International School/ Duhok The School day

1. International School/ DuhokTheSchool day A typical lecture by student Khatoon/Grade 11 Subject: Plant hormones & plant movement Supervised by : Ronak Ahmed

2. Plant hormones and plant movement Section(11_1)

3. Objectives • List the five major types of plant hormones , and give some effects of each. • List the environmental stimuli to which plants respond and the tropism each stimuli. • Explain the current hypotheses regarding auxins and their function in phototropism and gravitropism.

4. Introduction

5. Groups of hormones • Plant hormones are chemical messengers that affect a plant’s ability to respond to its environment. • Hormones are organic compounds that are affective at very low concentrations ; they are usually synthesized in one part of the plant and transported to another location . • They interact with specific target tissue to cause Physiological response , such as growth or fruit ripening .each response is often a result of 2 or more hormones acting together • Because hormones stimulate or inhibit plant growth, many botanists also refer to them as plant growth regulators. many hormones can be synthesized in laboratory, increasing the quantity of hormones available for commercial applications. How hormones are grouped! Hormones names

6. Table (11-1) five groups of plant hormones

7. Grapes on the right treated with gibberellins

8. Tropisms • a tropism is a plant movement that is determined by the direction of an environmental stimulus . Movement toward an environmental stimulus is calledpositive tropism,and movement away from a stimulus is called a negative tropism , each kind of tropism is named for it’s stimulus . For example , a plant movement in response to light coming from one direction is called phototropism. Light source are positively phototrophic , check table(11-2)

9. Table (11-2) various plant tropisms

10. Phototropism • Light causes the hormone auxin to move to the shaded side of the soot . The auxin causes the cell on the shaded side to elongate more than the cells on the lighted side . As a result ,the soot bends toward the light and exhibits positive phototropism. In some plants stems phototropism is not caused by auxin movement .in these instance , light causes the production of growth inhibitor on the lighted side

12. Thigmotropism • Thigmotropism is a plant’s growth response to touching a solid object . Tendrils and stems of vines , such as pea plants , coil when they touch a object . Thigmotropism allows some vines to climb other plants or objects , increasing its chance of intercepting light for photosynthesis

13. gravitropism • Gravitropism is a plant’s growth response to gravity . A root usually grows downward and stems are usually grows upward –that is , roots are positively gravitropic and stems are negatively gravitropic Like phototopism ,gravitropism appears to be regulated auxins. One hypothesis proposes that when a seedling is placed horizontally , auxine accumulate along the lower sides of both the root and stem . This concentration of auxins stimulates cell elongation along the lower side of the stem , and the stem grows upward . A similar concentration of auxinsinhabitis cell elongation in the lower side of roots , and the root grows downward

14. Chemotropism • A plant’s growth in the response to chemical is called chemotropism . After a flower is polinated , a pollen tube grows down through the stigma and style and enters the ovule through the micropyl . The growth of the pollen tube in response to chemicals produced by the ovule is an example of chemotropism

15. Questions

16. Thanks for listening