Mix of multiple choice, true/false, and fill-in-the-blank
Instant feedback after each question
Unlimited attempts for practice
Estimated time: 20โ25 minutes
QUESTION 1
What are the two main cell types that make up the functional unit of phloem transport?
โ Correct! Sieve elements are the conducting cells (enucleate), and companion cells provide metabolic support. Together they form the sieve element-companion cell (SE-CC) complex .
QUESTION 2
True or False: Phloem cells are dead at maturity, while xylem cells are alive.
โ Correct! It's False. Actually, the opposite is true! Phloem sieve elements are alive (though enucleate), while xylem vessels and tracheids are dead at maturity .
QUESTION 3
A mature, fully expanded leaf is typically a ________, while a developing fruit is a ________.
โ Correct! Mature leaves are sources (net exporters of photosynthates), while developing fruits are sinks (net importers) .
QUESTION 4
Sink strength is determined by which two factors?
โ Correct! Sink strength = sink size (physical size) ร sink activity (metabolic rate of import and conversion) .
QUESTION 5
What are the two components of starch?
โ Correct! Starch consists of amylose (linear ฮฑ-1,4 linkages) and amylopectin (branched with ฮฑ-1,6 linkages). The ratio affects food properties .
QUESTION 6
The key regulatory enzyme in starch synthesis, AGPase, is activated by ________ and inhibited by ________.
โ Correct! AGPase (ADP-glucose pyrophosphorylase) is activated by 3-PGA (a product of photosynthesis) and inhibited by inorganic phosphate (Pi). This ensures starch is made when photosynthesis is active .
QUESTION 7
What causes cold-induced sweetening in potatoes, and why is it a problem for chip manufacturers?
โ Correct! Cold temperatures cause starch to break down to reducing sugars (glucose, fructose). During frying, these sugars react with amino acids (Maillard reaction), producing dark, bitter chips .
QUESTION 8
What is the key regulatory enzyme in sucrose synthesis?
โ Correct! Sucrose-phosphate synthase (SPS) is the key regulatory enzyme. It's activated by glucose-6-phosphate and light, inhibited by Pi, and regulated by phosphorylation .
QUESTION 9
Which enzyme breaks down sucrose into UDP-glucose and fructose, and is important in sink tissues for starch synthesis?
โ Correct! Sucrose synthase (SuSy) cleaves sucrose + UDP โ UDP-glucose + fructose. UDP-glucose is then used for starch synthesis, cell wall biosynthesis, and other pathways .
QUESTION 10
Which sugar is the sweetest (highest relative sweetness)?
โ Correct! Fructose has the highest relative sweetness (1.2-1.8 ร sucrose). This is why fruits high in fructose (like apples) taste sweet even with moderate sugar content .
QUESTION 11
Brix measures ________ in fruits and vegetables, primarily sugars.
โ Correct! Brix measures soluble solids, primarily sugars. One degree Brix = 1 g sucrose per 100 g solution. It's the standard field measurement for fruit quality, with export markets often requiring minimum Brix levels .
QUESTION 12
In Ethiopian coffee production, higher ________ content in green beans is associated with better cup quality due to caramelization and Maillard reactions during roasting.
โ Correct! Sucrose in coffee beans caramelizes and participates in Maillard reactions during roasting, contributing to flavor and aroma. Higher sucrose content is associated with better cup quality .
๐ Section 2.3 Complete!
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๐ Section 2.3 Complete!
You have completed all units in Section 2.3: Carbohydrate Transport & Storage. You should now be able to:
Describe phloem structure and the roles of sieve elements and companion cells
Explain source-sink relationships and how sink strength determines assimilate partitioning
Understand starch synthesis (AGPase regulation) and degradation (amylases)
Describe sucrose metabolism, including synthesis (SPS) and degradation (invertase, SuSy)
Apply carbohydrate biochemistry to crop quality (sweetness, texture, storage, processing)