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

Yes but the insect may feed on something else which that something then feeds on to the producer, so you would never know for sure, so consumer would get the mark.

What was the 0 answer to ?

number of people who were homozygous dominant (e.g. DD)

Thank you. I can't remember but did the Grey stand for people who had the condition? (Trying to remember what I put) .

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

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)

1.g)
Lack of teeth decreases rate of digestion due to no mechanical digestion which would increase the surface area of the food for the enzymes to act upon to increaser rate of chemical digestion. (2)

1.f)
Factors effecting rate of digestion:
Optimal pH for enzyme activity increasing the rate of chemical digestion.
Optimal temperature for enzyme activity increasing the rate of chemical digestion due to increase ke or enzyme and substrate hence more successful collisions where substrate and active site align to produce product.
Size hence biomass of insect. Increase in biomass = increase in material to break down hence takes longer. (4)

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)

i think your missing out the genetic diagram question, one with D d

I believe it was (insect) pollination rather than (wind) pollination, as it asked why the insects were needed. Also I put secondary consumer instead of just consumer - do you think it will count? Also for 6b I just got retina. What was the answer for 'suggest why the black sheet meant the plant grew faster' (or something like that)
Overally I defo found this paper easier than paper 1 but then again I think I made a lot of mistakes and strange answers

The answer was secondary consumer and producer
Guy who made the markscheme is wrong

The answer was secondary consumer and producer
Guy who made the markscheme is wrong

I'm pretty sure writing consumer is correct because they never said the insect must feed off the plant. Take an example, the fly trap can eat a preying mantis, but the preying mantis is an insect that feeds off other insects, so in this case it would be a tertiary consumer.

'consumer' is not a trophic level
All plants are producers
insects feed on plants, trees and fruit
Venus flytraps feed on insects
Therefore the flytraps are producers and secondary consumers

An insect can also feed on other insects as I said with the preying mantis example.

im pretty sure they will accept secondary, territiary etc. consumer, maybe just not primary consumer

For 1E will i get a point for writing amylase??

guys could someone please clear up 4b for me, its killing me. I put the first deer because if you divided the mass by the days (or the other way round can't remember lol) then it gave you how many days it took for a kg of the deer to grow. By that calculation the first one took like 16 days and the second one took 6 (can't remember exactly) then the rest were less than 6. So that's why I put the first one, did anyone do the same? Please tell me they did lol.