Plant Kingdom

Step 1: Understanding the status of Psilotum nudum.
Psilotum nudum is a primitive, vascular plant and is classified as an endangered species. It is rare in the wild and is threatened due to habitat loss.
Step 2: Analyzing the options.
(A) endangered: Correct. Psilotum nudum is considered an endangered species due to its limited distribution.
(B) rare: Incorrect. Although rare, it is classified as endangered rather than just rare.
(C) extinct: Incorrect. Psilotum nudum is not extinct; it is still found in certain areas.
(D) exotic: Incorrect. Psilotum nudum is not considered an exotic species.
Step 3: Conclusion.
The correct answer is (A) endangered, as Psilotum nudum is considered an endangered species.

• Guttation is a process that occurs in plants where there is a water loss through hydathodes.
• Hydathodes are specialized glands located at the tips of leaves or stems that help in the expulsion of water.
• Guttation primarily happens during the night or early morning when there is high relative humidity and high soil moisture content.
• During these periods, transpiration rates are lower compared to the daytime, when plants are actively growing and water is evaporating.
• However, the roots are still absorbing water, leading to a buildup of root pressure inside the plant.
• The pressure created by water absorption forces the sap out through the hydathodes.
• This expelled mixture consists of water, carbohydrates, water-soluble minerals, and other soluble substances moving through the plant.
• As the sun comes out and the water evaporates, a white, crusty deposit is often left behind on the leaf or stem surface.

In summary: Guttation occurs due to excess root pressure in conditions of high humidity and soil moisture, leading to water loss through hydathodes. The expelled sap leaves behind a residue as the water evaporates.

The theory of root pressure was first proposed by Stephen Hales, an English botanist and physiologist in the 18th century.

Root pressure is a positive pressure that develops in the roots of some plants, especially when transpiration is low (typically at night or in humid conditions). It helps in pushing water and minerals upwards through the xylem vessels.

Key points about root pressure:

• Definition: Root pressure is the osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.
• Mechanism: It is caused by the continuous absorption of water from the soil by root hairs through osmosis.
• Involvement of minerals: Active transport of mineral ions into the xylem lowers the water potential, causing water to enter the xylem from surrounding root cells.
• Pressure buildup: As more water enters, a pressure builds up in the xylem vessels of the root, pushing the sap upwards.
• Guttation: Root pressure is responsible for guttation – the exudation of water droplets from the edges of leaves, commonly seen in the early morning.
• Limitation: Root pressure alone cannot lift water to the tops of tall trees; it is mainly effective in herbaceous and smaller plants.

Thus, Stephen Hales is credited with the discovery and explanation of this phenomenon, making him the correct answer to the question.

The large central vacuole in plant cells serves several important functions. One of its primary roles is the storage of water, nutrients, and waste products. The vacuole helps maintain turgor pressure within the cell by storing water, which provides rigidity to the plant. Additionally, the vacuole stores various substances that may be waste products or substances needed for the cell's function, and it plays a role in regulating the internal environment of the cell. Thus, the primary function of the central vacuole is the storage of water, nutrients, and waste products.