Mix of multiple choice, true/false, and fill-in-the-blank
Instant feedback after each question
Unlimited attempts for practice
Estimated time: 25–30 minutes
QUESTION 1
What is the formula for harvest index (HI)?
✅ Correct! Harvest index = economic yield / total biomass. It measures how efficiently a plant converts total dry matter into harvestable product. Modern wheat HI increased from 0.3 to 0.5 during the Green Revolution .
QUESTION 2
What genetic change was responsible for increasing harvest index in wheat during the Green Revolution?
✅ Correct! Dwarfing genes (Rht in wheat, sd1 in rice) reduced stem height, redirecting assimilates from straw to grain and increasing harvest index from ~0.3 to ~0.5 .
QUESTION 3
Which sugar has the highest relative sweetness?
✅ Correct! Fructose has the highest relative sweetness (1.2-1.8× sucrose), followed by sucrose (1.0), then glucose (0.6-0.7). This is why apples, high in fructose, taste sweet even with moderate sugar content .
QUESTION 4
Match the fruit with its dominant organic acid: (1) Apple, (2) Citrus, (3) Grape
✅ Correct! Apples are dominated by malic acid, citrus by citric acid, and grapes by tartaric acid. The sugar/acid ratio is a key quality index for all these fruits .
QUESTION 5
What class of aroma compounds gives bananas their characteristic smell?
✅ Correct! Bananas produce isoamyl acetate, an ester synthesized by alcohol acyltransferase (AAT). Esters are responsible for fruity, sweet aromas in many fruits .
QUESTION 6
Which vitamin is most commonly used as an indicator of nutritional quality because it is highly unstable?
✅ Correct! Vitamin C (ascorbic acid) is highly sensitive to heat, oxygen, and storage time. Its decline is often used as an indicator of overall nutritional quality loss during post-harvest handling .
QUESTION 7
True or False: Anthocyanins are primarily found in chloroplasts and function in photosynthesis.
✅ Correct! It's False. Anthocyanins are water-soluble pigments stored in vacuoles, not chloroplasts. They provide red/blue/purple colors and function in attracting pollinators and seed dispersers, UV protection, and as antioxidants .
QUESTION 8
What red carotenoid accumulates in ripening tomatoes?
✅ Correct! Lycopene is the red carotenoid responsible for tomato color. It is synthesized during ripening as chloroplasts convert to chromoplasts. Lycopene is also found in watermelon and pink grapefruit .
QUESTION 9
What enzyme breaks down chlorophyll during fruit ripening and leaf senescence?
✅ Correct! Chlorophyllase breaks down chlorophyll, revealing underlying carotenoids (bananas turning yellow) or allowing anthocyanin synthesis. This is why blanching vegetables before freezing inactivates chlorophyllase, preserving green color .
QUESTION 10
The Q₁₀ temperature coefficient for respiration is typically 2-3. What does this mean?
✅ Correct! Q₁₀ is the factor by which respiration increases for a 10°C temperature rise. A Q₁₀ of 2-3 explains why cold storage is so effective—reducing temperature from 20°C to 0°C can reduce respiration by 75-90% .
QUESTION 11
What enzyme breaks down pectin in the middle lamella, causing fruit softening?
✅ Correct! Polygalacturonase (PG) breaks down pectin in the middle lamella, causing cells to separate and fruit to soften. The Flavr Savr tomato used antisense RNA to suppress PG, slowing softening .
QUESTION 12
What is the primary biochemical cause of chilling injury in tropical fruits?
✅ Correct! Chilling injury occurs when membrane lipids undergo a phase transition from fluid to gel phase at temperatures above freezing. This causes loss of membrane integrity, electrolyte leakage, and cellular dysfunction. Tropical fruits (banana, mango, tomato) are especially susceptible .
QUESTION 13
1-MCP (SmartFresh™) extends storage life of apples by:
✅ Correct! 1-MCP (1-methylcyclopropene) binds to ethylene receptors, preventing ethylene from initiating ripening and senescence. This allows apples to remain firm and crisp for months .
QUESTION 14
What low-cost technology uses evaporative cooling to reduce storage temperatures in dry regions?
✅ Correct! A zero-energy cooler (or evaporative cooler) uses water evaporation through charcoal or other porous material to cool the interior. It can reduce temperatures by 10-15°C in dry climates, providing low-cost storage for smallholders .
QUESTION 15
Teff, Ethiopia's staple grain, has a relatively low harvest index (0.2-0.3). Why might breeding for higher HI in teff require careful consideration of trade-offs?
✅ Correct! Teff straw is valuable as animal feed in Ethiopia. Increasing harvest index by reducing straw could have negative consequences for farmers who rely on both grain and straw. Any breeding program must consider this trade-off .
📊 Module III Complete!
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Great job! Review the explanations for any questions you missed.
📌 Module III Complete!
You have completed all units in Module III: Biochemical Basis of Productivity & Quality. You should now be able to:
3.1 Harvest Index & Partitioning — Calculate HI and understand factors affecting it
3.2 Flavor Biochemistry — Explain the roles of sugars, acids, and aroma compounds
3.3 Nutritional Quality — Identify vitamins and antioxidants and factors affecting them
3.4 Pigments and Color — Describe chlorophylls, carotenoids, and anthocyanins
3.5 Post-Harvest Quality Changes — Understand biochemical changes after harvest and management strategies
👉 Next: Module IV explores Stress & Environmental Biochemistry.
Plant Biochemistry for Horticulture · HORT 202 · Dilla University · Last updated March 2026