1. Year 10 Human Biology Unit 1.2
Making new cells
Year 10 Human Biology
Unit 1.2

2. Why are cells important?
Cells are the building block of organisms.
Your life began as a single cell and over time that single cell has increased in number to create an organism that is now billions of cells.
Each cell (except RBC) contains a nucleus and an exact copy of your DNA.

3. What role does DNA have? DNA contains the genetic code
It is used to build proteins that are needed by the cells and develop characteristics seen at the organism level.
Each time a cell divides to create two new cells, the DNA is copied so there is no loss to our genetic material.

4. How does this occur? The process of copying DNA is called REPLICATION.
There are a number of steps involved to ensure that the new cells produced are genetically identical
There are enzymes involved in this process as well

5. The steps…
1 – The DNA molecule unwinds and unzips, exposing the nitrogen base code

6. Next…?
2 – Free nucleotides pair up to the exposed bases following the complimentary base pair rule.

7. And then?
3 – The sugar phosphate molecules bond with neighbouring nucleotides and 2 strands of DNA are formed.

8. Show me again?

9. Why is this important? Cell division is important for
Growth and repair of the human body
Creating gametes (sex cells) for reproduction
DNA is important as it controls ALL activities of the cells.

10. Cell division Cell division for growth and repair is called MITOSIS
The end result of mitosis is
TWO Diploid daughter cells
Genetically identical

11. MITOSIS DNA replication
Chromosomes become visible, nuclear membrane disappears
Chromosomes line up at the equator
Chromatids are pulled to opposite poles
The cell divides into 2 and the nuclear membrane reforms

12. Diploid vs Haploid? Diploid: the full compliment of DNA for a cell.
Haploid: half the compliment of DNA for a cell.
Therefore the diploid number for a human is 46 and the haploid is??
Why is this significant?

13. Making sex cells
Cell division is also important in the production of gametes (sex cells)
At fertilisation a sperm will unite with an ovum to create a zygote.
If both the sperm and the ovum were diploid, how many chromosomes would the zygote end up with?

14. Fixing the problem 92 chromosomes is too much…!
So the process of cell division to REDUCE chromosome number is called MEIOSIS
End result of meiosis
FOUR daughter HAPLOID cells
Not genetically identical

15. MEIOSIS
1 - DNA replicates 2 – Chromosomes appear and the nuclear membrane disappears 3 – Chromosome PAIRS are pulled to opposite ends of the cell and the cell splits 4 – In Meiosis 2 the chromatids now separate and are pulled to opposite ends of the cells 5 - The 2 cells split again to form 4 haploid cells

16. Chromosome Terminology!
Draw the following below and label the following: sister chromatids, centromere, gene.
An unreplicated chromosome
A replicated chromosome
An unreplicated pair of homologous chromosomes
A replicated pair of homologous chromosomes

17. Cell division in reproduction
Asexual reproduction
Sexual reproduction
Offspring are genetically identical to their one parent
This is achieved through mitosis
Many plants and animals are able to reproduce asexually.
Offspring are a mix of two parents
This is achieved through meiosis and the formation of gametes
The chromatids in each gamete are not exact copies of the parents chromosomes.