GCSE OCR GATEWAY BIOLOGY : CELL STRUCTURES COMPLETE REVISION

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GCSE OCR BIOLOGY CELL STRUCTURES Complete Revision Summary

CELL STRUCTURES

Cell measurement
Electron microscopes
Animal cells
Plant cells
Eukaryotes and prokaryotes
Investigating cells with a light microscope
Measuring cell size
Comparing sizes

Eukaryotic Cells – Plants and Animals

Prokaryotic Cells – Bacteria

EUKARYOTIC	PROKARYOTIC
Nucleus is present.	Nucleus is absent.
All membrane bound organelles are present	Membrane bound organelles are absent.
DNA is enclosed in the nucleus	DNA lies naked in the cytoplasm.
They are multicellular	They are mostly unicellular
DNA is linear	DNA Is circular
Ribosomes are big	Ribosomes are small
They are big cells	They are small cells.
Example: Plants and Animals	Example: Bacterial Cell

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Animal Cells

NUCLEUS

It is the brain of the cell
It controls the activities of the cells
It contains DNA which holds our genetic information.

RIBOSOMES

It is the site for protein synthesis.
They are involved in making of proteins and enzymes required by the cell

CYTOPLASM

Jelly like fluid which fills the cell.
It is the site where all the chemical reactions of the cells take place as it contains all the major enzymes

CELL MEMBRANE

It the membrane that surrounds the cells
It controls what goes in and out of the cell.

MITOCHONDRIA

It is the powerhouse of the cell
It produced energy for the cell as it is the site for aerobic respiration

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Plant Cell

PERMANENT VACUOLE

It is filled with cell sap.
It gives rigidity to the cells and makes the cell turgid

CELL WALL

Made up of cellulose.
It is the layer outside of the cell membrane
It supports the plant and maintain its shape.

CHLOROPLAST

It is the site for photosynthesis
It contains a green pigment, chlorophyll which absorbs light and prepared food.

Plant versus Animal Cell

ORGANELLE	Plant Cell	Animal Cell
Nucleus	Present	Present
Cell Membrane	Present	Present
Mitochondria	Present	Present
Ribosomes	Present	Present
Cytoplasm	Present	Present
Cell Wall	Present	Absent
Permanent Vacuole	Present	Absent
Chloroplast	Present	Absent

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Bacterial Cell

Cell Wall

No cellulosic
made up of peptidoglycan

Circular DNA

No nucleus
Single DNA loop found naked in the cytoplasm

Plasmid

Extra chromosomal materials
They are in the form of small rings
They give special properties to bacteria like antibiotic resistance

Pilli

Hair like structures
Found on the surface
That helps bacteria to reproduce

Capsule

Slime layer
that protects the bacteria

Flagellum

Tail like structure
Helps the bacteria to move.

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Cell Structure

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BACTERIAL VERSUS PLANT VERSUS ANIMAL CELLS

SPECIALISED ANIMAL CELLS

Special cells which have some extra features that allows them to perform specific functions

NERVE CELL

Function is to send electrical impusles round the body

Dendrites – They are hair like structures that receives the impulses
Axon – Long stalk the transmits the nerve impulses
Synapse – They transmit impulses from one neurone to another

MUSCLE CELL

Functions is to contract to bring about the movement of different parts of the body
They are made up of special fibres which helps them to contract and relax
Contain special proteins that allows them to contract and relax
They have loads of mitochondria which provides them energy to contract
They can store special storage carbohydrate called glycogen which acts as fuel for the muscles

SPERM CELL

Functions is to swim to the egg and fertilize it

Flagella – Helps it to swim to large distances
Mitochondria – Provides Energy to swim
Nucleus – Contains genetic information
Acrosome – Contains Hydrolytic enzyme to break the egg wall and penetrate inside the egg to fuse with the egg nucleus

Specialized Plant Cells

MICROSCOPES

Are the devices that use to see the cells which we cannot see by our naked eye.

MAGNIFICATION

The property of the microscope to enlarge the object.

RESOLUTION

The property of the microscope to distinguish between two closed placed objects.

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Light and Electron Microscopes

LI&HT MICROSCOPES	ELECTRON MICROSCOPES
Uses beam of light to focus on the object.	Use beam of electron.to focus on the object.
It is easy to handle	It is not easy to handle
It is small and compact	It is big and non portable
It does not require much expertise to handle	It requires proper training to handle
It can view the live samples	Samples have to be dead
No special sample preparations are required	Special sample preparations ace required
Lower resolving power – 0.2μm	Greater resolving power 0.5nm
Small magnifying power – x1000 -1500	Greater magnifying power – x100000
Can form colour images	Form 2D or 3D black and white images

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