CBSE Class 10 Science Control And Coordination Notes Set 08

TROPIC MOVEMENTS IN PLANTS

Tropic movement is the movement of the plant in response to stimulus present in the surroundings. Tropic movements can be either toward the stimulus or away from it. The important tropic movements are listed below-

• PHOTOTROPISM: Movement is response to light.
  Ex- shoot bending toward the light, root bending away from light, movement of sunflower
• CHEMOTROPISM: Movement in response to certain chemicals
  Ex- Growth of pollen tubes toward ovary
• GEOTROPISM: The movement of plants in response to the gravity.
  Ex- Roots of plant grow downwards, shoots usually grow upward
• HYDROTROPISM: Movement in response to water.
  Ex- Roots bend towards water.
• THIGMOTROPISM: The reflex action in response to touch.
  Ex- touch-sensitive plant leaves.

INTRODUCTION OF PLANT HORMONES

Growth and differentiation in plants depend on a few hormones calls as plant growth regulators/ plant growth hormones/ Phytohormones. These are organic substances that are synthesized in minute quantities in one part of the plant body and transported to another part where they show specificphysiological processes.

CONTROL AND CO-ORDINATION IN ANIMALS

In animals control and coordination is carried out with the help of -

• Nervous system
• Muscular tissue
• Endocrine system: Hormones
• Nervous system

NEURONS

Neurons are composed of cell body, dendrite, axon and nerve ending.

HOW NERVOUS IMPULSE TRAVELS IN BODY

• Dendritic tips receive stimulus and an electrical impulse is generated in neurons.
• This impulse travels from the dendrite to the cell body and then along the axon to its end.
• At the axon ending some chemicals are released that cross the synapse and start a similarelectrical impulse in next neuron.

REFLEX ACTION

• Reflex action is a sudden and involuntary response to any stimuli.
• It originates in the spinal cord.
• Ex- Drawing hand away from the hot plate, watering of mouth in response to food etc.
• The neural pathway that controls thereflex action is called as a reflex arch
• In these sensory neurons, spinalcord, relay neuron, motor neuron and effector muscles are involved.
• Stimulus is received by sensory neurons. The sensory neurons transfer sensory impulses to the spinal cord (CNS). Spinal cord process the stimulus. The motor nerve fiber relays the motor impulses from the nervous system to the effector organs like muscles.

HORMONES IN ANIMALS

Hormones are chemical messengers which are secreted by the ductless endocrine gland intothe blood. Hormones control the activity of certain cells and organs. Hormones can be peptides and steroid hormones. Some of the main endocrine glands are the pituitary gland, adrenal gland, thyroid gland, pancreas, testes, ovary etc.

• GOITER- Iodine is necessary for the formation of thyroxin hormone. If Iodine is in low concentration the thyroid gland swells and causes goiter.
• GIGANTISM and DWARFISM- Excess secretion of growth hormone from the pituitary gland causes excess growth of the body (gigantism) and less secretion results in dwarfism.