1.3 Transport in Cells Keywords List
Diffusion- Diffusion is the spreading of the particles of any substance in a solution, or particles of a gas, resulting in a
net movement from an area of higher concentration to an area of lower concentration. It does not require energy.
Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange,
and of the waste product urea from cells into the blood plasma for excretion in the kidney.
Factors which affect the rate of diffusion are:
 The difference in concentrations (gradient)
 The temperature
 The surface area of the membrane.
A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of
molecules into and out of the cell to meet the needs of the organism.
In multicellular organisms the smaller surface area to volume ratio means surfaces and organ systems are
specialized for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for
the organism’s needs.
The effectiveness of an exchange surface is increased by:
 Having a large surface area
 A membrane that is thin to provide a short diffusion path
 Having an efficient blood supply (in animals)
 Being ventilated (in animals for gaseous exchange).
Surface area- This needs to be large to increase the rate of diffusion/osmosis.
Temperature- Temperature affects diffusion. A high temperature will give the particles more kinetic energy causing
them to spread out faster and diffuse quicker.
Urea- A waste substance that diffuses out of the blood and into the kidneys from high to low concentration.
Oxygen- a gas which moves by diffusion from the air sacs (alveoli) in the lungs, into the red blood cells from high to
low concentration. It is then used by cells to respire.
Carbon dioxide- a gas which moves by diffusion from plasma in the blood, into the air sacs (alveoli) from high to low
concentration. It is a waste product of respiring cells.
Root hair cell- A plant cell found on a root, there are many of them on one root. It provides a large surface area so
substances can diffuse easily. Most of the time minerals will move into the root hair cell by active transport due to
their being such a high concentration in the root already. Water will move in by osmosis.
Villus-A structure in the small intestine. Google this! It has many microvilli (cells with small folds) to increase the
surface area. They also have a good blood supply to ensure a short diffusion pathway. Digested food particles will
move by both diffusion and active transport.
Osmosis- Water may move across cell membranes via osmosis. Osmosis is the diffusion of water from a dilute
solution to a concentrated solution through a partially permeable membrane. This happens in root hair cells and the
large intestine.
Solution- The solute (substance that’s dissolving) and the solvent (the liquid the solute dissolves into e.g water).
Active transport- Some dissolved substances move across cell membranes via active transport. Active transport
involves the movement of a substance against a concentration gradient and requires energy from respiration (this is
made in mitochondria). A cell with a lot of mitochondria will undergo a lot of active transport. Active transport
allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for
healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood
which has a higher sugar concentration. Sugar molecules are used for cell respiration.
Percentage change