In this bundle there are more than 5000 aqa a level biology questions and if you do every question and memorise the mark scheme you will get that A* without a doubt
2. (a) Mark for principle of placing quadrats at random;
marks for detail -
(method of) marking area out with grid/using tapes;
acceptable method of generating random numbers; e.g.
table/calculator; 3
(b) Any one correct change;
reason for diversity level;
explanation of how heather affects diversity; 3
–2 –1
(c) (i) Award two marks for 0.5 g m yr ;;
award one mark for answer without units
or 2.4 – 2.5 %; 2
(ii) Used for non photosynthesising/supporting organs;
eaten by grouse; 2
(iii) Younger plants have more shoots/provide more food;
Younger plants provide more cover;
Getting rid of old (unproductive) plants; max. 2
(d) (i) proteins/nucleic acids/amino acids/ATP/nucleotides;
(ii) ammonium/nitrate/nitrite;
– –
NH 4 NO 3 NO 2 [Formula must correspond if given] 1
(e) Organic material/proteins to ammonia/ammonium compounds; 1
by saprobiotic/putrefying bacteria;
ammonia to nitrite;
nitrite to nitrate;
by nitrifying bacteria/named bacteria; max. 4
(f) In older stands, greater proportion of/more nitrogen in plants;
more lost when burnt: 2
[20]
3. (a) Wood mouse; 1
(b) Decomposers/bacteria/fungi/saprophytes/saprotrophs/detritivores; 1
(c) Colonisation/pioneer species/examples from fig/seeds/fruits;
soil formation/improvement/change by organism;
succession/eq;
process repeated to climax community/forest; max. 3
diversity is reduced;
Sir George Monoux Sixth Form College 1
, (d) {trees form food source for many species/wide range of primary consumers;
{(primary consumers/named example/are eaten by other species)
{idea that trees are the basis of food chains/food webs;
productivity of area is reduced (with loss of trees);
so fewer organisms can be supported;
habitats are lost/ecological niches are lost (with each tree species lost); max. 3
[8]
4. (a) ‘Slash’ / cutting down trees reduces photosynthesis;
Reduces removal of carbon dioxide from atmosphere;
‘Burn’ combustion releases carbon dioxide;
OR ‘Slash’ cutting down trees removes respiring organisms;
Reduces removal of carbon dioxide into atmosphere;
‘Burn’ / combustion releases carbon dioxide; max 2
(b) (Before clearing) soil exists / already produced;
(After clearing) recolonisation by new plants / seeds;
(Brings about) change in environment / soil;
(Allows) succession;
(Leading to) climax (community); max 3
(c) 1 Ammonium compounds from proteins / amino acids urea / N-containing;
2 Converted into nitrite;
3 Into nitrate; [Reject: Incorrect sequence once]
4 By nitrifying bacteria / correctly named;
5 Nitrogen-fixing bacteria;
6 Fix nitrogen from atmosphere / air;
7 Nitrate taken up by plants;
8 Nitrogen needed for protein synthesis / plant growth; max 6
(d) Trees available as a sustainable resource;
Maintain habitats / niches / shelter;
Maintain diversity / avoid loss of species / protect endangered species.
Maintain stability (of ecosystem);
Maintain food chains / webs / supply of food;
Reduced loss of soil / erosion;
Reduced flooding;
Act as carbon sink / maintainO2and C02 balance reduce greenhouse effect
Reduce global warming;
Source of medicines;
[Ignore: eutrophication] max 4
[15]
5. (a) Tapes / string / axes laid out at right angles / grid area;
Method of obtaining random co-ordinates;
Do not allow “Use random number generator” 2
(b) (i) Decrease then remain constant;
From 200 cm / over 150 cm; 2
(ii) Oxygen decreasing because soil becomes more compacted/ not
replaced;
Decrease in oxygen leads to fewer aerobes surviving;
Respiration; max 2
(c) Anaerobic bacteria replace aerobic;
As oxygen decreased by aerobic bacteria;
Remove competition;
Sir George Monoux Sixth Form College 2
, Aerobic bacteria no longer able to survive in these conditions; max 3
Sir George Monoux Sixth Form College 3
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller ainhoa1. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £7.09. You're not tied to anything after your purchase.
