CHAPTER 17
REVIEW QUESTIONS
17.1 a. 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.
b. 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.
c. Intracellular digestion occurs within the cell whereas extracellular digestion takes place outside of the cell.
d. 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
Feature / Carnivore / HerbivoreIncisors / Small, close-fitting. / Large; may be replaced in upper jaw by a thick horny pad.
Canines / Large, pointed. / Absent, very small or developed as tusks.
Diastema / Absent. / Present.
Premolars/molars / Developed as carnassials – shearing action; molars small. / Broad grinding surfaces with alternating ridges of hard enamel and soft dentine.
Jaw articulation / Only up and down action. / Loose, allowing rotating movement.
17.7 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
Fish / Amphibian / InsectGas exchange surface / gills / lungs; buccal cavity and skin / tracheoles
Position of surface / pharynx / thorax / abdomen
Ventilation / buccal pump / buccal pump / contraction and relaxation abdominal muscles
Medium of gas exchange / water / air / 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. A single circulation is one in which the blood only passes through the heart once in a complete circuit through the body.
b. 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.
c. 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 / Main nitrogenous waste substance / Main site of nitrogenous excretionFreshwater protozoan / ammonia / cell membrane
Adult insects / uric acid / Malpighian tubules
Freshwater fish / ammonia / kidney
Mammals / urea / 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. 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.
b. 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.
c. 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.