Organisms Exchange Substances

• Explain the advantage of larger animals of having a specialised system that facilitates oxygen uptake?

  1. Larger organisms have a smaller surface area:volume ratio
  2. Faster diffusion
• Use knowledge of surface area:volume ratio to explain the higher metabolic rate of a mouse compared to a horse?

  1. Mouse is smaller so larger surface area:volume ratio
  2. Faster heat loss
  3. Faster rate of respiration releases heat
• Describe the relationship between size and surface area to volume ratio of organisms?

  1. As size increases, ratio of surface area to volume decreases
• Describe and explain 1 feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange?

  1. Single layer of cell/one cell thick
  2. Reduces diffusion distance
• Suggest and explain how a reduced tidal volume affects the exchange of CO2 between the blood and the alveoli?

  1. Less CO2 exhaled
  2. So reduced concentration gradient between blood and alveoli
  3. Slower movement of CO2 out of blood
• Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system?

  1. Blood and water flow in opposite directions
  2. Diffusion maintained along whole length of lamella
• Describe and explain the mechanism that causes lungs to fill with air?

  1. Diaphragm and external intercostal muscles contract
  2. Pressure decreases and volume increases in thorax
  3. Air enters from higher atmospheric pressure
• Explain why death of alveolar epithelium cells reduces gas exchange in human cells?

  1. Reduced surface area
  2. Increased distance for diffusion
  3. Reduced rate of gas exchange
• Explain 2 ways in which the structure of fish gills is adapted for efficient gas exchange?

  1. Many lamellae so large surface area
  2. Thin so short diffusion pathway
• Explain how the counter-current mechanism ensures the maximum amount of oxygen passes into the blood flowing through the gills?

  1. Water and blood flow in opposite directions
  2. Blood always passing water with a higher oxygen concentration
  3. Diffusion gradient maintained through length of gill
• Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly?

  1. Stomata close
  2. Less CO2 uptake for less photosynthesis
• Describe the pathway taken by an oxygen molecule from an alveolus to the blood?

  1. Across alveolar epithelium
  2. Endothelium of capillary
• Describe the gross structure of the human gas exchange system and how we breathe in and out?

  1. Trachea, bronchi, bronchioles, alveoli
  2. Inhalation - diaphragm contracts and external intercostal muscles contract
  3. Volume increase and pressure decreases in thorax, resulting in air moving in
  4. Exhalation - diaphragm relaxes and internal intercostal muscles contract
  5. Volume decreases and pressure increases in thorax, resulting in air moving out
• Explain 3 ways in which an insect's tracheal system is adapted for efficient gas exchange?

  1. Tracheoles have thin walls so short diffusion distance to cells
  2. Highly branched tracheoles so large surface area
  3. Trachea provides tubes full of air so fast diffusion
• Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs?

  1. Renal vein
  2. Vena cava to right atrium
  3. Right ventricle to pulmonary artery
• Explain how water from tissue fluid is returned to the circulatory system?

  1. Plasma proteins remain
  2. Creating water potential gradient
  3. Water moves to blood by osmosis
  4. Returns to blood by lymphatic system
• Explain how an arteriole can reduce the blood flow into capillaries?

  1. Muscle contracts
  2. Narrows arteriole
• Describe the advantage of the Bohr effect during intense exercise?

  1. Increases dissociation of oxygen
  2. For aerobic respiration at the tissues
• Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin?

  1. Increases dissociation of oxygen
  2. By decreasing pH
• Give 2 safety precautions that should be followed when dissecting a heart?

  1. Use a sharp scalpel
  2. Wear gloves
• Name the blood vessels that carry blood to the heart?

  1. Coronary arteries
• Binding of 1 molecule of oxygen of haemoglobin makes it easier for a second oxygen molecule to bind?

  1. Binding of first oxygen changes tertiary structure of haemoglobin
  2. Creates another binding site
• Explain the role of the heart in the formation of tissue fluid?

  1. Contraction of ventricles produces high hydrostatic pressure
  2. This forces water out of blood capillaries
• Suggest how a blockage in the lymphatic system could cause lymphoedema?

  1. Excess tissue fluid can not be reabsorbed
• Using understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube?

  1. Sucrose actively transported into phloem
  2. Reducing water potential
  3. Water moves into phloem by osmosis
• Describe the cohesion-tension theory of water transport in the xylem?

  1. Water lost from leaf because of transpiration
  2. Lowers water potential of mesophyll
  3. Water pulled up xylem, creating tension
  4. Water molecule 'stick' together by hydrogen bonds, forming continuous water column
  5. Adhesion of water to walls of xylem
• Describe the mass flow hypothesis for the mechanism of translocation in plants?

  1. In source/leaf sugars actively transported into phloem, by companion cells
  2. Lowers water potential of sieve cell and water enters by osmosis
  3. Increase in (hydrostatic) pressure causes mass movement towards sink
  4. Sugars used in root for respiration for storage
• Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels?

  1. Micelles contain bile salts and fatty acids/monoglycerides
  2. Make fatty acids/monoglycerides more soluble in water
  3. Fatty acids/monoglycerides absorbed by diffusion
  4. Triglycerides reformed in cells
  5. Vesicles move to cell membrane
• Describe the role of micelles in the absorption of fats into the cells lining the ileum?

  1. Micelles include bile salts and fatty acids
  2. Make the fatty acids more soluble in water
  3. Carry fatty acids to lining of the ileum
• Describe the role of enzymes in the digestion of proteins in a mammal?

  1. Hydrolysis of peptide bonds
  2. Endopeptidases act in the middle of protein
  3. Exopeptidases act at the ends of protein
  4. Dipeptidases act on dipeptides/between amino acids
• Explain the advantages of lipid droplet and micelle formation?

  1. Droplets increase surface area (for lipase action)
  2. So faster hydrolysis of triglycerides
  3. Micelles carry fatty acids and glycerol to (intestinal epithelial) cell
• Suggest how the Golgi apparatus is involved in the absorption of lipids?

  1. Modifies/processes triglycerides
  2. Combines triglycerides with proteins
  3. Exocytosis OR forms vesicles