1 A) With the extra energy provided by the light, the plant can grow selectively in the direction with more light. B) A hormone, auxin, is distributed in such a way that it promotes cell elongation in the tissue farthest from the light. C) Light causes inhibition of growth in the cells closest to it by creating a conformational change in a steroid receptor. D) Cells closest to the light become photobleached, making them unable to grow as fast as cells farther from the light. E) Blue light receptors near the light signal gene activation which changes the plant's growth aspect. 2 A) It causes apoptosis (programmed cell death) in cells, which therefore causes bending toward the region where auxin has accumulated. B) It allows rapid cell growth, so by accumulating in the lower regions of the plant, it bends the tissues upward. C) Auxin causes mutations in genes, making the cell less efficient in growing. As it accumulates at the tops of horizontal branches, it stimulates bending upwards. D) All of these possibilities are being investigated as to the role of auxin in gravitropism. E) Two of the above are valid explanations for the effect of auxin in plant growth. 3 A) It generates a charge in the plant's nervous system, which is transduced to distant cells. These lose water rapidly through their stomata to collapse. B) Genes in the pulvinus are stimulated for rapid cell growth in the side farthest from the stimulation. C) Apoptosis (programmed cell death) occurs in cells nearest the stimulation. D) An electrical stimulation of cell membranes causes pumping of ions from one side of the pulvinus to the other. This causes the depleted cells to collapse while the other cells swell. E) Both b and c explain the function of a pulvinus. 4 A) Appropriate temperatures B) Water leaching out inhibitory chemicals C) Mechanical cracking of the seed coat D) All of these have been shown to allow seeds to break dormancy. E) Only a and b have been demonstrated to break dormancy. 5 A) "Shootiness" B) Formation of callus (undifferentiated parenchyma) C) "Rootiness" D) Rapid general growth E) Rapid cell death
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