Q.Explain the mechanism of flagellar bending.

A kinety is a longitudinal row of ciliary basal bodies (kinetosomes) with their connecting fibril (kinetodesma) below the pellicle of ciliates; together the kineties form the infraciliature.

Explanation:

• In ciliate protozoans (such as Paramecium), the cilia arise from basal granules called kinetosomes (basal bodies) lying just below the pellicle.

• A KINETY is a longitudinal ROW of these kinetosomes, together with a fine fibril, the kinetodesma, that connects them along the row.

• All the kineties of the body collectively form the INFRACILIATURE.

• Function: the infraciliature coordinates the beating of the cilia so that ciliary movement is synchronised for locomotion.

A kinety is the basic unit of the infraciliature in ciliate protozoans - a row of kinetosomes and fibrils that anchors and coordinates a longitudinal line of cilia.

In ciliated protozoans such as Paramecium, the body surface is covered by rows of cilia arranged in longitudinal lines. Beneath the pellicle, each such row of cilia is underlain by a corresponding row of basal bodies (kinetosomes), interconnected by fine longitudinal and transverse fibrils. This entire longitudinal unit - one row of kinetosomes plus its associated fibril system - is called a kinety.

The complete set of kineties covering the body forms the infraciliature (the sub-pellicular fibrillar system). The kinety system:

• Anchors the cilia to the cell cortex.

• Coordinates the metachronal (wave-like) beating of the cilia within that row, and, together with neighbouring kineties, over the whole body surface - enabling smooth, directed swimming.

• Is used taxonomically, since the pattern and number of kineties is a stable, distinguishing feature used to classify ciliates.

A kinety is a longitudinal row of ciliary basal bodies (kinetosomes) with their connecting fibril (kinetodesma) below the pellicle of ciliates; the kineties together form the infraciliature.

Explanation:

• In ciliate protozoans (such as Paramecium), the numerous cilia arise from basal granules called kinetosomes (basal bodies), lying just below the pellicle.

• A KINETY is a longitudinal ROW of these kinetosomes together with a fine fibril, the kinetodesma, that runs along and connects them.

• All the kineties of the body collectively make up the INFRACILIATURE.

• Function: the infraciliature (the system of kineties) coordinates and controls the beating of the cilia, so that ciliary movement is synchronised for locomotion.

Synchronous movement = all cilia beat together at once; metachronous movement = cilia beat one after another in sequence, producing a wave that moves along the body.

Distinction between synchronous and metachronous movements (of cilia):

Synchronous movement:

• All the cilia in a transverse row beat together, at the SAME time and in the same phase (as if in unison).
• Such beating is less common.

Metachronous movement:

• The cilia beat one after another in a regular sequence (each cilium slightly out of phase with the one in front), so that a WAVE of beating passes along the length of the rows of cilia (like wind passing over a field of grass).

• This is the usual pattern in ciliates (e.g. Paramecium) and produces smooth, effective locomotion by pushing water backward.

Cilia and flagella are both hair-like locomotory organelles with a common 9+2 microtubule structure, but they differ in number, length and the way they beat.

Both cilia and flagella are motile, hair-like extensions of the cell membrane with an internal 9+2 arrangement of microtubules (the axoneme), and both are used for locomotion in protozoans (e.g., Paramecium uses cilia, Euglena/Trypanosoma use flagella). However, they differ in the following ways:

1. Number and length: Cilia are numerous and comparatively short, covering the cell surface densely (e.g., thousands in Paramecium). Flagella are few in number — usually only one or two per cell — and are much longer relative to the cell.
2. Pattern of beating: Cilia beat in a coordinated, wave-like sequence called a metachronal rhythm (like oars), each cilium performing an effective power stroke followed by a recovery stroke. Flagella move in an undulating, whip-like fashion, propagating a wave along their length to push or pull the cell.

(A further difference: ciliates like Paramecium rely on cilia mainly for both locomotion and feeding currents, while flagellates like Euglena rely on flagella chiefly for propulsion.)

Dynein arms are the molecular motors of cilia and flagella — they convert the chemical energy of ATP into the mechanical sliding of microtubules that produces ciliary/flagellar bending.

What are dynein arms?

In the 9+2 axoneme of a cilium or flagellum, nine peripheral doublet microtubules surround a central pair of single microtubules. Each peripheral doublet carries two rows of small projections called dynein arms — an outer dynein arm and an inner dynein arm — attached to microtubule A of the doublet and reaching toward microtubule B of the adjacent doublet. Dynein itself is a large motor protein with ATPase activity.

Significance:

1. Dynein hydrolyses ATP and uses the released energy to "walk" along the neighbouring doublet's microtubule B, causing the doublets to slide relative to one another (the sliding-microtubule mechanism of ciliary movement).

2. Because the doublets are held together at their base and by radial spokes/nexin links, sliding is converted into local bending of the axoneme instead of free sliding.

3. Coordinated, sequential activation of dynein arms along the length of the axoneme produces the characteristic whip-like or oar-like beating of cilia and flagella, which powers locomotion in ciliates/flagellates (e.g. Paramecium, Euglena) and movement of fluids over ciliated epithelium.

4. Defective dynein arms (as in genetic ciliary dyskinesia) abolish normal ciliary beating, underscoring their essential motor role.

A kinety is the basic organisational unit of a ciliate's ciliary system — a lengthwise row of basal bodies with connecting fibrils that anchors and coordinates a line of cilia.

In ciliate protozoans (e.g., Paramecium), the body surface is covered with numerous cilia arranged in longitudinal rows. Each cilium is anchored in the pellicle by a basal body (kinetosome). A single longitudinal row of these kinetosomes, together with the fine fibrous strands (kinetodesmal fibrils and other rootlet fibrils) that interconnect them, constitutes one kinety.

The complete set of kineties covering the ciliate's body is called the infraciliature — it lies just beneath the pellicle and forms a coordinating skeletal-cum-conductive network. The kinety system:

• Anchors the cilia mechanically to the cell surface.

• Provides a pathway believed to help coordinate the metachronal (wave-like) beating of the cilia within a row.

• Is an important taxonomic character, since the number, arrangement and pattern of kineties differ between ciliate species and are used in their classification.

Flagella and cilia are both microtubule-based (9+2) locomotory organelles, but they differ in number, length, and beat pattern.

Difference 1 — Number and length: A flagellated cell (e.g. Euglena) usually bears only one or two long flagella, whereas a ciliated cell (e.g. Paramecium) is covered by hundreds to thousands of short cilia arranged in longitudinal rows over the body surface.

Difference 2 — Movement pattern: Flagella move with an undulating, whip-like (sinusoidal) beat that pulls or pushes the cell along the flagellar axis, giving a smooth gliding motion. Cilia beat with an oar-like effective stroke followed by a recovery stroke, and neighbouring cilia beat in a coordinated, wave-like sequence called metachronal rhythm, propelling the cell in a direction roughly perpendicular to the row of cilia.

(Additional points, any two of which may be cited: flagella are chiefly used only for locomotion, while cilia may also move the surrounding medium/capture food; ciliary beating is generally faster and generates more force per unit length than flagellar beating.)