Question
Water is the medium of life.
a. Outline how hydrogen bonds form in water.[3]
b. Describe the processes that cause water to move from the roots of plants to their leaves.[4]
c. Explain the role of the kidney in osmoregulation.[8]
▶️Answer/Explanation
Ans:
a. a. water (molecules) are polar/dipolar/have partially positive and negative poles/have \(\bar{\delta}+\) and \(\bar{\delta}\)-;
b. attraction/bonding between positive and negative (poles);
c. hydrogen bond formed between hydrogen and oxygen; Reject if \(\mathrm{H}\) and \(\mathrm{O}\) in same molecule.
d. bond/attraction between different water molecules/intermolecular;
Marks can be awarded in an annotated diagram.
Reject answers stating or implying that there are whole positive or negative charges for mpa.
b. a. water moved/transported in xylem vessels;
b. transported under tension/suction/pulled up (in xylem vessels);
c. transpiration/loss of water (vapour) generates pulling forces/low pressure/tension;
d. tension/pull generated when water evaporates from cell walls (in mesophyll);
e. transpiration is loss of water vapour from leaf (surface)/stomata;
f. cohesivity/cohesion in water due to hydrogen bonding/attractions between water molecules;
g. cohesion/WTTE so chain/column of water (molecules) doesn’t break/remains continuous;
h. transpiration stream is a column of/flow of water in xylem from roots to leaves;
Do not award marks for absorption of water by roots.
c. a. osmoregulation is regulation of water and solute/salt balance/solute concentrations;
b. nephron (is the functional unit of the kidney/osmoregulates);
c. ultrafiltration in glomerulus / glomerular filtrate collected by Bowman’s capsule;
d. loop of Henle establishes/maintains hypertonic conditions in medulla;
e. osmosis/reabsorption of water (from filtrate) in the collecting duct;
f. brain/hypothalamus monitors blood solute concentration / pituitary secretes ADH;
g. ADH secreted when solute concentration of blood is too high/hypertonic/when dehydrated;
h. ADH increases permeability of collecting duct to water;
i. ADH causes more aquaporins (in membranes of collecting duct wall cells);
j. more water reabsorbed resulting in more concentrated/hypertonic urine/less volume of urine;
k. less/no ADH secreted when solute concentration (of blood) is too low/hypotonic;
I. less water reabsorbed resulting in dilute/hypotonic urine/large volume of urine;
Reject ‘water balance’ and ‘water concentration’ for mpa.
Question
Describe the role of \(\mathrm{ADH}\) in human osmoregulation.
▶️Answer/Explanation
Ans:
a. secreted when blood/plasma is hypertonic/too concentrated/water content too low
b. makes walls of collecting duct/distal convoluted tubule «more» permeable to water
c. more aquaporins in membranes «of collecting duct cells»
d. more water reabsorbed from filtrate/from urine/more water returned to blood
e. small volume of concentrated urine excreted[Max 3 Marks]
Question
a. Label region X and structure Y on the diagram of the kidney.
b. Distinguish between osmoregulators and osmoconformers.[2]
▶️Answer/Explanation
Ans:
a. X: cortex \(\checkmark\)
Y: ureter \(\sqrt{ }\)
b. a. concentration constant inside osmoregulators versus variable inside osmoconformers \(\checkmark\)
b. internal solute concentration can differ from the external environment in osmoregulators versus same/equal in osmoconformers OR
osmoregulators are independent of the external environment in solute concentration versus osmoconformers are tied to it \(\checkmark\)
c. birds/mammals/humans/freshwater fish are osmoregulators versus starfish/mussels/crabs/jellyfish/sea squirts/squid/sharks are