section 1: exchange & transport - topic 1: specialised exchange systems Flashcards
what substances do cells need to take in? and for what?
oxygen and glucose.
for aerobic respiration and other metabolic reactions.
what products do cells need to excrete?
waste products like carbon dioxide and urea.
smaller organisms have … SA:V ratios than larger organisms?
bigger.
how to calculate SA:V ratio?
divide the surface area by the volume.
how do single-celled organisms exchange substances?
substances can diffuse directly into or out of the cell across the cell surface membrane.
what is the diffusion rate of single-celled organisms? and why?
quick.
because of the short distances the substances have to travel and because single-celled organisms have a relatively high SA:V ratio.
in multicellular organisms, diffusion across the outer membrane is too …? and why?
slow.
1. some cells are deep within the body - large distance between them and the outside environment.
2. larger animals have a low SA:V ratio - it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.
3. multicellular organisms have a higher metabolic rate than single-celled - so use up oxygen and glucose faster.
what do multicellular organisms need in order to exchange substances?
specialised exchange surfaces.
what are the special features exchange surfaces have to improve their efficiency?
- large surface area.
- thin.
- good blood supply and/or ventilation.
what is an example of a large surface area? explain.
root hair cells.
the cells on plant roots grow into long ‘hairs’ which stick out into the soil, with each branch of a root being covered in millions of these microscopic hairs. this gives the roots a large surface area, which helps to increase the rate of absorption of water (via osmosis) and mineral ions (via active transport) from the soil.
what is an example of thinness? explain.
alveoli.
each alveolus is made from a single layer of thin, flat cells called the alveolar epithelium. the thin alveolar epithelium helps to decrease the distance over which oxygen (out alveolar space into the blood) and carbon dioxide (in) diffusion takes place, which increases the rate of diffusion.
what is an example of good blood supply and/or ventilation? explain.
alveoli.
the alveoli are surrounded by a large capillary network, giving each alveolus its own blood supply - the blood constantly takes oxygen away from the alveoli and brings more carbs dioxide. the lungs are also ventilated so the air in each alveolus is constantly replaced. these features help to maintain concentration gradients of oxygen and carbon dioxide.
