National 5 Biology Course Notes
Unit 1 : Cell Biology
Part 1 :
Cell Structure
Organelles
Cells of animals, plants and fungi contain specialised structures called organelles.
Bacteria are unicellular (exist as single cells) and do not have organelles in the same way as other cells.
Looking at Organelles
The diagram shows organelles in a cell
Chloroplast (only in plant cells)
Nucleus
mitochondrion
Cell membrane
Cell wall (not found in animal cells)
ribosomes
Function of cell organelles
Nucleus
Controls all the activities of the cell.
Contains the genetic material (DNA)
Cell membrane
Controls which substances enter and leave the cell.
The membrane is made of protein and lipid.
Mitochondrion
Part of cell
Nucleus
Cell membrane
Function
Controls cell activities
Contains genetic material
Controls entry and exit of substances
(Made of protein and lipid)
Mitochondria
Site of aerobic respiration
Ribosomes
Protein synthesis
The part of the cell where aerobic respiration takes place.
Ribosomes
Part of the cell where protein synthesis takes place
Chloroplasts
Part of the cell where photosynthesis occurs
(Found only in plant cells)
Chloroplasts
(only in plant cells)
Cell wall
Photosynthesis
Prevents cell from bursting when it
absorbs water by osmosis
Bacteria
Bacteria are single celled micro-organisms.
They come in a variety of shapes such as rod shaped, spherical and spiral shaped.
They have a cell wall and ribosomes, but lack other organelles.
A bacterial cell wall has a different structure to the cell wall of a plant or a fungus
The diagram represents the structures found in a bacterial cell:
Cell membrane
Cell
wall
Plasmid
Single circular chromosome
Ribosomes
Bacteria have a circular chromosome which contains all the genetic information needed to control all the activities of the
bacterial cell.
Some bacteria have plasmids – these are small, circular pieces of DNA in addition to the normal chromosomal material.
Plasmids are not found in all bacteria.
Plasmids can be transferred from one bacterial cell to another.
They give bacteria extra properties such as the ability to resist antibiotics.
Organelles found in different types of cell
Is the organelle found in:
Organelle
Animal cell
Plant cell
Fungus cell
(e.g. yeast)
Bacterial cell
Nucleus
YES
YES
YES
NO
YES
YES
YES
YES
Cell wall
NO
YES
YES
YES
Ribosomes
YES
YES
YES
YES
Chloroplasts
NO
YES
NO
NO
Other organelles, e.g. mitochondria
YES
YES
YES
NO
Plasmids
NO
NO
NO
YES
Cell membrane