3.1 exchange Flashcards
all organisms exchange substances with their environment in order to absorb useful substances needed for metabolic reactions to occur, and to remove waste products. in multicellular organisms, this exchange of substances takes place via a what?
a specialist exchange surface, known as a mass transport system.
what does this mass transport system maintain?
this mass transport system maintains the diffusion gradients that transport substances to and from cell-surface membranes.
give the two factors which affect the amount of each material that is exchanged between an organism and its external environment.
- the surface area to volume ratio of the organism.
- the metabolic rate of the organism.
explain why organisms with a high metabolic rate require a larger surface area to volume ratio than organisms with a low metabolic rate.
organisms with a high metabolic rate exchange more materials than organisms with a low metabolic rate, so require a larger surface area to volume ratio.
state the four main substances that need to be interchanged between an organism and its environment, including an example for each.
- respiratory gases, such as oxygen.
- nutrients, such as glucose.
- excretory products, such as urea.
- heat.
except for heat, give the two main ways in which the exchange of substances between an organism and its environment can take place.
- passively (no metabolic energy required), by diffusion and osmosis.
- actively (metabolic energy required), by active transport.
exchange takes place at the surface of an organism. give the two main features which organisms have evolved in order to increase the efficiency of exchange with their environment.
- a flattened shape, so that no cell is ever far from the surface of the organism, such as a leaf.
- specialised exchange surfaces, with large surface areas to increase the surface area to volume ratio, such as lungs in mammals, and gills in fish.
give three features of specialised exchange surfaces, which allow the efficient exchange of materials across it via diffusion or active transport.
- a large surface area relative to volume ratio, which increases the rate of exchange.
- very thin, so that the diffusion distance is short, allowing materials to move across the exchange surface rapidly.
- a transport system to ensure the movement of an internal medium, such as the blood, in order to maintain a steep diffusion gradient.
explain why fish need a specialist exchange surface to exchange respiratory gases.
- fish have a small surface area to volume ratio.
- because of this, their body surface is not accurate to supply and remove their respiratory gases.
- therefore, they have evolved a specialist exchange surface to counteract this.
describe what the gills are composed of, and where they are located.
the gills are located within the body of the fish behind the head, made up of gill filaments stacked in a pile.
describe the events that occur during the countercurrent exchange principle.
the flow of water over the gill lamellae, and the flow of blood, in opposite directions.
give two things that this countercurrent arrangement leads to.
- the diffusion of oxygen from water to the blood.
- a diffusion gradient for oxygen uptake, which is maintained across the entire width of the gill lamellae.
explain what would happen to the diffusion gradient if the flow of water and blood occurred in the same direction.
- the diffusion gradient would only be maintained across part of the length of the gill lamellae.
- this means that only 50% of the available oxygen would be absorbed by the blood.
explain why specialised exchange surfaces are usually located inside the body of an organism.
- being thin, specialised exchange surfaces are easily damaged and dehydrated.
- therefore, they are usually located inside the body of an organism.
give the name of the specialised exchange system insects have evolved in order to carry out gas exchange.
for gas exchange, insects have evolved a specialised internal network of tubes called tracheae, which are further divided into smaller tubes called tracheoles.
explain why there is a short diffusion pathway from a tracheole to any body cell within an insect.
- the tracheoles extend throughout all the body tissues of an insect.
- in this way, oxygen is brought directly to the respiring tissues, which results in a short diffusion pathway from a tracheole to any body cell.
give the three ways in which respiratory gases move in and out of the tracheal system.
- along a diffusion gradient.
- via mass transport.
- via osmosis.
when gas exchange occurs via osmosis, the final diffusion pathway occurs in a gas rather than a liquid phase. explain why diffusion is more rapid in this way.
- during periods of major activity, the muscle cells around the tracheoles respire anaerobically.
- this produces lactate, which lowers the water potential of the muscle cells, drawing water from the tracheoles into the cells via osmosis.
- the volume of water in the tracheoles decreases, which increases the rate at which air moves into the tracheoles.
give a limitation of the tracheal system.
- the tracheal system relies mostly on diffusion to exchange gases between the environment and an insect’s cells.
- for diffusion to be effective the diffusion pathway needs to be short, which limits the size that insects can obtain.
most gaseous exchange process in plants occur via diffusion in the leaf. explain three ways in which the leaf of a plant is adapted to allow for the rapid diffusion of gases.
- many stomata in the surface of the leaf, which creates a short diffusion pathway between plant cells and stomata.
- interconnecting air-spaces that occur throughout the mesophyll so that gases can readily come into contact with mesophyll cells.
- large surface area of mesophyll cells for rapid diffusion.
explain how stomata control the rate of gaseous diffusion, whilst limiting water loss from a plant.
- each stoma is surrounded by guard cells, which open and close the stoma pore.
- guard cells open stomata during gas exchange, and close stomata to limit excessive water loss.
- in this way, stomata control the rate of gaseous diffusion, whilst still limiting water loss from a plant.
most insects are terrestrial. this means that water easily evaporates from the surface of their bodies, which can lead to dehydration. give three adaptations that insects have evolved to limit water loss.
- a small surface area to volume ratio, to minimise the area over which water is lost.
- waterproof coverings, which limit the evaporation of water from the surface of the body.
- spiracles, which are openings of the tracheae at the body surface, which can be closed to reduce water loss.
xerophytes are plants that are adapted to living in areas where water is in short supply. give three ways in which xerophytes are adapted to limit water loss through transpiration.
- a thick cuticle, which forms a waterproof barrier, preventing the loss of water from the surface of the leaf.
- hairy leaves, which traps still, moist air next to the leaf surface.
- stomata in pits or grooves, which traps still, moist air next to the leaf surface, and reduces the water potential gradient.
what is transpiration?
the loss of water through the stoma of a plant leaf.
