One-Way Passage in an Ecosystem

In an ecosystem, the flow of energy and nutrients is essential for the functioning and stability of the system. While some components of the ecosystem, such as energy, move in a one-way passage, others, like carbon, nitrogen, and potassium, may cycle through the system.

1. Free Energy
- Free energy refers to the energy available to do work within an ecosystem.
- It is obtained primarily from the sun through photosynthesis, where plants convert solar energy into chemical energy.
- This energy is transferred to various organisms as they consume plants or other organisms.
- However, once the energy is utilized by an organism, it is no longer available for further use, resulting in a one-way passage of energy through the ecosystem.
- For example, when herbivores consume plants, they obtain energy from the plant, but once that energy is used for growth, movement, or reproduction, it cannot be passed on to the next trophic level.

2. Carbon
- Carbon is an essential element for living organisms and is present in various organic compounds.
- Carbon cycles through the ecosystem in a cyclic manner, rather than following a one-way passage.
- Plants take in carbon dioxide from the atmosphere during photosynthesis and convert it into organic compounds.
- When organisms consume plants or other organisms, they obtain carbon-containing compounds.
- When organisms respire or decompose, carbon dioxide is released back into the atmosphere, completing the carbon cycle.

3. Nitrogen
- Nitrogen is a crucial element required for the synthesis of proteins and nucleic acids.
- The nitrogen cycle involves the conversion of nitrogen gas in the atmosphere into forms that can be utilized by living organisms.
- Certain bacteria in the soil or root nodules of leguminous plants convert atmospheric nitrogen into ammonia through a process called nitrogen fixation.
- Ammonia is then converted into nitrites and nitrates through nitrification.
- Plants take up these nitrates from the soil and incorporate them into their tissues.
- When organisms consume plants or other organisms, they obtain nitrogen-containing compounds.
- Nitrogen is returned to the soil through the decomposition of dead organisms or waste products, and it can be further recycled.

4. Potassium
- Potassium is an essential nutrient required for various physiological processes in plants, such as enzyme activation and osmoregulation.
- Unlike energy, carbon, and nitrogen, potassium does not cycle through the ecosystem.
- It is primarily obtained by plants from the soil through their root systems.
- As organisms consume plants or other organisms, they obtain potassium, but it does not undergo further cycling.
- When organisms die or excrete waste, the potassium is deposited in the soil, contributing to its nutrient content.

In conclusion, while energy flows through an ecosystem in a one-way passage, carbon and nitrogen cycle through the system. On the other hand, potassium does not cycle and remains within the organisms or is deposited in the soil. Therefore, the correct answer to the question is option 'A' - free energy.