Control and Coordination Test 30

Chemotropism is defined as the movement caused by chemical stimulus in organisms such as bacteria and plants. An example of chemotropic movement is the growth of the pollen tube. The growth of the pollen tube is always towards the ovules. The response by the plant is termed positive if the growth is towards the stimulus or negative if the growth is away from the stimulus. Hence, conversion of flowers to fruits is an example of the same. 

Correct option: A

Explanation for correct option:

• Hydrotropism is a plant’s growth response toward water sources. 
• The hydrotropic movement of the plant roots helps in the absorption of water for plant growth. 

• Auxins are a group of hormones that positively influence cell enlargement, bud formation, and root initiation. 
• In conjunction with cytokinins, they control the growth of stems, roots, and fruits, and convert stems into flowers. Auxins were the first class of growth regulators discovered. 
• They affect cell elongation by altering cell wall plasticity. Auxins act to inhibit the growth of buds lower down the stems, and also to promote lateral and adventitious root development and growth. 
• Leaf abscission is initiated by the growing point of a plant ceasing to produce auxins. Auxins in seeds regulate specific protein synthesis, as they develop within the flower after pollination, causing the flower to develop a fruit to contain the developing seeds. 
• Auxins are toxic to plants in large concentrations, they are most toxic to dicots and less so to monocots. 

• Hippocampus is the portion of the cerebral hemispheres in basal medial part of the temporal lobe. 
• This part of the brain is important for learning and memory, for converting short term memory to more permanent memory and for recalling spatial relationships in the world about us. 

Auxins are the growth regulators which are used for shoot elongation, cell division, and cell growth.

• There are five major types of plant hormones.
• Abscisic Acid also called ABA is one of the most important plants growth regulators and under water stress, this hormone plays a role in closing the stomata. 
• Auxins are hormones that positively influence cell enlargement, bud formation, and root initiation. 
• Cytokinins tend to positively influence cell enlargement, bud formation, and root initiation. 
• Other are ethylene regulates the fruit ripening and Gibberellins stimulates the flower production, cell elongation. Whereas 2, 4-D is not a plant hormone but a chemical weedicide. 
• So, the correct answer is option A.

Hypothalamus is the portion of the brain that contains a no. of small nuclei with a variety of functions. It regulates heart rate, glandular secretion, body temperature.

Ethylene is gaseous hormone that promotes fruit ripening. 2,4-D (2,4-dichloro-phenoxyacetic acid) is selective weed killer which inhibit growth and exhibit toxic effects on plants. Gibberellins are responsible for breaking seed dormancy, mobilization of endosperm reserves and thereby, promote seed germination. Cytokinins (zeatin) are transported from roots to leaves and serve to inhibit the leaf senescence. Thus, the correct answer is option B.