Biology - Messages in the Body (AQA Syllabus A)

In GCSE Science students will look at how organisms use nerves and hormones. This is the second of five quizzes on that topic and it looks in particular at how nerves and hormones carry messages around the body.

The nervous system enables humans to react to their surroundings and coordinate their behaviour. Receptors detect stimuli outside the body and relay messages to the central nervous system and brain for processing. Certain actions are voluntary, like walking or waving your hand, and are dealt with by the brain. Others are automatic and save the body from harm e.g. pulling your hand away from fire or your pupils closing up when a light is too bright. These are called reflexes and the messages from the sensors are processed in the central nervous system without needing the brain. Other messages are automatic too, like the ones telling the heart muscles to contract and relax. These are autonomous and continue all of the time.

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The body also needs to control its temperature, ion content, water content and blood sugar levels. The nervous system plays its part but most of the control is done by hormones. They have a longer lasting effect and act more widely than a nerve or group of nerves. Hormones are secreted by glands and can spread throughout the body in the bloodstream. It is therefore possible for hormones to reach every cell in the body. If a cell has the right receptor chemicals, a hormone molecule will attach itself to the cell and make the cell carry out a specific action.

For example, if the blood sugar (glucose) level is high, the pancreas has cells that secrete the hormone insulin. This mixes with the blood plasma and is distributed around the body. The target organ for insulin is the liver, where glucose is changed into glycogen which can be stored and used to replenish blood sugars when the level is low. So you can see how nerves and hormones are used to carry messages around our bodies.

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  1. When you are too hot or too cold, the brain sends nerve messages to the skin to do several things. Which one of the following is not a response used to control body temperature?
    Raising the hairs will trap air close to the surface of the skin. Trapped air is a good insulator. Opening the blood vessels gets rid of excess heat carried by the blood, that is why you look 'flushed' during and after exercise
  2. What are the missing words in the correct order from this description of a reflex action?

    1. A ______ detects a stimulus.
    2. A sensory neurone sends impulses to a ______ neurone.
    3. A motor _______ sends impulses to an effector.
    4. An effector produces a ________.
    The relay neurone bypasses the brain, ensuring that the reflex action occurs as quickly as possible
  3. The central nervous system in humans is made up from what?
    When a receptor is stimulated it sends a signal along the nerve cells - neurones - to the brain which co-ordinates the response, unless it is a reflex action
  4. The messages are transmitted across the gap from one nerve cell to another. Which of the following pairs of words give the name for the gap and how the messages are transferred from one nerve cell to the next?
    There are two things that could lead you to the wrong answer here. Many students confuse dendrite and synapse. The signals travel through nerve cells as electrical impulses but between nerve cells by chemicals called neurotransmitters. Many students assume that the the messages passing through the nervous sytem are entirely electrical
  5. In a reflex action, what do we call the type of neurone which allows the message from the receptor to go directly to the effector without needing to go to the brain first?
    This makes reflex actions much faster, helping to protect the body from damage
  6. Which of the following statements about the nervous system and hormones is incorrect?
    A lot of reading for that one! The nervous system is much faster than the endocrine system (hormone system) because the messages travel through the nerves as electrical impulses
  7. Why is it important to maintain an even temperature of 37oC for the human body?
    The body can work at higher or lower temperatures but only for a while. If the temperature of the body drops to below 35oC, hypothermia sets in, when it drops below 28oC it is very serious and death can occur. A fever is when the body temperature is higher than normal, fevers of over 41.5oC can be fatal but a fever is usually a response to illness and will pass as your body recovers
  8. The main method of controlling the amount of water in the body is via the kidneys. How does this happen?
    The hormone that regulates the water content of the blood is ADH. It is made in the pituitary gland and the target organ is the kidneys. A nerve impulse is used but it is between the hypothalamus and the pituitary gland which is why the second option is incorrect
  9. Which of the following statements about insulin is correct?
    People with diabetes either don't produce insulin, don't produce enough insulin or their insulin receptors don't work, so their blood sugar levels can drop too low or go too high. Some of these people can control it by careful eating whilst others need to have insulin injections. Most insulin for diabetics to use is now made from genetically modified bacteria rather than taken from cow or pig pancreases, as it used to be
  10. What do we call the type of neurone that sends a message from the central nervous system to a gland?
    The message tells the gland to secrete a hormone

Author: Kev Woodward

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