Question

U (U TV Wua 7. When auxin is applied to the side of a Coleus stem near the tip, what do you expect to happen? Why? 8. When ink marks exactly 1 millimeter apart are applied to the side of a young Coleus stem, what do you expect to happen over the ensuing 2 to 3 weeks? 9. In the experiment with eosin and balsam (Impatiens) stem, in which tissue would you expect to find in the dye? Why? 10. Explain why the various plants appear the way they do in each of the following demonstrations: Phototropism: Gravitropism: Etiolation:

Answer 1

7. Auxin is a plant hormone or plant growth regulator having morphogen like characteristics. Auxin plays an important role in growth and behavioral process in the plant life cycle and it is very essential for body development of plants. It is present in all parts of the plant, in various concentrations. When we apply this auxin to the side of a coleus stem near the tip, it will affect both cell division and expansion. In this case auxin is applied at the stem tip, it will promote the axial elongation. This elongation points towards the direction of light source.

8. When we ink marks exactly 1 millimeter apart in the sides of the young coleus stem, after 2-3 weeks those markings will not be 1 millimeter apart. Markings will be like approximately 2-3 millimeters apart not as same as previous markings. This happens because the young stem has meristematic cells, these cells are undifferentiated cells that are capable of doing cell division. Meristem is the tissue that contains these meristematic cells. Young stem contains those meristem tissues, that give rise to the stem structure. That's why the ink markings are not exactly same as that of the previous markings.

9. In an experiment with eosin and balsam stem (Impatients), we can find the xylem tissues. Xylem is a vascular tissue that is responsible for transporting nutrients and water from the roots up to the shoots and the leaves. When we place the balsam stem in the eosin (red color dye) solution, after some time, xylem transport that dye substances from lower part to the upper part of the stem. And then red streaks are appear on the stem. When seeing this stem section under a microscope, xylem only present in red color. We cannot see the phloem in this color because it doesn't have any role in ascent of sap.

10. Phototropism: It is the process of growth of an organism towards the light source. It is often seen in plants and also occur in various organisms like fungi. Plant cells that are situated at the greatest distance from the light source have a hormone called auxin, that will reacts when phototropism happens. It will cause the plant to have the elongated cells on furthest side from a light source. There are two types phototropisms, positive phototropism - growth towards the light and negative phototropism - growth against the light source.

Gravitropism: It is the process of growth of an organism in response to the gravitational pull on it. Here the gravity can be either natural or artificial gravity. It is a common feature in many lower and all higher plants and also in other organisms like fungi. Here also two types are present, positive gravitropism (grow in direction of gravitational pull) shown by roots and negative gravitropism (grow against the gravitational pull) shown by stems. During cell division process, meristem located in the roots will sense the gravity and elongates the cells towards the gravitational pull.

Etiolation: It is the process of growth of flowering plants in partial or complete absence of the light. It is characterized as long and weak stems, smaller leaves because of longer internodes and chlorosis (pale yellow color). Development of seedlings in a dark environment will leads to the etiolated seedlings, it is known as skotomorphogenesis. Here the growing tip is strongly attracted towards the light source and it will elongates toward it.