CBSE Class 10 Science Notes: Control and Coordination

Tropic Movements in Plants

Plant movements are primarily growth-related, influenced by external stimuli. These movements are called tropic movements.

Definitions and Examples

• Phototropism: Growth response of a plant towards light.
  • Example: A plant bending towards sunlight.
• Geotropism: Growth response of a plant in response to gravity.
  • Example: Roots growing downwards (positive geotropism), and stems growing upwards (negative geotropism).

Plant Hormones

Plant hormones, or phytohormones, are chemical messengers that regulate plant growth and development.

Names and Roles

• Auxin: Promotes cell elongation, apical dominance, and fruit development.
• Gibberellin: Stimulates stem elongation, seed germination, and flowering.
• Other Hormones (Brief Introduction):
  • Cytokinins: Promote cell division.
  • Abscisic Acid (ABA): Inhibits growth, promotes dormancy, and causes stomatal closure.
  • Ethylene: Promotes fruit ripening and abscission (leaf fall).

Practical Uses

• Auxins are used to promote root formation in cuttings.
• Gibberellins are used to increase fruit size and speed up the ripening process.
• Herbicides are often auxins.

Nervous System in Animals

The nervous system coordinates body functions by receiving, processing, and responding to stimuli.

Basic Structure and Function Overview

• Brain: The central processing unit that controls all bodily functions.
• Spinal Cord: Transmits signals between the brain and the rest of the body.
• Nerves: Conduct electrical impulses throughout the body.

Types of Actions

Voluntary Actions

Actions under conscious control.

• Example: Walking, writing, eating.

Involuntary Actions

Actions not under conscious control.

• Example: Breathing, heartbeat, digestion.

Reflex Actions

Rapid, automatic responses to stimuli.

• Reflex Arc: The pathway of a reflex action.
• Example: The knee-jerk reflex. A tap on the patellar tendon stimulates receptors that send a signal to the spinal cord. A signal is then sent to the quadriceps muscle which then contracts causing the lower leg to extend.

Chemical Coordination in Animals

Hormones are chemical messengers secreted by endocrine glands that regulate various bodily functions.

Hormones and Their Functions

• Insulin: Regulates blood sugar levels.
• Adrenaline: Prepares the body for “fight or flight” response.

Nervous System and Hormones – Complementary Roles

The nervous system provides rapid responses, while the endocrine system offers slower, longer-lasting effects.

Both systems work together to coordinate bodily functions and maintain homeostasis.