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1. A student wanted to estimate the number of grasshoppers in 5km2 grass field near the school compound.
Using a sweep net he captured 36 grasshoppers. He used a red felt pen to mark the thorax of each insect before releasing back into the field. Three days later he made another catch of grasshoppers. He collected 45 grasshoppers of which only 4 had been marked with red mark.
a) Name the above method used in the population estimation b) Calculate the population of grasshoppers using the above data
2. What is the significance of the following in the ecosystem?
a) Decomposers
b) Predators
3. Birds feed on grasshoppers that feed on grass.
a) Draw a possible food chain from the above information
b) Explain why the biomass of organisms decreases at each preceding trophic level.
4. Define the following terms:-
(i) Autecology ;
(ii) Biomass;
5. State two most important factors that favour exponential growth of a population of gazelle
in a park
6. (a) Distinguish between habitat and niche.
(b) Explain why Biomass of producers is greater than that of primary consumers in a balanced
ecosystem.
(c) State two advantages of a biological control method over the chemical control method of
pests and parasites
7. Explain how oil as a pollutant may affect aquatic plants and animals?
8. The diagram below shows part of a food relationship in an ecosystem:-
(a) Name the food relationship above
(b) How many trophic levels are shown in the diagram above?
(c) State main source of energy in the ecosystem
9. Use the food web below to answer the questions that follow:-
(a) Construct a food chain ending with crocodile as a quartenary consumer
(b) Name the organisms in the food web hat has only one predator
10. 50 black mice and 50 white mice were released in an area inhabited by a pair of owls. After
four months, the mice in the area were recaptured and only 38 black mice and only a white mice
remained.
(a) How would you explain these results?
(b) Name the theory of evolution that support the results in (a) above
11. In a certain school Form three class did an experiment to estimate the number of Tilapia
in their fish pond. 725 tilapia were netted marked and released.
a) State the method used in this exercise
b) Calculate the tilapia population.
c) State two assumptions made by the students during the investigation
12. An investigation was carried out on a terrestrial ecosystem. The population sizes and species
biomass were determined and recorded as shown in the table
| SPECIES | POPULATION SIZE | SPECIES BIOMASS |
| A | 1×103 | 1×103 |
| B | 1×103 | 1×10-1 |
| C | 1×105 | 1×10 |
| D | 1×10 | 1×104 |
- If these organisms had a feeding relationship, construct a simple food chain involving all the organisms
- Construct pyramid of numbers using the data provided above
- State one disadvantage of using pyramid of number in expressing feeding relationships in ecological ecosystem
13. The figure represents a feeding relationship in an ecosystem
(a) Write down the food chain in which the Guinea Fowls are secondary consumers
(b) What would be the short term effects on the ecosystem if lions invaded the area
(c) Name the organism through which energy from the sun enters the food web
14. Outline three roles of active transport in human body
15. Distinguish between community and population
16. Describe how the belt transect can be used in estimating the population of a shrub in a
grass land
17. A fish farmer wanted to know the number of fish in a pond. He collected 10 fish from the pond
and labeled each, by a tag label on its fin and returned the ten fish to the pond to mix with
other fish . When he later collected 50 fish from the pond, he found only four of them had labels
a) Estimate the total number of fish in the pond (show your workings)
b) What two assumptions are being made in this methods of estimating population
18. What is the importance of saprophlic fungi and bacteria in an ecosystem
19. i) Name one main cause of global warming
ii)What are the effects of global warming
20. Explain how saliva is important in digestion
21. Give a reason why two species in an ecosystem cannot occupy the same niche
22. Below is a pyramid of numbers indicating trophic levels:-
(a) What do you understand by the term trophic level?
(b) Name the trophic level numbered 5 on the pyramid
(c) Name Q
(d)What is the significance of the arrow R
23. Two populations of the same species of birds were separated over a long period of time by an
ocean. Both populations initially fed on insects only. Later, it was observed that one population
fed entirely on fruits and seeds, although insects were available. Name this type of evolutionary
change
24. To estimate the population size of crabs in a certain lagoon, traps were laid at random. 400 crabs
were caught, marked and released back into the lagoon. Four days later, traps were laid again and
360 crabs were caught. Out of the 360crabs, 90 were found to have been marked
(i) Calculate the population size of the crabs in the lagoon
(ii) What is the name given to this method of estimating the population size
25. State the function of each of the following apparatus:
(a) Pooter …
(b) Sweep net …………
26. State the role of the following apparatus in the study of living things.
(a) Sweep nets.
(b) Pooter.
(c) Pit fall trap.
27. Name three density dependent factors in an ecosystem.
28. (a) What are the two main components of an ecosystem?
(b) Apart from mere observation of actual feeding suggest two methods that can be used
to determine the type of food eaten by animals
29. The chart below represents a simplified nitrogen cycle.
What is represented by X, Y and Z?
30. In an ecological study, a locust population and that of crows was estimated in a grassland area
over a period of one year. The results were tabulated as shown below.
| Months | J | F | M | A | M | J | A | S | O | N | D |
| No. of Adult locusts x 102 | 90 | 20 | 11 | 25 | 200 | 652 | 15 | 10 | 35 | 192 | 456 |
| Number of crows | 4 | 2 | 0 | 1 | 8 | 22 | 2 | 1 | 1 | 5 | 15 |
| Amount of rainfall | 20 | 0 | 55 | 350 | 520 | 350 | 10 | 25 | 190 | 256 | 350 |
a) Draw a graph of population of locusts and crows against time
b) i) State the relationship between rainfall and locust population
ii) Account for the relationship you have stated in b (i) above
c) What happens on the populations of locusts and crows in the months of January to March?
Give a reason.
d) If the area of study was one square kilometer, state one method used to estimate the
population of :- i) Locusts
ii) Crows
(e) (i) State the trophic levels of the (i) Locusts and (ii) crows
(ii) Construct a simple complete food chain involving these organisms
(f) If the locust were removed from the food chain, what would be its effect?
(g) Define biomass
31. Two species of antelopes were introduced into an ecosystem at the same time in equal numbers.
The graphs below show their relative numbers during the first eight years of their co-existence.
Study the graphs carefully and answer the questions that follow.
a) i) Which species of antelope has better survival adaptations.
ii) Give a reason for your answer above.
b) i) Name the type of curves shown.
ii) Name the phases labeled PQ, QR, RS, ST
c) Explain the shape of the curve for the species of Antelope A between
i) Q and R.
ii) S and T.
d) i) State the type of competition shown by the two species of antelopes.
ii) State any two symptoms of intraspecific competition in plants.
e) Suggest how the species B avoid competitive exclusion..
f) State any three adaptations that enable the antelopes to overcome predation.
g) State any two possible methods by which populations of the two antelopes’ species were
determined.
32. Explain five abiotic factors that affect the ecosystem
33. The data shown below was taken from Savannah grassland habitat. Examine it carefully and then
answer the questions that follow:-
| Organism | Population |
| Grasses | 1000 |
| Caterpillars | 500 |
| Squirrels | 300 |
| Frogs | 200 |
| Gazelles | 300 |
| Elephants | 100 |
| Snakes | 50 |
| Hunting dogs | 40 |
| Vultures | 40 |
| Lions | 40 |
| Hawks | 10 |
(a) Draw three food chains
(b) Draw a pyramid of numbers for a food chain with four trophic levels and indicate the trophic
levels at which each member feeds
(c) State the effect of removing the hunting dogs
(d) Why is it advisable to feed 100kg of grain to man instead of using it to fatten steers then
supply beef to human population? 34. Study the following food web and answer questions that follow:
(a) (i) Name the organisms that occupy the second trophic level
(ii) What is the other name for the second trophic level
(b) Write down two food chains from the food web that:
(i) End with hawks as tertiary consumer
(ii) End with hawks as quaternary consumer
(c) Giving reasons state; (i) the organism with largest biomass (ii) the organism with least biomass
35. (a) Explain how food as a factor regulates the population of animals in an ecosystem
(b) Describe the flow of energy from the sun through the different trophic levels in an ecosystem
36. (a) Describe how a population of grasshoppers in a given area can be estimated
(b) Describe how the belt transect can be used in estimating the population of a shrub in
a grassland
37. The flow chart below represents a feeding relationship in an ecosystem
(a) Name; (i) The producers in the ecosystem
(ii) Two organisms which are both secondary and tertiary consumers
(b) State two short term effects of immigration of insects in the ecosystem.
(c) Which organism has the least Biomass in the food web. Explain.
(d) State three disadvantages of using synthetic pesticides over Biological control.
(e) State the role of each of the following in an ecosystem;
(i) Saprophytes
(ii) Leguminous plants
(iii) Explain the role of producers in an ecosystem
(f) Name one method that would be used to estimate the population of small fish in the
ecosystem
38. How are leaves of mesophytes adapted to their functions?
