Living organisms respond to changes in their environment in a controlled and coordinated way. In this chapter, you will learn how animals and plants achieve this control and coordination. In animals, specialised nervous tissue and muscular tissue work together, while hormones provide chemical coordination. You will study the structure of a neuron, how nerve impulses travel across a synapse, and how reflex actions provide quick responses through reflex arcs. The human brain, its major parts, and the protection of the brain and spinal cord are also explained. In plants, you will learn about immediate responses to touch, growth-related movements such as tropism, and the role of plant hormones like auxin, gibberellins, cytokinins and abscisic acid. Finally, you will explore animal hormones, including adrenaline, thyroxin, growth hormone, insulin, testosterone and oestrogen, and how feedback mechanisms regulate their secretion.
What you'll learn
1Describe how nervous tissue detects information and transmits electrical impulses.
2Explain the structure of a neuron and the events that occur at a synapse.
3Trace the sequence of events in a reflex action and explain the role of the spinal cord.
4Identify the major parts of the human brain and state their functions.
5Differentiate between reflex actions, voluntary actions and involuntary actions.
6Explain how plants respond to stimuli through growth-dependent and growth-independent movements.
7List the functions of plant hormones such as auxin, gibberellins, cytokinins and abscisic acid.
8Describe the role of animal hormones and the feedback mechanism that regulates their secretion.
Chapter at a glance
01Chapter Overview
02Nervous System: Structure and Functions
03Reflex Arc and Reflex Actions
04Hormones and Endocrine System
05Coordination in Plants
Detailed chapter notes
01
Nervous System: Structure and Functions
In animals, control and coordination are provided by nervous and muscular tissues. Information from the environment is detected by receptors, which are specialised tips of some nerve cells. These receptors are usually located in sense organs such as the inner ear, nose and tongue. For example, gustatory receptors detect taste and olfactory receptors detect smell. When a receptor is stimulated, it sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, then along the axon to its end. At the end of the axon, the electrical impulse causes the release of chemicals. These chemicals cross the synapse, a gap between two neurons, and start a similar electrical impulse in the dendrite of the next neuron. Nervous tissue is thus an organised network of nerve cells or neurons, specialised for conducting information via electrical impulses.
Receptorsspecialised tips of nerve cells that detect information from the environment.
Synapsethe gap between two neurons where chemicals carry the signal forward.
Nervous tissue conducts information as electrical impulses from one part of the body to another.
02
Reflex Arc and Reflex Actions
A reflex action is a sudden, involuntary response to a stimulus. When we touch a hot object, we pull our hand back quickly without thinking. This happens because the nerves that detect heat are connected to the nerves that move muscles in a simpler way, forming a reflex arc. Reflex arcs are formed in the spinal cord, where nerves from all over the body meet in a bundle on their way to the brain. The information also reaches the brain, but the reflex action occurs before the brain's thinking process can respond. Reflex arcs are efficient for quick responses and have evolved because the thinking process of the brain is not fast enough. Many animals have very little or no complex neuron network for thinking, so reflex arcs are their main way of responding.
Reflex actiona sudden, involuntary response to a stimulus.
Reflex arcthe pathway taken by nerve impulses in a reflex action.
Reflex arcs are formed in the spinal cord.
Reflex actions are quick because they bypass the thinking part of the brain.
03
Human Brain
The brain is the main coordinating centre of the body. Along with the spinal cord, it forms the central nervous system. The brain has three major parts: the fore-brain, mid-brain and hind-brain. The fore-brain is the main thinking part. It receives sensory impulses from various receptors and has separate areas for hearing, smell, sight and so on. It also has centres for hunger and for controlling voluntary muscles. The mid-brain and hind-brain control involuntary actions. The medulla in the hind-brain controls blood pressure, salivation and vomiting. The cerebellum, also in the hind-brain, is responsible for precision of voluntary actions and maintaining posture and balance. The brain is protected by the skull, and the spinal cord by the vertebral column. Both are further protected by fluid-filled coverings.
Fore-brainthinking, sensory interpretation, hunger centre, voluntary muscle control.
Mid-brain and hind-braincontrol involuntary actions.
Cerebellumprecision of voluntary actions, posture and balance.
Protectionskull protects the brain; vertebral column protects the spinal cord.
04
Hormones and Endocrine System
Hormones are chemical messengers used by multicellular organisms for control and coordination. In animals, hormones are secreted by endocrine glands directly into the blood and carried to different parts of the body. Adrenaline, secreted by the adrenal glands, prepares the body for fighting or running away. It increases heart rate, breathing rate, and diverts blood to skeletal muscles. Thyroxin, made by the thyroid gland, regulates carbohydrate, protein and fat metabolism. Iodine is essential for its synthesis; deficiency can cause goitre. Growth hormone from the pituitary regulates growth and development; deficiency in childhood leads to dwarfism. Insulin from the pancreas regulates blood sugar levels. Testosterone in males and oestrogen in females bring about changes associated with puberty. Feedback mechanisms regulate the timing and amount of hormone release.
Adrenalineprepares body for emergency; increases heart rate and breathing.
Thyroxinregulates metabolism; iodine is needed for its synthesis.
Testosterone and oestrogenbring about changes during puberty.
Feedback mechanismregulates hormone secretion.
05
Coordination in Plants
Plants do not have a nervous system or muscles, but they respond to stimuli. Some movements, like the folding of leaves of the sensitive plant on touch, are quick and independent of growth. Information is conveyed from cell to cell by electrical-chemical means, and cells change shape by changing the amount of water in them. Other movements are due to growth and are directional, called tropic movements or tropism. Shoots bend towards light (phototropism) while roots bend away from it. Roots grow downwards and shoots upwards in response to gravity (geotropism). Growth of pollen tubes towards ovules is an example of chemotropism. Plant hormones like auxin, gibberellins, cytokinins and abscisic acid coordinate growth, development and responses to the environment.
Immediate responsesensitive plant leaves fold on touch; no growth involved.
Tropic movementsdirectional growth in response to light, gravity, water or chemicals.
Phototropismshoots bend towards light; roots away from light.
Control and coordination are functions of the nervous system and hormones in animals, and of hormones in plants.
Nervous tissue transmits information as electrical impulses through neurons.
A synapse is the gap between two neurons where chemicals carry the impulse forward.
Reflex actions are quick, involuntary responses mediated by reflex arcs in the spinal cord.
The brain has three major parts: fore-brain, mid-brain and hind-brain.
The fore-brain is the main thinking part; the cerebellum maintains posture and balance; the medulla controls involuntary actions like blood pressure and salivation.
Plant movements can be growth-independent (e.g., sensitive plant) or growth-dependent (tropism).
Plant hormones include auxin, gibberellins, cytokinins and abscisic acid.
Animal hormones include adrenaline, thyroxin, growth hormone, insulin, testosterone and oestrogen.
Feedback mechanisms regulate the timing and amount of hormone secretion.
Which of the following is the basic structural and functional unit of the nervous system?
ANeuroglia
BNeuron
CSynapse
DDendrite
Show answer
Answer: (B) Neuron
The neuron is the basic structural and functional unit of the nervous system that transmits nerve impulses.
Question 02
What is a reflex arc?
AA conscious decision to respond to a stimulus
BA simple connection of input and output nerves that bypasses the brain
CA part of the brain that controls voluntary actions
DA chemical signal that travels through the blood
Show answer
Answer: (B) A simple connection of input and output nerves that bypasses the brain
A reflex arc is a simple neural connection where sensory and motor nerves meet in the spinal cord, allowing rapid response without involving the brain.
Question 03
Which of the following is the master gland of the endocrine system?
AThyroid gland
BPituitary gland
CPancreas
DAdrenal gland
Show answer
Answer: (B) Pituitary gland
The pituitary gland is called the master gland because it controls the secretion of hormones from other endocrine glands.
Question 04
Which hormone is primarily responsible for promoting cell elongation in plants?
AGibberellin
BAuxin
CCytokinin
DEthylene
Show answer
Answer: (B) Auxin
Auxin promotes cell elongation and is responsible for phototropism and gravitropism in plants.
Question 05
The nervous system is divided into two main parts. Which one controls voluntary actions?
AAutonomic nervous system
BSomatic nervous system
CSympathetic nervous system
DParasympathetic nervous system
Show answer
Answer: (B) Somatic nervous system
The somatic nervous system controls voluntary actions and transmits sensory and motor information to and from the body.
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Q1. Why is control and coordination necessary in living organisms?
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Model answer
Living organisms need to respond to changes in their environment to survive. Controlled movements, like pulling hand from a flame or plants growing towards light, require systems that detect stimuli and produce appropriate responses. This is achieved through nervous and hormonal systems in animals and hormonal coordination in plants.
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Q2. What happens at the synapse between two neurons?
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At the synapse, the electrical impulse from the axon of one neuron triggers the release of chemicals. These chemicals cross the gap and start a similar electrical impulse in the dendrite of the next neuron. This allows transmission of nerve impulses from one neuron to another.
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Q3. What is a reflex arc? Explain its role in a reflex action.
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Model answer
A reflex arc is the neural pathway that controls a reflex action. It involves sensory neurons carrying impulses from receptors to the spinal cord, where they synapse directly with motor neurons (or via an interneuron), bypassing the brain for quick response. This allows rapid, involuntary actions like pulling hand from a hot object without conscious thought.
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Q4. What is the role of adrenaline in the human body? How does it help in dealing with emergency situations?
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Adrenaline is a hormone secreted by the adrenal glands in response to stress or danger. It is carried by blood to target organs like the heart, causing it to beat faster and supply more oxygen to muscles. It also reduces blood flow to digestive system and skin, diverting it to skeletal muscles. Breathing rate increases, preparing the body for fight or flight.
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Q5. How does phototropism occur in plants? Explain the role of auxin in this process.
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Phototropism is the directional growth of plant parts in response to light. When light comes from one side, auxin hormone synthesised at the shoot tip diffuses towards the shady side. This higher concentration of auxin stimulates cells on the shady side to grow longer, causing the shoot to bend towards light.
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What is the difference between a reflex action and walking?
A reflex action is a sudden, involuntary response to a stimulus, such as pulling your hand back from a hot object. Walking is a voluntary action that involves conscious thought and control by the brain. Reflex actions are controlled by the spinal cord through reflex arcs, while walking is controlled by the brain.
What happens at the synapse between two neurons?
At the synapse, the electrical impulse reaching the end of the axon causes the release of chemicals. These chemicals cross the gap and start a similar electrical impulse in the dendrite of the next neuron. This allows the nerve impulse to travel from one neuron to the next.
Which part of the brain maintains posture and equilibrium of the body?
The cerebellum, which is a part of the hind-brain, is responsible for maintaining posture and balance of the body. It also ensures precision of voluntary actions such as walking in a straight line, riding a bicycle or picking up a pencil.
How do we detect the smell of an agarbatti (incense stick)?
The smell of an agarbatti is detected by olfactory receptors located in the nose. These receptors are specialised tips of nerve cells. When they detect the smell, they set off a chemical reaction that creates an electrical impulse, which travels to the brain for interpretation.
Why is the use of iodised salt advisable?
Iodine is necessary for the thyroid gland to make the hormone thyroxin, which regulates carbohydrate, protein and fat metabolism. If iodine is deficient in the diet, thyroxin cannot be synthesised properly, and this may lead to goitre, a disease characterised by a swollen neck.
How does chemical coordination take place in animals?
Chemical coordination in animals takes place through hormones secreted by endocrine glands directly into the blood. These hormones are carried to different parts of the body and act on specific target organs. For example, adrenaline prepares the body for emergencies, insulin regulates blood sugar, and growth hormone regulates growth.