Tag: botany

If we cut a small soft-stemmed plant on a day, when there is plenty of atmospheric moisture, early in the morning we will soon see drops of solution ooze out of the cut stem; this comes out due to the positive root pressure. If we fix a rubber tube to the cut stem as a sleeve we can actually collect and measure the rate of exudation, and also determine the composition of the exudates. Root pressure is a positive pressure that develops in the xylem sap of the root of some plants. It is a manifestation of active water absorption. Root pressure is observed in certain seasons which favour optimum metabolic activity and reduce transpiration. It is more during rainy season in the tropical countries and during spring in temperate habitats. So, the correct answer is 'Root pressure'.

In the presence of NaCl in the environment causes exosmosis and removes water from the cell. Once the water leaves the elodea cell, the membrane collapses into the center of the cell with the other remaining organelles. At this point, the plasma membrane is clearly visible.

Water absorption takes place through root. There are two theories to explain the mechanism of water absorption. One is passive absorption and the other is active absorption. Osmotic theory of active water absorption was given by Atkins and Priestley. According to this theory, water is absorbed due to osmotic difference between soil water and tonoplasm. Water moves from soil to root xylem along the increasing gradient of suction pressure.

Xylem vessels are made up of a substance called lignin. In some xylem vessels contains lignocellulose which is the complex structure of lignin and cellulose also present in it. They are long hollow chains of which are made up of tough long dead xylem cells. Each of the vessels is interconnected to each other through a perforation in their common walls. Xylem vessels are hydrophobic in nature i.e, cell wall shows the greater affinity for water. With the help of this particular property only xylem vessel function as transportation of water and solutes from the roots to all parts of a plant. 

 Root pressure is the force in root region that helps to drive water or sap upwards into tracheary elements of xylem. Water is absorbed through the root hairs from the soil. When during low transpiration there is no transpiration pull that time root pressure increases and water moves upwards in xylem elements. Root pressure is actively push up the water to small height in the stem.

So the correct answer is 'Root pressure '.

Lotus have stomata on the upper surface of its leaves. Hence, Coating of Vaseline on its upper surface will hinder transpiration. 

When the concentrations of both the solution (cell sap as well surrounding solution) are same, there is no net movement in the cell. Such solutions are called isotonic solutions. Since it is specified that no change in volume occurs it means that the concentration of the cell sap will be same as that of the concentration of salt.

The example of Natural polymers are ;- wool, silk, amber, cellulose etc.

Nylon is a synthetic fibre.

Chloroplasts contain an internal system of membranes called thylakoids. The thylakoids may be arranged in stacks called as grana. The thylakoid membranes not arranged in stacks and are in direct contact with chloroplast stroma are called as stroma lamellae. During photosynthesis, light reaction occurs in grana.
Hill conducted experiments on isolated chloroplasts, having some oxidants like ferricyanide and benzoquinone (Hill reagents). By placing them in sunlight, he noticed evolution of oxygen from water. Hill concluded that if there was hydrogen acceptor in the medium, it would have been reduced. Arnon in 1951, 1954, repeated the experiment with isolated chloroplast and concluded that -
(i) The hydrogen acceptor present in plants is NADP. It is reduced to $NADPH _2$.
(II) An ADP molecule is converted to ATP in light by utilizing inorganic phosphorous. This phenomenon is called as photophosphorylation.