B3 Revision Exchanging Materials

Active transport is the movement of substances from an area of low concentration to an area of high concentration (against the concentration gradient). It requires energy from cellular respiration, because the active transport system has to carry a molecule across the membrane, and then return to its original position. The more active transport that takes place, the more mitochondria are needed (for energy)

Breathing is the constant intake of oxygen, and the removal of carbon dioxide. Lungs are found in the upper part of the body (chest/thorax), protected by the rib cage. Lower part of the body is the abdomen. The diaphragm is a sheet of muscle separating the thorax from the abdomen

When you breathe in, the rib move up and out and the diaphragm flattens from its dome shape, allowing air to move in. The lungs are made up of clusters of alveoli, which are tiny air sacs. They, have a large surface area, have a rich blood supply, maintaining a concentration gradient in both directions (oxygen is constantly removed into the blood and carbon dioxide in constantly delivered to the lungs,thin alveolus walls decreases diffusion distance and moist surfaces allow gases to dissolve, making diffusion easier.

Food in your gut is broken down into simple sugars (glucose, amino acids, fatty acids and glycerol). Food moves from the inside of the small intestine into the bloodstream by diffusion and active transport. There is a high concentration of food molecules in the gut, and a low concentration in the bloodstream, so food molecules diffuse into the blood across a concentration gradient.

Villi are tiny finger-like projections that line the small intestine, and have some features to increase the uptake of digested food by diffusion (only a certain number of food molecules can diffuse over a given area of gut lining at any one time). They have, a large surface area for more diffusion to take place, lining of small intestine has excellent blood supply, maintaining steep concentration gradient and thin wall for short diffusion distance. Glucose and other dissolved molecules move from small intestine into the blood by active transport so no digested food is wasted.

Gills in fish are made up of many thin layers of tissue with a rich blood supply, and moist surfaces. Tadpoles have external gills, which are then reabsorbed into the body when the tadpole becomes a frog, via metamorphosis. Adult frog has moist skin, rich blood supply, gas exchange take place through skin, and a pair of simple lungs.

Insects have an internal respiratory system, supplying oxygen directly to the cells. Insects have spiracles that open when the insect needs oxygen, and these lead to the tracheoles. The tracheoles are minute breathing tubes which penetrate right through the tissues- they have a large surface area, moist lining, air is pumped in and out of them and they are freely permeable to gases (no blood supply in an insect).

Plants have some features to allow maximum efficiency in gas exchange, flattened shape of leaves increases surface area, thin leaves decreases diffusion distance and many air spaces (stomata) allow carbon dioxide to come into contact with cells. However, plants need to make a compromise between letting carbon dioxide in and water loss by evaporation. Plants control water loss by, a waxy cuticle, which is waterproof and gas-proof, stomata are controlled by guard cells,most stomata are found on the underside of leaves, meaning they are not exposed to sunlight and heat of the sun and wilting is where the leave collapse so surface area is greatly reduced.

Roots are thin with a large surface area, and they have root hair cells with membranes that increase the surface area for diffusion (osmosis in this case). Plant roots take mineral ions in via active transport, and so contain plenty of mitochondria.

Transpiration is the loss of water vapour. Transpiration stream is the constant movement of water molecules through the xylem, form the roots to the leaves. Warm sunny conditions increase the rate of photosynthesis, so increase the rate of transpiration. Hot, dry, windy conditions increase the rate of evaporation, and so increase the rate of transpiration