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

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1. (Original post by TherealG)
Question 1 was what process do plants use to release glucose
Surely that's photosynthesis as that produces glucose whereas respiration uses it
No respiration changes glucose + oxygen to energy, water and Co2; whilst photosynthesis changes co2 and water into glucose and oxygen.
(Original post by melisss22)
i only managed to write in one point for that question. i ended up saying that black was a good absorber of heat therefore allowing sufficient light inside making it optimum for photosynthesis and respiration. but yeah awfully reminded me of physics
I couldn't think of any answers so wrote two rubbish asnwers - until the last 20 seconds when I realised that it stopped weeds growing - I scribbled it down, having crossed out an answer, and finsihed with seconds to spare. Turns out the rubbish answer I crossed out could have been right - it stops rain from causing soil erosion. Which was annoying, considering my other answer was genuine utter rubbish ...
(Original post by Hsevras)
I put the enzyme as amylase
Yeah, pretty much any enzyme was correct.
(Original post by niv1234)
Thanks for replying. Thats more or less what I wrote but I wasn't exactly sure.
No problem, I'm sure you'll get the marks.
(Original post by iah1700)
What will the grade boundaries for igcse biology be?
A* = 135
A = 120
B = 100
C = 85
(Original post by h_wxller1)
What do we think the grade boundary will be for an A*?
135
2. (Original post by Milzime)
do pH and humidity count as abiotic factors?
Yes, but you would have had to say pH of soil.
3. (Original post by Milzime)
do pH and humidity count as abiotic factors?
I think so as abiotic just means non living. I think I put temperature and nutrients in the soil but I can't really remember.
4. (Original post by Martins1)
Yes, but you would have had to say pH of soil.
damn I think i just put 'pH'
5. (Original post by Milzime)
damn I think i just put 'pH'
You may be lucky. But that implies air pH which doesn't make sense because its constant either way - I dont think you can really change/control it that much. Soil pH, on the other hand, is both relevant, highly important in gardening and can be easily changed/controlled. It was only one mark though.
6. (Original post by Martins1)
You may be lucky. But that implies air pH which doesn't make sense because its constant either way - I dont think you can really change/control it that much. Soil pH, on the other hand, is both relevant, highly important in gardening and can be easily changed/controlled. It was only one mark though.
yeah, true true

(obviously I meant soil pH -_- but I'm pretty sure I just said pH)

oh well; probably did fine anywhowhowho(hopefully)
7. can someone please explain how the probability question for 5b was .125?
8. (Original post by Martins1)
Yes, but you would have had to say pH of soil.
is this about the question where we had to state 3 non living things that had to be kept constant or something? i put
1. humidity
2. temperature
3. wind speed

would i get any marks ? lol
9. (Original post by Emilia1479)
I was just wondering, do you have to round for your answer?
You don't have to, but its better to because they gave the table values to 1 dp.
10. (Original post by melisss22)
is this about the question where we had to state 3 non living things that had to be kept constant or something? i put
1. humidity
2. temperature
3. wind speed

would i get any marks ? lol
They all look right to me. I put temperature, soil type and CO2 concentration.
(Original post by chantsareonfire)
can someone please explain how the probability question for 5b was .125?
OK so it asked for you to calculate the probability of the couple G and H having three children with the disease.
Because none of the people of family tree were homozygous dominant, we knew that G had the genes Dd and H the genes dd. Therefore, doing a punnett square, there is a 0.5 chance of having a child with the disease.
Therefore, basic maths, to have three children all with the disease was 0.5x0.5x0.5 = 0.125.
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 and hence average, used a variety of different independent variables and grew the plants for a long enough time (3 months). Helps to factor the anomalous results. (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)
Hi! I agree with all answers , however as for (1c) I specified with producer and secondary consumer rather than just consumer) any problem with that?
12. (Original post by Martins1)
They all look right to me. I put temperature, soil type and CO2 concentration.

OK so it asked for you to calculate the probability of the couple G and H having three children with the disease.
Because none of the people of family tree were homozygous dominant, we knew that G had the genes Dd and H the genes dd. Therefore, doing a punnett square, there is a 0.5 chance of having a child with the disease.
Therefore, basic maths, to have three children all with the disease was 0.5x0.5x0.5 = 0.125.
dammit, I did the punnet square and got a probability of 1/4 and so ended with with a probability of 1/64
13. (Original post by umang-23)
Hi! I agree with all answers , however as for (1c) I specified with producer and secondary consumer rather than just consumer) any problem with that?
No, I did that too. Primary consumer is wrong, but both secondary and tertiary consumer could be accepted, although I cannot think of a tertiary consumer which a Venus flytrap would eat. Personally i think that if they accept just consumer that is too lenient, but hopefully they will for all those who put that down!
14. A* = 135
A = 120
B = 100
C = 85

Thanks
15. (Original post by umang-23)
Hi! I agree with all answers , however as for (1c) I specified with producer and secondary consumer rather than just consumer) any problem with that?
No problem.
16. Ah...okay

Thanks

You don't have to, but its better to because they gave the table values to 1 dp.
17. (Original post by gcsemusicsucks)
Don't worry I put a mix, one of my points was the size of the food like you said, the other was temperature (optimum temp for enzymes means faster digestion) Hoping they will accept both approaches?
They were my two answers exactly 👌
18. Quick one if anyone still reads this thread - I put amylase down for the enzyme present in the fly trap but I'm starting to doubt it now. Since amylase breaks down starch into maltose, would this be an acceptable answer because I'm not sure a fly will contain starch because starch is gained from plants. Can anyone help?
19. (Original post by jose99)
Quick one if anyone still reads this thread - I put amylase down for the enzyme present in the fly trap but I'm starting to doubt it now. Since amylase breaks down starch into maltose, would this be an acceptable answer because I'm not sure a fly will contain starch because starch is gained from plants. Can anyone help?
Yeah, pretty much any enzyme would be allowed, so i think it would be allowed as it would be needed in order to break down parts of the fly.
20. (Original post by TherealG)
Question 1 was what process do plants use to release glucose
Surely that's photosynthesis as that produces glucose whereas respiration uses it
I put photosynthesis as thats the process written in the passage.

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