Chapter 27 Answers
Plant Reproduction and Growth
Visual Understanding
Figure 27.3
Bees tend to pollinate yellow flowers; hummingbirds cue in on red flowers. Why are there so
many white flowers?
White flowers are very visible at night, so the numerous species of night-flying moths pollinate
them. Some very large white flowers, such as the ones on the giant saguaro cactus, are also
pollinated by bats, another night creature.
Figure 27.5
If fruits are produced by plants to encourage organisms, especially birds and mammals, to eat
them and carry the seeds elsewhere, then speculate on the purpose of fruits such as peaches,
shown here, mangoes, and avocados.
Recall that, until about 10,000 – 15,000 years ago, there were huge land mammals on many
continents, the way there still are giraffes and elephants in parts of Africa. While not many
organisms alive today in the United States would be capable of swallowing a peach, mango or
avocado whole, that could certainly have been true of those now-extinct megafauna.
Challenge Questions
Flowering Plant Reproduction
Your friend, Shonille, says her teacher made the comment that “nectar is to pollination as fruit is
to dispersal.” She asks you to explain.
Nectar is the liquid, enticing food reward that a plant produces in order to attract pollinators to
its flowers so that the flowers can be fertilized. A fruit is a fleshy, enticing food reward that a
plant produces in order to attract herbivores that eat the fruit and carry the seeds inside their
digestive system to be excreted elsewhere, far from the parent plant, in their own little pile of
fertilizer.
Regulating Plant Growth
An old saying is “one bad apple spoils the whole barrel.” We even refer to troublemakers as “a
bad apple.” Can you explain the scientific basis for these statements?
Fruits that are ripening or ripe give off the gas ethylene, a hormone that induces ripening. When
apples are stored in a basket, sack, or barrel, if one apple begins to rot in the closed space the
amount of ethylene it produces can be sufficient to cause the apples around it to go bad as well.
They then produce even greater quantities of ethylene, and soon the entire basket, sack, or barrel
of apples has gone bad. Similarly, then, one troublemaking person can sometimes cause others
to get into trouble.
Plant Responses to Environmental Stimuli
If it is out in the open, trailing ivy grows along the ground and can form dense mats of ground
cover. If planted in a hanging pot, the stems dangle down, forming a graceful flow. If ivy is
planted next to a building, however, its stems attach to the side of the building and, in time, it
will cover the building. What causes this?
Ivy is subject to the tropism called thigmotropism; its stems are sensitive to touch. In a not-wellunderstood reaction the stems attach to anything nearby – tree, fence, building, and will grow
over it. Over many years some buildings become entirely covered in ivy.