Chapter 6: Control and Coordination
Class X Science
Key Concepts
- Stimuli: The changes in the environment to which living organisms respond are called stimuli.
- Coordination: The working together of various organs in an organism to produce a proper response to a stimulus is called coordination.
Coordination in Animals
In animals, control and coordination are done by the nervous system and endocrine system.
Parts of the Nervous System
- The Central Nervous System (CNS): Consists of the brain and spinal cord.
- The Peripheral Nervous System (PNS): Consists of cranial nerves arising from the brain and spinal nerves arising from the spinal cord.
Human Brain
The brain is the main coordinating centre in the human body. It is protected by the cranium and covered by three membranes called meninges filled with cerebrospinal fluid (CSF) which protects it from shocks.
- Forebrain: Consists of the cerebrum and olfactory lobes. It controls voluntary actions like touch, smell, hearing, taste, sight, and mental activities like thinking, learning, memory, and emotions.
- Midbrain: Controls involuntary actions and reflex movements of the head, neck, eyes, etc.
- Hindbrain: Consists of cerebellum, pons, and medulla.
- Cerebellum: Controls body movements, balance, and posture.
- Pons: Controls respiration.
- Medulla: Controls heart beat, blood pressure, swallowing, coughing, sneezing, vomiting, etc.
Spinal Cord
The spinal cord starts from the brain and extends through the vertebral column. It carries messages to and from the brain and controls reflex actions.
Nerve Cell (Neuron)
The neuron is the structural and functional unit of the nervous system.
- Structure: Cell body (cyton) with nucleus and cytoplasm, Dendrites (branched structures), Axon (long nerve fibre covered by Myelin sheath).
- Synapse: The junction between two neurons.
[DIAGRAM: Structure of Neuron showing Dendrite, Soma, Nucleus, Axon, Myelin Sheath, and Axon Terminal]
Reflex Action & Reflex Arc
- Reflex Action: A sudden, unconscious, and involuntary response of the effectors to a stimulus (e.g., withdrawing hand from a hot object).
- Reflex Arc: The pathway of a reflex action.
Path: Stimulus (Receptor) \(\rightarrow\) Sensory Neuron \(\rightarrow\) Spinal Cord (Relay neuron) \(\rightarrow\) Motor Neuron \(\rightarrow\) Effector (Muscle).
[DIAGRAM: Reflex Arc showing pathway from Receptor to Effector via Spinal Cord]
Coordination in Plants
In plants, control and coordination are done by chemical substances called plant hormones or phytohormones.
Plant Hormones (Phytohormones)
- Auxins: Help in cell division, cell elongation, and growth.
- Gibberellins: Help in growth of stem and branches.
- Cytokinins: Help in cell division, formation of fruits and seeds.
- Abscisic Acid: Inhibits growth and affects wilting of leaves.
- Ethylene: Helps in flowering and ripening of fruits.
Movements in Plants
- Tropic Movements: Directional movements towards or away from the stimulus dependent on growth (e.g., Phototropism, Geotropism, Chemotropism, Hydrotropism).
- Nastic Movements: Non-directional movements neither towards nor away from the stimulus and independent of growth (e.g., leaves of 'touch-me-not' plant folding up).
Endocrine Glands in Human Beings
| Gland | Hormone | Location | Function |
|---|---|---|---|
| Hypothalamus | Releasing hormone (RH), Inhibiting hormones (IH) | Forebrain | Regulates secretion of pituitary hormones. |
| Pituitary Gland | Growth hormone (GH), Tropic hormones | Forebrain | Controls growth (dwarfism/gigantism) and other organs. |
| Thyroid Gland | Thyroxin | Neck/Throat | Regulates carbohydrate, protein, and fat metabolism. |
| Adrenal Gland | Adrenaline | Above kidney | Prepares body for emergency ('Fight and flight'). |
| Pancreas | Insulin | Below stomach | Regulates blood sugar level. |
| Testis | Testosterone | Genital area | Development of male reproductive organs & secondary sexual characters. |
| Ovary | Oestrogen | Genital area | Development of female reproductive organs & secondary sexual characters. |
Feedback Mechanism
A mechanism that regulates the timing and amount of hormone secretion. Example: Insulin secretion increases when blood sugar rises and decreases when it falls.
[DIAGRAM: Flowchart of Feedback Mechanism for Insulin regulation based on blood sugar levels]
Question Bank
Section 1: Multiple Choice Questions
- Nerves throughout the body other than Brain and spinal cord form:
Ans: (B) PNS - The growth of pollen tubes towards ovules is due to:
Ans: (C) Chemotropism - In reflex action, the reflex arc is formed by:
Ans: (C) Receptor \(\rightarrow\) Spinal cord \(\rightarrow\) Muscles - Which of the following statements are true about the brain?
i. The main thinking part is hind brain (False).
ii. Centers of hearing, smell, memory, sight etc. are located in fore brain (True).
iii. Involuntary actions like salivation, vomiting are controlled by medulla in hind brain (True).
iv. Cerebellum does not control posture and balance (False).
Ans: (C) (ii) and (iii) - Posture and balance of the body is controlled by:
Ans: (C) Cerebellum - Artificial ripening of fruit is carried out by:
Ans: (B) Ethylene - ________ are also known as ductless glands.
Ans: (B) Endocrine gland - An example of a sex hormone is:
Ans: (A) Testosterone - Iodine is necessary for the synthesis of which hormone?
Ans: (B) Thyroxin - The longest fibre on the cell body of a neuron is called:
Ans: (C) Axon
Section 2: Short Answer Questions
Q1. A potted plant is made to lie horizontally on the ground. Which part of the plant will show (i) positive geotropism? (ii) negative geotropism?
Ans: (i) Root (Positive geotropism) (ii) Shoot (Negative geotropism).
Q2. Hema brought some unripe tomatoes... kept in brown paper bag... ripened faster. Why?
Ans: (a) Ethylene hormone facilitated ripening. (b) Ethylene is a gaseous hormone; the paper bag prevented it from diffusing into the air, concentrating it around the tomatoes.
Q4. (a) Name hormones released in humans at puberty. (b) Name a gland associated with brain and problem caused by its deficiency.
Ans: (a) Males: Testosterone; Females: Oestrogen.
(b) Pituitary gland. Deficiency of Growth Hormone causes Dwarfism.
Q7. Sheila saw a snake and instantly jumped back. Explain.
Ans: This is a Reflex Action. It is an involuntary, rapid, and automatic response to a stimulus (snake) controlled by the spinal cord to protect the body.
Q8. What events take place between the synapse of two neurons?
Ans: An electrical impulse travels along the axon. At the end, it releases chemicals (neurotransmitters) into the synaptic cleft. These chemicals cross the gap and generate a similar electrical impulse in the dendrite of the next neuron.
Q10. Write the difference between Cerebellum and Cerebrum.
Ans:
- Cerebrum: Part of forebrain, controls intelligence, memory, voluntary actions.
- Cerebellum: Part of hindbrain, maintains posture, balance, and coordinates muscular activity.
Section 3: Long Answer Questions
Q1. A person is advised to take less sugar. Name disease, hormone, gland, and consequences of growth hormone issues.
Ans:
Disease: Diabetes mellitus. Hormone: Insulin. Gland: Pancreas.
Growth Hormone Gland: Pituitary.
Deficiency: Dwarfism. Excess: Gigantism.
Q2. Difference between Nervous and Endocrine System.
Ans:
- Nervous: Electrical impulses, rapid response, short-lived effects, transmitted via neurons.
- Hormonal: Chemical messengers, slower response, prolonged effects, transmitted via blood.
CCT Based Question: Endocrine System
Context: The endocrine system consists of glands that secrete hormones. Some organs like the pancreas have both exocrine (enzymes) and endocrine (hormones) functions.
- Which gland secretes digestive enzyme as well as hormones?
Ans: Pancreas. - Which of the following endocrine gland is unpaired?
(A) Adrenal (B) Testes (C) Pituitary (D) Ovary
Ans: (C) Pituitary. - Explain feedback mechanism with Insulin example.
Ans: It is a mechanism to regulate hormone quantity. When blood sugar rises, pancreas detects it and secretes more insulin. When blood sugar falls, insulin secretion reduces.