topic 1 - cell biology: transport in cells Flashcards
what is diffusion?
diffusion is the spreading out of the particles of any substance in
solution, or particles of a gas, resulting in a net movement from an area
of higher concentration to an area of lower concentration.
what substances can be transported in and out of cells by diffusion?
oxygen and carbon dioxide in gas exchange, and the waste product
urea from cells into the blood plasma for excretion in the kidney.
how does concentration gradient affect the rate of diffusion?
the greater the difference in concentration, the more rapid the diffusion.
how does temperature affect the rate of diffusion?
higher temperatures increase the energy and therefore the movement of the molecules, increasing the rate of diffusion. Lower temperatures decrease the energy of the molecules, thus decreasing the rate of diffusion.
how does the surface area of a membrane affect the rate of diffusion?
a single-celled organism has a relatively large surface area to volume
ratio which allows sufficient transport of molecules into and out of the cell
to meet the needs of the organism.
explain the need for exchange surfaces and
a transport system in multicellular organisms in terms of surface area to
volume ratio.
most multicellular plants and animals have too small a surface area to volume ratio so diffusion would be too slow to provide the necessary molecules. Therefore, they require a system to transport nutrients and waste products around the organism.
explain how the small intestine and lungs in
mammals are adapted for exchanging materials.
villi: (small intestine)
1. increase the surface area to allow digested food to be efficiently absorbed into the bloodstream and delivered to cells around the body
2. filled with blood capillaries, and the blood constantly moving in them means that a steep concentration gradient is maintained. This increases the amount of dissolved, digested food that can be absorbed into the bloodstream from the small intestine.
alveoli: (lungs)
1. have a large surface area to volume ratio so a higher volume of air can diffuse in from the blood and bronchioles
2. moist walls allow gases to dissolve in the moisture, helping them pass across the exchange surface
explain how the gills in fish are adapted for exchanging materials.
- highly folded, giving them a large surface area and maximising the efficiency of gas exchange
- short distance required for diffusion – the outer layer of the gill filaments and the capillary walls are just one cell thick
explain how the roots and leaves in plants are adapted for exchanging materials.
- root networks have a large surface area and root hair cells have projections that reach out between soil particles to
increase the surface area for absorption - flat shape of leaves increase surface area for diffusion of gases, and reduced the rate of water loss by evaporation
how is the effectiveness of an exchange surface increased in multicellular organisms?
by having a large surface area
• a membrane that is thin, to provide a short diffusion path
• (in animals) having an efficient blood supply
• (in animals, for gaseous exchange) being ventilated.
what is osmosis?
the diffusion of water from a dilute solutiom to a concentrated solution through a partially permeable membrane
what is active transport?
active transport moves substances from a dilute solution to a more concentrated solution (against a concentration gradient) - this requires ENERGY from respiration
give a use of active transport either in plants or the body.
plants: allows mineral ions to be absorbed into plant root hairs
from very dilute solutions in the soil.
the body: allows sugar molecules to be absorbed from lower concentrations
in the gut into the blood which has a higher sugar concentration. Sugar
molecules are used for cell respiration.
