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N Biology A Level > 2.4 and 2.5 sexual reproduction > Flashcards

2.4 and 2.5 sexual reproduction Flashcards

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1
Q

what are 3 characteristics of the ova?

A
  • immobile
  • large (compared to sperm cells, 0.1 mm vs 0.05mm)
  • haploid nucleus
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2
Q

what is the procedure of oogenesis before birth?

A

the primordial germ cell divides a few times to form oogonia
some oogonia develops into larger diploid cells, into primary oocyte

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3
Q

how does the ova survive for so long?

A

It reserves oil droplets in lipid form to provide ATP for initial embryo development in the cytoplasm

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4
Q

where do oocytes and oogonia develop inside?

A

inside the follicles

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5
Q

what happens in oogenesis during pubety and monthly menstruation?

A

the primary oocyte goes through meiosis I, where a secondary oocyte and a polar body are formed
both are haploid
secondary oocyte released each month

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6
Q

are polar bodies and secondary oocytes haploid or diploid?

A

haploid

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7
Q

is the primary oocyte haploid or diploid?

A

diploid

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8
Q

what happens if fertilisation doesnt occur in oogenesis?

A

meiosis II starts but does not complete, stops at prophase

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9
Q

what happens to polar bodies?

A

they get discarded

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10
Q

what are the products of one oogenesis cycle?

A

2 polar bodies and 1 ovum

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11
Q

what happens if fertilisation occurs in oogenesis?

A

form the mature ovum in response to fertilisation

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12
Q

what happens if secondary oocyte isnt fertilised?

A

corpus luteum degenerates

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13
Q

what is the name of the outer layer of the ovary?

A

germinal epithelium

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14
Q

each follicle starts as a layer of cells and eventually develops into a fluid-like sac, what are they called?

A

Graafian follicle

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15
Q

what does an empty graafian follicle do?

A

becomes filled with hormone-secreting cells, forming a yellow body, or corpus luteum

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16
Q

what is corpus luteum?

A

a mass of cells that forms in an ovary

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17
Q

where are spermatozoa formed?

A

in the seminiferous tubule of the testes

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18
Q

what happens pre birth in spermatogenesis ?

A

mitosis, multiplication phase
forming spermatogonium

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19
Q

where are spermatozoa stored when they mature?

A

epididymus

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20
Q

what are the 3Ms of spermatozoa?

A

many, mini, motile

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21
Q

what are the 3 Fs of the female gamete?

A

few, fat, fixed

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22
Q

what happens in the growth phase of spermatogenesis?

A

primary spermatocyte undergoes meiosis and produces haploid secondary spermatocytes

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23
Q

are primary spermatocytes haploid or diploid?

A

diploid

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24
Q

what happens in the maturation phase of spermatogenesis?

A

secondary spermatocytes undergoes meiosis II and forms spermatids, that differentiate, gains tails and become spermatozoa

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25
Q

are secondary spermatocytes haploid or diploid?

A

haploid

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26
Q

give 3 differences between oogenesis and spermatogenesis

A
  • millions of spermatozoa formed each day ; one secondary oocyte forms graafian follicle
  • oogonia formed before birth ; spermatogonia during puberty
  • sperms are motile, ovum are immotile
  • polar bodies formed in oog. ; not in spermato.
  • meiosis II pauses in prophase until fertilisation ; both m I and II go to completion during spermato.
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27
Q

describe the structure of a spermatozoa

A

head contains acrosome (w hydrolytic enzymes) and nucleus (w haploid chromasomes)
middle piece packed with mitochondria
tail contains microtubules

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28
Q

how do sperms move their way up to fertilisation? (Route)

A

cervix > oviduct > secondary oocyte

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29
Q

what happens to the spermatozoa prior to fertilisation?

A

capacitation (change of sperm head surface)

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30
Q

what happens in capacitation? (2 processes)

A
  • cell surface is stripped of the glycoproteins it aquired in epididymus
  • acrosome reaction - releasing hydrolytic enzymes
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31
Q

how does a spermatozoa fertilise with an ovum?

A
  • acrosome reaction of sperm
  • enzyme digestion creates path for sperm to reach cell surface membrane of secondary oocyte
  • fusion of sperm and s.o.
  • cortical reaction
  • meiosis II is stimulated to complete
  • haploid nuclei fuse and become diploid
  • division of cytoplasm, 2 diploid nuclei formed
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32
Q

what is the cortical reaction?

A

release of cortical granules from a fertilised secondary oocyte, preventing entry of further sperm cells
- zona pellucida hardens

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33
Q

what is the newly formed nucleus of cell called after sperm and ovum fusing?

A

zygote

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34
Q

what is the temporary fast block of polyspermy?

A

depolarising the egg membrane by releasing Na+, repelling spermatozoa (Cortical reaction)

35
Q

what happens in the early development of the zygote? In animals

A

totipotent cells undergo mitosis and cell division.
cleavage occurs, forming a solid ball of blastomeres aka morula

36
Q

describe the structure of a blastocyst in about day 7

A

contains blastomere of the inner cell mass
hollow bit called blastocoel
surrounded by trophoblast

37
Q

how does the blastocyst survive

A

from uterine secretions, it is able to obtain oxygen and other metabolic substrates to excrete metabolic wastes

38
Q

where does the blastocyst implant?

A

uterus lining or endometrium

39
Q

what will the blastocyst develop into?

A

the placenta
as uptake of nutrients are facilitated

40
Q

what tissues does the placenta contain?

A

both embryonic and maternal tissues

41
Q

what begins to form after implantation? (Human)

A

blood sinuses

42
Q

what is the period called when the implanted blastocyst remains in the uterus for ~270-290 days?

A

gestation

43
Q

what is a hermaphrodite?

A

a plant that carries both male and female reproductive structures

44
Q

what are plants’ female reproductive structures called?

A

carpels

45
Q

what do carpels contain?

A
  • stigma
  • style
  • ovary
46
Q

what are plants’ male reproductive structures called?

A

stamens

47
Q

what do stamens contain?

A
  • anther
  • filament
48
Q

what are plants’ male gametes made?

A

pollens sacs in anther

49
Q

what is microgametogenesis?

A

formation of the male nuclei (gamete) of a plant

50
Q

what happens in microgametogenesis?

A

lobes in each anther contains microspore mother cells. Each divides via meiosis to produce 4 haploid pollen grains
each haploid nucleus (of each pollen grain) then divides by mitosis to produce 2 haploid nuclei: the (pollen) tube nucleus and generative nucleus

51
Q

what are the 2 nuclei called in a pollen grain?

A

tube nucleus
generative nucleus (the male gamete)

52
Q

what is pollination?

A

when a pollen grain lands of the stigma of a plant of the same species

53
Q

what are the 2 kinds of pollination?

A

self-pollination: transfer of the same plant
cross-pollination: transfer of pollen of one plant to the stigma of another

54
Q

what are the female gametes of plants made up of? (3 structures)

A
  • nucellus (central mass of tissue)
  • integuments (2 layers of cells surrounding egg cell)
  • micropyle (tiny hole)
55
Q

what is megagametogenesis?

A

formation of female nuclei in plants

56
Q

what are the stages in megagametogenesis?

A
  1. diploid megaspore mother cells (in ovule) divide via meiosis
  2. Form 4 haploid cells
  3. 3 degenerates, 1 develops into embryo sac
  4. it fills the nucellus, by mitosis x3 to make 8 haploid nuclei
  5. cytoplasm of embryo sac later divides, forming 7 cells
    where 1 cell has 2 haploid polar nuclei
57
Q

what are the 7 cells in the megaspore / mature embryo sac called?

A

3 antipodal cells
polar nuclei (has 2 haploid polar nuclei)
2 synergid cells
1 ovum in between synergid cells

58
Q

What do centrioles in spermatozoa do?

A

Source of centriole in zygotes
So spindle fibres can be synthesised
And the zygote can undergo mitosis

59
Q

In plants,
Ovules turn into ….
Ovaries turn into …

A

Seeds
Fruits

60
Q

Describe the process of fertilisation resulting of formation of a zygote (3 marks

A

Spermatozoa undergoes acrosome reaction
Cortical reaction in ovum so no more penetration
Genetic material fusses with nucleus of ovum

61
Q

Why do number of cells in blastocyst level off when inner cell mass is still growing?

A

Cells are differentiating

62
Q

What is the role of double fertilisation? (3 marks)

A

1 male nucleus fuses w the polar nuclei
Forms triploid endosperm nucleus, embryo that stores protein, oils and nutrients
Other male gametes fuses with ovum
+ diploid zygote that become seeds

63
Q

What are number of chromosomes in plant gametes during fertilisation?

A

All haploid

64
Q

What’s the role of enzymes in growth of the pollen tube?

A

Enzymes digest the tissues of style, forming a path down the style to reach ovary
provides nutrients for pollen tube growth

65
Q

What does an endosperm look like?

A

Takes up majority of the seed

66
Q

Why does nicotine reduce movement of sperm cells? Given that there are increased defects in head, midpiece and tail

A

Defected flagella impacts ability to swim to egg
Defected midpiece = no ATP for cellular respiration for movement
Defected head = inability to penetrate eg loss of acrosome reaction ability

67
Q

Why is acrosome reaction necessary?

A

To digest zona pellucida and fuse with nucleus of ovum

68
Q

What happens with the egg once the sperm cell nucleus has entered it in animals?

A

Meiosis II finishes
Cortical reaction, hardening zona pellucida to prevent polyspermy

69
Q

What 2 things are formed from double fertilisation in plants?

A

Tripoloid endosperm nucleus
Diploid Zygote

70
Q

How does meiosis create genetic variation? (4 marks)

A
  • random independent assortment at P1
  • crossing over at M1 and M2
  • random chromosomes movements pulled to each pole
  • via homologous paired chromosomes
71
Q

How does microgametogenesis take place?

A
  1. Pollen grains develop in pollen sacs in anther
    Diploid microspore mother cells undergo meiosis > 4 haploid microspores > mitosis into pollen grains , make pollen tube nucleus and generative nucleus
72
Q

Does megagametogenesis undergo meiosis?

A

Yes
And mitosis

73
Q

How does fertilisation take place in plants?

A
  • pollen grain attaches to stigma
  • pollen tube nucleus digest down the style using digestive enzymes and use it as nutrients, followed by generative nuclei
  • grows through micropyle into embryo sac
  • double fertilisation.
74
Q

What are 2 products of double fertilisation in plants?

A

Diploid zygote
Triploid endosperm nucleus (source of nutrients for embryo)

75
Q

How does implantation in mammals take place?

A

Zygote divides by cleavage division
Form a morula (ball of cells)
It Develops into a blastocyst (consists of hollow ball of cells w inner cell mass)
Embeds on wall of uterus

76
Q

Where does fertilisation occur?

A

Fallopian tube

77
Q

What is fertilisation in animals?

A

Where the nucleus of sperm fuses with nucleus of secondary oocyte

78
Q

What is cleavage division?

A

Mitosis without growth

79
Q

What’s the morula?

A

Ball of cells from cleavage division of zygote

80
Q

How does Plant fertilisation happen?

A
  1. Pollen grain lands on stigma
  2. Pollen tube germinates
  3. Starts to grow down the style by releasing hydrolysis enzymes which digest tissues of style
  4. Generative nucleus divide to form 2 haploid male gametes/nuclei
  5. Pollen nucleus goes first
  6. Enters ovule via micropyle
  7. Pollen tube nucleus disintergrates, 2 male nuclei enter embryo sac
  8. Double fertilisation
81
Q

Why is it good for pollen tube to digest down the style using hydrolysis enzymes? 2 marks

A

Provides nutrients for pollen tube
And forms a path down ovule

82
Q

What is the function of pollen tube?

A

Provides a pathway for male gametes to the ovule / embryo sac

83
Q

Explain how preventing the shortening of spindle fibres affect mitosis. (2 marks)

A
  • sister chromatids cannot be separated
  • mitosis at metaphase/anaphase cannot occur
  • daughter cells produced with incorrect number of chromosomes

N Biology A Level (18 decks)

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