AQA Biology Unit 2 Exam Question and Answer

1(d) An Artery/Arterioles contains smooth muscle in its walls. Explain how this muscle may reduce the blood flow to the small intestine.                   (2 marks)

1(e) Elastic tissue in the walls of an Artery helps to even out the pressure of blood through this vessel. Explain how.                                (2 marks)

1 (d) Contracts;

(Causes) vasoconstriction/narrows lumen;

1 (e) (Elastic tissue) stretches when pressure is high;

Springs back/recoils/returns to normal;

 3(a) Give one way in which a DNA molecule in a prokaryote, such as a bacterium, is different from a DNA molecule in a eukaryote. 

                                                                                               (1 mark)

3 (a) (Prokaryotic DNA) is circular/in a loop

/not associated withproteins/not in chromosomes

/does not contain introns/does not contain junk DNA/shorter;

 4(c) Drugs are used to treat cancer. At what phase in the cell cycle would each of the following drugs act?

 (i) A drug that prevents DNA replication                                            (1 mark) 

 (ii) A drug that prevents spindle fibres shortening                            (1 mark) 

(i) Interphase/S phase/synthesis phase;

(ii) Anaphase/A

5(a) What is a tissue?                                                                      (1 mark) 

(a) (Group of) similar/identical cells/cells with a common origin;

5 (c) Cellulose and starch are both carbohydrates. Describe two ways in which molecules of cellulose are similar to molecules of starch.

                                                                                                       (2 marks)

5 (c) Both are polymers/made of monomers;

Joined by condensation/molecules can be broken down by hydrolysis;

Both have 1-4 links;

Contain C(arbon), H(ydrogen) and O(xygen)/both made up of glucose;

Both insoluble;

Both contain glycosidic bonds;

6(c) Explain what is meant by genetic diversity.                                    (1 mark)

6(d) (i) what is meant by a genetic bottleneck.                                   

                                                                                                                 (1 marks)

6 (c) Difference in DNA/base sequence/alleles/genes;

6 (d) (i) Genetic bottleneck linked to low genetic diversity/smaller gene pool;

8(a) A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.                                                

                                                                                             (6 marks) 

8 (a) 1 Large surface area provided by lamellae/filaments;

2 Increases diffusion/makes diffusion efficient;

3 Thin epithelium/distance between water and blood;

4 Water and blood flow in opposite directions/countercurrent;

5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;

6 As water always next to blood with lower concentration

of oxygen;

7 Circulation replaces blood saturated with oxygen;

8 Ventilation replaces water (as oxygen removed);

 1 (a) Give one feature of starch and explain how this feature enables it to act as a storage substance.                                                        

                                                                                                      (2 marks)

 Helical /spiral/coiled;

Compact / description e.g. ‘tightly packed’;

Insoluble;

Prevents osmosis/uptake of water / does not affect water potential / (starch) does not leave cell;

Large molecule / long chain;

Does not leave cell;

 1 (c) The structure of cellulose is related to its role in plant cell walls. Explain how.                                                                                           

                                                                                           (3 marks)

1 (c)  Long/straight/unbranched chains (of glucose);

(Joined by) hydrogen bonds;

Form (micro)fibrils/(macro)fibrils;

Provide rigidity/strength/support;

 2 (c) Explain the importance of elastic fibres in the wall of the aorta.

                                                                                                           (2 marks)

 2 (c) (i) 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;

3 (a) What name is used for the non-coding sections of a gene?

                                                                                                          (1 mark)

3 (a) Introns

3

  (1 mark)

(d) Gene mutations occur spontaneously. During which part of the cell cycle are gene mutations most likely to occur? 

Interphase/ S/synthesis (phase)

As DNA/gene replication/synthesis occurs / longest stage;

 5 (a) What is an allele?                                                                   

5 (b) Explain the appearance of a Choromosome.

                                                                                            (2 marks)

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

5(b) Two/sister chromatids; Due to DNA replication; Joined by a centromere;

Describe how haemoglobin loads and unloads oxygen in the body.

(3 marks)

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;

9 (a) (iii)

                                                                                              (1 mark)

Haemoglobin has a quaternary structure. Explain what is meant by a quaternary structure.

More than one polypeptide chain

1

(a) Name the process in which cells become adapted for different functions. 

                                                                                               (1 mark)

2. Explain

one

way in which a palicade cell is adapted for photosynthesis.

                                                                                              (1 mark)

1. Differentiation/specialisation

2. Chloroplasts absorb light;

Large vacuole pushes chloroplasts to edge (of cell);

Thin/permeable (cell) wall to absorb carbon dioxide;

2

(a) (ii) This system of classification consists of a hierarchy. Explain what is meant by a hierarchy. 

                                                                                                         (2 marks)

Groups within (larger) groups;

No overlap;

3

(e) Explain how a change in a sequence of DNA bases could result in a non-functional enzyme. 

                                                                                                       (3 marks)

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;

5

(b) Suggest how A student could use a microscope slide to find the number of stomata per cm 

                                                                                                    (3 marks)

(c) The stomata on the leaves of pine trees are found in pits below the leaf surface.Explain how this helps to reduce water loss.

                                                                                                        (2 marks)

5 (b) Method of determining area of field of view/area seen using microscope;

Count number of stomata in field of view;

Repeats and calculation of mean;

(c)

Water vapour accumulates / increased humidity/ reduced air

movement (around stomata);

Water potential/diffusion gradient reduced;

6

(c) (i) The blood pressure is high at the start of the capillary. Explain how the left ventricle causes the blood to be at high pressure.                                                                                                             (1 mark)

6

(c) (ii) The blood pressure decreases along the length of the capillary. What causes this decrease in pressure? 

                                                                                                           (1 mark)

(i) Contracts

(ii)

Loss of fluid/volume;

Friction/resistance (of capillary wall);

8

(a) Gas exchange in fish takes place in gills. Explain how two features of gills allow efficient gas exchange.                                                                                                 (2 marks)

8

(b) (iv) Heat from respiration helps mammals to maintain a constant body temperature.Use this information to explain the relationship between body mass and oxygen uptake.

                                                                                                   (3 marks)

(a) Filaments/lamellae provide large surface area;

Thin/flattened epithelium/ one/two cell layers so short diffusion

pathway (between water and blood);

Countercurrent/blood flow maintains concentration/diffusion gradient;

(b)

Smaller animals have larger surface area to volume ratio;

Lose more heat per gram of tissue;

Respire more/faster (relative to body mass);

Oxygen used in respiration;

What does standard deviation show?

(Degree of) spread/variation from the mean;

 If there is any overlapping of results.

 10(a) Give two ways in which courtship behaviour increases the probability of successful mating. 

                                                                                                (2 marks)

Recognition of same species;

Stimulates release of gametes;

Recognition of mate/opposite gender;

Indication of sexual maturity/fertility;

Describe how comparisons of biological molecules in these two species could be used to find out if they are closely related.

                                                                                           (6 marks)

(Compare) DNA;

Sequence of bases/nucleotides;DNA hybridisation;

Separate DNA strands / break hydrogen bonds;

Mix DNA/strands (of different species);

Temperature/heat required to separate (hybrid) strands indicates relationship;

Compare same/named protein;Sequence of amino acids /primary structure;

Inject (seahorse) protein/serum into animal;(Obtain) antibodies/serum;

Add protein/serum/plasma from other (seahorse) species;Amount of precipitate indicates relationship;

1 (c) (i)

                                                                                                  (2 marks)

1 (c) (ii)

                                                                                             (1 mark)

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.

Hydrogen bonds are important in cellulose molecules. Explain why.

(i)

1. Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;

2. Providing strength/rigidity (to cellulose/cell wall);

3. Hydrogen bonds strong in large numbers;

(ii)

 Compact/occupies small space/tightly packed;

3 (b) (i)

                                                                                                (1 mark)

Explain what is meant by a phylogenetic relationship.

5 (a)

What information is required to calculate an index of diversity for a particular community?

                                                                                                    (1 mark)

(i) Shows evolutionary relationship;

(a) Number of a/each (species);

6 (a)

                                                                                                 (2 marks)

The gene that codes foran enzyme may be passed from one species of bacteria to another species. Describe how.

6 (c) (ii)

Adding antibiotics to the food of animals is now banned in many countries. Use your knowledge of selection to explain why adding antibiotics was banned.

                                                                                                   (2 marks)

(2 marks)

1. Horizontal (gene) transmission;

2. (Gene passed by) conjugation/through pilus;

1. (Adding antibiotics) selects in favour of antibiotic resistance/resistant bacteria more likely to survive;

2. Increase in numbers/higher proportion of resistant bacteria;

3. May infect humans/may spread resistance to other species/ horizontal transfer;

8 (b) (iii) 

The diameter of a tree was less at 12.00 than it was at 03.00 hours.Explain why the diameter was less at 12.00 hours.

                                                                                                    (2 marks)

1. Water pulled up trunk/moves up at fast rate;

2. (Water column under) tension;

3. Sticking/adhesion (between water and) cells/walls/xylem;

4. Pulls xylem in;

8 (c)

                                                                                              (6 marks)

 Arteries and arterioles take blood away from the heart.Explain how the structures of the walls of arteries and arterioles are related to their functions.

Elastic tissue

1 Elastic tissue stretches under pressure/when heart beats;

2 Recoils/springs back;

3 Evens out pressure/flow;

Muscle

4 Muscle contracts;

5 Reduces diameter of lumen/vasoconstriction/constricts vessel;

6 Changes flow/pressure;

Epithelium

7 Epithelium smooth;

8 Reduces friction/blood clots/less resistance;

9 (f) (i)

Describe how the biologists should carry out breeding experiments.

                                                                                                    (2 marks)

9 (f) (ii)

The results of breeding experiments would help the biologists to decide whether the organisms are members of the same species. Explain how.

                                                                                                     (1 marks)

1. Cross organisms and watch courtship;

2. Breed young together/observe mating;

1. If same species the organisms breed, they would produce fertile young/courtship species specific;