Transport (Diffusion, Active Transport, Osmosis) Flashcards
Diffusion
Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration. It describes the movement of particles in fluids (liquids and gases). The particles all move randomly. Substances can move in and out of cells across cell membranes via diffusion (e.g CO2, urea).
Diffusion Example
The random movement of particles through a gas or liquid from high concentration to a low concentration.
Perfume
When you spray perfume, the smell diffuses across the room from the high concentration (where you just sprayed it) to low concentration (the other side of the room).
When you spray perfume, the smell diffuses across the room from the high concentration (where you just sprayed it) to low concentration (the other side of the room).
Urea
a waste product of cells, diffuses out of cells and into the blood for excretion by the kidneys
Which of the following is a waste product removed during diffusion?
CO₂
Factors Affecting Diffusion
The rate of diffusion can speed up or slow down.
Concentration gradient
The concentration gradient is linked to the difference in concentration between two areas.
The bigger the difference in concentration between two areas, the greater the concentration gradient and the faster the rate of diffusion.
Membrane surface area
The larger the surface area of the membrane that a substance is diffusing through (e.g. the membrane around a cell), the faster the rate of diffusion.
Temperature
The higher the temperature, the faster the rate of diffusion.
Which of the following does NOT affect the rate of diffusion across membranes?
Colour of molecule
Select the factors that will create the highest rate of diffusion
Large membrane surface area, high temperature and high concentration gradient
The concentration gradient is the difference in concentration between two areas
The bigger the difference in concentration, the greater the concentration gradient and the faster the rate of diffusion.
What would happen to the rate of diffusion if the concentration got steeper and the temperature rose?
The speed of diffusion would increase
Osmosis
Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution (high concentration of water) to a concentrated solution (low concentration of water).
Partially permeable membrane
A partially permeable membrane allows water through, but won’t let larger molecules dissolved in water pass through.
Water movement
Water will move to make the concentrations the same on both sides of the membrane:
When there are lots of water molecules (in a dilute solution) on one side of a partially permeable membrane, but not many on the other side (in a concentrated solution), water will move from the dilute to the concentrated solution.
Net movement of water
It is important to remember that water molecules will move through the membrane in both directions, but the net (overall) movement of water will be from the dilute solution to a concentrated solution.
Osmosis
Osmosis
Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution (‘high concentration’ of water) to a concentrated solution (‘low concentration’ of water).
Which of the following is a specialised plant tissue that uses osmosis to absorb water
Root hair cell
Osmosis is the diffusion of water across a partially permeable membrane from a what solution?
Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution (‘high concentration’ of water) to a concentrated solution (‘low concentration’ of water).
Experiment definition
Experiment
An experiment is a test under controlled conditions. There are two main variables in an experiment - the independent variable and the dependent variable.
Independent variable
This is the variable that you control - it is changed to see how the dependent variable will change. For example, in an osmosis experiment, you change the concentration of the sugar solution each time. This is the independent variable.
Dependent variable
The dependent variable is the variable that you measure as an outcome of the experiment. In the osmosis experiment, it will be the change in the mass of the object being used.
Investigating Osmosis
This experiment shows the effect of water concentration on osmosis.
Measure change in mass
Cut discs of raw potato and measure their mass.
Put discs in different concentrations of sugar or salt solution.
After 30 minutes, measure the mass of each disc again.
Calculate percentage change in mass
Subtract the final mass from the initial mass of each disc.
Divide this number by the initial mass and then multiply by 100 to give a percentage change in mass.
The concentration in which the potato’s mass changed the least is closest to the water concentration of the potato (because the least water has moved into or out of the potato by osmosis).
Disc mass
Disc mass
By measuring the mass of each disc before and after being put in solution, the change in mass can be worked out; the mass of a disc may have increased, decreased or stayed the same.
Decreased
If the mass of a disc decreased, it has lost water by osmosis.
Stayed the same
Stayed the same
If the disc’s mass did not change, it has neither gained nor lost water by osmosis.
Increased
If the mass of the disc increased, it has gained water by osmosis.
Lost
Water moved out of the potato cells by osmosis because the water concentration of the solution was lower than that of the cells.
Neither
Water did not move into or out of the potato cells because the water concentration of the solution was equal to that of the cells.
Gained
Water moved into the potato cells by osmosis because the water concentration of the solution was higher than that of the cells.
Active Transport in Humans and Plants: Sugar absorption in human gut
Active transport allows sugar molecules, which are needed for cell respiration, to be absorbed into the blood from the gut, even when the sugar concentration of the blood is higher.
Active transport allows sugar molecules, which are needed for cell respiration, to be absorbed into the blood from the gut, even when the sugar concentration of the blood is higher.
Active transport in the root hairs of plants allows plants to absorb mineral ions, which are necessary for healthy growth, even though the concentration of minerals is usually lower in the soil than in the root hair.
In active transport, molecules are transported from
a low concentration to a high concentration.
Active transport is the process where dissolved molecules move from
a less concentrated solution to a more concentrated solution. As the net movement of molecules is against the concentration gradient, energy is required. This energy is provided by respiration.
Name the substances that are absorbed via active transport in the following structures:
Minerals: Roots of plants
Sugar: Guts of humans
Transport in Cells
The three main forms of transport in cells are: Diffusion
Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration.
Osmosis
Osmosis is a special case of diffusion where only water molecules move.
It requires a partially permeable membrane
Active transport
Active transport is the net movement of particles against a concentration gradient.
Energy is therefore required.
Select the processes that are forms of passive transport?
Osmosis, diffusion
Blackcurrant Squash - Diffusion or Osmosis?
The example of blackcurrant squash being added to water can be used to demonstrate the difference between osmosis and diffusion.
Diffusion
When you add blackcurrant squash to water, the particles in squash spread out, so that the strength of its flavour is the same throughout the whole drink.
The squash molecules move from the high concentration of squash molecules to the low concentration.
This is diffusion, not osmosis.
Osmosis
Osmosis
Osmosis would take place if the orange squash was trapped inside a membrane.
The water moves instead of the squash molecules.
To equalise the concentration, the water moves into the membrane:
The water moves from the dilute solution (outside the membrane) to the concentrated solution (where the squash is).
Pair the following definitions with a method of transportation in cells:
Diffusion
This is the net movement of particles from an area of high concentration to an area of lower concentration. This is a form of passive transport (which does not require any energy).
Active transport
This is the net movement of particles against a concentration gradient, and so energy is required.
Osmosis
This is a special case of diffusion, where only water molecules move. It requires a partially permeable membrane. This is a form of passive transport (which does not require any energy).
Complete the following sentences about forms of transport in cells:
Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.
Osmosis is a special case of diffusion where only water molecules move. It requires a partially permeable membrane.
Active transport is the net movement of particles against a concentration gradient. Energy is therefore required.
