Q.Give an account of pseudopodia.

Pseudopodia ('false feet') are temporary, extendable cytoplasmic projections used by sarcodine protozoans for crawling locomotion and for capturing food by phagocytosis.

What are pseudopodia?

Pseudopodia are temporary, finger-like or lobe-like extensions of the cell body found in amoeboid (sarcodine) protozoans such as Amoeba. They are formed and withdrawn as needed, and serve the dual function of locomotion and feeding.

Mechanism of formation (amoeboid movement):

The cytoplasm of Amoeba exists in two states - a more fluid, granular inner endoplasm (plasmasol) and a clear, more viscous outer ectoplasm (plasmagel). Movement occurs by a continuous sol-gel transformation:

• At the leading (advancing) end, the gel-like ectoplasm liquefies, allowing fluid endoplasm to stream forward into a bulging tip (often showing a clear hyaline cap).
• As this fluid endoplasm reaches the tip, it converts back into gel-like ectoplasm at the sides, forming a firm outer tube that maintains the shape of the emerging pseudopodium.
• At the trailing (posterior) end, the ectoplasm liquefies again, allowing that region of cytoplasm to flow forward and add to the advancing endoplasmic stream. This continuous, directed cytoplasmic streaming pushes the whole cell forward - this is amoeboid movement.

Functions:

1. Locomotion - the animal crawls along a substrate by repeatedly extending pseudopodia at the front and retracting the rear.
2. Feeding (phagocytosis) - pseudopodia are extended around a food particle from multiple sides, enclosing it within a food vacuole, which is then drawn into the cell for digestion. …