Economic and Applied Botany: Food, Fibre, Timber, Sugar, Beverages, Oils, Rubber, Dyes, Drugs, Microbes, GM Crops and Postharvest Processing

Practice questions (16)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

1. A cereal grain such as a wheat or rice kernel is correctly described botanically as which of the following?

   1. A seed, because the stored food lies in cotyledons within a seed coat
   2. A caryopsis, a one-seeded dry fruit whose fruit wall is fused to the seed coat
   3. A legume, a dry fruit that splits along two sutures to release its seeds
   4. A nut, an indehiscent dry fruit bearing a single seed enclosed within a hard, thick, woody pericarp
   Show answer

   Answer: B — A caryopsis, a one-seeded dry fruit whose fruit wall is fused to the seed coat

   A cereal grain is a caryopsis: a one-seeded dry fruit in which the pericarp is fused to the seed coat, so the whole grain is a fruit, not a seed. A pulse is a seed shed from a legume (pod). The grain is not woody enough to be a nut, and its wall does not split, so it is not a dehiscent legume.

2. A diet built almost entirely on a single cereal tends to be deficient in the amino acid lysine. Combining the cereal with a pulse improves the protein quality mainly because:

   1. Pulse protein is relatively rich in lysine and so complements the cereal's shortfall
   2. Pulses destroy the anti-nutritional factors that otherwise block cereal protein digestion
   3. Pulses convert the cereal's starch into additional protein during cooking
   4. Pulses supply the vitamin that the body needs in order to synthesize lysine itself
   Show answer

   Answer: A — Pulse protein is relatively rich in lysine and so complements the cereal's shortfall

   Cereal protein is low in lysine and pulse protein is low in methionine; each supplies what the other lacks, so the mixture has a more balanced amino-acid profile (mutual supplementation). Starch is not turned into protein, lysine is an essential amino acid the human body cannot synthesize at all, and the benefit is complementation, not the removal of anti-nutrients.

3. Which of the following correctly pair a plant fibre with the organ from which it is obtained?

   1. Cotton — surface hairs (trichomes) borne on the seed coat
   2. Jute — bast (phloem) fibre of the stem
   3. Coir — bast fibre of the stem, like jute and flax
   4. Sisal — surface hairs on the seed, like cotton
   Show answer

   Answer: A — Cotton — surface hairs (trichomes) borne on the seed coat; B — Jute — bast (phloem) fibre of the stem

   Cotton is seed-surface hairs and jute is a stem bast fibre, both correct. Coir is not a stem bast fibre: it is the fibre of the coconut's fruit husk (mesocarp). Sisal is not a seed hair: it is a leaf fibre of Agave sisalana.

4. After ginning, 400 kg of seed cotton (kapas) yields 136 kg of lint, the rest being seed and waste. Express the lint as a percentage of the seed cotton (the ginning percentage). Give the answer to one decimal place.

   Numerical answer — type the value.

   Show answer

   Answer: 34.0

   Ginning percentage = lint ÷ seed cotton × 100 = 136 ÷ 400 × 100 = 34.0%. Dividing lint by seed weight (the 264 kg remainder) instead of by the total seed cotton is the usual error.

5. Teak, sal and sheesham are valued as timber. In botanical terms, the timber of such trees is essentially which tissue?

   1. Secondary phloem laid down towards the outside by the vascular cambium
   2. Cork (phellem) produced towards the outside by the cork cambium
   3. Secondary xylem (wood) laid down towards the inside by the vascular cambium
   4. Primary ground tissue (pith) occupying the very centre of the stem
   Show answer

   Answer: C — Secondary xylem (wood) laid down towards the inside by the vascular cambium

   Wood is secondary xylem, laid down inwards by the vascular cambium year after year; the durable, non-conducting core is heartwood. Secondary phloem and cork lie outside the cambium and form the bark, not the timber, and pith is a small primary tissue at the centre, not the bulk of the trunk.

6. Natural rubber is tapped from Hevea brasiliensis. Which description of its source and chemistry is correct?

   1. A resin exuded from the heartwood, chemically a mixture of diterpene acids
   2. An oil pressed from the endosperm, chemically a mixture of triglycerides
   3. A gum exuded from the seed coat, chemically a branched polysaccharide
   4. Latex from laticifers in the bark, chemically cis-1,4-polyisoprene
   Show answer

   Answer: D — Latex from laticifers in the bark, chemically cis-1,4-polyisoprene

   Rubber is harvested as latex from laticifers in the bark of Hevea brasiliensis and is chemically cis-1,4-polyisoprene, a terpene polymer. It is not a heartwood resin, not a seed-coat gum, and not a triglyceride oil; those describe other plant products entirely.

7. Which of the following correctly link a drug or stimulant with its plant source and the part used?

   1. Morphine — latex of the unripe capsule of Papaver somniferum
   2. Quinine — bark of Cinchona species
   3. Reserpine — seeds of Camellia sinensis
   4. Caffeine — root of Rauvolfia serpentina
   Show answer

   Answer: A — Morphine — latex of the unripe capsule of Papaver somniferum; B — Quinine — bark of Cinchona species

   Morphine is obtained from the latex of the unripe poppy capsule and quinine from Cinchona bark, both correct. Reserpine comes from the root of Rauvolfia serpentina, not the seeds of tea; caffeine comes from tea leaf and coffee seed, not from Rauvolfia root. The two wrong statements swap the plants of the two correct ones.

8. Which pair of beverage plants both yield caffeine as their principal stimulant alkaloid?

   1. Cocoa (Theobroma cacao) and tea (Camellia sinensis)
   2. Coffee (Coffea arabica) and opium poppy (Papaver somniferum)
   3. Tea (Camellia sinensis) and coffee (Coffea arabica)
   4. Cocoa (Theobroma cacao) and Cinchona (Cinchona officinalis)
   Show answer

   Answer: C — Tea (Camellia sinensis) and coffee (Coffea arabica)

   Tea leaf and coffee seed both yield caffeine. Cocoa's principal stimulant is theobromine, not caffeine, so pairs containing cocoa are wrong; opium poppy yields morphine and Cinchona yields quinine, neither of which is caffeine.

9. Agar, the gelling agent of microbiological media, and carrageenan are both obtained from which group of organisms?

   1. Brown algae, which are also the source of alginates
   2. Nitrogen-fixing bacteria, such as Rhizobium and Azotobacter
   3. Filamentous fungi, such as Penicillium and Aspergillus
   4. Red algae, such as Gelidium and Gracilaria
   Show answer

   Answer: D — Red algae, such as Gelidium and Gracilaria

   Agar and carrageenan are cell-wall polysaccharides of red algae (Rhodophyta) such as Gelidium and Gracilaria. Brown algae give alginates, not agar; fungi and bacteria give antibiotics, enzymes and nitrogen fixation but not these gelling agents.

10. Which of the following statements about the economic roles of lower organisms are correct?

    1. Lichens are sensitive indicators of air pollution and are a source of litmus
    2. Many fungi form mycorrhizal associations that help plants take up phosphate from soil
    3. Rhizobium in legume root nodules fixes atmospheric nitrogen into a usable form
    4. Penicillin, the first widely used antibiotic, is obtained from a red alga
    Show answer

    Answer: A — Lichens are sensitive indicators of air pollution and are a source of litmus; B — Many fungi form mycorrhizal associations that help plants take up phosphate from soil; C — Rhizobium in legume root nodules fixes atmospheric nitrogen into a usable form

    Lichens indicate air pollution and yield litmus, many fungi form phosphate-scavenging mycorrhizae, and Rhizobium fixes nitrogen in legume nodules, all correct. Penicillin is from the fungus Penicillium, not from a red alga.

11. Bt cotton expresses a cry gene from Bacillus thuringiensis. How does the Cry protein protect the plant against bollworms?

    1. Activated in the alkaline insect midgut, it binds gut-cell receptors and lyses the lining of susceptible larvae
    2. It is a volatile terpene that repels adult moths before they can lay eggs on the plant
    3. It thickens the cuticle of the cotton boll so that larvae cannot chew through it
    4. It is a broad-spectrum toxin equally lethal to insects, earthworms and mammals that feed on the plant
    Show answer

    Answer: A — Activated in the alkaline insect midgut, it binds gut-cell receptors and lyses the lining of susceptible larvae

    The Cry protoxin is solubilized and proteolytically activated in the high-pH insect midgut, where it binds specific receptors on gut epithelial cells and lyses them, killing susceptible larvae. The specificity of those receptors is why it is toxic to certain insects but not to mammals, so it is neither a repellent terpene, nor a cuticle-thickener, nor a broad-spectrum poison.

12. Regarding the regulation of genetically modified crops in India, which statement is correct as commonly stated?

    1. Bt brinjal is approved for commercial cultivation, while Bt cotton remains under a moratorium
    2. All genetically modified crops are banned outright in India, including Bt cotton
    3. Golden rice is the only GM crop approved for commercial cultivation in India
    4. Bt cotton is approved for commercial cultivation, whereas Bt brinjal has been placed under a moratorium
    Show answer

    Answer: D — Bt cotton is approved for commercial cultivation, whereas Bt brinjal has been placed under a moratorium

    Bt cotton is the one GM crop approved for commercial cultivation in India, while Bt brinjal, though recommended by the regulator, was placed under a moratorium and is not cultivated commercially. Not all GM crops are banned (Bt cotton is grown), and golden rice is not under commercial cultivation in India.

13. Secondary metabolites are grouped into three main classes. A nitrogen-containing, usually bitter and physiologically active compound derived from an amino acid, such as morphine, nicotine or quinine, belongs to which class, and which statement about the classes is also correct?

    1. A terpenoid; terpenoids are built from C5 isoprene units and include menthol and carotenoids
    2. A phenolic; phenolics are nitrogen-free and include all the isoprene-derived pigments
    3. An alkaloid; terpenoids are built from C5 isoprene units and include menthol and carotenoids
    4. An alkaloid; alkaloids are nitrogen-free terpenes assembled from acetate units
    Show answer

    Answer: C — An alkaloid; terpenoids are built from C5 isoprene units and include menthol and carotenoids

    Morphine, nicotine and quinine are nitrogen-containing, amino-acid-derived compounds, i.e. alkaloids; and terpenoids are indeed built from C5 isoprene units and include menthol and carotenoids. Alkaloids are not nitrogen-free terpenes, and carotenoids are terpenoids, not phenolics, so the other combinations each contain a false clause.

14. What is the essential difference between the processing of black tea and green tea from the same Camellia sinensis leaf?

    1. Black tea is oxidized after rolling; in green tea the enzyme is inactivated first
    2. Black tea is fermented by added bacteria, whereas green tea is fermented by added yeast
    3. Black tea is made from mature leaves and green tea only from the terminal bud
    4. Black tea retains all its caffeine, whereas green tea is processed to remove the caffeine
    Show answer

    Answer: A — Black tea is oxidized after rolling; in green tea the enzyme is inactivated first

    The key step is the leaf's own polyphenol-oxidase-driven oxidation (loosely called fermentation): black tea is allowed to oxidize after rolling, while green tea is steamed or pan-fired first to inactivate the enzyme, so it stays green. No microbe is added, both can be made from the fine young shoot, and green tea is not decaffeinated by processing.

15. Freshly plucked tea leaf weighing 80 kg has a moisture content of 75% by mass. It is withered until the moisture content falls to 50% by mass, with no loss of dry matter. What is the mass, in kilograms, of the withered leaf?

    Numerical answer — type the value.

    Show answer

    Answer: 40

    Dry matter is conserved: initially 80 × (1 − 0.75) = 20 kg of dry matter. At 50% moisture the dry matter is half the total, so total mass = 20 ÷ 0.50 = 40 kg. Simply removing 25% of 80 kg (giving 60 kg) is wrong, because the percentage is of a shrinking total, not of the original mass.

16. A batch of 500 kg of lemongrass herbage is steam-distilled, and the essential oil recovered is 0.6% of the herbage mass. How many kilograms of oil are obtained? Give the answer to one decimal place.

    Numerical answer — type the value.

    Show answer

    Answer: 3.0

    Oil = 0.6% of 500 kg = 0.006 × 500 = 3.0 kg. The low yield (well under 1%) is typical of essential-oil crops, where large quantities of herbage give small quantities of oil.