Everyday Science - Fruit Ripening and Enzymes MCQs

Correct Answer: Ethylene

Ethylene is the plant hormone that triggers and coordinates fruit ripening.

Correct Answer: Ethylene

Climacteric fruits show a burst of ethylene production that drives their ripening.

Correct Answer: Amylase

Amylase breaks down stored starch into sugars, which is why ripening fruit becomes sweeter.

Correct Answer: Pectinase

Pectinase degrades pectin in the cell walls, so the fruit softens as it ripens.

Correct Answer: Polyphenol oxidase

Polyphenol oxidase (PPO) oxidises phenolic compounds when cut fruit is exposed to air, producing brown pigments.

Correct Answer: Methionine

Plants make ethylene from methionine through the S-adenosylmethionine (SAM) pathway.

Correct Answer: Ethylene

Continued ethylene action past the ripe stage drives over-ripening and decay.

Correct Answer: Pectinase

Pectinase hydrolyses pectin, the cementing polysaccharide of fruit cell walls.

Correct Answer: Polygalacturonase

Polygalacturonase breaks down pectin and is the key softening enzyme in ripening tomatoes.

Correct Answer: Amylase

In ripening bananas, amylase converts stored starch into sugars.

Correct Answer: Polyphenol oxidase

When apple flesh is cut and exposed to air, polyphenol oxidase oxidises phenols and the slices brown.

Correct Answer: Lipoxygenase

Lipoxygenase acts on fatty acids to produce the volatile compounds that give ripening fruit its aroma.

Correct Answer: Ethylene

The climacteric peak is the sharp rise in respiration accompanied by a burst of ethylene production.

Correct Answer: Pectin

Polygalacturonase cleaves the polygalacturonic acid chains of pectin in the cell wall.

Correct Answer: Ethylene

Ethylene is the ripening hormone of climacteric fruits such as banana, mango and tomato.

Correct Answer: Ethylene

Papaya is a climacteric fruit, so its ripening is regulated by ethylene.

Correct Answer: 1-MCP (1-methylcyclopropene)

1-MCP binds ethylene receptors and blocks ethylene action, delaying ripening in stored fruit.

Correct Answer: Sweetness

As starch is converted to sugars, the fruit tastes sweeter.

Correct Answer: Pectin

Softening is mainly the breakdown of pectin in the middle lamella and primary cell wall.

Correct Answer: Chlorophyll degradation

As the banana ripens, green chlorophyll breaks down, revealing the yellow carotenoid pigments underneath.

Correct Answer: Carbon dioxide (CO2)

The climacteric rise in respiration releases extra carbon dioxide as the fruit ripens.

Correct Answer: Amylase

Amylase converts starch to sugars, raising the fruit's sweetness.

Correct Answer: Polygalacturonase

Polygalacturonase degrades pectin in the pulp cell walls, softening the fruit.

Correct Answer: Plant hormone (gas)

Ethylene is a gaseous plant hormone, the only major plant hormone that is a gas at ordinary temperatures.

Correct Answer: Cell wall degradation

Enzymes degrade the cell-wall polysaccharides, so the fruit tissue loses firmness.

Correct Answer: Banana, Mango, Tomato

Banana, mango and tomato are classic climacteric fruits that ripen with an ethylene burst; grape, citrus, cherry, strawberry and pineapple are non-climacteric.

Correct Answer: Grape, Citrus

Grape and citrus are non-climacteric: they do not show an ethylene-driven ripening burst and must ripen on the plant.

Correct Answer: Heat and acid

Heat inactivates polyphenol oxidase (as in blanching) and acid conditions such as lemon juice inhibit it.

Correct Answer: Sugar (glucose/maltose)

Amylase hydrolyses starch into maltose and glucose.

Correct Answer: Pectinase

Pectinase breaks down cell-wall pectin, reducing the fruit's firmness.

Correct Answer: Polyphenol oxidase

Polyphenol oxidase oxidises phenolic compounds in mango flesh, causing browning on cutting or bruising.

Correct Answer: Ethylene

Ethylene triggers the climacteric rise in respiration and ripening.

Correct Answer: Low temperature

Cold storage slows respiration and ethylene action, delaying ripening.

Correct Answer: Amylase

Amylase is the main enzyme of banana ripening, converting its large starch reserves into sugars.

Correct Answer: Pectinase

Pectinase degrades apple cell-wall pectin, so the apple softens as it ripens.

Correct Answer: Phenolic compounds

Enzymatic browning is the oxidation of phenolic compounds to quinones, which polymerise into brown pigments.

Correct Answer: Artificial ripening

Ethylene (or ethylene-releasing compounds) is applied commercially to ripen harvested fruit uniformly.

Correct Answer: Excess softening

Past the ripe stage, continued cell-wall breakdown makes the fruit excessively soft and mushy.

Correct Answer: Slowly without ethylene

Non-climacteric fruits do not show an ethylene burst; they mature gradually on the plant without one.

Correct Answer: Ethylene

Mango is a climacteric fruit whose ripening is triggered by ethylene.

Correct Answer: Respiration rate

The climacteric is defined by a sharp rise in the fruit's respiration rate.

Correct Answer: Mesocarp

In fleshy fruits, ethylene production is concentrated in the mesocarp, the fleshy middle layer of the fruit wall.

Correct Answer: Starch-to-sugar conversion

Ethylene stimulates the ripening programme, including the conversion of stored starch into sugars.

Correct Answer: Pectin hydrolysis

Softening is driven by hydrolysis of pectin in the cell walls.

Correct Answer: Climacteric fruits

Papaya, banana and tomato are all climacteric fruits that ripen with an ethylene burst.