Control and Coordination | Class 10 Science Notes

6.2 COORDINATION IN PLANTS

Unlike animals, plants do not have a nervous system or muscles, yet they exhibit coordination and respond to stimuli. Plant movements can be classified into two types: movements independent of growth and movements dependent on growth. The sensitive plant (Mimosa pudica) exhibits rapid leaf folding when touched, a movement not involving growth. This movement occurs through changes in cell shape caused by water movement within cells. Plants detect stimuli and transmit signals using electrical and chemical means, but they lack specialized nervous tissue. In contrast, directional growth movements, such as roots growing downward and shoots growing upward, involve growth and are slower. These growth movements are responses to environmental stimuli like light and gravity and are called tropisms. For example, phototropism is growth towards light, and geotropism is growth in response to gravity. Plant hormones, such as auxins, gibberellins, cytokinins, and abscisic acid, regulate these growth responses. Auxins promote cell elongation on the shaded side of shoots, causing bending towards light. Gibberellins stimulate stem growth, cytokinins promote cell division, and abscisic acid inhibits growth and causes leaf wilting. Thus, plants coordinate their growth and movements through chemical signals to adapt and survive in their environment.

📊 Diagram: Figure 6.4 The sensitive plant; Figure 6.5 Response of the plant to the direction of light; Figure 6.6 Plant showing geotropism

🧪 Activity: Activity 6.2: Observing phototropism by placing germinated bean seeds on a wire mesh in a conical flask and exposing them to light from one side.

🔗 Connection: This section introduces chemical coordination in plants and leads to the next section on hormones in animals, which also use chemical signals for control.