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A2 Human Biology Unit 13
Text questions
| P270/Q1 |
The main ingredient of chocolate are lipids
("cocoa butter") and carbohydrates (sucrose). The
same mass of toast consists mostly of starch. Starch
is later digested into glucose. The number of
glucose molecules is much larger than the number of
glucose and fructose molecules from the hydrolysis
of sucrose. Hence a more rapid rise in blood glucose
concentration in the person who has eaten the toast. |
|
| P271/Q2 | a) |
Alpha and beta cells in pancreas; |
| b) |
Receptors activate effectors by secreting
hormones into the bloodstream (alpha cells - glucagon, beta cells - insulin); |
|
| c) |
Enzymes (which convert glycogen to glucose or
vice versa); |
Assignment
| P280-283 | Follow instructions in the coursebook; |
Examinations
| P283/Q1 | a) |
Temperature affects the rate of
reaction. At a lower temperature: lower number of
random collisions between substrate molecules. At a
higher temperature: higher number of collisions
between substrate molecules, but also, an increased
amount of vibration of atoms present in the
molecules of the enzyme. An increased temperature
may lead to the enzyme being denatured. Hence
maintaining optimum temperature for enzymatic action
is crucial. |
| b) |
Temperature of blood decreased
→ receptors in
hypothalamus : heat conservation centre
→
vasoconstriction/ shivering/ raising of hair/
increased metabolic rate. Temperature of blood
increased →
receptors in hypothalamus : heat loss centre
→ hair lowered/
sweating/ vasodilation/ decreased metabolic rate. |
|
| c) |
(i) Surface area/volume ratio small, hence less
heat lost through radiation/ convection/ conduction.
(ii) Short, stocky body confers an advantage on the
possessor of the characteristic, hence a higher
chance of survival →
higher chance of producing offspring
→ some offspring
will have inherited alleles for short/stocky body
→ repetition of
the cycle … |
|
| P284/Q2 | a) |
(i) Glucose ingested & absorbed into the
bloodstream →
rise in blood glucose detected by beta cells in
pancreas →
increase in insulin secretion; (ii) An increase in
the concentration of glucose (initial cause) causes
an increase in concentration of insulin . This
increase in concentration of insulin causes decrease
in the concentration of glucose (final effect). |
| b) |
During strenous exercise glucose present in the
blood is used by respiring muscles, consequently
glucose level in blood drops
→ the drop is
detected by alpha cells in pancreas
→ increase in
glucagon secretion : activation of enzymes
converting glycogen to glucose. |
|
| c) |
Insulin affects only cells which have specific
receptor molecules present in their cell membrane. |
|
| d) |
Insulin molecules bind to receptors in the cell-
surface membrane →
chemical signal (enzymes) are activated
→ vesicles (made
of phospholipid bilayer with glucose carrier
proteins incorporated into it) move and fuse with
the cell membrane. Glucose carrier proteins, which
are now incorporated into the cell surface membrane,
will allow glucose molecules to pass inside the cell
by facilitated diffusion. |
|
| e) |
Insulin activates enzymes which convert glucose
into glycogen. |
|
| f) |
(i) Insuficient insulin
→ insuficient
uptake of glucose by cells
→ substrates
other than glucose used up by cells for respiration
(e.g.lipids), hence RQ below 1. (ii) Strenous exercise : level of glucose in blood drops → glucagon produced → glycogen converted to glucose → glucose level increased. Therefore, as a result of a physical exercise the concentration of glucose in blood will increase. In healthy organisms, after exercise, this higher concentration of glucose is corrected by negative feedback (:increased glucose → increased insulin → decreased glucose). However, in diabetics the negative deedback doesn't function, therefore the concentration of glucose in blood remains high. |
