Gametes And Fertilisation

Question 1

What is a haploid cell and example

Answer 1

One that has half a set of chromosomes (23) eg sperm or egg so gametes

Question 2

What is a diploid cell

Answer 2

One that has a full set of chromosomes(46)

Question 3

Four adaptations of sperm that make it suited to its role

Answer 3

-lysosome modified into acrosome= contains hydrolytic enzymes to break through zona pellucida of ovum
-flagellum=allow motility so sperm can reach egg
-mid section contains mitochondria= to provide energy for flagellar rotation
-very little cytoplasm/non-essential organelles=increases sperm motility

Question 4

Four adaptations of ovum

Answer 4

-large cells with lots of cytoplasm=immediately after fertilisation cells are ready to divide
-zona pellucida=released chemicals to attract sperm
-cortical granules=contain enzymes to harden the zona pellucida once one sperm has penetrated it to prevent polyspermy
-lipid droplets=provide energy store for cell division

Question 5

Stages of acrosome reaction

Answer 5

-acrosome of sperm swells and fuses with sperm cell surface membrane
-digestive enzymes in acrosome are released which digest thought the follicle cells and the zona pellucida surrounding the ovum
-sperm fuses with ovum membrane and sperm nucleus enters the ovum

Question 6

What happens in cortical reaction

Answer 6

Once ovum’s cell membrane has been penetrated by a sperm the cortical granules(lysosomes) move towards the ovum cell surface membrane and release chemicals via exocytosis causing the zona pellucida to harden which prevents entry of other sperm

Question 7

What do cortical and acrosome reaction have in common

Answer 7

Both involve the release of enzymes from lysosomes

Question 8

Process of how sperm travel to ovum

Answer 8

-sperm enter vagina bathed in semen and swim up through the cervix
-sperm reach top of uterus and swim along an oviduct
-ovum is released and wafted along viaduct by ciliated cells
-sperm attracted to ovum by chemical it releases

Question 9

Why would it benefit offspring that are fertilised and develop in water to have a large egg

Answer 9

Large egg can contain more lipid droplets which provides more energy and the larger egg provides a bigger target for sperm to fuse with

Question 10

Layers of egg cell

Answer 10

Follicle cells on outside, them zona pellucida and then inside are cortical granules(lysosomes) and lipid droplets