6 human physiology (SL + HL)

Question 1

explain principles of vaccination [8]

Answer 1

• vaccination is injecting weakened form of pathogen
• antigens in the vaccine trigger antibody production, leading to specific immunity
• phagocytes engulf pathogen by phagocytosis
• phagocytes become antigen-presenting cells and activate T-helper
• activated T-helper activates the specific B-lymphocyte
• B-lymphocyte divide to form plasma cell and memory cell
• plasma cells produce specific antibodies
• antibody production is slow upon first vaccination
• antibody production is faster after second vaccination due to memory cells

Question 2

how are sperm produced from diploid cells and how this can be sustained over adult life [4]

Answer 2

• diploid spermatogonia divide by mitosis, giving continuous supply
• spermatogonia enlarge forming 1˚ spermatocyte
• 1˚ spermatocyte undergo meiosis I, forming 2˚ spermatocytes that are haploid
• 2˚ spermatocyte undergo meiosis II, forming spermatids
• spermatids are nurtured by Sertoli cells and differentiate to form sperm

Question 3

outline digestion, absorption and assimilation of proteins in humans [6]

Answer 3

digestion
- large molecules need to be digested into smaller molecules so can be absorbed
- achieved by enzymes that digest proteins into amino acids
- pepsin in stomach under acidic conditions, trypsin in small intestine under basic conditions

absorption
- A.A. absorbed by active transport
- into capillaries via microvilli in small intestine

assimilation
- assimilation is when amino acids become part of cell
- e.g. protein synthesis using A.A. in ribosome

Question 4

explain how skeletal muscle contracts, including interaction of actin and myosin [8]

Answer 4

• motor neuron sends electrical impulse to muscle fiber
• trigger Ca2+ ions release from sarcoplasmic reticulum
• Ca2+ ions bind to troponin, tropomyosin moves and exposes actin binding sites
• myosin head binds to actin, forming cross bridge
• ATP molecule binds to myosin, cross bridge broken, causing myosin head to bend
• myosin head binds to new actin site further away from center
• power stroke: ADP + Pi release, myosin head pushes actin towards center
• leads to sarcomere shortening and muscle contraction