BIOLOGY 375 INTRODUCTION TO PLANT DEVELOPMENT

Second Exam

From Bio 275, March 25, 1999

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Part I.

42 points (14 points each)

Each of these answers is restricted to about 1/2 page.
Answer 3 of the following 4 questions (1-4):

1. Explain what is going on in the diagrams below, and specifically what A, B, C, and D are.

(Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.)

2. Explain what is going on in the diagram below including A, B, and C. Also, explain the significance of this process in development.

(Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.)

3. Explain how hormones may control xylem and phloem differentiation.

4. Explain how plant cell shape is determined.

Part II.

32 points (8 points each)

Briefly, explain what 4 of the following (5-9) are.

Each of these answers is restricted to 3 lines.

5. Microfibril

6. Coconut milk

7. Teratomata

8. Proplastid

9. Meristem

Part III.

24 points (8 points each)

Briefly, explain the functions of any 3 of the following (10-13). Be careful not to explain what they are unless that is part of their function.

Please confine your answer to the lines provided.

10. Rhizobium root nodules

11. Microtubule (primary function only)

12. Amyloplast

13. Apical initial cells

Part IV.

2 points

14. Identify the structure indicated by the arrows. (Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.)

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ANSWERS to the First Exam

March 25, 1999

1. Explain what is going on in the diagrams below, and specifically explain what A, B, C, and D are.
(Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.)

A is the Ti plasmid, B is the TDNA, C is TDNA integrated into the host cell DNA, and D is a crown gall tumor.

A wound in the stem is infected with Agrobacterium tumefacians, and that activates the bacteria which induce crown gall. TDNA is transferred from the bacterium to the plant cell when it gets integrated into the plant and induces crown gall formation by producing auxin and cytokinin.

Go back to question 1 or go on to question 2.

2. Explain what is going on in the diagram below including A, B, and C. Also, explain the significance of this process in development.
(Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.)

This shows translation of mRNA to form a protein starting with the signal peptide (A). The signal peptide then binds to a special pore in the surface of the targeted organelle, here the endoplasmic reticulum, and the protein enters the targeted organelle. After entry the signal peptide is split off (B). Eventually, the whole peptide has entered the organelle (C) and then it may become functionally integrated into the organelle.

This protein targeting is important in development, specifically differentiation, because it directs the proteins to the sites where they are needed

Go back to question 2 or go on to question 3.

3. Explain how hormones may control xylem and phloem differentiation.

Hormonal controls of xylem and phloem differentiation have been demonstrated in several ways, and these also can be used to explain which hormones control vascular differentiation. Apical buds grafted onto callus tissues show vascular differentiation oriented toward the bud. Replacing the bud with auxin produces xylem, and addition of sucrose induces phloem as well. In the cambium of woody plants, auxin stimulates xylem formation, and gibberellin promotes phloem development. Auxin from nearby leaves is also required for xylem regeneration in severed vascular bundles in stems.

Thus, auxin plays a key role in controling xylem formation; however, phloem differentiation is more complex. Phloem differetiation seems to require auxin, but gibberellin or sucrose may also play important roles.

Go back to question 3 or go on to question 4.

4. Explain how plant cell shape is determined.

Ultimately, cell shape is controlled by the microtubules lying just inside the cell membrane. The microtubules may directly determine cell shape in cells with very flexible walls like Ochromonas, or they may act indirectly by controlling the orientation of the deposition of cell wall microfibrils. If the microfibrils are randomly oriented (not oriented by microtubules), the cells enlarge in all directions (isodiametrically). If the microfibrils are deposited in parallel, then the cells will expand perpendicular to the microfibrils, i.e., polar growth. Disrupting the microtubules. e.g., with colchicine, also disrupts the oriented deposition of the microfibrils and thereby polarized cell enlargement.

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5. Microfibril is a long, fiberlike aggregate of homopolysaccharides, e.g., cellulose. A major constituent of plant cell walls.

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6. Coconut milk is liquid endosperm. It is also a nutrient and hormone mix used to promote cell division in plant cell cultures.

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7. Teratomata are abnormal growths/structures. They take a variety of forms, e.g., organoid, cataplasmic or protoplasmatic.

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8. Proplastid is a relatively undifferentiated plastid, a precursor for other plastids.

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9. A meristem is a region of cell division.

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10. Rhizobium root nodules function to fix nitrogen for the plants that bear them.

Go back to question 10 or go on to question 11.

11. Microtubule (primary function only): to provide a cytoskeleton. Secondary functions received 1 pt. each.

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12. Amyloplast is a starch-storing plastid.

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13. Apical initial cells are special cells in the meristem, and all other cells in the plant body are derived from one of these cells.

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14. The black area indicated by the arrows is called the middle lamella. Click on the image to the left to enlarge it. Use the BACK button on your browser to return to this page.

Go back to question 14, to the top of this document, or return to the Biology 375 home page.