Exchange of Materials AQA B3.1

Osmosis- the diffusion of water from a dilute to more concentrated solution through a partially permeable membrane

• Moves from dilute to concentrated
• Dilute=contains lots of water particles
• Concentrated=doesn't contain many water particles

Keeps diffusing until water levels are the same on both sides, regardless of volume change

Active transport- the movement of particles from an area of low concentration to an area of high concentration against a concentration gradient using energy released in respiration by the mitochondria

• Allows ions from dilute solutions and other substances like glucose to be absorbed when they are needed, regardless of concentration gradient
• Uses energy
• Glucose can be reabsorbed into the kidney tubules by active transport

During exercise:

• Sweat- lose water and ions and become dehydrated
• Blood sugar reduces- needed for respiration

Sports drinks are solutions of sugar and mineral ions. They can:

• replace water
• replace lost mineral ions
• replace sugar

If water and ions are not replaces, cells become dehydrates and the ion balance of the body is disturbed so cells do not work as efficiently.

You could just drink a normal soft drink or water to fufil all of an athletes needs. Sports drinks are only good for long term endurance performers.

Exchange surface = A surface where materials are exchanged. Large organisms need them to obtain the food and oxygen they need.

Exchange surfaces are effective if:

• large surface area
• are thin (short diffusion path)
• have a good, efficient blood supply
• are ventilated

Lungs contain the gaseous exchange surface. The surface area is increased by the alveoli. The alveoli have thin walls, a large surface area and a good blood supply. Lungs are well ventilated to maintain a steep concentration gradient

Lungs are situated inside the thorax, above the diaphragm and abdomen.

When we breath in:

• Intercostal muscles contract
• Ribcage moves up and out
• Diaphragm flattens
• Volume of thorax increases
• Pressure of thorax decreases

When we breath out:

• Intercostal muscles and diaphragm relax
• Volume of the thorax decreases
• Pressure increases and air is forced out

Known as ventilation