AQA BIOL4 - 13th June 2014 - Unofficial Markscheme

yeast answer was 0.015

yeast answer was 0.015

does dna contain phosphorus because of the sugar phosphate backbone?

Hi everyone if people can contribute below. I am trying to write up an unofficial mark scheme for the exam. So far I have potential answers for the 15 marks at the end and I am typing up some other questions. I will edit this top post as people help with it!

Please contribute to the thread if you see any missing question. Obviously not all answers will be MS correct, that's why it's unofficial. Suggest questions on this paper were very unpredictable so their will be a very wide range of possible answers.

Population question
1. Describe two differences between the populations in 1700 and 2010 (2)
Mean number of children per woman lower in 2010.
Average life expectancy greater in 2010.

Suggest two reasons behind the differences you have described. (2)
Number of children per woman lower: increased access to birth control...
Life expectancy longer: improved healthcare, sanitation, more medicines, safer drinking water

Total population in 2011 (2)
60175920

Nitrogen cycle question
2. Give two biological molecules with these components: (2)
Nitrogen: amino acids, proteins, urea
Phosphorus: DNA, ATP, RNA, phospholipid

Describe how nitrogen in dead organic matter is made available to plants. (3)
Proteins/amino acids broken down
By saprophytes/saprobionts/decomposers
Deamination
Ammonia/ium formed
Ammonia/ium converted to nitrites
Then to nitrates by nitirfying bacteria

Upwelling causes areas of high gross productivity. Explain why coastal areas have large fish stocks? (2)
Nutrients near surface, means that nutrients aren't limiting producers
Fish feeds on producers near surface in coastal areas??

Succession question
3. What type of succession? (1)
(secondary) Succession - doubtful that secondary is needed as its not on spec.

What is there an increased diversity of birds in the woodland (3)
Increased diversity of plants
More variety of habitats/niches for birds
More variety of food sources for birds

Chickens genetics question
4. Explain why females are more likely to inherit sex-linked recessive allele. (1)
Females are XY and so cannot be carriers/only need one recessive allele instead of two it to be expressed.

Explain evidence from the diagram to show that the allele for rapid feather growth is recessive (2)
1+2 are unaffected yet produce affected offspring 5 so they must be heterozygous/carriers

Give the genotype of the following chickens: (2)
Chicken 5: Xf Y
Chicken 7: XF Xf and XF XF

I thought their was two possibilities for Chicken 7, anyone else???

Give the genotypes of the parents who produce the following offspring: 2 rapid growing feather males and 2 slow growing feather females (1)
Genotypes: XFXf, XfY

Note: unsure of these genotypes, it's just what's been suggested in the thread

H-W equation calculation (3)
Square root of 0.04 = 0.2
1 - 0.2 = 0.8
2 * 0.8 * 0.2 = 0.32 * 100 = 32%

Sickle cell anaemia inheritance question
Explain why results are given as ratios (2)
Total number of patients varies
Allows for comparison between values

Describe how blood group affects chances of severe malaria (2)
Blood group A has increased chance + quote figures
Blood group O has 1:1 chance + quote figures
Not sure whether you needed to mention sickle cell trait here...?

Explain why population has gradually got less HbA genotype in comparison to HbO (3)
HbA have more chance of severe malaria/ more chance of death
Less HbA survive / More HbO survive
Less reproductive success
Increase in allele freq. of HbO / decrease in allele freq. of HbA

Photosynthesis graph question
6.Describe two other limiting factors (2)
Temperature
CO2 concentration
Water

Explain why CO2 can be used as a measure of net productivity (1)
CO2 taken up in photosynthesis, photosynthesis used to produce energy

Shaded plants is more adapted to low light intensity than shaded plant. Use the graph to explain why. (2)
In lower light intensities, less CO2 is released
More CO2 in stomata so more CO2 to combine with RuBP in low light intensities
Could mention compensation point & faster growth rate of shaded plant in low light intensities.

Anaerobic respiration of yeast question
7. Why a thin layer of oil (1)
Ensure no O2 from the flask reaches yeast, must ensure anaerobic conditions

b) Calculation (2)
0.015

Repeat investigation to investigate aerobic respiration in yeast. What would happen to the amount of gas produced. (2)
Remains the same
O2 taken up for respiration (as it's terminal electron carrier)
Equal to CO2 produced

Why respiration in oxygen produces more ATP than without.(2)
Oxygen is a terminal electron acceptor. Without oxygen electron-transport-chain won't take place. Most ATP is made in ETC

Hydrilla - pest control question
8. Suggest two reasons why the Hydrilla is dominant? (2)
Wide variety of answers for this as it's a "suggest" I presume you have too guess characteristics of Hydrilla which makes it outcompete others:
Outcompetes others for light - can photosynthesise at a greater range of light intensities
Outcompetes others for nutrients - has a larger root system so can absorb more nutrients

Suggest two economic consequences of hydrilla.(2)
Again answers depend on AQAs mark scheme:
Hydrilla outcompetes the natural freshwater fishes food source, so natural fish die, less income in fish industry :/
Cost of having to remove/control hydrilla

Use a fungus as a biological control to Hydrilla. Fungus cultured from tissue of hydrilla in the origin country of species. Why is this form a fungus used? (2)
Specific to hydrilla
Hydrilla can't develop resistance?
Can't become a pest itself because can't survive on other species?

Why reheating/measuring cycle is a reliable way to measure biomass (2)
Removes water so you get dry mass
Reheating until mass is constant.?

Why only use 5 concentration of the pesticide (4)
Any less and the biomass of the hydrilla still increases
Any more and it would become:
not cost effective
may bioaccumulate
may not biodegrade?

Why use integrated pest control system useful in this scenario? (2)
Apply the pesticide, pesticide reduces the levels to low numbers
Biological control begins working after lag time, this maintains populations at these low numbers in the long term.

Longer answer/factual recall questions
9. Explain how the LIR reactions use CO2 to produce organic substances. (6 marks)
Calvin cycle - in stroma
CO2 diffuses in through stomata and enters stroma
Combines with RUBP using an enzyme
This produces 2 molecules of GP
ATP and reduced NADP from LDR are used to reduce the GP into TP.
The NADP reformed goes back to LDR to be reduced again
Some TP is converted into useful organic substances e.g. glucose
Most TP is used to regenerate RuBP using ATP from LDR


Explain how human activities have led to global warming.(4 marks)
Deforestation
Less CO2 taken up in photosynthesis
Burning of felled trees
CO2 released into the atmosphere
Methane produced during decay/farming
CO2 and methane are greenhouse gases
Contribute to greenhouse effect so more infrared radiation reflected back to earth
Increased global temperatures


Explain how you could estimate the population size of bluebell population. (5 marks)
Map the area using grid
Use random number generator on calculator/computer to choose coordinates
To ensure sample is unbias
Place quadrat at coordinates
Measure abundance - frequency
Then calculate (No. of quadrat used / total area) * Avg. no of species per quadrat
Use running mean to make sure you have done enough samples
Do enough samples for statistical test

My grade boundary predictions:
I thought this paper was similar to June 2013, perhaps a bit easier...
A* = 58
A= 53
B = 48
C = 44
D = 39
E = 35

In question 7 I remember one that said 'why was a control used?' dont think thats in the unofficial mark scheme currently...


Posted from TSR Mobile

for the oil Q. I think the repeat investigation was looking at volume of gas in the syringe, not the volume produced, in which case it would be less b/c oxygen is taken in for use as TEA?

population q definitely wrong has to be less than 60000 mill. Fish question: saprobionts use aerobic respiration which takes up all the O2 so fish die. Also limiting factors light and co2 not TEMP.


Posted from TSR Mobile

no.