Movement of Substances Into & Out of Cells (Edexcel GCSE Biology)
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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.
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.
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 happens to an animal cell placed in a concentrated sugar solution?
If an animal cell is placed into a strong sugar solution (with a lower water concentration than the cell) it will lose water by osmosis and will shrivel up.
What happens to a plant cell placed in distilled water?
A plant cell placed in distilled water will gain water by osmosis and swell up. The cell wall will prevent the cell from bursting.
What is the independent variable in the practical that involves immersing potato cylinders in solutions of different concentration?
The independent variable in the osmosis and potato practical is the solute concentration of the solution in which the potato cylinders are placed.
In the osmosis and potato practical why is it important to dry the potato cylinders before weighing?
The potato cylinders are blotted with paper towels before weighing to remove any surface water that could affect the mass measurement.
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.
Give one example of a control variable in the osmosis and potato practical.
Examples of control variables in the osmosis and potato practical include:
volume of (e.g. sucrose) solution
surface area of potato cylinders
potato cylinders are all thoroughly dried before weighing
potato cylinders are left in the solutions for the same length of time
True or False?
When a potato cylinder placed in a sucrose solution does not change in mass, this indicates no overall movement of water.
True.
If a potato cylinder does not change mass, it means the solution it is in has the same concentration as the cell cytoplasm, so there is no overall movement of water by osmosis.
What is the purpose of repeating the osmosis experiment with multiple potato cylinders?
Repeating the experiment with multiple potato cylinders allows for the identification and exclusion of anomalous results when calculating the mean.
How can the percentage change in mass of potato cylinders be calculated in the osmosis and potato practical?
Percentage change in mass of potato cylinders in the osmosis and potato practical can be calculated using the formula:
percentage change = (change in mass ÷ starting mass) x 100
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.