AQA AS Level Biology- Gas Exchange (Fish, Insects, Plants, Humans)

• In a fish's gills, blood and water flow in opposite directions. What is the name of this system?

  Countercurrent flow
• Finish the sentence: The larger an organism, the smaller the...

  surface area to volume ratio
• How do larger animals compensate for having a smaller surface area to volume ratio?

  . Body adaptations that help them to exchange substances forexample. having an effective transport system. having a body shape that increases surface area without increasing volume for example having lungs or gills that are specialized for gas exchange
• Label the fish's gills.

  
• In which part of the fish's head are the gills found?

  Under the operculum
• Why is it difficult to obtain oxygen from water rather than air?

  . Oxygen is not very soluble in water. .Oxygen moves more slowly through water than through air. . Water has a higher density than air so is harder to move over a gas exchange surface during ventilation.
• How does the countercurrent exchange system maximise oxygen absorbed by the fish?

  .Water flows over the gills in an opposite direction to the blood. Countercurrent flow ensures that equilibrium is not reached. This ensures that a diffusion gradient is maintained across the entire length of the lammellae.
• When a fish is out of water, surface tension sticks the gill lamellae together. Explain why this can quickly be fatal.

  . Surface area of lamellae is reduced. . Not enough oxygen can be transported in to the gills.
• Label the tracheal system of an insect.

  . Countercurrent mechanism only works when ventilation current moves in one direction . In humans air moves in and out of lungs by going back and forth along the same pathway.

  
• Define ventilation.

  The active movement of air to the gas exchange system
• What name is given to special types of plants which have evolved adaptations to reduce water loss from gas exchange surfaces?

  Xerophytes
• What is the exoskeleton of an insect made out of?

  Chitin, covered by a cuticle
• What are the small openings inside the cuticle of an insect called and what is their function?

  Spiracles to let gases and carbon dioxide in and out
• How do the structure of the tracheae inside an insect's gas exchange system help to reduce water loss?

  . Tracheae are protected inside the insect's body, reducing water loss. . Air inside tracheae contain large quantities of water vapour, so has a high water potential which reduces loss of water by evaporation from gas exchange surface. . Spiracles can close to prevent water loss.
• Where is the main area of gas exchange by diffusion between air and body cells in an insect?

  Tracheoles
• What do very active insects have in their tracheal systems


  Muscles that pump air in and out
• Why do plants have a relatively large surface area: volume ratio

  They are branched
• Where is the gas exchange surface in a plant leaf located

  surface of mesophyll cells
• Why do palisade mesophyll contain a lot of chloroplasts?

  Palisade mesophyll cells are the site of photosynthesis. Having many chloroplasts means chlorophyll can be produced to allow photosynthesis to take place.
• Label the leaf.

  label the leaf

  
• What does xylem transport?

  water and mineral ions
• What does phloem transport?

  glucose
• What is the process by which the xylem transports water called and how can you measure the rate of this?

  Transpiration. Rate is measurable using an equipment called a potometer
• What is the process by which the phloem transports glucose and sugar called?

  Translocation
• What cells control the opening and closing of the stomata?

  Guard cells
• What are the openings in the leaf called that allow for gases to diffuse through?

  Stomata (singular = stroma)
• Describe two features of the plant leaf that provide a short diffusion pathway for gases.

  . large number of stomata. air spaces
• Which gases will move across the gas exchange surface in plants during the day and night and in what direction?


  Night:carbon dioxide = out oxygen = in Day:carbon dioxide = in Oxygen = out
• Explain how amobea are adapted for ideal gas exchange.

  .High surface area to volume ratio due to being relatively small. The rate at which oxygen and carbon dioxide are exchanged is then faster.
• Suggest why insects are generally not as big as mammals.

  . To prevent having a small surface area to volume ratio. To prevent having a too large surface area which can result in more evaporation of water
• What are the air sacs inside human lungs called

  Alveoli
• What are the walls that surround alveoli called?

  Alveolar epithelium
• State how alveoli are well adapted to their function as an exchange surface for gases.

  . Epithelial cells support a rich network of blood capillaries meaning there is a good supply to the alveoli. This is essential to carry oxygen away from the air and bring carbon dioxide back to the alveoli from the rest of the body. A good blood supply maintains a steep diffusion gradient so that oxygen will continue to diffuse in due to the oxygen-rich blood being replaced with oxygen-poor blood. . The alveolar walls are thin and cells are flattened, ensuring a short diffusion pathway and as a result a rapid rate of diffusion. . Permeable walls of alveoli, means there is a moist exchange surface, so that the cells making up the epithelium do not dry out and die. . Air inside alveoli are saturated with water vapour which reduces rate of water loss from cells via evaporation.
• Why does the inner surface of the alveolus have to be moist?

  So inner cells making up epithelium do not dry out
• Why is ventilation of human body described as tidal?

  flow of air occurs in both directions- in and out
• What does cartilage and how does it help with ventilation?

  Cartilage is a strong flexible tissue. It helps keep tubes open during pressure changes that happen when we breathe in and out.
• What is breathing in called scientifically?

  inspiration
• What is the name for the set of muscles between the ribs that are involved in gas exchange in the human body?

  external intercostal muscles
• What happens when we breathe in?

  Diaphragm muscles contract pulling diagraphm downwardsRib cage pushed upwards and outwards which increases thoraic volume Air inside the lungs has a lower pressure than air outside the body Air therefore flows into lungs, down pressure gradient.
• What happens when we breathe out?

  . Diaphgram muscles relax . Lungs and chest wall recoil returning thorax to original shape and volume. external intercostal muscles relax. decreased volume of thorax means increased pressure inside the lungs. . Air therefore flows out of the lungs, down pressure gradient, from high concentration to low concentration.