A2 Human Biology Unit 7

Text questions

P133/Q1		Testis are held in scrotum outside the abdomen (at a temperature lower by about 5�C then the temperature of the body). This lower temperature is essential for spermatogenesis. Tight trousers → scrotum close to the abdomen → temperature of the testis similar to the temperature of the abdomen (i.e. 36-37�C) → impaired spermatogenesis.
P145/Q2	a)	To allow fair comparisons to be made. (temperature of the body is subjected to some variations over the course of the day)
	b)	Any illness may affect the temp. of the body.
	c)	Before ovulation: 36.6-36.7�C; After ovulation: 37.0-37.1�C.
	d)	Body temperature will increase.
	e)	1-2 January
P145/Q3		Mixing of the foetal & maternal blood would trigger an immune reaction (different genotypes of mother and the foetus) If mother ill → micro-organisms would be carried to the foetal blood circulation and cause infection of the foetus.
P148/Q4		Rate of diffussion = (s.a. x concentration gradient) / distance Large s.a.→ villi/microvilli High concentration gradient → continuous supply of oxygen in uterine arteries, removal of oxygenated blood by the umbilical vein, higher affinity of foetal haemoglobin (than adult haemoglobin) for oxygen, counter-current system Short diffusion pathway (1-cell-thick endothelium → connective tissue → 1-cell-thick epithelium)
P148/Q5	a)	Contains high concentration of nutrients: glucose, aminoacids, ions, etc.
	b)	Contains oxygenated blood.
P148/Q6	a)	Foetus has a higher respiration rate due to its rapid growth → heat is produced during respiration.
	b)	Maternal blood is cooler → there is a heat gradient → heat transferred to the mother's blood.

Assignment

P156/Q1

Type of contraceptive	Immature follicle	Mature ovarian follicle	Corpus luteum
No hormonal control	V	V	V
Combined contraceptive pill	V	V	V
Mini-pill	V	V	V

P156/Q2

Steroids = lipids (structure: three rings made of 6 carbon atoms each + one five-carbon ring).

Human chorionic gonadotrophin (hCG) = hormone produced by the cells of blastocyst → maintains
corpus luteum (→ oestrogen + progesterone).

P156/Q3

Combined contraceptive pill = oestrogen (O) + progesterone (P). (O) +(P) inhibit production of LH by pituitary gland. (Normally surge in concentration of LH in blood → ovulation).

The mini-pill = progesterone → interferes with meiosis II
(which occurs after the sperm nucleus enters the oocyte).

Morning after pill = single large dose of progesterone → stimilates development of endometrium. Single large dose of (P) = rapid fall in (P) concentration a short time after taking the pill (=similar condition to that, which triggers menstruation → implantation of the blastocyst will not take place).

P157/Q4

GnRH = polypetide (10 aminoacids). 300 molecules similar to GnRH may differ from the "real" GnRH as a result of a different primary structure of the polypeptide:

Sequence of aminoacids
Presence of other aminoacids, not normally found in GnRH
Number of aminoacids other than 10

A "fake" molecule of GnRH may block the receptor sites on the plasma membrane of the cells of the pituitary gland which produce FSH, hence FSH not produced.

Polypeptides (including GnRH) are easily digested in the gut → the polypeptide contraceptive will not be present in the blood → it will not block the receptor sites on the membrane of the cells which produce FSH → FSH produced. If the contraceptive is injected, it will block the receptor sites → FSH not produced.

Examinations

P157/Q1

(i) Pituitary

(ii)

Cells	% of cells containing a Y chromosome
Sertoli cells	100
Mature sperm cells	50

Golgi bodies responsible for synthesis of lipids; Testosterone is a steroid/lipid; LH stimulates synthesis of testosterone, hence more Golgi bodies needed.

(i) Negative feedback

(ii) An increase in LH → increase in testosterone →decrease in LH → decrease in testosterone;

(i) 12/13th of May

(ii) 4 days before secretion of hCG is started by blastocyst (fertilisation → 4 days → blastocyst)

(i) production of hCG possible only if blastocyst present/concentration of progesterone may vary due to reasons other than pregnancy;

(ii) After the first three months of pregnancy corpus luteum degenerates → progesterone/oestrogen secreted by the placenta (= pregnancy confirmed).

P159/Q2

(i) Mitochondria → ATP (lactation is an energy-demanding process);

(ii) Amino acids → diffusion inside the cell → ribosomes/ER → polypeptide/protein synthesis → polypeptides/proteins → Golgi app. → modification → modified proteins → vesicles → exocytosis;

(i) Diagram of a lactose molecule

(ii) Progesterone produced by the placenta; the placenta removed from the mother's uterus ("afterbirth") → progesterone not secreted/no progesterone in the mother's blood → no more inhibition of the synthesis of aminoacids into lactalbumin/galactosyltransferase → enzyme lactose synthase produced/available for the reaction: galactose + B-glucose → lactose;

(i) Nipple

(ii) Muscle in the milk ducts;

(i) Suckling: receptors/nipple → sensory neuron → hypothalamus → motor neurone → posterior pituitary gland → hormone oxytocin → muscle in milk ducts: milk ejection;

(ii) Oxytocin causes contractions of the myometrium of the uterus;

Mutation/change in the sequence of nucleotides of DNA → change in the sequence of nucleotides in mRNA → sequence of aminoacids in the protein changed → primary/secondary/tertiary structure of the protein changed → if enzyme: active site altered/enzyme may not be able to create ES complexes → if the affected enzyme is involved in regulatory processes that control cell division: the cell may continue to divide → tumor.

(i) The cells in the tissues divide frequently → more processes of DNA replication, hence more possibilities for errors/mutations during replication;

(ii) The total number of divisions of the mammary-gland cells will be lower → fewer possibilities of errors/mutations occurring during DNA replication;