Cell Division (AQA GCSE Combined Science: Trilogy: Biology): Flashcards
Exam code: 8464
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Chromosome
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Chromosome
A thread-like structure found in the nucleus, made from a long molecule of DNA, that carries a large number of genes.
How are chromosomes arranged in body cells, and how many do humans have?
They are found in pairs.
Humans have 46 chromosomes, arranged in 23 pairs.
Each chromosome carries a large number of .
Each chromosome carries a large number of genes.
What molecule are chromosomes made of?
DNA – each chromosome is made from one long DNA molecule.
True or False?
Chromosomes are found in the cytoplasm of a cell.
False.
Chromosomes are found in the nucleus of the cell.
What are the three overall stages of the cell cycle?
Growth – DNA and sub-cellular structures are doubled
Mitosis – the nucleus divides
Cytokinesis – the cytoplasm and cell membrane divide
What happens during the growth phase of the cell cycle?
The DNA replicates, so there are two copies of each chromosome.
The number of sub-cellular structures (e.g. ribosomes and mitochondria) increases.
What happens during mitosis?
One set of chromosomes is pulled to each end of the cell, then the nucleus divides into two.
What does one division by mitosis produce?
Two genetically identical daughter cells.
Why is cell division by mitosis important?
For the growth and development of multicellular organisms, and for the repair and replacement of damaged cells.
Mitosis produces two genetically daughter cells.
Mitosis produces two genetically identical daughter cells.
How can you estimate how long one stage of the cell cycle lasts from a sample of cells?
(number of cells in that stage ÷ total number of cells) × total cell cycle time
Stem cell
An undifferentiated cell that can divide to produce many more cells of the same type, from which other cell types can arise by differentiation.
A stem cell is described as because it has not yet become specialised.
A stem cell is described as undifferentiated because it has not yet become specialised.
What can embryonic stem cells differentiate into?
Most types of specialised human cell.
Where are adult stem cells found, and what can they form?
Found in bone marrow.
They can form a limited range of cell types, mainly blood cells.
Where are stem cells found in plants, and what can they do?
In the meristems.
They can differentiate into any type of plant cell throughout the plant's life.
Name two medical conditions that stem cells may be able to treat.
Diabetes and paralysis.
In therapeutic cloning, why are the stem cells not rejected by the patient's body?
The embryo is produced with the same genes as the patient, so the stem cells are not rejected.
Give one risk and one objection to using stem cells in medicine.
Risk: transfer of viral infection.
Objection: some people have ethical or religious objections (an embryo is destroyed).
Give two uses of cloning plants from meristem stem cells.
Clone rare species to protect them from extinction
Clone crop plants with useful features (e.g. disease resistance) quickly and economically for farmers
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