IGCSE Biology, Model Answers and Discussion

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silliva
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#1
Report Thread starter 12 years ago
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Hey!

I thought since the exam is only a few day away, now would be a time to start discussing questions which, commonly come up and the model answers to them. I'll start :deal:

(Marks in brackets after key word/phrase)

1. Describe how genes can be transferred from one organism to another using genetic modification. (5 marks)

The desired gene should be isolated and cut out (1) using restrictive enzymes (1). The corresponding gene should then be cut out out of target animal (1) using the same restrictive enzyme (1). The desired gene should then be inserted into target animal DNA (1) using ligase (1) to join them together.

A variation on this question may be about how bacteria can be used to make insulin. Here you'd use same method but say that the gene for insulin is put into a vector, inserted into a fermenter of bacteria where the bacteria will take up this vector and multiply.

2. Describe how white blood cells prevent ill-health and disease (4)

Phagocytes engulf and digest the pathogen (3!). Lymphocytes omit antibodies which clump and neutralise pathogens (4!!)

3. Explain the method for creating a clone of a mammal (5)

Nucleus from chosen adult mammal (1) is inserted into ennucleated egg cell (1), this then undergoes mitosis (1) to form an embryo (1). This embryo is then inserted into the womb (1) of the surrogate mother.

4. Explain how greenhouse can increase the yield of crops. (5/6) {This one comes up a lottttt}


Temperature can be controlled and increased (1) which speeds up rate of enzyme controlled reactions (1).
Increased concentration of CO2 enables more photosynthesis(2).
Increased nitrates in soil, which are needed for making amino acids for new cell growth (3!)
:yes:
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sgvaibhav
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Report 12 years ago
#2
is there cloning also
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tsr4life
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Report 12 years ago
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(Original post by silliva)
Hey!

I thought since the exam is only a few day away, now would be a time to start discussing questions which, commonly come up and the model answers to them. I'll start :deal:

(Marks in brackets after key word/phrase)

1. Describe how genes can be transferred from one organism to another using genetic modification. (5 marks)

The desired gene should be isolated and cut out (1) using restrictive enzymes (1). The corresponding gene should then be cut out out of target animal (1) using the same restrictive enzyme (1). The desired gene should then be inserted into target animal DNA (1) using ligase (1) to join them together.

A variation on this question may be about how bacteria can be used to make insulin. Here you'd use same method but say that the gene for insulin is put into a vector, inserted into a fermenter of bacteria where the bacteria will take up this vector and multiply.

2. Describe how white blood cells prevent ill-health and disease (4)

Phagocytes engulf and digest the pathogen (3!). Lymphocytes omit antibodies which clump and neutralise pathogens (4!!)

3. Explain the method for creating a clone of a mammal (5)

Nucleus from chosen adult mammal (1) is inserted into ennucleated egg cell (1), this then undergoes mitosis (1) to form an embryo (1). This embryo is then inserted into the womb (1) of the surrogate mother.

4. Explain how greenhouse can increase the yield of crops. (5/6) {This one comes up a lottttt}


Temperature can be controlled and increased (1) which speeds up rate of enzyme controlled reactions (1).
Increased concentration of CO2 enables more photosynthesis(2).
Increased nitrates in soil, which are needed for making amino acids for new cell growth (3!)
:yes:

you got 2 questions right!

for the cloning one, do you think putting an unfertilised cell would be accepted aswell as unnucleated?
thanks
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Magnus Bane
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Report 5 years ago
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(Original post by tsr4life)
you got 2 questions right!

for the cloning one, do you think putting an unfertilised cell would be accepted aswell as unnucleated?
thanks
No. The unfertilized egg would have already have a haploid nucleus inside it.
so now there would be one and a half times as many as normal number of chromosomes.
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