CLASS 10 SCIENCE · CHAPTER 6 · STUDY NOTES
Control and Coordination in Living Organisms
A comprehensive guide to how animals and plants perceive their environment and respond through complex nervous and chemical systems, covering neurons, the human brain, plant tropisms, and endocrine hormones.
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Detect a change. Choose a response.
Connect a stimulus to a coordinated response.FOLLOW THE SIGNAL
A cue changes what the organism does.
Compare a growing shoot with a withdrawing hand.
A shoot responds to one-sided light by directional growth. This is slower than muscle movement.
- Stimulus
- A change detected by an organism that can lead to a response.
A change such as light or touch can be detected and followed by a response. Coordination connects the information to an appropriate action.
A growing shoot changes direction slowly. A withdrawing hand moves existing tissues; these movements use different mechanisms.
Go deeper: Growth is not every movement
A seedling pushing through soil moves because it grows. A muscle moving a limb does not need the limb to grow first.
Plants have chemical and electrical signalling, but they do not have an animal-like nervous system or muscles.
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Question
A shoot bends towards a window over several days; a hand moves away from a hot surface quickly. Does the word movement mean the same mechanism in both cases?
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Follow a nerve message
Trace electrical signalling within a neuron and chemical transmission across a synapse.FOLLOW THE SIGNAL
One message. Two forms of signalling.
Predict what crosses the gap between these two cells.
Input at dendrites → cell body.
- Neuron
- A specialised cell that receives and conducts information in the nervous system.
In this simplified pathway, input reaches dendrites and the cell body, then an electrical impulse travels along the axon.
At an axon ending, chemicals are released across a synaptic gap. They can start a new electrical impulse in the next cell; the gap is not an uninterrupted wire.
Go deeper: Connected cells are still separate
Receptors detect particular stimuli. Gustatory receptors respond to taste and olfactory receptors to smell; both contribute to how food is experienced.
A chemical synapse can connect a neuron to another neuron, a muscle cell or a gland. Electrical signalling along one cell and chemical transmission between cells have different roles.
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Question
A nerve impulse reaches the end of one axon. A student draws one uninterrupted wire into the next neuron. What feature of the connection has been missed?
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A short route to a fast response
Follow a withdrawal reflex while keeping the brain connection visible.FOLLOW THE SIGNAL
Follow the short route—and the branch to the brain.
Does withdrawal need to wait for a conscious decision?
A receptor detects the hot object.
- Reflex arc
- The pathway linking a receptor, sensory input, coordinating connections and a motor response.
For the spinal withdrawal example, receptors detect the stimulus. A sensory neuron carries information to relay connections in the spinal cord.
A motor neuron signals the muscle, which contracts to withdraw the hand. Information also reaches the brain; the response does not wait for a conscious decision.
Go deeper: The brain is informed, not absent
The pictured route is a spinal reflex example. It does not mean that every reflex is organised in the spinal cord; a pupil response uses brain pathways.
Voluntary actions involve decisions, while involuntary processes can continue without a conscious decision. A reflex is an automatic response to a stimulus, not a synonym for every involuntary action.
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Question
A diagram shows a spinal withdrawal route and a branch carrying information towards the brain. Does the branch prove that withdrawal must wait for conscious thought?
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Different regions work together
Connect each named brain region to its role and protective structures.FOLLOW THE SIGNAL
Locate each part before connecting its job.
Which parts help you decide, balance and regulate involuntary activity?
Cerebrum: sensory integration, thinking and control of voluntary actions.
- Central nervous system
- The brain and spinal cord, which integrate information and coordinate responses.
| Brain Region | Specific Part | Primary Function |
|---|---|---|
| Fore-brain | Cerebrum | Thinking, memory, sensory interpretation, and voluntary actions. |
| Fore-brain | Hunger Center | Detecting the sensation of being full after eating. |
| Mid-brain | General | Control of various involuntary movements. |
| Hind-brain | Medulla | Involuntary actions like blood pressure, salivation, and vomiting. |
| Hind-brain | Cerebellum | Maintaining posture, balance, and precision of movements. |
The forebrain integrates sensory information, stored information and decisions about voluntary actions. The cerebellum helps with precision, posture and balance.
The medulla contributes to important involuntary functions. The skull and cushioning fluid protect the brain; the vertebral column protects the spinal cord.
Go deeper: Parts of a connected system
The chapter groups the brain into forebrain, midbrain and hindbrain. The cerebellum and medulla belong to the hindbrain; a side view is a map of regions, not separate independent machines.
Cranial nerves and spinal nerves link the central nervous system with the body as the peripheral nervous system. Sensory input and motor output both use these connections.
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Question
A learner decides to pick up a pencil and then steadies the hand to grasp it accurately. Why is it misleading to assign the whole action to the cerebellum alone?
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A signal changes muscle shape
Relate a motor signal to fibre shortening without shortening the proteins.FOLLOW THE SIGNAL
More overlap. A shorter fibre.
Can the fibre shorten without making its proteins shorter?
A relaxed muscle fibre is longer. A nerve signal can trigger a change in its protein arrangement.
- Muscle contraction
- A change in muscle activity and shape that can produce force and movement.
A motor nerve signal can trigger a change in how muscle proteins are arranged. The muscle fibre becomes shorter as their overlap changes.
The simplified picture keeps each filament the same length. It models rearrangement, not proteins shrinking or a nerve physically pulling the muscle.
Go deeper: Message and movement have different jobs
Nervous tissue carries the signal; muscle tissue performs the mechanical action. A neuromuscular junction connects these roles through signalling.
Muscles can act in voluntary and involuntary movements. The diagram isolates one fibre and omits the detailed molecular cycle; it is not a measurement of contraction speed or force.
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Question
Two muscle drawings have equal filament lengths but greater overlap in the second. Can the fibre shorten even though the filaments do not?
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A leaf folds without growing
Explain the sensitive plant’s rapid response through changing cell water content.FOLLOW THE SIGNAL
The leaflet folds; it does not lose tissue.
Predict whether folding needs new growth.
Open Mimosa leaflets. Touch can lead to rapid folding through changes in cells at their bases.
- Turgor
- Pressure of cell contents against the wall associated with water inside a plant cell.
After touch, Mimosa leaflets fold and the leaf can droop. Changes in water content alter cells at the leaf bases, changing their shape.
This movement uses existing tissues and does not need new growth. Plants transmit information between cells but have neither animal muscles nor a nervous system.
Go deeper: Folding is not a miniature animal reflex
Touch at one place can lead to movement elsewhere, so information must be communicated. Electrical and chemical signalling can coordinate the plant response.
Changing turgor is different from changing the arrangement of muscle proteins. Folded leaflets appear narrower in projection; they have not been cut down or suddenly become smaller leaves.
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Question
A Mimosa leaflet appears narrow after folding. A student concludes that it lost half its leaf tissue. What other explanation matches the movement?
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