Quiz 30: Plant Reproduction
Nitrogen is a macronutrient which is indispensable for a plant's growth. Macronutrients are the elements which are required in fulfilling the various metabolic role of the plant. They are required in amounts above 0.5 percent of the plant's dry weight. Carbon, hydrogen, oxygen, potassium, calcium, phosphorus, magnesium and sulfur are the other 8 macronutrients. The deficiency of nitrogen in plants causes stunted growth in plants, the young leaves becomes yellow and dies. Plants use nitrogen to carry on various metabolic activities and to make essential nutrients to build tissues. Nitrogen is an important component in the structure of various amino acids, DNA, RNA and proteins. Also nitrogen is required in various metabolic pathways like C₃ and C₄pathways, either as certain cofactors or as essential part of various enzymes involved in various electronic transfer reactions. If requisite amount of nitrogen is not available then the plants cannot form various amino acids, DNA, RNA and proteins. The cell growth and development will be hindered without these biomolecules. Hence the plant tissues would start deteriorating due to lack of this essential nutrient.
Carbon, hydrogen, and oxygen are examples of macronutrients for plants. Macronutrients are those which are indispensable for a plant's growth as these elements are required in fulfilling the various metabolic role of the plant. The macronutrients are required in amounts above 0.5 percent of the plant's dry weight. Carbon, hydrogen, oxygen, nitrogen, potassium, calcium, phosphorus, magnesium and sulfur are the 9 macronutrients. Hence, the correct answer is option (a). Micronutrients are usually required in less amounts; parts per million of a plant's dry weight by the plants. There are 7 micronutrients namely chlorine, iron, boron, manganese, zinc, copper and molybdenum. Micronutrients usually act as cofactors in various enzymes or acts as catalyst in various metabolic reactions of the plant. Micronutrients are usually trace elements whereas macronutrients are essential elements as no other elements can substitute the role they play.
Water transport from roots to leaves occurs by cohesion-tension among water molecules. Xylem conducts water and ions. The xylem consists of 2 types of cells known as vessel members and tracheids. Both these cells are dead at maturity and with only lignin deposited at their cell walls making these cells stiff. Water and ions flow through the adjacent pits along the walls laterally, thus maintaining a constant flow through the xylem. Water evaporation from plant parts is called as transpiration. Transpiration is the loss of water molecules from the stomata of the leaves and other plant parts due to evaporation. Air dries up the atmosphere around the stomata and other plant parts creating a negative pressure called tension. This tension pulls the water molecules in a continuous flow through the xylem of the leaves, stems and roots. The fluid columns of water are in continuity due to cohesion tension theory. The water molecules are linked together due to strong hydrogen bonds between them. Due to this theory more and more water molecules are pulled up inside the xylem. But due to lack of watering to the plants for the last 3 days, the rate of transpiration was more as compared to the water being restored to the plants from the soil. Hence the plants have wilted due to transpiration.