energy and ecosystems exam questionsw

Question 1

suugest appropriate units for gross productivity

Answer 1

g/m2 per year

Question 2

explain the decrease in gross productivity as the woodland matures. 2)

Answer 2

-less light
-reduced photosynthesis

Question 3

use the infromation in figure 3 and your knowledge of net productivity to explain why biomass shows little increase after 100 years. (2)

Answer 3

-net productivity= gross productivity- respiratory losses
-increase in respiration.

Question 4

explain how the intense rearing of domestic livestock increases net productivity (4)

Answer 4

-movement restrictede
-heating
reduces losses from respiration.

controlled diet- less lost in faeces

genetically selective breeding.

Question 5

describe the reasons for the low efficiency of energy transfer through ecosystems. (5)

Answer 5

-some light reflected
-some light misses leaf
-heat losses
-energy lost through respiration
-and faeces.

Question 6

suggest why the efficiency of energy tranfser from producers to primary consumers in this food web is higher than 10%

Answer 6

-less respiration
-parts of plant not eaten

Question 7

energy from the sun may ultimately end up in dead plant matter. Explain how (2)

Answer 7

-photosynthesis
-carbon containing compounds.

Question 8

in some countries, pigs are reared in intensive units in whic the temperature is controlled. agricultural scientists investigated the effect of teperature on pig growth and on te efficiency with which pigs converted food to biomass.
in this investigation, te scientists used pigs of the same breed, with similar genotypes. Explain why. (2)

Answer 8

-same breed- similar genes
-removes genes as a variable

Question 9

the pigs were allowed to eat as much food as they wanted
how could this have decreased te reliability of any conclusions drawn from the investigation (2)

Answer 9

-different growth rates
-not due to temperature.

Question 10

pigs can survive at temperatures above 35 degrees celcius. Use the data to suggest why scientists did not carry out any investigations at temperatures higher than 35 degrees.

Answer 10

-growth rate decreases
-scientists looking for high growth rate.

Question 11

The athelete continues to breathe deeply several minutes after the race is over. Explain why this is necessary (2)

Answer 11

oxidise pyruvate into lactate
by aerobic respiration

Question 12

A hedgerow is a line of shrubs and trees bordering a field, together with the herbaceous plants at their base. In the last 50 years farmers have removed many hedgerows.
(a) Explain two advantages for a farmer of removing hedgerows
(2)

Answer 12

-source of pests
-source of weeds

Question 13

Use the data in the graph above to evaluate the use of artificial fertilisers on grain
producing crops in India. (3)

Answer 13

using more but getting less response over time
less cost effective
the graph shows ocrrelation but does not prove that changes in yield due to fertiliser.

Question 14

Explain why an increase in shoot biomass can be taken as a measurement of net
primary productivity. (2)

Answer 14

represents gross primary productivity- respiratory losses
represents dry mass of carbon.

Question 15

Yield can be determined by measuring the dry mass of plants.
(a)
(b)
Suggest how you could determine the dry mass of a sample of plant material. (2)

Answer 15

-heat to temperature to evaporate water
-weigh and heat until constnat mass reached

Question 16

What is the advantage of using dry mass and not fresh mass to compare the yield
of plants? (2)

Answer 16

water content varies
which will affect fresh mass

Question 17

(b)
Q15.
The scientists monitored the number of hours of sunshine per month. Explain why
they monitored the number of hours of sunshine. (2)

Answer 17

to monitor factors which cannot be controlled
-can elimiate this factor from affecting the yield.

Question 18

Between 1982 and 1992 the number of fish in the lake decreased. Explain how the
change in phosphate concentration may have resulted in this decrease in the fish
population (6)

Answer 18

-increase in phosphate concentration causes growth of algal blooms
-plants below cannot photosynthesise
-increase in bacteria
-use up oxygen for aerobic respiration
-plants cannot photosynthesise so less oxygen produced