2.3 eukaryotic cell division

Question 1

what is a chromosome

Answer 1

a mass of coiled dna threads and proteins
when cells divide they become more condensed and become much shorter, denser and take up stains

Question 2

why do cells divide

Answer 2

to bring about growth and asexual reproduction

Question 3

what is interphase

Answer 3

period of non division when the cell increase in mass and size, DNA produced, chromosomes replicate, organelles synthesised and the cell prepares for division

Question 4

describe each phase of the cell cycle

Answer 4

G1- end of the previous round of division, start of chromosome duplication, cell material grows and develops
S- chromosomes replicate to become double stranded chromatids
G2- organelles and other materials needed for division are synthesised
M- mitosis
C- cytokinesis

Question 5

what happens in prophase

Answer 5

chromosomes coil up and take up stains to become visible, each chromosome consists if two daughter chromatids
nucleolus breaks down, centrioles pull apart to begin to form the spindle

Question 6

what happens in metaphase

Answer 6

the spindle is forming and chromatids move for a position on the equator of the spindle

Question 7

what happens in anaphase

Answer 7

the centromeres that linked the two chromatids split, chromatids separate and move to opposite sides of the cell

Question 8

what happens during telophase

Answer 8

spindle breaks down, nuclear envelopes begin to form around the two sets of chromosomes
nucleoli and centrioles reform
chromosomes unravel to become less dense

Question 9

what happens during cytokinesis in plants

Answer 9

division of the cytoplasm, contractile fibres tighten around the centre of the cell until they are separated

Question 10

what happens during cytokinesis in animals

Answer 10

division of the cytoplasm, contractile fibres tighten around the centre of the cell until they are separated
two identical daughter cells are formed

Question 11

what does mitosis produce

Answer 11

genetically identical individuals or clones
two identical diploid daughter cells

Question 12

what are the advantages and disadvantages of mitosis

Answer 12

it does not rely on finding a mate
gives rise to large numbers of offspring very quickly

however, offspring are genetically identical, doesn’t allow for variation, if living conditions change it could cause destruction for a group of genetically identical organisms

Question 13

what is sporulation

Answer 13

the production of asexual spores that are capable of growing into new individuals
these spores can survive adverse conditions and spread over great distances

Question 14

what is regeneration

Answer 14

form of asexual reproduction that occurs when organisms need to replace parts of their body that have been lost

Question 15

what is fragmentation

Answer 15

a form of regeneration that happens when animals reproduce themselves asexually from fragments of their body

Question 16

what is reproductive budding

Answer 16

when their is an outgrowth from the parent organism that produces a smaller but identical individual by mitotic cell division ]
the bud eventually detaches and has an independent existence from the parent

Question 17

what is vegetative propagation and where does it occur

Answer 17

occurs in flowering plants and is when a plant forms a structure that develops into as fully differentiated new plant that is identical to the parent, and involves only mitotic cell division

Question 18

define growth

Answer 18

growth is a permanent increase in the number of cells, or in the mass or size of an organism

Question 19

what are the factors that growth is affected by

Answer 19

availability of food, temperature, light intensity, genetic make up of an organism

Question 20

why is dry mass a better measurement of growth than linear measures

Answer 20

growth involves increase of the cell content
height and weight are deceptive
just because height has increased doesn’t mean the content of the organism has increased, and water content of cells vary which affects mass, so dry mass is the most accurate

Question 21

why is it hard for scientists to measure growth accurately

Answer 21

must be measured with dry mass so water must be removed
if all water is removed then organism dies
it is hard and unethical to grow large samples of genetically similar organisms and take random samples to get a dry mass

Question 22

what is the difference between a growth patters of an animal and the growth pattern of a plant

Answer 22

animals often have a relatively slow start, then a rapid period of growth until maturity where it slows down then eventually stops
plants often continuously grow throughout their lives

Question 23

when does the largest amount of growth take place in the human body

Answer 23

during development of the embryo

Question 24

how does mitosis take place in plants

Answer 24

it continues throughout the entire life of the plant and takes place in the meristems, and after they have divided they absorb water into their vacuoles and become more rigid

Question 25

what happens when skin is damaged

Answer 25

rapid mitosis is triggered in the body and cells regenerate lost skin tissue