Edexcel Biology IGCSE 2B Unofficial Mark Scheme 10th June 2016

Omg so for the homozygous recessive did people get 11 (all the ones who did not suffer from FH) and for homozygous dominant did people get 0? (because the first generation parents were only Dd and dd so it was impossible for a DD to be offspring)

i think it is temperature and pH for the digestive enzymes to have optimum conditions

I thought of that but ended up only putting temperature for optimum conditions and size of insect as a larger insect means more matter to digest? idk

ahhhh didnt think of that, as smaller insects would mean quicker digestion

Tell me the questions which I'm missing out - I'll add them in.

1.a)
Respiration. (1)

1.b)
[Insect] pollination. (1)

1.c)
Producer and consumer. (2)

1.d)
Advantages of brushing hairs twice before closing:
Ensures the insect is there hence can catch it for a source of food hence energy for respiration.
Plant is efficient as it prevents wasting of energy by closing trap when no insects are present. (2)

1.e)
Protease enzyme pepsin etc. (1)

1.f)
Issue with microbes entering plant:
Can cause disease hence cause plant to die.
Can use up all the nutrients etc. by decomposing the food ingested by the plant. (2)

2.a)
Fish have different amounts of nitrogenous excretory products because they may be different species, have eaten different quantities and type of food etc. (1)

2.b)
Eutrophication when organic matter is leached into aquatic environment, decomposers e.g bacteria decompose the matter, releasing high concentration of nutrients and mineral ions hence algal bloom (rapidly growing algae population). Hence algae at surface block light from reaching algae at bottom of river/lake hence can't photosynthesise hence die hence large biomass which is decomposed by bacteria, using all the oxygen in the water, hence lack of oxygen for respiration in fish hence fish kill.

(Maybe) Could also talk about the ammonia being converted into nitrates and then hence amino acids and protein hence increasing growth and obviously the death of plants hence producers have negative effect on food chain. Main points however are above. (5)

2.c)
Increase in immunity to disease as an immune response is launched where lymphocytes create antibodies for the antigens of the foreign cell/pathogen. Once the specific antibody has been made, it is replicated and hence bind to the antigens and destroy the cell. Phagocytes engulf them via phagocytosis and break the cell down with digestive enzymes. This helps prevent disease and spread of disease, preventing death and hence contributing to growth as the antibodies remain in the blood at a low level and can be quickly replicated when infected with the actual disease. (4)

3.a)
Independent variable is the type of plastic. (1)

3.b)
72.3 x 0.4 = 28.9 cm. (2)

3.c)
Reliable as repeats (equivalent) were used as he used 10 trays for each, used a variety of different independent variables and grew the plants for a long enough time (3 months). (2)

3.d)
Abiotic factors:
Temperature.
Type of soil.
Concentrations of CO2 and O2 for photosynthesis and respiration. (3)

3.e)
Why the black sheet resulted in faster growth:
Black is a good absorber of thermal radiation from the sun hence increases temperature to the optimal temperature for enzyme activity hence increase in photosynthesis and respiration rate.
Also prevents other organisms getting into soil and taking nutrients hence decreases competition. Also helps prevent growth of weeds etc. (4)

4.a)
Increase in gestation period resulted in an increase in female mass on average. (1)

4.b)
Roe as it had the same mass as the Silo (can't remember name but it started with an S) but it had a longer gestation period. This difference in can only be explained as it took a longer time for the same growth and development due to mitosis etc. to get to the same mass as a result of no development during a few months of this period. (3)

4.c)
Placenta. Embryo hence foetus is connected to it via the umbilical cord. It allows the transfer of substances between the mother's and baby's blood as the blood can't mix as they may have different blood types. This transfer is done by the maternal and umbilical vessels. Substances for growth and development etc. are transferred from mother to baby/embryo i.e glucose, salts, oxygen, hormones etc. and waste products to the mother i.e CO2, urea and water. (4)

5.a)
11 and 0. (2)

5.b)
.125 (1)

5.c)
Arteries narrow due to build up of cholesterol hence constricts flow of blood hence less glucose and oxygen delivered to cells hence cells can't respire (aerobically) hence cells die hence muscle decay. Could talk about lactic acid and anaerobic respiration. (5)

6.a)
7mm. (1)

6.b)
Retinal cells in the back of the eye. (1)

6.c)
The pupil dilates to allow more light to enter the eye as the antagonistic radial muscles contract and circular muscles relax, allowing the diameter of the pupil to expand. (3)

Do you think I'd get a mark for putting amount of digestive fluid secreted?

Guys the paper and solutions is here!! http://www.thestudentroom.co.uk/showthread.php?t=4155673#primary_content

i think it is temperature and pH for the digestive enzymes to have optimum conditions

What about size of insect?

Will i still get the mark for primary consumer instead of just consumer for the second question?

i thought it was producer and secondary consumer, as the plant feeds on the fly, which feeds on something else

Yes that is correct but will the word consumer get me a mark??

For the placenta question, shouldn't we also mention about how it helps maintain the uterus lining?


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i thought it was producer and secondary consumer, as the plant feeds on the fly, which feeds on something else