2(a) and 2(b) Levels of Organisation and Cell Structure

Order of organisation from smallest to largest

Organelles → cells → tissues → organs → organ systems.

Organelle

A structure inside a cell that carries out a particular function.

Tissue

A group of similar cells working together to perform a particular function.

Organ

A structure made from different tissues working together to perform a particular function.

Organ system

A group of organs working together to perform a particular function.

Function of the nucleus

It contains genetic material and controls the activities of the cell.

Function of the cytoplasm

It is where many of the cell’s chemical reactions take place.

Function of the cell membrane

It controls the movement of substances into and out of the cell.

Function of the cell wall

It strengthens and supports the plant cell.

Function of mitochondria

They are the site of aerobic respiration.

Function of chloroplasts

They contain chlorophyll and are the site of photosynthesis.

Function of ribosomes

They are the site of protein synthesis.

Function of the vacuole

It contains cell sap and helps maintain pressure inside a plant cell.

Structures found in both plant and animal cells

Nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.

Structures found in plant cells but not animal cells

Cell wall, chloroplasts and a large permanent vacuole.

Main differences between plant and animal cells

Plant cells have a cell wall, chloroplasts and a large permanent vacuole; animal cells do not.