1. Differentiation - cell specialisation and cellular organisation

2. Stem Cells Learning Objectives
Define a stem cell as able to turn into any type of cell
Know where stem cells are found - in early human embryos
State that stem cells are found in adults, in the bone marrow.
Explain how stem cells can be used to cure diseases

3. Learning outcomes You should be able to:
Explain the term DIFFERENTIATION
Describe how the structure of some specialised plant and animal cells relates to their functions
- sperm
- red blood cells
- nerve cells (neurones
- palisade leaf cells

4. Key Words Photosynthesis guard cells Chloroplasts vacuole ribosomes
Mitochondria cell wall / membrane
Stomata cytoplasm nucleus

5. Sponges
Sponges are amongst the earliest multicellular animals on Earth (600 million years old)
Some cells are tubular, providing pores through which the water can circulate

6. Sponges
Other sponge cells secrete calcium carbonate or silica, which makes a skeleton for the sponge
Sponges are multicellular animals like us but...
... the different types of cells are scattered throughout their bodies
They have no tissues and no organs
A silica ‘spicule’

7. A North Wales sponge crab
Sponges
Recently drugs companies have become very interested in sponges!
Unable to move sponges cannot run away from predators
Instead, they have evolved chemical defenses
Some other organisms carry sponges because of this
A North Wales sponge crab

8. Sponges
Some of these chemicals show promise as drugs to fight human diseases
For example, a compound called halichondrin, derived from Lissodendoryx is being trialled as an anti-cancer drug
Another sponge produces a chemical called avarol, which could be used to treat psoriasis

9. Differentiation and cell specialisation
Multicellular organisms consist of many cells – all derived from the single fertilised egg formed from the fusion of egg and sperm
Some cells become specialised to perform certain functions = differentiation
Cells can differentiate in a number of different ways:
- the number of specialised parts
- the shape / size of the cell
- some of the contents of the cell

10. Differentiation and cell specialisation
Once a human cell has differentiated it cannot change into another type of cell
The cells of the early embryo– they can become any of the different types of cells in a human
These are stem cells
Stem cells:
- are unspecialised
- can divide repeatedly to make new cells
- can differentiate into several kinds of specialised cells

11. Differentiation and cell specialisation
So far, all of the stem cells identified are only able to differentiate into a limited range of cells
For example, stem cells in bone marrow can form white or red blood cells but not neurones, or any other kind of cell
There is much interest in stem cells, as they could cure many diseases
For example, Parkinson’s disease is caused by the death of a particular group of cells in the brain, which could be replaced using stem cells

12. Specialised animal cells
Red blood cells transport oxygen in the blood
They have a very short life-span: every second, 10 million old erythrocytes are destroyed in your spleen and 10 million new ones are made
They are made from stem cells in the bone marrow, especially in the ribs, vertebrate, pelvis and skull
These cells also make white blood cells (leucocytes)– cells that attack and destroy invading microorganisms

13. Red blood cells transport O2 and CO2
They are very small, to fit through capillaries and get close to cells in body tissues
They are packed with haemoglobin, which combines with O2 or CO2
There is no nucleus, to make room for more haemoglobin

14. Red blood cells
The ‘biconcave’ (refresher) shape of erythrocytes provides a high surface area: volume ratio
This increases the amount of oxygen and CO2 that can pass into and out of the cell in a certain period of time

16. White blood cells leucocytes (white cell)
They destroy bacteria and other foreign material
They move toward bacteria
They are the predominant cell in pus!

17. Multilobed nucleus
Cytoplasm

19. Specialised plant cells
Plants do not have stem cells – most of their cells retain the ability to differentiate throughout their lives