TOEFL Question

Biology

Compared to the busy lives of humans, it would seem that plants are just stationary companions that beautify gardens and brighten rooms. Surprisingly, plants actually move a great deal. From the interweaving of an ivy plant on a pole to the sunflower that cranes its neck to reach for the sunlight, plants are in constant motion. Although their efforts go mostly unnoticed, most plants depend on daily movement in order to get proper nutrition, repel enemies, or reproduce. Two common types of plant movements are tropisms and nastic movements.

 Tropism is when a plant moves in response to a stimulus. Moreover, the stimulus is always directional, meaning that the plant will move to face the direction of the stimulus. The movement caused by tropism indicates that the plant is growing, thus making it an irreversible movement. There are many kinds of tropisms. The different types are typically denoted by a prefix that goes before tropism. For example, phototropism is movement that responds to light. A familiar example of phototropism is when a houseplant turns and grows toward the brightest source of light available, usually a window. If the houseplant is moved, one would observe that it changes direction yet again and starts growing toward the light. This mechanism helps plants receive enough light to be go through the process of photosynthesis and create food.

 In contrast, nastic movements are plant movements that occur in response to environmental stimuli, such as temperature or humidity. Unlike tropic movements, they are not directional. Also, because they do not have to do with plant growth, nastic movements are reversible. Different stimuli are responsible for nastic movements. When referring to a specific type, the same system of adding an appropriate prefix to nasty is used. For example, a nastic movement that occurs in response to a touch is called thigmonasty. Thigmonasty is the type of plant movement that is responsible for the rapid shutting motion of the carnivorous Venus flytrap. The plant is equipped with highly sensitized hairs on each leaf. When an insect touched the hair, the leaves snap shut, trapping the insect. Although more dramatic than a phototropic houseplant, thigmonasty is just a mechanism that allows the Venus flytrap to secure the nutrients it needs to survive.

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Stationary: stuck in one place; not able to move

Interweave: to combine two or more elements so they cannot be separated

Crane: to stretch in order to look at something

Repel: to force away

Stimulus: something that causes growth or activity

Mechanism: a method or means of doing something

Photosynthesis: a process in plants by which light is converted into chemical energy

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Q. The word it in the passage refers to

1. indication

2. growth

3. plant

4. tropism

A. (D) tropism