Chapter 5: Maintaining a balance (30 questions)
1. The graph represents the basis of enzyme reactions – lowering the activation energy required for a reaction to complete itself.



Which labelled part of the graph, A–E, represents the overall energy change of the reaction?
  Hint

    a) A
     b) B
     c) C
     d) D
     e) E


2. The graph represents the basis of enzyme reactions – lowering the activation energy required for a reaction to complete itself.



Which labelled part of the graph, A–E, represents the change in activation energy required when the enzyme is present?
  Hint

    a) A
     b) B
     c) C
     d) D
     e) E


3. Enzymes are biological catalysts, present in living systems. A catalyst is a substance that increases the rate of a chemical reaction without being changed itself. Which of the following statements concerning enzyme function is correct?
  Hint

    a) Enzymes increase the activation energy of a reaction and therefore cause it to occur more quickly.
    b) Enzymes provide an alternative pathway for a chemical reaction, allowing the reaction to proceed more quickly.
    c) Enzymes cause the reactants to reach higher activation energies faster.
    d) Enzymes catalyse a number of different substrate types over and over again.
    e) Enzymes catalyse a number of different substrate types over and over again.





4. The diagram represents a step in the process of enzyme function according to the lock and key model. In the diagram:



  Hint

    a) A and B represent the reactants and C the products of the reaction.
    b) A and B represent the products of the reaction and C is the enzyme.
    c) C is the enzyme–substrate or E-S complex, while A and B are the reactants.
    d) C is the substrate while A and B are the reactants.
    e) A is the reactant, B is a co-factor and C is the substrate.



5. When studying the effects of physical conditions such as temperature on the rate of an enzyme-catalysed reaction, it is important to ensure that:
  Hint

    a) enzymes are used at different temperatures and different volumes to allow a comparison.
    b) the volume is changed while temperature is increased.
    c) different enzymes are used at different temperatures.
    d) temperature can be varied while studying the effect of increasing pH.
    e) all other factors must be kept constant.



6. The graph shows the effects of temperature on the rate of reaction.



Label B would represent:
  Hint

    a) the point where the substrate no longer has an active site with which to bind.
    b) the point where the active enzyme has been completely destroyed.
    c) the point where the activity of the enzyme is low and the enzyme molecules are working at capacity.
    d) the optimum temperature, where the enzyme molecules are acting at their maximum capacity.
    e) the point where the reaction rate is increasing faster than temperature.



7. The graph shows the effects of temperature on the rate of reaction.



Label C would represent:
  Hint

    a) the point where the substrate no longer has an active site with which to bind.
    b) the point where the active enzyme is being destroyed (denatured) by increasing temperature, affecting reaction rate.
    c) the point where the activity of the enzyme is low and the substrate has low energy.
    d) the optimum temperature, where the enzyme molecules are acting at their maximum capacity.
    d) the point where the reaction rate is increasing faster than temperature.



8. What will be the effect of increasing the substrate concentration of a reaction while keeping the enzyme concentration constant?
  Hint


    a) Reaction rate will continue to increase in a linear relationship with the enzyme.
    b) The enzyme will be unable to cope and the active site may start to break down (denature).
    c) The rate of the reaction will continue to increase proportionally.
    d) The active sites on the enzyme molecules will all become occupied by substrate and the reaction will proceed at its maximum rate.
    e) There will be no change in speed of the reaction since the concentration of the substrate is not relevant.



9. Self-regulating systems such as homeostatic systems require:
  Hint

    a) a detector device, which sends feedback to a control centre, which changes the original condition back to normal.
    b) some type of receptor, which sends feedback to a control centre, causing an effector to restore a particular condition.
    c) a regulator, which is operated by the control centre to correct any deviations from the set value.
    d) a constant internal composition or steady state mechanism with no changes to any conditions.
    e) none of the above.



10. The diagram represents an example of:



    Hint

    a) closed circuit monitoring.
    b) open loop control.
    c) a primitive control system.
    d) a negative feedback mechanism.
    e) a positive feedback mechanism.



11. The range at which most organisms can survive and be active lies between 0°C and 45°C. This is because:
    Hint

    a) living cells function within a narrow range of temperature.
    b) proteins will denature above 45°C in most organisms.
    c) structural, physiological and behavioural adaptations enable them to survive better within this temperature range.
    d) cells in most organisms are at risk of forming ice crystals within themselves below 0°C.
    e) all of the above.



12. A behavioural method of heat gain in ectothermic organisms is to bask in the sun. This method involves:
    Hint

    a) conduction of heat.
    b) evaporation of water from the surface of the skin.
    c) radiation of heat to the exterior parts of the body.
    d) slowing of metabolic rate.
    e) presenting a small surface area to the sun.



13. Endotherms may use behavioural adaptations to regulate their body temperature in the same way as ectotherms. Which alternative represents such an adaptation?
    Hint

    a) Reduced blood flow to the feet of penguins, to reduce heat loss to the ice.
    b) The large ears of the African elephant, acting like radiators to lose heat.
    c) Altering metabolic rates to regulate body temperature.
    d) Releasing water from sweat glands, which has an evaporative cooling effect on the body.
    e) A kangaroo seeking shade in the hottest parts of the day.



14. Most carbon dioxide in the blood is carried:
     Hint

    a) bound to haemoglobin, forming carbamino-haemoglobin.
    b) as hydrogen carbonate (bicarbonate) ions in the plasma.
    c) as radiation of heat to the exterior parts of the body.
    d) as carbonic acid in the plasma.
    e) directly as a gas in the plasma.



15. The essential role of the plasma protein known as fibrinogen is:
    Hint

    a) ion transport.
    b) immune function.
    c) osmotic balance.
    d) blood clotting.
    e) lipid transport.



16. The functions of haemoglobin include transport of oxygen and carbon dioxide and maintaining a constant blood pH (buffering). Oxygen is carried by haemoglobin in the red blood cells as oxyhaemoglobin. The formation of oxyhaemoglobin because of the:
     Hint

    a) interaction of iron ions in haemoglobin with oxygen when the concentration of oxygen is high.
    b) activity of the body tissues, which produces deoxyhaemoglobin and causes oxyhaemoglobin to be formed.
    c) decrease in oxygen pressure in the lungs, resulting in formation of the oxyhaemoglobin unit.
    d) the levels of carbon dioxide concentration in blood.
    e) interaction of iron ions in haemoglobin with oxygen when the concentration of oxygen is low.



17. The graph shows the relationship between temperature and oxygen saturation of haemoglobin.



From this graph it can be seen that:
     Hint

    a) as temperature rises, haemoglobin becomes saturated more quickly, and as temperature declines, haemoglobin becomes less saturated.
    b) as temperature rises, haemoglobin releases less oxygen, and as temperature declines, haemoglobin becomes less saturated.
    c) as temperature rises, haemoglobin releases more oxygen, and as temperature declines, haemoglobin becomes more saturated.
    d) the lower the temperature, the more the shape of the haemoglobin molecule is changed, causing it to release oxygen more easily.
    e) it takes less time for haemoglobin to reach saturation as temperature is increased.



18. The following word equation represents: glucose + oxygen → carbon dioxide + water + energy (as ATP)
   Hint

    a) fermentation.
    b) respiration.
    c) photosynthesis.
    d) metabolism.
    e) glycolosis.



19. The transpiration stream is the movement of water from the roots of plants up through the stems to the leaves. Select the response below that provides one reason for the movement of water from the root cells into the xylem vessels of the plant.
    Hint

    a) The concentration gradients cause the movement of water.
    b) Mineral ions cause a net movement of water due to osmosis
    c) Higher water potential of the cells on the inside of the root causes a net movement of water into the xylem.
    d) Root pressure caused by water pushing water ahead of it forces water into the xylem vessels.
    e) Active transport, which requires that cells use energy (ATP), moves water into the xylem vessels.



20. Translocation is the movement of sugars in the phloem of plants. The mechanism for this movement that is supported by the most evidence is known as the:
  Hint

    a) sink to source mechanism.
    b) pressure-flow mechanism.
    c) diffusion mechanism.
    d) sap transport model.
    e) active transport model.



21. The diagram represents a nephron – the functional unit of the kidney.



Choose the response from the list below that lists the labels A–F in order.
    Hint

    a) Glomerulus, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, collecting duct
    b) Bowman’s capsule, glomerulus, proximal tubule, loop of Henle, distal tubule, collecting duct
    c) Glomerulus, Bowman’s capsule, proximal tubule, loop of Henle, collecting duct, distal tubule
    d) Glomerulus, proximal tubule, Bowman’s capsule, loop of Henle, distal tubule, collecting duct
    e) Glomerulus, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, ureter



22. The diagram represents a nephron – the functional unit of the kidney. Which of the responses below represents what is happening in the Bowman’s capsule (label B).



     Hint

    a) Reabsorption
    b) Filtration
    c) Dialysis
    d) Excretion
    e) Active transport



23. The purpose of the reabsorption process which takes place in the nephrons of the kidney is:
    Hint

    a) the removal of small molecules by diffusion across thin membranes into the collecting tubule.
    b) to ensure that there is sufficient water in the filtrate so that osmoregulation can occur.
    c) to maintain a constant concentration of essential metabolites (such as glucose) in blood and consequently in body tissues.
    d) to excrete the substances not required by the body in order to maintain homeostasis.
    e) to facilitate the active movement of urea into the collecting tubules.



24. Water loss in the urine (dieresis) is prevented when a hormone targets the collecting ducts of the kidneys, causing increased membrane permeability and increased water retention. What is the name of the hormone that prevents dieresis?
    Hint

    a) Diuretic hormone
    b) Aldosterone
    c) Antidiuretic hormone (ADH).
    d) Diupressin
    e) Sterone



25. Enantiostasis would best be defined as:
    Hint

    a) the regulation of the concentration of water and salts in body cells.
    b) maintaining the constant internal composition or steady state of an organism.
    c) maintaining the concentration of metabolites and/or physical conditions within a narrow range.
    d) the matching of metabolic and physiological to the environment.
    e) the maintenance of metabolic and physiological functions in response to variations in the environment.



26. One of the mechanisms used by estuarine plants to maintain appropriate salt concentration is exclusion. This mechanism is best summarised as the:
    Hint

    a) alteration of the concentration of solutes in their cells to match the concentration of the external environment
    b) use of special tissues in the roots and lower stems that act as a barrier to salt uptake although allowing the passage of water.
    c) concentration and excretion (or release) of salt through special glands.
    d) accumulation of salt in older tissue (and leaves), which is then discarded.
    e) none of the above.



27. Plants like cacti and other succulents that are typically found in deserts are adapted to low ground-water levels. They have specific features such as swollen stems that enable them to retain water, and are collectively known as:
    Hint

    a) sclerophytes.
    b) pneumatophytes.
    c) tracheophytes.
    d) xerophytes.
    e) mesophytes.



28. During this topic you will have completed a dissection of a mammalian kidney. In carrying out a risk assessment for this practical, you should have considered:
    Hint

    a) drawing a carefully labelled sketch of the kidney in cross-section.
    b) writing a clear method that was unambiguous so that other people could complete your practical.
    c) minimising the risk of cross-contamination by wearing gloves.
    d) the cost of the kidneys in comparison to the benefits gained by doing the dissection.
    e) the rights of the animals whose kidneys have been used in the experiment.



29. An ammonotelic organism converts amino groups for excretion into:
    Hint

    a) hydrochloric acid.
    b) nitric acid.
    c) uric acid.
    d) ammonia.
    e) urea.



30. A ureotelic organism converts amino groups for excretion into:
    Hint

    a) hydrochloric acid.
    b) nitric acid.
    c) uric acid.
    d) ammonia.
    e) urea.






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