chapter 6

• Factors affecting water balance in vascular plants (transpiration rate)


  • Temperature
  • Air movement (wind)
  • Humidity
  • Light intensity
• Effect of temperature on transpiration rate

  1. High temperatures: increase in energy of water molecules leads to increase in evaporation rate

  2. Low temperatures: decrease in energy of water molecules leads to decrease in evaporation rate
• Effect of air movement on transpiration rate


  1. High air flow: water vapour from outside the leaf is quickly removed, creating a large concentration gradient from inside to outside the leaf, increasing transpiration rate

  2. Low air flow: water vapour accumulates outside the leaf, decreasing the concentration gradient and reducing transpiration rate
• Effect of humidity on transpiration rate


  1. Low humidity: lower concentration of water molecules outside the leaf, higher concentration gradient, increased transpiration rate

  2. High humidity: higher concentration of water vapour outside the leaf, lower concentration gradient, decreased transpiration rate
• Effect of light intensity on transpiration rate


  Increased light intensity stimulates stomata opening, allowing more water vapour to evaporate, increasing transpiration rate
• Homeostasis


  The body's ability to maintain a stable internal environment within narrow limits
• Homeothermy


  The body's internal thermostat that maintains a constant body temperature
• Physiological adaptations to high body temperature


  1. Sweating

  2. Panting

  3. Vasodilation of arterioles
• Physiological adaptations to low body temperature


  1. Shivering of skeletal muscles

  2. Vasoconstriction of blood vessels

  3. Contraction of arrector pili muscles
• Behavioural adaptations


  Homeotherms use behaviours to help regulate body temperature
• Animals in hot environments tend to have a large surface area to volume ratio, while animals in cold environments tend to have a small surface area to volume ratio
• Glycogen


  Insoluble glucose polymer used to store glucose in cells
• Islets of Langerhans


  Endocrine tissue in the pancreas that measures blood glucose and releases insulin and glucagon
• Insulin


  Hormone secreted by beta cells that targets the liver, skeletal muscle and other cells to regulate blood glucose
• Glucagon


  Hormone secreted by alpha cells that targets the liver to regulate blood glucose
• ADH (anti-diuretic hormone)


  Peptide hormone released from the posterior pituitary that targets the collecting tubules in the nephron to increase water reabsorption
• Most water loss from the body cannot be regulated, but the amount lost in urine can
• Diabetes is a failure in the regulation of glucose uptake by cells
• Early signs of diabetes


  • Frequent urination
  • Sweet smelling urine/sweat
  • Increased thirst
  • Increased hunger
  • Fatigue
• Untreated diabetes can cause ketoacidosis, damage to blood vessels, kidneys, nerves, and death
• Hypoglycaemia


  Blood sugar level that is below normal
• Signs of hypoglycaemia


  • Clumsiness
  • Trouble talking
  • Confusion
  • Loss of consciousness
• Reactive hypoglycaemia


  Sudden spike in blood glucose level caused by eating a very carbohydrate-rich meal
• Hyperthyroidism


  Condition resulting from an overactive thyroid gland producing excess thyroxine
• The most common cause of hyperthyroidism is an autoimmune disorder called Graves' disease
• Graves' disease


  Autoimmune disorder where antibodies mistakenly bind to and stimulate TSH receptors on thyroid cells