responses

• Hormones are chemical messengers that travel through the blood to target cells, where they bind with receptors on the cell surface or inside the cell.
• Control mechanisms

  Set point is monitored by receptors, controllers analyse information from different receptors and decide on the best course of action, effectors bring about the changes needed to return to the set point, feedback loop informs the receptor about the changes brought about by the effector
• How to lose heat

  1. Evaporation of water

  2. Heat loss to the environment through conduction, convection, and radiation
• Regulation of body temperature in Endotherms

  Most heat gained through internal metabolic activities
• Losing heat in warm environments

  Large surface area to volume ratio, larger extremities, light coloured fur to reflect heat, vasodilation, lower body hair, behavioural mechanisms like seeking shade, burrows, increased sweating
• Homeostasis involves

  Maintaining the volume, chemical make up, and other factors of blood and tissue fluid within restricted limits and set-points
• Ectotherms


  • Obtain most heat from the external environment
• Endotherms

  • Birds
  • Mammals
• How to gain heat

  1. Metabolism of food during respiration

  2. Heat gain from the environment through conduction, convection, and radiation
• Homeostasis


  The maintenance of a constant internal environment
• Importance of homeostasis


  • Enzymes and other proteins are sensitive to changes in pH and temperature
  • Water potential of blood and tissue fluid should be kept constant to ensure cells do not burst or shrink due to osmosis
  • Independence of the external environment allows a wider geographical range and a greater chance of finding food and shelter
• Regulation of body temperature in Ectotherms


  Body temp fluctuates with the environment, controlled by exposure to the sun, shelter, heat from the ground, metabolic heat from respiration, colour variations to alter heat radiation
• Conserving heat in cold environments

  Small surface area to volume ratio, smaller extremities, thick fur/feathers/fat, vasoconstriction, shivering, raising hair, increased metabolic rate, behavioural mechanisms like bathing in the sun, decreased sweating
• Control of body temperature

  The hypothalamus measures the internal temperature of blood passing through it, thermoreceptors in the skin measure the external temperature, impulses are sent to the hypothalamus via the autonomic nervous system from the thermoreceptors, impulses are sent along motor neurones to effectors to conserve/lose heat
• Effectors to conserve/lose heat

  • Cold receptors in skin activate HEAT GAIN CENTRE in hypothalamus
  • Hypothalamus sends signals to effectors: vasoconstriction, shivering, hair raised, faster metabolic rate, adrenaline released
  • More heat produced and conserved
• Adrenaline

  1. Binds to specific receptors on the surface membrane of target cells, forming a hormone-receptor complex

  2. Activates an enzyme inside the cell membrane which produces a response (converts ATP to cyclic AMP - secondary messenger)

  3. Cyclic AMP then activates several other enzymes that can convert glycogen to glucose
• Insulin

  1. Beta cells in the pancreas detect an increase in glucose and release insulin

  2. Insulin binds to receptors on the plasma membrane of cells

  3. Causes a change in the tertiary structure of the glucose transport protein channels

  4. Channels change shape and open, allowing more glucose into the cell

  5. Insulin binding increases the number of carrier molecules in the membrane

  6. Activates enzymes involved in converting glucose to glycogen & fat
• Adrenaline

  1. Activates an enzyme causing glycogenolysis (converting glycogen to glucose)

  2. Inhibits enzyme for glycogenesis (creating glycogen from glucose)
• Symptoms of diabetes

  • High blood glucose level, Presence of glucose in the urine, Increased thirst/hunger, Excessive urination, Tiredness, Weight loss, Blurred vision
• Hormones and Glucose regulation

  • Hormones are produced by endocrine glands and secreted into the blood
  • Hormones are carried in the blood plasma to target cells with complementary receptors on the cell surface membrane
• Regulation of Blood Glucose

  • Too much glucose = lower blood water, potential dehydration
  • Too little glucose = cells deprived of energy
  • Blood glucose comes from: directly from the diet, glycogenolysis, gluconeogenesis
• Glucagon


  1. Alpha cells in pancreas detect a decrease in glucose and release glucagon

  2. Glucagon binds to receptors on liver cells and activates an enzyme converting glucagon to glucose

  3. Liver cells increase gluconeogenesis - conversion of amino acids & glycerol to glucose

  4. Respiration decreases so cells use up less glucose
• Type 1 diabetes
• Hormones interact using NEGATIVE FEEDBACK
• Feedback mechanisms


  Feedback loops inform the receptor of changes brought about by the effector, corrective measures being turned off to return to set point
• Type 1 diabetes

  • Develops during childhood
  • Glucose levels remain high after eating, leading to glucose secretion in urine
  • Helped with insulin injections
• Symptoms of diabetes

  • Increased thirst/hunger
  • Excessive urination
  • Tiredness
  • Weight loss
  • Blurred vision
• Type 2 diabetes

  • Developed later, usually with obesity
  • Glycoprotein receptors on cells lose responsiveness to insulin or beta cells don't produce enough insulin
  • Helped by regulating carbohydrates, exercise, and sometimes drugs
• Feedback mechanisms

  • Temperature regulation
  • Glucose regulation
• Menstrual cycle

  1. Pituitary gland produces FSH

  2. FSH stimulates follicles to grow and mature

  3. Follicles secrete oestrogen which causes the rebuilding of the uterus lining and inhibits the production of FSH and LH

  4. Follicle grows and produces more oestrogen until reaching a critical point, stimulating FSH and LH

  5. Surge in FSH and LH production causes ovulation

  6. LH stimulates the empty follicle to develop into a corpus luteum which secretes progesterone

  7. Progesterone maintains the uterus lining and inhibits the production of FSH and LH

  8. If the egg is not fertilised, the corpus luteum degenerates, no longer producing progesterone, and the uterus lining breaks down

  9. Less progesterone produced leads to FSH no longer being inhibited, and the cycle resumes
• Oestrous cycle

  1. The pituitary gland releases FSH to stimulate follicles to grow and mature and start producing oestrogen

  2. LH causes ovulation and stimulates the ovary to produce progesterone

  3. Ovaries produce oestrogen which rebuilds the uterus lining and stimulates LH production

  4. Progesterone maintains the uterus lining and inhibits FSH production
• Homeostatic mechanisms involve negative feedback loops to maintain stable internal conditions despite external changes.
• Components of DNA nucleotides

  • Deoxyribose, phosphate group, organic bases adenine, cytosine, guanine, thymine
• Components of RNA nucleotides


  • Ribose, phosphate group, organic bases adenine, cytosine, guanine, uracil
• Nucleotides


  Consist of pentose (5 carbon sugar), nitrogen-containing organic base, and a phosphate group
• Nucleotides join together


  Phosphodiester bonds formed in condensation reactions
• DNA molecule


  • Double helix composed of two polynucleotides joined by hydrogen bonds between complementary bases
• RNA molecule


  • Relatively short polynucleotide chain
• Genetic code


  Order of bases on DNA, consists of triplets coding for amino acids (codons), genes code for amino acids in polypeptide chains
• Non-coding sections of DNA are called introns, coding regions are called exons