Irritability/Cell Reactions To Its Environment

Irritability And Response Types   Irritability denotes the capacity of organisms to react to stimuli, where stimuli refer to alterations in external or internal environmental conditions capable of influencing the activity of the entire organism or specific parts.   The term “response” characterizes the changes in the organism’s activity. Three primary response types exist: taxis […]

Irritability And Response Types

 

Irritability denotes the capacity of organisms to react to stimuli, where stimuli refer to alterations in external or internal environmental conditions capable of influencing the activity of the entire organism or specific parts.

 

The term “response” characterizes the changes in the organism’s activity. Three primary response types exist: taxis (tactic movement), nastism (nastic movement), and tropism (tropic movement).

 

Taxis or tactic movement:

This involves directional movement or responses of entire organisms from one location to another in reaction to external stimuli like light, temperature, water, and specific chemicals. Examples include Euglena or Chlamydomonas swimming away from high light intensity (negative phototaxis) and moss plant sperm moving toward the chemical produced by the egg cell (positive chemotaxis).

 

Nastism or nastic movement:

Non-directional sleep movement or responses of a plant part to non-directional stimuli like light intensity, temperature, and humidity. Examples include the folding of mimosa plant leaflets when touched and the closing of morning glory flowers in low light intensity.

 

Tropism Or Tropic Movement:

Unilateral growth and directional movement of a plant part in response to directional stimuli, controlled by plant hormones known as auxins. Examples include shoots bending towards light (positive phototropism) and roots bending away from light (negative phototropism).

 

Movement:

Organisms move in search of food, water, mates, or to escape predators or harsh weather conditions.

 

Cyclosis in cell:

Cyclosis, or cytoplasmic streaming, involves the rotational movement of the cytoplasm and its contents within cells. This facilitates substance transportation and material exchange between cell organelles, occurring in protozoa like amoeba (amoeboid movement) and chloroplasts of some plants adjusting their position for optimal sunlight exposure during photosynthesis.

 

Organelles for movement:

  1. Flagella: Long whip-like projections, usually one or two on the cell surface, serving as movement organelles in organisms such as Euglena, Trypanosome, Spermatozoa, and Chlamydomonas.
  2. Cilia: Short hair-like structures densely packed on the cell surface, found in organisms like Paramecium and on cells lining the human windpipe.

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