exam questions

• Describe acrosome reaction (1)

  -       The sperm cell releases enzymes that digest the zona pellucida 
• Application, explain why it is advantageous for the eel to have a larger egg cell (2)

  -       Larger egg contains more food/lipid droplets 

  -       Providing more energy for the development of the embryo 

  -       A larger egg is a bigger target for sperm to hit, aiding fertilisation
• Describe the events of fertilisation that occur after the acrosome reaction (3)

  -       Fusion of sperm cell membrane with egg cell membrane 

  -       Cortical granules release contents into the zona pellucida

  -       Contents of cortical granules react with zona pellucida causing it to harden 

  -       Fusion of sperm and egg cell nuclei to form a zygote.
• Explain why a second sperm cell cannot fertilise the egg cell (3)

  -       Cortical reaction occurs, fusion of cortical granules with egg cell membrane

  -       Resulting in the hardening of the zona pellucida

  -       Therefore, sperm cells cannot reach egg cell surface membrane.
• Explain why the production of sperm cells with abnormal flagella may reduce fertility (3)

  -       Would affect the motility of the sperm 

  -       This prevents sperm reaching the egg

  -       Which prevents fertilisation
• Explain how vesicles are involved in the successful fertilisation of an egg cell by only one sperm (3)

  -       Cortical granules fuse with the egg cell surface membrane, exocytosis 

  -       Releasing its contents that harden zona pellucida
• Describe how the acrosome is involved in the digestion of the zona pellucida (2)

  -       The membrane of the acrosome fuses the membrane of the sperm cell 

  -       Releasing enzymes from the acrosome 

  -       By exocytosis
• Give a reason for high density of mitochondria found in the midpiece of a sperm cell (1)

  -       Provides energy from respiration for movement of the flagellum
• Describe the role of the acrosome in fertilisation (3)

  -       Acrosome membrane fuses with the cell membrane of the sperm 

  -       Releasing digestive enzymes via exocytosis 

  -       Which digest/breakdown the zona pellucida
• Compare and contrast the acrosome reaction and the cortical reaction (3)

  -       Both release enzymes via exocytosis 

  -       Both involve vesicles 

  -       Acrosome reaction causes digestion of ZP and cortical reaction causes the hardening of ZP
• Describe and explain how in mammals events following the acrosome reaction prevent polyspermy (4)

  -       Once sperm cell membrane fuse with the egg cell membrane

  -       Cortical granules are released for egg cell 

  -       Cortical granule contents bind to the zona pellucida causing it to harden 

  -       Therefore, sperms cannot meet the egg cell membrane 

  -       Preventing fertilisation of another sperm