Diffusion, osmosis and active transport

Diffusion is the spreading out of particles resulting in a net movement from an area of high concentration to an area of low concentration. This is a passive process.

Difference in concentration is called the concentration gradient. The larger the gradient, the faster the rate of diffusion. In addition, the higher the temperature, the faster the rate of diffusion. Finally, the greater the surface area, the greater the rate of diffusion.

For plant cells, being in a dilute solution once again causes it to expand, but it becomes swollen instead, as the cell wall stops it from bursting. This is called turgid. If the cell shrinks after being placed in a concentrated solution, the cell shrinks and becomes flaccid. For animal cells, dilute solutions can cause them to burst, or they can die in a concentrated solution by having no water.

Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Active transport is when a cell uses energy from respiration to bring molecules from an area of low concentration into an area of high concentration. Thus, it goes against the concentration gradient. It can also be required to maintain molecules inside a cell, to stop them from diffusing out into an area of lower concentration.

In the small intestine, it is used where enterocytes want to absorb more nutrients, but the concentration is greater inside the cell than outside. This is why these cells have lots of mitochondria for respiration on order to produce enough energy. Similarly, it is used in plants where root hair cells must absorb ions such as magnesium, used to make chlorophyll. Energy is needed, as the concentration is greater inside the root hair cell rather than outside. Once inside, the ions are transported via xylem cells towards where they are needed. Again, it can be seen that the root hair cells have lots of mitochondria, required for respiration order to create enough energy for the active transport to take place.