CHAPTER 8
EXTENDING YOUR IDEAS
1.
a.
Decomposers
Blood sucking flies

Bats

Insects

Trees
2.
spiders

spiders, insects, scorpions

cave crickets

moulds
droppings
b.
There is no strict boundary to this community since the original energy comes from
outside the cave, as the bats feed on the insects which feed on the plants.
a.
The control trees have the same conditions as the experimental plants but have no
nitrogen fertiliser and no nitrogen fixing Frankia bacteria.
b.
The control trees are used as a guage to measure the effects of phosphate fertiliser,
nitrogen fertiliser and association with Frankia on tree growth.
c.
At all levels of application of phosphorus and nitrogen fertiliser, tree growth is greatest
when Frankia is present. The rate at which phosphorus fertiliser is applied gives varied
results in tree growth for those plants both treated and not treated with nitrogen fertiliser,
with best results at 5 kg/hectare. It would appear that trees inoculated with Frankia are
better able to utilise nitrates in the soil at higher levels of phosphorus. Thus plants require
nitrogen and phosphorus to grow. Nitrate, though a symbiotic relationship with Frankia,
provides the best growth, and it appears that there is an optimal association between
available phosphate and nitrate.
3.
a.
100
xo
o
90
Percentage
leaf
remaining
o
80
x
70
o
60
o
o
50
40
30
x
20
x
10
x
x
0
June
August October December February April
Month
x = 7mm mesh; o = 0.5 mm mesh
4.
b.
The larger the mesh size the faster the rate of leaf removal. This is most likely because
small litter organisms are able to move through the 7 mm mesh but not the 0.5 mm mesh
to get to the leaf discs. With the 0.5 mm mesh, only bacteria and fungi are able to pass
through resulting in a slower breakdown rate.
c.
It is possible that between October and December there was good rainfall which provided
good conditions for fungal and bacterial growth and thus rapid decomposition. During
the other months it was either too cold (June, August, April) or too dry (October,
February) for optimal growth of decomposers.
Variable answers. Possible ideas:
Chemicals at the tips of the algae control growth. Under conditions where there is no feeding
by Daphnia, these chemicals inhibit growth. Feeding by Daphnia removes these chemicals
and so growth is induced.
The algae have a genetically determined maximum size. Once that size is reached,
photosynthetic activity is at a rate which maintains the algae. If the size is reduced (by
predation), the algae increases photosynthetic activity to again reach maximum size.
5.
Dig hollows of various depths in an area in which water is able to accumulate. Line the hollow
and an area surrounding the hollow with an impervious lining to decrease the possibility of
litter organisms entering the area. At various times, measure the depth of the leaf litter which
has accumulated and take a sample of litter, of the same volume, to analyse for number of
litter organisms. The number and variety of litter organisms will affect the amount of
accumulated litter.
An increase in leaf litter should result in an increase in springtails which feed on the leaf litter.
They provide food for mites which are eaten by ants. The ants also eat springtails, and are
eaten by echidna. Thus the greater the amount of leaf litter the more diverse the litter
organism.
6
a.
b.
Productivity is an increase in biomass per unit time. This depends on photosynthesis
and photosynthetic efficiency of producers. Light cannot penetrate more than a few
metres into the ocean and thus productivity is limited to surface waters only. In
tropical rainforests with high light intensity, rainfall and nutrient recycling, all of the
canopy is exposed to light and this results in maximum growth.
Dry hot area, e.g. 1.3 desert scrub: by closing stomata in the hot part of the day the
plants reduce water loss by evaporation. This decreases the rate of photosynthesis
and thus productivity.