topic 6 biology

• Neonatal diabetes is a disease that affects newly born children. The disease is caused by a change in the amino acid sequence of insulin. This change prevents insulin binding to its receptor. Explain why this change prevents insulin binding to its receptor. (2 marks)

  Change in tertiary structure of insulin

  No longer complementary to receptor
• Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes. (3 marks)


  High glucose conc in filtrate

  Some of it not reabsorbed at proximal convoluted tubule

  As channel proteins fully saturated
• Describe the role of glucagon in gluconeogenesis. (2 marks)

  Activates enzymes

  Which convert glycerol/fatty acids/ amino acids into glucose
• Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration (3 mark)

  Less ATP converted to cyclic AMP

  Less protein kinase activated

  Less glycogenolysis
• Each year, a few people with type I diabetes are given a pancreas transplant. Pancreas transplants are not used to treat people with type II diabetes. Give two reasons why pancreas transplants are not used for the treatment of type II diabetes. (2 marks)

  Their glycoproteins have reduced responsiveness to insulin

  Controlled by diet or exercise
• Scientists investigated the control of blood glucose concentration in mice. They kept a group of normal mice without food for 48 hours. After 48 hours, the blood glucose concentrations of the mice were the same as at the start of the experiment. Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours. (3 marks)

  glucagon released

  activates enzymes for formation of glucose

  from non carbohydrates.
• A diabetic person and a non-diabetic person each ate the same amount of glucose. One hour later, the glucose concentration in the blood of the diabetic person was higher than that of the non-diabetic person. Explain why. (3)

  Diabetic person lacks insulin

  so less glucose uptake by cells

  Less glycogenesis
• The urine of a non-diabetic person does not contain glucose. Explain why. (2)

  All the glucose is reabsorbed from filtrate into blood

  at PCT
• Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours. (3)

  Glucagon released

  Causing conversion of glycogen to glucose in liver cells

  Gluconeogenesis, forming glucose from non carbohydrates
• Binding of insulin leads to an increase in the rate of respiration in cells such as osteoblasts.

  Explain how. (2)

  Insulin causes increase in number of glucose channel proteins

  More glucose enters cell
• Define negative feedback

  Stimulus causes corrective measures to be turned off. System is returned to original level.
• Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process?

  1. baroreceptors detect rise in blood pressure
  2. they send impulses to medulla
  3. more impulses are sent to the SAN by parasympathetic
• When the heart beats, both ventricles contract at the same time.Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN?

  1. Electrical activity only through Bundle of His2. Wave of electrical activity passes over / through both ventricles at the same time
• What is a stimulus?

  Detectable change in the environment
• Tropism

  • when plants respond to light and gravity via growth
  • controlled by specific growth factors eg. IAA
• IAA

  • controls cell elongation in shoots and inhibits in roots
  • made in tips, roots and shoots
• Describe positive phototropism?

  1. shoot tip cells produce IAA
  2. IAA diffuses to other cells
  3. IAA diffuses towards shaded sided and cases cell elongation
• Taxes:

  • organism moves towards (positive) or away (negative) from stimuli
• Kinesis:

  • Organism changes speed and rate of change of direction
  • Positive: Increases rate of change of direction to stay in area
  • Negative: decreases rate of change of direction to stay in a a relative straight line
• What are 3 examples of receptors?

  1. Pacinian corpuscle
  2. Rods
  3. Cones
• What is a pacinian corpuscle?

  Mechanoreceptor found in skin which respond to pressure.

  Structure: cocentric rings of tissue surrounding sensory neurone
• How is a generator potenital created in pacinian corpuscle?

  1. Pressure is applied (stimulus)
  2. This deforms neurone plasma membrane
  3. Stretches sodium ion channels
  4. Generator potential created
• What part of the brain controls heart rate?

  Medulla oblongata
• How does the heart rate change when there is a higher conc of carbon dioxide?

  1. Chemoreceptors detect change in pH
  2. More impulses sent via sympathetic nervous system to SAN
  3. Heart rate increases
  4. Carbon dioxide diffuses into alveoli
• How does heart rate change when there is high blood pressure?

  1. Baroreceptors detect high blood pressure
  2. More impulses sent via parasympathetic nervous system
  3. Heart rate decreases
• Where are chemoreceptors and baroreceptors found?

  carotid artery and aorta
• SAN (sinoatrial node):

  • located in rate atrium
  • known as pacemaker
  • transmits waves of electrical activity along atria at regular intervals
• How is AVN and SAN involved in the change of heart rate?

  1. Atria contracts and SAN releases wave of depolarisation
  2. AVN releases another wave of depolarisation
  3. Bundle of His conducts wave down septum and Purkyne fibres
  4. Short delay before ventricle contracts
  5. cells repolarise and cardiac muscle relaxes
• What are the factors that affect speed of nerve impulses?

  1. Myelination and saltatory conduction
  2. Axon diameter
  3. Temperature
• explain how the banding pattern is shown

  1. light band / I band only actin
  2. H zone only myosin
  3. Overlapping region actin and myosin

  
• Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction

  1. tropomyosin moved from binding site
  2. actin and myosin do not bind to form a cross bridge
  3. myosin head does not move
• In muscles, pyruvate is converted to lactate during prolonged exercise. Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration

  1. regenerates NAD
  2. so glycolysis continues
• Label the skeletal muscle below

  label

  A) M line/ myosin filament

  B) mitochindrion

  C) myofibril

  
• During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction. Why?

  1. Low pH changes shape of calcium ion receptors
  2. Fewer calcium ions bind to tropomyosin
  3. Fewer tropomyosin molecules move away so less binding sites on actin revealed
  4. Fewer cross bridges formed
• Describe the roles of calcium ions and ATP in the contraction of a myofibril

  1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
  2. This causes movement of tropomyosin on actin
  3. Exposure of the binding sites on the actin
  4. Myosin heads attach to binding sites on actin
  5. Hydrolysis of ATP causes myosin heads to bend;
  6. Bending pulls actin molecules
  7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach
• ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use

  • Releases relatively small amount of energy instantaneously
  • Phosphorylates other compounds, making them more reactive
  • Can be rapidly re-synthesised
  • Not lost from cells
• What is the role of ATP in myofibril contraction?

  1. breaks binding of myosin to actin
  2. provides energy to move myosin head
• AS is an inherited disorder that affects kidney glomeruli of both men and women. Affected individuals have proteinuria (high quantities of protein in their urine) Suggest how AS could cause proteinuria?

  1. damages basement membrane
  2. proteins can pass into filtrate
• Describe how ultrafiltration occurs in a glomerulus

  1. high hydrostatic pressure
  2. glucose, water and ions forced out pores in endothelium
  3. through basement membrane
• Why does conc of urine increase as medulla thickness increases?

  1. Thicker medulla means a longer loop of Henle
  2. Increase in sodium ion conc in medulla
  3. Water potential gradient maintained for longer so more water reabsorbed