1.6 - cell division

Question 1

Outline the structures of a chromosome

Answer 1

long, thin structure of DNA.
-2 sister chromatids held together at the centromere

Question 2

How many pairs of chromosomes do humans have?

Answer 2

23 homologous pairs
diploid
2n

Question 3

Describe interphase

Answer 3

-longest division of cell cycle
-DNA doubles
Organelles replicate
-proteins are synthesised
-active process , requires ATP

Question 4

Prophase

Answer 4

-Chromatids condense + become visible
-nuclear envelope disintegrates
-centrioles move to opposite poles
-nucleolous disappears
-spindle fibres form

Question 5

Metaphase

Answer 5

The chromosomes align themselves along the equator
-centromere attaches to spindle fibres

Question 6

Anaphase

Answer 6

-Spindle fibres begin to contract
-centromeres separate -chromatids move to opposite poles

Question 7

Telophase

Answer 7

• chromatids reach poles and referred to as chromosomes again
  -chromasomes disperse and lengthen
• nuclear envelope redevelops
• nucleolus reforms
  -spindle fibres break down

Question 8

Cytokenesis
in animals vs plants

Answer 8

-splitting of the cytoplasm to form two new cells
ANIMALS - constriction of the parent cell around the equator. Cleavage furrow
PLANTS - cell plate form across equator, they extend to form new cell

Question 9

Where does mitosis occur in plants and animals ?

Answer 9

• animals = bone marrow, tissue, muscle tissue
  -plants- meristems

Question 10

What is the significance of Mitosis?

Answer 10

• Growth and repair
  -Aesexual reproduction
  -red and white blood cell production
  -increase in call number in plants

Question 11

Define Proto-oncogene

Answer 11

A gene that controls mitosis, before it is exposed to radiation

Question 12

Oncogene

Answer 12

A gene wich causes uncontrolled cell division

Question 13

Meiosis

Answer 13

A two staged cell division which creates 4 haploid cells.

Question 14

difference between meiosis 1 and 2

Answer 14

Meiosis 1= bivalente chromosomes separate
meiosis 2 = chromatids separate
Meiosis 1 = corssing over, meiosis 2 has no crossing over.

Question 15

Prophase 1

Answer 15

-Chromatids condense and are in bivalent pairs.
-joined at the chiasmata where crossing over occurs
-intorduces genetic variation
-genes are swapped between chromosomes.

Question 16

Metaphase 1

Answer 16

-arrange themselves along the equator in pairs
- One chromosome is from the mother, the there is from the father, they face opposite poles randomly
-independent assortment occurs

Question 17

independent assortment

Answer 17

2 pairs chromosomes = 2^2
3 pairs = 2^3

Question 18

Anaphase 1

Answer 18

chromosomes in each bivalent spearate as spindle fibres shorten
moving to opposite poles.

Question 19

Telophase 1

Answer 19

Some species will condense, others lengthen

Question 20

Significance of Meiosis

Answer 20

• genetic stability
  -chromosome number constant through generations

Question 21

Where does meiosis occur ?

Answer 21

animals = testes and ovaries
plants = ovary