1. What is a cell?
A cell is the basic unit of life, from which larger structures such as tissue and organs are made.
Unicellular organisms, such as bacteria, consist of just a single cell.
Multicellular organisms consists of many cells – humans are made from an estimated 50 trillion cells!
Photo credit: © 2007 Jupiterimages Corporation
Image shows the phytoplankton Pleurosigma angulatum. Phytoplankton are microscopic algae that live close to the surface of oceans and fresh water. Pleurosigma angulatum belong to a group of phytoplankton called diatoms, which are often unicellular.
Teacher notes
There is considerable uncertainty about the number of cells in a human body. Estimates vary from 10 trillion to 100 trillion cells.

2. A typical animal cell

3. How big is a cell?
Most plant and animal cells are between µm and 60 µm in size – around half the diameter of a human hair – and too small to see without a microscope.
The largest cell in the human body is the female egg cell, (ovum) at around 1,000 µm in diameter.
Photo credit: Eye of Science / Science Photo Library
Coloured scanning electron micrograph (SEM) of sperm (blue) attempting to penetrate a human egg (red). Each sperm (spermatozoa) has a rounded head and a long tail with which it swims. Women usually release one egg (ovum) per month, whereas men release millions of sperm in each ejaculation. Only one of these sperm can penetrate the egg's thick outer layer (zona pellucida) and fertilise it. Fertilisation occurs when the sperm's genetic material (deoxyribonucleic acid, DNA) fuses with the egg's DNA. When this occurs the egg forms a barrier to other sperm. Magnification: x650 when printed 10 centimetres wide.
Teacher notes
One micrometer (µm), also known as a micron, is equal to one-millionth of a meter. 1 µm = m.
The smallest human cell is the sperm cell – the head is around 5 µm long.

5. Label your diagram and complete the tabel
Animal cells and
organelles

7. Exploring animal cells
Teacher notes
This click and reveal activity could be used to check students’ understanding of the organelles found in animal cells.

8. Controls the activities of the cell
Part of the cell
Found in
Function
Nucleus
Plants and animals
Cell Membrane  
Cytoplasm
Mitochondria
Ribosomes
Controls the activities of the cell
Partially permeable barrier which controls substances entering and leaving the cell
Jelly-like substance in which most of the cellular processes and chemical reactions happen
Site of energy release by respiration
Site of protein synthesis (manufacture)

9. A closer look at animal cells
Photo credit: Dr. Gopal Murti / Science Photo Library
Light micrograph of squamous epithelial cells from the human mouth. These flat, scale-like cells have oval nuclei (purple) and granular cytoplasm. The epithelia are tissues that cover all body surfaces, cavities and tubes apart from the blood and lymph vessels. Epithelial cells form a protective layer within the mouth. Normally, they rest on a basement membrane which separates the epithelium from underlying connective tissue. Blood vessels do not extend beyond the basement layer, and epithelial cells are dependent on oxygen and metabolites diffusing from underlying tissue. Magnification: x1000 at 35mm size.
Teacher notes
This five-stage animation shows how to make and examine a cheek cell. Suitable prompts could include:
How are animal cells different to plant cells?
Why are cheek cells a good example of a typical animal cell?
Which organelles can you identify within the cheek cells?

10. Electron Microscopes
Electron microscopes
BBC active video

11. Specialized cells
Most plants and animals are multicellular. The human body is made up of around 200 different types of cell, all working together.
Most cells are specialized, meaning that each type of cell has a specific structure and function.
All cells with a nucleus contain the same genes, but different cells activate different genes so they only produce the proteins they need.
Photo credit: © 2007 Jupiterimages Corporation
Cross section of the leaf from a Dianthus (carnation) plant. Image shows epidermis, spongy and palisade cells.
Teacher notes
Red blood cells are an example of a type of cell which has no nucleus. Gametes (such as egg cells and sperm cells) only have half a full set of genes.
See the ‘Cell Division’ presentation for more information about gametes.
However, all cells have certain common features and structures called organelles. 12

12. How are animal cells adapted?
Teacher notes
This click and reveal activity could be used to check students’ understanding of animal cell structures and function.

13. Specialised animal cells

14. How do animal cells specialize?
In animals, the first type of cells in the developing embryo are stem cells. These are unspecialized cells that go on to form all the different cell types in the adult.
stem cell
red blood cell
sperm cell
Teacher notes
See the ‘Growth and Development’ presentation for more information about stem cells and human growth.
nerve cell
muscle cell

15. Animal cells: fit for a purpose
Teacher notes
This matching activity could be used as a plenary or revision exercise on animal cells. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.

16. Extension: The Golgi Apparatus
A system of membranes and folded vessicles found in both animal and plant cells
Involved in storage and transport of products that are secreted from the cell. e.g. hormones and enzymes

17. Membrane surrounds old/unwanted structures
Extension: Lysosomes
Membrane surrounds old/unwanted structures
Lysosomes fuses with membrane around unwanted structures
Lysosome releases digestive enzymes into membrane
Old/wanted structures break down
Cell reabsorbs products back into cytoplasm

18. Extension function part of cell label controls activities of the cell
4. Below is a drawing of an animal cell as seen under an electron microscope.
Extension
function
part of cell
label
controls activities of the cell
nucleus A
carries out aerobic respiration
attaches to mRNA in protein synthesis
produces secretory vesicles
contains digestive enzymes
Complete the following table by:
identifying the parts of the
cell A to E
naming the part of the cell
responsible for the function stated.
[Total 8 marks]

19. controls activities of the cell nucleus A
function
part of cell
label
controls activities of the cell
nucleus A
carries out aerobic respiration
mitochondrion / mitochondria; D;
attaches to mRNA in protein synthesis
ribosome(s) / rough ER / RER; C;
produces secretory vesicles
Golgi; B;
contains digestive enzymes
lysosome(s); E;

20. Animal cells: fit for a purpose
Teacher notes
This matching activity could be used as a plenary or revision exercise on animal cells. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB. 21

22. B2 1.1 – Questions and answers
1 Explain how it is possible to see the parts of human cells, such as the nucleus.
A By using a light microscope or an electron microscope.  
2 Explain how substances that enter and leave cells are controlled.
A The cell membrane controls which substances enter and leave the cell.

23. B2 1.1 – Questions and answers
3 Why are mitochondria found in large numbers in muscle cells?
A Mitochondria use glucose to release energy (respiration). Movement needs a large amount of energy so muscle cells can contract. Muscle cells therefore need large numbers of mitochondria to provide that energy.
4 Ribosomes synthesise proteins. Explain what this means.
A Ribosomes build up proteins from smaller, simpler components (amino acids).

24. B2 1.1 – Questions and answers
5 Explain why the nucleus of the cell is important.
A The nucleus contains DNA, which gives instructions for the synthesis of chemicals in the cytoplasm. This controls all activities of the cell. Without it the cell will die.