Chemical co ordination

CBSE class 10-Bio presentations (NCERT)

1. CLASS 10 CBSE SCIENCE CHAPTER- 7 CONTROL AND COORDINATION PART- 1 CHEMICAL COORDINATION IN PLANTS Presented by, SARANYA D SECONDARY SCHOOL TEACHER 1

2. Plants show two different movements 2

3. Points to remember Stimuli- a detectable change in the internal and external environment Coordination- process through which two or more organs interact and complement the functions of one another Curvature movement - curving or bending of a plant in response to any stimuli ( a type of trophic movement) e g ., curving of the stem tip towards light (due to auxin ) 3

4. TROPIC MOVEMENTS IN PLANTS 4 Positive tropism Growth of plant towards the stimuli Negative tropism Growth of plant away from the stimuli

5. Phototropic movement –stimuli light Growth of stem towards light ( positive tropism ) Growth of root away from the light ( negative tropism ) 5

6. Hydrotropic movement- stimuli water Growth of root towards water ( positive tropism ) Growth of root away from the water, seen in mangrove trees for getting oxygen ( negative tropism ) 6

7. Chemotropic movement- stimuli chemical Growth of pollen towards ovary ( positive tropism ) Growth of root away from the toxic chemicals ( negative tropism ) 7

8. Geotropic movement- stimuli gravity 8 Growth of root towards gravity ( positive tropism ) Growth of stem away from gravity ( negative tropism )

9. Thigmotropic movement- stimuli touch Growth of tendril towards the support e g ., Pea plant Auxin is diffused in the part of the tendril away from the object This causes the tendril to circle around the object and thus cling to it When tendril come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object 9

10. Nastic movement Thigmonastic or seismonastic – stimuli touch Drooping of leaves by the movement of water. Nictinastic - stimuli darkness sleeping movement of plants in night time Photonastic - stimuli light Many flowers open with the increasing illumination of the day and close up with the dawn of the day 10

11. Plant hormones Growth promoters Growth inhibitors 11 Auxin Gibberellin Cytokinin Ethylene Abscisic acid

12. Auxin Cell elongation and cell differentiation initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering e.g. in pineapples. They help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits. In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance . Auxins also induce parthenocarpy , e.g., in tomatoes. 12

13. Gibberellins Elongation of stem ability to cause an increase in length of axis is used to increase the length of grapes stalks. Gibberellins , cause fruits like apple to elongate and improve its shape. They also delay senescence. Thus , the fruits can be left on the tree longer so as to extend the market period. GA3 is used to speed up the malting process in brewing industry. 13

14. Cytokinins Cell division helps to produce new leaves , chloroplasts in leaves, lateral shoot growth and adventitious shoot formation. Cytokinins help overcome the apical dominance. They promote nutrient mobilisation which helps in the delay of leaf senescence. 14

15. Ethylene (gaseous hormone) Ripening of fruit Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in flowers and fruits (thinning of cotton, cherry, walnut ). It promotes female flowers in cucumbers thereby increasing the yield. 15

16. Abscisic acid (stress hormone) regulating abscission and dormancy inhibits seed germination stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses . 16