Biology unit 2

Q & A from unit 2 papers. Answers taken directly from the mark scheme.

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  • Created by: Fabiha
  • Created on: 17-03-12 18:19

Explain the importance of elastic fibres in the wa

Stretches/’expands’ under high pressure/when ventricle 

contracts / systole;

Recoils/’springs back’ under low pressure/when ventricle 

relaxes / diastole;

Smooths blood flow / maintains blood pressure / reduces

pressure surges;

1 of 12

Explain the importance of muscle fibres in the wal

(Muscle) contracts;

(Arteriole) constricts / narrows/alters size of lumen / 

reduces/regulates blood flow (to capillaries);

2 of 12

) Efficient exchange of substances in the capillar

(More) time for exchange of substance

3 of 12

During which part of the cell cycle are gene mutat

Interphase/ S/synthesis (phase);

(explanation : DNA/gene replication/synthesis occurs / longest stage;)

4 of 12

What is an allele?

(Different) form/type/version of a gene / different base 

sequence of a gene

5 of 12

describe how haemoglobin loads and unloads oxygen

Loading/uptake/association of oxygen at high p.O2;

In lungs (haemoglobin) is (almost) fully saturated / in lungs 

haemoglobin has a high affinity for oxygen; 

Unloads/releases/dissociates oxygen at low p.O2;

Unloading linked to higher carbon dioxide concentration; 

6 of 12

Heat from respiration helps mammals to maintain a

Smaller mammal has greater surface area to volume ratio;

Smaller mammal/larger SA:Vol ratio more heat lost (per unit 

body mass);

Smaller mammal/larger SA:Vol ratio has greater rate of 

respiration/metabolism;

Oxygen required for respiration;

(Haemoglobin) releases more oxygen / oxygen released more 

readily / haemoglobin has lower affinity;

7 of 12

Suggest two ways to reduce the transmission of MRS

Isolation / quarantine / ‘kept separate’;

Screening/testing (of patients/doctors etc);

Sterilisation of wards/equipment / method to improve hygiene;

8 of 12

Suggest two ways in which a double-blind trial imp

Prevents bias;

Vested interest (of scientists);

Prevents ‘placebo’/positive/negative/psychological 

effects/’demand characteristics’ (in volunteers); 

9 of 12

Explain what is meant by a quaternary structure.

More than one polypeptide chain;

10 of 12

Scientists’ analysis of blood proteins has indicat

1. Mark for general principle of - reduced variety/number of   

    different alleles/DNA / reduced gene pool 

2. Founder effect;

3. A few individuals from a population become isolated/form   

    colonies:

4. (Genetic) bottlenecks;

5. (Significant) fall in size of population

6. Selective breeding / artificial selection;

7. Using organisms with particular 

    alleles/traits/phenotypes/characteristics;

11 of 12

Explain how a change in a sequence of DNA bases co

Change in (sequence of) amino acids/primary structure; 

Change in hydrogen/ionic/disulfide bonds; 

Alters tertiary structure/active site (of enzyme); 

Substrate cannot bind / no enzyme-substrate complexes form;

12 of 12

Comments

Gabriella Earl

on question 6, does p. stand for pressure?

Xenxen

where can i get past edecxel papers for biology 1 and 2 ?

Fabiha

Gabriella Earl wrote:

on question 6, does p. stand for pressure?

Yes, it stands for partial pressure :)

Fabiha

Tish wrote:

where can i get past edecxel papers for biology 1 and 2 ?

I don't do edexcel biology, but the papers should be on the website. Click GCE from 2008 for A-level papers. 

Here's the link-->http://www.edexcel.com/i-am-a/student/Pages/Pastpapers.aspx 

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