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Unit 3 - Blood

In this GCSE Biology quiz we examine blood and look at its components - plasma, red and white blood cells, and platelets. We learn about the functions of these components and also look at the different types of blood vessels - arteries, veins and capillaries.

Blood is the delivery and waste collection system of your body. It also protects you against invading pathogens. It is pumped round the body by the heart at high pressure through the arteries and returns at lower pressure via the veins. Between the two, blood flows through capillaries which allow it to reach every single cell in your body.

Blood consists of a fluid called plasma in which red blood cells, white blood cells and platelets are suspended. Blood plasma also transports dissolved chemicals; carbon dioxide from the organs to the lungs, hormones, soluble products of digestion from the small intestine and urea from the liver to the kidneys.

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Red blood cells are extremely small so that they can pass through the capillaries. The contain an amazing protein called haemoglobin. This can pick up oxygen where the concentration is high (in the lungs) and release it where the concentration is low (as it passes cells). Oxygen is important for aerobic respiration. Red blood cells are the only cells in your body not to have a nucleus.

The platelets are there to help your blood to clot when you cut yourself. They combine with substances in the plasma called clotting factors to make the blood much thicker and stickier. There are some people (heamophiliacs) who don't have these clotting factors and it is possible that they could bleed to death from even a minor cut.

The white blood cells are your body's first line of defence. There are hundreds of different types, each with a specific job to do. Some engulf the invading cells and slowly digest them, dying in the process and forming pus at the site of the infection. Others produce antibodies that either destroy or render the pathogen inactive and some produce antitoxins. They are triggered by specific antigens which are protein molecules on the surface of the pathogens. When an antigen is detected, the matching type of white blood cell rapidly multiplies to deal with the pathogen. Your immune system contains specialised cells that learn and remember how to deal with the different antigens, which is the reason why vaccination works.

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  1. Which of the following is another name for a red blood cell?
    They contain the protein haemoglobin which carries oxygen round the body
  2. Most arteries carry blood which is...
    Textbooks use red and blue in diagrams to show oxygenated (red) and deoxygenated (blue) blood. The blood in arteries is just a different shade of red compared with the blood inside veins
  3. Plasma carries carbon dioxide away from the...
    The carbon dioxide is a waste product of respiration
  4. Which parts of the circulatory system have thin walls, allowing diffusion of gases?
    This allows the exchange of carbon dioxide and oxygen with the blood
  5. Platelets are involved in blood...
    They combine with chemicals in the blood plasma called clotting factors
  6. Arteries carry blood in which direction?
    The aorta and pulmonary arteries carry blood away from the heart
  7. What are the smallest blood vessels, requiring a microscope in order to be seen?
    They ensure that every cell in your body receives a supply of blood
  8. Red blood cells have a special shape to allow maximum...
    Having a large surface area to volume ratio allows the oxygen to be absorbed more efficiently in the lungs
  9. Blood plasma is...
    It has a pale straw colour
  10. Valves preventing the backflow of blood and are found in which of the following?
    Veins contain valves. Exceptions are the semi lunar valves at the top of the heart inside the aorta and pulmonary artery. These prevent backflow of blood back into the heart

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