Extension Questions 28. Plants and animals are part of all of the nutrient cycles through the foods they eat and what eats them (food chains and food webs). Name the four classes of organic compounds (containing carbon) and explain how the carbon cycle and nitrogen cycle contribute to the usable supplies of these macromolecules.

The four classes of organic compounds are carbohydrates, proteins, lipids, and nucleic acids. In the carbon cycle, carbon dioxide is absorbed by plants during photosynthesis to create carbohydrates, which are then consumed by animals, forming the foundation of the food web. When these organisms respire or decompose, carbon is returned to the atmosphere, completing the cycle and making carbon available for new organic compounds. In the nitrogen cycle, nitrogen gas is converted into forms usable by plants (like nitrates) through processes such as nitrogen fixation. Plants utilize these nitrates to build proteins, integral for growth and cellular function. Animals consume these plants, obtaining proteins themselves. Upon decomposition, nitrogen is returned to the soil, ensuring a continuous supply for future generations of plants, keeping the cycle thriving!