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Ch 39 for Bio
Plant Responses to Internal and External Signals
| Question | Answer |
|---|---|
| What are the morphological differences between dark and light grown plants? | Dark grown plants have long stems, underdeveloped root systems, unexpected leaves, and their shoots lack chlorophyll. |
| Explain how etiolation helps a seedling compete successfully. | By devoting more energy to stem elongation and less to leaf expansion and root growth, a plant increases the likelihood that the shoot will reach the sunlight before its stored foods run out. |
| Cycloheximide is a drug that inhibits protein synthesis. Predict what effect cycloheximide would have on de-etiolation. | Cycloheximide should inhibit de-etiolation by preventing the sythesis of new proteins necessary for de-etiolation. |
| The sexual dysfunction drug Viagra inhibits an enzyme that breaks down cyclic GMP. If tomato leaf cells have a similar enzyme, would applying Viagra cause a normal de-etionlation of aurea mutant tomato leaves? | No, applying Viagra shoul cause only a partial de-etiolation response. |
| Suggest a physiological reason for the old adage "One bad apple spoils the bunch." | The release of ethylene by the damaged spple stimulates ripening in the other apples. |
| Suggest a reaason of why cut flowers such as carnations are often treated with cytokins prior to shipping. | Because cytokinins delay leaf senescene and floral parts are modified leaves. Cytokins also delay the senescence of cut flowers. |
| Fusicoccin is a fungal toxin that stimulates the plasma membrane H+ pumps of plant cells. How may it affect the growth of isolated stem sections? | Fusicoccin's ability to cause an increase in plasma H+ pump activity is similar to an effect of auxin and leads o an auxin-like effect, a promotion of stem cell elongation. |
| If an enzyme in field-grown soybean leaves is most active at noon and least active at midnight, is its activity under circadian regualtion? | Not necessarily.To determine if its under circadian control, the scientist would have to demonstrate that its activiity osicillates even when enviromental conditions are held constant. |
| A guard absentmindedly turns on the lights in a greenhouse one night, but the plants still flower on schedule. Suggest two reasons why they were not affected by the interuption of darkness. | Flowering of the species may have been day-neutral or required multiple exposures to short nights. |
| Some vine seedlings grow toward darkness until reaching an upright structure. This adaptation helps them "find" a shaded object to climb. How might you test whether this negative phototrophism is meditated by blue-light phtotrophism or by phytochrome? | You might determing which wave-lengths of light are most effective and plot on an action spectrum. If the action spectron indicates phytochrome, you could do further experiments to test for red/far-red photosensitivity. |
| Thermal images are photographs of the heat emitted by an object. Researchers have used thermal imaging of plants to isolate mutants that overproduce abscisic acid. Suggest a reason why these mutants are warmer that wild-type plants. | A plant that overproduces ABA would undergo less evaporative coling because its stomata would not open as widely. |
| A greenhouse worker finds that potted chrysanthemums nearest to the aisles are often shorter than those in the middle of the bench. Explain this "edge effect", a common problem in horticulture. | Plants close to the aisles may be more subject to mechanical stresses caused by passing workers and air currents. The plants nearer to the center of the bench may also be taller as a result of shading and less evaporative stress. |
| Plants normally subjected to drought stress are often more resistant to freezing stress than plants that are not drought adapted. Suggest s reason why. | Like drought stress, freezing leads to cellular dehydration. Any process that helps mitigate drought stress will tend to also reduce freezing stress. |
| If you removed the root cap from a root, would the root still respond to gravity? Explain. | No, because root caps are involved in sensing gravity. Roots that have their root caps removed are almost completely insensitive to gravity. |
| What are some drawbacks of spraying fields with general-purpose insecticides? | Some insects increase plants' productivity by eating harmful insects or aiding in pollination. |
| Chewing insects mechanically damage plants and lessen the surface area of leaves for photosynthesis. In addition, these insects make plants more vulnerable to pathogens attack. Suggest a reason why. | Mechanical damage breaches a plant's first line of defense against infection, its protective dermal tissue. |
| Many fungal pathogens get their food by causing plant cells to become leaky, thereby releasing nutrients into the intercellular spaces. Would it benefit the fungus to kill the host plant in a way that results in all the nutrients leaking out. | No, pathogens that kill their hosts would soon run out of victims and might go extinct themselves. |
| Suppose that a scientist finds that a population of plants growing in a breezy location is more prone to herbivory by insects than a population of the same species growing in a sheltered area. Suggest a hypothesis to account for this observation. | Perhaps the breeze dilutes the local concentration of a volatile defense compound that that the plant produce. |
Created by:
titiwalton
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