Database results:
examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Nitrates and Amino Acids
Plants need more than just carbon dioxide and water to grow. They also need minerals from the soil, especially nitrogen in the form of nitrates. These nitrates are essential for making amino acids, which are the building blocks of proteins. Without proteins, plants couldn't grow, repair themselves, or make enzymes for all their chemical reactions.
Key Definitions:
Nitrogen is a crucial element for plants because it's used to make:
Without enough nitrogen, plants develop yellow leaves (chlorosis) and stunted growth.
Although nitrogen makes up about 78% of our atmosphere, plants can't use it directly in its gaseous form (N₂). Instead, they need nitrogen that has been 'fixed' into compounds like:
The nitrogen cycle is the process by which nitrogen moves between the atmosphere, soil, water and living organisms. Understanding this cycle helps us see how plants get the nitrogen they need.
Atmospheric nitrogen (N₂) is converted to ammonia (NH₃) by:
Ammonia is converted to nitrites (NO₂⁻) and then to nitrates (NO₃⁻) by nitrifying bacteria in the soil. Plants can absorb these nitrates through their roots.
Some bacteria convert nitrates back to nitrogen gas (N₂), which returns to the atmosphere. This happens mainly in waterlogged soils with little oxygen.
Leguminous plants like peas, beans and clover have a special relationship with nitrogen-fixing bacteria called Rhizobium. These bacteria live in nodules on the plants' roots and convert atmospheric nitrogen into ammonia that the plant can use. In return, the plant provides the bacteria with carbohydrates.
Farmers often plant legumes to naturally enrich soil with nitrogen - a practice called 'crop rotation'. After harvesting the legume crop, the next crop benefits from the extra nitrogen in the soil, reducing the need for artificial fertilisers.
Plants absorb nitrates from the soil through their root hair cells by active transport. This means they use energy to move nitrates against the concentration gradient (from where there's less nitrate to where there's more).
Unlike carbon dioxide and water, nitrates don't just diffuse into plants - they need to be actively pumped in. This process:
Once inside the plant, nitrates undergo a transformation:
Amino acids are organic compounds containing carbon, hydrogen, oxygen and crucially, nitrogen. Plants synthesise amino acids by combining the nitrogen from nitrates with carbon compounds produced during photosynthesis.
Once plants have made amino acids, they can link them together in long chains to form proteins. This process is called protein synthesis and happens in the ribosomes. Proteins serve many vital functions in plants:
When plants don't get enough nitrogen, they show specific symptoms:
Farmers and gardeners look for these signs to know when to add nitrogen fertilisers.
To boost crop yields, farmers often add nitrogen fertilisers to soil. While this helps plants grow, it can also cause environmental problems if not managed carefully.
When excess fertiliser washes into lakes and rivers (leaching), it can cause:
Farmers can reduce nitrogen pollution by:
Nitrates are essential for plant growth because they provide the nitrogen needed to make amino acids. These amino acids are then used to build proteins, which are vital for all aspects of plant structure and function. The nitrogen cycle ensures that nitrogen moves between the atmosphere, soil and living organisms, making it available to plants.
Understanding how plants use nitrates and synthesise amino acids helps us grow better crops while protecting the environment. By managing nitrogen carefully, we can ensure plants get what they need without causing pollution in our waterways.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.