PEDAGOGY-BIOLOGICAL SCIENCE-II

UNIT-1

PLANT PHYSIOLOGY

LIVING WORLD OF

MOVEMENT IN PLANTS

INTRODUCTION

Animals move in search of food, shelter and for reproduction, even microorganism’s show movement. Understanding of the processes by which plants keep alive and grow is the aim of Physiology. Thus deals with the life processes. Any chemical or physical change occurring within a living plant or any interaction between the organism and its environment would be considered as a physiological process.

For example: We see a branch of a tree shaking in heavy thunder storm; and dancing in gentle wind. These movements are caused by an external agency.

DEFINITION OF PLANT PHYSIOLOGY

The word Plant Physiology is derived from the Greek word “Physis” means nature and “logos” means word. Plant Physiology is defined as “the science of how plants develop, grow and respond to their environment at the cellular and biochemical level.”

Plant physiology refers to the study of the functions occurring in plants, several vital processes included and their working. For instance, metabolism, mineral nutrition and development; water relations, movement, growth and transport process, etc. are some of the things that are covered in it.

Plant Physiology helps in understanding better about plants because:

• In ecosystems, plants are the primary source of food.

• Plants possess the ability convert the solar energy into organic molecules.

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• Plants provide us several economical and important products like cotton, medicines, wood, fibers, etc.

TROPIC MOVEMENTS

TROPISM

The response to stimulus may be Directional or Non-Directional in Plants. The response of plants to directional stimuli like sunlight and gravity is referred as . It results in differential growth in plants whereby some plants elongate on one side and some bend to a lesser side.

Nastic Movement refers to the movement of plants where they respond to Non-Directional stimuli such as temperature and humidity. These movements are independent of the position of stimuli and the frequency and rate of response increases with the increase in stimulus.

Forms of tropism include

✓ (Response to Light), ✓ Geotropism (Response to Gravity), ✓ (Response to Particular Substances), ✓ (Response to Water), ✓ (Response to Mechanical Stimulation), ✓ Traumatotropism (Response to Wound Lesion), And

PHOTOTROPISM:

This kind of movement is induced by light. Not all plants and not all parts respond in the same way to this stimulus. In general, the stem mostly grows and turns towards the source of light, while the roots away from it. The leaves also positively respond toward the source of light. The leaves, however, take up such a position in which the broad surface of the blade is at right angles to the light rays. A stem is, therefore, said to be positively phototropic, a root negatively phototropic, and a transversely phototropic or diaphotropic. Phototropism is also known as .

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GEOTROPISM

Stem mostly grows away from the centre of gravity and is thus negatively geotropic. However, stems in prostrate plants have lost their negative geotropism and even develop into root stock or tubers which behave exactly like roots. Most of the leaves take up their positions at right angles to the centre of gravity and are, therefore, called transversely geotropic or diageotropic. Geotropism is of three types: orthogeotropism (e.g. primary root), plageotropism (e.g., secondary roots) and diageocropism (movement of tertiary roots)

HYDROTROPISM

The Paratonic curvature movements of growth in relation to the stimulus of water are called hydrotropic movements. The tropic response to the stimulus of water is called hydrotropism. The roots show positive hydrotropic response, i.e., they bend towards the water Hydrotropism is stronger in roots compared to geotropism.

PHOTONASTY

It is the non-directional movement of a plant part (e.g. petals of flowers) in response to light. The opening and closing of petals of dandelion flowers in response to light intensity is an example of this process.

THIGMONASTY:

It is the non-directional movement of a plant part in response to the touch. The folding up of leaves when touching is an example of this process.

THERMONASTY

A nastic movement in response to a change in temperature. For example, when subjected to a temperature increase of between 5 and 10°C, Crocus flowers open in a few minutes due to a relative increase in growth rate on the inner side of the petals.

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