Chromosomes, the cell cycle, mitosis and stem cells, including therapeutic cloning and the arguments around embryonic stem cell use.
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1.Where is the genetic material found in a eukaryotic cell?
In the nucleus, in structures called chromosomes.
2.What is a chromosome made of?
A long molecule of DNA, which carries a large number of genes.
3.What is a gene?
A short section of DNA that codes for a particular protein, and therefore for a particular characteristic.
4.How are chromosomes arranged in body cells?
In pairs. A human body cell has 23 pairs, which is 46 chromosomes in total.
5.What are the stages of the cell cycle?
Growth and DNA replication, then mitosis, then division of the cytoplasm and cell membranes to form two cells.
6.What happens in the first stage of the cell cycle?
The cell grows, the number of subcellular structures such as ribosomes and mitochondria increases, and the DNA replicates so each chromosome has two copies.
7.What happens during mitosis itself?
One set of chromosomes is pulled to each end of the cell and the nucleus divides.
8.What happens after mitosis?
The cytoplasm and cell membranes divide, producing two genetically identical daughter cells.
9.Are the cells produced by mitosis identical?
Yes. They are genetically identical to each other and to the parent cell.
10.Give three reasons why organisms need mitosis.
Growth, development, and repair or replacement of damaged cells. It is also used in asexual reproduction.
11.What can happen if cells divide by mitosis uncontrollably?
A mass of cells called a tumour can form, which may lead to cancer.
12.Why must DNA be copied before a cell divides?
So that each daughter cell receives a complete and identical set of genetic information.
13.What is a stem cell?
An undifferentiated cell that can divide to produce more cells of the same type, or differentiate into other types of cell.
14.Where are embryonic stem cells found?
In early human embryos.
15.What can embryonic stem cells differentiate into?
Any type of human cell.
16.Where are adult stem cells found?
In some adult tissues, for example bone marrow.
17.What can adult stem cells form?
Only a limited range of cell types. Bone marrow stem cells, for example, form blood cells.
18.Where are stem cells found in plants?
In the meristems, at the tips of roots and shoots.
19.What can plant meristem cells do?
Differentiate into any type of plant cell, and they keep this ability throughout the life of the plant.
20.Give two uses of plant stem cells.
Producing clones of rare plants to protect them from extinction, and cloning crop plants with useful features such as disease resistance or high yield.
21.What is therapeutic cloning?
Producing an embryo with the same genes as the patient, so that stem cells taken from it are not rejected by the body of the patient.
22.Give two conditions that stem cell treatment may help with.
Diabetes and paralysis.
23.Why might transplanted stem cells be rejected?
If the cells have different genes from the patient, the immune system recognises them as foreign and attacks them.
24.Give an objection some people have to embryonic stem cell research.
The embryo is destroyed in the process, and some people object on ethical or religious grounds because they regard the embryo as a potential human life.
25.Give a medical risk of using stem cells.
Viruses could be transferred if the cells are grown in a contaminated culture, and the transplanted cells might divide uncontrollably.
26.What is the advantage of using stem cells taken from the patient themselves?
They have the same genes, so they are not rejected by the immune system.
27.How does mitosis differ from meiosis in what it produces?
Mitosis produces two genetically identical diploid cells. Meiosis produces four genetically different haploid gametes.
28.What does diploid mean?
A cell that contains two sets of chromosomes, which is 46 in humans.
29.What does haploid mean?
A cell that contains one set of chromosomes, which is 23 in humans. Gametes are haploid.
30.Why is mitosis important in an embryo?
It produces the very large number of cells needed for growth and development from a single fertilised egg.
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