Phagocytosis, or 'cell eating', is a type of endocytosis where the cell membrane engulfs large solid particles, such as bacteria or cellular debris, forming a vesicle called a phagosome. This phagosome then fuses with a lysosome for digestion. It is primarily performed by specialized cells like macrophages and neutrophils.
Explanation:
Megaloblastic anemia is characterized by large, immature RBCs due to impaired DNA synthesis from B₁₂ or folate deficiency. Microcytic is iron deficiency, sickle cell is genetic.
In plant physiology, the 'Transpiration pull' theory, also known as the cohesion-tension theory, was proposed to explain the ascent of sap in tall trees. The key forces involved are:
A.Root pressure and capillarity
B.Active transport by xylem parenchyma
C.Osmotic pressure in the leaves
D.Cohesion between water molecules, adhesion to xylem walls, and tension created by transpiration
Explanation:
The cohesion-tension theory, primarily proposed by Dixon and Joly (and later supported by Denison), is the most widely accepted mechanism for the ascent of sap in tall trees. It relies on the physical properties of water. Transpiration from the leaves creates a negative pressure (tension) in the xylem. This tension pulls the water column upwards. The water column remains unbroken due to the high cohesive force between water molecules (hydrogen bonding) and the adhesive force of water to the hydrophilic walls of the xylem vessels and tracheids. This creates a continuous, passive pull from the top.
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