Exchange in organisms

• How do single-celled organisms exchange substances?

  Substances diffuse directly through the membrane from its immediate environment
• Why do multicellular organisms require transport systems?

  Because most of their cells are not in direct contact with their immediate surroundings
• The smaller the animal...

  The greater the SA:V ratio
• Describe the tracheal system of insects

  Holes where gases diffuse - spiracles

  Main tracheal tube - trachea

  Smaller tracheal tubes - trachioles
• How do insects maintain a steep rate of diffusion?

  Trachioles are bathed in tracheal fluid that keep the tracheal system moist in order to maintain a steep concentration gradient

  -Spiracles can close to prevent water loss
• What adaptation do fish have to respire?

  Gills
• What process do fish use to maximise respiration by maintaining a concentration gradient?

  Counter current flow mechanism
• How does the countercurrent exchange system work?

  The blood flows in the opposite direction to water passing the gills, which maintains a constant concentration of oxygen throughout
• What are the layers of a leaf cell

  Waxy cuticle, upper and lower epidermis, palisade mesophyll, spongy mesophyll, stomata and guard cells
• How are stomata adapted for their function?

  - More stomata on the base of the leaf which is cooler and shaded, minimising water loss

  - Guard cells control the state of passage depending on water concentration, meaning water won't be lost to transpiration

  - They are only open during the day as photosynthesis can only occur in the presence of sunlight
• How is a leaf adapted for gas exchange?

  - Air space to allow gas movement

  - Short diffusion pathway
• How do xerophytic plants reduce water loss?

  Thick waxy cuticles, Extensive root systems and thin needle-like spines all act to reduce water loss through transpiration via surface area
• What are the sections of the respiratory system?

  The trachea, bronchi, lungs, bronchioles and alveoli
• How is the trachea adapted?

  Cartilage rings to keep airway open to maintain reliable gas source
• How are the bronchioles adapted?

  Lined with goblet cells that produce mucus to trap foreign particles

  Ciliated epithelial cells waft mucus up to be coughed up as phlegm or swallowed and destroyed by stomach acid
• How does inspiration occur?

  -The diaphragm moves down

  -external intercostal muscles contract

  -internal intercostal muscles relax

  -rib cage moves upward and outward

  -increase in thoracic volume

  -Atm. pressure > thoracic pressure causes air to rush in
• How does expiration occur?

  -The diaphragm moves up

  -external intercostal muscles relax

  -internal intercostal muscles contract

  -rib cage moves downward and in

  -decrease in thoracic volume

  -Thoracic pressure > atm. pressure forcing air out
• What is the equation for pulmonary ventilation rate?

  Tidal volume x breathing rate
• How are the alveoli adapted?

  One cell thick - Short diffusion pathway

  Moist- Allows gases to diffuse

  Rich blood supply - Steep concentration gradient

  Folded - Large surface area increases rate of diffusion
• What enzymes are involved in digestion?

  Amylase, protease, lipase
• Where is amylase produced?

  The pancreas and salivary glands
• Where is protease produced?

  The pancreas and stomach
• Where is lipase produced?


  The pancreas and small intestine
• How are carbohydrates digested?

  First by amylase produced in the salivary glands, then by maltase, sucrase, and lactase to break down disaccharides into their constituent monosaccharides
• How are proteins digested?

  -Endopeptidase hydrolyses bonds in the middle of the polypeptide to increase surface area and make exopeptidase more efficient

  -Exopeptidase hydrolyses bonds at the end of the polypeptides

  -Dipeptidase hydrolyses dipeptides into individual amino acids
• How are lipids digested?

  -Lipids = emulsified by bile • increases surface area produces micelles (lipid droplets)

  -Micelles are broken down upon contact of the epithelial lining into monoglycerides and fatty acids, absorbed directly through the epithelial lining

  -The ER recombines them into triglycerides

  -The Golgi apparatus modifies them into chylomicrons

  -exit via exocytosis into the lacteal/ the lymphatic system
• Structure of haemoglobin


  Quaternary polypeptide with 4 haem groups with Fe2+ to bind to oxygen
• Haemoglobin with a high affinity to oxygen


  Take up oxygen more readily but lose it less readily (left side of oxy. dis. curve)
• Haemoglobin with a low affinity for oxygen


  Take up oxygen less readily but lose it more readily (right side of oxy. dis. curve)
• Explain the shape of the oxygen dissociation curve

  Positive correlation - each binding makes subsequent bindings easier

  Curve plateaus when all four binding sites are full
• What is the Bohr shift?

  Shifts left for low concentration - low oxygen affinity

  Shifts right for high concentration - high oxygen affinity
• What does a double circulatory system refer to?

  A double circuit system, where blood travels from the heart to the lungs, then back to the lungs to be pumped around the body
• What is the name of the blood vessel that receives blood from the rest of the body?

  Vena cava
• What is the name of the blood vessel that delivers blood to the body?

  Aorta
• What is the name of the blood vessel that takes blood to the lungs?

  Pulmonary artery
• What is the name of the blood vessel that takes blood to the heart from the lungs?

  Pulmonary vein
• What is the name of the blood vessel that takes blood to the kidneys?

  Renal artery
• What is the name of the blood vessel that takes blood back to the heart from the kidneys?

  Renal vein
• What are the four chambers of the heart?

  Right and left atria, right and left ventricles
• What are the names of the valves between atria and ventricles?

  Atrioventricular (AV) valves