Biology

Eukaryotic

Animal and plant cells which have a cell membrane, cytoplasm, nucleus containing DNA

Prokaryotic

Bacterial calls which are much smaller than eukaryotic and they have a cell wall, cell membrane, cytoplasm, singular circular strand of DNA and plasmids (small rings of DNA found in the cytoplasm

Centi

0.01

Milli

0.001

Micro

0.000,001

Nano

0.000,000,001

Nucleus

Contains DNA coding for a particular protein needed to build new cells, enclosed in a nuclear membrane

Cytoplasm

Liquid substance in which chemical reactions occur, contains enzymes (biological catalysts, ie proteins that speed up the rate of reaction), organelles are found in it

Cell membrane

Controls what enters and leaves the cell

Mitochondria

Where aerobic respiration reactions occur, providing energy for the cell

Ribosomes

Where protein synthesis occurs, found on a structure called the rough endoplasmic reticulum

Chloroplasts (plant only)

Where photosynthesis takes place, providing food for the plant, contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis

Permanent vacuole (plant only)

Contains cell sap, found within the cytoplasm, improves cell’s rigidity

Cell wall (plant only)

Made from cellulose, provides strength to the cell

Cell wall (bacterial)

Made of a different compound (peptidogylcan)

Singular circular strand of DNA (bacterial)

As they have no nucleus, this floats in the cytoplasm

Plasmids (bacterial)

Small rings of DNA

Cell specialisation

Cells specialise by undergoing differentiation: a process that involves gaining new sub-cellular structures in order for it to be suited to its role.

Stem cells

Cells can either differentiate once early on or have the ability to differentiate their whole life-these are called stem cells). In animals, most cells only differentiate once, but in plants many cells retain the ability

Sperm cells

Specialised to carry the male’s DNA to the egg cell (ovum) for successful reproduction.

It has: Streamlined head and long tail to aid swimming, many mitochondria (where respiration happens) which supply the energy to allow the cell to move, the acrosome (top of the head) has digestive enzymes which break down the outer layers of membrane of the egg cell

Nerve cells

Specialised to transmit electrical signals quickly from one place in the body to another.

It has: axon which is long, enabling the impulses to be carried along long distances, having lots of extensions from the cell body (called dendrites) means branched connections can form with other nerve cells, the nerve endings have many mitochondria which supply the energy to make special transmitter chemicals called neurotransmitters. These allow the impulse to be passed from one cell to another.

Muscle cells

Specialised to contract quickly to move bones (striated muscle) or simply to