2.3

Question 1

define mitosis

Answer 1

the process by which a cell divides to produce two genetically identical daughter cells

Question 2

what is asexual reproduction

Answer 2

the production of genetically identical offspring from a single parent or organism

Question 3

what is sexual reproduction

Answer 3

the production of offspring which are genetically different from the parent organism or organisms by the fusing of 2 gametes

Question 4

define meiosis

Answer 4

a form of cell division in which the chromosome number of the original cell is halved leading to the formation of gametes

Question 5

what is the order of the stages which occur in the cell cycle

Answer 5

G1
S
G2
mitosis
cytokinesis

Question 6

what are histones

Answer 6

positively charged proteins involved in the coiling of DNA to form dense chromosomes in cell division

Question 7

what are nucleosomes

Answer 7

dense clusters of DNA wound around histones

Question 8

explain the structure of DNA

Answer 8

DNA winds around histones to form dense clusters such as nucleosomes
these then interact to produce more coiling and then supercoil to form dense chromosomes

Question 9

what is interphase

Answer 9

the period between active cell divisions when cells increase their size and mass, replicate their DNA and carry out normal metabolic activities

Question 10

what occurs in G1 phase

Answer 10

this is the time between the end of a previous round of cell division and the start of chromosome replication

Question 11

what occurs in S phase

Answer 11

chromosomes replicate and become double stranded chromatids

Question 12

what is a chromatid

Answer 12

one strand of the replicated chromosome pair that is joined to the other chromatid at the centromere

Question 13

what occurs in G2 phase

Answer 13

the time that organelles and other materials needed for cell division are synthesized

Question 14

what are cyclins

Answer 14

small proteins which build up during interphase and are involved in the control of the cell cycle by their attachment to cyclin-dependent kinases

Question 15

what are cyclin-dependent kinases

Answer 15

enzymes involved in the control of the cell cycle by phosphorylating other proteins activated by attachments to cyclins

Question 16

what is prophase

Answer 16

the first stage of active cell division where the chromosomes are coiled up and consist of two daughter chromatids joined by the centromere and nuclear membrane brakes down

Question 17

what are the stages of mitosis in order

Answer 17

prophase
metaphase
anaphase
telophase

Question 18

what is metaphase

Answer 18

second stage of active cell division where a spindle of overlapping protein microtubules forms and the chromatids line up on the metaphase plate

Question 19

what is anaphase

Answer 19

third stage of active cell division where centromeres split of chromatids become chromosomes and are pulled to opposite poles of the cell by contractions of microtubules of the spindle

Question 20

what is telophase

Answer 20

fourth stage of active cell division where a nuclear membrane forms around the two sets of chromosomes, the chromosomes unravel and spindle breaks down, the nucleoli and centrioles re-form

Question 21

what are the meristem

Answer 21

the region of mitosis & growth in plants roots & shoots (very sensitive to stimuli)

Question 22

what is dry mass and how can it be used to measure growth

Answer 22

dry mass- the mass of the body of an organism with all the water removed from it
must grow large samples of genetically identical organisms under similar conditions and take random samples to measure mass

Question 23

what is growth and the 3 main aspects it can be defined by

Answer 23

growth - permanent increase in the number of cells or the mass/size of an organism
involves: cell division - mitosis
assimilation - nutrition
cell expansion - materials are incorporated into cells

Question 24

explain the advantage of budding and vegetative propagation to farmers

Answer 24

increase plant numbers cheaply
clones are produced
cuttings can be taken to grow new plants

Question 25

what is vegetative propagation

Answer 25

asexual reproduction of plants which forms genetically identical new plant
often used in flowering plants to survive between growing seasons

Question 26

what is budding

Answer 26

the production by mitosis of an outgrow from the parent organism that develops into an individual organism so becomes detached
e.g. yeast cells

Question 27

what is fragmentation

Answer 27

the use of mitosis to regenerate a whole organism from a fragment of the original

Question 28

define binary fission

Answer 28

the splitting of one individual to form two new individuals

Question 29

what is regeneration

Answer 29

use of mitosis to regrow a body part which has been lost

Question 30

what is sporulation

Answer 30

production of asexual spores capable of growing to new individuals
survive adverse conditions
easily spread
common in fungi & plants

Question 31

what are the advantages and disadvantages of asexual reproduction

Answer 31

+/ produces clones
does not rely on finding a mate
large numbers of offspring produced rapidly

-/ changes in conditions can cause total destruction of the entire population

Question 32

what are plasmodesma

Answer 32

small gaps left between the vesicles during cytokinesis of plant cells when the cellulose cell wall begins to form

Question 33

how does cytokinesis occur in plants

Answer 33

cellulose cell wall builds up from inside of the cell:
- remaining spindle fibers guide Golgi vesicles to the equator of the cell
- golgi vesicles fuse with all surface membrane once large vacuoles have formed
- vesicles fuse together forming cell plate
- cellulose walls with middle lamella form between cells

Question 34

how does cytokinesis occur in animals

Answer 34

a ring of contractile fibers contract around the center of the cell until the 2 cells have been separated

Question 35

what is cytokinesis

Answer 35

final stage in the cell cycle division of the cytoplasm at the end of mitosis to form two independent genetically identical cells