Notes On Coordination in Plants - CBSE Class 10 Science
All living things respond to environmental stimuli.  Plants also respond to stimuli with the help of chemical compounds secreted by the cells. Plants being living organisms, exhibit some movements. Types of movements The movement of a plant during its growth can be directional or non-directional. Directional movements: These are also called as tropic movements. Tropic movements are the movements which occur in the direction of the stimulus.        • Positive phototropism is seen in shoots which respond by bending towards light.  Negative geotropism is seen in shoots by growing away from the ground.        • Roots bend away from light exhibiting negative phototropism. They grow towards the ground exhibiting positive geotropism.        • Thigmotropism is the directional growth of a plant part in response to the touch stimulus of an object.          • Hydrotropism is a growth response in which the direction is determined by the stimuli of water.        • Chemotropism is a growth movement of a plant part in response to chemical stimulus. e.g. Growth of pollen tubes towards ovules. Non- directional movements:  These are also called as nastic responses.  These are exactly the movement of plant parts.        • These movements are independent of growth.          • Plant cells must change their shape for this movement to happen.         • The movement in plants occurs in the direction opposite to the stimulus. Plant hormones Plants have various hormones, which help to coordinate growth, development and response to the environment.  Hormones are the chemical compounds released by stimulated cells. Hormones diffuse all around the cell.  Different hormones secreted by the plant are auxins, gibberellins, cytokinins, abscisic acid.        • Auxins are the hormones synthesised at the tip of the stem.  These help the plant in  growth by cell elongation.        • Gibberellins are hormones that help in the growth of the stem, seed germination, bolting, and flowering.        • Cytokinins are hormones present in the areas of rapid cell division, such as fruits and seeds. They also promote the opening of the stomata.        • Abscisic acid is a hormone that inhibits the growth in various parts.  It is also responsible for the closure of stomata.

#### Summary

All living things respond to environmental stimuli.  Plants also respond to stimuli with the help of chemical compounds secreted by the cells. Plants being living organisms, exhibit some movements. Types of movements The movement of a plant during its growth can be directional or non-directional. Directional movements: These are also called as tropic movements. Tropic movements are the movements which occur in the direction of the stimulus.        • Positive phototropism is seen in shoots which respond by bending towards light.  Negative geotropism is seen in shoots by growing away from the ground.        • Roots bend away from light exhibiting negative phototropism. They grow towards the ground exhibiting positive geotropism.        • Thigmotropism is the directional growth of a plant part in response to the touch stimulus of an object.          • Hydrotropism is a growth response in which the direction is determined by the stimuli of water.        • Chemotropism is a growth movement of a plant part in response to chemical stimulus. e.g. Growth of pollen tubes towards ovules. Non- directional movements:  These are also called as nastic responses.  These are exactly the movement of plant parts.        • These movements are independent of growth.          • Plant cells must change their shape for this movement to happen.         • The movement in plants occurs in the direction opposite to the stimulus. Plant hormones Plants have various hormones, which help to coordinate growth, development and response to the environment.  Hormones are the chemical compounds released by stimulated cells. Hormones diffuse all around the cell.  Different hormones secreted by the plant are auxins, gibberellins, cytokinins, abscisic acid.        • Auxins are the hormones synthesised at the tip of the stem.  These help the plant in  growth by cell elongation.        • Gibberellins are hormones that help in the growth of the stem, seed germination, bolting, and flowering.        • Cytokinins are hormones present in the areas of rapid cell division, such as fruits and seeds. They also promote the opening of the stomata.        • Abscisic acid is a hormone that inhibits the growth in various parts.  It is also responsible for the closure of stomata.

#### Activities

Activity 1 Sumanasinc.com has sparked an interactive audiovisual session to explain different types of tropisms in plants. It is devised into 7 separate modules giving explanations along with activities. It has also emphasised on different types of hormones in plants. Defense mechanisms in plants are also elucidated. Activities in between test the knowledge gaine dby the students from these modules. Go to Activity Activity 2 mpls.k12.mn.us has created a n interactive lesson which brings in the significance of plant hormones in different types of tropisms. It has also illustrated the roles of different plant hormones. It also depicts internal structure of the plant organs to show the changes at cellular level. Go to Activity Activity 3 Prenhall.com has demonstrated role of plant hormones in bringing response to the environment. Plant hormones are described form tropism point of view. The hormone IAA was chosen as an example to explain the activity of hormones in plants to exhibit their response to various environmental stimuli. Go to Activity

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