Response and Regulation

• Homeostasis

  The maintenance of a stable internal environment in the body despite fluctuations in internal and external conditions
• Importance of homeostasis

  • To ensure optimum conditions for enzymes and cellular processes in the body
• Hormones

  Cell signalling molecules produced by endocrine glands and released into the blood, which travel to a target organ and bind, initiating a response
• Conditions within the body that must be controlled by homeostasis

  • Temperature
  • Blood glucose concentration
  • Water levels
• Why body temperature must be controlled

  • Enzymes work best at their optimum temperature
  • Deviations from this optimum temperature decrease the rate of enzyme-controlled reactions
• Responses of the body to an increase in temperature above 37°C

  1. Vasodilation

  2. Sweating

  3. Erector muscles relax, hairs lie flat
• Structures that produce sweat

  Sweat glands
• How sweating helps to reduce body temperature

  Heat energy is used to evaporate sweat. Increased heat transfer from the skin to the environment decreases body temperature.
• Vasodilation

  Dilation of blood vessels near the skin surface, causing blood to flow closer to the skin surface and greater heat loss to the surroundings
• Responses of the body to a decrease in temperature below 37°C

  1. Vasoconstriction

  2. Shivering

  3. Hair erector muscles contract

  4. Little sweat is produced
• How shivering helps to increase body temperature

  Involuntary contraction of muscles generates heat energy from respiration
• How contraction of hair erector muscles helps to increase body temperature

  Hairs stand on end creating pockets of air between hairs and a layer of insulation
• Vasoconstriction

  Constriction of blood vessels near skin surface, causing less blood to flow close to the skin surface and less heat loss to the surroundings
• Why blood glucose concentrations must be controlled

  • If too high, the body risks dehydration
  • If too low, the rate of cellular respiration decreases
• How blood glucose concentrations are controlled

  Blood glucose is controlled by insulin (a hormone) which is secreted by the pancreas
• Role of insulin in the regulation of blood sugar levels

  • Causes liver and muscle cells to increase their uptake of glucose from the blood
  • Glucose is converted into glycogen, a storage molecule
• Role of glucagon in the regulation of blood sugar levels (higher)

  • Causes the breakdown of glycogen to glucose in the liver
  • Glucose is released into the blood
• Control of blood glucose concentration is an example of (higher)

  Negative feedback
• What happens when blood glucose concentrations become too high (higher)

  1. Blood glucose concentration increases above a set point

  2. Pancreas secretes insulin and stops producing glucagon

  3. Liver cells convert glucose to glycogen which is stored

  4. Blood glucose concentration decreases, returning to normal level
• What happens when blood glucose concentrations become too low (higher)

  1. Blood glucose concentration decreases below a set point

  2. Pancreas secretes glucagon and stops producing insulin

  3. Liver cells convert glycogen into glucose which is released into blood

  4. Blood glucose concentration increases, returning to normal level
• Diabetes


  A condition where the homeostatic control of blood glucose levels stops working
• Types of diabetes

  • Type 1 diabetes
  • Type 2 diabetes
• Cause of type 1 diabetes

  Immune system attacks and destroys insulin-producing cells, so the pancreas does not produce enough insulin
• How type 1 diabetes is treated

  1. Daily insulin injections at meal times

  2. Managing diet (limiting intake of refined sugars)

  3. Regularly testing blood glucose levels
• Cause of type 2 diabetes

  Person develops insulin resistance (often due to obesity)
• How type 2 diabetes is treated

  1. Managing diet (limiting intake of refined sugars)

  2. Regular exercise

  3. Drugs e.g. metformin
• Drug


  A substance that affects chemical processes within the body
• Effects of alcohol on the body

  • Decreased reaction time
  • Addictive
  • Causes liver damage, cardiovascular disease etc.
• Plant tropisms


  The growth response of a plant to a stimulus
• Positive tropism


  The growth of a plant towards a stimulus
• Negative tropism


  The growth of a plant away from a stimulus
• Two main types of plant tropism

  • Phototropism
  • Gravitropism
• Phototropism

  A plant's growth response to light
• Plant shoots

  • Positively phototropic, grow towards the light
• Plant roots

  • Negatively phototropic, grow away from the light
• Gravitropism

  A plant's growth response to gravity
• Plant roots

  • Positively gravitropic, grow downwards towards gravity
• Plant shoots

  • Negatively gravitropic, grow upwards away from gravity
• Auxins

  A group of plant hormones involved in plant tropisms, control growth in plant roots and shoot tips
• Auxins are produced in root and shoot tips