Movement and locomotion

A child runs after a ball

A child runs after a ball. Her legs swing, her heart beats, and the tiny hairs in her windpipe sweep dust upward. All of these are movements. But only one of them carries her from one place to another.

Movement is any change in the position of the body or of a part of the body. Locomotion is a voluntary movement that changes the place of the whole body. Walking, running, climbing, flying and swimming are locomotions.

Every locomotion is a movement. But not every movement is a locomotion. The tentacles of Hydra move to catch a prey, yet the animal stays where it is.

Why do animals move from place to place? They search for food, shelter, a mate, a breeding ground or a favourable climate. They also run away from enemies.

The kinds of movement

NCERT names three kinds of movement: amoeboid, ciliary and muscular. The syllabus of NEET names ciliary, flagellar and muscular. This lesson covers all four, because a cell may use any of them.

Amoeboid movement

Amoeba has no limbs and no cilia. It puts out finger-like extensions of the cell, the pseudopodia, by the streaming of its cytoplasm. The cell then flows into them and creeps forward. The microfilaments of the cytoskeleton help in this movement.

Some cells of our own body move in the same way. The macrophages and the leucocytes of the blood move through tissues by amoeboid movement.

This part is not in the NEET syllabus, but NCERT teaches it, and cell movement is also part of A-Level and IB cell biology.

Ciliary movement

Cilia are fine hairs on the surface of a cell, and they beat together. Most of the tubular organs inside our body are lined by a ciliated epithelium.

• In the trachea, the cilia sweep the mucus and the dust that we breathe in upward and out of the airways.
• In the female reproductive tract, the cilia help the ovum to pass along the tube toward the uterus.

Paramecium is a single cell that swims by the beating of its cilia.

Flagellar movement

A flagellum is also a hair-like outgrowth of the cell. But it is long, and a cell has only one or a few of them. The sperm of a human swims with one flagellum, which is its tail. Euglena also swims with a flagellum.

Cilia are short and many. Flagella are long and few. Both have the same inner plan of microtubules, the 9 + 2 pattern, which you met in the chapter on the cell.

Muscular movement

The movement of the limbs, the jaws and the tongue needs muscles. A muscle can contract, which means that it can become shorter. Human beings and most many-celled animals use this property for locomotion and for other movements.

About 40 to 50 per cent of the body weight of an adult is muscle. Locomotion needs three systems to work together: the muscular, the skeletal and the nervous systems.

You should find that cilia in the windpipe and the tentacles of Hydra are movements, but the body of the organism stays where it is.

Try it in Python

The program lists six examples, with the kind of movement and whether the whole body changes place.

Practise with new numbers

Common mistakes

• Saying that every movement is a locomotion. Locomotion changes the place of the whole body. A heartbeat or the beating of cilia in the windpipe does not.
• Saying that cilia and flagella are different in structure. They have the same 9 + 2 plan. They differ in length and in number.
• Giving the ciliary movement of the windpipe to the muscles. The cilia sweep the dust. The windpipe is not moved by muscles for this work.
• Forgetting the nervous system. Locomotion needs the muscular, skeletal and nervous systems together.

Remember these

• Movement: any change in the position of a part of the body. Locomotion: a voluntary movement that changes the place of the whole body.
• Kinds of movement: amoeboid (pseudopodia), ciliary (cilia), flagellar (flagellum) and muscular (muscles).
• Cilia line the trachea and the female reproductive tract. A sperm swims with a flagellum.
• About 40 to 50 per cent of the body weight of an adult is muscle.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. What is the difference between a movement and a locomotion? Give one movement that is not a locomotion.

2. Which kind of movement removes the dust that we breathe in, and which tissue does the work?

3. Where in the female reproductive tract does ciliary movement help?

4. Give two differences between cilia and flagella.

5. Which three systems must work together for locomotion?

References

• Betts J. G. et al. (2022). Anatomy and Physiology 2e, OpenStax, chapter 10, Muscle Tissue.
• Alberts B. et al. (2015). Molecular Biology of the Cell, 6th edition, Garland Science, chapter 16, The Cytoskeleton.
• NCERT (2023). Biology, Textbook for Class XI, chapter 17.