GCSE Biology: B2 - Cell division

What do chromosomes consist of?

- chromosomes are made up of the molecule DNA

Where are chromosomes found?

- chromosomes are found in the nucleus of a cell

How many chromosomes do body cells contain?

- body cells contain 2 of each chromosome

- they are paired

How many pairs of chromosomes do human body cells contain?

- human body cells contain 23 pairs of chromosomes

How many chromosomes do human gametes contain?

- human gametes have 23 single chromosomes

- that are not paired

How are human features determined?

- chromosomes carry a large number of genes which determine many of our features

What is the cell cycle?

the process in which cells divide

Describe the stages of the cell cycle by mitosis

- in the first stage of the cell cycle, the DNA replicates to form 2 copies of each chromosome

- the cell also grows and copies its internal structures, such as mitochondria and ribosomes

- in the second stage of the cell cycle, mitosis takes place

- one set of chromosomes is pulled to each end of the cell and the nucleus also divides

- in the final stage of the cell cycle, the cytoplasm and the cell membrane divide to form 2 identical cells

What are the functions of mitosis?

- mitosis is essential for growth and development of multicellular organisms

- mitosis takes place when an organism repairs itself

- mitosis happens during asexual reproduction

What is a stem cell?

an undifferentiated cell which can give rise to more cells of the same type and can differentiate to form other types of cells

What are embryonic stem cells?

- embryos can change and form specialised cells

- this is called differentiation

- cells in the early-stage embryo are undifferentiated cells capable of differentiating into any type of body cell

- these cells are called embryonic stem cells

What are some arguments against using embryonic stem cells in medicine?

- some people think that human embryos should not be used to create stem cells, as each embryo is a potential human life

- there is a risk of stem cells being infected with viruses and these viruses then being passed on to patients

What are stem cells in bone marrow?

- stem cells in bone marrow differentiate to form cells found in our blood

- such as red blood cells, white blood cells and platelets

Are stem cells used in medicine?

- stem cells are used widely in medicine

Describe how bone marrow transplants can be used in medicine

- leukaemia is a cancer of the bone marrow

- to treat this, the patient's existing bone marrow is destroyed using radiation

- the patient then receives a transplant of bone marrow from a donor

- the stem cells in the bone marrow divide to form new bone marrow, also they differentiate to form blood cells

What are some problems with bone marrow transplants?

- the donor must be compatible with the patient

- otherwise, the white blood cells produced by the donated bone marrow could attack the patient's body

- there is a risk that viruses can be passed from the donor to the patient

Describe how therapeutic cloning is used in medicine

- in therapeutic cloning, an embryo is produced with the same genes as the patient

- stem cells from the embryo can be transplanted into the patient without being rejected by the patient's immune system

- once inside the patient, the stem cells can differentiate to replace cells that have stopped working correctly

What are some problems with therapeutic cloning?

- some people have ethical or religious objections to therapeutic cloning

What are plant stem cells?

- roots and buds of a plant contain meristem tissue

- these stem cells can differentiate into any type of plant tissue at any point in the life of the plant

What can the stem cells in meristem tissue in plants be used for?

- meristem tissue can be used to clone a rare plant to stop it from going extinct

- or to produce cloned crop plants for farmers to improve crop yields