1. Differentiation in multicellular organisms
Key Area 4
Differentiation in multicellular organisms

2. Learning intention
What is cellular differentiation and what does differentiation produce in plants?

3. Success Criteria All pupils will……. Most pupils will….
State the difference between differentiated and undifferentiated cells.
Most pupils will….
Identify how old a tree is using annual rings.
Some pupils will…..
Explain how lateral meristems are formed.

4. Cellular differentiation
Multi-cellular organisms are comprised of a large number of cells. These are specialised to carry out specific roles in the body.
Differentiation is the process by which unspecialised cells become altered and adapted to form a special function in the body.

5. Selective gene expression
Every cell in your body has all the genes necessary for constructing the whole organism.
Genes can be switched on or switched off when they are required (see Unit 2) otherwise the body would waste energy producing proteins in cells where they are not needed.
e.g. insulin produced in pancreas cells only, not in brain or heart cells.

6. Growth and differentiation in plants
In multicellular plants growth is restricted to regions called meristems. These are groups of unspecialised plant cells capable of dividing repeatedly through out the life of the plant (by Mitosis). Some of the cells formed remain merisematic and go on to produce new cells while others become differentiated.

7. Types of meristem
Apical meristem at the tip of the root and the shoot – adding length to the plant. Lateral meristems allow the stems to thicken.

8. GROWTH IN PLANTS When do plants grow? Where do plants grow?
(Hint: What differences can you see in the pictures below)

9. Apical meristems
Apical meristems in the shoot and root allow elongation – or lengthening by production of new cells making a plant grow taller
This is called primary growth

10. The root apical meristem has two roles:
1. Those toward the top differentiate into cells of the dermal (epidermis), ground, and vascular tissue, lengthening the root.
2. Those cells produced toward the bottom of the meristem replenish root cap cells.
The root cap protects the apical meristem

11. The shoot apical meristem :
A shoot's apical meristem is a dome-shaped mass of dividing cells at the very tip of the terminal bud
UPWARDS GROWTH
When these cells elongate they push the apical meristem upwards leaving pockets of meristematic cells behind. These leave lateral buds at bases of new leaves

12. PLANT TRANSPORT TISSUES
Two types of vessels are responsible for transport in plants.
Phloem
Transport sugar through
the plant
Xylem
Transport water from roots

13. GROWTH OF TREES Get bigger year after year Needs more xylem for
transport of water and for
support
Extra xylem produced by
lateral meristems
Causes stem to increase in thickness

14. Lateral meristems
Lateral meristems are secondary growth tissues in woody plants
These increase the diameter of roots and stems

15. Cambium is found in between phloem and xylem in stems.
Epidermis
Phloem
Xylem
Cambium
The cambium cells divide to form new xylem to the inside and some phloem to the outside.
It is the xylem tissue that forms annual rings in stems.

16. By looking at a tree trunk scientists can:
Tell how old the tree is
Comment on the environmental conditions during each growing season
 Each tree ring (annual ring) represents a year's growth.
 It consists of a cylinder of spring wood surrounded by a cylinder of denser summer wood. 

17. How old is this tree?
Answer = 3 years

18. How old are these trees? A B
Answer = 3 years
Answer = 2 years

19. Spring/Summer wood
summerwood
springwood

20.  In spring the vessels are wide in diameter with thin walls, whilst in the summer/autumn they are more compact and have thicker walls.

21. Annual rings Each annual ring represents a years growth.
Xylem cells, produced by cambium form the rings.
An annual ring is a cylinder of spring wood (light) surrounded by a cylinder of summer wood (dark).
Differences in ring width show variation in weather patterns from year to year, such as a particularly wet or dry spring.
Thick ring = Good growth, wet spring
Thin ring = poor growth, dry spring or environmental
factor

22. Learning intention
What is cellular differentiation and what does differentiation produce in animals?

23. Success Criteria All pupils will……. Most pupils will…..
State what the basic role of a stem cell is.
Most pupils will…..
Describe how even though all cells share the same genetic code they can perform different functions.
Some pupils will……
Explain the difference between a multipotent and pluripotent cell.

24. Differentiation in animals
Each human life begins life as a fertilised egg (zygote) and divides to become approximately 37.2 trillion ( )
With almost 200 different cell types.

25. Recap - Mitosis Cell division is the process in living
organisms that produces new cells.
When organisms grow and repair
(e.g cuts or broken bones) they produce
new cells by the process of cell division.

26. HOW DOES A CELL BECOME SPECIALISED?
The sequence of DNA = the sequence of amino acids.
Amino acids join to form proteins.
What roles can proteins play?

27. CELL SPECIALISATION The cells of our body are
controlled by their genetic
information.
All cells in multicellular
organisms contain the same
genetic information.
So… how does our body create so many
different types of cell?

28. Stem cells
Before a cell has differentiated, or specialised, it is called a stem cell. Stem cells are cells that can make more of themselves and can become almost any specialised cell. STEM cells are involved in growth and repair.

29. GENETIC CONTROL AND SPECIALISATION
Cells differ because genes can be switched on and off
When a new cell is produced by mitosis it is non-specialised or undifferentiated.
Specialisation depends on which genes are switched on and off

30. GENETIC CONTROL AND SPECIALISATION
Not all of the proteins encoded by a cell’s DNA are needed for its specific function
To perform their specific function certain genes need to be switched on and certain genes need to be switched off.
This means different types of cells make different proteins

31. Why differentiate and specialise?
Differentiated cells have a limit to the number of times they can divide
The only 2 cells which can replicate indefinitely are STEM cells and CANCER cells
This is what eventually causes old age

32. VIDEO – STEM CELLS

33. Types of Stem cells EMBRYONIC STEM CELLS
Embryonic STEM Cells are obtained from in-vitro fertilisation embryos that were not used and are cultured in the lab in order to grow more cells.
Embryonic STEM cells become differentiated to all possible types of specialised cells.
This is known as PLURIPOTENT

34. Types of stem cells ADULT/TISSUE STEM CELLS Few in the body.
Can only form a limited range of cell types.
Main function is to maintain growth and repair of the body.
They can only specialise if they are taken out of the body and are started by chemicals which switch certain genes on or off.
Are more limited than embryonic stem cells and so are known as MULTIPOTENT.

35. Where can Stem Cells be found?
surface of the eye
brain
skin
breast
intestines (gut)
testes
bone marrow
muscles

36. Animation

37. To finish
In your own words write in your jotter your understanding of a what a stem cell is to summarise the lesson.
You should be including the words
Unspecialised, develop, specialised, genes, tissue, embryonic, multipotent and pluripotent.

38. Success Criteria All pupils will……. Most pupils will…..
State what the basic role of a stem cell is.
Most pupils will…..
Describe how even though all cells share the same genetic code they can perform different functions.
Some pupils will……
Explain the difference between a multipotent and pluripotent cell.