CHAPTER 17
REVIEW QUESTIONS
17.1
a.
b.
c.
d.
Nutrition is the intake of specific materials by an organism to sustain life, whereas a
nutrient is any substance used by an organism in the process of nutrition.
An autotroph is able to synthesise the organic molecules needed for its life processes
from simple inorganic molecules. A heterotroph must take in organic molecules, using
another organism as its nutrient supply.
Intracellular digestion occurs within the cell whereas extracellular digestion takes place
outside of the cell.
Chemical digestion involves chemical reactions mediated by enzymes to break food into
small particles whereas physical digestion refers to crushing or biting actions to break
food into smaller pieces to increase the efficiency of enzyme action.
17.2
Only small, soluble molecules can pass through cell membranes. Most food, either within the
cell or ingested is in the form of large, insoluble macromolecules.
17.3
With the development of the coelom, the inner endoderm, forming the alimentary canal lining,
becomes associated with muscle. Thus the entire alimentary canal is capable of movement
independent of the body wall. Food can travel through specific parts of the canal at different,
controlled rates. Thus specialisation of the alimentary canal is possible with the development
of the coelom.
17.4
There are two layers of muscle associated with the alimentary canal – one layer oriented
around the diameter (circular muscle) and the other along the length (longitudinal muscle).
Contraction of these muscles behind the food and relaxation in front of the food, forces the
food forward. Rhythmic contraction and relaxation of these muscles is termed peristalsis.
17.5
Large, complex, insoluble organic molecules of food are ingested into a mouth where both
physical and mechanical digestion starts. The food is moved to various parts of the alimentary
canal by peristaltic movement where further physical and chemical digestion takes place,
reducing most of the food to small, soluble molecules. These are absorbed across the
alimentary canal wall into the body cells where they are assimilated in the metabolic
requirements of the organism. Water is also absorbed. Any undigested food is eliminated in
the process of egestion as faeces.
17.6
17.7
Feature
Incisors
Carnivore
Small, close-fitting.
Canines
Large, pointed.
Diastema
Premolars/molars
Absent.
Developed as carnassials –
shearing action; molars small.
Jaw articulation
Only up and down action.
Herbivore
Large; may be replaced in upper
jaw by a thick horny pad.
Absent, very small or developed
as tusks.
Present.
Broad grinding surfaces with
alternating ridges of hard enamel
and soft dentine.
Loose,
allowing
rotating
movement.
Leaves: the hard mouthparts with serrated edges would allow cutting and grinding of the leaf
material.
17.8
Nectar is composed of simple sugars in solution. Thus the amount of digestion required is very
minimal and absorption would occur rapidly after ingestion. Thus there would be no need for
a stomach (storage, physical digestion and protein digestion), the small intestine would be
long with a large surface area to provide adequate time for glucose absorption and the large
intestine would be short since these is no intake of indigestible food.
17.9
Animals do not have the enzymes necessary for cellulose digestion. In order to release the
nutrients in the plant cells this cellulose has to be penetrated. Although physical digestion will
break open some of the cell walls, this process is inadequate for the dietary needs of the
animal. Bacteria do produce the enzyme cellulase. Thus a symbiotic relationship with bacteria
ensures that the herbivore procures the plant nutrients.
17.10
The efficiency of diffusion is determined by
 the area over which diffusion takes place
 the length of the diffusion pathway
 the concentration gradient.
17.11
Since gases must pass across cell membranes in solution, aquatic animals do not have to have
mechanisms which keep the gas exchange surfaces moist and so these surfaces may be the
entire body or gills. In air, which is less buoyant than water, gills would collapse and stick
together and thereby decrease the surface area for absorption. They would also dry out and
thus be ineffective exchange sites. Thus terrestrial animals are either small and live in moist
places (and exchange gases across a moist body surface) or have some form of gas exchange
surface which is internal and supported.
17.12
Gas
exchange
surface
Position of surface
Ventilation
Medium
exchange
of
gas
Fish
gills
pharynx
buccal pump
Amphibian
lungs; buccal cavity
and skin
thorax
buccal pump
water
air
Insect
tracheoles
abdomen
contraction
and
relaxation abdominal
muscles
air
17.13
Unlike other terrestrial vertebrates, amphibia have no diaphragm and thus thoracic pressure
cannot be achieved in ventilation. The buccal pump mechanism achieves both ventilation and
gas exchange across the moist buccal lining. Their lungs are relatively primitive, having few
alveoli, and thus do not have a large surface area. They are, therefore, unable to supply the
amphibian with all its gas exchange requirements, which are significantly supplemented by
skin breathing through the moist skin.
17.14
a.
b.
c.
A single circulation is one in which the blood only passes through the heart once in a
complete circuit through the body.
An open circulation system is one in which blood is pumped from the heart to a
haemocoel which directly bathes the tissues and organs with blood. As the blood is
pumped out of the heart a negative pressure is created and this draws blood back into it
from the haemocoel and thus maintains circulation.
A haemocoel is a specialised body cavity which obliterates the true coelom and in which
blood circulates and bathes the body tissues.
17.15
The sinus venosus collects venous blood which it passes on to the atrium, acts as a pressure
booster and contains pacemaker material.
17.16
Blood pressure is lost as it passes through capillaries. Deoxygenated blood from the heart
passes the capillary bed in the gills where it is oxygenated. These capillaries reform into
efferent arteries which join to form the dorsal aorta which takes oxygenated blood to the body.
17.17
There is only a single ventricle and although a spiral valve is present between the right and left
sides of the ventricle, and the viscosity of oxygenated and deoxygenated blood is different,
there is some mixing of the two types of blood in the ventricle. Thus blood leaving in the
dorsal aorta is not fully oxygenated.
17.18
Osmoregulation is control of water balance whilst excretion is the removal of metabolic
wastes.
17.19
Animals require high levels of proteins in their diet for enzyme, hormone and muscle
production as well as in the structure of their cell walls. If the intake of protein is higher than
required, excess amino acids are deaminated for conversion to other organic molecules. In this
process nitrogenous wastes are produced.
17.20
Ammonotelic animals are aquatic organisms which excrete ammonia as their nitrogenous
waste. Ammonia is slightly soluble and toxic and so can only be excreted by animals which
live in habitats in which there is no water stress and can produce high volumes of dilute urine.
In mammals and adult amphibians the ammonia is converted to the less toxic but more soluble
urea which requires less water for its elimination than ammonia. These animals are termed
ureotelic.
Uricotelic animals excrete uric acid which is virtually insoluble in water and non-toxic. This is
a very energy consuming process and thus an adaptation to high conservation of water in
terrestrial animals and the production of a shelled egg. These animals include insects, reptiles
and birds.
17.21
Their body fluids are at the same concentration as that of the surrounding water.
17.22
Marine bony fish evolved in fresh water environments and then moved out to sea. In their
marine habitat, their body fluids are hypotonic to the sea water. Thus there is a tendency for
them to lose water by osmosis. This tendency is reduced by an impermeable coating of scales
which restricts water loss to the gills and gut. They drink large amounts of water, excrete salts
through glands in their gills and have a kidney with few glomeruli which produces a low
volume hypertonic urine.
17.23
An osmoconformer allows the concentration of their body fluids to fluctuate with external
salinity, e.g. the spider crab Maia. These organisms normally live in a stable salinity which
may vary for short periods of time. Osmoregulators have well-developed powers of regulation
regardless of changes in environment salinity, maintaining a constant internal environment.
These animals would be found in brackish water where the salinity of the water is very
variable due to both evaporation of sea water (which is shallow in this area and leads to
increased concentration) and influx of freshwater from the surrounding land (which decreases
the concentration), e.g. soldier crabs.
17.24
Organisms
Freshwater protozoan
Adult insects
Freshwater fish
Mammals
Main nitrogenous waste
substance
ammonia
uric acid
ammonia
urea
Main site of nitrogenous
excretion
cell membrane
Malpighian tubules
kidney
kidney
17.25
Simultaneous release of eggs and sperm, protection of gametes, a pathway for sperm to reach
the eggs and a liquid medium in which the sperm can swim to the eggs.
17.26
In external fertilisation both the eggs and the sperm are shed into the external environment.
This can only occur in an aquatic environment in which the eggs, and developing zygote, will
not dehydrate and there is a liquid medium for sperm to swim to the eggs. Internal fertilisation
is an adaptation to living on land. The egg is retained in the female body and the sperm are
inserted, in their own liquid environment produced by the male, into the female reproductive
opening.
17.27
A hermaphrodite is an individual in which both male and female sex organs are present. Most
flowering plants are hermaphrodites and the tapeworm is an animal example.
17.28
Courtship behaviour is a complex, integrated, species-specific communication in higher
animals which serves several functions – varies depending on gender and species of the
performer and mating receptiveness.
Variable responses to second part of question depending on animal selected for research.
17.29
Discussion should include a description of the following processes: parthenogenesis, binary
and multiple fission, budding and fragmentation; as well as examples of animals which utilise
each process.
17.30
The ability to regenerate which is associated with a low level of organ development and
complexity of the overall organisation of the animal.
17.31
Growth is the increase in dry mass of an organism or cell whereas development refers to the
changes in the organism as it matures.
17.32
Cell differentiation is the process whereby a generalised cell becomes specialised for a
specific function.
17.33
The four phases of growth follow a sigmoid curve.
The initial lag phase is a brief period in which little growth occurs due to the small number of
cells. As the cells proliferate, there is an larger number both dividing and increasing in size
during maturation, resulting in a very rapid increase in growth. As the organism reaches its
final size (the inflexion point), limiting factors in the external or internal environment decrease
the rate of growth until at the plateau phase no further growth occurs, the cellular activities
being involved in maintenance and repair.
17.34
a.
b.
c.
Limited growth occurs in an organism which ceases growth after a period of time, e.g.
mammals, whereas in unlimited growth the organism continues to grow throughout its
life, e.g. sea weeds.
Positive growth occurs when anabolism exceeds catabolism – there is an increase in the
dry mass of the organism – and occurs during the development of an organism from
fertilisation to maturation. Negative growth occurs when catabolism exceeds anabolism –
there is a decrease in dry mass of the organism – which occurs during senescence.
During isometric growth an increase in size is not accompanied by changes in shape or
external form. This is displayed in fish and reptiles. If different body parts develop at
different stages of growth or at different rates, as in human development, allometric
growth is said to occur.
17.35
Since arthropods, unlike other animals, are completely covered in an external skeleton that
limits growth, the skeleton must be periodically shed to allow increase in size of the animal.
During this vulnerable stage, the arthropod takes in large amounts of water, making room for
new growth as the newly secreted exoskeleton hardens. Thus growth in arthropods is
characterised by periods of very limited growth interspersed with short periods of rapid
increase in dry mass. In other animals, the rate of growth is relatively constant up to the
limiting size.
17.36
In some animals, such as mammals, light has a direct effect on production of vitamin D,
although its influence on animal growth is far more significant through the indirect effect of
nutrient supply through the food chain. Seasonal changes have a significant effect on plant
growth which again flows on from the availability of nutrients for animals and thus their
growth. Similarly water availability, nutrient supply, temperature, and amount of oxygen
influence animal growth. Internal factors controlled by genes or controlling gene expression,
which may be species or individual specific, can also influence the growth of the organism.
17.37
External development occurs in the environment outside the mother’s body, in the water or
enclosed in an egg case or shell. Internal development occurs within the mother’s uterus, e.g.
vivipary as seen in some fish and snakes or placentation in eutherian mammals.
17.38
Yolk provides food or the developing embryo. The presence of a large amount of yolk
provides adequate nutrients for the full development of the young within an egg. It does,
however, inhibit cleavage which is restricted to an area above the yolk. If there is only a small
or moderate amount of yolk present, cell division of the entire egg will only be slightly
inhibited, if at all, but there are inadequate nutrients for full development of the embryo. The
young either hatch at an incomplete stage and complete development in the external
environment, or a placenta (a diffusion pathway between the young and the mother) is formed
to provide nutrients and remove metabolic wastes of the young.
17.39
a.
b.
c.
Cleavage: formation of a ball of cells through cell division of the zygote.
Gastrulation: establishment of the basic body plan and the formation of the three basic
tissue layers of endoderm, mesoderm and ectoderm from which tissues and organs will
develop.
Organogenesis: formation of organs and organ systems.
17.40
In both complete and incomplete metamorphosis the young hatch at an immature form that
must complete development out of the egg as an independent individual obtaining food from
the environment.
In complete metamorphosis the hatched young is very different from the adult and exploits
different parts of the environment, e.g. the frog tadpole is aquatic and herbivorous whilst the
adult is terrestrial and insectivorous.
In incomplete metamorphosis the hatching nymph is similar to an immature adult that requires
further phases of growth and development to reach maturity.
17.41
The young are born in an embryonic state. The nourishment required to complete their
development is supplied from the mother’s milk which is secreted from her mammary glands.
17.42
Tissues formed by the embryo that aid in its further development, but that do not become part
of the final form.
17.43
Embryonic blood vessels in the placenta and maternal blood vessels in the endometrium of the
uterus are in close proximity, allowing rapid exchange of materials. Nutrients and oxygen pass
from the maternal blood to the embryonic blood and wastes and carbon dioxide from the
embryonic to the maternal blood along a diffusion concentration gradient.
17.44
Development is external with little or no parental care of the eggs or the newly hatched young.
They are thus susceptible to environmental hazards and predation. In birds and mammals there
is a high degree of parental care (pre- and post-birth) until the young are independent.
17.45
Fanning increases the flow of water over the eggs and thus oxygen supply to them, providing
the developing fish fry with adequate oxygen for respiration and thus energy for development.
17.46
The activities of one part of the body influences the activities of other parts of the body.
Without coordination, each part of the body acts as an independent unit which could have a
detrimental effect on other organs and tissues.
17.47
A feedback system is a control mechanism whereby hormones interact with each other in a
coordinated manner to maintain optimum internal conditions, e.g. ACTH secreted by the
anterior pituitary stimulates the adrenal cortex to release cortisone or aldosterone which
regulate aspects of metabolism.
17.48
a.
b.
Unicellular organism: receptor molecules on the surface of the membrane detect changes
in the environment that are significant to the organism. This may cause changes in
chemicals inside the cell (communication) which result in chemical changes which are
seen as the response.
A multicellular animal uses both hormonal and nervous communication. Detection of an
environmental change chemically activates sense organs which transmit their information
to appropriate cells for chemical response either via hormones travelling in the blood
stream or electro-chemical changes along a series of nerve tracts.
17.49
Hormones are chemicals which regulate body functions in multicellular plants and animals.
17.50
Hormones may be made in one part of the body and travel to the target site in either a
transport system or by diffusion.
17.51
Hormones are released into the blood stream and must pass throughout the body to reach the
target organ, whereas a nerve impulse goes directly to the effector organ.
17.52
The actual nerve impulse is a series of chemical changes across the nerve membrane. At the
nerve ending released transmitter substances (noradrenalin and acetylcholine) are chemicals
that influence the activity of the target cells of the effector organ.
17.53
Central control
Nerve tracts
Hydra
Prawn
none
cerebral ganglia
none – network double, ventral
Cat
complex brain
single, dorsal