Cell Division Flashcards
Give 2 reasons why mitosis of different garlic root tip was different?
- Temperature
- Genetic differences
Could be more
Describe and explain what the student should have done when counting cells to amke sure the mitotic index obtained for garlic root tip was accurate?
What is mitotic index?
Examine large number of cells
To ensure representative sample
Proportion of cells undergoing cell division
A student investigated the stages of mitosis in a garlic root. This was placed on a slide with a stain. Explain why:
- A root tip was used
- A stain was used
- Root tip was firmly squashed
- Mitosis occurs more rapidly
- Chromosomes not visible without stain
- To let light through as is a thin layer
What is a tumour? (2)
Mass of cells/tissue
Uncontrolled mitosis/cell division
Describe the process of crossing over + explain how it increases genetic diversity? (4)
- Homologous pairs of chromosomes form a bivalent
- Chiasmata forms
- Equal lengths of chromatids are exchanged
- Producing new combinations of alleles
Describe binary fission in bacteria? (3)
- Replication of circular DNA
- Replication of plasmids
- Division of cytoplasm
What is independent segregation?
The random order of maternal + paternal chromosomes lining up on equator during meiosis 1 to produce genetic variation
Explain how meiosis results in cells that have the haploid number of chromosomes + show genetic variation? (6)
- Homologous chromosomes pair up
- Maternal + paternal chromosomes are arranged in any order
- Independent segregation + crossing over occurs
- Equal lengths of chromatids are swapped between chromosomes
- Produces new combination of alleles
- Chromatids separate at meiosis
How do you calculate the number of possible combinations of chromosomes?
2^n
n = number of different pairs of homologous chromosomes
Describe the features of telophase? (2)
- Nuclear membrane begins to reform
- Chromosomes unwind
Describe the features of anaphase? (4)
- Spindle fibres shorten + contract
- Centromere splits
- Sister chromatids are separated
- Chromatids are pulled to opposite poles of cell
Describe the features of metaphase (2)
- Spindle fibres form + attach to centromere of chromosomes
- Chromosomes align on equator of cell
Describe the features of prophase? (3)
- Nuclear membrane begins to breakdown
- Centrioles move to poles of the cell
- Chromosomes condense
Stages of meiosis? Draw?
How to calculate length of time on each stage of mitosis?
Total number of cells in mitosis (visible chromosomes)
—————————————— X time of 1 cell cycle (minutes)
total number of cells
What control genes can switch cell division on + off? What do they do? (2)
- Tumour suppressor genes - code for proteins that slow down the cell cycle
- Proto-onco genes - code for proteins that speed up the cell cycle
How is cancer treated?
The drug inhibits cell division (mitosis) which stops DNA replication, cytokinesis, spindle formation
Differences between mitosis + meiosis? (4)
Mitosis:
- One division
- Genetically identical
- Two produced
- Crossing over/independent segregation only in meiosis
What is a homologous pair of chromosomes?
2 chromosomes that carry the same genes in the same loci
What is mitosis used for? (3)
Increasing cell numbers + growth of organism
Repair of damaged cells
Replacement of dead cells
Diagram of chromosome?
Difference between diploid + haploid cells?
Diploid = 2n —–> 46
Haploid = n —–> 23 (gametes)
What are chromosomes?
Independant DNA molecule thats coiled into condensed form
What happens at the end of the cell cycle?
Cytokinesis - division of cytoplasm to produce new cells (not all cells go through this)
What are the 3 stages of interphase + what do they do?
G1 - Cell increases in size + new biomass is made (proteins)
S - DNA replicates by semi-conservative replication
G2 - Cell prepares for division, synthesis + stores ATP
