Control Coordination 2(educationpoint.co.cc)

STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY

CONTROL & COORDINATION Stimulus: The change in the environment to c the organisms responds & reacts is called stimulus e.g. Light, Touch, Small, Taste Response: The reaction to stimulus is called response c is a characteristic property of living beings. Plants & Animals respond to stimulate in different ways. •

Animals (have nervous system, endocrine sys) so they can react to stimuli in many ways.

•

Plants (nervous syst is absent only endocrine syst is +nt) so reaction towards stimulus is in a limited way. CONTROL & COORDINATION IN PLANTS

In plants only Endocrine syst is + nt. (Nervous syst is absent so use harmones to respond against environmental changes. (Stimuli) This is why they respond to stimuli very slowly by GROWING Thus we conclude that function of control & coordination in plants is performed by PHYTOHORMONES (plant hormones) •

Dormancy: A resting; inactive condition in which Melabolism almost stops. e.g. Seed, Bud.

•

Breaking of dormancy: Seed must have certain conditions like water, warmth, air a hormones to break dormancy & germinate to form a seedling. PHYTOHORMONES

•

They are responsible for control & coordination plants.

•

They are also called Plant growth substances.

Types:

(i)

Auxins

(ii)

Gibberellins

(iv)

Abscisic Acid

(v)

Ethene (Ethylene)

(iii)

Cytokinin

Functions: (i)

Auxins:

promote cell enlargement, cell differentiation.

(ii)

Gibberellins:

promote cell enlargement, cell differentiation in the presence of Auxins.

Promote fruit growth. Help in breaking dormancy Promote growth in fruit. (iii)

Cytokinins:

promote cell division breaking dormancy delay ageing in leaves promote opening of stomata promote fruit growth

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STEPS … A T C Y P r og r am _______________________________________________________________________________________ (iv) Abscisic Acid: promotes dormancy in seeds & buds LECTURE NOTES – BIOLOGY

promotes closing of stomata promotes falling of leaves (v)

Ethene:

promotes ripening of fruit help in breaking bud dormancy PLANT MOVEMENTS

•

Plants don’t show locomotion.

•

They respond towards stimuli by movements of individual part.

•

The movement in any part of a plant is usually Growth movement

•

The movement of a part of a plant in response to an external stimulus is called TROPISM.

Tropism is a directional movement of the part of plant caused by its growth. If growth (movement) is towards stimulus Æ POSITIVE TROPISM If growth (movement) is away from stimulus Æ NEGATIVE TROPISM Types of Tropism On the basis of stimuli + ve Æ Plant part moves towards light (Stem) 1.

Light Æ Photoropism – ve Æ away from light (Roots) + ve Æ plant part moves in the direction of gravity (Roots)

2.

Gravity Æ Geotropism – ve Æ against direction of gravity (shoot)

3.

Chemical substances Æ Chemotropism

+ ve Æ shows movement towards chemical (growth of pollen tube towards ovule during fertilization) – ve Æ growth away from chemical

Nastic Movements in plants: The movement of plant parts in response to a stimulus which take place in any direction (neither towards the stimulus nor away from the stimulus) Also called nastics: This is not a directional movement. Such movements are mostly shown by few organs of plant like leaves, petals. e.g. Touch–me–not plant (Mimosa). If we touch its leaves, they fold up & droop. PHOTOPERIODISM: The day length during which light is available to the plants is called Photoperiod. The effect of day length (photoperiod) on the developmental processes of plant (like germination of seeds & flowering) is called PHOTO PERIODISM

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STEPS … A T CY Pr ogr am _______________________________________________________________________________________ LECTURE NOTES – BIOLOGY

Plants respond to photoperiodic stimulus which the help of a pigment called Phytochrome. It is a blue green pigment which responds to light. e.g. 1. 2.

Photoperiodism is involved in germination of seeds. Flowering of tobacco plants is a photoperiodic response. NERVOUS SYSTEMS OF GRASSHOPPER (insect)

The nervous system of a grasshopper consists of a Brain (bilobed), a long nerve cord, Nerve ganglion and nerves (which are attached to the ganglia). Brain of grasshopper is Biolobed ganglion & in called Cerebral ganglion. Specialized sense organs + nt are: Antinnae Æ Sensitive to feeling & Smell. Bilobed Brain

nerves

Antinnae

nerve cord

ganglia

Nervous Systems of an INSECT (GRASSHOPPER)

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