2.3-eukaryotic cell division (mitosis)

Question 1

1.prophase

Answer 1

-before this, genetic material has been replicated to produce exact copies of the chromosomes
1.chromosomes coil up, can take stains and become visible
2.each chromosome consists of 2 daughter chromatids that are attached at centromere
3.the nucleolus breaks down and the centrioles begin to pull apart, forming spindles

Question 2

2.metaphase

Answer 2

1.chromatids appear the jostle about for position on equator of spindle
2.they eventually line up along this plate, with each centromere associated with a microtubule of the spindle

Question 3

3.anaphase

Answer 3

1.chromatids split and act as completely different entities
2.chromatids from each pair are drawn towards opposite poles of the cell
3.at the end of anaphase, the two sets of chromatids have been spereated to opposite ends of the cell

Question 4

4.telophase

Answer 4

1.spindle fibres break down and nuclear envelopes form around the 2 sets of chromosomes
2.nucleoli and centrioles are re formed
3.chromosomes begin to unravel, become less dense and harder to see

Question 5

phases of the cell cycle

Answer 5

G1= time between previous round of mitosis and the start of chromosome duplication- lasts hours to years
S= chromosomes replicate and become double stranded chromatids, ready for next step
G2=organelles and other materials are synthesized
M=mitosis
C= cytokenisis- cells are seperate

Question 6

Cytokinesis

Answer 6

1. in animal cells, a ring of contractile fibres tightens around centre of cell
   2.they continue to contract until the two cells have been separated
2. in plant cells, a cellulose cell wall builds up from the inside of the cell outwards

Question 7

facts about the cell cycle

Answer 7

-it is controlled by a number of chemical signals made in response to different genes
-control chemicals are small proteins (cylins), they build up and attach to enzymes (cylin dependent kinases)

Question 8

chromosome structure

Answer 8

-made up of a mass of coiled threads of DNA and proteins
-when DNA molecules condense, they must be packaged very efficiently (pos charged basic proteins called histones)
-DNA winds around histones to form dense clusters known as nucleosomes which coil even more in to a thread
-in humans, 46 are produced

Question 9

3 types of growth patterns

Answer 9

1. continuous growth- S shaped graph
   2.discontinuous growth- step shaped (height)
   3.discontinuous growth, pos line measured as mass

Question 10

how growth occurs, in 3 steps

Answer 10

1. division
   2.assimilation
   3.expansion

Question 11

how is growth measured?

Answer 11

-mass can be deceptive as they contain the water content of cells, urine and facael matter
-dry mass is most accurate way of measuring growth as it tells us the amount of biological material
-however, removing all of an organisms water will kill it, so height and mass used in most cases

Question 12

types of asexual reproduction- budding

Answer 12

-does not include flowers or leaves
-outgrowth from parent organism that produces a smaller but identical individual by mitosis
-very rare in animals
-e.g. yeast cells

Question 13

types of asexual reproduction- vegetative propagation

Answer 13

-occurs in flowering plants
-a plant forms a structure that develops into a fully differentiated new plant, identical to the parent
-involves only mitotic division
-exploited by gardeners to produce new plants
advantageous as identical

Question 14

types of asexual reproduction- sporulation

Answer 14

-involves mitosis, and production of asexual spores that are capable of growing into new individuals e.g. fungi and mosses

Question 15

types of asexual reproduction- regerneration

Answer 15

-when organisms can replace lost body parts, some can even reproduce themselves from fragments (fragmentation)
-e.g. starfish

Question 16

products of mitosis

Answer 16

-two identical daughter cells