AQA Biology 3: Dissolved Materials, Circulation and Kidneys

So far these cards detail dissolved materials (active transport, diffusion), the circulatory system and how the kidneys work. All of B3 should be done eventually.

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  • Created by: Becky_
  • Created on: 04-04-12 11:53

Active Transport

  • Where substances are absorbed against a concentration gradient, e.g. from a low to high concentration. The process requires energy

Example 1: This happens in the Root hair cells, where the concentration of mineral ions is higher in the root hair cell than in the soil around it, so diffusion cannot occur. However, root hair cells are specialised for active transport:

  • Many mitochondria which provide energy (from respiration) for active transport
  • The root hair cells have long 'hairs' which stick out into the soil, this gives the plant a large surface area

Example 2:  In the gut, where glucose/ions are absorbed back into the blood:

  • Diffusion occurs here first, as there is a higher concentration in the gut
  • As time goes on, the concentration of nutrients in the blood increases
  • Therefore, active transport has to take place from a low concentration (gut) to a high concentration (blood)
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Diffusion Through Cell Membranes

Gas and solute exchange happens frequently in the lungs and small intestine. The human body is adapted so substances can diffuse through them most effectively.

Example 1: Gas exchange happens in the lungs so oxygen can be taken in and CO2 can be exhaled:

  • Lungs contain millions of air sacs called alveoli
  • The alveoli have 4 main adaptions which help to maximise the diffusion of these gases: large surface area, moist lining (helps for diffusion), thin walls (short distance to travel), rich blood supply!

Example 2: Solute Exchange happens in the villi in the small intestine, where they're adapted for maximum effectiveness:

  • Finger-like shape increases surface are, rich blood supply
  • Single layer of surface cell, food moves into blood through diffusion and active transport
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The Circulation Sytem

  • Main function of the circulation system: to get food and oxygen to every cell in the body
  • Also carries waste products (co2 and urea) to be removed from the body

The Circulation System is known as the Double Circulation System, where blood is pumped from the heart to the lungs, and blood is pumped from the heart to the rest of the body

-this allows the circulation system to be more efficient as oxygenated and deoxygenated blood are separate

The Heart: 

  • Left side pumps oxygenated blood around the body
  • Arteries carry blood away from the heart at high blood pressure -oxygenated blood, split of into capillaries
  • Right side pumps deoxygenated blood to the lungs to collect oxygen and remove carbon dioxide
  • Veins carry blood to the heart at low blood pressure - deoxygenated blood

EXPECTIONS: Pulmonary artery and pulmonary vein

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The Kidneys

Function: get rid of toxic waste (e.g. urea) as well as adjusting the amount of dissolved ions and water in the blood.

Nephrons - the filtration units in the kidneys

Ultra-filtration: high pressure which squeezes water, urea, ions and sugar out of the blood and into the Bowman's capsule

Membranes between the blood vessels and the Bowman's capsule act like filters, so big molecules like proteins and blood cells are not squeezed out


As the liquids flows along the nephron, useful substances are reabsorbed back into the blood:

  • Sugar, sufficient ions and sufficient water - involves the process of active transport

Substances that continue out of the nephron include:

  • The remaining substances - excess ions, urea: which goes down the ureter to bladder as urine
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What happens to your body when you exercise?

  • Heart rate increases - so  more oxygen can be delivered to muscles, increases breathing rate which increases oxygen intake
  • Arteries dilate - which supplies blood to the muscles (more oxygen), heat can be removed at a faster rate
  • Carbon Dioxide can be removed at a faster rate


  • Glucose from food is stored as glycogen
  • Glycogen's mainly stored in the liver, but is stored in muscles as well
  • Muscles use glucose rapidly during exercise, have to use glycogen stores too

Anaerobic Respiration

  • Used if there's not enough oxygen
  • Glucose --> energy + lactic acid
  • Lactic acid builds up in the muscles, which can get muscles tired
  • Doesn't release as much energy
  • Muscles can be used for longer
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Oxygen Debt

Anaerobic Respiration leads to OXYGEN DEBT

  • Where you have to repay the oxygen that didn't get to your muscles
  • You have to keep breathing hard after you stop - oxidise lactic acid
  • High levels of CO2 and lactic acid need to be removed

Glucose + Oxygen --> Carbon Dioxide + Water 

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The Blood consists of white blood cells, red blood cells, plasma and platelets

Red Blood Cells are adapted to carry oxygen in 3 main ways:

  • Large Surface Area: to absorb as much oxygen as possible
  • No nucleus: more room to carry oxygen
  • Contain haemoglobin for carrying the oxygen

Haemoglobin + Oxygen --> Oxyhaemoglobin The reaction is reversible, so ignore my arrow sign!

Fact: At high altitudes, there's less oxygen in the air so more blood cells are produced

Platelets: small fragments of cells that help blood to clot a wound

What is Plasma?

Pale, straw coloured liquid which carries: everything else in the blood ^, soluble products of digestion, waste products (e.g. co2 and urea), hormones, antibodies and antitoxins

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Kidney Failure

Treatment 1: Dialysis

  • If your kidneys don't work, then Dialysis will do the kidneys job and filter the blood
  • The person's blood flows alongside a partially permeable membrane, surrounded by dialysis fluid
  • Dialysis fluid has the same concentration of solutes that are in the blood so the useful solutes aren't lost
  • Only waste substances (e.g. urea, excess water and ions) diffuse across the barrier
  • 3x a week, 3-4 hours :(

Treatment 2: Kidney Transplant

  • From people who have died suddenly or carry a donor card
  • Pros: Cheaper, still able to resume a normal life (less time-consuming), don't have to control diet, Cons: Body might reject the kidney, have to take immunosuppresant drugs, long waiting list
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