AQA A2  (Module 6) Human Biology

 

ANSWERS TO IN-CHAPTER QUESTIONS

 

Unit 13: Homeostatsis

 

 

 

 

 

COMPARE YOUR ANSWER WITH THE SUGGESTED RESPONSE GIVEN BELOW: RETURN YOUR MARKED SCRIPT TO YOUR TUTOR

 

IF YOU ARE UNCLEAR OR UNCERTAIN ABOUT ANY ASPECT OFTHIS CHAPTER IT IS ESSENTIAL THAT YOU ARRANGE FOR EXTRA TUTOR HELP AND GUIDANCE

 

 

Q1.      Neither substance contains much water, so the question refers to the composition of the two foods.  Chocolate contains a mixture of fat and sugar (sucrose).  The enzymes that digest these are produced in the pancreas and thus found in the small intestine, so there will be little absorbed from the stomach.  The fat in chocolate will ‘line’ the stomach and slow down the absorption of substances by creating a barrier to water-soluble sugars.  This can be used to slow down the uptake of alcohol too.  A large fatty meal slows down uptake (thus getting you drunk slower); little or nothing to eat and a fizzy drink make the alcohol reach the bloodstream fastest.  This gives rise to the observation that champagne does not give you a hangover – in fact you get as drunk on less booze, thus less hangover!  If any student wishing me to demonstrate this, I will be happy to oblige!! 

Toast contains mainly starch and protein and the enzymes that digest these chemicals are found in the mouth and stomach as well as in the pancreatic secretions (remember – the pancreas produces every digestive enzyme!).  Since the original food molecules are too big to be absorbed directly, they can only be absorbed (assimilated = absorbed and used) once they have been digested.  So there can be some absorption of maltose from the stomach.  Hence toast faster.

            N.B.  This is a dumb question!  Chocolate invariably contains either invert syrup or glucose (since they are cheap) and so these hit the bloodstream very quickly indeed.  In any case, sucrose can be absorbed directly from the stomach, so the basic premise of the question is wrong.

 

Q2.      (a)  b cells of pancreas detect high blood glucose levels; a cells of pancreas detect low blood glucose levels.

(b) b cells secrete the hormone insulin; a cells secrete the hormone glucagon.  Both hormones are transported in the bloodstream to the responding cells – mainly in the liver and muscles.                                                                                                                             

(c) The effectors are mainly the liver and muscle cells, but most cells in the body respond to some extent (e.g. with insulin being necessary for the uptake of glucose; the presence of glucagon limiting glucose uptake by cells).