Gametes, Fertilisation and Stem Cells 3.6, 3.7, 3.9-3.11

Question 1

Define fertilisation

Answer 1

The exact moment the nuclei of the male and female gametes fuse to create a zygote with a diploid number of chromosomes

Question 2

How are egg cells specialised for their function? x3

Answer 2

• Large cytoplasm which contains huge amounts of nutrients
• Zone pellucida is a protective glycoprotein layer
• Cortical granules form a protective coating

Question 3

How are sperm cells specialised for their function?

Answer 3

• Lots of mitochondria in the mid piece to provide energy for swimming
• Flagellum allows sperm to swim towards egg
• Acrosome contains digestive enzymes to break down zona pellucida

Question 4

Where does fertilisation occur in mammals?

Answer 4

Oviduct

Question 5

What are the 3 components of fertilisation?

Answer 5

1) Acrosome Reaction = sperm makes contact with zona pellucida and digestive enzymes are released from the acrosome. Enzymes digest the zp so sperm can move to cell membrane of egg cell. Sperm head fuses with cell membrane which triggers cortical reaction.
2) Cortical reaction = egg cell releases the contents of the cortical granules into space between cell membrane and zp which causes zp to thicken and makes it impenetrable to other sperm - only one sperm fertilises the egg.
3) Nuclei fusion = nucleus of the sperm fuses with the nucleus of the egg cell

Question 6

What does meiosis produce?

Answer 6

4 genetically varied haploid daughter cells = gametes

Question 7

How many chromosomes do gametes have?

Answer 7

Half the number = haploid

Question 8

Describe briefly the process of meiosis:

Answer 8

1) DNA replicates so that there are 2 identical copies of each chromosome
2) DNA condenses
3) Chromosomes arrange into homologous pairs
4) First division = homologous pairs are separated (halving chromosome number)
5) Second division = pairs of sister chromatids are separated
6) Four genetically different daughter cells produces

Question 9

What are the two methods of producing genetically varied gametes?

Answer 9

Crossing over

Independent assortment

Question 10

Describe crossing over

Answer 10

• Before first division homologous pairs line up
• Two of the chromatids twist around each other and a section breaks off to rejoin onto other chromosome, recombining genetic materials

Chromatids now have the same genes but different combination of alleles

Question 11

Describe independent assortment

Answer 11

When gametes are produced, different combinations of maternal and paternal chromosomes go into each cell

Question 12

What are stem cells?

Answer 12

Undifferentiated cells that can become new cells which become specialised through differentiation

Question 13

What is potency?

Answer 13

The ability for stem cells to differentiate into specialised cells

Question 14

Define totipotency

Answer 14

The ability to produce ALL cell types, including all the specialised cells in an organism and extraembryonic cells (placenta and umbilical cord)
Only present in mammals in the first few cell divisions of an embryo

Question 15

Define pluripotency

Answer 15

The ability to produce all the specialised cells in an organism BUT NOT extra-embryonic cells

Question 16

Why are adult stem cells much less flexible than embryonic stem cells?

Answer 16

They can only develop into SOME cell types

Question 17

Where are plant stem cells found?

Answer 17

In regions of growth eg. Roots or shoots

Question 18

Give an example of a stem cell therapy

Answer 18

Treatment for leukaemia (cancer of the bone marrow) kills all the stem cells in the bone marrow so that bone marrow replacements can replace them.

Question 19

What are the potential benefits of stem cells

Answer 19

• Save many lives eg. Many people waiting for organ transplant die before donor organ is available so stem cells can be used to grow organs instead
• Improve quality of life eg. Used to replace damaged cells in blind people

Question 20

What are the two potential sources of human stem cells? + explain

Answer 20

Adult stem cells = simple operation with little risk where needle is inserted into centre of bone and a small amount of bone marrow is removed
Not as flexible as embryonic due to limited range of cells
Less risk of rejection if patient uses their own stem cells

Embryonic stem cells = embryos created in IVF and stem cells removed when 4-5 days old with rest of cells being destroyed
Very flexible
High risk of rejection

Question 21

Name two ethical issues of using embryonic stem cells

Answer 21

1) People believed fertilised embryos have a right to life from the moment of fertilisation
2) People believe it is wrong to destroy viable embryos

Question 22

What has been established to consider the benefits and ethical issues of embryonic stem cell research?

Answer 22

Regulatory authorities

Question 23

Name 5 things regulatory authorities do:

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Answer 23

1) Monitoring developments in scientific research (regulated appropriately)
2) Advice to governments and professionals (promote science)
3) Licensing and monitoring centres (ensures only fully trained staff carry out research to avoid unregulated research)
4) Guidelines and codes of practice (scientists working in similar manner and controls methods used to extract eg. Maximum age of embryo)
5) Proposals of research

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