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What does a nucleus do?
It contains genetic material and controls the activities of the cell
What does cytoplasm do?
It's a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions
What does a cell membrane do?
It holds the cell together and controls what goes in and out
What do mitochondria do?
These are where most of the reactions for aerobic respiration occur. Respiration transfers energy that the cell needs to work
What do ribosomes do?
This is where protein synthesis takes place - where proteins are made in the cell
What do cell walls do?
They are made of cellulose and they support and strengthen the cell
What does a vacuole do?
It contains cell sap and helps maintain the shape of the cell
What do chloroplasts do?
This is where photosynthesis occurs, which makes food for the plant. They contain chlorophyll - a green pigment - which absorbs light needed for photosynthesis
What do bacterial cells contain?
Cytoplasm, cell membrane, cell wall, flagella, ribosomes, mitochondria, slime capsule, plasmids (small rings of DNA) and a single circular strand of DNA that floats freely in the cytoplasm
What do bacterial cells NOT contain?
A nucleus
What is the equation for magnification?
Image size divided by actual size
What is differentiation?
The process by which a cell changes to become specialised for its job
What are undifferentiated cells called?
Stem cells
What are sperm cells specialised for and how are they specialised?
Reproduction - they transport the male DNA to the female DNA -It has a flagella and a streamlined head to help it swim towards the egg -There are lots of mitochondria in the cell to provide the energy needed -It carries enzymes in its head to help digest through the egg cell membranes
What are nerve cells specialised for and how are they specialised?
Rapid signalling - they carry electrical signals from one part of the body to another -They are long to cover more distance -They have branched connections at their ends to connect to other nerve cells and form a network throughout the body
What are muscle cells specialised for and how are they specialised?
Contraction - they need to contract quickly -They are long so they have space to contract -They contain lots of mitochondria to generate the energy needed for contraction
What are root hair cells specialised for and how are they specialised?
Absorbing water and minerals -They are cells on the surface of plant roots which grow into long hairs that stick out into the soil -They have a large surface area for absorbing water and mineral ions from the soil
What are chromosomes?
Coiled up lengths of DNA molecules that are found in the nuclei
What is mitosis?
The stage of the cell cycle where the cell divides
What do multicellular organisms use mitosis for?
To grow or replace cells that have been damaged
Describe each stage of mitosis
Prophase - The chromosomes shorten and duplicate Metaphase - The chromosomes line up on the equator of the cell Anaphase - The chromosomes are pulled to the opposite ends of the cell. The chromatids are now known as daughter cells. Telophase - New membranes form around the daughter nuclei which becomes the nuclei of the two new cells - the nucleus has divided. The cytoplasm and cell membrane divide to create two daughter cells.
What are stem cells?
They are undifferentiated cells that divide to produce lots more undifferentiated cells. They then differentiate into different types of cell
Where are stem cells found?
In early human embryos or the bone marrow of adults
What do embryonic stem cells do?
Used to replace faulty cells in sick people - insulin-producing cells for diabetes and nerve cells for paralysed spinal injuries
Used to replace faulty blood cells
Where are stem cells found in plants?
Meristems
What is diffusion?
Diffusion is the movement of particles from an area of high concentration to an area of low concentration
Name the substances that can diffuse through cell membranes
Glucose, water, oxygen and amino acids
Name two substances that can't diffuse through cell membranes
Protein and starch
What is osmosis?
Osmosis is the passive movement of water molecules through a partially permeable cell membrane from an area of high water concentration to an area of low water concentration
What are the two main differences between active transport and diffusion?
Active transport uses energy whereas diffusion doesn't. Active transport goes against the concentration gradient whereas diffusion goes along it
Adaptations of Exchange Surfaces
Large surface area - lots of substances can diffuse at once
Lots of blood vessels - to get stuff into and out of the blood quickly
Thin membrane - short distance for substances to diffuse
Often ventilated - air moves in & out
Give two ways that the villi in the small intestine are adapted for absorbing digested food
A single layer of surface cells
A very good blood supply to assist quick absorption
Explain how the leaves are adapted to maximise the amount of carbon dioxide that gets into their cells
The exchange surface in a leaf is covered in stomata which the carbon dioxide diffuses through
The leaf has a flattened shape which increases the area of its exchange surface, therefore it's more effective
The walls of the cells inside the leaf act as another exchange surface
The air spaces inside the leaf increase the area of the exchange surface which increases the chance for carbon dioxide to enter the cells
What affects the rate of diffusion?
Concentration gradient - the steeper the gradient, the faster the rate Temperature - the higher the temperature, the faster the rate (the particles have more energy thus move around faster) Surface area - the larger it is, the faster the rate Diffusion distance - the shorter the distance, the faster the rate
Examples of active transport
Plants = Root hairs absorb minerals and water. Each branch of a root will be covered in tiny hairs, therefore increasing the surface area for the absorption of minerals and water. The concentration of minerals is usually higher in the root hair cells than in the soil around them, therefore they can't use diffusion for this process. Animals = Glucose is taken in from the gut and from kidney tubules.
How are alveoli in the lungs specialised to maximise the diffusion of oxygen and carbon dioxide?
-an enormous surface area -a moist lining for dissolving gases -very thin walls -a good blood supply
How do fish respire?
-Water enters the fish through the mouth and passes out through the gills -During this process, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water
How are fish adapted for gas exchange?
-Each gill is made up of lots of gill filaments which create a large surface area for the exchange of gases -Gill filaments are covered in lamellae which increase the surface even more -The lamellae have lots of blood capillaries to speed up diffusion -The lamellae have a thin surface layer of cells to minimise the diffusion distance -Blood flows through the lamellae one way and water flows over in the opposite direction which maintains a higher concentration gradient between the blood and the water -The concentration of oxygen in the water is always higher than that in the blood to maximise the amount of oxygen diffusion from the water into the blood
Microscopy Practical - Preparing the Slide
Add a drop of water to the middle of a clean slide
Cut up an onion & separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers
Using the tweezers, place the epidermal tissue into the water on the slide
Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them
Place a cover slip on top - stand the cover slip upright on the slide, next to the water droplet. Then, carefully tilt & lower it so it covers the specimen. Try not to get any air bubbles under there - there'll obstruct your view
Microscopy Practical - Using a Light Microscope
Clip the slide you've prepared onto the stage
Select the lowest-powered objective lens
Use the coarse adjustment knob to move the stage up to just below the objective lens
Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus
Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide
Microscopy Practical - Drawing Observations
Draw what you see under the microscope using a pencil with a sharp point
Make sure your drawing takes up at least half of the space available & that it is drawn with clear, unbroken lines
Your drawing should not include any colouring or shading
If you are drawing cells, the subcellular structures should be drawn in proportion
Include a title & write down the magnification that it was observed under
Label the important features of your drawing using straight, uncrossed lines
What happens during binary fission?
The circular DNA & plasmid(s) replicate
The cell gets bigger & the circular DNA strands move to opposite poles of the cell
The cytoplasm begins to divide & new cell walls begin to form
The cytoplasm divides & two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s)
What is binary fission?
A type of simple cell division used by prokaryotic cells to reproduce & split into two
What conditions do bacteria need to divide?
Warm environment
Lots of nutrients
What is the mean division time?
The average amount of time it takes for one bacterial cell to divide into two
How do you make an agar plate?
Hot agar jelly is poured into shallow Petri dishes. When the jelly's cooled & set, inoculating loops can be used to transfer the microorganisms to the culture medium. Alternatively, a sterile dropping pipette & spreader can be used to get an even covering of bacteria. The microorganisms then multiply
Investigating the Effect of Antibiotics on Bacterial Growth - Method
Place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria. Leave some space between the discs
The antibiotic should diffuse into the agar jelly. Antibiotic-resistant bacteria that aren't affected by the antibiotic will continue to grow on the agar around the paper discs, but non-resistant strains will die. A clear area will be left where the bacteria have died - an inhibition zone
Make sure you use a control - a paper disc that has not been soaked in an antibiotic. Instead, soak it in sterile water so you can be sure that any difference between the growth of bacteria around the control disc & around one of the antibiotic discs is due to the effect of the antibiotic alone
Leave the plate for 48 hours at 25°C
The more effective the antibiotic is, the large the inhibition zone will be
Avoiding Contamination
The Petri dishes & culture medium must be sterilised before use (heating to a high temperature), to kill any unwanted microorganisms
If an inoculating loop is used to transfer the bacteria to the culture medium, it should be sterilised first by passing it through a hot flame
After transferring the bacteria, the lid of the Petri dish should be lightly taped on - stops any microorganisms from the air getting it
The Petri dish should be stored upside down - stops drops of condensation falling onto the agar surface
Investigating the Effect of Sugar Solutions on Plant Tissue - Method
Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them: one should be pure water & another should be a very concentrated sugar solution
Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours
Take them out, dry them with a paper towel & measure their masses again
If the cylinders have drawn in water by osmosis, they'll have increased in mass. If water has been drawn out, they'll have decreased in mass
The dependent variable is the chip mass & the independent variable is the concentration of the sugar solution. All other variables must be kept the same
Possible Errors of the Potato Chip Experiment
Some potato cylinders were not fully dried
Water evaporated from the beakers
The potato chips weren't identical sizes
The volumes of water weren't identical
Types of eukaryotic cells
Animal cells Plant cells
What are light microscopes?
They use light & lenses to form an image of a specimen & magnify it Allow us to see individual cells & large subcellular structures e.g. nuclei
What are electron microscopes?
They use electrons to form an image They have a higher magnification & a higher resolution Allow us to see smaller things in more detail e.g. internal structure of mitochondria & chloroplasts & ribosomes & plasmids
Stem Cells - Bone Marrow
They can't turn into any cell type at all They can only turn into certain ones e.g. blood cells
Stem Cells - Embryonic
They have the potential to turn into any kind of cell All the different types of cell found in a human being have to come from the few cells in an embryo
What is therapeutic cloning?
An embryo could be made to have the same genetic information as the patient The stem cells produced from it would also contain the same genes - they wouldn't be rejected by the patient's body if used to replace faulty cells
Disadvantages of Stem Cells
Stem cells grown in the lab may become contaminated with a virus - this will be passed onto the patient & make them sicker
Some people think that human embryos shouldn't be used for experiments - each one is a potential human life
Scientists should focus more on finding & developing other sources of stem cells
Advantages of Stem Cells
Curing existing patients who are suffering is more important than the rights of embryos
Embryos used in the research are usually unwanted ones from fertility clinics - they'd be destroyed otherwise
Advantages of Plant Stem Cells
Used to produce clones of whole plants quickly & cheaply
Used to grow more plants of rare species - prevents them being wiped out
Used to grow crops of identical plants that have desired features for farmers e.g. disease resistance
What is a tissue?
A tissue is a group of similar cells that work together to carry out a particular function
Examples of tissues
Muscular tissue - contracts to move whatever it's attached to Glandular tissue - makes and secretes chemicals like enzymes and hormones Epithelial tissue - covers some parts of the human body e.g. the inside of the gut
What is an organ system?
An organ system is a group of organs working together to carry out a particular function
Example of an organ system
Digestive system - glands (pancreas and salivary glands), stomach, liver, small intestine and large intestine
Why can enzymes be described as biological catalysts?
They speed up useful chemical reactions in the body
Why do enzymes only usually catalyse one reaction?
Their active site is only complimentary to one type of substrate
What does it mean when an enzyme is denatured?
Its active site has changed shape due to intense heat or acidic conditions
Where is amylase found?
It's made in the salivary gland and the pancreas and it works in the small intestine
What is the role of lipases?
They break down lipids into fatty acids and glycerol
Where is bile made and stored?
It's made in the liver and stored in the gall bladder
What does bile do?
It emulsifies fats into smaller, more soluble pieces which gives the fat a bigger surface area for lipase to work on. It also neutralises the stomach acid to make the conditions alkaline, therefore the enzymes can work in the small intestine
What are organs?
Organs are groups of tissues that work together to perform certain functions
What are the tissues in the stomach and what do they do?
Muscular tissue - moves the stomach wall to churn up the food Glandular tissue - makes digestive juices to digest food Epithelial tissue - covers the inside and outside of the stomach
What is the name of the substance when a substrate fits into the enzyme's active site?
Enzyme substrate complex
What is the name of the substance when the enzyme's active site has turned the substrate into two products?
Enzyme product complex
What is the optimum pH for enzymes?
The pH level that they are most active at. E.g., pepsin has an optimum pH of 2
What does amylase break down?
It catalyses the breakdown of starch to maltose
What do carbohydrases break down?
Carbohydrates into simple sugars
What do proteases break down?
Proteins into amino acids
Where are proteases found?
They're made in the stomach (called pepsin here) and the pancreas and found in the small intestine
Where are lipases found?
They're made in the pancreas and work in the small intestine
Name three substances and what they test for
Benedict's Test - testing for sugars - goes red Iodine solution - tests for starch - goes blue-black Biuret Test - tests for proteins - goes purple
What do the salivary glands do?
They produce amylase in the saliva
What does the stomach do?
-It pummels the food with its muscular walls -It produces pepsin -It produces hydrochloric acid to kill bacteria and give the right pH for pepsin to work
What does the pancreas do?
It produces amylase, protease and lipase then releases them into the small intestine
What does the small intestine do?
It contains protease, amylase and lipase to complete digestion. Digested food is absorbed into the blood here
What does the rectum do?
It stores faeces
What does the large intestine do?
It's where excess water is absorbed from the food
What does the gall bladder do?
It stores bile before it's released into the small intestine
What does the liver do?
It produces bile which neutralises stomach acid and emulsifies fat
Where are the lungs?
The thorax
What are the lungs surrounded by?
Pleural membrane
What protects the lungs?
The ribcage
What goes down the trachea?
The air that you breathe in
What tubes join onto the trachea?
The bronchi
What do the bronchi split off into?
Bronchioles
What are the small bags at the end of bronchioles called?
Alveoli
What happens in an alveolus?
Gas exchange. The blood passing next to the alveoli contains lots of carbon dioxide and little oxygen. The oxygen diffuses out of the alveoli (high concentration) and into the blood (low concentration) and the carbon dioxide diffuses out of the blood (high concentration) and into the alveoli (low concentration) to be breathed out.
What surrounds the alveoli?
Lots of blood capillaries
What happens when blood reaches body cells?
Oxygen is released from the red blood cells and diffuses into the body cells. At the same time, carbon dioxide diffuses out of the body cells and into the blood. It's then carried back to the heart
What makes up the circulatory system?
The heart, blood vessels and blood
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