Mix of multiple choice, true/false, and fill-in-the-blank
Instant feedback after each question
Unlimited attempts for practice
Estimated time: 25β30 minutes
QUESTION 1
Which of the following is NOT a compatible solute accumulated during drought stress?
β Correct! Starch is a storage carbohydrate, not a compatible solute. Compatible solutes (proline, glycine betaine, trehalose, sucrose) accumulate during stress to maintain cell turgor without interfering with metabolism .
QUESTION 2
The SOS pathway in plants is involved in tolerance to which stress?
β Correct! The SOS (Salt Overly Sensitive) pathway regulates NaβΊ homeostasis. SOS3 senses CaΒ²βΊ, activates SOS2 kinase, which phosphorylates SOS1 (NaβΊ/HβΊ antiporter), leading to NaβΊ efflux or compartmentalization .
QUESTION 3
The CBF/DREB transcription factors are master regulators of response to:
β Correct! CBF/DREB transcription factors are induced by cold and activate downstream genes involved in cold acclimation, including those for cryoprotectants and membrane modifications .
QUESTION 4
To which class of secondary metabolites does caffeine belong?
β Correct! Caffeine is a purine alkaloid. It acts as a natural pesticide in plants and is a stimulant in humans. Coffee, tea, and cacao all contain alkaloids .
QUESTION 5
What is the first committed enzyme in the phenylpropanoid pathway?
β Correct! PAL (phenylalanine ammonia lyase) converts phenylalanine to cinnamic acidβthe first committed step in phenylpropanoid metabolism. It is highly regulated by stress and development .
QUESTION 6
True or False: Abscisic acid (ABA) promotes stomatal opening to increase photosynthesis during drought.
β Correct! It's False. ABA actually promotes stomatal closure during drought to reduce water loss. It activates ion channels in guard cells, causing efflux of KβΊ and anions, leading to loss of turgor and stomatal closure .
QUESTION 7
Jasmonates are primarily involved in defense against:
β Correct! Jasmonates are key regulators of defense against herbivores and necrotrophic pathogens (those that kill host cells). They induce proteinase inhibitors, secondary metabolites, and volatile signaling .
QUESTION 8
Which enzyme converts superoxide (Oββ») to hydrogen peroxide (HβOβ)?
β Correct! Superoxide dismutase (SOD) catalyzes the dismutation of superoxide to hydrogen peroxide and oxygen. It's the first line of defense against ROS, with isoforms in chloroplasts (Cu/ZnSOD), mitochondria (MnSOD), and cytosol .
QUESTION 9
In the ascorbate-glutathione cycle, which enzyme regenerates reduced glutathione (GSH) from oxidized glutathione (GSSG)?
β Correct! Glutathione reductase (GR) uses NADPH to reduce GSSG back to GSH. This is essential for maintaining the cellular redox balance and antioxidant capacity .
QUESTION 10
What is the primary function of heat shock proteins (HSPs)?
β Correct! Heat shock proteins (HSPs) are molecular chaperones that help refold denatured proteins, prevent protein aggregation, and assist in protein import and degradation. They are essential for heat tolerance .
QUESTION 11
The Sub1A gene confers tolerance to which stress?
β Correct! The Sub1A gene confers submergence tolerance in rice. It allows plants to enter a quiescent state during flooding, conserving energy until the flood recedes. Sub1A rice is now grown on millions of hectares in South Asia .
QUESTION 12
An early-maturing wheat variety that completes its life cycle before seasonal drought is an example of:
β Correct! Stress escape involves completing the life cycle before stress occurs. Early maturity is a classic escape mechanism for drought-prone environments .
QUESTION 13
Quinoa is considered a model crop for tolerance to which stress?
β Correct! Quinoa is remarkably salt-tolerant. It accumulates glycine betaine and other osmoprotectants and has specialized epidermal bladder cells that sequester salt. It can grow in seawater dilutions .
QUESTION 14
Carotenoids such as Ξ²-carotene and lycopene belong to which class of terpenes?
β Correct! Carotenoids are tetraterpenes, built from 8 isoprene units (C40). They function as accessory pigments in photosynthesis and as antioxidants .
QUESTION 15
Enset (Ensete ventricosum), a staple crop in southern Ethiopia, is known for tolerance to which stress?
β Correct! Enset is remarkably drought-tolerant, surviving extended dry seasons through succulent stems, deep roots, and osmotic adjustment. Its mechanisms are not well studied but could provide insights for other crops .
π Module IV Complete!
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π Module IV Complete!
You have completed all units in Module IV: Stress & Environmental Biochemistry. You should now be able to:
4.1 Abiotic Stress β Understand plant responses to drought, salinity, and temperature extremes
4.2 Secondary Metabolites β Identify terpenes, phenolics, and alkaloids and their ecological roles
4.3 Plant Hormones in Stress β Explain ABA, jasmonate, and ethylene signaling pathways
4.4 Reactive Oxygen Species β Describe ROS production, damage, and antioxidant defense systems
4.5 Stress Tolerance Mechanisms β Distinguish escape, avoidance, and tolerance strategies in crops
π Congratulations! You have completed all four modules of Plant Biochemistry for Horticulture.
Plant Biochemistry for Horticulture Β· HORT 202 Β· Dilla University Β· Last updated March 2026