18. Explain why food webs and energy pyramids show the flow of energy but the cycling of matter.
© The Earth has a constant amount of energy and matter.
• The Sun continually replenishes the Earth's matter, but the Earth has a constant amount of energy.
© The Sun continually replenishes the Earth's energy and matter.
• The Sun continually replenishes the Earth's energy, but the Earth has a constant amount of matter.
Food webs and energy pyramids show the flow of energy because energy is transferred from one organism to another as they consume and are consumed by each other. This transfer of energy can be represented by arrows in a food web or energy pyramid.
On the other hand, the cycling of matter refers to the movement and recycling of elements and compounds through different organisms and ecosystems. This is because matter on Earth is not created nor destroyed but is constantly recycled through biogeochemical cycles such as the carbon, nitrogen, and water cycles.
In terms of the statements provided, the one that most accurately explains why food webs and energy pyramids show the flow of energy but the cycling of matter is that "the Sun continually replenishes the Earth's energy, but the Earth has a constant amount of matter." This is because the Sun is the primary source of energy for Earth, constantly providing it through processes like photosynthesis. However, the matter on Earth remains relatively constant and is recycled through various processes, such as decomposition and nutrient uptake by plants.