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Plants respond to their environment.

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Introduction

PLANTS RESPOND TO THEIR ENVIRONMENT Key Points * Light is vital for photosynthesis, but is also necessary to direct plant growth and development. * Light acts as a signal to initiate and regulate photomorphogenesis, which are the light mediated changes in plant growth and development. * The developmental changes characteristic of photomorphogenesis shown by the shorter, greener seedlings are induced by light. Typically, plants are responsive to wavelengths of light in the red and far-red regions of the spectrum through the action of several different photosensory systems. * The photoreceptors for red and far-red wavelengths are know as phytochromes. Plants use phytochrome to detect and respond to red and far-red wavelengths. * Phytochromes are proteins with a light absorbing pigment attached, called chromophores. * The phytochrome is synthesized in the Pr form. Upon binding the chromophore, it becomes sensitive to light. If it absorbs red light it will change conformation to the biologically active Pfr form. ...read more.

Middle

Data from Table 1 shows, when taking standard errors into account, epicotyl length is not significantly affected whether the seedlings were grown in the light or the dark. On the other hand, measurements of hypocotyl length differ greatly. This may be primarily due to internode and hypocotyl elongation in etoliated plants which are grown in the dark. Plant no. Blade Length [cm] Petiole Length [cm] Light [+] Light [-] Light [+] Light [-] 1 4.6 2.0 2.5 0.8 5.6 1.7 2.1 0.6 2 5.0 2.2 2.2 1.0 4.6 2.1 2.5 0.9 3 6.1 2.5 2.5 1.0 5.7 2.9 2.2 1.2 4 5.9 1.6 2.6 0.6 6.0 1.5 2.9 0.5 Mean 5.437 2.063 2.438 0.825 �SE 0.288 0.222 0.122 0.1139 Table 2: The effect of light on Leaf Expansion in bean seedlings. Analysis of data from Table 2 illustrates that the seedlings grown in light have more than 200% longer blade lengths on average compared to those grown in he dark, and almost 300% longer petioles. ...read more.

Conclusion

This is a light dependent reaction, which cannot proceed in the absence of light, therefore having repercussions on those plants that are to grow and develop in the dark. Data from Table 1 illustrates that epicotyl length is not significantly affected whether the seedlings were grown in the light or the dark. On the other hand, measurements of hypocotyl length differ greatly. This may be primarily due to internode and hypocotyl elongation in etoliated plants which are grown in the dark. Etoliation is the intense elongation that usually characterises seedlings that are cultivated in the dark, as the internodes become extremely long. The shoots are a yellow colour since nearly no chlorophyll is produced. Table 2 suggests that light may play a vital role in the size and length of the blades and petioles of the seedlings. Larger petioles and blades were observed in the plants that were grown in the presence of light. This may be due to light playing a role in activating certain plant hormones responsible for cell elongation and division. ...read more.

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