Fertilisation

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  • Created by: Lotto65
  • Created on: 03-11-17 15:47
What is external fertilisation?
Fertilisation that takes place outside the body
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How does external fertilisation occur?
The female releases unfertilised eggs and the male puts sperm over the eggs to fertilise them
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Give examples of animals that have external fertilisation
Frogs, salmon, other fish and other amphibians
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What is internal fertilisation?
Fertilisation that takes place inside the body
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How does internal fertilisation occur?
The male passes his sperm into the female's body where fertilisation takes place
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Give examples of animals that have internal fertilisation
Pythons and other reptiles, albatrosses and other birds, humans and other mammals
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What attracts sperm to the egg?
A chemical signal released by the egg
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Where is the egg at the time of human fertilisation?
Oviduct
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What must happen for fertilisation to occur?
Many sperm must reach the egg
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What is the first thing the sperm has to push through when it reaches the egg?
Follicle cells
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What does the sperm bind to after it has broken through the follicle cells?
Zona pellucida
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What triggers the acrosome reaction?
The binding of the sperm to the zona pellucida
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How does the acrosome reaction occur?
Contents of acrosome are released due to separation of acrosome cap from sperm. Enzymes from acrosome digest route for sperm, allowing it to reach the plasma membrane
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Where does the acrosome reaction get the sperm to in the egg?
The plasma membrane
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What happens when the sperm reaches the plasma membrane of the egg?
The plasma membranes fuse and the sperm nucleus enters the egg and joins with the egg nucleus
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Which parts of the sperm remain outside in the fusion process?
Tail and mitochondria
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What does the fusion reaction cause?
Cortical reaction
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What are cortical granules and what do they contain?
Small vesicles that contain lysozyme enzyme
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What do the cortical granules do once the reaction has been triggered?
Move to the plasma membrane, fuse with it and release their contents by exocytosis
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What does the lysozyme do in cortical granules?
Causes cross-linking of glycoproteins in the zona pellucida, making it hard to prevent polyspermy
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Do the sperm and egg nuclei fuse?
No
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What happens to the sperm and egg nuclei?
They both carry out mitosis using the same centrioles and microtubules
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What is it called when the cell has divided into two?
Embryo
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Is a zygote haploid or diploid?
Diploid
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What is polyspermy?
Fusion of two or more sperm with the egg cell
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What is a consequence of polyspermy?
Three of each chromosome (triploid)
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What happens to the cells with polyspermy?
Often die or are sterile
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What is the latest finding from sperm research?
Average number of sperm per unit volume of semen has dropped by about 50% in 50 years and continues to drop 2% a year
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What are possible reasons for the drops in sperm counts?
Presence of estrogen and progesterone in the environment from the contraceptive pill. Steroids chemically related to female sex hormones found in plastics, food packaging and furniture
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What can we learn from the sperm count decrease and possible reasons?
The importance of testing for harmful side effects before scientific and technological developments are introduced
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What is the name of the process by which the sperm can detect the chemicals an oocyte releases?
Positive chemotaxis
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What is the name of the process where sperm finally mature?
Capacitation
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Where does capacitation take place?
Female genital tract
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What does sperm bind to on the zona pellucida?
Specific glycoproteins
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What is activated and happens when the sperm comes into contact with the zona pellucida?
Calcium pump so uptake of calcium ions into sperm head
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What triggers the second meiotic division of the oocyte?
Binding of the sperm to receptors on the plasma membrane
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What does penetration of the plasma membrane cause the release of by the oocyte?
Calcium 2+ ions stored in the oocyte endoplasmic reticulum
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What does the release of Ca2+ ions trigger?
Exocytosis of cortical granules
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What is a name for the hardened zona pellucida?
Fertilisation membrane
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After how long does the sperm and egg nucleus fuse? Why the delay?
Several hours to allow the egg to complete oogenesis
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What are the names of the two mechanisms to prevent polyspermy?
Fast block and slow block
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At what voltage can the sperm plasma membrane fuse with the oocyte plasma membrane?
-70mV
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How does the binding of plasma membranes change the voltage of the oocyte membrane?
Allows sodium ion channels to open so an influx of sodium ions into the egg causes depolarisation
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Depolarisation prevents...
Further sperm binding
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Why do we need two methods of preventing polyspermy?
The oocyte will repolarise and so a second one is required
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What three things do the contents of the cortical granules do?
Remove proteins linking the plasma membrane to the zona pellucida; creates water absorption to lift the zona pellucida away from the plasma membrane; Removes sperm binding receptors and hardens the zona pellucida
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What type of enzymes are in the acrosome?
Proteases
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Other cards in this set

Card 2

Front

How does external fertilisation occur?

Back

The female releases unfertilised eggs and the male puts sperm over the eggs to fertilise them

Card 3

Front

Give examples of animals that have external fertilisation

Back

Preview of the front of card 3

Card 4

Front

What is internal fertilisation?

Back

Preview of the front of card 4

Card 5

Front

How does internal fertilisation occur?

Back

Preview of the front of card 5
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