Question
Feedback mechanisms are used in living organisms both to promote and respond to change.
(a) Outline the role of ADH in osmoregulation.
(b) Explain the regulation of metabolic pathways by end-product inhibition.
(c) Describe the hormone feedback mechanisms that help to prepare a woman’s body for
pregnancy, sustain the pregnancy and then give birth.
Answer/Explanation
Answer:
(a)
a. ADH (secreted by pituitary) if body/blood is dehydrated/hypertonic/has high solute concentration;
b. more aquaporins / aquaporins open (in collecting duct);
c. collecting duct more permeable to water/reabsorbs more water (from filtrate/urine);
d. water reabsorbed by osmosis/water reabsorbed because medulla is hypertonic;
e. (reabsorbed) water passes (from filtrate) to blood / blood solute concentration reduced;
f. less water lost in urine / smaller volume of (more concentrated) urine;
g. negative feedback / less/no ADH secreted when blood solute concentration returns to normal;
(b)
a. final product in pathway acts as an inhibitor/blocks (reaction)/slows (reaction);
b. first/early/earlier enzyme (in pathway is inhibited);
c. non-competitive / binds at allosteric site / causes active site to change;
d. production of end-product reduced/paused when there is an excess;
e. isoleucine inhibits enzyme using threonine as substrate at start of pathway to isoleucine;
f. negative feedback / production restarts when end-product used up/concentration drops;
(c) Preparing the woman’s body for pregnancy
a. FSH stimulates estrogen secretion (by the developing follicle);
b. estrogen increases FSH receptors so boosting estrogen production/so causing positive feedback;
c. estrogen stimulates repair/thickening of the endometrium/uterus lining;
d. high levels of estrogen stimulate LH production/inhibit FSH secretion (negative feedback);
e. LH (surge/peak) stimulates ovulation; Sustaining pregnancy
f. LH stimulates the development of corpus luteum / corpus luteum secretes progesterone;
g. progesterone inhibits FSH/LH secretion (negative feedback);
h. progesterone maintains lining of uterus/endometrium (for pregnancy/implant of embryo);
i. progesterone inhibits uterine contractions;
j. HCG (secreted by embryo) stimulates maintenance of corpus luteum; Childbirth
k. oxytocin stimulates uterine/myometrial contractions which stimulate oxytocin secretion;
l. positive feedback (mechanism used to stimulate childbirth);
Question
(a) The graph shows blood pressure changes on the left side of the heart during one heartbeat.
Identify the two parts of the circulatory system that produce traces I and II on the graph. [2]
(b)Outline the actions taken by the body to avoid infection when the skin is cut. [3]
(c) Hormones are distributed throughout the body by the blood. Outline the roles of two reproductive hormones during the menstrual cycle in women. [2]
▶️Answer/Explanation
Ans:
a I. aorta 2 II: «left» atrium
b
a. platelets/cut tissues release clotting factors Mp a requires student to identify source ofclotting factors.
b. «clotting factors» activate thrombin «from prothrombin»
c. thrombin converts fibrinogen to fibrin
d. «fibrin» forms a clot/scab/mesh that seals the cut
e. phagocytic white blood cells ingest pathogens
c
a. FSH/follicle stimulating hormone stimulates the development of follicles/follicle cell division in the ovary «to produce eggs»
b. LH/luteinizing hormone triggers ovulation/development of the corpus luteum
c. estrogen stimulates development of the uterine lining/endometrium Two different hormones must be identified. Description of role required as well as name of hormone.
d. progesterone maintains the uterine lining/endometrium OR
inhibits other hormones by negative feedback eg, FSH
e. HCG stimulates ovary to produce progesterone «in early pregnancy» f. other verifiable hormone and roles relevant to the menstrual cycle
Question
Outline how reproductive isolation can occur in an animal population.
Describe the different cell types in the seminiferous tubules that are involved in the process of spermatogenesis.
Explain the roles of specific hormones in the menstrual cycle, including positive and negative feedback mechanisms.
▶️Answer/Explanation
Markscheme
a. can be sympatric or allopatric
b. temporal isolation by members of difference populations reproducing at different times OWTTE
c. behavioural isolation by difference in courtship behaviours OWTTE
d. geographic isolation by a population being separated by river/mountain/barrier to contact
An example of a geographic barrier is required.
e. polyploidy
a. spermatogonia «2n» are undifferentiated germ cells OWTTE
b. spermatogonia mature and divide «by mitosis» into primary spermatocytes «2n»
c. primary spermatocytes divide by meiosis I into secondary spermatocytes «1n»
d. secondary spermatocytes divide by meiosis II into spermatids «1n»
e. spermatids differentiate/mature into spermatozoa/sperm
f. Sertoli/nurse cells provide nourishment/support to these developing cells
g. Leydig/interstitial cells produce testosterone
a. anterior pituitary/hypophysis secretes FSH which stimulates ovary for follicles to develop
b. follicles secrete estrogen
c. estrogen stimulates more FSH receptors on follicle cells so respond more to FSH
d. increased estrogen results in positive feedback on «anterior» pituitary
e. estrogen stimulates LH secretion
f. estrogen promotes development of endometrium/uterine lining
g. LH levels increase and cause ovulation
h. LH results in negative feedback on follicle cells/estrogen production
i. LH causes follicle to develop into corpus luteum
OR
follicle cells produce more progesterone
j. progesterone thickens the uterus lining
k. high progesterone results in negative feedback on pituitary/prevents FSH/LH secretion
l. progesterone levels drop and allow FSH secretion
m. falling progesterone leads to menstruation/degradation of uterine lining
Award [5 max] if no reference to feedback is made.
Question
Outline how and where energy is stored in plants.
Ecologists sometimes display data from an ecosystem using a diagram called a pyramid of energy. Describe what is shown in pyramids of energy.
Explain the control of body temperature in humans.
▶️Answer/Explanation
Markscheme
a. glucose (from photosynthesis) stored as starch;
b. starch stored (as granules) in chloroplast/in plastids;
c. (starch stored) in seeds/storage roots/stem tubers;
d. stored as lipids/oils;
e. (lipid/oils storage) in seeds;
f. lipids store twice as much energy per gram as starch;
a. pyramid of energy shows the flow of energy from one trophic level to the next (in a community);
b. units of pyramids of energy are energy per unit area per unit time/kJ m–2 yr –1;
c. bar width is proportional to the energy stored (in the biomass) in that trophic level;
d. the first/lowest trophic level is producers;
e. second level is primary consumers/herbivores;
f. third level of secondary consumers/carnivores;
g. only a small amount (10 to 20 %) of energy of one level is passed to the next;
h. bar width/energy stored in the trophic level decreases (proportionally) as you go up each level;
i. pyramid shows that there is a limit to the length of food chains;
Award any of the above marking points to a correctly drawn and clearly labelled pyramid.
a. normal body core temperature constant/36.5 to 37.5°C; (accept single values within this range)
b. regulated by negative feedback/homeostatic mechanisms;
c. hypothalamus is the centre of thermoregulation;
d. hypothalamus sends impulses to the body to increase/decrease temperatures;
e. release of sweat (by sweat glands in the skin) if skin temperature rises;
f. evaporation of water cools the body; (concept of evaporation must be mentioned)
g. heat is transferred by blood;
h. transfer of heat from body core in blood to surface;
i. if temperature rises, increased flow of blood/heat to the skin/vasodilation of skin blood vessels/arterioles; (do not accept veins, arteries or capillaries)
j. if temperature drops, decreased flow of blood/heat to the skin/vasoconstriction of skin blood vessels/arterioles; (do not accept veins, arteries or capillaries)
k. shivering increases heat production (in muscles);
l. example of one behavioural mechanism; (eg reducing activity (to lower body temperature) / reducing exposed surfaces (to reduce heat loss)