Movement of substances into and out of cells

What is diffusion, osmosis and active transport?

TERM	DEFINITION
DIFFUSION	Passive net movement of particles down the concentration gradient (from region of high concentration to region of low concentration) until equilibrium
OSMOSIS	Passive net movement of Water molecules down the Water potential gradient (from region of lower solute concentration to region of higher solute concentration) across a partially permeable membrane
ACTIVE TRANSPORT	Movement of substances against the concentration gradient (from region of low concentration to region of high concentration) using energy (commonly in the form of ATP)

What factors affect the rate of movement of substances into and out of cells?

FACTOR	EXPLANATION
SURFACE AREA TO VOLUME RATIO	As the surface area to volume ratio (SA:V) increases, the rate of movement of substances into and out of cells will increase This is because there is a larger surface area in which substances can move through, hence increasing the rate of movement of substance
TEMPERATURE	As temperature increases, the rate of movement of substances into and out of cells will increase This is because particles gain more kinetic energy and so will move faster, hence increasing the rate of movement of substance
CONCENTRATION GRADIENT	As concentration gradient increases, the rate of movement of substances into and out of cells will increase This is because a stronger concentration gradient is present, hence increasing the rate of movement of substance

How do you investigate diffusion and osmosis using living and non-living systems?

INVESTIGATING DIFFUSION:

INVESTIGATING DIFFUSION

LIVING SYSTEM Diagram showing Diffusion in Alveoli

EXPLANATION: For diffusion in gas exchange to be efficient, high concentration gradient needs to be maintained between Alveoli and blood capillaries As a result of gas exchange, Oxygen diffuses from the Alveoli into the bloodstream where it is transported and consumed by cells via cellular respiration, producing Carbon Dioxide as a waste product that diffuses out into the Alveoli to be exhaled Hence, during inhalation, Oxygen enters the Alveoli which results in a high concentration of Oxygen relative to the bloodstream, causing Oxygen to continuously diffuse out from the Alveoli into blood capillaries down the concentration gradient Correspondingly, there is a high concentration of Carbon Dioxide (produced as a waste product in cellular respiration) in the bloodstream relative to the Alveoli, therefore continuously diffusing out into the Alveoli down the concentration gradient to be exhaled out of the lungs A high concentration gradient is maintained between Alveoli and bloodstream to allow continuous gas exchange (diffusion of Oxygen and Carbon Dioxide) to occur

NON - LIVING Diagram showing Diffusion of Potassium Permanganate in Solvent (Water)

EXPLANATION: When dye of Potassium Permanganate is added into Water, molecules of Potassium Permanganate will diffuse from regions with high concentration of Potassium Permanganate molecules to regions with low concentration of molecules Hence overtime, the colour of solvent will be weaker compared to initial dye as molecules of Potassium Permanganate will be less concentrated and diffused throughout the Solvent until equilibrium (hence the colour of Water is constant)

INVESTIGATING OSMOSIS:

INVESTIGATING OSMOSIS

LIVING

EXPLANATION: For plants to absorb Water from the soil (using their root hair cells) via osmosis, high water potential gradient needs to be maintained between soil and root hair cells As Water is collected in the soil (from rain or watering by farmers), this results in a higher concentration of Water molecules outside in the soil relative to the inside of root hair cells As a result, Water in the soil will move through the partially permeable membrane into the root hair cells via osmosis to be transported to the Xylem for use Root hair cells have large surface area to volume ratio and thin cell walls for efficient absorption of Water via osmosis

NON - LIVING Diagram showing Osmosis in Visking Tube containing Sucrose Solution in Water

EXPLANATION When visking tube filled with Sucrose solution is placed in beaker of Water, Sucrose molecules will remain trapped as they are too large to diffuse through the small pores on the tube, whilst Water can move in and out of tube via osmosis as they are small enough to diffuse through the small pore As Sucrose solution in visking tube has a higher solute concentration relative to the Water in the beaker, a strong concentration gradient is established, therefore allowing Water molecules to diffuse (down the water potential gradient) through the partially permeable membrane into the visking tube until equilibrium is met As a result, the inflow of Water via osmosis will result in the size of visking tube to increase

Osmosis

Water