B2 Flashcards
Where can genes be found?
Most cells have a nucleus. This contains genetic material in the form of chromosomes. Chromosomes are coiled up lengths of DNA molecules. Each chromosome carries a large number of genes (these control different characteristics). Body cells normally have two copies of each chromosome. Body cells have two copies of each chromosome (one from the father, one from the mother).
Describe the cell cycle.
Body cells in mulitcellular organisms divide to produce new cells as part of a series called the cell cycle. The stage of the the cell cycle when the cell divides is called mitosis. 2) The stage of the cell cycle when the cell divides is called mitosis. Multicellular organisms use mitosis to grow or replace cells that have been damaged. The end of the cell cycle results in two new cells identical to the original cell, with the same number of chromosomes.
How is DNA organised in cells that arent dividing?
It is all spread out in long strings.
Desrcibe the stages of the cell cycle. 1
Before it divides it has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes.
Describe the stages of the cell cycle. 2
It then duplicates its DNA so theres one copy for each cell. The DNA is copied and forms X-shaped chromosomes. Each arm of the chromosome is an exact duplicate of the other.
Describe the cell cycle. 3
The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.
Describe the cell cycle. 4
Membranes form around each of the sets of chromosomes. These become nuclei of the two new cells. The nucleus has divided.
Describe the cell cycle. 5
Lastly the cytoplasm and the cell membrane divide.
Why is the cell cycle important?
For growth, development and repair.
What is differentiation?
The process by which a cell changes to become specialised for its job.
What happens as cells change?
They develop different sub-cellular structures and turn into different types of cells. This allows them to carry out specific functions.
When does most differentiation occur?
As an organism develops.
What is differentitation in mature animals mainly used for?
Repairing and replacing cells
What is the difference between animal cells and plant cells?
Most animal cells differentiate permanently in the embryo however lots of plants can undifferentiate.
What is the cell cycle?
The process of division in a body cell that involves mitosis and results in the formation of two identical daughter cells.
What is a stem cell?
An undifferentiated cell
What can stem cells be used for?
Can divide to produce lots more undifferentiated cells. They can then differentiate into different types of cell, depending on what instruction they’re given.
Where are stem cells found?
In early human embryos
Where are stem cells found in adults?
Certain places like bone marrow. But they can’t turn into any cell type, only certain ones like blood cells.
What can stem cells be used for?
In a lab, stem cells from embryos and bone marrow can be grown to produce clones
Made to differentiate into specialised cells used in medicine or research
How can stem cells cure?
Stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells.
Embryonic stem cells could make insulin-producing cells for people with diabetes or nerve cells for people paralysed by spinal injuries.
What is therapeutic cloning?
When an embryo is made to have the same genetic information as the patient. This means that the stem cells produced from it would also contain the same genes and so wouldn’t be rejected by the patients body if used to replace faulty cells.
Explain cloning in a plant.
In the right conditions, a plant cell will become unspecialised and undergo mitosis many times. Each of these undifferentiated cells will produce more cells by mitosis. Given different conditions, these will then differentiate to form tissues such as xylem, phloem, photosynthetic cells, and root hair cells that are needed to form a tiny new plant. The new plant will be identical to the original parent.
What can clning plants be used for?
To grow more plants of rare species.
Grow crops of identical plants with desired features.
Explain how and why you would expect the length of the cell cycle to vary between an early embryo and a 5 year old.
early embryo
cell cycle very rapid with little time for growth
stage 1 as short as possible as embryo forming new cells
5-year-old child
cell cycle rapid as child growing quickly but not as fast as early embryo
longer periods of growth between divisions
Explain how and why you would expect the length of the cell cycle to vary between a 13 year old and a 70 year old.
13-year-old student
cell cycle rapid as growth and development taking place during puberty
requiring new cells
70-year-old adult
cell cycle slow as new cells still needed for repair
but not for growth
cell death beginning to overtake cell division
When is the cell cycle likely to be rapid in a human and when is it likely to be slow?
very rapid
• at any time when rapid growth is needed
• examples (embryonic development, childhood, puberty,
pregnancy, after injury)
relatively slow
• throughout adult life (excepting pregnancy or injury)
• in sports training
• cell cycle slows with age
