Cell Division & Stem Cells (WJEC GCSE Science (Double Award): Biology): Flashcards
Exam code: 3430
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Define chromosome.
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Define chromosome.
A linear, thread-like structure in the nucleus, made from highly coiled DNA and carrying a linear arrangement of genes.
Where in the cell are chromosomes found?
In the nucleus.
What are chromosomes made of?
Highly coiled strands of DNA.
Define gene.
A section of DNA on a chromosome that codes for a characteristic.
How are chromosomes arranged in body cells?
They are found in pairs.
The two chromosomes of a pair carry the same genes.
Where does each chromosome of a pair come from?
One is inherited from the mother and one is inherited from the father.
How many chromosomes are in a human body cell?
46 chromosomes, arranged in 23 pairs.
Why can it be said that genes come in pairs?
Chromosomes come in pairs, and both chromosomes of a pair carry the same genes. So each gene is present twice.
Human body cells contain ＿＿＿＿＿＿＿＿ pairs of chromosomes.
Human body cells contain 23 pairs of chromosomes.
Chromosomes are made from highly coiled strands of ＿＿＿＿＿＿＿＿.
Chromosomes are made from highly coiled strands of DNA.
True or False?
All human cells contain 46 chromosomes.
False.
Red blood cells have no nucleus, so they contain no chromosomes at all. Gametes contain only 23.
True or False?
Different species have different numbers of chromosome pairs.
True.
Humans have 23 pairs while horses, for example, have 32 pairs.
Why are chromosomes sometimes drawn as an X shape?
The X shape appears when a chromosome has been copied before cell division, so it has two identical arms joined together.
What is the relationship between DNA, genes and chromosomes?
DNA is coiled up to form a chromosome.
A gene is a short section of that DNA which codes for a characteristic.
Define mitosis.
Nuclear division that produces two genetically identical daughter cells with the same chromosome number as the parent cell.
Define meiosis.
Nuclear division that produces four genetically different daughter cells with half the chromosome number of the parent cell.
State four functions of mitosis.
Growth, producing new cells so the organism increases in size
Replacement of old cells as they die
Repair of damaged tissues
Asexual reproduction in some organisms
What is the function of meiosis?
To produce gametes for sexual reproduction.
Why must meiosis halve the chromosome number?
So that fertilisation restores the normal number.
If gametes had the full number, the chromosome number would double every generation.
How does meiosis increase genetic variation?
It recombines maternal and paternal chromosomes in different ways, so every gamete is genetically different from the others and from the parent cell.
Describe what happens to the chromosomes during mitosis.
The chromosomes are copied, then line up along the equator of the cell.
The chromatids are separated and pulled to opposite ends.
A new nucleus forms around each group of chromosomes.
Describe the two divisions of meiosis.
First division: the pairs of chromosomes line up in the centre and are pulled apart, so each new cell has only one of each pair.
Second division: the chromosomes line up again and the arms of the chromosomes are pulled apart.
Compare the number of daughter cells produced by mitosis and meiosis.
Mitosis: two daughter cells
Meiosis: four daughter cells
Compare where mitosis and meiosis take place in the body.
Mitosis: in normal body cells
Meiosis: in the reproductive organs
Compare the genetic make-up of the daughter cells from mitosis and meiosis.
Mitosis: daughter cells are genetically identical to each other and the parent
Meiosis: daughter cells are genetically different
Mitosis produces ＿＿＿＿＿＿＿＿ genetically identical daughter cells.
Mitosis produces two genetically identical daughter cells.
＿＿＿＿＿＿＿＿ is the type of cell division that produces gametes.
Meiosis is the type of cell division that produces gametes.
True or False?
Gametes are produced by mitosis.
False.
Gametes are produced by meiosis. Mitosis produces body cells.
True or False?
Meiosis involves two rounds of cell division while mitosis involves one.
True.
This is why meiosis produces four daughter cells while mitosis produces two.
Name four examples of gametes.
Sperm cells and egg cells in animals
Pollen grains and ovules in plants
Why do body cells divide by mitosis?
For growth and to repair damaged cells.
How is mitosis normally controlled in the body?
It is regulated by many different genes, which ensure cells divide only when needed and stop when required.
What happens if mitosis becomes uncontrolled?
Cells divide uncontrollably, which is the cause of cancer.
Define tumour.
A mass of cells formed as a result of uncontrolled cell division.
True or False?
Mitosis is always harmful to the body.
False.
Mitosis is essential for growth, replacement and repair. It is only harmful when it becomes uncontrolled.
True or False?
Genes control when cells divide and when they stop dividing.
True.
Many different genes regulate mitosis. Mutations in these genes can cause cell division to run out of control.
Explain the link between exposure to ionising radiation and cancer.
Ionising radiation increases the rate of mutation in DNA.
Mutations in the genes that regulate mitosis can lead to uncontrolled cell division, and so to cancer.
Why is the control of mitosis so important in a healthy body?
It ensures new cells are made only when they are needed for growth or repair, and that division stops once that need is met.
Define stem cell.
An undifferentiated cell that can differentiate into other types of cell.
What happens to the ability of cells to differentiate as tissues mature?
Cells in mature tissues have generally lost the ability to differentiate.
Some cells in both plants and animals keep this ability, and these are the stem cells.
Where are stem cells found in plants?
In the tips of growing roots and shoots, in tissue known as meristem tissue.
Name the two broad categories of animal stem cell.
Embryonic stem cells
Adult stem cells
Compare the potential of embryonic and adult stem cells.
Embryonic stem cells can differentiate into any cell type in the body
Adult stem cells can only differentiate into a few different cell types
Where are adult stem cells found, and what is their main role?
In certain locations such as bone marrow and skin.
They mainly replace old cells and repair damaged tissue.
Give two conditions that stem cell treatment could help.
Type 1 diabetes: producing new insulin-producing pancreatic cells
Paralysis: producing healthy nerve cells to repair the nervous system
Give three advantages of using tissue grown from a patient's own stem cells.
No need for tissue typing
Avoids the shortage of organ donors
Reduces the risk of transplant rejection
Give two risks associated with stem cell treatments.
Cultured stem cells could become infected with a virus that is passed to the patient
Cultured cells could accumulate mutations and develop into cancer cells
Give one ethical concern about the use of embryonic stem cells.
Embryos are destroyed to obtain the cells, raising the question of whether an embryo should be treated as a person with human rights.
＿＿＿＿＿＿＿＿ stem cells have the potential to differentiate into any type of cell in the body.
Embryonic stem cells have the potential to differentiate into any type of cell in the body.
In plants, stem cells are found in ＿＿＿＿＿＿＿＿ tissue at the tips of roots and shoots.
In plants, stem cells are found in meristem tissue at the tips of roots and shoots.
True or False?
Adult stem cells are already used successfully in medical treatments.
True.
Adult stem cells have already been used to replace faulty blood cells in sickle cell disease.
True or False?
Adult stem cells can differentiate into any cell type in the body.
False.
Only embryonic stem cells can do this. Adult stem cells can form only a few cell types.
Give one social issue surrounding stem cell treatment.
Storing stem cells collected before or after birth is expensive, so it is not an option available to everyone.
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