Cell Division

Question 1

What is the cell cycle

Answer 1

a highly ordered sequence of events that takes place in a cell in order to grow and divide
resulting in two genetically identical daughter cells

Question 2

What is Interphase

Answer 2

the first stage of the cell cycle
not a resting phase as this is when the cell carries out all of its major functions such as producing enzymes whilst also preparing for cell division

Question 3

What occurs during Interphase

Answer 3

G1 - cell grows and new proteins and organelles are synthesised
G1 Checkpoint - checks all chemicals needed for respiration are present and that there is no damage to DNA before entering the S phase
S - DNA replicated in the nucleus
G2 - cell grows more in preparation for mitosis
G2 Checkpoint - ensures all DNA has been replicated correctly and that there is no damage to DNA so cell can enter mitosis

Question 4

What is G0 phase

Answer 4

when the cell temporarily or permanently leaves the cycle

Question 5

What would cause a cell to enter the G0 phase

Answer 5

• cell differentiation
• DNA damage

Question 6

What is meant by senescent

Answer 6

majority of normal cells can only divide a limited number of times and eventually become senescent
as you get older the amount of these cells in your body increases and is linked with age related diseases such as cancer and arthritis

Question 7

What does mitosis ensure

Answer 7

both daughter cells are genetically identical

Question 8

What is mitosis used for

Answer 8

growth, replacement and repair of tissues in multicellular organisms
necessary for asexual reproduction

Question 9

Why is it important that the chromatids are kept close together during mitosis

Answer 9

so that they can be precisely manoeuvred and segregated equally; one each into the two new daughter cells

Question 10

What occurs during Prophase

Answer 10

chromosomes condense becoming shorter, fatter and more visible

small proteins called centrioles begin moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle

nuclear envelope breaks down so the chromosomes lie free in the cytoplasm

Question 11

What occurs during metaphase

Answer 11

chromosomes line up in the middle of the cell forming the metaphase plate, and begin attaching to the spindles by their centromeres

Metaphase checkpoint occurs and ensures that all chromosomes are attached to the spindle before mitosis continues

Question 12

What occurs during anaphase

Answer 12

centromeres divide separating the sister chromatids
the spindles contract pulling the chromatids to opposite poles of the cell

Question 13

What occurs during telophase

Answer 13

spindles break down and the chromosomes uncoil
nuclear envelopes form around each new set of chromosomes, forming nucleolus

Question 14

What is the difference between cytokinesis in an animal cell vs a plant cell

Answer 14

Animal cells;
cleavage furrow forms around the middle of the cell and the cell membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle, forming two cells

Plant cells;
due to cell walls, cleavage furrow cannot form so vesicles from Golgi apparatus begin to assemble in the same place as where the metaphase plate was, vesicles then fuse with each other and the cell surface membrane, dividing the cell into two.

Question 15

What is Meiosis

Answer 15

Type of cell division that happens in the reproductive organs to produce gametes
It produces 4 genetically different/unidentical haploid cells as each cell ends up with a different combination of chromosomes

Question 16

What is reduction division

Answer 16

Meiosis invokes a reduction division as the cells that divide by meiosis have a full number of chromosomes to begin with (diploid) but the cells that are formed have half the number (haploid)

Question 17

What are homologous chromosomes

Answer 17

Chromosomes are paired together from each parent that are the same size and have the same gene
(e.g gene for eye colour)
However they can have alleles which are different versions of the same gene
(e.g eye colour blue vs brown)

Question 18

What happens in Meiosis 1

Answer 18

Prophase 1 - same as mitosis plus homologous chromosomes pair up forming bivalents/homologous pairs and crossing over occurs due to the chromatids entangling - the chromatids will contain the same genes but have a different combination of alleles

Metaphase 1 - homologous pairs randomly assemble along the metaphase plate so maternal or paternal chromosomes/many different allele combinations can end up facing either pole; random assortment, which results in genetic variation

Anaphase 1 -