Page 133 - Science Course 1 (Book 1)

Mo4-L4b: How Do Plants Respond to Chemical Stimuli?

CYTOKININS
Rapidly growing Humans make plants more productive by using plant
areas of a plant, hormones.
such as roots and
stems, produce Some crops now are easier to grow because humans
gibberellins, which understand how plants respond to hormones.
increase the rate
of cell division and
cell elongation.

Root tips produce cytokinins, a hormone that
increases the rate of cell division and, in some plants,
slows the aging process of flowers and fruits.

SUMMARY
Radicle How Do Plants Respond to Chemical
Stimuli?

Plant hormones are
internal chemical stimuli
that produce different
responses in plants.

Mo4-L4: Vocabulary Review

Directions: On each line, write the term from the word bank that correctly replaces the underlined words in
each sentence. NOTE: You may need to change a term to its plural form.

photoperiodism plant hormone stimulus tropism

1. Plants may respond to a change in the environment by growing toward

it or away from it.

2. Seedlings bending toward light and roots curving away from light are
examples of plant growth toward or away from environmental changes.

3. Due to a response to the number of hours of darkness in their
environment, carnations only flower in the summer, when the number of
daylight hours is greater than the number of hours of darkness.

4. Auxins, ethylene, gibberellins, and cytokinins are substances that act as
chemical messengers within plants.
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