1 Give a reason why carnivores need to eat less regularly than herbivores.
2 Explain why food spends longer in the herbivore’s diges-tive system than it does in a carnivore’s digesdiges-tive system.
FIGURE 2.57
Koalas, wombats and kangaroos are herbivores and use symbiotic bacteria for the digestion of cellulose. Koalas and wombats are hind-gut fermenters, whereas kangaroos are fore-gut fermenters.
Plant matter is more difficult to digest than animal tissues. Plant cells have tough cellulose cell walls that must be broken down before the cell contents can be released. Animals are not able to do this unaided.
Herbivoresuse micro-organisms that live symbiotic-ally in their digestive systems to help them. The breakdown of cellulose occurs during a fermentation process in a specialised part in the digestive tract.
These structures are found in either the fore-gut or the hind-gut of different parts of the digestive system (see Figure 2.57):
● Fore-gut fermenters carry out digestion in a chamber that is before the stomach. In cattle, this is called the rumen. Sheep, kangaroos and wallabies are other examples of fore-gut fermenters.
● Hind-gut fermenters carry out cellulose digestion in the caecum, a chamber that comes after the small intestine. Horses, rabbits, possums and koalas are examples of hind-gut fermenters.
Because animal cells do not have a cell wall, they can be digested more rapidly. Muscle (meat) contains a lot of protein, so carnivores do not have to consume the large quantity of materials that herbivores do to obtain the same amount of nutrients. Plant cells also
provide less energy than meat per gram eaten, and their breakdown time in the digestive system is much longer. In contrast, animal foods release a higher proportion of energy per gram, and they can be digested much more quickly.
As a result, carnivore digestive systems are shorter and less complex than those of herbivores.
The structures and functions found within the digestive systems of different animals can usually be clearly related to their dietary patterns; that is, to the types of food they eat.
Food does not spend long in a carnivore’s mouth and is quickly gulped down. A dog, for example, may spend only 15 minutes per day eating. The intestines are short and unspecialised compared with those of herbivores.
Carnivores in the wild are hunters and eat irregu-larly. Herbivores, such as as cows and kangaroos, spend much of the day chewing grass and other soft plants.
Omnivores usually eat for a moderate amount of time each day; humans typically eat for about 90 minutes each day. Our digestive systems are inter-mediate in length between herbivores and carnivores and do not show particular specialisation. We cannot digest cellulose—it is passed through as ‘roughage’.
oesophagus oesophagus oesophagus
small intestine small intestine small intestine
Kangaroo Wombat
Koala
80 Heinemann Biology
Q
Qu ue essttiio on nss
3 Distinguish between the autotrophic and heterotrophic nature of plants and animals.
4 Explain the following statement: ‘All living things depend on plants.’
5 Write out the word equation that summarises the process of photosynthesis.
6 a Compare aquatic and terrestrial plants in relation to the site of water and mineral uptake.
b Terrestrial plants need a large surface area in order to maximise water uptake. How is this achieved?
7 Explain how the structure of typical leaves and the distribution of specialised tissue within them are adaptations to photosynthesis. Use clearly labelled diagrams in your answer.
8 a Explain the difference between mechanical and chemical digestion.
b Teeth are involved in the process of mechanical digestion. Describe the significance of their role in terms of preparing foods for chemical digestion.
9 Identify the structures labelled W, X, Y and Z in the diagram of the herbivore digestive system shown.
What is the major function of each structure you have identified?
10 Outline the importance of villi and microvilli in the digestive system.
11 a Compare the digestive systems of dogs (Figure 2.54) and koalas (Figure 2.57). Include a description of their respective digestive systems, commenting on length, complexity and role of different structures.
b Make a statement relating the length and complexity of the digestive systems of dogs and koalas to the chemical composition of their respective diets.
W X
Z
Y
C
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nerve cell
lining cell of small intestine
root hair cell
leaf mesophyll cell
1 Define the following terms, and provide examples of each:
a tissue b organ c system.
2 Cell specialisation in multicellular organisms is an adaptation that allows all of the organism’s
requirements to be met. Complete the table below, showing some different kinds of specialised cells in multicellular organisms and their functions.
F
Fu urrtth he err q qu ue essttiio on nss
1 Visit your local nursery or consult an encyclopaedia of plants to find out the answers to each of the following.
a What is the difference between macronutrients and micronutrients?
b Packets of fertiliser purchased from nurseries often list ‘NPK’ as major ingredients.
i For what nutrients are these letters an abbreviation?
ii How are each of these nutrients important to plants?
2 A green pot-plant was placed in a position to receive plenty of sunlight during the day. It was watered regularly. Very little new growth occurred, and the plant soon began to lose its leaves and turn brown. Suggest a possible explanation for this observation.
3 Complete the table, which summarises actions of enzymes.
4 Examine the following graph, which shows the rate of photosynthesis occurring at a fixed level of light intensity.
a What is happening to the rate of photosynthesis between the points X and Y? Explain.
b Why does the graph level off after point Y?
c What is the limiting factor in this experiment?
Why do you think so?
d List two factors that are being controlled in this experiment.
5 Design a simple experiment to test the effect of temperature on photosynthesis.
6 Explain the importance of the liver in relation to the products of digestion.
7 Use a reference book to find out about the
appendix in humans. What role, if any, does it play?
How does it compare to similar structures in herbivorous animals? What does the presence of the appendix in humans suggest about our relationship to other species?
8 Prepare a poster that would appeal to your classmates, providing information about diet.
Include
● a summary of what is meant by the term
‘balanced diet’.
● the five major food groups, with examples of the kinds of foods offered by each and the recommended daily allowance of each.
Y
X rate of
photosynthesis
concentration of CO2
F
Foooodd TTyyppee ooff FFiinnaall pprroodduucctt ooff e
ennzzyymmee cchheemmiiccaall ddiiggeessttiioonn
carbohydrate lipid
protein
Cell formation
2
2..2 2
O
OB BJJE EC CT TIIV VE ES S
When you have completed this section you should be able to:
● distinguish between abiotic and biotic factors in the environment
82 Heinemann Biology