BIOLOGY 375 INTRODUCTION TO PLANT DEVELOPMENT

Image Final Exam

From Bio 275, April 29, 1999

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PART I.

30 pts.

Answer 1 of the following 2 questions (1-2):

Each of these answers is restricted to about 1/2 page.

[Image] 1. Explain what the diagrams represent and what they tell about the control of dormancy in black-currant buds. (Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.)

[Image] 2. Explain what the diagram shows. Also, explain where the long-day and short-day plants flower and why.(Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.)

Part II.

90 points (30 points each)

Answer 3 of the following 4 questions (3-6):

Each of these answers is restricted to about 1/2 page.

    3. Explain how you would determine whether of not a biological rhythm is endogenous.

    4. Explain the adaptive value (s) of autumnal senescence of leaves on trees and top senescence of spring-flowering bulbs?

    5. Explain what the quiescent zone is and what its relationship to the apical initials is.

    6. For one of the major plant hormones, give an example of the function of the hormone and show how the system fits the complete definition of a hormone.

Part III.

50 points (10 points each)

Briefly, explain what 5 of the following (7-12) are and give an example (where appropriate) of each:

    7. Differentiation.

    8. Thigmotropism.

    9. Chromoplast.

    10. Critical daylength.

    11. Heterosis.

    12. Decurrent branching.

Part IV.

30 points (10 points each)

Briefly, explain the functions of any 3 of the following (13-16). Be careful not to explain what they are unless that is part of their function.

    13. Promoter (genetic).

    14. Dictyosomes.

    15. Endosperm.

    16. Abscission zone.

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[Image] 1: Explain what the diagrams represent and what they tell about the control of dormancy in black-currant buds.

The diagrams represent bioassays of chromatograms of growth inhibitor (ABA) and growth promoter (gibberellin) activity in extracts from black currant buds taken at three stages as they emerge from dormancy during the winter. Progressing from January to March, the growth-inhibiting activity disappears, while the gibberellin activity appears and rises dramatically. These data suggest that the presence of an inhibitor like ABA and the absence of gibberellin could maintain dormancy, while disappearance of the ABA and appearance of gibberellin could break their dormancy.

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[Image] 2: Explain what the diagram shows. Also, explain where the long-day and short-day plants flower and why.

The graph shows the photoperiods that occur at different times of the year at this latitude. The long-day plants mainly flower from mid May through mid July, and they are triggered to flower during this time period by the increasing daylengths that occur before this time. The short-day plants flower mainly in August and September, and the decreasing daylengths preceding this time induce them to flower.


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3: Explain how you would determine whether or not a biological rhythm is endogenous.

To be considered endogenous, a biological rhythm must be:

1) free running, that is it continues in the absence of the environmental oscillator, and

2) resetable. This means that after the day-night cycle has been shifted, the rhythm will run free on the new cycle in a constant environment.

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4: Explain the adaptive value (s) of autumnal senescence of leaves on trees and top senescence of spring-flowering bulbs.

In both cases, senescence of the leaves helps the plant to avoid and reduce its exposure to the rigors of winter. The leaves would be very vulnerable to damage from the cold and desiccation during winter, and they would not be productive. In addition, senescence allows reclamation of most of the nutrients, e.g., N, invested in the leaves.

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5: What is the quiescent zone and what is its relationship to the apical initials?

The quiescent zone is a group of cells (100-400) in the apical meristem of roots and shoots. As the name implies, it is characterized by low activity, i.e., little or cell division and low metabolic activity. The apical initials occur within the quiescent zone. There is only one group (ca. 3) of apical intitials in roots or 3 groups (ca. 12) in shoots, so they comprise only a very small proportion of the quiescent-zone cells. They are in effect "stem" cells from which all the other cells ultimately are derived.

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6: For one of the major plant hormones, give an example of the function of the hormone showing how the system fits the complete definition of a hormone.

There are many possible approaches to answering this question. Basically, a hormone is a chemical messenger/signal. One case that could be used is auxin control of coleoptile elongation. The auxin, IAA, is produced in the coleoptile tip and transported downward into the coleoptile where small quantities promote growth. So, it is an organic chemical and it is produced in one site and transported to another (target) where it acts in small quantities to promote cell enlargement.

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7: Differentiation is structural and functional changes in a cell; cell specialization. Example: Xylem cell development is one of many possibilities.

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8: Thigmotropism is a directional growth movement due to a directional stimulus, in this case a mechanical or touch stimulus. Example: a pea tendril wrapping around a pole.

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9: A chromoplast is a plastid with large amounts of non-green pigments, i.e., visibly colored, but not green. Examples: The orange pigmentation of carrot roots or the red of tomato fruits.

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10: Critical daylength is the photoperiod threshold for long-day and short-day qualitative developmental responses. LD responses require days longer than the CDL, and SD responses require less.

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11: An Heterosis (allotetraploid) is hybrid vigor. This is the phenomenon that often makes the F1 hybrid from two inbred lines much more robust (and higher yielding) than either parental line. Example: Hybrid corn

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12: Decurrent branching is the branching pattern in trees without a single, dominant axis, e.g., with multiple axes. Examples: Walnut tree, mimosa.

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13: Promoter (genetic) is a genetic control element (DNA) just upstream from the gene controlled. This is where RNA polymerase and transcription factors bind to transcribe (express) the gene.

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14: Dictyosomes are cytoplasmic organelles that process and secrete proteins and polysaccarides.

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15: Endosperm provides hormones and nutrients for the early developing embryo and later may serve as a depot for storage of nutrients needed in the early development of the seedling.

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16: The abscission zone is a specialized zone of cells which facilitate/allow abscission.

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