1. Investigating Cells
Cell Division
G Davidson

2. Cell Division
Single celled animals and plants simply divide into 2 identical, but smaller, cells when they are fully grown.
Cell division occurs in 2 separate phases:
The nucleus divides to form 2 identical nuclei which move apart in the cell.
The whole cell divides into 2 new, but smaller, cells.
Saturday, 08 December 2018
G Davidson

3. Cell Division
Saturday, 08 December 2018
G Davidson

4. Cell Division
In plant cells a new cellulose wall forms between the 2 new nuclei.
In animal cells the cell divides into 2 by the membrane becoming pinched off between the 2 nuclei.
Saturday, 08 December 2018
G Davidson

5. Cell Division
Saturday, 08 December 2018
G Davidson

6. Root Growth
The growth of an animal or plant body involves 2 distinct processes
Cell division.
Cell enlargement.
Growth only takes place in restricted parts of a plant such as the tips of roots and stems.
It occurs throughout the bodies of most animals.
Saturday, 08 December 2018
G Davidson

7. Root Growth
There are different types of cells and shapes of cells in plant roots.
The base of the root is the root cap which protects the root as it grows.
Just behind this is the root tip where cell division occurs and new cells are made.
Behind this is the area of CELL ELONGATION where growth is occurring.
Saturday, 08 December 2018
G Davidson

8. Root Growth Cell elongation Root tip Root Cap
Saturday, 08 December 2018
G Davidson

9. Root Growth
In the root tip the cells look different because their nuclei have been replaced with thread-like structures called CHROMOSOMES.
Saturday, 08 December 2018
G Davidson

10. Observing Chromosomes
When plant and animal cells divide, the chromosomes in their nuclei always pass through the same series of changes.
The name MITOSIS is given to this kind of cell division.
At the end of mitosis, 2 cells are produced which have the identical number of chromosomes to the original cell.
Saturday, 08 December 2018
G Davidson

11. Observing Chromosomes
Chromosomes appear as double threads, made up of two chromatids.
When separation occurs the single chromatids are pulled to opposite ends of the cell and pass into the nuclei of the new cells which are to be formed.
Saturday, 08 December 2018
G Davidson

12. Observing Chromosomes
At a stage between the end of one cell division and the start of the next, the chromosomes themselves are duplicated.
This restores once more the original structure of 2 chromatids per chromosome.
Saturday, 08 December 2018
G Davidson

13. Observing Chromosomes
The cells of every kind of animal and plant contain a fixed number of chromosomes within their nuclei.
These chromosomes are grouped into identical pairs.
Saturday, 08 December 2018
G Davidson

14. Observing Chromosomes
All the cells of an organism have the same number of chromosomes, except the gametes (sex cells).
E.g.
Onion – 8 pairs
Man – 23 pairs Privet hedge – 23 pairs
Chimp – 24 pairs
Dog – 39 pairs
Saturday, 08 December 2018
G Davidson

15. Observing Chromosomes
If 2 kinds of organism have the same number of chromosomes, it is clear that some extra factor must make them different.
Each pair of chromosomes carries information in the form of a code.
Each piece of information is called a GENE.
This coded information is unique to every individual plant or animal.
Saturday, 08 December 2018
G Davidson

16. Cell Growth
Individual cell cannot grow indefinitely, getting bigger and bigger.
There is a maximum size to which they can grow.
As cells get bigger, the ratio of their surface area to their volume changes.
This affects their ability to take in sufficient raw materials from their surroundings.
Saturday, 08 December 2018
G Davidson

17. Cell Growth
If we imagine a cell takes the form of a cube, we can calculate the surface area, the volume, and, therefore, the SA:V ratio.
Length
Breadth
Height
Saturday, 08 December 2018
G Davidson

18. Cell Growth We first need to calculate the surface area:
Surface area = Length x Breadth x number of sides
Surface area is measured in cm2
We now need to calculate the volume:
Volume = Length x breadth x height
Volume is measured in cm3
Saturday, 08 December 2018
G Davidson

19. We can now work out the ratio:
Cell Growth
We can now work out the ratio:
Surface area : Volume
e.g. if the cube has sides 1cm long:
Surface area = 1 x 1 x 6
So S.A. = 6 cm2
Volume = 1 x 1 x 1
So V = 1 cm3
S.A. : V
Therefore:
=6 : 1
Saturday, 08 December 2018
G Davidson

20. Cell Growth Length of side S.A. (cm2) Volume (cm3) S.A. : V 1 6 6:1 24 5
Complete the table.
Saturday, 08 December 2018
G Davidson

21. Cell Growth Length of side S.A. (cm2) Volume (cm3) S.A. : V 1 6 6:1 224 8
3:1 3 54 27
2:1 4 96 64
3:2 5
150
125
6:5
216
1:1
Complete the table.
Saturday, 08 December 2018
G Davidson

22. Mitosis
Saturday, 08 December 2018
G Davidson

23. Mitosis Anaphase Prophase Metaphase Telophase Mitosis Animation
Saturday, 08 December 2018
G Davidson

24. The Cell as a Factory CELL
A cell can be thought of as being like a factory which manufactures a range of different products.
Raw Materials
Products
CELL
Energy
Waste
Saturday, 08 December 2018
G Davidson

25. The Cell as a Factory
All of the substances that the cell needs to take in or get rid of, must pass through the membrane at the surface of the cell.
As the volume of the cell increases, so the manufacturing capacity increases.
However as this increases the surface area : volume ratio is decreasing and it can’t take in enough raw materials to work properly.
This is why cells have maximum size to which they can grow.
Saturday, 08 December 2018
G Davidson

26. Chromosomes
The chromosomes control all the processes which occur in a cell.
In order to do this, chromosomes must contain a store of information and be able to use this information.
Saturday, 08 December 2018
G Davidson

27. Chromosomes
This storage of information is very similar to a computer database.
A cell’s records are in the form of packets of information arranged along the length of each chromosome.
Each packet of information is called a gene.
Saturday, 08 December 2018
G Davidson

28. Chromosomes Each chromosome carries a number of genes.
In order to function properly the cell must have a complete information store.
Saturday, 08 December 2018
G Davidson

29. Chromosomes
If any part of the store is missing, or if any of the information is incorrect, then the cell or even the entire organism will not be able to function correctly.
It is essential that the information stored in all the chromosomes is copied accurately before the cell divides so that complete and correct information is passed on to the new cells.
Saturday, 08 December 2018
G Davidson