students enrolled at that school and campus only, for non-profit, educational use only. 3. School staff may allow students enrolled at that school and campus only to obtain copies of the disk files and store them in each student’s personal computer for non-profit, educational use only. IN THIS CASE, THE SCHOOL SHOULD MAKE PARTICIPATING STUDENTS AWARE OF THESE SITE LICENCE CONDITIONS AND ADVISE THEM THAT FURTHER COPYING OR DISTRIBUTION OF KISS FILES BY STUDENTS MAY CONSTITUTE AN ILLEGAL ACT. 4. The KISS logo and copyright declaration must be included in every usage of KISS Resources. 5. NO time limit applies to the use of KISS Resources when used in compliance with these conditions. Please Respect Our Rights Under Copyright Law keep it simple science ® keep it simple science ® KISS Resources for NSW Syllabuses & Australian Curriculum. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 2 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only Cells as the Basis of Life 1. Different Types of Cells c) Biochemical Control... Enzymes What is this topic about? To keep it as simple as possible, (K.I.S.S. Principle) this topic covers: 1. DIFFERENT TYPES of CELLS Eukaryotic & prokaryotic cells. How we know... light microscopes, electron microscopes, x-ray crystallography, isotopic “tracers”. 2. CELL STRUCTURES Main features of plant & animal cells. Organelles... the nucleus, mitochondria, E.R., ribosomes, golgi body, lysosomes, chloroplasts. Structure of membranes. 3. CELL FUNCTIONS a) STUFF GETS IN & OUT Diffusion & osmosis. Active v. passive transport. Endocytosis & exocytosis. Importance of the SA/Vol. ratio. b) FOOD & ENERGY for CELLS Photosynthesis & cellular respiration. What cells need, and need to get rid of. c) BIOCHEMICAL CONTROL... ENZYMES Properties & importance of enzymes. Effects of temperature & pH on enzyme activity. Topic Outline 2. Cell Structures 3. Cell Functions b) Food & Energy for Cells a) Stuff Gets In & Out Eukaryotic & Prokaryotic Plant v. animal Diffusion & osmosis Photosynthesis Properties of enzymes Effects of temperature & pH on enzyme activity Cellular respiration What cells need Active v. passive transport Endocytosis & Exocytosis Importance of SA/Vol. ratio Major organelles visible with light & electron microscopes. Membrane structure Technologies to understand cells Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 3 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. Introduction Comparison: Light & Electron ‘Scopes Light (Optical) Electron Microscope Microscope How the beam of light beam of electrons image focused by focused by magnetic is formed glass lenses fields Magnification generally about up to 10,000,000 X 500 X. (5000 times more Maximum powerful) about 2,000 X Resolution about 0.2 μm about 0.0002 μ m (ability to see max. (1,000 times better fine details) detail) micrometres ( μm) 1 μm = 0.000001(10-6)metre. 1 micrometre is 1/1000 of a millimetre. The Cell Theory The “Cell Theory” is one of the fundamental concepts in Biology. It simply states: • All living organisms are composed of cells or are the product of cells. (e.g. viruses) • All cells are produced from pre-existing cells. The evidence supporting the Cell Theory has come mainly from the use of microscopes to examine living things. Our knowledge of cell structure and function has developed as the technology of microscopes advanced over the last 300 years or so. Initially only light (optical) microscopes were available, but since the 1930’s, electron microscopes have revealed more detail of cell structure and function. How Big Are Cells Anyway? Typical Plant Cell 20-100 μ m Bacterial Cells 0.1 - 5 μ m Typical Animal Cell 5 - 20 μ m SCALE: 100 μ m (0.1 mm) keep it simple science ® Pathologist using a “Light” (or “Optical”) Microscope to view blood cells. University students using a “Scanning Electron Microscope” (SEM). Photo by Daniel Schwen (used under Creative Commons Attribution-Share Alike 2.5 Generic Licence) Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 4 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® 1. Different Types of Cells The first scientific observation of cells was made with a newly-invented (and very primitive) microscope by Robert Hooke (English, 1665). He saw a lot of boxy, identical cells, but soon it was realised that cells occur in many sizes, shapes and types. However, the full details of the different cell types had to wait about 300 years until modern technologies could unravel all the scientific facts. Some of these technologies will be described shortly, but meanwhile, what are the different cell types? Eukaryotic Cells Familiar living things, including fungi, plants & animals, are composed of cells described as “eukaryotic”. (“eu” = true, “karyo” = “kernel” (Greek). Here karyotic refers to the nucleus of a cell) All eukaryotic cells have a distinct cell nucleus containing thread-like structures called chromosomes. The chromosomes hold the genetic information in the form of DNA. Essentially, the nucleus is the “control-centre” of the cell. As well as the nucleus, every eukaryotic cell also contains a variety of other structures built from, or surrounded by, membranes. Collectively, these are called “organelles”. In this topic you will study some details of the important organelles. Any living thing composed of eukaryotic cells may be described as a “eukaryote”. This includes all plants & animals, the fungi and a variety of single-celled creatures such as protozoa & diatoms. Prokaryotic Cells (“pro” = before) In contrast to a plant or animal cell, a bacterial cell is very different. There is NO nucleus with chromosomes. Certain structures are present within the cell, but none are membrane-based. Prokaryotic cells are generally much smaller than any eukaryotic cell for reasons that will be covered later. In an evolutionary sense, the prokaryotes are the more ancient & primitive, while eukaryotes are more advanced & more recent. Archaea & Eubacteria A relatively recent discovery has complicated the simple division between prokaryotes & eukaryotes: it is now known that there are 2 distinct types of prokaryotes. The “Eubacteria” (true-bacteria) have been known for 150 years and were thought to be the full story of prokaryotic cells. In the 1980’s new technology revealed another totally different type: the “Archaea” (means “ancient”) Archaean cells are prokaryotic, but very different chemically to “normal” bacteria. Their lineage dates back perhaps 3.5 billion years! Hooke’s microscope EUKARYOTIC Animal Cell with lots of membrane-based organelles. PROCARYOTIC Bacterial Cell has no organelles bound by membranes. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 5 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Technologies to Understand Cells The Light Microscope Our understanding of cells and their structure & function was initially due entirely to the optical microscope. Here is a brief history: Robert Hooke 1665 Hooke is credited with being the first person to see cells and name them. Using a primitive microscope, he looked at a piece of cork (dead tree bark) and saw tiny “boxes” like the rooms and compartments of a gaol or monastery. (hence “cells”) Anton van Leeuwenhoek In 1676, van Leeuwenhoek used a very simple microscope, but it was equipped with an excellent lens, through which he saw living micro-organisms swimming around in a drop of water. What Hooke saw These are Hooke’s drawings of what he saw in the cork. Van Leeuwenhoek’s sketches of the “animalcules” (microscopic living things) which he discovered. Over the next 150 years, microscopes improved, and it was suspected that cells were present in all living things. Robert Brown, 1827 Brown was the first to discover structures inside cells. He discovered and described the nucleus inside plant cells. By about 1840, the “Cell Theory” was becoming accepted by most biologists, because cells were observed in every organism studied. Louis Pasteur’s discoveries showed that infectious diseases were caused by “germs”, which were microscopic, cellular organisms. Rudolf Virchow, 1859 and Walther Flemming, 1879 Between them, these two German scientists clarified the process of cell division, by which cells produce more cells. This established the principle that all cells come from pre-existing cells. Portrait of Louis Pasteur in his laboratory Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 6 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Technologies to Understand Cells (cont.) The Electron Microscope The electron microscope was invented between about 1926 to 1933. A number of scientists, engineers & companies were involved. For full details you should search a reliable website such as Wikipedia. The first commercial equipment became available about 1938, but because of WWII this technology did not have much scientific impact until the 1950’s. Electron microscopes use beams of electrons, focused by electric & magnetic fields, to form images at magnifications & resolutions far superior to a light microscope. (see slide 3) Objects cannot be viewed by eye, but are displayed on screens, as photos, or captured as digital images in computers. In the sections which follow, you will see examples of images of cells seen by both light microscope and by electron ‘scope. The electron microscope revealed cellular details which hugely increased our understanding of the structure & function of living cells. You need to be aware that there are 2 main types of electron microscope. Each has its own advantages & disadvantages. Transmission Elect. Micro. (TEM) To form a biological image with a TEM the sample has to be dried & fixed into a special resin, then sliced extremely thinly. The electrons pass through the sample so the image is flat and 2-D and shows the fine details of the structures within. TEM images can achieve extremely high magifications & resolution, but the preparation of the specimens is difficult & highly technical. Scanning Elect. Micro. (SEM) A Scanning Electron Microscope image often appears 3-D and can show amazing surface details. This is because the specimen has been coated with a layer of heavy metal (eg gold) only one or 2 atoms thick. The electron beam does not pass through it, but is scattered from it. Computer analysis of the scattering effects generate an image of the surface topography. Any colours are artificial and computer-generated. Modern Electron Microscope Photo by David J Morgan (used under Creative Commons Attribution-Share Alike 2.0 Licence) TEM image of a single bacterial cell. Photo by Peter Highton (used under Creative Commons AttributionShare Alike 1.0 Generic Licence) SEM image of bacterial cells being attacked by a human immune cell. Photo: NIAID (used under Creative Commons Attribution-Share Alike 2.0 Licence) Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 7 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. Technologies to Understand Cells (cont.) Microscopes, both optical & electron, have allowed detailed images of cells and cell parts. However, understanding exactly what is going inside a cell is largely a matter of molecular structures and chemical reactions. The technologies described here will give you a simple over-view of how we have discovered the functioning of cells. keep it simple science ® X-Ray Crystallography We now know that all of the thousands of chemical reactions in a living cell are dependant on, or controlled by, huge biological molecules, especially the proteins & the nucleic acids (of which DNA is the most famous). Furthermore, we know that it is the precise 3-dimentional shape of these “macro-molecules” which is critical to their functioning. (More on this later in this topic.) How can we study the shape of a molecule? Just over 100 years ago, x-rays were discovered and immediately scientists began using x-rays for all sorts of reasons, including medical imaging of broken bones, etc. An Australian father & son team, William & Lawrence Bragg, used x-rays to probe the structure of matter. They beamed x-rays through pure crystals & captured on film the patterns of the scattered rays. They figured out how the diffraction patterns related to the arrangement of atoms within the crystal. They were awarded the Nobel Prize for Physics in 1915. At the time, no-one could predict how important this would be for Biology! Crystal x-ray beam X-rays diffracted by the crystal lattice & form Interference patterns which are captured on the film. Photographic film sensitive to x-rays Unravelling of DNA By the 1950’s it was known that a substance known as DNA was the basis of heredity. Its chemical composition was known, but noone could figure out how it could function as a gene. James Watson (USA) & Francis Crick (UK) (and others) used x-ray scattering patterns from crystallised DNA to discover the now famous double-helix shape. Armed with the chemical analysis AND the shape, Watson & Crick were able to develop a theory for the functioning of DNA. This led to understanding the “genetic code” and later to the “Human Genome Project”. The knowledge gained is now a cornerstone for modern Biology & Medicine. Meanwhile, X-Ray Crystallography continues to quietly contribute more & more knowledge of the shapes of biological molecules, helping us understand how it all works. Part of an x-ray diffraction image of a large protein. Mathematical analysis of this pattern by computer can determine the 3-D shape of the molecule. Photo: Jeff Dahl (used under Creative Commons Attribution-Share Alike 3.0 Licence) Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 8 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. Isotopic Tracers Within each microscopic living cell, thousands of chemical reactions are constantly occurring. Many processes involve a sequence or chain of reactions which need to occur in strict order, each one controlled by huge macromolecules with a precise shape to “grab” chemicals and either ram them together, or tear them apart, then “hand them on” to the next step. How have we been able to unravel such complexity occurring within a pin-point-sized bag of life? Traditional, test-tube chemical analysis does NOT get you very far. Isotopes You should already be aware that all chemical elements occur in 2 or more variant forms called isotopes. The difference is the number of neutrons in the nucleus of each atom. Some isotopes are unstable & may spontaneously emit various radiations... they are “radioactive”. One of the best known examples concerns 2 of the isotopes of carbon: “Carbon-12” “Carbon-14” Example of the “Tracer” Method You should be familiar with the overall chemistry of photosynthesis in plants: carbon + water glucose + oxygen dioxide CO 2 + H 2O glucose + O 2 Now, here is a simple question about this process: Where does the oxygen (O2) come from? Is it the oxygen originally in the CO2 or is it from the H2O? If a plant is exposed to CO2 containing some atoms of a different isotope of oxygen, that isotope will be later detected entirely in the glucose. However, if a plant is exposed to H2O containing some atoms of the different isotope of oxygen, the isotope will be later detected entirely in the oxygen gas released from the plant. Therefore, all the oxygen gas in our atmosphere (which has been released from photosynthesising plants) was originally in water molecules. This experiment has “traced” the pathway of oxygen atoms through the process. This is an extremely simple example of how the “tracer method” can be used to study chemical pathways in living cells. More Technologies to Understand Cells keep it simple science ® 6p+ 6n0 6p+ 8n0 C12 6 C14 6 Since they have the same number of electrons, these atoms are chemically identical and react the same way. However, carbon-14 is radio-active and can be identified by the radiation it emits. This is just a “taste” of some important technologies. If interested, you might research the “Ultra-Centrifuge” (allows parts of cells to be separated), Gas Chromatography (allows separation & identification of the dozens of chemicals in a chain of reactions) and Automatic Sequencing equipment to study DNA and/or proteins. Slide 9 Discusssion / Activity 1 The following activity might be for class discussion, or there may be paper copies for you to complete. If studying independently, please use these questions to check your comprehension before moving on. Cell Types & Technologies Student Name ................................. 1. a) Outline the major differences between eukaryotic & prokaryotic cells. b) For each named living thing, identify it as either eukaryote or prokaryote. (E or P) palm tree ........... mouse ........... anthrax bacteria ............ mushroom ......... 2. What accident of history led to our use of the word “cell” for these “units of life”? 3. a) In general terms, (no numbers required) how does the magnification & resolution of an electron microscope compare to that of an optical (light) microscope? b) What is the meaning of the 2 words underlined in part (a)? c) There are 2 types of electron microscope. Name them, and outline the differences in terms of the pathway of electrons and how you would recognise an image formed from each type. 4. a) Outline what x-ray crystallography is, and what it can tell us about cell structure or function. b) Outline what “isotopic tracing” is, and what it can tell us about cell structure or function. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 10 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. Examining Cells The syllabus requires that you examine a variety of cells; prokaryotic and eukaryotic. Hopefully, you will do some prac.work using a microscope to examine fresh, living cells as well as prepared slides of eukaryotic cells. With a typical school light microscope you might not be able to examine prokaryotes at all. You will probably study TEM & SEM images to become familiar with prokaryotic cells. keep it simple science ® You will probably learn how to use a microscope, look at some cells through it and sketch them. You probably will NOT view bacteria (too small), but might see the following examples. Try to identify all the visible cell parts that you see and label them. cytoplasm nucleus cell membrane Paramecium (unicellular organism) magnified 100X cytoplasm nucleus cell membrane Human Cheek Cells magnified 400X cytoplasm nucleus cell wall Onion Skin magnified 100X Human Blood magnified 400X Learn to sketch inside a circle which represents the “field of view” of the microscope. Sketch only a few of the cells, to scale. Always label your sketches Even at maximum magnification you will probably not see any detail Sketching Cells Through the Microscope Photos Taken Through a Microscope Cross-Section of part of a Plant Stem. Colours are due to staining. SEM photo. Colours are computer enhanced. The red cells are bacteria infecting human tissue. These round cells are in human blood. The rod-shaped cells are bacteria which cause a disease called Anthrax. Colours are caused by using a dye to stain cells for easier viewing. A simple water plant which grows in hair-like filaments. Low magnification, natural colour. Lots more images in the following section 2. Cell Structures Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 11 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Cell Organelles Visible with a Light Microscope Generalised ANIMAL CELL Small Vacuoles (if any at all) Generalised PLANT CELL There are probably no actual cells which looks just like these. Real shapes vary greatly. Cell Membrane Nucleus Cytoplasm Cell Wall on the outside of the cell membrane Chloroplasts which absorb light and make food for the plant Large VACUOLE Differences Between Plant & Animal Cells Plant cells have a tough CELL WALL on the outside of their cell membrane. Animal cells never have a cell wall. Many plant cells contain a large VACUOLE. Animal cells rarely have vacuoles, and if present they are small. Many plant cells contain CHLOROPLASTS. These are green in colour because they contain the pigment chlorophyll. Chloroplasts are the sites of PHOTOSYNTHESIS, where plants make food. Note: not all plant cells have chloroplasts... for example, cells in the underground roots cannot photosynthesise, so do not contain any chloroplasts. The Electron Microscope reveals much more detail than this... next slide. Photo (through a microscope) of a mass of plant cells. The dark blobs are vacuoles of stored food. What else can you identify? Complete Worksheets 1 & 2 after this slide Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 12 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. What the Electron Microscope Reveals The superior magnifying power and resolution of the electron microscope has given us a much more detailed knowledge of the cell and its organelles. The diagram below left shows a plant cell with the added details that the electron microscope has revealed. The extra organelles (labelled in blue) shown are generally NOT visible with a light microscope. Chloroplast internal structure Stacks of flat membranes (grana) contain the chlorophyll. Mitochondrion. Site of cellular respiration. Lysosome Golgi apparatus Vacuole Cell Wall Cell Membrane Nucleus Extra detail revealed. The tiny Ribosomes are often attached to the E.R. Endoplasmic Reticulum (E.R.) A network of membrane structures connected to the nucleus & extending throughout the cytoplasm. Nucleus Nucleolus Cell membrane Golgi Mitochondria Lysosomes Electron Microscope (TEM) view of an animal cell 2 μ m Photo by Itayba (used under Creative Commons Attribution-Share Alike3.0 Unported Licence) keep it simple science ® Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 13 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Cell Organelles... Structure & Function Note that the organelles detailed in the following slides are typically found ONLY in eukaryotic cells. In fact, the presence of these structures defines a eukaryote. Nuclear material “chromatin”. (Chromosomes unwound and spread out) The Nucleus This is the control centre of the cell. Inside the nucleus are the chromosomes containing DNA, the genetic material. There is often a nucleolus present. This is the site for production of RNA, a “messenger” chemical which leaves the nucleus carrying instructions to other organelles. The nuclear membrane has holes or “pores” to allow RNA to exit. This structure helps the organelle do its job more efficiently. Mitochondria (singular: mitochondrion) This is where cellular respiration occurs Glucose + Oxygen Carbon + Water + ATP (sugar) Dioxide The ATP produced by respiration carries chemical energy all over the cell to power all the processes of life. The mitochondria are therefore, the “power stations” of the cell, converting the energy of food into the readily usable form of ATP. Inside a mitochondrion is a folded membrane with many projections (“cristae”). This structure provides a greater surface area, where the enzymes (control chemicals) for respiration are attached in correct sequence for the steps of the process. Inner membrane folded into “cristae” with respiration enzymes attached. Sketch of a Mitochondrion Image of actual MITOCHONDRIA using an Electron Microscope (TEM) Nuclear membrane with pores, for RNA exit Nucleolus for RNA manufacture Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 14 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® More Cell Organelles The Golgi Apparatus is a semi-circular arrangement of membranes which are concerned with packaging chemicals into small membrane sacs (“vesicles”) for storage or secretion. One type of “vesicle” produced by a Golgi Body is the Lysosome. These membrane sacs contain digestive enzymes which can destroy any foreign proteins which enter the cell. Lysosome enzymes also rapidly digest the contents of a cell which has died, so that your body can clean up the remains and replace the dead cell. GOLGI BODY Curved membrane sacs Vesicles pinch-off for storage or secretion Lysosomes form this way Endoplasmic Reticulum (E.R.) E.R. is a network of membranes which form channels and compartments throughout the cytoplasm of the cell. Its function can be compared to the internal walls of an office building which divide the building into “rooms” where different operations can be kept separate so that each does not interfere with others. The E.R. structure provides channels for chemicals and “messengers” to travel accurately to the correct locations, and for chemical production to occur in isolation from other operations. This structure helps cells function Often found attached to the E.R. are the tiny Ribosomes. These are the sites of production of proteins, the main structural and functional chemicals of living cells. RNA “messengers” from the nucleus attach to a ribosome to make the specific proteins that the cell needs. ENDOPLASMIC RETICULUM RIBOSOMES attached to membranes Membranes Membranes enclose channels and “rooms” Nucleus Mitochondrion E.R. membranes coated with ribosomes Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 15 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Chloroplasts Chloroplasts are found only in photosynthetic plant cells. The electron microscope has revealed that the chloroplast is not just a bag of chlorophyll, but has an organised internal structure which makes its functioning more efficient. CHLOROPLAST Double membrane envelope Membrane stacks (“grana”) containing chlorophyll “Stroma” zone Yet More Cell Organelles The “grana” are stacked membrane sacs containing chlorophyll, which absorbs the light energy for photosynthesis. This light-capturing step is kept separate from the “stroma” zone, where the chemical reactions to make food are completed. The Importance of Membranes Except for the tiny ribosomes, all the cell organelles are built from, and surrounded by, membranes. The membranes provide:- • the infrastructure of the cell. • channels for chemicals to move through. • packaging for chemicals which need to be stored. • points of attachment for chemicals (“enzymes”). • control over what moves in or out of each organelle, and in or out of the entire cell. The “membrane-bound” organelles help the cell’s various functions to be carried out with greater efficiency. Having these membrane-based organelles is the defining characteristic of the “Eukaryotic” group of organisms, which includes all plants & animals. Prokaryotic cells (such as bacteria) do have lots of tiny structures inside, but do NOT have any membrane-type organelles, and can only operate efficiently by being very small. TEM Photo by and3k & caper437 (used under Creative Commons Attribution-Share Alike3.0 Unported Licence) 1 μ m Grana Stroma Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 16 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Chemicals in Cells INORGANIC CHEMICALS These include small simple molecules like water (H2O) and carbon dioxide (CO2), as well as mineral ions such as calcium, nitrate, phosphate, chloride, etc. Although these are often considered of lesser importance, you should remember that all living things are 75%- 95% water. The Chemicals That Cells Are Made From ORGANIC CHEMICALS “Organic” chemicals are based on the element carbon, which can form chains, rings and networks and so build the very complex molecules needed to make a living cell. Many are “polymers” made by joining together many smaller molecules to form huge “macro-molecules”. There are four main categories to know about... Next slide. Carbohydrates Proteins Nucleic Acids Lipids Although not specified by the syllabus, it will help greatly if you have some basic knowledge about... Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 17 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® CARBOHYDRATES include the sugars, starch and others. monosaccharides (mono = one, saccharide = sugar) are simple sugars such as glucose C6H12 O6 disaccharides (di = two) are sugars made from TWO monosaccharides joined together, such as “table sugar” (sucrose). polysaccharides (poly = many) are huge molecules made from thousands of sugar molecules joined in chains or networks. Examples are: Starch... made by plants, to store excess sugar. Glycogen... made by animals, to store sugar. Cellulose... made by plants as a structural chemical. The CELL WALL of a plant cell is made from cellulose. Uses of Carbohydrates Sugars are energy chemicals. Glucose is made by plants in photosynthesis, and is the “fuel” for cellular respiration to make ATP to power all cells. Starch & Glycogen are polymer molecules used to store sugars as a food reserve. Starch is the main nutrient chemical in the plant foods we eat. Cellulose & Lignin are polymers of sugar used by plants structurally. Cellulose makes the tough cell wall of all plant cells. Lignin is a strong material used to reinforce the walls of “veins” in plants. Polysaccharide. Small part of a Starch molecule Monosaccharide sugar molecules Disaccharide sugar PROTEINS are the main structural chemicals of organelles, cells, bone, skin & hair. Life is built from protein. Proteins are polymers, made from amino acid molecules joined in chains. Amino acid molecules Part of a protein molecule... a chain of amino acids LIPIDS are the fats and oils. All cell membranes are built from lipid & protein. Lipids are used as a way to store excess energy. Carbohydrates can be converted to fat for storage. NUCLEIC ACIDS (DNA & RNA) are the most complex of all. DNA is the genetic information of every cell. RNA is the “messenger” sent out from the nucleus to control all cell activities. DNA is a huge polymer of sugars, phosphate and “bases” coiled in a double helix shape. ORGANIC CHEMICALS Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 18 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® The Structure of the Cell Membrane The electron microscope and other modern analysis methods have revealed the structure of the membranes which surround a cell and form most of the cell organelles. The membrane is extremely thin; just two molecules thick. The basic chemical unit is a “phospholipid” molecule; a lipid (fat) with phosphate groups attached. Each molecule has two distinct ends; one which is attracted to water molecules (“hydrophilic”) and the other is repelled by water (“hydrophobic”). “Hydro” = water. “philic” = to like. “phobic” = hate / fear. Two layers of phospholipids form each membrane. The molecules cling to each other, and line up with their hydrophilic ends outwards. The water-loving ends are attracted to the watery environment both inside and outside the cell. The hydrophobic ends are repelled from the watery surroundings, and cling together inside the membrane itself. A membrane is like a thin layer of oil floating on water. It is fluid and flexible, but clings together forming an unbroken “skin” on the surface of a cell. The membrane is NOT solid: it is in fact a liquid or “fluid” structure. It is held together by the mutual attractions of the phospholipid molecules. At the microscopic level, these attractive forces are strong enough for the fluid layer to form a barrier between the inside & outside of the cell. Other molecules are embedded in the phospholipid bilayer. They are mostly proteins, many with carbohydrates attached. These other molecules have various functions: • “receptors” for messenger chemicals. • identification markers, so your body knows its own cells from any foreign invaders. • to help chemicals get through the membrane. This concept of the membrane is called the “Fluid-Mosaic Model”: this refers to a liquid structure and the different molecules embedded within it are like the different shapes & colours in a “mosaic” tile pattern. Membrane proteins One phospholipid -philic -phobic MEMBRANE STRUCTURE Outside of cell Inside of cell Double layer of phospholipid molecules Nucleus Golgi Electron Microscope (TEM) view of part of a cell. The double-layer structure of the cell membrane is clearly visible. Complete Worksheets 3, 4, 5 after this slide Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 19 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. Modelling the Cell Membrane A simple model may help you understand the cell membrane a little better. You might make a more sophisticated model in class. If not, you can easily do this at home. You need about 100 “cotton buds”, plastic drinking straw, sticky tape, rubber band. keep it simple science ® Step 1 Line up about a dozen cotton buds in a neat row. Use sticky tape to hold them together in a flat “panel”. Repeat, until you have at least 5-6 “panels” of cotton buds. How the Model Relates to a Cell Membrane 1. Chemical Structure Each cotton bud represents two phospholipid molecules joined tail-totail. In the top photo a texta line has been drawn to emphasise this. The cotton wool represents the hydrophilic “head” of the molecule. The shaft represents the two hydrophobic tails clinging together. 2. Flexibility If you gently manipulate your model, you can see that the entire structure is flexible. Real membranes are thought to be even more flexible and in fact are a liquid structure: the phospholipid molecules cling together, but the wall of molecules can warp & bend without rupturing. 3. Acts as a Barrier, but Some Things Can Get Through Stand your model upright on the bench. Now gently sprinkle a few grains of rice (or similar) onto the cotton wool heads. Notice that the rice sits on top & cannot penetrate your “membrane”. Now sprinkle a few grains above the drinking straws. Your membrane can also let things through! (Be aware that this is a very simplistic model of what really happens!) Step 2 Stack your panels neatly on top of each other so the model becomes more & more 3-dimensional. Between two of the middle panels, place one or two cut pieces of plastic drinking straw. Step 3 Gently wrap a rubber band loosely around your stack of panels. This holds the entire model together so it can be placed upright & gently manipulated. Be gentle & careful or else the cotton buds will tend to begin pointing in all directions & lose their nice parallel pattern. Outside of cell Intside of cell Schematic diagram of a cell membrane, according to the “Fluid Mosaic Model”. Image by Lady of Hats (Mariana Ruiz) Membrane Slide 20 Discusssion / Activity 2 The following activity might be for class discussion, or there may be paper copies for you to complete. If studying independently, please use these questions to check your comprehension before moving on. Cell Structure Student Name ................................. 1. Name the parts labelled a,b,c,etc. in this plant cell. All are visible with a light ‘scope. 2. Match the lists. (connect matching items with an arrow) Cell Organelle Function or Description Mitochondria Makes proteins Endoplasmic Reticulum Makes food using light energy Nucleus Control centre of cell Golgi Apparatus Cellular respiration site Ribosome Packaging of chemicals Chloroplast Network of membranes, internal compartments 3. Underline any organelle in Q2 which is usually only visible using an electron microscope. 4. a) The basic chemical unit in a membrane is a “phospholipid”. What is this? b) In what important way are the 2 ends of each molecule different? (In your answer use “hydrophilic” & “hydrophobic”, and define these words) c) The structure of the cell membrane is described by the “Fluid-Mosaic Model”. In what way is it “fluid”? In what way is it “mosaic”? Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® a b c d e f Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 21 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. 3. Cell Functions a) How Stuff Gets In & Out How Chemicals Pass Through Membranes The cell membrane as the boundary of a cell is a bit like growing a plant hedge as the boundary of a field. It stops the cows and horses getting out, but a mouse, or a lizard, can easily crawl through it. Similarly, a membrane is “semi-permeable”; it prevents most (especially large) molecules getting through, but allows others to pass through easily. Small molecules like water (H2O), oxygen (O2) and carbon dioxide (CO2) pass freely through the membrane like a lizard through a hedge. To understand how this happens, you must learn about the processes of DIFFUSION & OSMOSIS. keep it simple science ® Diffusion Diffusion occurs in every liquid or gas because the atoms and molecules are constantly moving. The particles “jiggle” about at random in what is called “Brownian motion”. (Named for its discoverer Robert Brown, the same man who discovered the cell nucleus.) Imagine a water solution containing a dissolved chemical, but it is NOT evenly distributed... it is more concentrated in one place than elsewhere. As the molecules jiggle about at random, they will automatically spread out to make the concentration even out. This process is called DIFFUSION. To start with, the dissolved material is not evenly distributed. Diffusion causes the dissolved solute to spread out uniformly. High concentration Lower concentration Equal concentration throughout Later In a living cell, there is often a “concentration gradient ” from the outside to the inside of the cell. For example, because a cell keeps consuming oxygen for cellular respiration, the inside of the cell usually has a low concentration of O2 dissolved in the water of the cytoplasm. On the outside, there may be a lot of O2. DIFFUSION DRIVES MOLECULES THROUGH THE MEMBRANES along the concentration gradient. DIFFUSION of SMALL MOLECULES into a CELL If the molecules can cross the membrane, diffusion will cause them to move from higher to lower concentration. Higher concentration outside cell Lower concentration inside Many chemical substances constantly move in and out of a living cell. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 22 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Osmosis Osmosis is a special case of diffusion which occurs when the concentration gradient involves dissolved molecules or ions which CANNOT get through the membrane. The opposite situation can also happen. A cell’s cytoplasm contains many dissolved chemicals. If the outside environment around the cell is more watery (less concentrated in dissolved substances) then osmosis will cause water to diffuse inwards. This can cause cells to “pump up” with water and helps maintain their shape. It can also cause problems for organisms living in fresh water environments. For example, consider a cell which is surrounded by a solution containing a lot of dissolved sugar. The sugar cannot diffuse through the membrane to equalise the concentrations. In such a situation, water (which can go through the membrane) will diffuse toward the high sugar concentration, as if attempting to equalise by diluting the sugar. In this case, the cell will lose water and might shrink and shrivel up. Loss of water by osmosis can be a problem for living things in water environments with high levels of dissolved chemicals such as salt. Sugar cannot get in through the membrane OSMOSIS Water diffuses OUT of cell H2O H2O H2O Dissolved chemicals cannot diffuse out... ...so water diffuses into the cell. This is how plants absorb water into their roots, even when the soil seems almost dry. H2O H2O H2O High concentration of sugar outside cell Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 23 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Observing Diffusion & Osmosis Diffusion You might do one of these activities yourself, or see it demonstrated. Osmosis Your teacher may have a more sophisticated experiment for you to do. If not, this is a simple activity you could do in class or even at home. Cut 2 pieces of fresh celery from the same stick. Trim them to be exactly the same length. If possible, pat dry with a tissue, then weigh each to the nearest 0.1g and record. Place each into a small beaker of water or salt solution, as shown and leave overnight. Fluids (liquids and gases) seem to be able to mix themselves together automatically... “Diffusion”. The explanation is in the Moving-Particle Model of matter. In liquids and gases, the particles are moving around. If 2 different gases or liquids are side-by-side, then the moving particles will automatically mix. Any dissolved molecules will spread out evenly. Is diffusion faster in liquid or gas? What effect would temperature have? Next day, pat each piece dry with a tissue and re-weigh. One piece of celery may have lost a small amount of mass. Compare their lengths. They might not be exactly the same any more. Bend or cut each piece and note the texture and “crispness”. One will be hard and crisp, the other softer and “rubbery”. Try to explain these results on the basis of movement of water (NOT salt!!) in/out of the living celery cells. Gas Jar of air glass separator When the separator is removed, the two gases mix themselves Gas Jar of together. brown gas The food colour spreads out through the water by itself. Without any stirring, it automixes through the water. one drop of food colour dye Water Identical pieces of celery soaked in different liquids for 24 hours. One loses water due to osmosis. Pure Water conc. Salt soln. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 24 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Other Ways Substances Get Through Membranes Passive & Active Transport Diffusion and Osmosis are vitally important for many chemicals (especially water) to get in and out of cells. Diffusion and osmosis happen automatically and without the cell having to use any energy. We say these are “passive transport” processes. What about all the other important chemicals which cannot get through the membrane? Many proteins, carbohydrates and other molecules regularly move into or out of cells. How do they get in or out? Cells have other ways to deliberately move substances across the membrane apart from diffusion and osmosis. The membrane contains special protein channels & mechanisms which can “carry” chemicals through the membrane. These ways to transport materials across membranes require the cell to use energy (ATP from cellular respiration) to move substances. We say these are “active transport” processes. Not only can “active transport” move substances which cannot normally penetrate the membrane, but it can even do so against the concentration gradient. An analogy to this might help: a passive process, such as diffusion, is like water running downhill in a pipe. It happens naturally without any energy expenditure. However, active transport is like using a pump to force water uphill through the pipe. Energy will be required to run the pump to push water against gravity. Some Active Transport Mechanisms Sodium-Potassium Pump One notable example of an active transport mechanism is the “Na-K pump” which is present in every animal cell. Background info: Animal cells are the only cell type with NO cell wall. This means that if they swell up tightly with water (become “turgid”) they are in danger of bursting open. In contrast, a plant cell has a tough, rigid cell wall. If a plant cell becomes turgid there is little danger of bursting... plants habitually keep their cells turgid to support their leaves, etc. The Na-K pump is like an air-lock system with 2 doors, but only one door can ever be open at any one time. By oscillating between these 2 “doors” the mechanism actively pumps sodium ions (Na+) OUT of the cell and potassium ions (K+) INTO the cell. This allows the cell to maintain an “osmotic pressure” which prevents it absorbing excess water and bursting. Note how the “2-door system” requires ATP (the energy chemical made in the mitrochondria) to power it... it is “active” transport. As well as maintaining osmotic pressure in every animal cell, the Na-K pump is essential for the sending of nerve signals, for kidney function & many other body processes. Outside of Cell Inside of Cell Concentration maintained Schematic of the Na-K Pump Image by Lady of Hats (Mariana Ruiz) As well as the Na-K pump, there are other “channel-based pumps” which move specific chemicals through the membrane. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 25 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Endocytosis (“endo” = into / inside, “cyto” = cell, “-sis” implies a process) Another, quite different mechanism involves a number of related processes collectively known as “endocytosis”. To keep it as simple as possible (KISS Principle) this involves the membrane pinching outwards to surround the desired substance and envelop it. The membrane then rejoins to itself to seal the cell, leaving the target substance inside, sealed in a small vacuole or “vesicle”. Phagocytosis (“Phago” = eating, “cyto” = cell) is a version of endocytosis which takes solid particles into a cell. The best known occurrence involves a type of white blood cell called a “phagocyte” (literally an “eating cell”) which absorbs infectious germs, dead cells & fragments. Once inside the phagocyte the encapsulated solids are destroyed & digested by a cocktail of enzymes. This is also the mechanism which many single-cell organism eat food particles. Image by Lady of Hats Pinocytosis (“Pino” = drink) is a version of endocytosis by which cells take in a small parcel of fluid, including any dissolved chemicals. Receptor-Mediated Endocytosis is another variation which can target specific chemicals which the cell needs to absorb, such as hormones or specific types of protein. The “targetting” is achieved by receptor molecule s embedded on the outer surface of the membrane in a shallow “coated pit”. A receptor can recognise (by shape) the target molecules & “lock-on” by forming a loose chemical bond. Once the receptors are “loaded”, the membrane is stimulated to encapsulate the pit into a vesicle taken inside the cell. Later, the vesicle membrane is dissolved to release the absorbed chemical, possibly after being transported to the appropriate cell location which needs the target substance. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 26 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Exocytosis (“exo” = outside) As well as moving substances into the cell, there are many substances which need to be moved out of the cell. “Secretion” refers to chemicals being released by a cell for some useful purpose. For example, the cells of your salivary glands secrete saliva into the food while you chew it. This moistens the food for easier swallowing, but also begins digesting the food with a digestive enzyme in the saliva. Nerve cells secrete a “neurotransmitter” chemical across the nerve synapse to make the nerve signal carry on into the next neuron cell. Chemicals destined for secretion are often packaged inside small vacuoles by the golgi body organelles. The actual secretion process occurs rather like endocytosis running in reverse. (However, in full technical detail there are significant differences.) “Excretion” refers to the removal of unwanted, possibly toxic, waste materials. These may be encapsulated in small vesicles to protect the inside of the cell from possibly dangerous substances. The actual removal of these wastes follows the same pathway as for secretion... the process of exocytosis. Both Endocytosis & Exocytosis, in all their variations, require the cell to use energy... they are ACTIVE TRANSPORT processes. The energy is supplied in the form of ATP, manufactured in the mitochondria by cellular respiration. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 27 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Length of one side = 1 unit Length of one side = 2 units Length of one side = 3 units Importance of the Surface Area to Volume Ratio Why are cells so small? The answer requires a mathematical study... Length of one side = 4 units Consider this series of cubes of increasing size: Surface Area: Six squares, each 1x1 SA = 6 sq.units Volume = 1x1x1 = 1 cu.unit SA = 6 vol Surface Area: Six squares, each 2x2 SA = 24 sq.units Volume = 2x2x2 = 8 cu.unit SA = 3 vol Surface Area: Six squares, each 3x3 SA = 54 sq.units Volume = 3x3x3 = 27 cu.unit SA = 2 vol Surface Area: Six squares, each 4x4 SA = 96 sq.units Volume = 4x4x4 = 64 cu.unit SA = 1.5 vol What’s this got to do with cells? The amount of food, oxygen or other substances a cell needs depends on its volume... the bigger the cell, the more it needs according to its volume. But, all cells have to get whatever they need in through their cell membrane, and the size of the membrane is all about surface area. As any cell gets bigger, it becomes more and more difficult for it to get enough food, water and oxygen because its SA/Vol. ratio keeps shrinking. Getting rid of waste products also becomes more difficult. Large cells are impossible... all single-celled organisms are microscopic, and all larger organisms are multi-cellular. The only way to be big is to have lots of small cells. Notice that as the cubes get larger: • Surface Area increases, and... • Volume increases, but... • SA / Vol Ratio DECREASES, because the volume grows faster than the surface area. This pattern is the same for any shape... as any object gets bigger, the ratio between its Surface Area and its Volume gets smaller. Cells must feed their Volume, through their Surface Area What is true for cells, is also true for membrane-based organelles. It is better to have many, small mitochondria rather than a few larger ones. A larger mitochondrion has a lower SA/Vol. ratio. It will be less efficient at absorbing glucose & oxygen & getting rid of wastes, and exporting ATP to where it is needed. In a cell which uses a lot of energy (eg muscle cell) it is always found that there are a multitude of small mitochondria, never just a few very large ones. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 28 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Why are Prokaryotes so Small? Now we will try to answer a question which arose near the very beginning of this topic. Typically, a prokaryotic cell (eg bacterium) is only about 1/10 the size of an average animal cell, or even less in many cases. In this photo we can only see a small part of the human cell... it is 100 times larger than the 2 bacterial cells. There are 2 things to consider to understand why prokaryotes are so small: Organelles The presence of membrane-based organelles in eukaryotes makes all their functions much more efficient. Organelles allow the cell to carry out specialist functions in an enclosed space with all the control chemicals (enzymes) in place. The chemicals involved in a process are concentrated together where needed and other cellular processes cannot interfere with whatever the organelle is doing. SA / Vol. Ratio Without any membrane-based organelles, a prokaryotic cell is inherently far less efficient. The only way it can thrive is to be as efficient as possible by having a high SA/Vol. ratio. This can only be achieved by being very small. Therefore, all prokaryotic cells are relatively small. Get it? SEM image of bacterial cells being attacked by a human immune cell. Photo: NIAID (used under Creative Commons Attribution-Share Alike 2.0 Licence) How Stuff Gets In & Out... a Summary When you think about substances moving through a membrane, there are 3 factors to be considered: SA / Vol. Ratio This ratio basically determines whether a cell (or organelle) is able to transport enough materials in & out across the membrane to meet its needs. You now know that the smaller the cell is, the higher the ratio, so the more likely it is to achieve sufficient supply of nutrients and removal of wastes. Be aware that this is NOT entirely about size... shape matters as well. Elongated, irregular shapes with lots of folds & projections have higher ratios than compact, regular shapes like a sphere. Concentration Gradient For substances which can cross a membrane by passive transport (diffusion & osmosis of water) the difference in concentration of the substance inside the cell compared to its concentration on the outside is another important factor. The bigger this difference, or “concentration gradient”, the faster will be the rate of diffusion. The Nature of the Substance Finally, the nature of the chemical substance itself can have a big effect. For example, think about oxygen, a small molecule which can pass through the membrane easily. If there is a large concentration gradient, its rate of diffusion through the membrane can be so fast that this can partly compensate for a poor SA/Vol ratio. Conversely, dissolved ions or large proteins must rely on active transport to cross the membrane. In this case, not only is the SA/Vol ratio involved, but also the rate at which the cell can supply energy to drive the “pump”, or endocytosis cycle, or whatever active process is involved. Complete Worksheet 6 after this slide Slide 29 Discusssion / Activity 3 The following activity might be for class discussion, or there may be paper copies for you to complete. If studying independently, please use these questions to check your comprehension before moving on. Stuff Gets In & Out Student Name ................................. 1. Membranes are described as “semi-permeable”. What does this mean? Give examples. 3. Explain the difference between Diffusion & Osmosis using the phrase “concentration gradient”. 4. a) What is the difference between “active” & “passive” transport? b) To which category do diffusion & osmosis belong? c) In general terms, what are “endocytosis” & “exocytosis”? How are they different? 5. As any shape gets larger, what happens to its: a) surface area? b) volume? c) SA/Vol ratio? b) How does this relate to living cells and why they are always microscopically small? Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 30 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® 3. Cell Functions b) Food & Energy for Cells Autotrophs & Heterotrophs (auto = “self”, hetero = “other, not self”, troph = “to eat, feeding”) An autotroph is an organism that makes its own food. All plants are autotrophic, making their own food by photosynthesis. A heterotroph cannot make its own food and must eat complex, high-energy compounds made by other living things. All animals are heterotrophic, and so are the fungi and most bacteria. A heterotrophic animal eats plants or other animals which have eaten plants, and so on according to the food chain involved. Photosynthesis in Plants All plants make their own food from the simple, low-energy raw materials water (H2O) and carbon dioxide (CO2) using the energy of sunlight, to make the high-energy sugar glucose (C6H12 O6), with oxygen gas (O2) as a by-product. light Phase 1 In the grana, chlorophyll absorbs light energy and uses it to split water molecules into hydrogen and oxygen. The oxygen is released. PHOTOSYNTHESIS in the CHLOROPLAST Phase 2 In the stroma, a cycle of reactions builds glucose from CO2 and the hydrogen from the water. Summarising photosynthesis with this brief equation is very deceptive. Photosynthesis actually occurs as a complex series of chemical steps inside the chloroplast. There are 2 main stages, which take place in different parts of the chloroplast, as summarised below. WATER + CARBON GLUCOSE + OXYGEN DIOXIDE chlorophyll light energy The energy of light is absorbed by chlorophyll, the green pigment in the leaves of plants. high-energy sugar (food) from soil from air released to air Water & CO2 are low-energy chemicals 6H 2O + 6CO2 C 6 H12 O 6 + 6O 2 The energy of the light is being stored as chemical energy in the glucose molecules Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 31 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® How Organisms Use Energy Everything that an organism does requires energy. Organisms:- Move Grow new cells & Repair body tissue Reproduce Seek, Eat and Assimilate their food Respond to happenings around them Keep their bodies warm Cellular Respiration is the process which releases the energy stored in food. It takes place in every living cell on the planet and after photosynthesis is the next most important biological process on Earth. Although the process can be written as a simple chemical reaction, this is very deceptive. Cellular respiration actually takes place as a sequence of about 50 chemical steps... this equation is merely a summary of the overall process. Don’t forget that the essential product of respiration is the energycarrier “ATP”. The CO2 and H2O are merely waste products to be recycled in the ecosystem like all chemicals. Each 1 molecule of glucose results in the production of up to 38 molecules of ATP. A common misconception is that plants do PHOTOSYNTHESIS and make food, while animals do RESPIRATION to use the food. It’s true that plants do photosynthesis and make (virtually) all the food on Earth, but respiration is carried out by all living things... animals AND plants. Luckily for us animals, the plants carry out enough photosynthesis to feed themselves AND produce a surplus to feed us as well. C 6 H12 O 6 + 6O 2 6CO 2 + 6H 2 O ADP+P energy transfer ATP Cellular Respiration More About ATP ATP stands for “adenosine tri-phosphate”. The molecule can be represented by this simple diagram: The bond holding the 3rd phosphate group contains a lot of chemical energy. ATP will readily transfer the 3rd phosphate group to other chemicals (with help from an enzyme). When this occurs, energy is transferred which can force other reactions to go. P P P Adenosine 3 phosphate groups High-energy bond The molecule now has only 2 phosphate groups, so it is called “ADP”. ATP is the “energy currency” of a cell. It can transfer energy to power any process. Then, the ADP goes back to a mitochondrion and is “re-charged” when energy from glucose (via cellular respiration) is used to join another phosphate group on to make ATP again. P P P ADP=adenosine di-phosphate Energy transfer when P-group is detached Glucose + Oxygen Carbon + Water (sugar) Dioxide ATP The process transfers energy to Major energy compound in foods in air Waste products Energy-carrying chemical used in all cells to power life processes. Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 32 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® As you have learned previously, in all ecosystems there is a constant input and flow of energy via the food chains, while the chemicals such as H2O, O2, and CO2 simply get re-cycled over and over. The Most Important Process on Earth Photosynthesis makes virtually all the food on Earth, for all living things. It also makes all the oxygen in the atmosphere for us animals to breathe. For these two reasons, photosynthesis has to be considered the most important biological process on the planet. Photosynthesis & Cellular Respiration What is really happening is ENERGY FLOW through the food chains of an ecosystem. Photosynthesis captures the energy of light and stores it in a high energy food compound like glucose. Cellular respiration releases that stored energy in the form of ATP which can power all cellular and life activities... growing, moving, keeping warm etc. Light energy MITOCHONDRIA - site of cellular respiration GLUCOSE + OXYGEN ATP CHLOROPLAST - site of photosynthesis CARBON DIOXIDE + WATER You will have noticed that these two vital processes, when written as summary equations, are exact opposites. This is really not true because the precise chemical pathway of one process is NOT the opposite of the other. They both follow complex, multi-stage, quite different pathways. Complete Worksheet 7 after this slide Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 33 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® What Happens to Glucose in a Plant? If photosynthesis only makes glucose, where do all the other biological chemicals in a plant come from? Glucose is a monosaccharide sugar, a member of the carbohydrate group. It is easy for a plant to convert glucose into other types of carbohydrate. GLUCOSE molecules joined in pairs joined in 1000’s (polymerisation) Other sugars, such as sucrose CELLULOSE for building new cell walls STARCH for storage of food In fact, plants convert glucose to STARCH so rapidly that the cells in a plant leaf become packed with starch grains when it is photosynthesising. THIS IS THE BASIS OF EXPERIMENTS YOU MAY HAVE DONE (See next slide) Glucose can also be converted chemically into lipids... fats and oils, since they contain exactly the same chemical elements (carbon, hydrogen & oxygen only - CHO). GLUCOSE LIPIDS (oils) Making proteins and nucleic acids is more difficult, since these contain additional chemical elements, especially nitrogen, phosphorus and sulfur. This is where the “minerals” such as nitrate, phosphate and sulfate come in. Soil minerals are often called “plant nutrients”, and a gardener may say he/she is “feeding” the plants when applying fertiliser, but these minerals are NOT food. They are the essential ingredients needed so plants can make proteins and DNA etc, from the real food... glucose. GLUCOSE Polymerisation Amino acids PROTEIN Amino acids chemical conversion Soil minerals nitrate, sulfate, etc Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 34 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. Experiments with Photosynthesis The classic experiment you have probably done, is to partly cover a leaf with light-proof aluminium foil, and then expose it to light for several days. The aim is to prove that light is necessary for photosynthesis. Light Iodine test shows lots of starch here No light, no starch After several days, the leaf is decolourised (so the test can be seen more easily) and then tested with IODINE solution. Why Iodine? It detects STARCH, not glucose. As explained before, the glucose produced by photosynthesis is immediately converted to starch. The iodine test is used because it is the test for starch. Sure enough, you probably found that any part of the leaf exposed to light turned black when soaked in iodine, while parts under the foil did not go black. This shows that any part of a leaf allowed to photosynthesise will build up a store of starch from the glucose it makes. The first product of photosynthesis is glucose, but it is rapidly converted to other things. Experimental Set-up Result Aluminium foil keep it simple science ® Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 35 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Summary: What Cells Need Plant Cells eukaryotic autotrophic Light for photosynthesis Cell Requirements ENERGY SIMPLE CHEMICALS WASTE REMOVAL NEEDS Animal Cells eukaryotic heterotrophic Complex, high energy carbohydrates (or lipids & proteins which can be converted) made by other organisms Bacterial Cells prokaryotic Varied. Some are autotrophs requiring light. Others are “chemotrophs” requiring certain inorganic chemicals (eg SO2 ) as energy sources. Many are heterotrophs which feed on plant/animal wastes. Somes weirdos can feed on chemicals such as petrol. H2O & CO2 (photosynthesis) O2 (cellular resp.) A range of simple inorganic “minerals” (ions) including nitrates, phosphates, sulfates, calcium, magnesium, etc. In daylight, surplus O2 is “excreted” by simple diffusion from cells, then to the air via stomates. Plants such as mangroves may need to excrete excess salt by active transport from specialist cells. Most animals cannot tolerate a build-up of CO2. Individual cells excrete it by simple diffusion, but then a specialist system involving blood transport, lungs or gills, etc. is needed to remove it from the body. Another critical toxic waste is urea (from protein metabolism) excreted in urine via the kidneys, or similar. Waste products can be CO2, methane, metal sulfides, lactic acid, etc. depending on exactly how each species gets its energy. However, since all prokaryotes are singlecelled, excretion is carried out by simple diffusion, or by active transport across the cell membrane. All need H2O Beyond that, the needs are highly varied. Many require O2, but others are poisoned by it. Photosynthetic types need CO2, while some need SO2 or CO2 & H2 for chemosynthesis. All have a need for simple ions like calcium, potassium or iron, but precise details vary. H2O O2 A range of “minerals” & “vitamins” which are generally supplied in a “balanced diet”. (What this means varies from one species to another) Slide 36 Discusssion / Activity 4 The following activity might be for class discussion, or there may be paper copies for you to complete. If studying independently, please use these questions to check your comprehension before moving on. Food & Energy for Cells Student Name ................................. 1. a) In plants, photosynthesis occurs in 2 stages, in different parts of a chloroplast. Outline these 2 stages and precisely where each occurs. b) How many molecules of water & CO2 are required to produce one molecule of glucose? 2. When you look at the summary chemical equations for photosynthesis & cellular respiration, they seem to be exactly opposite processes. Comment on this statement. 3. Describe the ATP ADP cycle & explain why ATP can be considered as the “energy currency” of a living cell. 4. Compare & contrast what exactly is needed to supply energy to an autotroph compared to a heterotroph (assume eukaryotic cells). Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 37 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Metabolism is Chemistry Everything that happens inside a living cell is really a matter of chemistry... “metabolism”. For example... • For your body to grow, cells must divide and add more membranes, cytoplasm and organelles. This involves the chemical construction of new DNA molecules, new phospholipids for membranes and so on. • All these chemical reactions require energy. Energy is delivered by the ATP molecule, itself the product of a series of chemical reactions in the mitochondria... cellular respiration. All of these reactions are “metabolism”: the sum total of all the thousands of chemical reactions going on constantly in all the billions of cells in your body. Enzymes Every reaction requires a catalyst... a chemical which speeds the reaction up and makes it happen, without being changed in the process. In living cells there is a catalyst for every different reaction. Biological catalysts are called enzymes. • Enzymes are protein molecules. • Each has a particular 3-dimensional shape, which fits its “substrate” perfectly. • Enzymes are highly “specific”. This means that each enzyme will only catalyse one particular reaction, and no other. • Enzymes only work effectively in a relatively narrow range of temperature and pH (acidity). The Importance of Shape Many of the properties of enzymes are related to their precise 3- dimensional shape. The shape of the enzyme fits the “substrate” molecule(s) as closely as a key fits a lock. This is why enzymes are “substrate-specific”... only one particular enzyme can fit each substrate molecule. Each chemical reaction requires a different enzyme. Changes in temperature and pH (acidity) can cause the shape of the enzyme to change. If it changes its shape even slightly, it might not fit the substrate properly any more, so the reaction cannot run as quickly and efficiently. This is why enzymes are found to work best at particular “optimum” temperature and pH values. Various Different Substrate Molecules Only this one fits Enzyme molecule Enzyme shape at optimum pH and temperature Shape changes slightly at different pH or temp. Substrate... ...no longer fits enzyme 3. Cell Functions c) Biochemical Control... Enzymes Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 38 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Polymerization Polypeptide chain Product released from enzyme Substrate molecules are chemically attracted to the enzyme’s active site Protein, with precise 3-D shape... Substrate molecules brought together and react with each other Amino acid molecules Twists & folds ...becomes an ENZYME molecule Enzyme’s “Active Site” has a shape to fit the substrate(s) exactly ENZYME ENZYME ENZYME can react with more substrate From Amino Acids to Enzyme to Metabolic Control Precisely folded protein is an enzyme This schematic diagram outlines how an enzyme is made & how it can control a metabolic reaction in a cell. ATP supplies the energy needed Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 39 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® Temperature 1/time taken for reaction (rate) You may have measured the rate of a chemical reaction being catalysed by an enzyme, such as: • the rate of milk clotting by junket tablets. • the rate of digestion of some starch by amylase. • the rate of decomposition of hydrogen peroxide by “catalase” enzyme. Enzyme Activity Graphs You may do experimental work to measure the “activity” of an enzyme under different conditions of temperature or pH. A common way to measure the rate of a reaction is to measure the time taken for a reaction to reach completion... the shorter the time taken, the faster the reaction. This is why the reciprocal of time taken (1/time) is used as the measure of rate of reaction. The Effect of Temperature When enzyme activity is measured at different temperatures, the results produce a graph as below. Explanations As temperature rises the rate increases because the molecules move faster and are more likely to collide and react. All chemical reactions show this response. However, beyond a certain “peak” temperature, the enzyme’s 3-D shape begins to change. The substrate no longer fits the active site so well, and the reaction slows. If the temperature was lowered again, the enzyme shape, and reaction rate could be restored. If the temperature reaches an extreme level, the distortion of the enzyme’s shape may result in total shut-down of the reaction. The enzyme may be permanently distorted out of shape, and its activity cannot be restored. We say the enzyme has been “denatured”. Experimental Points Not all enzymes will “peak” at the same temperature, or have exactly the same shape graph. In mammals, most enzymes will peak at around the animal’s normal body temperature, and often work only within a narrow range of temperatures. An enzyme from a plant may show a much broader graph, indicating that it will work, at least partly, at a wider range of temperatures. An enzyme from a thermophilic bacteria from a hot volcanic spring will show a totally different “peak” temperature, indicating that its metabolism will perform most efficiently at temperatures that would kill other organisms. 0 20 40 60 80 100 Temperature (oC) Reaction Rate Mammal Enzyme Plant Enzyme Thermophilic bacteria enzyme Optimum Temperature of Enzymes Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 40 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® The pH Scale The acidity or alkalinity of any solution is measured on a numerical scale known as “pH”. On the pH scale, anything which is neutral (neither acid nor alkaline) has a pH = 7. The inside environment of a cell, and most parts of an organism’s body, is always very close to pH 7... i.e. neutral. An exception is in the stomach where conditions are strongly acidic. (approx. pH 2) 3 4 5 6 7 8 9 10 11 Neutral increasing acidity increasing alkalinity The shape of the pH graph is usually symmetrical on either side of the “peak”. The explanation for the shape is as follows: At the optimum pH the enzyme’s 3-D shape is ideal for the substrate, so reaction rate is maximum. At any pH higher or lower than optimum, the enzyme’s shape begins to change. The substrate no longer fits, so activity is less. At extremes of pH, the enzyme can be 2 3 4 5 6 7 8 9 10 denatured and shows no activity at all. pH 1/time (rate) Enzyme Activity Enzyme Activity 1 2 3 4 5 6 7 8 9 10 11 pH Intra-cellular enzyme Pepsin. (Stomach enzyme) The Effect of pH When the temperature is kept constant and an enzyme tested at various pH levels, the results will produce a graph as shown. Generally, all intra-cellular enzymes (i.e. those from within a cell) will show peak activity at about pH = 7, very close to neutrality. The digestive enzyme “pepsin ” from the stomach shows an optimum pH about 2 or 3, meaning that it works best in the acidic environment. Complete Worksheets 8, 9, 10 Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Slide 41 Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ® The “Bottom Line” for a Cell to Thrive Now that you know some basics about enzymes, we can end this topic by discussing just why animals (and people) can die in a “heat wave” (or a blizzard), why pouring vinegar on weeds kills them and why it is so important to get rid of the CO2 your cells are constantly producing while making their vital ATP. Temperature Impacts on Cells To stay alive, a human’s body temperature must be close to 37oC. If it varies by more than about 4oC either side of this, it is life-threatening! Now you can figure out why. Impacts of Changing pH Likewise, the pH of your cellular & body fluids (eg blood) is also critical for your survival. Same reason... if the pH goes up or down by just 0.5 of a pH unit some critical enzyme molecules will change their 3-D shape & might not fit their substrate properly. This could slow down, or stop, some vital biochemical pathway. This is why it is (for example) very important to get rid of the CO2 you constantly produce in your hundreds of billions of cells busily making ATP by cellular respiration. The problem with CO2 is not that it is “poisonous” in some vague, mysterious way. Specifically, its danger is pH change! When CO2 dissolves in your blood beyond certain concentrations, it increases acidity. This can quickly lead to “acidosis” in your body fluids which can kill you (by malfunction of vital enzymes) within minutes. Temperature 32 37 42 Enzyme Activity Somewhere in your cells there are critical chemical pathways controlled by enzymes with very narrow activity curves, as shown by this graph. These pathways might be in one of the many steps in cellular respiration in all your mitochondria. Maybe it’s an enzyme involved with exocytosis of a neuro-transmitter which passes nerve signals from one nerve cell in your brain to another. Whatever it is, it is vital to your survival. Now look at the graph: If your body temperature drops to 32o, or goes above, say, 40o, this enzyme will STOP FUNCTIONING. This could stop ATP production, or stop nerve signals in your brain. Either one could stop your heart! Body temperature & pH are critical to survival because vital enzymes can only perform efficiently in a narrow range of temperature and/or pH. Slide 42 Discusssion / Activity 5 The following activity might be for class discussion, or there may be paper copies for you to complete. If studying independently, please use these questions to check your comprehension before moving on. Enzymes Student Name ................................. 1. What is meant by “metabolism”? 2. a) Enzymes are said to be “substrate specific”. What does this mean? b) Explain how the shape of an enzyme molecule is linked to this specificity. 3. Sketch the shape of the graph of enzyme activity plotted against: a) temperature. b) pH. Act. Act. temp pH 4. How is the shape of these graphs connected to enzyme shape? Biology Module 1 “Cells as the Basis of Life” Format: OnScreen copyright © 2005-17 KEEP IT SIMPLE SCIENCE www.keepitsimplescience.com.au Usage & copying is permitted according to the SITE LICENCE CONDITIONS only KISS Resources for NSW Syllabuses & Australian Curriculum. keep it simple science ®