Unit 3 - How organisms exchange substances with their environment Flashcards
What is the relationship between the size of an organism or structure and its SA: V ratio?
The size of the surface area available for diffusion relative to the size of an object has important consequences for living organisms. The bigger the surface area, the quicker diffusion can occur.
What adaptations do larger organisms have that facilitate exchange as this ratio reduces?
Multicellular organism have mass transport systems and well as specialised exchange organs to facilitate their reduced SA: V ratio. In mammals the circulatory system is and example of mass transport and the lungs are an exchange organ. In plants the xylem and phloem are responsible for mass transport.
What adaptations would increase the SA: V ratio of an exchange surface?
1)Folds in a surface increases the surface area without making much change to the volume.
2)Dividing a single structure into smaller structures increases the surface area without changing the volume.
3)Elongating or stretching a structure only increases its size in one or two directions, but not all three, which means the SA:V ratio does not fall away as sharply.
How to single-celled organisms respire?
Tiny single-celled organisms have a very large surface area-to-volume ratio, providing a rapid rate of diffusion, so they simply diffuse across the cell membrane.
What is the gas exchange system of an insect?
What is the gas exchange system of a fish?
What is the gas exchange system of a plant?
How do insects limit water loss?
The key to survival for terrestrial organisms, then, is finding the right balance between gas exchange and water loss. Insects have a number of adaptations that allow them to maintain this balance:
- Overall, they have a small SA: V ratio to minimise the area over which water can be lost.
- Their exoskeleton has a waterproof outer layer.
- The spiracles are valve-like and can be opened and closed. When an insect is at rest, the spiracles are usually closed to reduce water loss but open when the insect becomes active to meet the increased demand for oxygen.
How do plants limit water loss?
Plants known as xerophytes (plants in areas with a restricted water supply) have evolved a range of adaptations to limit water loss. Some of their adaptions include:
Having hairy leaves that are able to trap most air next to the leaf surface, reduces evaporation (water loss).
Having stomata in grooves/pits traps the moist air against the leaf surface and reduces the water potential gradient (as does hairy leaves).
Having a thicker cuticle than average is an efficient way of reducing transpiration through the plant leaves.
Leaves that are able to roll up in a way that protects its underside and creates an area of still air that can become saturated with water vapour.
