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Define the term diffusion.
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Define the term diffusion.
Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration.
What is a concentration gradient?
A concentration gradient is the difference in concentration between two regions.
What is the result of the random movement of molecules during diffusion?
The result of the random movement of molecules during diffusion is that molecules spread out until their concentration throughout the available space is even; this is the point of equilibrium.
Define the term osmosis.
Osmosis is the movement 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.
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 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 when a plant cell is placed in distilled water?
A plant cell placed in distilled water will gain water by osmosis; the vacuole gets bigger, pushing the cell membrane against the cell wall, and the plant cell is described as being turgid.
True or False?
Plant cells can burst due to osmosis.
False.
Plant cells have a supporting cell wall that prevents them from bursting due to osmosis.
Define the term active transport.
Active transport is the movement of particles through 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 during the cellular process of respiration.
True or False?
Active transport involves carrier proteins in the cell membrane.
True.
Molecules move across the cell membrane via specialised membrane carrier proteins during active transport.
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.
True or False?
The rate at which red pigment leaks out of damaged beetroot cells indicates the rate of diffusion.
True.
The red pigment in beetroot cells can leak out when the beetroot cell membranes are damaged. The rate at which this occurs is the diffusion rate.
Why is it important that all pieces of beetroot have the same surface area when measuring the effect of temperature on diffusion in beetroot?
Surface area affects diffusion rate, so differences in the surface area of the beetroot pieces would affect the results. This means that the investigation would not be measuring the effects of temperature alone on diffusion.
Why does red pigment leak out of damaged beetroot cells faster at higher temperatures?
Red pigment leaks out of beetroot cells faster at higher temperatures because increasing temperature increases the rate of diffusion. This is due to increased kinetic energy of the pigment molecules.
Define the term dependent variable.
The dependent variable is the variable that is measured during an investigation.
What is the independent variable in the practical that investigates osmosis using potato cylinders?
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.