Control And Coordination Class 10 Science: Chapter Notes

Key Points to Remember

• Control and coordination in animals is performed by the nervous system (for rapid responses) and the endocrine system (for slower, sustained responses).
• The structural and functional unit of the nervous system is the Neuron.
• The human nervous system consists of the Central Nervous System (CNS: Brain and Spinal Cord) and the Peripheral Nervous System (PNS: Nerves extending from CNS).
• The brain is protected by the cranium (skull) and cerebrospinal fluid. It has three main parts: Forebrain (thinking, memory), Midbrain (reflexes of head/neck), and Hindbrain (balance, vital involuntary actions).
• Reflex Arc is the pathway of a reflex action, which is an immediate, involuntary response to a stimulus. It typically involves the spinal cord for faster processing.
• Endocrine glands are ductless glands that secrete chemical messengers called hormones directly into the bloodstream.
• The 'Master Gland' is the Pituitary Gland, as it controls the secretions of many other endocrine glands.
• In plants, coordination is achieved through chemical substances called plant hormones or phytohormones (e.g., Auxin, Gibberellin, Cytokinin, Abscisic Acid).
• Plant movements can be tropic (directional, growth-dependent) or nastic (non-directional, growth-independent).

Key Terms and Definitions

Neuron

The structural and functional unit of the nervous system, responsible for transmitting nerve impulses.

Synapse

A small gap between the axon terminal of one neuron and the dendrite of the next, where nerve impulses are transmitted via neurotransmitters.

Receptor

Specialized cells or nerve endings that detect stimuli from the environment (e.g., photoreceptors in eyes, thermoreceptors in skin).

Effector

A muscle or gland that responds to a nerve impulse from a motor neuron, causing an action.

Reflex Action

A sudden, involuntary, and rapid response to a stimulus, controlled primarily by the spinal cord.

Hormones

Chemical messengers secreted by endocrine glands that travel through the bloodstream to target organs to regulate physiological processes.

Tropism

Directional growth movement of a part of a plant in response to an external stimulus like light, gravity, or water.

Phototropism

The growth of a plant part in response to a light stimulus. Shoots are positively phototropic; roots are negatively phototropic.

Geotropism

The growth of a plant part in response to gravity. Roots are positively geotropic; shoots are negatively geotropic.

The Reflex Arc: Pathway of a Rapid Response

A reflex action is an unconscious and involuntary response to a stimulus, designed to protect the body from harm. The neural pathway taken by this action is called the reflex arc. This mechanism is crucial because it is extremely fast, often bypassing conscious thought in the brain for immediate reaction.

Let's trace the path using the classic example of touching a hot object.

1. Stimulus and Receptor: The heat from the object is the stimulus. This stimulus is detected by specialized receptors (thermoreceptors) in the skin of your hand.
2. Sensory Neuron: The receptors trigger a nerve impulse in a sensory neuron. This neuron transmits the electrical signal from the hand towards the central nervous system.
3. Relay Neuron in Spinal Cord: The sensory neuron enters the spinal cord and passes the signal to a relay neuron (or interneuron). The spinal cord acts as the processing center in most reflexes, allowing for a quicker response than if the signal had to travel all the way to the brain and back.
4. Motor Neuron: The relay neuron passes the impulse to a motor neuron.
5. Effector: The motor neuron carries the command signal away from the spinal cord to the effector, which is a muscle or a gland. In this case, the effector is the biceps muscle in your arm.
6. Response: The muscle contracts, causing you to pull your hand away from the hot object. This entire sequence happens in a fraction of a second. Only after the hand is pulled away does the signal also reach the brain, making you aware of the pain and the event.

Nervous System vs. Endocrine System

Major Human Endocrine Glands and Hormones

Plant Hormones (Phytohormones) and Their Functions

Exam Tips and Common Mistakes

Diagrams are your best friend: Practice drawing and labeling the neuron, reflex arc, and human brain. These are frequently asked 3 or 5-mark questions. Use a pencil and label clearly on the right side.

Hormone Table: Don't just memorize hormone names. For exams, you MUST know the Gland, the Hormone it secretes, and its specific Function. A common mistake is confusing the functions of Insulin and Glucagon, or Testosterone and Estrogen. Create a table to revise.

Plant Hormones: Students often mix up growth promoters (Auxin, Gibberellin, Cytokinin) and the growth inhibitor (Abscisic Acid). Remember ABA is the 'stress hormone' that causes negative effects like wilting and dormancy.

Tropism vs. Nastic movements: Remember Tropism is directional and growth-dependent (e.g., bending towards light). Nastic movement is non-directional and not dependent on growth (e.g., folding of 'touch-me-not' plant leaves).

Practice Questions with Solutions

• Q: What is a synapse and what happens there? A: A synapse is the tiny gap between two neurons. At the synapse, the electrical signal from the first neuron is converted into a chemical signal (neurotransmitter) that diffuses across the gap and triggers a new electrical signal in the next neuron.
• Q: Which hormone is released when you are in a scary situation and from which gland? A: Adrenaline is released from the Adrenal glands. It prepares the body for a 'fight or flight' response.
• Q: Differentiate between phototropism and geotropism. A: Phototropism is the directional growth of a plant in response to light (shoots grow towards it). Geotropism is the directional growth in response to gravity (roots grow towards it).
• Q: Which part of the hindbrain is responsible for maintaining posture and balance? A: The Cerebellum, a part of the hindbrain, is responsible for maintaining the body's posture and balance, and for coordinating voluntary movements.

Frequently Asked Questions

Frequently Asked Questions