Cell Division Flashcards
Disadvantages of becoming multi cellular?
Specialised organs systems needed
Advantages of becoming multi cellular?
- organisms becomes larger
- organisms become more complex
- cell differentiation
What do the specialised organ systems of multicellular organisms enable?
- communication between all cells in body
- supply cells with nutrients
- control exchanges with outside environment
Describe a unicellular organism
An amoeba consists of one cell. It reproduces by dividing to make 2 clones of the parent cell. It then doubles the genetic information within he cell.
What does mitosis produce?
Diploid cells
What is a diploid cell?
A cell with 46 chromosomes/ a cell containing 2 copies of each chromosome.
What is mitosis used for?
- Growth and repair
- Replacement of worn out cells
- Asexual reproduction
What is D.N.A replication?
The process in which genetic information is doubled.
Why is D.N.A replication needed?
To ensure that each cell produced by mitosis has 2 copies of each chromosome.
Describe D.N.A replication
- The double helix of a D.N.A molecule unzips to form single strands.
- New strands are formed by D.N.A bases lining up in complimentary base pairings.
What is mitosis?
The process in which new, diploid cells are produced for growth.
Describe mitosis
- A resting cell undergoes D.N.A replication (chromosomes are copied).
- A spindle forms with the chromosomes aligned along equator of the cell.
- The spindle splits, dragging the chromosome single strands to opposite poles of he cell.
- New nuclear membranes form around the new sets of chromosomes, producing 2 new, genetically identical cells.
What is a homologous cell?
A cell containing identical, paired chromosomes.
What are gametes?
Sex cells, e.g. Sperm and egg cells.
What is a haploid cell?
A cell which contains only 23 chromosomes / one chromosome from each pair. (Half the number of chromosomes a normal cell would have).
What happens during fertilisation?
- 23 chromosomes within the mother cell pair up with 23 chromosomes from the father cell.
- This creates a diploid zygote that is genetically varied from its parents (since it has a mix of the D.N.A).
- The 23rd chromosome decides the gender of the baby, X + Y = Male, X + X = Female.
How is a sperm cell adapted to its function?
- Many produced - increase fertilisation chances.
- Tail - to swim to egg.
- Streamlined body shape - make swimming to egg quicker and easier.
- Acrosome (tip of head) containing enzymes - to break down egg cell membrane.
- many mitochondria - produce energy for long swim.
Describe meiosis.
There are 2 divisions (of x-shaped chromosome not of the cell).
- In the first division, the single strand chromosome is copied to make an x - shaped chromosome ( 2 single strands together) - the x - shape is made of 2 single strand chromosomes with the same genes.
- Genetic information is swapped between chromosomes.
- In the second division, the chromosomes from each x - shaped pair split and move to the opposite poles (each corner) of the cell.
- The cell splits into 4 new haploid cells, all genetically different from each other.
