In body cells what do they contain?
Chromosomes in matching pairs
Explain why the chromosomes have to be copied to produce new cells for growth
To replace damaged cells and repair worn out tissue
What is mitosis needed for?
- replacement of worn out cells
- repair to damaged tissue
- asexual reproduction
What is sexual reproduction?
When gametes join in fertilisation
What do gametes contain?
Half the number of chromosomes of body cells
Explain why sperm cells are produced in large numbers?
To increase the chance of fertilisation
In sexual reproduction what s needed to produce a unique individual?
Half the genes from each parent
Explain the advantages or being multicellular
Allows organisms to be larger
Allows for cell differentiation
Allows organisms to be more complex
What are new cells for growth produced by?
Mitosis
Explain why new cells are genetically identical in mitosis?
Because the DNA replicates
In mammals what type of body cells do they have?
Diploid (two copies of each chromosome)
Explain why DNA replication must take place
So that all new cells produced have all the DNA of the original cell otherwise the cells would not receive all the chromosomes and genes necessary for life processes
What are gametes produced by?
Meiosis
Describe gametes
Haploid (contain one chromosome from each pair)
Explain how the structure of a sperm cell is adapted to its function
Many mitochondria to provide energy
An acrosome that releases enzymes to digest the egg membrane
Explain why fertilisation results in genetic variation
- gametes combine to form a diploid zygote
- genes on the chromosome combine to control the characteristics of the zygote
Explain why in meiosis the chromosome number is halved and each cell is genetically different
- one chromosome from each pair separate to opposite poles of the cell in the first division
- chromosomes divide and the copies move to opposite poles of the cell in the second division
Describe what happens in mitosis
- chromosomes line up along the centre of the cell
- they then divide
- the copies more to opposite poles of the cell
Describe how DNA replication occurs
- the double helix unzips
- new bases pair up with exposed bases on each strand
- an enzyme bonds the new bases together to form complementary strands
- two identical strands of DNA are formed
Explain why becoming multicellular requires the development of specialised organ systems
Communication between cells
Supplying the cells with nutrients
Controlling exchanges with the environment
Describe the difference between simple organisms which are unicellular and more complex organisms which are multicellular
Single-cell organisms are very small and have to rely on diffusion to obtain glucose and oxygen, to remove waste products
- multicellular are larger and more complex. Require specialised organs to carry out functions like gas exchange and digestion.
