Define competition, commensalism, niche, and describe the carbon cycle.

Here are short notes on the requested terms:

i) Competition:
Competition is an interaction between organisms or species that require the same limited resources, such as food, water, territory, or mates. This interaction can be intraspecific (between individuals of the same species) or interspecific (between individuals of different species). Competition generally has a negative effect on both parties involved, as it reduces the availability of resources for each.

ii) Commensalism:
Commensalism is a type of symbiotic relationship between two organisms where one organism benefits, and the other organism is neither significantly harmed nor helped. The commensal organism often uses the host for shelter, transport, or food scraps without affecting the host's fitness.
Example: Barnacles attaching to whales, benefiting from transport and food particles in the water, while the whale is unaffected.

iii) Niche:
A niche refers to the specific role and position a species has within its ecosystem. It encompasses all the biotic and abiotic factors that a species needs to survive, grow, and reproduce, including its habitat, food sources, interactions with other species, and its impact on the environment. It describes how an organism "makes a living" in its environment.

Here is how carbon circulates in the ecosystem:

Carbon cycle:
Carbon circulates through the ecosystem primarily via the carbon cycle. Atmospheric carbon dioxide ($\text{CO}_2$) is absorbed by plants during photosynthesis to produce organic compounds. These compounds are then consumed by animals, transferring carbon through the food chain. Both plants and animals release $\text{CO}_2$ back into the atmosphere through respiration. When organisms die, decomposers break down their organic matter, releasing carbon into the soil and atmosphere. Over long periods, buried organic matter can form fossil fuels. The burning of fossil fuels and volcanic activity also release $\text{CO}_2$ into the atmosphere. Oceans also play a significant role, absorbing and releasing $\text{CO}_2$ and storing carbon in marine organisms and sediments.

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