Define the term diffusion.
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Define the term diffusion.
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.
What is a concentration gradient?
A concentration gradient is a difference in concentration between two regions.
True or False?
Diffusion is an active process.
False.
Diffusion is a passive process that occurs when molecules spread out due to their random movement.
Where does the energy for diffusion come from?
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)
Name an example of diffusion that takes place in the human lungs.
Examples of diffusion in the lungs include:
oxygen diffuses from the inhaled air into the blood through the alveolar lining
carbon dioxide diffuses from the blood into the exhaled air through the alveolar lining
Define the phrase surface area to volume ratio.
Surface area to volume ratio is the surface area of an object in relation to its volume.
What happens to the surface area to volume ratio as cell size increases?
As cell size increases the surface area to volume ratio decreases.
True or False?
Root hair cells have a high surface area to volume ratio.
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.
Define diffusion distance
Diffusion distance is the distance molecules have to travel when they diffuse from one region to another.
What is the effect of decreasing diffusion distance on the rate of diffusion?
As diffusion distance decreases, the rate of diffusion increases.
True or False?
Increasing temperature decreases the rate of diffusion.
False.
As temperature increases, the rate of diffusion also increases. Molecules move around faster at higher temperatures, resulting in faster diffusion.
What is the effect of increasing temperature on the movement of particles?
At higher temperatures particles move around faster; this is because they have more kinetic energy.
True of False?
Increasing the concentration gradient will increase the rate of diffusion.
True.
As the concentration gradient increases, the rate of diffusion also increases.
Define the term solvent.
A solvent is a substance in which other substances can dissolve.
Water is an example of a solvent.
True or False?
Water as a solvent allows for easy transport of substances around organisms.
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.
How does water as a solvent assist in digestion?
Water as a solvent allows digested food molecules to be moved from the alimentary canal to cells all over the body.
What role does water play in the excretion of toxic substances?
Water allows toxic substances like urea and excess salts to dissolve, making them easy to remove from the body in urine.
True or False?
Water is an important component of cell cytoplasm.
True.
Water is an important part of the cytoplasm in cells.
What are two examples of plant systems that rely on water as a solvent?
The xylem and phloem of plants rely on water as a solvent for transporting substances.
Define the term osmosis.
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 or False?
Only water can move by osmosis.
True.
Only water can be transported by osmosis.
What type of concentration difference leads to 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.
What is a partially permeable cell membrane?
A partially permeable cell membrane allows some substances to pass through while preventing others from entering or leaving a cell.
True or False?
Osmosis only occurs across a partially permeable membrane.
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.
What does it indicate if plant tissue loses mass when immersed in a solution of a different concentration?
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.
What is the independent variable in a practical that involves immersing potato cylinders in solutions of different concentration?
The independent variable in the osmosis and potatoes practical is the solute concentration of the solution in which the potato cylinders are placed.
In an investigation into plant tissue and osmosis, why is it important to dry the plant tissue samples before weighing?
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 or False?
When a potato cylinder placed in a sucrose solution does not change in mass, this indicates that no overall movement of water has occurred.
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 or False?
Potato cylinders placed in distilled water should gain mass due to osmosis.
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.
What is the role of dialysis tubing in osmosis experiments?
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).
In a dialysis tubing experiment, what observation indicates that osmosis has occurred?
A change in the water level outside the tubing indicates that osmosis has occurred.
How does osmosis affect plant cell structure?
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).
What is the importance of osmosis-induced cell rigidity in plants?
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.
What is water potential? (Extended Tier Only)
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.
What happens to plant cells in a solution with higher water potential than the cell contents? (Extended Tier Only)
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.
Define the term plasmolysis. (Extended Tier Only)
Plasmolysis is when the cell membrane of a plant cell pulls away from the cell wall due to water loss in a concentrated solution.
How do animal cells respond to being placed in a concentrated sugar solution? (Extended Tier Only)
Animal cells placed in a concentrated sugar solution (lower water potential) will lose water by osmosis and become crenated (shrivelled up).
What happens to animal cells placed in distilled water? (Extended Tier Only)
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 or False?
The cell wall prevents plant cells from bursting due to excessive water intake. (Extended Tier Only)
True.
The cell wall in plant cells creates pressure that stops too much water from entering and prevents the cell from bursting.
What causes a plant to wilt? (Extended Tier Only)
A plant wilts when it does not receive enough water, causing its cells to lose turgor and become flaccid rather than rigid and firm.
Define the term active transport.
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.
True or False?
Active transport is the movement of particles down a concentration gradient.
False.
Active transport moves particles against a concentration gradient.
Which cellular process releases energy for active transport?
Energy for active transport is released by respiration.
Why do root hair cells use active transport? (Extended Tier Only)
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.
How does active transport aid glucose absorption in the small intestine (Extended Tier Only)
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.
What is the function of protein carriers in active transport? (Extended Tier Only)
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.
Describe the process of active transport using protein carriers. (Extended Tier Only)
The process of active transport using protein carriers involves:
The substance combines with the protein carrier in the cell membrane
The carrier transports the substance across the membrane using energy from respiration to change shape and move the substance
The substance is released into the cell