6. Exchange Flashcards
What is meant by the term ‘passive exchange’?
No metabolic energy required for exchange, by diffusion or osmosis.
What is meant by the term ‘active exchange’?
Metabolic energy required for exchange, by active transport.
Name features of specialised exchange surfaces for effective transfer of materials
- A large surface area to volume ratio of the organism increases the rate of exchange.
- Very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly.
- Selectively permeable membrane to allow selected materials across.
- Movement of the environmental medium
- A transport system to ensure movement of the internal medium, eg blood, in order to maintain a concentration gradient.
Define ‘tissue fluid’
Fluid that surrounds the cells of the body. Its composition is similar to that of blood plasma, except it lacks proteins. It supplies nutrients to the cells and removes waste products.
Name 4 general things that need to be exchanged between organisms and their environment.
- respiratory gases
- nutrients
- excretory products
- heat
Name the process by which carbon dioxide is removed from a single celled organism
Diffusion over the body surface
Explain why there is a conflict between gas exchange and conserving water in terrestrial insects.
Gas exchange requires a thin permeable surface with a large area.
Conserving water requires thick, waterproof surfaces with a small area.
Explain how the tracheal system effects the size of insects
because it relies on diffusion to bring oxygen to the respiring tissues.
Name the system of gas exchange in insects.
Tracheal system
Describe the features of the tracheal system.
Insects have evolved an internal network of tubes called tracheae. The tracheae are supported by strengthened rings to prevent them collapsing. The trachea divide into smaller, dead-end tubes called tracheoles. The tracheoles extend throughout the body tissues of the insect. Atmospheric air, containing oxygen, is brought directly to the respiring tissues, as there’s a short diffusion pathway from tracheole to any body cell.
How do respiratory gases move in and out the tracheal system?
- Along a diffusion gradient
- Mass transport
- The ends of the tracheoles are filled with water.
In relation to fish gills, describe what is meant by countercurrent flow
The movement of water and blood in opposite directions across the gill lamellae.
Outline why countercurrent flow is an efficient means of exchanging gases along gills of fish
Because a steady diffusion gradient is maintained over the whole length of the gill lamellae. Therefore more oxygen diffuses from the water into the blood.
Mackerel are active, fast-swimming fish, while plaice move slowly along the seabed. Suggest the differences in the gills of these two types of fish.
Mackerel have more gill lamellae, filaments, larger surface area compared to plaice.
Water flow over fish gills is one-way, whereas the flow of air in and out of the lungs is two-way. Suggest why one-way flow is an advantage to fish.
Less energy is required because the flow
doesn’t have to be reversed (water is dense and difficult to move).
Describe the structure of the gills.
The gills are located within the body, behind the fish’s head. They’re made up of gill filaments, which stack up in a pile. At right angles to the filaments are gill lamellae, which increase the surface area of the gills. Water is taken in through the mouth and forced over the gills and out through an opening on each side of the body.
Name the process of gas exchange in plants
Gases move in and out of plants by diffusion.
Name three adaptations of the leaves for rapid diffusion of gases
- many small pores, stomata, no cell is far from a stoma so diffusion distance is short
- numerous interconnecting air spaces occurring throughout the mesophyll so gases can readily come into contact with mesophyll cells.
- large surface area of mesophyll cells for rapid diffusion.
Explain the advantage to a plant being able to open and close the stomata via guard cells.
Helps control water loss by evaporation
State two similarities between gas exchange in a plant leaf and gas exchange in a terrestrial insect.
- No living cell is far from the external air
- Diffusion occurs in the gas phase
- Need to avoid excessive water loss
- Diffuse air through pores in their outer covering
State two differences between gas exchange in a plant leaf and gas exchange in a terrestrial insect.
- Insects may create mass air flow; plants never do
- Insects have a smaller surface area to volume ratio than plants.
- Insects have special structures (trachea) which gases diffuse along; plants don’t
- Insects do not interchange gases between respiration and photosynthesis; plants do
Name adaptations developed by insects to limit water loss
- Small surface area to volume ratio (minimises area of water loss)
- Waterproof coverings over body surfaces
- Spiracles at tracheae and body surface openings, closed to limit water loss.
What are xerophytes?
Plants with a restricted supply of water, that have evolved a range of adaptations to limit water loss through transpiration
Name adaptations developed by xerophytes to limit water loss
- Thick cuticle (waxy cuticle forms a waterproof barrier, but the thicker the less water lost)
- Rolling up leaves (protects stomata on lower epidermis by trapping a region of still air within the rolled leaf. This region becomes saturated with water vapor so has a very high water potential- no water potential gradient- no water loss).
- Hairy leaves (traps still, moist air next to leaf surface, reducing water potential gradient and heat loss)
- Stomata in pits/grooves (traps still, moist air next to leaf surface, reducing water potential gradient and heat loss)
- Reduced surface area to volume ratio (smaller sa:vol, slower rate of diffusion, reducing water loss, balanced with need for sufficient area for photosynthesis.
What is the main problem both insects and plants share when it comes to living on land?
Conflict of conserving water and gas exchange.
Efficient gas exchange requires a thin, permeable surface with a large area. On land these features can lead to a considerable amount of water loss by evaporation.
State one modification to prevent water loss shared by plants and insects
Waterproof covering to the body.
Insects limit water loss by having a small surface area too volume ratio- why is this not a feasible way of limiting water loss in plants?
Plants photosynthesise and therefore need a large surface area to capture light.
Why would rolling leaves with the upper epidermis on the inside not be effective in reducing water loss?
Almost all stomata are on the lower epidermis. This would be exposed to air currents that would reduce the water potential immediately outside the leaf. The water potential gradient would be increased and a lot of water vapor would be lost.
