cell division

Question 1

what happens during prophase 1

Answer 1

chromosomes condense
nuclear envelop disintegrates
nucleolus dissapears
spindle formation begins
homologous chromosomes pair up forming bivalents
movement of chromosome causes chromatids to entangle this is called crossing over

Question 2

what happens during metaphase 1

Answer 2

same at mitosis
expect the homologous pairs of chromosome assemble along the metaphase plate of the individual chromosomes
orientation of each homologous pair on the metaphase plate is random and independent
independent assortment occurs

Question 3

what happens during anaphase 1

Answer 3

is different from mitosis
as homologous chromosomes are pulled to opposite poles and the chromatids stay joined to each other
chromatids entangle and cross over then break and rejoin
the point at which they break and rejoin is called chiasmata

Question 4

what happens during telophase 1

Answer 4

same as mitosis

chromosome assemble at each pole

Question 5

what happens during prophase 2

Answer 5

the chromosomes - two chromatids condense and become visible
nuclear envelope breaks down
spindle formation begins

Question 6

what happens during metaphase 2

Answer 6

individual chromosomes assemble on the metaphase plate
due to crossing over chromatids are no longer identical so there is independent assortment
more genetic variation

Question 7

what happens during anaphase 2

Answer 7

chromatids of the individual chromosomes being pulled to opposite poles after division of centromeres

Question 8

what happens during telophase 2

Answer 8

chromatids assemble at the poles
chromosomes uncoil and from chromatin again
nuclear envelope reforms
nucleolus appears
cytokinesis results in four daughter cells- haploid
genetically different due to the process of independent assortment and crossing over

Question 9

what happens during prophase

Answer 9

chromatin fibres coil and condense to form chromosomes to be visible
protein microtubules form spindle shaped linking the poles of the cells
two centrioles migrate to opposite poles of the cells
spindle fibres attach to specific areas on the centromere
nuclear envelope disappears
nucleolus disappears

Question 10

what happens during metaphase

Answer 10

spindle fibres form a plane in the centre called a metaphase plate and then held in position

Question 11

what happens during anaphase

Answer 11

chromatids divide and separate

chromatids pulled to opposite poles of the cell

Question 12

what happens during telophase

Answer 12

chromatids have reached the poles and now called chromosomes
chromosomes uncoil and are at opposite poles
nuclear envelope reforms
nucleolus is formed
cytokinesis begins

Question 13

what happens in cytokinesis in animal cells

Answer 13

a cleavage furrow forms around the middle of the cell
the cell surface membrane is pulled inwards by the cytoskeleton and fuses around the middle
forming two cells

Question 14

what happens in cytokinesis in plant cells

Answer 14

due to the cell wall in plant cells a cleavage furrow is not possible
therefore vesicles from the golgi apparatus begin to assemble in the same place the metaphase plate
vesicles fuse with each other and the cell surface membrane
therefore dividing the cell into two

Question 15

what happens in the first growth phase - G1

Answer 15

proteins synthesis
organelles replicate
cell increases in size

Question 16

what happens in the synthesis phase - S

Answer 16

DNA replication in the nucleus

Question 17

what happens in the second growth phase- G2

Answer 17

cell continues to increase in size
duplicated DNA is checked for errors
energy stores are increased

Question 18

what are stem cells?

Answer 18

undifferentiated cells that have the potential to differentiate and specialise into any other type of cell

Question 19

what is potency?

Answer 19

the ability for stems cell to differentiate into any different type of cells

Question 20

describe and explain totipotent stem cells

Answer 20

stems cells which can differentiate into any type of cell
for example : fertilised egg, zygote
they can turn into whole organisms

Question 21

describe and explain pluripotent stem cells

Answer 21

stem cells which can form all tissue types but not whole organisms
present in early embryos

Question 22

describe and explain multipotent stem cells

Answer 22

stem cells which can only form a range of cells within a type of tissue

Question 23

describe and explain the replacement of erythrocytes

red blood cells

Answer 23

erythrocytes have a lifespan of 120 days

and are produced 3 billion times per kilogram per day of body mass to keep up with demand

Question 24

describe and explain the replacement of neutrophils

white blood cells

Answer 24

essential role in the immune system
life span of only 6 hours
are produced 1.6 billion times per kilogram per hour of body mass

Question 25

what are the 2 types of animal stem cells

Answer 25

embryonic stem cells

tissue stem cells

Question 26

describe and explain the embryonic stem cells

Answer 26

present at a very early stage of embryo development
are totipotent
after 7 days a mass of cells, called a blastocyst
has formed and the cells are now in a pluripotent state
remain in this state until fetus is born

Question 27

describe and explain the tissue stem cells

Answer 27

are present throughout life from birth
found in bone marrow 
are multipotent 
harvested from umbilical cords of newborn babies
for this invasive surgery is not needed

Question 28

where are stem cells found in plant cells?

Answer 28

meristematic tissue

at the tip of roots and shoots

Question 29

give three uses of stem cells

Answer 29

treats
heart disease
Parkinson disease
type 1 diabetes
spinal injuries

Question 30

what are the ethics for stem cells

Answer 30

removal of stem cells from embryos results in destruction of embryos
many people believe life begins at conception and destruction of embryo is murder (religious objectives)