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Biology > 2.4 > Flashcards

2.4 Flashcards

meiosis & sexual reproduction

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1
Q

what are the male sex organs in plants and where are they found

A

pollen
found in anthers

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2
Q

what are where are the female sex organs in plants

A

ovules
found in ovaries

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3
Q

what are the name of male and female gametes

A

spermatozoa
ova

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4
Q

define meiosis

A

cell division in which the chromosomes number of the original cell is halved leading to the formation of gametes

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5
Q

how are gametes produced in plants

A

meiosis forms male microspores and female megaspores which then produce gametes

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6
Q

what is crossing over (recombination)

A

large multi-enzyme complexes cut and rejoin parts of the maternal and paternal chromatids at the end of prophase 1

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7
Q

summarize meiosis (prophase 1 -> telophase 2)

A

P1 - condensed chromatids, crossing over occurs
M1 - spindle fibers, metaphase plate
A1 - poles of cell, centromeres don’t divide
T1 - nuclear membrane reforms
P2 - spindle fibers form
M2 - metaphase plate
A2 - centromeres now divide
T2 - nuclear membrane reforms

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8
Q

what is a chiasmata

A

the points where the chromatids break during recombination

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9
Q

what is a polysomy

A

when a cell or an organism has more than 2 sets of chromosomes

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10
Q

what are gonads

A

sex organs in animals

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11
Q

define fertilization

A

the fusing of the haploid nuclei from two gametes to form a diploid zygote in sexual reproduction

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12
Q

what is a zygote

A

the cell formed when two haploid gametes fuse at fertilization

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13
Q

what is independent assortment

A

the process by which the chromosomes from the male and female parent are distributed at random to the offspring

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14
Q

what is translocation

A

a mutation in which part of one chromosome breaks off and rejoins another chromosome, it may be balanced or unbalanced

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15
Q

what is non-disjunction

A

when members of a pair of chromosomes fail to separate during the reduction division of meiosis resulting in one gamete with two copies of a chromosome and one gamete with no copies of that chromosome

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16
Q

what is a monosomy

A

when only one member of a pair of chromosomes is present in a cell

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17
Q

what is an aneuploidy

A

when a cell contains too few or too many chromosomes

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18
Q

what are mutagens

A

chemicals known to increase the rate of mutation

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19
Q

what disease is caused by trisomy (3 copies of) chromosome 21

A

down syndrome

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20
Q

what is turners syndrome

A

when an individual only has 1 X chromosome

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21
Q

what is Kleinfelder’s syndrome

A

when an individual has 3 sex chromosomes XXY

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22
Q

what is gametogenesis

A

the formation of gametes by meiosis in the sex organs

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23
Q

what are primordial germ cells

A

cells which divide by meiosis to form sperm and ova

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24
Q

define spermatogenesis

A

formation of sperm cells in the testes

25
Q

define oogenesis

A

formation of ova in the ovaries

26
Q

explain the steps in spermatogenesis

A

diploid primordial germ cell in testes divides by mitosis to form diploid spermatogonia
spermatogonia then grow into primary spermatocytes
primary spermatocytes undergo meiosis to form 2 haploid secondary spermatocytes
these then undergo a second meiosis division to form 4 haploid spermatids
spermatids then differentiate to form spermatozoa

27
Q

explain the steps in oogenesis

A

diploid primordial germ cell divides by mitosis to form diploid oogonia (usually many are produced and only 1 survives)
the oogonia then grows into a primary oocyte
the primary oocyte undergoes its first meiosis to form a secondary oocyte and a polar body
the oocyte does not divide until after ovulation now
the second meiotic division occurs after fertilization and the secondary oocyte forms a haploid ovum and a polar body, then the first polar body divides into two more polar bodies

28
Q

how many sperm are formed in spermatogenesis

A

many

29
Q

how many ovum are formed in oogenesis

A

1

30
Q

what happens to the polar bodies formed in oogenesis

A

degenerate and die as the ovum develops

31
Q

roughly what size are spermatozoa

A

50micrometers

32
Q

roughly what size are ovum

A

0.1mm

33
Q

what features are present on a spermatozoa and why

A

acrosome - contains enzymes for penetration of ova
haploid nucleus
mitochondria - for energy
flagellum - for movement
microtubules - produce whip like movements

34
Q

what features are present on a ovum

A

cytoplasm - contains nutrients
polar bodies
zona pellucida - jelly coat protects the cell
corona radiata - protects ovum

35
Q

what are the 2 phases of gametogenesis in plants

A

sporophyte generation
gametophyte generation

36
Q

what is sporophyte generation

A

the diploid generation in plants that produce spores by meiosis

37
Q

what is gametophyte generation

A

the haploid generation in plants that gives rise to the gametes by mitosis

38
Q

where are pollen grains developed

A

pollen sacs

39
Q

explain pollen formation

A

microspore mother cell undergoes 2 meiosis to produce 4 haploid cells
these cells then undergo mitosis to produce a pollen tube nucleus and a generative nucleus both encased in the same cell wall
when pollination occurs 2 male gametes are produced from the generative nucleus

40
Q

what is the structure of a mature embryo sac

A

3 antipodal cells
2 polar nuclei
female gamete
2 synergids

41
Q

explain the formation of a mature embryo sac

A

diploid megaspore mother cell undergoes 2 meiosis to produce 4 haploid megaspores (of which only 1 survives) the 1 then undergoes 3 mitotic divisions which result in the formation of an embryo sac containing 3 antipodal cells, 2 polar nuclei, a female gamete and 2 synergids

42
Q

define pollination

A

the transfer of pollen from the anther to the sigma often from one flower to another

43
Q

state 2 ways pollination can occur

A

wind
transfer via other organisms

44
Q

what is external feralization

A

the process of fertilization in which the male and female gametes are released outside of the body to meet and fuse in the environment

45
Q

what is internal fertilisation

A

the fertilisation of the female gamete by the male gamete which takes place in the body of the mother

46
Q

what is the acrosome

A

the region at the head of the sperm that contains enzymes to break down the protective layer around the ovum

47
Q

what is the zona pellucida

A

layer of protective jelly around the unfertilized ovum

48
Q

why do many sperm need to reach the ovum

A

as one sperms enzymes are not enough to penetrate the protective layer around the ovum

49
Q

summarise the steps of fertilisation in mammals

A

sperm reach the ovum and begin to digest the protective barrier
one sperm reaches the surface membrane of the oocyte triggering the second mitotic division of the oocyte to produce a haploid egg and ion channels change so that the cell becomes positively charged stopping the entry of further sperm
then a fertilisation membrane will form when cortical granules are released and take on this role so that the charge can return to normal
the head of the sperm fuses with the oocyte membrane causing the sperm nucleus to be released into the oocyte where it rapidly decondenses and the male and female chromosomes group together

50
Q

how do plants avoid self-fertilisation

A

only germinate when the pollen grain is recognized as the same species but a different plant or it begins to germinate however won’t be able to penetrate the carpel

51
Q

summarise the steps in fertilisation in plants

A

pollen grain lands on surface of sigma
pollen grain germinates and a pollen tube begins to form through the sigma into the style as the tip produced hydrolytic enzymes which digest the tissue and use it as a nutrient source
as the pollen tube grows the generative nucleus travels down and and divides by mitosis to produce 2 male nuclei
the pollen tube grows through the ovary and tip passes through the micropyle of ovary where the male nuclei are passed on for fertilisation

52
Q

what is double fertilisation

A

one male nucleus fuses with 2 polar nuclei to form an endosperm and the other male nucleus fuses with the egg cell to form the diploid zygote

53
Q

what is an endosperm nucleus needed for

A

supplies embryo plant with food

54
Q

define totipotent

A

a cell is able to develop into all different cell type

55
Q

define pluripotent

A

a cell is able to develop into most different cell types

56
Q

what is a cleavage

A

a process involving a special type of mitosis with no interphase that results in a mass of small undifferentiated cells

57
Q

what occurs after fertilization

A

cleavage occurs forming a morula then a blastocyst as the embryo travels down the oviduct to the uterus
when it reaches the uterus the blastocyst hatches and implants into the lining of the uterus

58
Q

what is cell determination

A

the predestination of cells to become particular types of tissue from early in development of the embryo

59
Q

define differentiation

A

to develop into specific types of tissues

Biology (33 decks)

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