Biology

For the exam: Know what active transport is and why it is important to us.

There are 2 main ways in which dissolved substances move in and out of cells.

 1) Diffusion (substances) and 2)Osmosis (water)

Both of them go along the concentration gradient.

Active Transport on the other hand, goes against the concentration gradient.

Going against the concentration gradient means going from a low concentration to a high concentration.

- This is useful in the body as cells can absorb ions from a very dilute solution.

- It also means that substances such as sugar and ions move from one place to another through cell membranes.

To move substances across the concentration gradient in active transport requires energy. This energy comes from respiring cells (or in exam speech "by cellular respiration"). Links show that the rate of active transport relates to the rate of respiration- so if a cell respires a lot and makes lots of energy, it can carry out lots of active transport.

Some examples of these types of cells are: root hair cells and gut lining cells.

As cells which provide lots of energy have lots of mitochondria, here’s a flow diagram for how all these things relate to active transport.

Active transport is important and is widely used in cells. Here are some examples of when it is used effectively:

1. There is a lower concentration of mineral ions in the actual soil around plant because plant mineral ions around the soil are usually found in dilute solutions. However by active transport, even

though there is already a higher concentration of mineral ions in the plant, even more can be absorbed from the soil by active transport.

2. Glucose always moves from the kidney tubules and the gut into the blood no matter what the concentration gradient- and when it moves against the gradient, it moves by active transport.

3. In animals, marine animals often take in too much salt for their kidneys to handle. To solve this problem, there are special salt glands in the body, which get rid of the salt from the animal even against the concentration gradient- by active transport. This is vital for the survival of marine animals.

MAIN POINTS TO REMEMBER:

1) SUBSTANCES CAN SOMETIMES BE ABSORBED AGAINST THE CONCENTRATION GRADIENT BY ACTIVE TRANSPORT.

2) ACTIVE TRANSPORT REQUIRES ENERGY FROM RESPIRING CELLS.

3) THROUGH ACTIVE TRANSPORT, CELLS CAN ABSORB IONS FROM VERY DILUTE SOLUTIONS AND ALSO MOVE MOLECULES THROUGH CELL MEMBRANES.