7. (a) What is meant by:
(i) internal environment?
(ii) homeostasis? [ 4 m]
(b)Diagram 7.1 and 7.2 shows two different environmental condition.
Describe the regulatory mechanisms carried out to maintain the body temperature at 36.7⁰C in both the conditions above. [ 8 + 8 marks]
Suggested Answer:
(a)(i)
P1: (Physical and chemical) condition within our body
P2: Extra cellular fluid that surrounds our body cells
P3: Examples are body temperature, blood glucose level, pH,
blood osmotic potential and blood pressure.
P1 & any other P
(ii)
P4: A process of maintaining internal environment / physical
and chemical conditions in our body at a constant value.
P5: through corrective mechanism based on negative or
positive feedback
P6: which reverts the internal environment back to normal
condition if there is a change. P4 & any other P
(b)
Hot condition
F1: Erector muscle relax so that hair is lowered.
P1: A thin layer of air is trapped by the hair.
P2: Heat can be lost easily.
F2: Blood capillaries in the dermis of the skin dilate //
vasodilation
P3: More blood flows near the surface of the skin.
F3: Sweat glands secrete sweat actively.
P4: When sweat evaporates, it absorbs heat from the skin.
F4: Less thyroxine and adrenaline are produced.
P5: Body’s metabolic rate decreases // Less heat is generated
within the body.
4F & corresponding P
Cold condition
F1: Erector muscle contracts so that hair is raised.
P1: A thick layer of air is trapped by the hair.
P2: The layer of air acts as an insulator to prevent loss of heat
from the body.
F2: blood capillaries in the dermis of the skin constrict //
vasoconstriction.
P2: Less blood flows near the surface of the skin.
F3: Skeletal muscles contract involuntarily // shivering
P3 Generates heat to raise the body temperature.
F4: More thyroxine and adrenaline are secreted
P4: Body’s metabolic rate increases // more heat is generated
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