2.4 and 2.5 sexual reproduction Flashcards
what are 3 characteristics of the ova?
- immobile
- large (compared to sperm cells, 0.1 mm vs 0.05mm)
- haploid nucleus
what is the procedure of oogenesis before birth?
the primordial germ cell divides a few times to form oogonia
some oogonia develops into larger diploid cells, into primary oocyte
how does the ova survive for so long?
It reserves oil droplets in lipid form to provide ATP for initial embryo development in the cytoplasm
where do oocytes and oogonia develop inside?
inside the follicles
what happens in oogenesis during puberty and monthly menstruation?
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
are polar bodies and secondary oocytes haploid or diploid?
haploid
is the primary oocyte haploid or diploid?
diploid
what happens if fertilisation doesnt occur in oogenesis?
meiosis II starts but does not complete, stops at prophase
what happens to polar bodies?
they get discarded
what are the products of one oogenesis cycle?
2 polar bodies and 1 ovum
what happens if fertilisation occurs in oogenesis?
form the mature ovum in response to fertilisation
what happens if secondary oocyte isnt fertilised?
corpus luteum degenerates
what is the name of the outer layer of the ovary?
germinal epithelium
each follicle starts as a layer of cells and eventually develops into a fluid-like sac, what are they called?
Graafian follicle
what does an empty graafian follicle do?
becomes filled with hormone-secreting cells, forming a yellow body, or corpus luteum
what is corpus luteum?
a mass of cells that forms in an ovary
where are spermatozoa formed?
in the seminiferous tubule of the testes
what happens pre birth in spermatogenesis ?
mitosis, multiplication phase
forming spermatogonium
where are spermatozoa stored when they mature?
epididymus
what are the 3Ms of spermatozoa?
many, mini, motile
what are the 3 Fs of the female gamete?
few, fat, fixed
what happens in the growth phase of spermatogenesis?
primary spermatocyte undergoes meiosis and produces haploid secondary spermatocytes
are primary spermatocytes haploid or diploid?
diploid
what happens in the maturation phase of spermatogenesis?
secondary spermatocytes undergoes meiosis II and forms spermatids, that differentiate, gains tails and become spermatozoa
are secondary spermatocytes haploid or diploid?
haploid
give 3 differences between oogenesis and spermatogenesis
- 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.
describe the structure of a spermatozoa
head contains acrosome (w hydrolytic enzymes) and nucleus (w haploid chromasomes)
middle piece packed with mitochondria
tail contains microtubules
how do sperms move their way up to fertilisation? (Route)
cervix > oviduct > secondary oocyte
what happens to the spermatozoa prior to fertilisation?
capacitation (change of sperm head surface)
what happens in capacitation? (2 processes)
- cell surface is stripped of the glycoproteins it aquired in epididymus
- acrosome reaction - releasing hydrolytic enzymes
how does a spermatozoa fertilise with an ovum?
- 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
what is the cortical reaction?
release of cortical granules from a fertilised secondary oocyte, preventing entry of further sperm cells
- zona pellucida hardens
what is the newly formed nucleus of cell called after sperm and ovum fusing?
zygote
what is the temporary fast block of polyspermy?
depolarising the egg membrane by releasing Na+, repelling spermatozoa (Cortical reaction)
what happens in the early development of the zygote? In animals
totipotent cells undergo mitosis and cell division.
cleavage occurs, forming a solid ball of blastomeres aka morula
describe the structure of a blastocyst in about day 7
contains blastomere of the inner cell mass
hollow bit called blastocoel
surrounded by trophoblast
how does the blastocyst survive
from uterine secretions, it is able to obtain oxygen and other metabolic substrates to excrete metabolic wastes
where does the blastocyst implant?
uterus lining or endometrium
what will the blastocyst develop into?
the placenta
as uptake of nutrients are facilitated
what tissues does the placenta contain?
both embryonic and maternal tissues
what begins to form after implantation? (Human)
blood sinuses
what is the period called when the implanted blastocyst remains in the uterus for ~270-290 days?
gestation
what is a hermaphrodite?
a plant that carries both male and female reproductive structures
what are plants’ female reproductive structures called?
carpels
what do carpels contain?
- stigma
- style
- ovary
what are plants’ male reproductive structures called?
stamens
what do stamens contain?
- anther
- filament
what are plants’ male gametes made?
pollens sacs in anther
what is microgametogenesis?
formation of the male nuclei (gamete) of a plant
what happens in microgametogenesis?
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 male nucleus
Generative nucleus mitosis into 2 male nuclei
what are the 2 nuclei called in a pollen grain?
tube nucleus (then degenerates)
generative nucleus (then mitosis into 2 male gametes)
what is pollination?
when a pollen grain lands of the stigma of a plant of the same species
what are the 2 kinds of pollination?
self-pollination: transfer of the same plant
cross-pollination: transfer of pollen of one plant to the stigma of another
what are the female gametes of plants made up of? (3 structures)
- nucellus (central mass of tissue)
- integuments (2 layers of cells surrounding egg cell)
- micropyle (tiny hole)
what is megagametogenesis?
formation of female nuclei in plants
what are the stages in megagametogenesis?
- diploid megaspore mother cells (in ovule) divide via meiosis
- Form 4 haploid cells
- 3 degenerates, 1 develops into embryo sac
- it fills the nucellus, by mitosis x3 to make 8 haploid nuclei
- cytoplasm of embryo sac later divides, forming 7 cells
where 1 cell has 2 haploid polar nuclei
what are the 7 cells in the megaspore / mature embryo sac called?
3 antipodal cells
polar nuclei (has 2 haploid polar nuclei)
2 synergid cells
1 ovum in between synergid cells
What do centrioles in spermatozoa do?
Source of centriole in zygotes
So spindle fibres can be synthesised
And the zygote can undergo mitosis
In plants,
Ovules turn into ….
Ovaries turn into …
Seeds
Fruits
(Think ovules spelt by less letter so is smaller so seeds bcs seeds are smaller)
Describe the process of fertilisation resulting of formation of a zygote (3 marks)
- Spermatozoa undergoes acrosome reaction
- hydrolytic enzymes released
- to digest zona pellucida
- Cortical reaction in ovum so no more penetration
- Genetic material fusses with nucleus of ovum
Why do number of cells in blastocyst level off when inner cell mass is still growing?
Cells are differentiating
What is the role of double fertilisation? (3 marks)
1 male nucleus fuses w the polar nuclei
Forms triploid endosperm nucleus, embryo that stores protein, oils and nutrients
Other male gametes fuses with female gamete
+ diploid zygote that become seeds
What are number of chromosomes in plant gametes during fertilisation?
All haploid
What’s the role of enzymes in growth of the pollen tube?
Enzymes digest the tissues of style, forming a path down the style to reach ovary
provides nutrients for pollen tube growth
What does an endosperm look like?
Takes up majority of the seed
Why does nicotine reduce movement of sperm cells? Given that there are increased defects in head, midpiece and tail
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
Why is acrosome reaction necessary?
To digest zona pellucida and fuse with nucleus of ovum
What happens with the egg once the sperm cell nucleus has entered it in animals?
Meiosis II finishes
Cortical reaction, hardening zona pellucida to prevent polyspermy
What 2 things are formed from double fertilisation in plants?
Tripoloid endosperm nucleus
Diploid Zygote
How does meiosis create genetic variation? (4 marks)
- random independent assortment at P1
- crossing over at M1 and M2
- random chromosomes movements pulled to each pole
- via homologous paired chromosomes
How does microgametogenesis take place?
- 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
Does megagametogenesis undergo meiosis?
Yes
And mitosis
How does fertilisation take place in plants?
- pollen grain attaches to stigma
- pollen tube nucleus digest down the style using digestive enzymes and use it as nutrients, followed by generative nuclei - that divides into 2 male nuclei
- grows through micropyle into embryo sac
- double fertilisation.
What are 2 products of double fertilisation in plants?
Diploid zygote
Triploid endosperm nucleus (source of nutrients for embryo)
How does implantation in mammals take place?
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
Where does fertilisation occur?
Fallopian tube
What is fertilisation in animals?
Where the nucleus of sperm fuses with nucleus of secondary oocyte
What is cleavage division?
Mitosis without growth
What’s the morula?
Ball of cells from cleavage division of zygote
How does Plant fertilisation happen?
- Pollen grain lands on stigma
- Pollen tube germinates
- Starts to grow down the style by releasing hydrolysis enzymes which digest tissues of style
- Generative nucleus divide to form 2 haploid male gametes/nuclei
- Pollen nucleus goes first
- Enters ovule via micropyle
- Pollen tube nucleus degenerates, 2 male nuclei enter embryo sac
- Double fertilisation
Why is it good for pollen tube to digest down the style using hydrolysis enzymes? 2 marks
Provides nutrients for pollen tube
And forms a path down ovule
What is the function of pollen tube?
Provides a pathway for male gametes to the ovule / embryo sac
Explain how preventing the shortening of spindle fibres affect mitosis. (2 marks)
- sister chromatids cannot be separated
- mitosis at metaphase/anaphase cannot occur
- daughter cells produced with incorrect number of chromosomes
Explain the importance of dna replication during the development of a zygote into a blastocyst. (3 marks)
- zygote divides by mitosis
- make identical copies of DNA
- so all cells are diploid
Silver trumpet tree contain several ovules.
Explain how the silver trumpet tree produces seeds that are genetically different from each other. (4 marks)
- each male nucleus and egg cell nucleus are genetically different from each other
- due to crossing over alleles
- due to independent random assortment
- in meiosis
Explain how the structure of a mammal egg cell is related to its function. (4 marks)
- lipid droplets to store energy
- haploid nucleus
- allow restoration of diploid number at fertilisation
- cortical granules
- can have cortical reaction - hardening of zona pellucida
- mitochondria provide ATP
Describe how the acrosome reaction allows fertlisation to take place. (3 marks)
- acrosome fuses w cell membrane of SPERM cells
- hydrolytic enzymes released
- to digest through zona pellucida
- sperm membrane fuses with cell membrane of egg cell
(- fusion of genetic material in nuclei)
Why do more recombinants mean more genetic variation in gametes produced?
- more crossing over
- more exchange of alleles
What is codominance?
two alleles of the same gene are expressed separately to yield different traits in an individual
What is the function of the generative nuclei? (1 mark)
divides by mitosis into 2 male gametes
What is the function of the tube nucleus? (1 mark)
produce digestive enzymes to digest a path down the style to reach the ovary
Describe how soya bean plants can be genetically modified to produce large numbers of GM soya bean plants. (4 marks)
- restriction enzyme to cut plasmid
- ligase to insert DNA
- use vector
- use plasmid to inject
- use cloning
