CHAPTER 18
EXTENDING YOUR IDEAS
1.
You would also need to show that the trait does not develop if the hormone is not present,
otherwise you are not sure if the development of the trait is due to the hormone or to some
other factor.
2.
The glucose is carried in the capillaries to the hepatic portal vein and to the liver. Molecules
not converted to glycogen are passed to the hepatic vein which joins with the Inferior Vena
Cava which enters the heart. From the right atrium it travels to the right ventricle, the
pulmonary arteries to capillaries in the lung which rejoin to form the pulmonary vein. This
vessel returns to the left side of the heart – the left atrium to the left ventricle – where it is
pumped to the aorta. The carotid artery branches from the aorta and further branches into
internal and external carotid arteries. The glucose molecules travel in the internal carotid
artery to the brain.
3.
C: Although the axon has a small diameter, it has the fastest speed of conduction. The
presence of a myelin sheath speeds up the rate of conduction as the impulse jumps from one
Node of Ranvier to the next, and so the whole neurone membrane does not undergo
depolarisation and repolarisation.
4.
The parasympathetic nervous system stimulates secretions from the salivary glands, which
may interfere with certain dental procedures. Similarly, it stimulates the tear glands, which
may be a disadvantage in eye surgery.
5.
a.
b.
c.
d.
6.
a.
b.
Predators contacting the skin would be immobilised, allowing the frog to escape.
Warning colouration. It also serves as a recognition for prey to learn to avoid the frog.
Curare acts as a neuromuscular block competing with the transmitter substance, ACh, for
receptor sites on the muscle fibre membranes. When the arrow tipped with curare enters
the prey, the curare is rapidly taken up by the blood and transported to muscles where it
achieves its response of muscle paralysis.
The prey is rapidly immobilised, so that it cannot move far from where it was struck by
the arrow, ensuring that it is caught. Although its muscles are paralysed, other life
functions operate and the prey can be kept for a period of time before it is eaten, without
deterioration due to bacterial decomposition.
Dark objects absorb heat whereas light objects reflect heat. The amount of light present
in a natural habitat reflects the heat available for absorption. Thus by changing the
expansion and contraction of the melanocytes the amount of heat absorbed by the lizard
can be controlled.
At night, light intensity is low and temperature is low. Thus the thermal skin receptors
and light intensity receptors stimulate relaxation of the melanocytes and the skin
becomes dark to absorb all available heat. Between dawn and midday the light intensity
increases and much of the radiant energy is converted to heat energy. This heat energy
continues to re-radiate from the earth’s surfaces throughout the early afternoon. Thus as
the day passes, more and more heat energy is available for the lizard – the heat and light
sensors bring about contraction of the melanocytes as the day progresses, thereby
preventing overheating of the animal by reflecting radiant energy. Towards dusk, light
intensity decreases as does the amount of re-radiated heat energy. The melanocytes are
again stimulated to relax and thus increase heat absorption.
7.
a.
b.
c.
d.
8.
a.
b.
A: it has a very reduced caecum.
L: small intestine (ileum) – absorption of digested food molecules.
M: large intestine (colon) – bacterial digestion of cellulose; absorption of water.
Microbial fermentation of cellulose occurs here. The caecum is large as it is the major
site for the chemical release of cell contents of the plant matter which the animal eats.
Production and secretion of digestive enzymes and alkaline solution.
Yes. The alimentary canal of the human is effectively an invagination of the external
environment, an adaptation which allows animals to eat, move to a safe habitat and then
to digest the food.
In both organisms digestion is extracellular and small, soluble organic molecules are
absorbed across cell membranes for assimilation inside the cell(s) of the body. The
decomposer secretes digestive enzymes onto its food which is outside the body, and then
absorbs the digested matter. It remains attached to the food source during this process.
The human ingests chunks of food which undergo both physical and chemical digestion
in various parts of the alimentary canal before it is absorbed and then transported to the
cells via the blood steam. Most of the assimilation of the absorbed molecules occurs in
the liver. Undigested food is egested as faeces. The human can therefore ingest food and
move away from it whilst it is digesting and absorbing the molecules.
9.
Different hypotheses are possible. For example:
Cleaning of the teeth is less effective, and thus dental caries is more prevalent, in the side of
the mouth associated with handedness.
To test this hypothesis two variables need to be tested: the effectiveness of cleaning, and the
association between cleaning and dental caries.
To test cleanliness, the teeth of a large number of subjects of physically able people of
approximately the same age and medical history should be treated with a chemical which
stains tartar on the teeth. Half of the subjects should be right-handed and half left-handed.
Each would be requested to clean their teeth for a specified length of time. The distribution,
and intensity of stain (and thus tartar) remaining after cleaning should be recorded and
correlated with handedness.
To test the prevalence of dental caries, the teeth of each subject should be examined for
distribution and number of fillings and evidence of soft spots (the start of decay), and the
results correlated with handedness.
10.
In underground car parks there is an accumulation of both carbon dioxide and carbon
monoxide due to the combustion of fuel by motor vehicles. There is also a deficit of oxygen
due to this process. With an increase in carbon dioxide tensions in the alveolar air, there is less
loss of carbon dioxide from the blood and higher than normal oxygen levels (not available) are
required for loading of oxygen by haemoglobin (Bohr shift). The carbon monoxide taken in
also competes for sites on haemoglobin more successfully than oxygen. The combined effects
of high carbon dioxide, low oxygen and carbon dioxide in the atmosphere result in lowered
oxygen uptake by the blood and thus to brain, which results in faintness.
11.
The loop of Henle is associated with water reabsorption. The longer the loop, the greater the
achievement of a concentration difference (due to salt diffusion from the ascending limb)
between tissue fluids and the descending limb and thus removal of water from the descending
limb. Thus the greater the water conservation by the animal.
12.
During hibernation metabolic activities are reduced and blood supply to muscles and most
organs except the brain greatly reduced. The brain needs to maintain a normal oxygen supply.
Since ventilation depends on muscular activity, this will be reduced leading to a decreased
lower gas exchange rate. By shifting the oxygen dissociation curve to the left, full loading of
the blood with oxygen occurs at the much lower oxygen tension which would occur with
reduced ventilation, thus ensuring the brain has an adequate oxygen supply.
13.
A total of (180 – 1.5) x 103 g is reabsorbed by the kidney. 80% of this is reabsorbed by the
proximal convoluted tubule and loop of Henle = 142.4 x 10 3 g.
The ascending loop of Henle is impermeable to water so there is no reabsorption.
Thus reabsorption in the distal convoluted tubule and collecting duct = 36.1 x 103 g.
150
100
water reabsorbed
(x 103 g)
50
0
PCT +
descending
limb loop of
Henle
14.
Ascending
limb of
loop of Henle
DCT +
collecting
duct
Fat is a high energy storage substance which is formed when there is excess carbohydrate
(such as glycogen in the liver) in the body. Thus the bush people are able to convert this
excess to fat which is stored in special fat cells in the buttocks. During late summer through
winter both water and food supplies are low. The fat is digested to glycerol and fatty acids.
The glycerol then undergoes glycolysis to form pyruvic acid and enters the mitochondria
where aerobic respiration converts this to carbon dioxide, metabolic water and energy. This fat
therefore sustains the women throughout winter (and invariably through pregnancy) until the
next spring when food again becomes plentiful. It is a genetic trait that the fat is stored in the
buttocks. In most women excess fat is invariably stored in the abdominal region and the
thighs. This could hinder movement of the bush women.