1. Cell continuity
Biology Leaving Cert
2.3 Cell continuity

2. Learning objectives Today you should learn about
Biology Leaving Cert
2.3 Cell continuity
Learning objectives
Today you should learn about
What cell continuity is
The difference between haploid and diploid cells
The two main stages in mitosis
What happens during interphase in the cell cycle

3. Cell continuity This requires:
Biology Leaving Cert
2.3 Cell continuity
Cell continuity
Cell continuity means that new cells can only be produced by the division of existing live cells.
This requires:
1. Synthesis of materials needed in the cell,
2. Growth of the cell
3. Cell reproduction

4. Biology Leaving Cert
2.3 Cell continuity
2.3.1 Chromosomes
Chromosomes are the structures made of DNA and protein which are located in the nucleus of the cell.
Nuclear membrane
Nuclear pore
Exist as chromatin during Interphase – stage of non division
At end of interphase they contract and can be seen as shorter strands, each is made up of a duplicated strand.
Single stranded to double stranded
Each chromosome will contain hundreds or thousands of genes.
Genes are short sections of DNA which contain coding information for the production of proteins in a cell.
Chromatin

5. Haploid cells A haploid cell has only one of each type of chromosome.
Biology Leaving Cert
2.3 Cell continuity
Haploid cells
A haploid cell has only one of each type of chromosome.
Def Haploid number is the number of chromosomes in a haploid cell
Haploid number is represented by the letter n
n = 4 describes a haploid cell that has four chromosomes.
Every cell contains chromosomes.
A human has a n = 23
Human sex cells are haploid.

6. Diploid cells A diploid cell has two of each type of chromosome.
Biology Leaving Cert
2.3 Cell continuity
Diploid cells
A diploid cell has two of each type of chromosome.
Def Diploid number is the number of chromosomes in a diploid cell
Diploid number is represented by the letter 2n
2n = 4 describes a Diploid cell that has four chromosomes.
A pair of homologous chromosomes that are found in diploid cells are called homologous pairs.
Each pair has two chromosomes that contain similar genes
One of these chromosomes would have came from the mother and one form the father during reproduction.
Human cells are all diploid, except for the sex cells

7. Check your learning.. What cell continuity is
Biology Leaving Cert
2.3 Cell continuity
Check your learning..
What cell continuity is
The difference between haploid and diploid cells

8. Learning objectives The two main stages in mitosis
Biology Leaving Cert
2.3 Cell continuity
Learning objectives
The two main stages in mitosis
What happens during interphase in the cell cycle
What mitosis is and how it happens

9. The Cell Cycle Dividing stage Non dividing stage
Biology Leaving Cert
2.3 Cell continuity
The Cell Cycle
Dividing stage
Mitosis
Interphase
Non dividing stage
The cell is usually in a state of non division – called Interphase
During Interphase the chromosomes are elongates – as chromatin
It is producing new organelles, making chemicals, enzymes and proteins
Later the chromosomes make copies of themselves!
During mitosis the genetic material divides and the cytoplasm, the organelles and the biomolecules are partitioned into two cells.
The Cell Cycle is the sequence of events in a cell which includes a state of non division and division.

10. During Interphase The chromosomes:
Biology Leaving Cert
2.3 Cell continuity
During Interphase
Mitosis
Interphase
The chromosomes:
Elongate – as chromatin
then make copies of themselves!
The cell also produces new organelles and makes chemicals, enzymes and proteins

11. Biology Leaving Cert
2.3 Cell continuity
2.3.4 Mitosis
Mitosis
Interphase
Def Mitosis is the division of the nucleus to produce two daughter nuclei, containing identical sets of chromosomes.
Daughter nuclei with chromosomes identical to parent cell

12. Learning check… What does cell continuity mean?
Biology Leaving Cert
2.3 Cell continuity
Learning check…
What does cell continuity mean?
Distinguish between haploid and diploid
Define mitosis

13. Today’s objectives To learn the names of the four stages of mitosis
Biology Leaving Cert
2.3 Cell continuity
Today’s objectives
To learn the names of the four stages of mitosis
To learn about what happens in each stage of mitosis

14. Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 1
The chromatin shortens, thickens and double stranded chromosomes become visible in the nucleus.
The Nuclear membrane breaks down
Fibres are formed :
Fibres
Cell membrane
Double stranded chromosomes
There are four main stages in Mitosis
Nucleus
Nuclear membrane

15. Mitosis: Stage 2 Fibres attach to the chromosomes.
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 2
Fibres attach to the chromosomes.
The chromosomes line up along the centre of the cell.

16. Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 3
Chromosomes are pulled apart to opposite ends of the cell
Chromosomes pulled apart

17. Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 4
A nuclear membrane forms around each set of new chromosomes and the cell divides in two
Cell divides in two

18. Biology Leaving Cert
2.3 Cell continuity
Mitosis
Mitosis – stage 4
Mitosis – stage 2
Interphase
Mitosis – stage 3
Mitosis – stage 1
The end result of mitosis is two new daughter cells – each with the same number of chromosomes as the parent cell

19. Mitosis: Stage 1 - Prophase
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 1 - Prophase
H 2.3.8
The chromatin shortens, thickens and double stranded chromosomes become visible in the nucleus.
The Nuclear membrane breaks down
Spindle fibres are formed :
Cell membrane
Double stranded chromosomes
There are four main stages in Mitosis
Spindle Fibres
Nucleus
Nuclear membrane

20. Mitosis: Stage 2 - Metaphase
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 2 - Metaphase
H 2.3.8
Fully formed Spindle fibres attach to the chromosomes pairs at the centromere.
The chromosomes line up along the centre of the cell – the equator line.
Centromere
Chromosomes line up on the equator line
Spindle Fibre

21. Mitosis: Stage 3 - Anaphase
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 3 - Anaphase
H 2.3.8
Spindle fibres contract and chromosome pairs are pulled apart at the centromere
Chromosomes are pulled to opposite ends of the cell
Centromere
Chromosomes pulled apart

22. Mitosis: Stage 4 - Telophase
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 4 - Telophase
H 2.3.8
A nuclear membrane forms around each set of new chromosomes and the cell divides in two
Cell divides in two

23. Biology Leaving Cert
2.3 Cell continuity
Today’s objectives
Difference in Telophase between plant and animal cells
Function of mitosis in unicellular organisms
Function of mitosis in multicellular organisms

24. Mitosis: Stage 4 - Telophase
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 4 - Telophase
H 2.3.8
Cell division
in an animal cell involves cleavage furrow formation
Chromosomes appear as chromatin again

25. Mitosis: Stage 4 - Telophase
Biology Leaving Cert
2.3 Cell continuity
Mitosis: Stage 4 - Telophase
Cell division
in a plant cell involves cell plate formation

26. Biology Leaving Cert
2.3 Cell continuity
Mitosis - PMAT
Telophase
Metaphase
Interphase
Anaphase
Prophase
The end result of mitosis is two new daughter cells – each with the same number of chromosomes as the parent cell

27. Biology Leaving Cert
2.3 Cell continuity

28. Biology Leaving Cert
2.3 Cell continuity
Function of Mitosis
1. A method of reproduction for single celled organisms
mitosis allows single celled organisms to multiply and produce offspring identical to themselves. E.g. Amoeba

29. Biology Leaving Cert
2.3 Cell continuity
If living organisms are composed of cells, what do they need in order to grow bigger? …
…MORE CELLS !!

30. Biology Leaving Cert
2.3 Cell continuity
2.3.5 Function of Mitosis
2. A method of growth for multicellular organisms .

31. Biology Leaving Cert
2.3 Cell continuity
The Cell Cycle 2.3.4
Def Cancer is a group of disorders in which cells lose the ability to control the number of times that mitosis happens and how fast it happens. It results in uncontrolled multiplication of cells.
The cell cycle is normally carefully controlled so that just enough new cells are formed.
Sometimes cells lose the ability to control cell division.
Picture a mouse with a breast tumour removed.
Carcinogen- a cancer causing chemical
Oncogenes – normal genes turned onto cancer causing genes
Tumours can be benign or malignant – invade other cancer cells
Two possible causes of cancer:
Cigarette smoke
Ultraviolet radiation

32. Check your learning How mitosis happens in haploid and diploid cells
Biology Leaving Cert
2.3 Cell continuity
Check your learning
How mitosis happens in haploid and diploid cells
Difference in Telophase between plant and animal cells
Functions of mitosis
Cancer – definition and possible causes

33. Biology Leaving Cert
2.3 Cell continuity
2.3.6 Meiosis
Def Meiosis is division of the cell to produce daughter cekks which contain half the chromosome number of the parent cell.
Diploid cell with 2n = 4
Haploid cells with n = 2

34. Biology Leaving Cert
2.3 Cell continuity
2.3.7 Function of Meiosis
1. Sexual reproduction in Multicellular organisms
Meiosis produces haploid cells with half the number of chromosomes as body cells.

35. 2.3.7 Function of Meiosis 2. Meiosis produces variation
Biology Leaving Cert
2.3 Cell continuity
2.3.7 Function of Meiosis
2. Meiosis produces variation
through the random sorting of genetic material which takes place during meiosis.
The cells resulting from meiosis are not identical to the parent cell
NEW GENE COMBINATIONS ARE PRODUCED IN THE GAMETE
VARIATION PRODCUED DIFFERENCES IN ORGANISMS RESULTING FROM SEXUAL REPRODUCTION.#BASIS FOR EVOLUTION – ALLOWS ANIAMSL TO ADAPT TO THEIR ENVIRONEMNT.