B3.1 Movement in and out of Cells

Osmosis is the diffusion of water. It is a way of moving water into and out of cells.

Water is able to move through a partially permeable membrane through osmosis.They will move because of a high concentration gradient. This allows the more concentrated solution to be diluted. When there is no concentration gradient there is no net movement.

Active transport - substances that are absorbed against a concentration gradient. This requires the use of energy from respiration.

•  Allows cells to absorb sugar and ions, which can pass through cell membranes and very dilute solutions.
• Active transport happens in the roots of plants; root hair cells as well as the small intestine (uptake of glucose)

Many organ systems are specialised for exchanging materials. Features that make exchange surfaces efficient include...

• a large surface area
• being thin, providing a short diffusion path
• having an efficient blood supply (In animals)
• being ventilated (in animals) for gas exchange.

The larger and more complex an organism is, the more difficult it is to exchange materials. Exchange surfaces in organisms are adapted to maximeise their effectiveness. In humans..

• Villi increase the surface area of the small intestine
• alveoli increase the surface area of the lungs.

Villi line the walls of the small intestine. They have...

• a massive surface area for exchanging materials across.
• an extensive network of blood capillaries to absorb the products of digestion by diffusion and active transport.

The breathing system...

• is located in your thorax
• involves your lungs
• is protected by your ribcage

Your thorax is divided from your abdomen by a muscular sheet called the diaphram. The breathing system takes air into and out of your body so that...

• oxygen from the air can diffuse into and out of your blood
• carbon dioxide can diffuse from your blood into the air

The air that your breathe in reaches the lungs through the trachea, which has rings of cartilage to prevent it from collapsing.

• The trachea divides into two tubes ( the bronchi)
• The bronchi divide into bronchioles
• The bronchioles divide until they end in air sacs called alveoli

The alveoli are very close to the blood capillaries. They are efficient at exchanging oxygen and carbon dioxide because they have...

• a large moist surface area
• an excellent blood supply

The movement of air into and out of your lungs is known as Ventilation.

When you breathe in (Inhale), your ribcage move up and out and your diaphragm flattens (contracts). When you breathe out (exhale) your ribcage moves in and down and your diaphragm moves up (relaxes).

Artificail aids for breathing, such as ventilators have been developed for medical use. They aim to improve gas exchange in the body.

In Plants...

• carbon dioxide enters  leaves by diffusion
• water and mineral ions are absorbed by the roots.

Roots and leaves are adapted to carry out the exchange of materials:

• Root hairs provide a large surface area in roots
• Leaves are broad, thin and flat with lots of internal air spaces to provide the largest surface area possible.

Plants have tiny holes called stomata on their leaves. During photosynthesis, the stomata...

• let carbon dioxide in (needed for photosynthesis)
• let oxygen out (a product of photosynthesis)

Plants mainly lose water vapour from their leaves. Most of this loss takes place through the stomata. The movement of water through a plant is called transpiration.

Evaporation of water is more rapid in hot, dry and windy conditions.

If plants lose water through the leaves faster than it's replaced by the roots then the stomata can close to prevent wilting. But this means that photosynthesis can't take place.