Mix of multiple choice, true/false, and fill-in-the-blank
Instant feedback after each question
Unlimited attempts for practice
Estimated time: 20–25 minutes
QUESTION 1
What are the two enzymes responsible for reducing nitrate (NO₃⁻) to ammonium (NH₄⁺) in plants?
✅ Correct! Nitrate reductase (NR) in the cytoplasm reduces NO₃⁻ to NO₂⁻, and nitrite reductase (NiR) in plastids reduces NO₂⁻ to NH₄⁺. GS-GOGAT then assimilates ammonium into amino acids .
QUESTION 2
The nitrate transporter NRT1.1 is unusual because it functions both as a transporter and as a:
✅ Correct! NRT1.1 is a "transceptor"—it acts as both a transporter and a nitrate sensor, regulating gene expression and root development in response to nitrate availability .
QUESTION 3
The enzyme nitrogenase, which fixes atmospheric N₂, is extremely sensitive to:
✅ Correct! Nitrogenase is irreversibly damaged by oxygen. This creates the "oxygen paradox"—nitrogen fixation requires ATP (from respiration), but oxygen destroys the enzyme. Legumes solve this with leghemoglobin, which buffers oxygen in nodules .
QUESTION 4
What is the function of leghemoglobin in nitrogen-fixing nodules?
✅ Correct! Leghemoglobin binds oxygen with high affinity, maintaining a low free O₂ concentration to protect nitrogenase while delivering enough O₂ for bacterial respiration. It gives nodules their characteristic pink color .
QUESTION 5
Where in the plant cell does fatty acid synthesis occur?
✅ Correct! Fatty acid synthesis occurs in plastids (chloroplasts in leaves, leucoplasts in seeds). The key regulatory enzyme is ACCase (acetyl-CoA carboxylase) .
QUESTION 6
High-oleic sunflower oil (>80% oleic acid) is produced by mutations in which gene?
✅ Correct! FAD2 encodes the desaturase that converts oleic acid (18:1) to linoleic acid (18:2). Mutations in FAD2 block this step, causing oleic acid to accumulate. High-oleic oils have better oxidative stability for frying .
QUESTION 7
What are the two main components of the fruit cuticle?
✅ Correct! The fruit cuticle consists of cutin (a polymer of hydroxy fatty acids) and waxes (very-long-chain fatty acids and their derivatives). It prevents water loss, protects against pathogens, and affects appearance .
QUESTION 8
True or False: Tropical fruits like mango and banana are more susceptible to chilling injury because their membranes have more saturated fatty acids.
✅ Correct! It's False. Actually, tropical fruits have membranes with more unsaturated fatty acids, but they are still susceptible to chilling injury because their membranes undergo phase transition at higher temperatures than temperate fruits. The statement is reversed .
QUESTION 9
What is the primary pathway for ammonium assimilation in plants?
✅ Correct! The GS-GOGAT pathway (glutamine synthetase + glutamate synthase) is the primary route for ammonium assimilation. GS incorporates NH₄⁺ into glutamine; GOGAT transfers the amino group to form glutamate .
QUESTION 10
Approximately what percentage of applied nitrogen fertilizer is taken up by crops globally?
✅ Correct! Global nitrogen use efficiency for cereal production is only about 33%—meaning two-thirds of applied nitrogen is lost to the environment, causing pollution and economic loss. Improving NUE is a major goal for sustainable agriculture .
QUESTION 11
In the Kennedy pathway for triglyceride synthesis, what is the role of DGAT (diacylglycerol acyltransferase)?
✅ Correct! DGAT catalyzes the final step in triglyceride synthesis, adding a fatty acid to diacylglycerol (DAG) to form triacylglycerol (TAG). It is the only enzyme specific to TAG synthesis and is a target for increasing oil content .
QUESTION 12
Niger seed (nug), an important oilseed crop in Ethiopia, has oil that is very high in which fatty acid?
✅ Correct! Niger seed oil is very high in linoleic acid (up to 75%), making it prone to oxidation. Breeding for higher oleic acid (via FAD2 mutations) could improve its oxidative stability for export markets .
📊 Section 2.4 Complete!
0/12
Great job! Review the explanations for any questions you missed.
📌 Section 2.4 Complete!
You have completed all units in Section 2.4: Nitrogen & Lipid Metabolism. You should now be able to:
Describe nitrogen assimilation via NR, NiR, and GS-GOGAT
Explain biological nitrogen fixation and the legume-rhizobia symbiosis
Understand fatty acid synthesis, desaturation, and triglyceride assembly
Identify the roles of lipids in fruit cuticles, membranes, and chilling injury
Apply this knowledge to improve fertilizer management and oil quality
👉 Next: Module III explores the Biochemical Basis of Productivity & Quality.
Plant Biochemistry for Horticulture · HORT 202 · Dilla University · Last updated March 2026