AQA GCSE Biology Year 10: Cell division, cancer, and reproduction

What are chromosomes?

. Found in nucleus of cell

. 23 pairs in normal human body cells

. Made up of long lengths of DNA

What are genes?

. Short section of a chromosome

. Each gene codes for a different characteristic

Describe the first stage of the cell cycle

. Longest stage of cell cycle

. Cell grows and increases number of sub-cellular structures such as ribosomes and mitochondria

. DNA replicates to form 2 copies of each chromosome

Describe the second stage of the cell cycle

. Called mitosis

. One set of chromosomes is pulled to each end of the cell and the nucleus divides

Describe the third stage of the cell cycle

The cytoplasm and cell membranes divide to form 2 identical cells

What is cancer?

The result of changes in cells that lead to uncontrolled growth and division

What are benign tumours?

. Growths of abnormal cells

. Contained in 1 area, usually within a membrane

. Do not invade other parts of the body

What are malignant tumour cells?

. Cancers

. Invade neighbouring tissues and spread to different parts of body in the blood where they form secondary tumours

What are some risk factors for cancer?

. Genetic risk factors

. Lifestyle risk factors e.g smoking, exposure to ionising UV light from sun

What does there being a correlation between factor A and B mean?

. Doesn't mean A causes B or vice-versa

. Both could be caused by another variable

. Scientists have to carry out research to discover if there's a causal mechanism

What is the main difference between mitosis and meiosis?

. Meiosis leads to non-identical cells being formed

. Mitosis leads to identical cells being formed

What does sexual reproduction involve?

the joining (fusion) of male and female gametes

What are the male and female gametes in animals?

sperm and egg cells

What are the male and female gametes in flowering plants?

pollen and egg cells

Why does sexual reproduction lead to variety in the offspring?

. There is a mixing of genetic information

. The formation of gametes involves meiosis

How is asexual reproduction different to sexual reproduction?

. Involves only 1 parent

. No fusion of gametes

. No mixing of genetic information

. Leads to genetically identical offspring (clones)

. Only mitosis is involved

Where does meiosis happen?

Cells in reproductive organs divide by meiosis to form gametes

What happens during meiosis?

. Copies of the genetic information are made

. Cell divides twice to form 4 gametes, each with a single set of chromosomes

. All gametes are genetically different to each other

What happens at fertilisation?

. Gametes join to restore the normal number of chromosomes

. New cell divides by mitosis

. Number of cells increases

. As the embryo develops cells differentiate

What are some advantages of sexual reproduction?

. Produces variation in the offspring

. If the environment changes variation gives a survival advantage by natural selection

. Natural selection can be sped up by humans in selective breeding to increase food production

What are some advantages of asexual reproduction?

. Only one parent needed

. More time and energy efficient as do not need to find a mate

. Faster than sexual reproduction

. Many identical offspring can be produced when conditions are favourable

Give 3 examples of organisms which reproduce by both methods (sexual and asexual) depending on the circumstances

. Malarial parasites

. Many fungi

. Many plants

How do malarial parasites reproduce?

. Asexually in human host

. Sexually in mosquito

How do many fungi reproduce?

. Asexually by spores

. Also reproduce sexually to give variation

How do many plants reproduce?

. Produce seeds sexually

. Also reproduce asexually by runners (e.g strawberry plants), or bulb division (e.g daffodils)

What do you call a fertilised egg?

zygote