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6.10. Cell motility

When changes occur in the environment, cells can respond by moving to these environmental stimuli, a phenomenon called taxia or tactismThese stimuli can be chemical (chemotaxis) or light (phototaxis).

For example, these movements are carried out by bacterial flagella, or the cilia and flagella of protists.

Chemotaxis

The chemotaxis causes changes in the direction or type of movement in response to the stimulus produced by a chemical. Can be:

  • Positive. When the cell moves towards the area of ​​highest concentration of a substance, such as nutrients.
  • Negative. When the cell detects a toxic substance and moves to where there is less concentration of that substance.

Phototaxis

The phototaxis is the ability of many photosynthetic cells (using light as an energy source) to move according to the light intensity where the wavelength is more suitable for photosynthesis.

Cyclosis movements

The cyclosis consists in producing currents inside the hialoplasma displacing the cellular organelles.

Amoeboid movements

It is carried out by cells that can change their shape and consists of the emission of pseudopods or cytoplasmic processes, which is why they are carried out by free cells without a rigid membrane, such as amoebae, myxomycetes, and leukocytes.

The displacement is achieved by changing different parts of the cytosol from the gel state to the sun state, and emitting the pseudopods.

There are several types of pseudopodia :

  • Philopods: thin and spindle-shaped.
  • Reticulopods: slender, long, and intertwined.
  • Lobopods: short, thick and isolated.

Video: Amoeboid movements.

Vibrational movements

They are produced in cells that have cilia or flagella (sperm, ciliated protozoa, etc.). They have already been discussed in this topic.

Video: Bacterial flagellum movement.

Contractile movements

This movement consists of shortening and stretching of the cell due to the existence in the cytoplasm of contractile proteins. For example, muscle cells have fibrous proteins in the hyaloplasm that allow this movement.