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42 Cards in this Set
- Front
- Back
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What are the steps of spermatogenesis? |
1. Primordial germ cell divides by mitosis to make diploid spermatogonia 2. This grows and develops and once it is beg enough it is the primary spermatocyte 3. This undergoes the 1st meiotic division to make secondary spermatocyte 4. Then this divides again in meiosis division to make 4 haploid spermatids. 5. Spermatids differentiate in the testes tubules to make spermatozoa |
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What are the stages of oogensis? |
1. Primordial germ cells divide by mitosis to make diploid oogonia 2. Only one grows and develops and takes in lots of materials to be called a primary oocyte. 3. In meiosis 1, secondary oocyte and polar body is made and this is the ovum 4. After fertilisation, meiosis 2 makes two more polar bodies and a haploid ovum. The polar bodies all die once ovum develops. |
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What is the zona pellucida? |
A jelly like layer that protects the egg cell |
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How does pollen form in the anthers? |
1. Each anther has 4 pollen sacs 2. In the pollen sacs, the microspore mother cells divides by meioisis --> 4 haploid gametophytes 3. They divide by mitosis to make pollen which is the has 2 haploid nuclei - the tube and generative nucleus. |
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What is the role of the tube nucleus? |
The tube nucleus produces the pollen tube which grows and pentrates through the style, ovaries and to the ovule. |
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What does the generative nucleus do in pollination? |
It fuses with the ovule nucleus to make the new individual |
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Decribe the spermatozoa... |
Many, mini, motile Suspended in semen so ut can move Has acrosome with enzymes needed to pentrate barriers Has mitochondria in middle of head Has microtubles in fleggelum to allow whip like movement to get it through the reproductive tract. |
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What is the main difference between egg cells in different animals? |
The size is different because of the amount of food stored. -Mammals have smaller eggs as the mother provides nutrients while it develops. -Also birds and reptiles have larger eggs because there is much more food inside because the animal tends to do most development before birth. |
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What is the sporophyte generation? |
The diploid generation that produces spores via meiosis |
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What is the gametophyte generation? |
The haploid generation that gives rise to gametes by mitosis. |
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How is an ovule produced in plants? |
1. Diploid megaspore mother cells divide by meiosis to make 4 gametophyte megaspores. 3 dies - one develops 2. The one divides by mitosis 3x to make embryo sac, 2 haploid nuclei and other smaller cells. |
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What is the advantages of internal fertilisation? |
The ovum remains in a protected, moist environment. Also because the sperm is directed it makes is more likely that fertilisation will occur |
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What happens when one sperm touches the surface membrane of the egg cell? |
1. The secondary oocyte undergoes meioisis 2 to make haploid nucleus 2. Alteration in charge blocks to prevent polyspermy. |
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How is polyspermy prevented? |
Ion channels in cell membrane of ovum open close so that the relatively negative inside becomes positive. The alteration of charge prevents more sperm entering. This is a temporary until a tough fertilisation membrane forms. |
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Why are many spermatozoa released during ejaculation? |
Because you need the acrosome enzymes in many sperm to weaken the egg cells defences |
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What is the acrosome reaction? |
When enzymes from the acrosome are released to digest the egg cell's defences |
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What is the corticle reaction? |
The permanent prevention of polyspermy is from the build up of a tough fertilisation membrane. This membrane is made from cortical granules that are released from the oocyte - the granules react and combine with zona pellucida to make membrane. |
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What happens when the head of the sperm is in the ovum? |
Only the head is inside and then the head absorbs water and swells so that it releases its chromosomes to fuse with the ovum's. This is fertilisation. |
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Can plants pollinate itself? |
Not usually but pollen grain from the same plant can germinate but be unable to penetrate the carpel. |
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What are the stages of plant fertilisation? |
1. The pollen grain lands on stigma of different plant of same species. 2. If they recognise each other, the pollen grain will start to germinate/grow. 3. Pollen tube grows from tube nucleus through stigma into style. 4. Generative cell with generative nucleus travels down pollen tube 5. This nucleus divides by mitosis to make 2 male nuclei 6. Pollen tube grows into ovary and the tips passed into micropyle of ovule. - rapid elongation 7. 2 male nuclei pass into ovule for fertilisation. Pollen tube nucleus will degenerate |
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How does the pollen tube go through the style? |
The tip of the pollen tube produces hydrolytic enzymes. This digested tissue acts as nutrients for the pollen tube growth. |
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How is fertilisation different in flowering plants? |
They undergo double fertilisation 1. One male nucleus fuses with the two polar nuclei to form endosperm nucleus which is triploid. 2. Other male nucleus fuses with egg cell to form diploid zygote Fertilisation is complete and seed and embryo development begins. |
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What is the role of the endosperm? |
Involved in supplying embryo plant with food when it starts to generate. |
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What are the polar nuclei? |
When ovule is formed it consists of a embryo sac, 2 haploid/polar nuclei and smaller cells |
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What is cell determination? |
The predestination of what type of cells are going to differentiate into, in an early embryo |
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What are the steps after fertilisation in humans? |
1. Cleavage - the zygote travels down the oviduct and undergoes mitotic division without interphase. 2. Cleavage results in a blastocyst - a small mass of undifferentiated cells that form hollow sphere - 5th/6th day 3. embryonic stem cells are made 4. The outer layer of blastocyst makes the placenta and inner layer differentiates into different cells. 5. The blastocyst hatches and imbeds in uterus lining. - 7th day |
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Why is a zygote totipotent? |
It has the ability to differentiate into all the 216 types of cell in the body |
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Why is the embryonic stem cells in the inner layer of the blastocyst described as pluripotent? |
Because they have the ability to differentiate into most, but not all, types of cells. |
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After how many days does the blastocyst form? |
5 or 6 days |
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What determines cell determination? |
The mechanism is unkown But it is thought that it is the position of the cells in the embryo |
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As cells differentiate, what changes do they undergo? |
- produce more protein for the function - shape - arrangement of organelles - different combinations of DNA are activated |
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How has improvements in culturing embryos improved the success of IVF? |
Used to implant many embryos within 2 or 3 days - as they wouldn't survive for longer in labs But now they what until healthy blastocyst is formed, 5 days. So less implanted, reduced multiple pregnancy and increases chance of one healthy baby at the end. |
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How is IVF carried out? |
Egg cells are removed from the ovary of the woman and mixed with sperm of the man. The fertilised zygote will be grown in Petri dishes in lab, providing warmth and nutrients until ready to reimplant into the uterus. |
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What are the two types of translocation mutations in chromosomes? |
Balanced - swapping of genetic material from different homologous pairs Unbalanced - one chromosome gives and the other receives. Much more dangerous, could be incompatible with life. |
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What is the non disjunction of chromosomes? |
When a whole chromosome is either lost or an extra is present during during the reduction division of meiosis. |
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What type of mutation is Down's syndrome? |
Non disjunction of the chromosome 21 - trisomy the individual receives 3 copies of the same chromosome due to the fact that in anaphase 2, the chromosome did not split in middle and move to opposite side s so one cell get 2 and one gets none. And the one with 2 fuses with a healthy gametes to make an embryo with 3 copies of ch.21. |
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What are the effects of Down's syndrome on the individual? |
Severe learning difficulties, heart abnormalities, reduced mental and physical growth etc. |
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What is Turner's syndrome? |
This when a sperm has no sex chromosome so when it fuses with the healthy egg cell, the zygote has the genotype XO. The individual will be female but could be infertile. This is a type of monosomy |
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What is Kleinfelter's syndrome? |
-This is polysomy of the sex chromosomes. -Sperm with X and Y fuse with egg cell to make genotype XXY. -This leads to the individual exhibiting both female and male attributes and will be infertile. -The severity ranges hugely. |
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What happens to create Edward's syndrome? |
Trisomy of chromosome 18 - the embryo receives 3 copies of the chromosome Embryo will spontaneously abort Or could be born and die within a year. |
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What is polyploidy??? |
When a cell or and organism has more than 2 sets of chromosomes |
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How do the ova form in plants? |
1. Diploid megaspore mother celld divide by mitosis to make 4 haploid megaspores. 3 die. 2. The megaspore undergoes 3 mitotic divisions - result in embryo sac, 2 polar nuclei and other cells. |
