Biology 3

Didn't get it completely finished, only up to B3.3 (not B3.4)


Biology 3

B3.1 Movement of molecules in and out of cells

B3.2 Transport systems in plants and animals

B3.3 Homeostasis

B3.4 Humans and the environment

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B3.1 Movement of molecules in and out of cells

Cells, tissues and organs in plants and animals are adapted to take up and get rid of dissolved substances.

Different conditions affect the rate of transfer.

Sometimes, energy is needed for transfer to take place.

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B3.2 Transport systems in plants and animals

In animals, substances are transported around the body by the circulatory system. This organ system is made up of the heart, the blood vessels and the blood.

Substances like oxygen and glucose are transported from the lungs or small intestine to the cells where they are needed for respiration.

Waste products, like carbon dioxide, are transported from the cells to where they are removed from the body, like the lungs.

Modern developments in biomedical and technological research have enabled us to intervene when the circulatory system is not working effectively.

Plants have 2 transport systems:

  • Xylem - water
  • Phloem - nutrients
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The blood system

The heart is an organ that pumps blood around the body. Much of its wall is made from muscle tissue and it is made up of 4 chambers: left and right atria and left and right ventricles.

  • Blood enters the atria via the vena cava (right) or pulmonary vein (left)
  • The atria contract and blood is forced into the ventricles.
  • Ventricles contract and force blood out of the heart via the pulmonary artery (right) or aorta (left)
  • Valves in veins ensure that blood flows in the right direction.
  • Blood flows from the heart to the cells in arteries and returns to the heart in veins.
  • The heart is known as a double circulation system because it has 2 seperate systems, one for the lungs and another for all the other organs.

Arteries have thick walls of muscle and elastic fibre. Veins have thinner walls and valves. Stents can be used to keep arteries open if they begin to narrow.Blood flows through narrow, thinwalled blood vessels called capillaries. Substances needed by the cells pass out of the bloos and substances produced by the cells pass into the blood through the wall of the capilaries.

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The blood

The blood is a tissue made up of red blood cells, white blood cells and platelets, suspended in plasma. Blood plasma transports:

  • carbon dioxide - from organs to lungs
  • soluble products of digestion - from small intestine to cells
  • urea - from liver to kidneys

Red blood cells transport oxygen form the lungs to the cells. They have no nucleus so that they can pack in more of a red pigment called haemoglobin. Haemoglobin combines with oxygen to form oxyhaemoglobin. In other organs, oxyhaemoglobin splits into haemoglobin and oxygen.

White blood cells have a nucleus and form part of the body's defence system (immune system) against pathogens.

Platelets are small fragments of cells that also have no nucleus. They help the blood to clot at the site of a wound.

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Transport systems in plants

Flowering plants have 2 separate transport systems:

  • xylem tissue - water and mineral ions from roots to stem and leaves
  • phloem tissure - dissolved sugars from leaves to the rest of the plant
  • the transpiration system is the movement of water through the xylem and out of the leaves
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B3.3 Homeostasis

The internal environment of our bodies needs to be kept relatively constant. Things that need to be kept constant include:

  • water content
  • ion content
  • blood glucose levels
  • body temperature

The kidneys are important in keeping the water and ion content and the blood glucose levels constant. They filter the blood and keep only what is needed, excreting the rest as urine. If a person's kidneys are diseased, the result can be death, as tosic substances buuild up in the blood. They can be treated with kidney dialysis or have a kidney transplant.

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Removal of waste and water control

Waste products: carbon dioxide (respiration, removed via lungs), urea (produced in the liver from the breakdown of amino acids, removed by the kidneys,  excreted as urine).

Urine is produced by the kidneys, they:

  • filter the blood
  • reabsorb all the sugar and the ions and water that is needed by the body
  • release urea, excess ions and water as urine
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Temperature Control

The thermoregulatory centre in the brain monitors body temperature. It has receptors that are sensitive to the temperature of the blood flowing through the brain. Temperature receptors in the skin also send impulses to the brain about skin temperature.

If the body temperature is too high:

  • Blood capillaries close to the skin dilate increasing blood flow so that more heat is lost
  • Sweat glands produce more sweat which cools the body as it evaporates

If the body temperature is too low:

  • Blood vessels close to the skin constrict reducing blood flow so that less heat is lost
  • Muscles 'shiver' - they need to respire to contract, this releases some energy in the form of heat, to warm the body

When it is hot, more water is lost through sweating. This water has to be replaced in food and drink.

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Sugar control

The pancreas control the blood sugar concentration.

  • To lower sugar levels, the hormone insulin is produced - this allows glucose to move from the blood into the cells as glycogen
  • When sugar levels get too low, the hormone glucagon is produced - this allows glycogen to be converted back into glucose and released into the blood

If the pancreas does not produce enough insulin, the person's blood glucose concentraion might rise to a high level. This can lead to Type 1 Diabetes.

Type 1 Diabetes can be controlled by paying attention to diet and exercise and by injecting insulin into the blood.

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Kidney Dialysis and Kidney Transplants

A dialysis machine:

  • restores the concentrations of dissolved substances in the blood to normal levels
  • will keep the patient alive, but it can limit their freedom and they will have to have the treatment a few times a week for a few hours
  • blood flows through a partially permeable membrane. The dialysis fluid has the same concentrations of useful subtances as the blood ensuring that glucose and useful mineral ions are not lost. Urea passes into the dialysis fluid.

A kidney transplant gives the patient much more freedom, but there is the risk that the kidney will be rejected by the body by the immune system. Antigens are on the surface of cells, anitbodies may attasc the anitgens of the donor organ bcause they don't recognise them as a part of the recipient's body.

To prevent rejection:

  • A donor kidney with a similar tissue-type is used
  • The recipient is treated with drugs that suppress the immune system (but also makes them more susceptible to other illness)
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