Diffusion
Diffusion is the random movement of a substance from a region of high
concentration to a region of low concentration (i.e.: down the concentration
gradient). This does not require energy and is a natural process that takes place.
Substances (oxygen, carbon dioxide, water, dissolved nutrients and urea) can move
into and out of a cell or organism via diffusion. This happens across the cell
membrane which is selectively permeable. The particles will move in both directions,
but there will be a net movement from high to low concentration and the particles
will end up evenly spread throughout the liquid or gas, but will continue to move.
For example, oxygen moves from a high concentration in the lungs to a low
concentration in the blood. (Water actually leaves cells by osmosis, which is the
diffusion of water across a membrane.)
The rate of diffusion is affected by the:
Concentration gradient - a larger difference in the high and low concentrations
increases the diffusion rate.
Temperature - a higher temperature provides the particles with more kinetic
energy increasing the diffusion rate.
Surfacearea - a larger surface area through which diffusion can happen
increases the diffusion rate.
, Active transport
Often, substances have to be moved from a low to a high concentration - against a
concentration gradient. Active transport is a process that is required to move
molecules against a concentration gradient. The process requires energy.
In animals, glucose molecules have to be moved across the gut wall into the blood.
The glucose molecules in the intestine might be in a higher concentration than in the
intestinal cells and blood – for instance, after a sugary meal – but there will be times
when glucose concentration in the intestine might be lower. All the glucose in the gut
needs to be absorbed. When the glucose concentration in the intestine is lower than
in the intestinal cells, movement of glucose involves active transport. The process
requires energy produced by respiration.
For plants to take up mineral ions, ions are moved into root hairs, where they are in a
higher concentration than in the dilute solutions in the soil. Active transport then
occurs across the root so that the plant takes in the ions it needs from the soil
around it.
Diffusion is the random movement of a substance from a region of high
concentration to a region of low concentration (i.e.: down the concentration
gradient). This does not require energy and is a natural process that takes place.
Substances (oxygen, carbon dioxide, water, dissolved nutrients and urea) can move
into and out of a cell or organism via diffusion. This happens across the cell
membrane which is selectively permeable. The particles will move in both directions,
but there will be a net movement from high to low concentration and the particles
will end up evenly spread throughout the liquid or gas, but will continue to move.
For example, oxygen moves from a high concentration in the lungs to a low
concentration in the blood. (Water actually leaves cells by osmosis, which is the
diffusion of water across a membrane.)
The rate of diffusion is affected by the:
Concentration gradient - a larger difference in the high and low concentrations
increases the diffusion rate.
Temperature - a higher temperature provides the particles with more kinetic
energy increasing the diffusion rate.
Surfacearea - a larger surface area through which diffusion can happen
increases the diffusion rate.
, Active transport
Often, substances have to be moved from a low to a high concentration - against a
concentration gradient. Active transport is a process that is required to move
molecules against a concentration gradient. The process requires energy.
In animals, glucose molecules have to be moved across the gut wall into the blood.
The glucose molecules in the intestine might be in a higher concentration than in the
intestinal cells and blood – for instance, after a sugary meal – but there will be times
when glucose concentration in the intestine might be lower. All the glucose in the gut
needs to be absorbed. When the glucose concentration in the intestine is lower than
in the intestinal cells, movement of glucose involves active transport. The process
requires energy produced by respiration.
For plants to take up mineral ions, ions are moved into root hairs, where they are in a
higher concentration than in the dilute solutions in the soil. Active transport then
occurs across the root so that the plant takes in the ions it needs from the soil
around it.
