AQA GCSE Further Biology B3.1

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Osmosis
Osmosis is the movement of water across a partially permeable membrane. It requires no energy
from the cell and the movement of water molecules is random. The water moves from an area of
high water concentration to an area of low concentration, along the concentration gradient.
Active Transport
Sometimes cells need to absorb substances which are in short supply in that particular area of the
body, this requires energy as it moves against the concentration gradient. Substances move across a
partially permeable membrane and energy is required from respiration. Cells absorb ions from dilute
solutions, so against the concentration gradient. An example of this is root cells absorbing mineral
ions from dilute solutions in the soil. Glucose is reabsorbed in the kidney tubules, if necessary, by
active transport.
Sports Drinks
Muscles release energy during exercise, and glucose, a sugar is used in respiration which provides
energy for the muscles. After a period of exercise, the body sweats more to cool down; this contains
water and mineral ions. Body cells may become dehydrated if a lot of sweat is produced and the
water isn't replaced. After a long period of exercise, it may be necessary to provide your body with
more sugar, mineral ions and water which have been used or lost during the exercise. Sports drinks
are solutions of sugar and mineral ions, which make them good at replacing lost substances. The
water in the drinks contributes to rehydrating the body cells as the drinks are designed to rebalance
the concentration of body fluids along with the concentration inside the cells. If the drink
concentration matches the body fluids, then the drink is isotonic. The evidence behind sports drinks is
inconsistent as some scientists think it would be just as beneficial to have water for short periods of
exercise, however the drinks may help athletes who need to replace mineral ions and sugar as well
as water.
Exchange Gases
If an organism is larger and more complex, they could have exchange surfaces, which obtain all the
food and oxygen they need. Solutes, which are soluble food materials, are absorbed by the
intestine, where oxygen is absorbed by the lungs and carbon dioxide is removed by them. The
larger the surface area is, the more efficient the exchange surface is, thin walls and a short diffusion
path also make the surface more efficient. Lungs contain the gaseous exchange surface, where the
surface area of the lungs is increased by the alveoli. The alveoli have thin walls and a large surface
area, as well as a good blood supply to quickly transport oxygen away from the lungs. In order to
maintain a steep diffusion gradient, the lungs are ventilated and oxygen diffuses into many capillaries
surrounding the alveoli, and carbon dioxide diffuses back out into the lungs, we then breathe this out.
Ventilating the Lungs

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The breathing system's exchange surface is in the lungs, the lungs are in the thorax, inside the
ribcage just above the diaphragm, the diaphragm separates the lungs from the abdomen. As we
breathe in, the intercostal muscles contract, the diaphragm flattens out and the ribcage expands by
moving up and out, the volume of the thorax also increases and the pressure in the thorax decreases
as air is drawn in. The movement of air in and out of the lungs is known as ventilation.…read more

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Transpiration
The roots of the plant take up the water that the plants need. The water moves through the plant to
the leaves, where water evaporates from the leaf cells and diffuses out through the stomata. This
movement is the transpiration stream. The plant dehydrates when the rate of evaporation is greater
than water uptake; this is more likely to occur in hot, dry, windy or bright conditions.…read more

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