The diagram shows the carbon cycle. Which letter indicates respiration?
Answer/Explanation
Answer: B
Explanation:
- In the carbon cycle, respiration is the process by which organisms break down organic compounds (like glucose) and release carbon dioxide (CO₂) into the atmosphere. This happens in plants, animals, and decomposers.
- In the diagram, Arrow B shows carbon moving from organic compounds in plants to CO₂ in the atmosphere, which directly represents plant respiration.
- Other forms of respiration (by animals or decomposers) also release CO₂, but B is the most direct example in this diagram.
Answer Evaluation:
A. Incorrect – This represents photosynthesis, where CO₂ is taken in by plants.
B. Correct – This represents respiration, where plants release CO₂ into the atmosphere.
C. Incorrect – This represents feeding, the transfer of carbon from plants to animals.
D. Incorrect – This represents decomposition, not respiration directly, though it can involve microbial respiration.
Question
Which processes occur in an ecosystem?
I. Biomass increases in each successive trophic level.
II. Inorganic nutrients are recycled.
III. Chemical energy is stored in carbon compounds.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
Answer: C. II and III only
Explanation:
- An ecosystem involves interactions between living organisms and their environment, including the flow of energy and cycling of nutrients.
- Inorganic nutrients (like carbon, nitrogen, and phosphorus) are recycled through processes like decomposition and photosynthesis, so they can be reused by organisms.
- Chemical energy is stored in carbon compounds (like glucose) made during photosynthesis, and this energy is used by organisms in the food chain.
- Biomass does not increase at each trophic level; in fact, it decreases due to energy loss as heat, waste, and respiration at each level.
Answer Evaluation:
A. Incorrect – I is incorrect; biomass decreases at higher trophic levels.
B. Incorrect – I is incorrect; although chemical energy is stored, biomass doesn’t increase.
C. Correct – II (nutrient recycling) and III (energy in carbon compounds) are true ecosystem processes.
D. Incorrect – Includes I, which falsely claims biomass increases with trophic level.
In ecosystems the amount of energy that passes from one trophic level to the next is called the conversion efficiency. What is the average conversion efficiency from primary to secondary consumers in most ecosystems?
A. 1 %
B. 10 %
C. 50 %
D. 90 %
Answer/Explanation
Answer: B. 10%
Explanation:
- In most ecosystems, only about 10% of the energy stored in the biomass of one trophic level is passed on to the next level. This is known as the energy conversion efficiency.
- The remaining 90% of the energy is lost as heat through respiration, used for movement, or lost as waste (like undigested material or excreted products).
- Therefore, when primary consumers (herbivores) eat producers (plants), only about 10% of the energy is transferred to their biomass.
Answer Evaluation:
A. Incorrect – 1% is too low for trophic transfer between consumers; it’s closer to the energy captured by plants from sunlight.
B. Correct – On average, 10% of the energy is transferred from primary to secondary consumers.
C. Incorrect – 50% is too high; much of the energy is lost at each level.
D. Incorrect – 90% represents energy lost, not transferred.
Question
What is exchanged between a sealed mesocosm and the surrounding external environment?
A. Energy
B. Water
C. Air
D. Nothing can pass
▶️Answer/Explanation
Answer: A. Energy
Explanation:
- A mesocosm is a small, controlled ecosystem set up to study ecological processes under natural conditions. It is sealed to prevent the exchange of matter (like water or air), but it still allows energy (usually in the form of light or heat) to move in and out.
- This makes it a closed system for matter but an open system for energy. Light energy from the sun enters to support photosynthesis, and heat energy can be released to the environment.
Answer Evaluation:
A. Correct – Energy, such as light and heat, can pass in and out of a sealed mesocosm.
B. Incorrect – Water is matter, and in a sealed mesocosm, water is recycled internally and not exchanged with the surroundings.
C. Incorrect – Air (gases) cannot enter or leave a sealed mesocosm; gas cycles occur within the system.
D. Incorrect – Energy can pass through; it’s not completely closed to everything.