2- MOVEMENT IN AND OUT OF CELLS Flashcards
what is diffusion?
diffusion is the net movement of particles from an area of their higher concentration to an area of their lower concentration, down the concentration gradient, due to the random movement of particles
what happens: gas diffusion at the leaves of a plant?
- CARBON DIOXIDE is in a higher concentration in the air than inside the leaves, so it diffuses into the leaves through holes called stomata in the lower surface of the leaf, and is used for photosynthesis.
- OXYGEN is produced during photosynthesis inside the leaf, so it is in a higher concentration inside the leaf than outside, so it diffuses out of the leaf.
during the day, plants absorb ________ _________ for photosynthesis. ___________ diffuses into the leaf, and ______ diffuses out.
light energy, carbon dioxide, oxygen
during the day, plants do not absorb _______. _______ diffuses into the leaf, and ________ diffuses out.
light energy, oxygen, carbon dioxide
what happens: gas exchange at the alveoli in the lungs
- oxygen is in a higher concentration in the alveoli, so it diffuses from the alveoli into the blood.
- carbon dioxide is in a higher concentration in the blood than in the alveoli, so it diffuses out of the capillary and into the alveoli
what happens: diffusion in body cells
- oxygen from capillaries into body cells
- carbon dioxide from body cells into capillaries
solutes such as glucose, mineral salts/mineral ions, vitamins and amino acids are in a higher concentration in the blood than in the body cells, so they diffuse from the blood into the body cells
what are factors that influence diffusion?
- temperature: the higher the temperature the higher the rate of diffusion as the particles have more kinetic energy so they move faster
- surface area: the larger the surface area, the more particles can diffuse across it at any one time
- concentration gradient
- diffusion distance/pathway: the shorter the diffusion distance, the quicker the particles can diffuse across it
- ph
OSMOSIS
osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane
why is osmosis a special case of diffusion?
it applies only to the movement of water molecules down their concentration gradient, when these water molecules cross through a partially permeable membrane (such as the cell membrane, which controls the entry and exit of substances from cells)
how does turgor pressure the whole plant?
the uptake of water by plant cells‘ vacuoles and the subsequent turgor pressure that builds up is important in supporting the plant cells
this support ensure that the whole plant is erect. when cells are flaccid or plasmolysed, the plant wilts
what is turgor pressure?
when plant cells are placed into water they take in water by osmosis, from an area of higher water potential outside the cell into the cell where there is a lower water potential. the water molecules will pass into the vacuole, causing the vacuole to expand outwards, pushing the cytoplasm + cell membrane out against the cell wall with a pressure called turgor pressure
what happens when you place a plant cell into a solution of equal water potential?
the water molecules will move into and out of the cells equally, so the shape of the cell will not change
what happens when you place plant cells into a solution with slightly lower water potential?
when plant cells lose water by evaporation and cannot replace it, or if they are placed in a solution with a slightly lower water potential than themselves, they will lose water by osmosis and the turgor pressure in the cell decreases. the cells are no longer strong and are said to be FLACCID
much lower water potential
when plant cells are placed into a solution with a much lower water potential than themselves, water molecules pass out of the plant cells by osmosis. the cytoplasm + vacuole contents shrink so much that the cell membrane tears away from the cell wall. these cells are plasmolysed
how do plants take up water from the soil?
osmosis ensures the water uptake by plants. the concentration of water in the soil will be higher than it is inside the plant tissues, so the soil has a higher water potential than the plant tissues. this means there is a water potential gradient between the soil and the plant roots so water molecues pass from the soil in through the cell membrane of the root hair cells into the root by osmosis.
