B3: Cell division + sex determination

Question 1

what happens during interphase

Answer 1

cell grows
chromosomes in nucleus replicated
cell respires to provide energy for respiration

Question 2

why is replication important

Answer 2

allows for full set of chromosomes

identical to parent cell

Question 3

what does a chromosome look like after replicaiton

Answer 3

two sister chromatids

held together by centromere

Question 4

roles of mitosis

Answer 4

allows organisms to increase in size by increasing total no. of cells
allows worn out + dead cells to be repaired + replaced
allows reproduction by asexual reproduction

Question 5

what does the cell do when preparing for interphase

Answer 5

cell cycle pauses

to check cell is healthy + DNA has been copied correctly

Question 6

what happens if errors detected in cell

Answer 6

cell destroyed

Question 7

what happens if errors not detected

Answer 7

cell cycle contines + divided by mitosis

may lead to defective cells

Question 8

how does cancer develop

Answer 8

group of defective cells that divide uncontrollably

forming a tumour

Question 9

in fertilisation, the gametes fuse to form…

Answer 9

a zygote

Question 10

where and how are sperm cells produced

Answer 10

testes

meiosis

Question 11

where and how are ova produced

Answer 11

ovaries

meiosis

Question 12

importance of meiosis

Answer 12

• meisosis halves no. of chromosomes
• gametes produced are genetically different from each other + parent cell
  = produces genetic variation

Question 13

use of meisosis

Answer 13

gamete production during sexual reproduction

Question 14

what takes place during asexual reporduction

Answer 14

one parent needed
no production / fusion of gametes
offspring genetically identical to parent

Question 15

binary fission

Answer 15

• bacterial cell reproduces by binary fission- produces copy of loop of chromosomal DNA in cytoplasm
• cell divided into two, each daughter cell gets copy of loop
• not always identical as DNA can be mutated= daughter cells get diff chromosomal DNA

Question 16

what happens in sexual reporducion

Answer 16

• two parents involved
• each parent produces specialised cells - gametes
• gametes produced by meiosis
• gametes fuse at fertilisation
• offspring genetically different

Question 17

why are offspring genetically different in sexual reproduction`

Answer 17

• to their parents : receive half of their genetic information
  from each parent in the gametes

-to each other : the gametes produced by meiosis are genetically different from each other
it is completely random which of the gametes from each parent will then fuse at fertilisation to form the zygote.

Question 18

Importance of producing genetically different offspring

Answer 18

• so genetic variation is maintained within a species.
• Genetic variation is essential for natural selection.
• Natural selection enables populations of organisms to adapt to changes in the environment. It ensures the successful continuation of a species over time.
• Genetic variation within a species also helps to reduce the frequency with which recessive inherited conditions occur.

Question 19

females have… chromosomes

Answer 19

XX

Question 20

males have….chromosomes

Answer 20

XY

Question 21

why cant a male be produced with the x chromosome

Answer 21

Y chromosome contains key genes

needed to intiate male secual development