AQA A2  (Module 6) Human Biology

 

ANSWERS TO IN-CHAPTER QUESTIONS

 

Unit 7: Reproduction & Development

 

 

 

 

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Q1

The scrotal muscles cannot relax allowing the scrotal sac to drop below the abdomen in order to maintain the temperature of the testes at 5oC lower than the core body temperature; which is essential for sperm production.

 

 

Q2

a)     Presumably the woman would be undertaking the same level of activity at that time and therefore the readings are normalised and not skewed.  There is a daily (diurnal) variation in our body temperature of approx. 2oC.  Highest in early afternoon (1-4 pm) and lowest in the early morning (2-6 am).

b)     Any illness is often accompanied by a raised core body temperature due to the infection.  This is one of the body’s responses to infection to try and destroy the organism causing the infection.

c)     Before ovulation: 36.8oC.
After ovulation: 37.1oC

d)     Causes the body temperature to stay at 37.1oC, which is slightly higher than normal core body temperature.

e)     The 1st and 2nd (possible on the 26th).  Sperm can survive in the female for 1-3 days but are only highly fertile for 12-24 hours.

 

 

Q3

The mother and the baby could have different blood groups; if their blood mixed the red blood cells would clump (agglutination), which could result in their deaths.

The foetus could be Rhesus +ve and the mother Rhesus –ve.  If the blood mixed the mother’s blood could respond by producing anti-bodies, which would attach the foetus and seriously damage or kill it.

 

 

Q4

There is a large SA of chorionic villi membrane in close proximity with the endometrium.  Both the villi and endometrium have large capillary networks through which exchange can occur, e.g. of O2 and CO2.  Blood is flowing through blood vessels maintaining high concentration gradients.  All membranes are very thin, cutting down diffusion distances for the molecules concerned.  The blood of the mother is flowing in the opposite direction to that of the foetus, i.e. a counter-current system.

 

 

 

Fick’s Law =

SA of the respiratory surface x concn. difference

Thickness of the respiratory surface

 

 

Q5a

Similarities:

Both blood vessels contain high concentrations of glucose, amino acids, fatty acids and glycerol.

 

Q5b

Differences:

The umbilical vein has high levels of O2 and low levels of CO2.

The hepatic portal vein does not: higher levels of CO2 and lower levels of O2 especially after passing through the gut

 

 

Q6

  1. The tissues of the foetus are actively respiring and therefore their temperature is slightly elevated.
  2. The excess heat in the foetal blood present in the chorionic capillaries are in close proximity to the maternal blood capillaries in the endometrium.
    A heat gradient exists, as the maternal blood is cooler. 
    Excess heat is passed on into the maternal blood from the foetal blood: making for an efficient heat exchange mechanism, due to a large surface area.