1). Which of the following seeds would likely germinate even if it were located on the floor of a densely leaved forest?
a). a seed lacking chlorophyll a
b). a seed lacking phytochrome Pr
c). a seed lacking phytochrome Pfr
d). a seed lacking phototropin
2). Which of the following statements provides a true example of both photomorphogenesis and phototropism?
a). phototropism is growth toward blue light, and photomorphogenesis is growth toward red light.
b). phototropism is growth toward blue light, and photomorphogenesis is germination triggered by near-red light.
c). phototropism is growth toward red light, and photomorphogenesis is germination triggered by blue light.
d). phototropism is movement toward blue light, that does not involve growth; photomorphogenesis is movement toward red light that does involve growth.
3). If you were to plant a de-etiolated (det2) mutant Arabidopsis seed and keep it in a dark box, what would you expect to happen?
a). The seed would germinate normally, but the plant would not become tall and spindly while it sought a light source.
b). The seed would fail to germinate because it would not have light.
c). The seed would germinate, and the plant would become tall and spindly while it sought a light source.
d). The seed would germinate, and the plant would immediately die because it could not make sugar in the dark.
4). Growing plants in zero gravity on the space shuttle prevents
a). phototropism because it is dark in space.
b). photomorphogenesis because only near-red light filters into space.
c). gravitropism because there is little gravity in space.
d). aerotropism because there is no oxygen in space.
5). When a Venus flytrap closes, it is an example of
b). cell migration.
c). muscle contraction.
d). a nervous twitch.
6). We often have the misconception that plants are unable to move in their environment. Many plants, however, display daily movements to maximize their capacity to absorb light energy (e.g., bean leaves). These daily changes in shape are caused by
a). changes in turgor in specific cells.
b). growth of specific cells.
c). muscle contraction in the leaves.
d). temperature changes in the environment.
7). When Charles and Francis Darwin investigated phototropisms in plants, they discovered that
a). auxin was responsible for light-dependant growth.
b). light was detected at the tip of a plant.
c). light was detected along the shoot of a plant.
d). only red light stimulated phototropism.
8). The chemical defoliant Agent Orange was banned because
a). the synthetic auxin used in the preparation, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), caused premature growth in humans.
b). the synthetic auxin used in the preparation, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), caused plants to grow more vigorously than the environment could sustain.
c). a contaminant in the preparation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) caused disease and birth defects in humans.
d). a contaminant in the preparation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) killed beneficial plants.
9). You have come up with a brilliant idea to stretch your grocery budget by buying green fruit in bulk and then storing it in a bag that you have blown up like a balloon. As you need fruit, you would take it out of the bag, and it would miraculously ripen. How would this work?
a). The bag would block light from reaching the fruit, so it would not ripen.
b). The bag would keep the fruit cool, so it would not ripen.
c). The high CO2 levels in the bag would prevent ripening.
d). The high O2 levels in the bag would prevent ripening.
10). If you were to accidentally plant a mutant strain of barley that could not synthesize the plant hormone abscisic acid (ABA), what would you expect to happen?
a). The shoots would elongate too much and fall over because they could not support themselves.
b). The shoots would not elongate normally, and you would get short plants.
c). The seeds would germinate prematurely.
d). The leaves would fall off the plant.
Test Your Visual Understanding
1). Images a–c show tobacco cells cultured under different auxin:cytokinin ratios. Label each image with the appropriate hormone ratio.
Auxin: high low intermediate
Cytokinin: low high intermediate
Apply Your Knowledge
1). Discuss the similarities and differences between thigmotropism and turgor movement.
Answer: A thigmotropism is a directional growth movement in response to touch. Cells on one side of a stem may grow faster than cells on the other side, allowing the plant to bend towards or away from the source of the touch. Turgor movements can also occur in response to touch. But unlike thigmotropisms, they are not growth responses. For example, the leaflets on a Mimosa plant fold almost instantly when touched. This happens because water leaves cells on one side of the pulvinus (stem-like region at base of the leaflet), but not the other side. Water later returns to the cells that have lost turgor pressure, but no growth has occurred.
2). Compare the mechanisms that animals and plants use to survive harsh environments by thinking of an equivalent animal response for each of the following:
Answer: a). Dormancy in an animal is somewhat like hibernation, but a hibernating animal maintains a higher water content than a dormant seed. Also, hibernation cannot be extended for as long as dormancy is extended in some seeds.
b). Thigmomorphogenesis is growth in response to touch. Animals respond to touch in a variety of ways, including moving away when they sense danger from touch. A possible example of a thigmomorphogenesis analogy in humans would be wearing a brace for scoliosis (a condition that causes abnormal spine development). The pressure (extended touch) from the brace allows the spine to develop in a more normal pattern. In plants, growth responses can occur in response to a much briefer touch with less pressure.
c). Abscission is analogous to a male deer naturally losing its antlers (its rack). In both cases, cells die at the point of attachment and the body part is discarded.
d). Phototropism is a growth movement towards light. Since most animals move, there is a greater tendency for an animal to move towards or away from light rather than grow towards or away from light. Tanning would not be a good example of a phototropism equivalent in plants, because it does not involve a directional growth response.