Explanation:
The correct answer is B. Food chain.
Here is a detailed explanation of each option:
A. Food web:
- A food web is a complex network of interconnected food chains that shows the flow of energy and matter through an ecosystem.
- It includes multiple species and their interactions, including predator-prey relationships and the transfer of nutrients.
- While a food web is related to the movement of organic molecules in a community, it does not specifically refer to the sequence of species through which these molecules pass.
B. Food chain:
- A food chain is a linear sequence of organisms, where each organism is a source of food for the next organism in the chain.
- It represents the transfer of energy and nutrients from one organism to another in a community.
- In a food chain, organic molecules move from one species to another in a specific sequence, starting from producers (plants) to primary consumers (herbivores) to secondary consumers (carnivores) and so on.
- Therefore, the correct answer is B. Food chain.
C. Nutrient cycle:
- The nutrient cycle refers to the movement and recycling of nutrients through biotic and abiotic components of an ecosystem.
- It involves the cycling of elements such as carbon, nitrogen, phosphorus, and others through living organisms, soil, water, and the atmosphere.
- While organic molecules are involved in nutrient cycles, the nutrient cycle does not specifically represent the sequence of species through which these molecules pass.
D. Pyramid of energy:
- A pyramid of energy is a graphical representation of the flow of energy through different trophic levels in an ecosystem.
- It shows the decrease in energy as it moves from one trophic level to another, with each level consuming a fraction of the energy from the level below.
- While organic molecules contribute to the energy flow in a pyramid of energy, it does not specifically represent the sequence of species through which these molecules pass.
To summarize, the correct answer is B. Food chain, as it represents the linear sequence of species through which organic molecules pass in a community.