Exam questions on unit 2 (answers)

The answers to my other resource 'exam questions on unit 2 (snab)'

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  • Created on: 06-06-10 11:44
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1. Identify these two organelles from their descriptions and state their functions:
a. An oval shaped organelle surrounded by a double membrane. The inner membrane is
folded and projects into the inner space, which is filled with grainy material
Mitochondrion
Site of aerobic respiration
(2 marks)
b. A collection of flattened membrane sacs arranged roughly parallel to each other,
getting smaller. Small, circular structures are seen at the edges of these sacs, for
transportation.
Golgi apparatus
Processes and packages new lipids and proteins/makes lysosomes
(2 marks)
2. Describe how to prepare a root tip to observe mitosis
Cut a root tip from a growing root
Place it on a watch glass and add a few drops of Hydrochloric acid to the
root tip
Followed by an appropriate stain (e.g. toluidine blue)
Warm the watch glass
Place the root tip on a microscope slide and use a mounted needle to break
it open and spread the cells out
Add a few more drops of stain and place a cover slip over the root tip
Gently squash the cover slip down
Warm the slide to intensify the stain
Safety: do not break the cover slip/ do not get stain in eyes
(6 marks)
3.
a. Explain what crossing over is and how it leads to genetic variation
Before the 1st division of meiosis, homologous pairs of chromosomes come
together and pair up
The chromatids twist around each other
Bits of the chromatids break off and rejoin onto the other chromatid
The chromatids now contain different combinations of alleles
This means each of the four daughter cells will contain chromatids with
different combinations of alleles
(4 marks)
b. Explain how independent assortment leads to genetic variation
Mean the chromosome pairs can split up in any way
The cells produced can contain any combination of maternal and paternal
chromosomes with different alleles (2 marks)
4.
a. Describe the fertilisation process in mammals, starting with the acrosome reaction
During acrosome reaction digestive enzymes are released from the
acrosome of the sperm
These enzymes digest the zona pellucida
Which allows the sperm to pass through and fuse with th cell membrane of
egg cell
This triggers cortical reaction

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Where the contents of the cortical granules are released from the egg
cell
The chemicals from the cortical granules make the zona pellucida thick and
impenetrable to other sperm
So that only one sperm can fertilise the egg cell
The sperm nucleus enters the egg cell
And fuses with the egg cell nucleus - fertilisation
(6 marks)
b. In what type of plants does double fertilisation occur?
Flowering plants
(1 mark)
5.
a.…read more

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Over generations adaptations become more common in population
(5 marks)
7.…read more

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­ testing drug on small group of healthy people
Done to determine any side effects/ Safe dosage
2nd phase ­ testing group on large group of patients
To see how well drug works
3rd phase ­ larger group of patients
Compare effectiveness compared to existing drugs
Patients randomly slit into two groups ­ existing drug + new drug
(5 marks)…read more

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