GCSE Biology 1.1

What are cells?

The basic building blocks of all living organisms

Approximately how many cells are there in the human body?

37.2 trillion

Approximately how many types of cells are there in the human body?

200

What are cells made up of on an molecular level? What do these form?

Trillions of molecules—these form organelles

What are organelles? What does the term literally mean?

Sub-cellular structures that carry out different functions contained within cells—little organs

What are the two major categories of cells based on their structure?

Prokaryotic and eukaryotic

What are prokaryotic cells (brief)? Example? What are prokaryotic organisms also known as?

Simple cells lacking a nucleus and other mebrane-bound organelles, such as bacteria—prokaryotes

What are eukaryotic cells (brief)? 3 examples? What are eukaryotic organisms also known as?

Complex cells with a nucleus and other membrane-bound organelles, such as plant, animal and fungal cells—eukaryotes

What defines a prokaryote (detail)?

Unicellular organisms of the most simple, primitive cells, with no organelles, such as a nucleus or other organelles with specialised functions, other than ribosomes, which are not-mebrane bound

What is membrane-bound? What does this result in?

Organelles are surrounded by their own little membrane—their functions work quicker and more efficiently

How long have prokaryotes lived?

At least 3.5 billion years

For how long were prokaryotes the only cells on Earth?

Nearly 2 billion years

How big are prokaryotes? How big is this in cell terms?

0.5-2µm—very small

Where are prokaryotes found?

Everywhere on the planet and maybe even on other planets

How are prokaryotic cells drawn (the shape)?

Flexible or more rigid, depending on whether or not they have a cell wall

What defines a eukaryote? What defines a eukaryotic cell? (Detail)

Unicellular or multicellular organisms made up of eukaryotic cells—very complex cells containing many membrane-bound organelles with specific functions, including a nucleus

What were the first types of cells to appear on Earth with specialised internal compartments?

Eukaryotic cells

Approximately how long have eukaryotic cells existed for?

1.5 billion years

How big are eukaryotic cells? How big is this in cell terms?

Around 10µm—very large

What else can eukaryotic cells do since they have organelles and organised DNA? Examples?

Create parts—flagella, cilia

What are 2 of the main types of eukaryotic cells?

Plant, animal

How are plant cells drawn (shape)?

Rigid, almost rectangular

How are animal cells drawn (shape)?

Flexible, irregular shape

What is DNA? Purpose? Where is it found in prokaryotes? Eukaryotes?

Deoxyribonucleic acid, the chemical that carries a genetic code on how the organism is made—found in a double-stranded loop of free circular chromosomal DNA in prokaryotes, found in a membrane-bound nucleus in eukaryotes

What is cytoplasm? Purpose? Where is it found in prokaryotes? Eukaryotes?

A jelly-like liquid, mostly made up of water, with dissolved salts and biomolecules, that takes up most of the cell, where most of the chemical reactions needed for life take place—found within the cell membrane of all cells

What are ribosomes? Purpose? Where are they found in prokaryotes? Eukaryotes?

Tiny organelles where protein synthesis occurs—contained in the cytoplasm of all cells

What is protein synthesis?

The process by which cells make proteins

What is the cell membrane? Purpose? Where is it in prokaryotes? Eukaryotes?

A thin, flexible barrier that encloses all cells, controlling the movement of substances in and out of the cell and keeping the cell together—found in all cells around the outside of the cytoplasm

What are cell membranes more specifically called? What are they primarily made up of?

Plasma cell mebranes—fats and proteins

What is the cell wall? Purpose? Where is it found?

A rigid outer layer of the cell, to provide the cell with strength and support—prokaryotes sometimes have them around the outside of the cell, plant cells always do, animal cells do not contain cell walls

What is the main difference between a prokaryote cell wall and a plant cell wall?

A prokaryote has a peptidoglycan cell wall, whilst a plant cell has a cellulose cell wall

What is a flagellum? Plural? Purpose? Where found?

A long, hair-like structure that protrudes from the cell’s surface, used to move the cell faster and attach to things (pl. flagella)—sometimes found on the outside of prokaryotes, also sometimes found on the outside of eukaryotic cells

What are the 2 main differences between prokaryotic and eukaryotic flagella?

Prokaryotic flagella are made of a protein called flagellin and move in rotations like a propeler—eukaryotic flagella are made of microtubles that move in a whip-like fashion

What are microtubles?

Tiny hollow tubes made of a protein called tubulin

What are chloroplasts? Purpose? Where found?

Green discs containing chlorophyll, where light is absorbed for photosynthesis—only found in plant cells, in the cytoplasm

Other than absorbing light, what else is chlorophyll?

The green pigment that gives plants their colour

What are mitochondria? Purpose? Where found?

Organelles that are the site of aerobic respiration where energy is released—contained in the cytoplasm of eukaryotes

What is the nucleus? Purpose? Where found?

The structure in the cell that contains DNA and controls the cell’s activities—found in the cytoplasm of eukaryotes

What is the nucleolus? Purpose? Where found?

A spherical structure within the nucleus—its primary purpose is to produce ribosomes

What is a permanent vacuole? Purpose? Where found?

A large fluid-filld sac, used to provide structural support to keep the cell firm and rigid, to store various useful substances and waste products, and for osmoregulation, managing water balance within the cell—found in the centre of plant cells and ocassionally in animal cells

What is a plasmid? Purpose? Where found?

Small, double-stranded closed off loops of DNA, that can replicate and move between cells, in order to share beneficial genetic information—found in the cytoplasm of prokaryotes

What is a nucleoid? Purpose? Where found?

A region that houses a cell’s DNA and isn’t membrane-bound—found in the cytoplasm of prokaryotes

What is a slime capsule? Purpose? Example? Where found?

A gelatinous, sticky layer on the outside of the cell, which protects the cell, stops it drying out, and helps it ti stick to things, such as skin, teeth and the intestines—prokaryotes sometimes have them on the outside of the cell

What cell components/organelles do prokaryotes typically contain? How many core? How many extra?

Cytoplasm, cell membrane, ribosomes, plasmids, cell wall (almost always) [5]—sometimes a slime capsule or flagella [2]

What cell components/organelles do animal cells typically contain? How many core? How many extra?

Cytoplasm, cell membrane, ribosomes, mitochondria and a nucleus [5]—occasionally flagella or vacuoles [2]

What cell components/organelles do plant cells typically contain? How many core? How many extra?

Cytoplasm, cell membrane, ribosomes, mitochondria, nucleus, chloroplasts, permanent vacuole, cell wall [8]—occasionally flagella [1]

What type of cells are fungal cells? Example?

Eukaryotic—eg; yeast

What type of cell wall/cell membrane do fungal cells have?

Chitin cell wall—plasma cell membrane

What cell components/organelles do fungal cells contain? How many core? How many extra?

Cell membrane, cytoplasm, ribosomes, mitochondria, nucleus, permanent vacuole, cell wall [7]—sometimes flagella [1]

What does a structure have to do to classify as a cell? What does this exception mean?

Originate with a cell membrane, cytoplasm and ribosomes—cells can differentiate to fulfill specialised functions

What is the purpose of a microscope?

Magnify and show in greater detail things to small to see in order to study and understand them

What are the two types of microscopes? Which is used in schools?

Light microscopes, electron microscopes—light microscopes

What is the microscope lens that the user looks into? Purpose?

Eyepiece lens—magnifies the specimen

What is the large knob on a microscope? Purpose?

Coarse focus—moves the stage up and down significantly to get the specimen roughly into focus

What is the small knob on a microscope? Purpose?

Fine focus—moves the stage up and down slightly to get the specimen precisely and sharply into focus

What is the microscope lens closest to the specimen? Purpose?

Objective lens—further magnifies the specimen

What is the platform that a microscope specimen is placed on?

The stage

What is the prepared microscope specimen known as?

The slide

What is at the bottom of a light microscope? Why?

A light—to illuminate the specimen

What is magnifiaction? How does a microscope do this?

Making something appear larger—using lenses

How do you calculate the total microscope magnification across the lenses?

Magnification = eyepiece x objective

What is usually the magnification of the eyepiece lens in a light microscope?

x5 or x10

How do you observe an onion cell with a light microscope?

• Carefully peel a very thin layer of cells from the onion

• Place the sample on the slide

• Stain the sample with iodine solution

• Lower a coverslip on with a mounted needle

• Look at the cells through the eyepiece lens, starting with the lowest magnification

Why when viewing onion cells under a microscope does the layer of onion have to be thin?

Light needs to pass through the specimen for us to see it, so if it is too thick the cell will appear dark and blurry—it is also preferable to have it a single cell thick, so the different layers don’t overlap and cause it to be unclear, allowing us to make out individual cells and organelles

Why do we stain the onion microscope sample with iodine solution?

Onion cells are naturally transparent, but the iodine solution reacts with the complex carbohydrates, turning them blue-black, creating contrast and a clearer picture

Why must a coverslip be lowered with a mounted needle?

To avoid air bubbles getting trapped and blocking the view of the cell

Why should you always start with the lowest magnification when viewing a specimen?

To make it easier to locate the specimens

How do you draw a microscope cell diagram? (8 rules)

Use a pencil, ensure it has a sharp point, draw with clear unbroken lines, no colouring or shading, needs to take up at least half of the amount of space given—needs to include labels, a title, and the magnification used

What is an order of magnitude? What are they useful for? What is 1 order of magnitude? 2 orders of magnitude?

An exponential factor of 10, used to make approximate comparisons between objects—1 order = x10, 2 orders = x10² (x100)

What is resolution? What is the term for a microscope’s resolution?

The ability to distinguish between 2 separate points, and therefore the detail than can be shown—resolving power

How does a low resolution image appear? High resolution? Why?

More blurred, smaller details are visible—more pixels across the same distance

An image is expanded—how does the magnification change? Resolution? Why?

Greater magnification, same resolution—smallest difference between 2 separate points is still the same

What are 6 advantages of light microscopes?

Cheap, small, portable, easy to use, can view cells in colour, can view alive cells

What are 2 disadvantages of light microscopes? What does this mean?

Low magnification—you can’t see organelles other than the nucleus and certain small specimens such as viruses and atoms cannot be viewed, low resolution—images lack detail and clarity

What are 6 disadvantages of electron microscopes?

Expensive, large, not portable, difficult to operate, can’t view cells in colour, can’t view alive cells

Why can’t you view living cells in an electron microscope?

Electron microscopes operate inside a vacuum—nothing can live in a vacuum

What are 2 advantages of electron microscopes? What does this mean?

High magnification, high resolution—you can see all the organelles and many tiny structures with detail and clarity

What is the equation for image size and magnification?

Image size = specimen actual size x magnification (I = AM)

What are stem cells?

Unspecialised cells that can differentiate to become specialised

What happens as cells differentiate? Examples?

They get their own jobs—some become heart cells, blood cells, eye cells etc.

When do most animal cells differentiate? What does this mean?

At an early age—they can’t differentiate into anything else

When do plant cells differentiate?

They remain the ability to differentiate if they are alive at maturity

What does plant cells remaining the ability to differentiate mean can happen to a cutting from a parent plant?

It can grow into a whole new plant

How must a cutting from a parent plant be cut? Why?

At an angle—increases surface area so more cells have the chance to differentiate into root cells which also allows for better water absorption, also prevents rot

What do specialised cells have to carry out special jobs? Do they work individually?

Adaptations—some do, others work as part of a tissue or organ

What are the 11 main specialised cells to know for GCSE?

Sperm cells, nerve cells, root hair cells, muscle cells, phloem cells, xylem cells, ovum cells, palisade cells, epithelial ciliated cells, red blood cells and microvilli

Where are sperm cells found?

The male reproductive system

What is the function of sperm cells?

Reproduction, by fertilising the egg and ensuring that the male and female DNA meet

What are 4 adaptations of sperm cells? What is the purpose of these adaptations?

• Head contains a vacuole called an acrosome—essential for the reaction that releases the necessary enzymes to break down substances in the egg’s jelly coat and burrow inside

• Long tail, streamline head, extra mitochondria in the tail—helps it swim quickly to navigate and travel through the female reproductive tract and be the first sperm there to fertlise the egg

Where are nerve cells found? What are they also known as?

Throughout the body—neurons

What is the function of neurons?

To carry electrical signals from one part of the body to another

What are 4 adaptations of neurons? What is the purpose of these adaptations?

• Long—cover more distance

• Carry electrical signals, have branched connections at their ends—connect to other nerve cells and form a network throughout the body, to enable the body to react to its surroundings using electrical impulses

• Lots of mitochondria—nerve impulses require a lot of energy

What are the connections on the ends of neurons called? What do they each do?

Axons—transmit signals, dendrites—receive signals

Where are RHCs found?

On the outer surface of plant roots

What is the function of RHCs?

To absorb water and minerals from the soil

What are 3 adaptations of RHCs? What is the purpose of these?

• Long protrusion—large surface area for faster absorption

• Thin cell wall—shorter diffusion distance

• Lots of mitochondria—provides energy for active transport

What is the function of muscle cells?

To contract quickly for movement

What are 2 adaptations of muscle cells? What is the purposes of these?

• Long—space to contract

• Lots of mitochondria—release energy for contraction

What is the function of phloem cells?

To transport sugars from the leaves to other areas of the planet

What are 4 adaptations of phloem cells? What is the purpose of these?

• They can form tubes—to transport substances

• They lose a lot of their sub-cellular structures—so substances can go through them

• They are supported by ordinary, fully-living companion cells—to keep them alive

• Cell walls between the cells break to form special sieve plates—to regulate the movement of sugars and hold things together