movement into and out of cells

what is diffusion

the net movement of particles from a region of high concentration to a region of low concentration down the concentration gradient

where does the energy for diffusion come from

the kinetic energy of the random movement of molecules and ions

what is the role of water

being a solvent in organisms with reference to digestion, excretion and transport

what is osmosis

the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane

how do substances move into and out of cells through the cell membrane

substances move in and out of cells by diffusion through the cell membrane

what are the factors that influence diffusion

• surface area

• molecular mass

• temperature

• concentration gradients

• distance

how does water diffuse into cells

water moves in and out of cells by osmosis through the partially permeable cell membrane

describe the effects of plant tissues on immersing them in solutions of different concentrations

turgid = the blown up state after water has diffused into the plant cell by osmosis

turgor pressure = the cytoplasm and the vacuole swell after water diffuses in the plant cell by osmosis, the swelling presses against the cell membrane which presses against the cell wall, the cell wall is stronger than the membrane and does not swell

plasmolysis = too much water diffuses out of the plant cell, the cytoplasm and vacuole shrink, the cell membrane tears away from the cell wall and the cell becomes plasmolysed

flaccid = when too much water diffuses out the plant cell by osmosis, the cytoplasms stops pushing against the wall and the cell becomes floppy

what is turgor pressure

turgor pressure is the pressure of water pushing the plasma membrane against the cell wall of a plant cell

what is active transport

the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

describe the importance of diffusion of gases and solutes

diffusion helps to provide important gases and solutes and also helps to dispose of toxic substances

explain the importance of water potential and osmosis uptake of water by plants

• plants obtain water by osmosis through their roots

• the water acts as a transport for minerals and nitrate ions

• the water also maintains the turgidity of the cell

• if the plants lose more water than what they gain their cells will become flaccid

what is the importance of active transport as a process for movement across membranes

• active transport takes place in plant roots. When ions which are needed for metabolism is in short supply in the soil water, the ions are absorbed by root hair cells by active transport

• active transport is also important in the small intestines of an animal. Digested food is absorbed by the epithelial cells of the villi by active transport

explain how protein molecules move particles across a membrane by active transport

• carrier proteins embedded in the cell membrane open up to the outside of the cell and molecules or ions enter the carrier and attach to it

• using energy the carrier proteins change shape and open up into the cell releasing the molecule or ion