3 1 diffusion osmosis and active transport

Diffusion is the spreading out of particles in a solution or a gas, resulting in net movement of particles from a region of higher concentration to a region of lower concentration.

A concentration gradient is a difference in concentration between two regions.

False. Diffusion is a passive process that occurs when molecules spread out due to their random movement.

The energy for diffusion comes from the kinetic energy of the random movement of molecules and ions. (Although diffusion is a passive process, the molecules still require energy to move)

Examples of diffusion in the lungs include:

Surface area to volume ratio is the surface area of an object in relation to its volume.

As cell size increases the surface area to volume ratio decreases.

True. Root hair cells have a large surface area in relation to their volume; this increases the rate at which they can absorb water and minerals from the soil.

Diffusion distance is the distance molecules have to travel when they diffuse from one region to another.

As diffusion distance decreases, the rate of diffusion increases.

False. As temperature increases, the rate of diffusion also increases. Molecules move around faster at higher temperatures, resulting in faster diffusion.

At higher temperatures particles move around faster; this is because they have more kinetic energy.

True. As the concentration gradient increases, the rate of diffusion also increases.

A solvent is a substance in which other substances can dissolve. Water is an example of a solvent.

True. Water as a solvent allows for easy transport of substances around organisms, such as in the xylem and phloem of plants and dissolved food molecules in the blood.

Water as a solvent allows digested food molecules to be moved from the alimentary canal to cells all over the body.

Water allows toxic substances like urea and excess salts to dissolve, making them easy to remove from the body in urine.

True. Water is an important part of the cytoplasm in cells.

The xylem and phloem of plants rely on water as a solvent for transporting substances.

Osmosis is the diffusion of water molecules from a region of higher water concentration (dilute solution) to a region of lower water concentration (solution with a high solute concentration), through a partially permeable membrane.

True. Only water can be transported by osmosis.

The type of concentration difference that leads to osmosis is a difference in water concentration between two regions. This can also be referred to as water potential.

A partially permeable cell membrane allows some substances to pass through while preventing others from entering or leaving a cell.

True. Osmosis must take place across a partially permeable membrane. If water moves in any other way, e.g. water vapour moving out of a leaf via the stomata, this is diffusion.

If plant tissue loses mass when immersed in a solution, it indicates that water has moved out of the plant tissue by osmosis. This shows that the surrounding solution has a higher solute concentration than the contents of the plant tissue.

The independent variable in the osmosis and potatoes practical is the solute concentration of the solution in which the potato cylinders are placed.

Plant tissue is patted dry before measuring the mass so that excess water on the surface of the plant tissue does not alter the results.

True. When a potato cylinder is placed in a sucrose solution and does not change in mass, this indicates no overall movement of water. This occurs when the solution has the same concentration as the cell cytoplasm.

True. Potato cylinders placed in distilled water will gain mass due to the movement of water into the cells by osmosis. This will occur because distilled water has a higher water concentration than potato cell cytoplasm.

Dialysis tubing allows smaller molecules (e.g. glucose and water) to pass through by diffusion and osmosis but prevents the passage of larger molecules (e.g. sucrose).

A change in the water level outside the tubing indicates that osmosis has occurred.

When water moves into a plant cell by osmosis, the vacuole enlarges, pushing the cell membrane against the cell wall, making the cell rigid and firm (called turgid).

The rigidity of plant cells due to osmosis provides support and strength for the plant, helping it stand upright with leaves held out to catch sunlight.

Water potential is a measure of the tendency of water to move from one area to another, with high water potential in dilute solutions and low water potential in concentrated solutions.

When plant cells are in a solution with higher water potential (more dilute), water moves into the cells via osmosis, increasing turgor pressure and making them turgid.

Plasmolysis is when the cell membrane of a plant cell pulls away from the cell wall due to water loss in a concentrated solution.

Animal cells placed in a concentrated sugar solution (lower water potential) will lose water by osmosis and become crenated (shrivelled up).

Animal cells placed in distilled water (higher water potential) will gain water by osmosis and may burst due to the lack of a cell wall to create turgor pressure.

True. The cell wall in plant cells creates pressure that stops too much water from entering and prevents the cell from bursting.

A plant wilts when it does not receive enough water, causing its cells to lose turgor and become flaccid rather than rigid and firm.

Active transport is the movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration; this requires energy.

False. Active transport moves particles against a concentration gradient.

Energy for active transport is released by respiration.

Root hair cells use active transport to move mineral ions from a region of lower concentration in the soil to a region of higher concentration inside the cell cytoplasm.

Active transport allows glucose to be transported into the bloodstream from the lumen of the small intestine when the concentration of glucose in the blood is higher than that in the intestine.

Protein carriers in active transport are embedded in the cell membrane and move molecules or ions across a membrane during active transport, against their concentration gradient, using energy from respiration.

The process of active transport using protein carriers involves: