EXCHANGE

• Describe the mass flow hypothesis for the mechanism of translocation in

  plants.(4)

  1. In source / leaf sugars actively transported into phloem;

  2. By companion cells;

  3. Lowers water potential of sieve cell / tube and water enters by

  osmosis;

  4. Increase in pressure causes mass movement (towards sink /

  root);

  5. Sugars used / converted in root for respiration for storage.
• The rate of water movement through a shoot in a potometer may not be the

  same as the rate of water movement through the shoot of a whole plant.

  Suggest one reason why (1)

  Plant has roots
• The student wanted to determine the rate of water loss per mm2 of surface

  area of the leaves of the shoot in Figure 1.

  Outline a method she could have used to find this rate. You should assume

  that all water loss from the shoot is from the leaves. (3)

  1. Method for measuring area;

  e.g. draw round (each) leaf on graph paper and count squares;

  2. Of both sides of (each) leaf;

  3. Divide rate (of water loss / uptake from potometer) by (total)

  surface area (of leaves);
• Describe the cohesion-tension theory of water transport in the xylem. (5)

  1. Water lost from leaf because of transpiration / evaporation of water

  (molecules) / diffusion from mesophyll / leaf cells;

  OR

  Transpiration / evaporation / diffusion of water (molecules)

  through stomata / from leaves;

  2. Lowers water potential of mesophyll / leaf cells;

  3. Water pulled up xylem (creating tension);

  4. Water molecules cohere / 'stick' together by hydrogen bonds;

  5. (forming continuous) water column;

  6. Adhesion of water (molecules) to walls of xylem;
• Unlike plants, Ulva lactuca does not have xylem tissue.

  Suggest how Ulva lactuca is able to survive without xylem tissue. (1)

  Short diffusion pathway (to cells)
• The student used a sharp scalpel to cut the celery. Describe how she should ensure she handled the scalpel safely during this procedure. (2)

  1. Cut away from body;

  2. Against hard/non-slip/flat surface;
• A different student used coloured water to investigate the movement of

  water in leaf stalks of celery.

  During the procedure she:

  • cut equal lengths of stalk from each plant

  • put the cut end of each stalk into coloured water

  • left these stalks to take up the coloured water for 20 minutes

  • used a sharp scalpel to cut slices from the stalks at 1 mm intervals

  until she reached a slice with no coloured water.

  Figure 2 shows a slice of leaf stalk with coloured water inside groups of

  xylem vessels.

  Figure 2

  Explain why coloured water moved up the stalks. (3)

  1. Water evaporates/is transpired (from leaves/ stalk/celery/plant);

  2. Water potential gradient/lower water potential creates tension

  3. Hydrogen bonds/cohesion/adhesion maintains column;
• Give the reason for adding a layer of oil to the water in the beaker. (1)

  Prevent evaporation/water loss
• The student measured the time taken for water movement.

  Give two other measurements he made to calculate the rate of water

  movement. (2)

  1. Initial and final mass (of beaker and all contents);

  2. Number of (groups of) xylem vessels;
• Phloem pressure is reduced during the hottest part of the day. Use

  information in the graph above along with your understanding of

  transpiration and mass flow to explain why (3)

  1. High (rate of) transpiration/evaporation;

  2. Water lost through stomata

  3. (Causes) less water movement from xylem to phloem
• Describe the relationship between phloem pressure and the rate of water

  movement in xylem in this plant. (1)

  Phloem pressure falls as (rate of) water movement (in xylem) increases
• MASS TRANSPORT IN PLANTS

  . The mass flow hypothesis is used to explain the movement of substances

  through phloem.

  Use your understanding of the mass flow hypothesis to explain how

  pressure is generated inside this phloem tube. (3)

  1. Sucrose actively transported (into phloem);

  2. Lowering/reducing water potential

  3. Water moves (into phloem) by osmosis (from xylem);
• Lymphoedema is a swelling in the legs which may be caused by a

  blockage in the lymphatic system.

  Suggest how a blockage in the lymphatic system could cause

  lymphoedema.(1)

  Excess tissue fluid cannot be (re)absorbed / builds up;
• Explain the role of the heart in the formation of tissue fluid (2)

  1. Contraction of ventricle(s) produces high

  blood / hydrostatic pressure;

  2. (This) forces water (and some dissolved

  substances) out (of blood capillaries);
• Binding of one molecule of oxygen to haemoglobin makes it easier for a

  second oxygen molecule to bind.

  Explain why. (2)

  1. Binding of first oxygen changes tertiary / quaternary (structure) of

  haemoglobin;

  Ignore ref. to 'positive cooperativity' unqualified

  Ignore ref. to named bonds

  Accept conformational shift caused

  2. Creates / leads to / uncovers second / another binding site
• Name the blood vessels that carry blood to the heart muscle (1)

  Coronary arteries
• The increase seen in Group I could be due to the combination of caffeine

  and sugar.

  Suggest one drink to be given to an additional group that should be

  investigated to find out if this is true.

  Give a reason for your answer. (2)

  Group to be given

  1. Sugar solution (only)t

  Reason

  2. To show/prove that sugar (alone) is not causing the increases

  (in HR)
• Caffeine affects the autonomic nervous system.

  Suggest how caffeine could account for the results of Group I in Figure 2

  at 60 minutes. (2)

  1. More impulses/action potentials along sympathetic (nervous

  system pathway/branch);

  2. To SAN increasing the heart rate
• Give two safety precautions that should be followed when dissecting a

  heart.(1)

  Use a sharp scalpel/scissors

  Wash hands/wear gloves

  Disinfect bench/equipment

  Cover any cuts

  Cut away from self/others/on a hard surface
• Use information in the graph to explain how the seal's myoglobin

  dissociation curve shows the seal is adapted for diving.(2)

  1. High(er) affinity for O2 (than haemoglobin)

  OR

  Dissociates oxygen less readily

  OR

  Associates more readily;

  Accept holds O2 at lower ppO2

  2. Allows (aerobic) respiration when diving/at low(er) pO2

  OR

  Provides oxygen when haemoglobin unloaded

  OR

  Delays anaerobic respiration/lactate production;

  Accept acts as an oxygen store
• Describe and explain the effect of increasing carbon dioxide concentration

  on the dissociation of oxyhaemoglobin(2)

  1. Increases/more oxygen dissociation/unloading

  OR

  Deceases haemoglobin's affinity for O2;

  Accept more readily

  Accept releases more O2

  2. (By) decreasing (blood) pH/increasing acidity;

  Reject if reference made to active site
• The normal haematocrit for human males is 47(±5)%. For professional

  male cyclists, the maximum haematocrit allowed is 50%.

  A student suggested that professional male cyclists should be allowed to

  use EPO until their haematocrit is 50%. (2)

  1. Some cyclists will gain a bigger advantage/increase

  OR

  Cyclists with a haematocrit of 50% would not be able to gain an

  advantage;

  Accept use of the data, or suitable calculations, eg

  some may have an 8% increase, others 0%

  Some cyclists might naturally have a haematocrit

  over 50% (and so not be allowed to compete)

  2. There are health risks (associated with) taking EPO;
• EPO is another performance-enhancing drug. It can increase the haematocrit

  (the percentage of red blood cells in blood).

  (f) A heart attack is caused by a lack of glucose and oxygen being delivered to

  cardiac muscle via the coronary arteries. The overuse of EPO can increase

  the risk of a heart attack.

  Suggest how.(2)

  1. (EPO) causes blood to thicken;

  Accept descriptions of thickening, eg more viscous

  2. (The thickened blood) could block the coronary arteries

  OR

  (The thickened blood) slows blood flow

  OR

  (The thicker blood) could cause clots;
• An increase in the intensity of exercise produces an increase in the volume

  of carbon dioxide produced.

  However, the graph above shows that the pCO2 in air breathed out did not

  show a large increase during the exercise.

  Suggest one physiological change that would cause this result. Explain

  how the physiological change would allow for the removal of the increase

  in the volume of carbon dioxide produced (2)

  1. Increases dissociation of oxygen;

  Accept unloading/ release/reduced affinity for

  dissociation

  2. For aerobic respiration at the tissues/muscles/cells

  OR

  Anaerobic respiration delayed at the tissues/muscles/cells

  OR

  Less lactate at the tissues/muscles/cells;
• Describe the advantage of the Bohr effect during intense exercise (2)

  Smooths the blood flow

  OR

  Maintains rate of blood flow

  OR

  Maintains blood pressure;
• What can you conclude from the appearance of valves in the image above

  about heart muscle activity and blood movement between:

  1. atria and ventricles? (2)


  3. Atria (muscle) contracted;

  4. Blood movement from atria (into ventricles);
• What can you conclude from the appearance of valves in the image above about heart muscle activity and blood movement between:

  1. ventricles and arteries?(2)

  1. Ventricle (muscles) relaxed

  2. No (blood) backflow (into ventricles)
• Explain how an arteriole can reduce the blood flow into capillaries. (2)

  1. Muscle contracts;

  2. Constricts/narrows arteriole/lumen;
• Describe two precautions the student should take when clearing away after the dissection. (2)

  1. Carry/wash sharp instruments by holding handle

  OR

  Carry/wash sharp instruments by pointing away (from body)/down;

  Accept for 'instruments', a suitable named example,

  eg. scalpel

  2. Disinfect instruments/surfaces;

  Accept for 'instruments', a suitable named example,

  eg. scalpel

  Accept for 'disinfect', sanitise OR use antiseptic

  3. Disinfect hands
• Suggest two ways the student could improve the quality of his scientific

  drawing of the blood vessels in this dissection. (2)

  1. Only use single lines/do not use sketching (lines)/ensure lines are

  continuous/connected;

  2. Add labels/annotations/title;

  3. Add magnification/scale (bar);

  4. Draw all parts to same scale/relative size;

  5. Do not use shading/hatching;
• Tissue fluid is formed from blood at the arteriole end of a capillary bed.

  Explain how water from tissue fluid is returned to the circulatory system (4)

  1. (Plasma) proteins remain;

  Accept albumin/globulins/fibrinogen for (plasma)

  protein

  2. (Creates) water potential gradient

  OR

  Reduces water potential (of blood);

  3. Water moves (to blood) by osmosis;

  4. Returns (to blood) by lymphatic system;
• Identify the type of blood vessel labelled M in the figure above.

  Explain your answer.

  Type of blood vessel

  Explanation(2)

  1. Vein;

  2. Wide(r) lumen

  OR

  Thinner wall;
• MASS TRANSPORT IN ANIMALS

  Give the pathway a red blood cell takes when travelling in the human

  circulatory system from a kidney to the lungs.

  Do not include descriptions of pressure changes in the heart or the role of

  heart valves in your answer. (3)

  1. Renal vein;

  2. Vena cava to right atrium;

  3. Right ventricle to pulmonary artery;
• Cells lining the ileum of mammals absorb the monosaccharide glucose by

  co-transport with sodium ions. Explain how.(3)

  1. Sodium ions actively transported from ileum cell to blood;

  2. Maintains / forms diffusion gradient for sodium to enter cells from gut

  (and with it, glucose);

  3. Glucose enters by facilitated diffusion with sodium ions;
• Name structure Q in the diagram above and suggest how it is involved in the absorption of lipids. Name How it is involved(4)

  1. Golgi (apparatus);

  2. Modifies / processes triglycerides;

  3. Combines triglycerides with proteins;

  4. Packaged for release / exocytosis

  OR

  Forms vesicles;
• Explain the advantages of lipid droplet and micelle formation. (3)

  1. Droplets increase surface areas (for lipase /

  enzyme action);

  2. (So) faster hydrolysis / digestion (of

  triglycerides / lipids);

  3. Micelles carry fatty acids and glycerol /

  monoglycerides to / through membrane / to

  (intestinal epithelial) cell;
• the name of the process by which fatty acids and glycerol enter the intestinal epithelial cell. (1)


  Diffusion
• The food eaten by a rabbit is digested mainly by microorganisms in its

  caecum. The caecum is a section of intestine attached between the ileum

  and the large intestine. The resulting semi-digested material leaves the

  anus of a rabbit as soft, caecal droppings. The rabbit then eats these

  caecal droppings.

  Use this information and Figure 2 to suggest how eating its own caecal

  droppings helps a rabbit's digestion and absorption of dietary protein. (3)

  1. More/remaining/undigested (protein) broken down;

  Accept all (protein) broken down

  2. (So more) amino acids absorbed;

  3. (Because) protein/food passes again through stomach/ileum;
• Describe the role of enzymes in the digestion of proteins in a mammal (4)

  1. (Reference to) hydrolysis of peptide bonds;

  2. Endopeptidase act in the middle of protein/polypeptide

  OR

  Endopeptidase produces short(er) polypeptides/ increase number of

  AQA Biology A-Level - Digestion and Absorption MS PhysicsAndMathsTutor.com

  ends;

  3. Exopeptidases act at end of protein/polypeptide

  OR

  Exopeptidase produces dipeptides/amino acids;

  4. Dipeptidase acts on dipeptide/between two amino acids

  OR

  Dipeptidase produces (single) amino acids;
• Describe the role of micelles in the absorption of fats into the cells lining

  the ileum. (3)

  1. Micelles include bile salts and fatty acids;

  Ignore other correct components of micelles.

  2. Make the fatty acids (more) soluble in water;

  For 'fatty acids' accept fats / lipids.

  3. Bring/release/carry fatty acids to cell/lining (of the ileum);

  For 'fatty acids' accept fats/lipids.

  4. Maintain high(er) concentration of fatty acids to cell/lining (of the

  ileum);

  5. Fatty acids (absorbed) by diffusion;

  Reject if absorbed by facilitated diffusion

  Ignore if micelles themselves are being absorbed.

  Ignore references to monoglycerides.