Final answer:
Plant use nitrogen to synthesize the molecules rubisco and chlorophyll, which are essential for proteins and the photosynthesis process. Nitrogen must be bioavailable, typically through nitrogen fixation, for plants to utilize it.
Step-by-step explanation:
Much of the nitrogen taken in by a plant is used to synthesize the molecules rubisco and chlorophyll. Nitrogen is vital for plants as it is a key component of amino acids, the building blocks of proteins, which in turn are essential for the structure and function of plant cells. The enzyme rubisco is crucial for photosynthesis, a process that converts carbon dioxide and water into glucose using sunlight, which the plant then uses for growth and energy. Nitrogen is also important for the synthesis of other molecules such as chlorophyll, the green pigment that captures light energy. Since atmospheric nitrogen (N₂) is not readily accessible to plants, it must be converted into more bioavailable forms, like ammonia (NH₃), through the process of nitrogen fixation, sometimes with the help of symbiotic bacteria in the soil.