Topic 3 questions

• The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why

  Loss of water
• High blood pressure leads to an accumulation of tissue fluid. Explain how [3]

  High blood pressure = high hydrostatic pressure;

  Increase outward pressure from (arterial) end of capillary;

  (So) more tissue fluid
• The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why [3]

  Water has left the capillary;

  Proteins too large to leave capillary;

  Increasing higher concentration of blood proteins;
• Describe and explain the mechanism that causes forced expiration [4]

  Contraction of internal intercostal muscles;

  Relaxation of diaphragm muscles;

  Causes decrease in volume of thoracic cavity;

  Air pushed down pressure gradient;
• One theory of translocation states that organic substances are pushed from a high pressure in the leaves to a lower pressure in the roots.

  
  

  Describe how a high pressure is produced in the leaves. [3]

  Water potential becomes lower;

  Water enters phloem by osmosis;

  Increased volume (of water) causes increased pressure;
• During their experiment, the scientists ensured the rate of photosynthesis of their plants remained constant.

  
  

  Explain why this was important [2]

  Rate of photosynthesis related to rate of sucrose production;

  Rate of translocation higher when sucrose concentration is higher;
• Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required. [5]

  ​

  Trachea and bronchi and bronchioles;

  Down pressure gradient;

  Down diffusion gradient;

  Across alveolar epithelium;

  Across capillary endothelium;
• The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the advantage of this shift. [3]

  Lower affinity for oxygen;

  (To) muscles;

  (For) rapid respiration;
• Explain how the body shape of a Weddel seal is an adaptation to living in a cold environment [2]

  Small SA:Vol;

  reduces heat loss;
• Describe the role of enzymes in the digestion of proteins in a mammal. [5]

  (Reference to) hydrolysis of peptide bonds;

  Endopeptidase act in the middle of protein/polypeptide OR

  Endopeptidase produces short(er) polypeptides/ increase number of ends;

  Exopeptidases act at end of protein/polypeptide

  OR

  Exopeptidase produces dipeptides/amino acids;

  Dipeptidase acts on dipeptide/amino acids

  OR

  Dipeptidase produces (single) amino acids;
• Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. [5]

  Micelles contain bile salts and fatty acids/monoglycerides;

  Make fatty acids/monoglycerides (more) soluble (in water)

  OR

  Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);

  Fatty acids/monoglycerides absorbed by diffusion;

  Triglycerides (re)formed (in cells);

  Vesicles move to cell membrane;
• Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how. [3]

  Sodium ions actively transported from ileum cell to blood;

  Maintains/forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);

  Glucose enters by facilitated diffusion with sodium ions;
• Explain the advantages of lipid droplet and Michelle formation [3]


  Droplets increase surface areas (for lipase/ enzyme action);

  (So) faster hydrolysis/ digestion (of triglycerides/ lipids);

  Micelles carry fatty acids and glycerol/ monoglycerides carry fatty acids and glycerol/monoglycerides to/through membrane/ to (intenstinal epithelial) cell;
• Describe the role of micelles in the absorption of fats into the cells lining the ileum. [3]

  Micelles include bile salts and fatty acids;

  Make the fatty acids (more) soluble in water;

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

  Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);

  Fatty acids (absorbed) by diffusion;
• Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake. [2]


  1. Large(r) organisms have a small(er) surface area:volume (ratio);

  OR

  Small(er) organisms have a large(r) surface area:volume (ratio);

  2. Overcomes long diffusion pathway

  OR

  Faster diffusion;

  Accept short diffusion pathway
• Mammals such as a mouse and a horse are able to maintain a constant body temperature. Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. [3]


  Accept converse answers in relation to the horse.

  Mouse

  1. (Smaller so) larger surface area to volume ratio;

  Accept larger SA:V. Must be comparative.

  2. More/faster heat loss (per gram/in relation to body size); Ignore heat lost more easily/readily. Must be comparative.

  3. (Faster rate of) respiration/metabolism releases heat;

  Accept respiration/metabolism replaces heat.

  Reject produce/generate heat/energy.
• Describe the relationship between size and surface area to volume ratio of organisms. [1]

  As size increases, ratio (of surface area to volume) decreases;
• Explain why oxygen uptake is a measure of metabolic rate in organisms. [1]

  (Oxygen used in) respiration, which provides energy / ATP;

  OR

  (Oxygen is used in) respiration, which is a metabolic process / chemical reaction;
• Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to surface area or moisture in your answer. [2]

  1. Flattened cells OR Single layer of cells;

  Reject thin cell wall/membrane

  Accept thin cells

  Accept 'one cell thick'

  2. Reduces diffusion distance/pathway;

  OR

  3. Permeable;

  4. Allows diffusion of oxygen/carbon dioxide;
• Tidal volume is the volume of air inhaled and exhaled during a single breath when a person is resting. The tidal volume in a person with emphysema is reduced compared with the tidal volume in a healthy person. Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli. [3]

  1. Less carbon dioxide exhaled/moves out (of lung)

  OR

  More carbon dioxide remains (in lung);

  2. (So) reduced diffusion/concentration gradient (between blood and alveoli);

  3. Less/slower movement of carbon dioxide out of blood OR

  More carbon dioxide stays in blood;
• Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system. [2]

  1. Blood and water flow in opposite directions;

  2. Diffusion/concentration gradient (maintained) along (length of) lamella/filament;
• Describe and explain the mechanism that causes lungs to fill with air. [3]

  1. Diaphragm (muscle) contracts and external intercostal muscles contract; Ignore ribs move up and out

  2. (Causes volume increase and) pressure decrease;

  3. Air moves down a pressure gradient Ignore along

  OR

  Air enters from higher atmospheric pressure;
• Two solutions often used to stain tissues are haematoxylin solution and iodine solution.

  • Haematoxylin solution stains DNA a blue colour.

  • Iodine solution stains starch a blue-black colour.

  
  

  The scientist used haematoxylin solution and not iodine solution to stain the lung tissue. Suggest why [2]

  1. This/animal/lung tissue does not contain starch; Accept cell(s) for 'tissue'

  2. (Makes) nucleus visible;

  OR

  Nucleus contains DNA;
• Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills. [3]

  1. Water and blood flow in opposite directions; Allow diagram showing counter-flow

  2. Blood always passing water with a higher oxygen concentration;

  3. Diffusion gradient maintained throughout length (of gill)

  OR

  Diffusion occurs throughout length of gill

  OR

  If water and blood flowed in same direction equilibrium would be reached;
• Explain two ways in which the structure of fish gills is adapted for efficient gas exchange. [2]

  1. Many lamellae / filaments so large surface area;

  2. Thin (surface) so short diffusion pathway;

  1 & 2 must each have a feature and a consequence
• The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water.

  Some other species of insect have larvae that are a similar size and shape to damselfly larvae and also live in water.

  These larvae do not actively hunt prey and do not have gills.

  
  

  Explain how the presence of gills adapts the damselfly to its way of life. [2]

  1. Damselfly larvae has high(er) metabolic / respiratory (rate);

  2. (So) uses more oxygen (per unit time / per unit mass);
• The adult damselfly uses a tracheal system for gas exchange. Explain three ways in which an insect's tracheal system is adapted for efficient gas exchange. [3]


  1. Tracheoles have thin walls so short diffusion distance to cells;

  2. Highly branched / large number of tracheoles so short diffusion distance to cells;

  3. Highly branched / large number of tracheoles so large surface area (for gas exchange);

  4. Tracheae provide tubes full of air so fast diffusion (into insect tissues);

  5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface; OR Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);

  6. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
• Describe the gross structure of the human gas exchange system and how we breathe in and out. [6]

  1. Named structures - trachea, bronchi, bronchioles, alveoli;

  Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.

  2. Above structures named in correct order

  OR

  Above structures labelled in correct positions on a diagram; Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.

  3. Breathing in - diaphragm contracts and external intercostal muscles contract;

  4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);

  For thoracic cavity accept 'lungs' or 'thorax'.

  Reference to 'thoracic cavity' only required once.

  5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;

  Accept diaphragm relaxes and (external) intercostal muscles relax and lung tissue elastic (so recoils).

  6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);

  For thoracic cavity accept 'lungs' or 'thorax'.
• Describe the pathway taken by an oxygen molecule from an alveolus to the blood. [2]

  1. (Across) alveolar epithelium;

  2. Endothelium / epithelium of capillary;
• Explain how one feature of an alveolus allows efficient gas exchange to occur. [2]

  1. (The alveolar epithelium) is one cell thick;

  Reject thin membrane

  2. Creating a short diffusion pathway / reduces the diffusion distance;
• Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly. [2]

  1. Stomata close;

  2. Less carbon dioxide (uptake) for less photosynthesis/glucose production;
• Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill. [3]

  1. Water and blood flow in opposite directions;

  2. Maintains diffusion/concentration gradient of oxygen Accept: converse for carbon dioxide

  Accept: equilibrium not reached

  OR

  Oxygen concentration always higher (in water);

  3. (Diffusion) along length of lamellae/filament/gill/capillary; Accept: all/whole of lamellae/filament//gill/capillary
• Particulate matter is solid particles and liquid particles suspended in air. Polluted air contains more particulate matter than clean air.

  A high concentration of particulate matter results in the death of some alveolar epithelium cells.

  If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue.

  
  

  Explain why death of alveolar epithelium cells reduces gas exchange in human lungs. [3]

  1. Reduced surface area;

  2. Increased distance for diffusion;

  Accept description of efficient gas exchange in healthy alveolar epithelium as long as reference made to the damaged tissue changing this.

  3. Reduced rate of gas exchange;
• Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. [5]

  1. Micelles contain bile salts and fatty acids/monoglycerides; Ignore other correct components of micelles

  2. Make fatty acids/monoglycerides (more) soluble (in water) OR

  Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem)

  OR

  Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);

  Accept lipid/fat for fatty acid/ monoglyceride

  3. Fatty acids/monoglycerides absorbed by diffusion;

  Reject if absorbed by facilitated diffusion

  Ignore if micelles themselves are being absorbed

  4. Triglycerides (re)formed (in cells);

  Accept chylomicrons form

  5. Vesicles move to cell membrane;

  Accept exocytosis for 'vesicles move
• Explain the function of this ATP hydrolase. [2]

  1. (ATP to ADP + Pi ) Releases energy;

  Reject 'produces/makes/creates energy'.

  2. (energy) allows ions to be moved against a concentration gradient

  OR

  (energy) allows active transport of ions;

  For 'ions' accept Na+ or K+.

  Do not accept if this movement is of glucose not ions.
• The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum. Explain how. [2]

  1. (Maintains/generates) a concentration/diffusion gradient for Na+ (from ileum into cell);

  Accept '(Maintains/generates) a lower concentration of Na+ inside the cell compared with outside the cell'.

  2. Na+ moving (in) by facilitated diffusion, brings glucose with it

  OR

  Na+ moving (in) by co-transport, brings glucose with it;
• 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.
• 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 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;

  Accept chain/chain of amino acids/peptide for polypeptide Accept digest/breakdown/ break for 'act'

  Mark points 2, 3 and 4 reject answers where substrate or product is incorrect eg 'Endopeptidase produces dipeptides'

  Ignore references to source and location of enzymes
• 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;
• 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;