Q.Macrophages and leucocytes exhibit

Concept and Intuition

Protozoan locomotory structures differ fundamentally in their permanence and mode

of formation:

• Pseudopodia ("false feet") are temporary outgrowths of cytoplasm (as seen in Amoeba), formed transiently by cytoplasmic streaming to engulf food or move the cell, and retracted once no longer needed.
• Flagella and cilia are permanent, whip-like or hair-like organelles with a fixed microtubule (9+2) internal structure, always present on the cell surface even when not actively beating.
• The pellicle is a semi-rigid or rigid outer covering of the cell (as in Euglena or Paramecium), providing shape and protection — it is not a locomotory projection at all.

Step-by-Step Solution

1. Flagellum — a permanent, structurally fixed organelle used for swimming, not a temporary cytoplasmic projection.
2. Cilium — likewise a permanent, structurally fixed organelle, present in large numbers on the cell surface.
3. Pseudopodium — formed transiently by extending cytoplasm in a chosen …

Cytoplasmic streaming (cyclosis) is the directed flow of cytoplasm within a living cell, aiding distribution of nutrients and organelles. Endocytosis/exocytosis are membrane transport, and c …

Concept and Intuition

Protozoan locomotion ranges from simple to complex: amoeboid movement relies on reversible sol-gel transformations of cytoplasm forming temporary pseudopodia, without any permanent specialised organelle — this makes it slow and is regarded as evolutionarily the most primitive strategy. Flagellar movement uses a long whip-like flagellum for propulsion, and ciliary movement uses coordinated beating of numerous short cilia, both of which are faster and more "advanced" forms of locomotion than amoeboid movement.

Step-by-Step Solution

1. List protozoan locomotion types: amoeboid (pseudopodia), flagellar (whip-like flagellum), ciliary (coordinated cilia beating), and undulatory/undular membrane movement. …

Concept and Intuition

Ciliary movement is coordinated across rows of cilia: cilia in longitudinal rows typically beat in a metachronal rhythm (a wave-like, sequential pattern, each cilium slightly out of phase with its neighbour), while cilia in transverse rows tend to show synchronous beating (all beating together at the same time) — the reverse of what two of the given options claim. Functionally, cilia are used in two broad contexts: to propel a free-living single-celled or small organism through its liquid environment (e.g., Paramecium), or to move fluid and suspended particles over the surface of an otherwise stationary organism or tissue (e.g., mucus transport in the respiratory tract, or feeding currents in sessile filter feeders).

Step-by-Step Solution

1. (A) claims longitudinal cilia are synchronous — this reverses the actual pattern (longitudinal rows are metachronal); false.
2. (B) claims transverse cilia are metachronous — this also reverses the actual pattern (transverse rows are synchronous); false. …

Concept and Intuition

A cell bounded only by a fluid lipid bilayer would be a featureless sphere, like a soap bubble — it could not hold a shape and it could not push itself anywhere. What rescues it is an internal, dynamic protein scaffolding: the cytoskeleton. Its three components divide the labour:

• Microfilaments (actin, ~6 nm) — thin, flexible, concentrated just under the plasma membrane. They generate the cell cortex, drive amoeboid movement (pseudopodia), cytoplasmic streaming, and the contractile ring of cytokinesis. With myosin they form a force-generating pair.
• Microtubules (tubulin, ~25 nm) — hollow, stiff tubes. They are the cell's compression struts and its highways: motor proteins (kinesin, dynein) walk cargo along them; they build the mitotic spindle and the axoneme of cilia and flagella.
• Intermediate filaments (~10 nm) — rope-like and stable; they bear mechanical stress and anchor the nucleus, giving the cell tensile strength.

Crucially, the cytoskeleton is dynamic — filaments polymerise at one end and depolymerise at the other, so the cell can remodel its shape and move directionally rather than drift passively.

Step-by-Step Solution

1. Check A. Eukaryotic cells do adopt a variety of shapes (a neuron, a columnar epithelial cell, a biconcave RBC, an amoeba) and do carry out directed movement (leukocyte chemotaxis, amoeboid crawling, ciliary/flagellar locomotion). A is correct.
2. Check R. The cytoskeleton is, by definition, composed of microfilaments, microtubules and intermediate filaments. R is correct as a statement of fact. …

Concept and Intuition

Protozoan locomotion methods, roughly in order of increasing structural specialisation and speed, are: amoeboid movement (pseudopodia; e.g., Amoeba) → flagellar movement (e.g., Euglena) → ciliary movement (e.g., Paramecium). Amoeboid movement relies purely on reversible cytoplasmic sol-gel transformations that push out pseudopodia, with no discrete motile organelle — this makes it structurally the simplest (most primitive) and, because it depends on slow cytoplasmic streaming rather than rhythmic organelle beating, also the slowest.

Step-by-Step Solution

1. Compare the mechanisms: gliding (no clear organelle, used e.g. by gregarines), amoeboid (pseudopodia/cytoplasmic flow), ciliary (many short hair-like cilia beating in coordinated waves), euglenoid/flagellar (whip-like flagellum).
2. Ciliary locomotion is actually the fastest and most coordinated among protozoans (e.g., Paramecium is a fast swimmer).
3. Flagellar/euglenoid locomotion is faster and more directional than amoeboid movement. …

Concept and Intuition

Ciliates like Paramecium are covered with hundreds of cilia. If every cilium beat in unison (synchronous movement), organisms would experience jerky, inefficient propulsion. Instead, cilia beat in a coordinated sequence — each cilium begins its stroke a fraction later than the one before it in the row — producing a travelling wave down the row. This pattern, called metachronism/metachronal rhythm, ensures smooth, continuous, and efficient locomotion.

Step-by-Step Solution

1. Distinguish the terms: "undulation" describes wave-like movement of flagella/membranes, not sequential ciliary beating per se.
2. "Synchronous movement" is the opposite of what's described — that would mean all cilia beat together, not one after another.
3. "Effective stroke" refers to just one phase of a single cilium's beat cycle (the power stroke), not the row-wise sequential pattern. …

Concept and Intuition

Protozoans use a variety of specialised organelles for movement and other functions:

• Pseudopodia ("false feet") are temporary cytoplasmic extensions/protrusions of the cell body used in amoeboid movement — these are the "cellular extensions."
• Flagella are long, whip-like organelles used for propulsion, moving in an undulating fashion — the "whiplike organelles."
• Myonemes are contractile fibrils found in some protozoans (e.g., Stentor, Vorticella) that allow rapid contraction of the body — the "contractile fibrils."
• Cilia are numerous short, hair-like organelles covering the cell surface, beating in coordinated waves for locomotion/feeding — the "short hair-like organelles."

Step-by-Step Solution

1. Match "Cellular extensions" (i) to Pseudopodia (c) — pseudopodia are literally extensions of the cell body.
2. Match "Whiplike organelles" (ii) to Flagella (d) — flagella have a characteristic whip-like undulating motion.
3. Match "Contractile fibrils" (iii) to Myonemes (a) — myonemes are the specific contractile protein fibrils in protozoan cells. …