Biology IGCSE - Movement In and Out of Cells

Diffusion

net movement of particles from a high to low concentration (down concentration gradient) because of their random movement

How substances move by diffusion

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

Importance of diffusion of gases for living organisms

Makes gas exchange possible (e.g. carbon dioxide and oxygen) → gives plants their proper shape (becomes turgid when water diffuses) → able to transpire

factors that influence diffusion: surface area

surface area of the membrane increase → more space for molecules to diffuse across membrane → rate of diffusion increases

factors that influence diffusion: temperature

increase in temperature → increases kinetic energy of particles → moves more rapidly → increases diffusion

factors that influence diffusion: concentration gradient

the greater the concentration gradient → greater rate of diffusion

factors that influence diffusion: distance

shorter distances → particles don’t have to travel as far → increases rate of diffusion

Osmosis

net movement of water molecules from a high (diluted) to low (concentrated) water potential through a partially permeable membrane

Flaccid

plants cells that are lacking water and therefore turgidity

Turgid

plant cells that are full of water and are experiencing high turgor pressure

Plasmolysis

Plant cells that've lost so much water that the cell membrane begins to pull away from the cell wall

Turgor Pressure

the force within the cell where water in the cell pushes the cell membrane against the cell wall

effects on plant tissues of immersing them in solutions of different concentrations: concentrated salt solution

put into salt concentrated solution → cell A has undergone plasmolysis → lots of water has diffused out of the cell by osmosis → from high to low water potential outside the cell

effects on plant tissues of immersing them in solutions of different concentrations: pure solution

put into pure water → cell B is turgid → water diffuse into cell by osmosis → high to low water potential inside the cell

effects on plant tissues of immersing them in solutions of different concentrations: unchanged solution

put into solution with same water potential as cell → cell C unchanged → no osmosis has occured

effects on plant tissues of immersing them in solutions of different concentrations: slightly lower water potential than cytoplasm

put into solution with slightly lower water potential than cytoplasm → cell D flaccid → small amount of water diffused out of cell by osmosis → high to low water potential outside cell

Importance of water potential and osmosis in uptake and loss of water by organisms

Preserves the water content of the plant cells, allows them to retain water despite ongoing water loss.

Active Transport

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

Importance of active transport

a process for movement of molecules or ions across membranes, including ion uptake by root hair → Root hair cells allow plants to absorb mineral ions, necessary for healthy growth