Free Ecosystems MCQs with Answers

51. The organisms of the third trophic level are:

• A. Primary consumer
• B. Primary producer
• C. Tertiary consumer
• D. Secondary consumer

Explanation: Secondary consumers belong to trophic level three, they feed on primary consumers.

52. The ultimate source of energy in an ecosystem is

• A. Photosynthesis
• B. Sun
• C. Plants
• D. Water

Explanation: Sun is the ultimate source of energy because it is the source of most of the energies on Earth. It provides solar energy, it is responsible for photosynthesis in plants and also provides vitamin D to humans.

53. All the food chains and food webs begin with:

• A. Detritus
• B. Herbivores
• C. Green plants
• D. Omnivores

Explanation: The living part of the food chain always begins with plant life, as plants are the only organisms that get their energy from a nonliving source, Sun. We know that the Sun is the ultimate source of energy because it does not depend on anything else.

54. The change from bare rock or open area is rapid, especially in the initial stages and follows a series of recognizable and hence predictable stages. This process is called

• A. Pioneers
• B. Xerosere
• C. Succession
• D. Secondary succession

Explanation: A broad definition of succession states: 'Ecological succession is the process by which the mix of species and habitat in an area changes over time. Gradually, these communities replace one another until a "climax community" is reached.' (via news.uchicago.edu) This fits the description provided in the question hence it's the correct option.

55. How denitrification does occur in soils?

• A. Bacterial reduction of NO3- ions to N2 gas.
• B. Active uptake of Nitrate ions by plant roots
• C. Drainage of manure from fields
• D. Leaching of nitrate ions

Explanation: Denitrification is a natural soil microbial process where nitrate ions are converted to nitrogen gas which is then lost to the atmosphere. Denitrification occurs when soil bacteria use nitrate for their respiration in place of oxygen in the air.

56. How much energy will be fixed by the primary carnivores?

• A. 2317 Kcal
• B. 232 kcal
• C. 1564 kcal
• D. None of above.

Explanation: The correct answer is 'None of above.' This is because as organisms move up trophic levels, there is a significant loss of energy, with only a small percentage being transferred to the next trophic level. Without specific information on the number of herbivores or primary carnivores, it is impossible to determine the exact amount of energy that will be fixed by the primary carnivores. Therefore, the correct answer is 'None of above.'

57. Corpuscular animals are active during:

• A. Night
• B. Day
• C. Twilight
• D. Spring

Explanation: Crepuscular animals are active during the twilight period, which is the time between day and night. Nocturnal animals are active during the night, diurnal animals are active during the day, and spring is a season rather than a time of day. Therefore, the correct answer is option C:Twilight.

58. Rabbits, pabulus, rats grasshoppers and grasses constitute a

• A. Habitat
• B. Biome
• C. Community
• D. Population

Explanation: A community is a group or association of populations of two or more different species occupying the same geographical area at the same time.

59. The association in which an organism gets advantage and the other suffers is called:

• A. Symbiosis
• B. Parasitism
• C. Predation
• D. Mutualism

Explanation: A parasitic relationship is one in which one organism, the parasite, lives off of another organism, the host, harming it and possibly causing death.

60. Each organism has a definite functional position different from either organisms of the locally is called :

• A. Community
• B. Niche
• C. Habitat
• D. Species

Explanation: In ecology, a niche refers to the specific role or position that an organism occupies within an ecosystem. It includes the range of conditions and resources that the organism requires for survival and reproduction, as well as its interactions with other organisms in the community. The niche of an organism is defined by its unique combination of habitat requirements, behavior, and ecological interactions.