Two of the main ways in which diffused substances are transported across cells are osmosis and diffusion. Diffusion is the movement of particles across a concentration gradient useful to the cells; osmosis is the movement of water across a semi-permeable membrane. However, sometimes substances need to be transported against a concentration gradient or membrane, which is when active transport takes place.
By active transport, cells are able to move substances from an area of low concentration to and area of high concentration. This is what is meant by moving against the gradient. Because the substances are being transported against a gradient, energy is required for an active transport system to carry a molecule across the membrane and then return to its original position (see below diagram).
The energy required for active transport to take place coms from cellular respiration. The rate of active transport and rate of respiration in cells are closely linked. The process of respiration releases energy – so in other words, the more respiration happening, the more active transport is taking place. This is why cells involved in active transport (e.g. root hair cells and gut lining cells) usually have a lot of mitochondria to provide the energy needed from respiration.
Active transport is an important process in plants. The uptake of mineral ions through the soil requires active transport because the ions are found in very dilute solutions, whereas the solution inside the plant cells is a lot stronger. This means the ions have to be taken in against the gradient (from dilute to concentrated). Glucose is moved out of the gut and kidney into your blood, even though that is against a gradient. Active transport is also used in marine birds and reptiles, because they consume large amounts of salt when they drink water, and as the kidneys cannot get rid of it all, they have salt glands which use active transport. Without the ability for the cells to do active transport, these marine animals would die, so active transport is essential to their lives.
We require a constant supply of oxygen to allow for respiration. Breathing in and out takes in oxygen as a supply for the cells and removes the waste carbon dioxide produced by the cells. The lungs (found in the thorax) are protected by the rib cage. The lungs are separated from the digestive organs, found in the abdomen, by the diaphragm.
When you breathe in…
- your ribs move UP and OUT
- your diaphragm flattens
- air is pulled INTO the lungs
When you breathe out…
- your ribs move DOWN and IN
- your diaphragm returns to its domed shape
- air is forced OUT OF the lungs
The lungs have been adapted especially for making gas exchange more efficient. They are made up of clusters of alveoli, which are tiny air sacs with large surface areas, and are kept moist. They also have a rich blood supply, which maintains a concentration…