B2 Cell Divison Flashcards
What do chromosomes do?
Chromosomes carry genes that contain instructions for making new cells, organs, and tissues.
Define gene
A small packet of information that controls a characteristic (or part of it) of your body.
How many pairs of chromosomes do we have?
23 pairs = 46 chromosomes
Where are chromosomes found?
In the nucleus of cells
How many chromosomes do gametes have?
23 chromosomes (1 per pair)
Why is mitosis needed?
For growth and replacement of cells (e.g. at the site of a wound, during production of RBS in bone marrow, during growth spurts etc…)
How does the length of the cell cycle vary during: baby development (before birth), childhood, and after puberty?
Baby development before birth: Short
Childhood: Fairly rapid
After puberty: Slows down
Summarise the stages of the cell cycle (3 stages)
1) Cells grow bigger, increase mass to carry out normal cell activities. Cells replicate their DNA to form two copies of each chromosome. Cells increase the amount of sub-cellular structures (e.g mitochondria, ribosomes) {Longest Stage}.
2) Mitosis: One set of chromosomes is pulled to each end of the cell and the nucleus divides.
3) Cytoplasm and cell membrane divide to form two identical daughter cells.
Why is cell division by mitosis important?
It’s important in the growth and development of multicellular organisms.
Define DNA
A unique molecule which makes up our chromosomes
Define stem cells
An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type.
What happens as an organism develops?
Cells differentiate to form different types
of cells.
When do animal cells become specialised?
In animals, most cells become specialised in early life.
What happens when a cell becomes specialised?
Some of its genes have been switched on; others have turned off. The cell acquires different sub-cellular structures to carry out specific functions.
Describe the restriction of cell division in mature animals
In mature animals, cell division is mainly restricted to repair and replacement.
How do specialised cells divide and what are the restrictions of specialised cells dividing?
Specialised cells can divide by mitosis; they can only form the same sort of cell (e.g muscle cells divide to form more muscle cells).
List 2 examples of cells which can’t divide and describe how they are replaced
Red blood cells and skin cells can’t divide so they are replaced by adult stem cells.
Can nerve cells divide? If not, how are they replaced?
Nerve cells can’t divide, once differentiated and they can’t be replaced by stem cells. Therefore, damaged nerve cells usually aren’t replaced.
How does plant cell differentiation differ from animal cell differentiation?
Plant cells can differentiate throughout their lives.
Where are undifferentiated cells formed (plants)?
At the meristems (active regions of stems and roots).
What happens at the meristems?
Mitosis continuously happens at the meristems. The cells grow and elongate before they differentiate.
Describe how plant cells can redifferentiate
Plant cells can move from one part of a plant to another, where it can redifferentiate and become a different cell.
Explain how a piece of leaf tissue can produce identicall plant clones
1) In right conditions, a plant cell will become unspecialised and undergo mitosis many times.
2) Undifferentiated cells will produce more cells by mitosis.
3) These cells will then differentiate to form tissues.
What does an egg and sperm cell form?
A zygote (single new cell)
