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XBI11 > Unit 2 Topic 3Bii Reproduction of Mammalians and Plants > Flashcards

Unit 2 Topic 3Bii Reproduction of Mammalians and Plants Flashcards

1
Q

Define gametes

A
  • sex cells of organism
  • only has 1 member of each homologous pair of chromosomes each (haploid cells)
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2
Q

Define gametogenesis

A
  • the process of forming gametes in sex organs (including the process of meiosis)
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3
Q

Define ovum

A

mature female egg

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4
Q

What are the structures of an ovum

A

1.Follicle cell
2.Zona pellucida
3.Cortical granule
4.Nucleus
5.Cytoplasm

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5
Q

Why is large food storage in human egg unnecessary

A
  • Main difference between egg of various species: quantity of stores food they contain
  • Mammals: developing foetus is supplied with nutrients from mother’s blood supply
  • Others: takes places before animal hatches in birds / repltiles ==> egg must contain large food storage
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6
Q

What are the main strucutres in a female reproductive system

A
  1. Uterus
  2. Oviduct (fallopian tube)
  3. Cervix
  4. Ovary
  5. Vagina
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7
Q

What are the characteristics and function of uterus

A
  • pear-shaped, thick muscular wall with a lining rich in blood supply
  • site of implantation of embryo
  • protects embryo / foetus
  • provides stable environment for embryo / foetus to develop in
  • musclar wall contracts -> push out foetus during childbirth
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8
Q

What are the characteristics and functions of oviduct

A

Site of fertilisation

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9
Q

What are the characteristics and functions of cervix

A

Dilutes to allow foetus to pass through during childbirth

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10
Q

What are the characteristics and functions of ovary

A

Where human egg cells are formed

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11
Q

Adaptive features of sperm’s mitochondria

A

Mitochondria
- tightly packed into the middle
- aerobic respiration to produce ATP for lashing of the tail

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12
Q

Adaptive features of the flagellum

A
  • provides propulsion ==> swim up the vagina, uterus, oviduct, reach oocyte
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13
Q

Adaptive features of the acrosome

A
  • special membrane-bound
  • contains enzymes which digest the zona pellucida of ovum to allow the sperm’s head to penetrate
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14
Q

Adaptive features of the sperm’s nucleus

A
  • highly condensed haploid chromosomes
  • condensed state reduce amount of energy needed to transport
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15
Q

Adaptive features of a sperm’s microtubules

A
  • produce whip-like movement of the tail
  • keep the mature sperm in suspension
  • help sperm ‘swim’ towards the oocyte in the oviduct
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16
Q

State two adaptive features of ovum

A
  1. cytoplasm containing a store of energy: provides energy for dividing zygote after fetilisation
  2. jelly like coating that changes after fertilisation: impenetratable barrier after fertilisation to prevent other sperm nuclei entering the egg cell
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17
Q

(past paper) Egg cells are produced by many organisms. The development of fish embryos can be studied using fertilised egg cells. Explain how an egg cell is specialised for its function. (2)

6 points

A
  • haploid so that when it is fertilised a diploid zygote is formed
  • contains lipid droplets as source of energy
  • large cell to store more energy / lipid
  • cortical granules / enzymes to harden zona pellucida to prevent polyspermy
  • releases chemicals to attract sperm
  • sperm bind to glycoproteins on egg shell
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18
Q

(past paper) Describe and explain three ways in which a human sperm cell is specialised for its functions (6)

A
  1. shape: hydrodynamic, streamlined ==> reduce resistance
  2. acrosome containing enzyme involved in digestion / breaking down of the zona pellucida to allow penetration
  3. haploid nucleus to allow restoration of diploid chromosomes at fertilisation
  4. large number of mitochondria to supply ATP for movement
  5. presence flagellum for propulsion and motility
  6. receptors in the cell surface membrane, to bind to egg cell surface membrane + detect chemicals released by ovum
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19
Q

Explain the acrosome reaction

A

Allow sperm to fuse
- when sperm reaches the egg cell, binds to zona pellucida through attachment to sperm-binding proteins
- acrosome fuses with cell membrane of egg to release enzymes to disperse follicle cells + digest glycoprotein jelly of zona pellucida around egg cell
- enzymes digest a tunnel through zona pellucida => sperm reach plasma membrane of egg cell
- plasma membrane of sperm cell and egg cell fuse
- sperm releases its nucleus into egg cell cytoplasm + fuse
- zygote formed

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20
Q

Explain the cortical reaction

A

Prevent polyspermy
- channels in plasma membrane of the ovum open and close
- fusion of sperm cell and egg cell membranes => triggers release of calcium ions: temporary, blocks entry of further sperm
- cortical granules released by exocytosis from oocyte
- cortical granules to move and fuse with egg cell membrane, releasing enzymes by exocytosis into zona pellucida
- caused cross linking of glycoproteins in zona pellucida
- removing remaining sperm-binding proteins ==> no further sperm can bind

  • cortical granules produce new outer layer: thick, impenetrable to sperm cells
  • prevents multiple sperm cells from fertilising egg (might have abnormal number of chromosomes)
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21
Q

Define double fertilisation

A

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

22
Q

Define pollination

A
  • transfer of pollen grains from anther to stingma
23
Q

Properties of seminal fluid

A
  • slightly alkaline fluid, contains sugar
  • medium for sperm to swim
  • activates and nourishes sperm
  • neturalises the acidity of female reproductive tract
24
Q

Gametogenesis in female and male mammals

A

Female
- mitotic divisions occur before birth to form diploid primary oocytes
- remains inactive until after puberty
- second meiotic divisions completed only if ovum is fertilised

male
- mitosis and meiosis happens constantly from puberty onwards

25
Outline the formation of gametes in flowering plants
1. sporophyte generation: diploid, produce spores by meiosis 2. gametophyte generation: haploid, produce gametes by mitosis Flowering plants: two phases combined in one plant Moses: two phases in separated plants
26
Explain copulation for fertilisation in mammals
- transfer of semen containing sperm into female reproductive tract during sexual intercourse 1. man is sexually aroused and the erectile tissue tilled with blood to erect the penis 2. when penis insert into vagina and ejaculation occurs 3. sperms ejaculated into vagina, swim up cervic and uterus
27
Explain why large number of sperm is released during ejaculation
- one sperm alone does not produce enough enzymes to penetrate the zona pellucida - large number provides enough sperm to surround the occyte and digest the zona pellucida
28
Recovery of charge after cortical reaction
tough fertilisation membrane around fertilised ovum repels over sperm ==> electrical charge returns from positive to negative
29
How do a diploid zygote form after the head of sperm enters the oocyte
- head of sperm in oocyte, tail left outside - absorbs water and swells - releasing its chromosomes to fuse with the ovum - forming diploid zygote - nuclei from sperm and egg fuse together
30
Define fertilisation
fusion of haploid nuclei from a male gamete and female gamete to form a diploid zygote in sexual reproduction
31
Outline the steps of fertilisation in mammals
1. Copulation 2. Acrosome reaction 3. Plasma membrane fusion 4. Alternation of charges 5. Cortical reaction
32
Outline the steps of fertilisation in plants
1. Pollination 2. Fertilisation 3. Seed dispersal
33
Will pollen grains germinate on same or different plants? Explain.
will only germinate on **different plant of the same species** ==> prevents self-fertilisation + increase genetic variation
34
List the process of fertilisation in angiosperms
1. pollen grain lands on the stigma of another plant (**anther to stigma**) 2. pollen grain germinates to **develop pollen tube** from tube cell 3. tip of pollen tube secretes hydrolytic **enzymes => digest stigma and style** 4. pollen tube grows down towards **ovary** 5. pollen tube nucleus and generative nucleus travels down along the pollen tube 6. **generative nucleus** divides by mitosis + move down the pollen tube **forming two male nuclei** 7. tip of pollen tube **reaches ovule** in ovary, grows through micropyle into embryo sac inthe ovule 8. **pollen tube** **nucleus degenerates and bursts**, releasing **two male nuclei into ovule**
35
Nucleus in mature pollen grains
tube nucleus generative nucleus
36
Steps in double fertilisation for flowering plants
1. 1 male nucleus **fuses with the two polar nuclei** to form **triploid endosperm nucleus** ==> supply embryo with food for **germination** 2. 1 male nucleus **fuses with egg cell** to form **diploid zygote** ==> **plant embryo** 3. fertilisation completed, development of seed and embryo within begin
37
Major function of anther
where pollen is produced
38
Major function of stigma
part of the female reproductive organ which receives the pollen
39
Major function of ovary
where female gametes are located
40
(past paper) The diagram shows the nuclei in an ovule of a flowering plant. Double fertilisation takes place in the ovules. Describe the events that occur from the time a pollen grain lands on the stigma to the production of a triploid endosperm nucleus and a zygote. (5)
- **pollen tube grows down style to ovary**, transports male nuclei donw the style - by r**eleasing hydrolytic enzymes**, generative nucleus divides and **undergo mitosis** to **form two male haploid nuclei** - one male haploid nucleus **fertilises the egg cell to form the zygote** - one male haploid nucleus **fertilises the two polar nuclei to form the endosperm nucleus**
41
(past paper) Describe the process of fertilisation that takes place in flowering plants
- **generative nucleus divdes** to form two male gametes ***by mitosis *** - pollen tube **fuses with embryo sacs ** - **double fertilisation** occurs - one male haploid nucleus **fertilises the egg cell to form the zygote** - one male haploid nucleus **fertilises the two polar nuclei to form the endosperm nucleus**
42
Describe the seed and fruit development after fertilisation
- ovule developes into **seeds**: contains **plant embryo with food reserve in endosperm** - ovary develops into **fruit enclosing seed** seed dispersal through animals, wind, water, force ==> seed germination occurs
43
Define self pollination
transfer of pollen grains to stigma of the same flower / another flower on the same plant - genetically different offspring can be produced
44
Define external fertilisation
in aquatic species - egg released followed by sperm to environment - suspectible to environmental variation ==> large quantities of eggs and sperms need to be produced to compensate for losses
45
Define cross pollination
transfer of pollen grains to stigma of the flower on a different plant of the same species
45
Benefits of internal fertilisation
in terrestrial animals - prevents dehydration of gametes or developing embryo, placed close together as possible - protected and nourished - less vulnerable to predators and other environmental conditions - sperm deposited into female in easy reach of the ova during intercourse therefore, - maximises chances of successful fertilisation - higher survival rates of gametes and offspring - less wastage of gametes
46
Function of follicle cell of ovum
* provides **nutrients** to support the **early development** of a fertilised egg
47
Function of zona pellucida of ovum
* **jelly-like layer** that surrounds the egg * consists of **glycoproteins** that protects the egg and restricts entry of sperm
48
Function of cortical granule of ovum
- **make zona pellucida hard** so sperm cannot penetrate after occyte is fertilized to form ovum * prevents **polyspermy** (fertilisation of an egg cell by more than 1 sperm)
49
Properties of nucleus of an ovum
* contains a haploid number of chromosomes
50
Properties of the cytoplasm of the ovum
* contains **limited nutrients / food reserves to support early development** of fertilised egg
51
（past paper) Describe how the acrosome reaction allows fertilisation to happen
- when the sperm comes in contact with the egg cell - the acrosome fuses with the sperm membrane to release enzymes by exocytosis - these enzymes digest a pathway thorugh the zona pellucida to allow sperm membrane to fused with the egg cell membrane

XBI11 (14 decks)

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