Sample Qs-Pond ecosystem

1.Figure 1 shows pond ecosystem.

(a) (i) Based on Figure 1, name TWO factors for each of the following:-

-Biotic factor

-Abiotic factor [4m]

(ii) Name the abiotic factor that controls the distribution of submerged plants in the pond. [1m]

(iii) State the relationship between the factor you have named in (a)(ii) and the distribution of submerged plants. [1m]

(b) (i) Based on Figure 1, construct :
- A food web showing the interaction of all the organisms in the figure. [2m]

- A pyramid of numbers consisting of four trophic levels [2m]

(ii) Explain how energy is transferred from the sun to the organisms in food chain. [3m]

(iii) Explain why the amount of energy received by an organism via the food chain gradually decreases from one trophic level to the other trophic levels. [3m]

(c) (i) Name the organism that is known as the pioneer species in the pond. [1m]

(ii) Most of the pioneer species have adaptations that enable them to live in the bare
habitat. Give TWO adaptations of the pioneer species you have named in (c)(i). [2m]

(iii) Explain how the ecosystem in Figure 1 can turn into a climax ecosystem. [5m]

(d) Vegetables were planted near the pond in Figure 1. A farmer used chemical fertilizers to
enhance the growth of the vegetables. He also used pesticide to control the pests.
Predict the effects arising from those activities to the pond ecosystem after several years. [5m]

Suggested Answer:

1(a)(i) Biotic factor : Producer, consumer
Abiotic factor : light intensity, pH of water , depth of the pond.

(ii)light intensity

(iii)The lower the light intensity in the pond, the higher the population of submerged plant

(b)(i)Marks given for : all organisms correct- 1 , arrow correct - 1

(ii)- light energy trap by chlorophyll (in producers) and changed to chemical
energy in food (via photosynthesis)
- producer eaten by primary consumer, so energy from producer transfer to
the primary consumer
- primary consumer eaten by other consumer, so energy will transfer to that
organism via feeding

(iii)- energy lost directly from organisms to the surrounding through radiation
- lost through excretion such as urination, constipation and sweating
- lost through respiration

(c)(i)Hydrilla sp. / Elodea / Cabomba

(ii)- Reproduce asexually
- need only low light intensity to carry out photosynthesis

(iii)- submerged plants died and sink at the bottom of the pond, it change the
nutrient content and depth of the pond.
- submerged plants replaced by the floating plants, which at the end covered
surface of the water
- light cannot enter the inner part of the pond, so all submerged plants will
die and the pond become more shallow
- now the amphibian plants will replace the floating plant, and the pond
become less water
- at the end , terrestrial plants will take over the pond and form the climax
community

(d)Pesticide :-
- the toxic substances accumulate in the organisms via the food chain
- the concentration of toxic become higher as the trophic level increase
- this will cause extinction

Fertilizers :-
- more nitrates and phosphates in the pond
- enhance the growing of floating plants which caused algal bloom
- this will reduce amount of oxygen in the pond; situation known as eutrophication