Contains answers for all LAQs from topic 11 in IB Biology HL from past papers between May 2016 to November 2022; full processes written out and checked against markschemes.
Describe how monoclonal antibodies are produced. [5 marks]
- Antigen producing antibody is injected into a mouse
- Plasma B cells are formed to produce the desired antibody
- The B cells are removed and combined with a myeloma cell, which forms a hybridoma
- The hybridoma cell producing the correct antibody is removed
- It is then allowed to divide and is cultured
- Once a large quantity of antibodies is made, it can be used in treatment
Humans need to balance water and solute concentrations and also excrete nitrogenous wastes.
Explain how the different parts of the kidney carry out these processes. [7 marks]
− Blood is gathered at the glomerulus and enters the bowman’s capsule via the wide afferent
arteriole
− Using high pressure, molecules in the blood are forced out as solute, leaving blood and
plasma proteins to leave via the efferent arteriole
− In the proximal convoluted tubule, much of the solute is reabsorbed
− The remaining solute containing salts and water moves to the loop of Henlé
− The Loop of Henlé is initially only permeable to water, so water diffuses by osmosis into the
interstitial space, leaving a concentrated salt solution of sodium and chloride ions
− The Loop then becomes permeable to ions to allow the sodium and chloride to diffuse into
the interstitial space to rebalance the concentration gradient
− The Loop of Henlé uses a counter current multiplier to constantly refresh the concentration
gradient for more complete diffusion
− The remaining solute moves to the distal convoluted tubule, past here the composition of
the solute cannot be changed, only its water concentration. A final check is performed.
− The solute moves to the collecting duct where it can move to the ureter. ADH regulates the
dilution of the urine based on the amount of water available in the body and how much
needs to be absorbed
Describe adaptations in mammals living in desert ecosystems to maintain osmolarity in their
bodies. [4 marks]
− Increase levels of ADH to increase permeability and lower urine output
− Thicker skin to reduce evaporation
− Longer Loop of Henlé to reabsorb more water
− Reduced sweat
Outline how sperm are produced from diploid cells in the testis and how this production can be
sustained over many decades of adult life. [4 marks]
- Sperm are produced in the seminiferous tubules
- Spermatogonia are diploid cells
- Spermatogonia enlarge to form primary spermatocytes
- They undergo the first meiotic division to form secondary spermatocytes, which are haploid
- Secondary spermatocytes undergo second meiotic division to form spermatids
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