Control and Coordination
This chapter explains how living organisms respond and adapt to changes in their environment through the nervous system and hormones, including reflex actions and plant movements.
A reflex action is a rapid, automatic, involuntary response to a stimulus (such as touching a hot object) that does not initially involve conscious thought, allowing the body to react quickly and protect itself from harm.
A reflex arc is the pathway taken by nerve impulses during a reflex action: Receptor -> Sensory neuron -> Spinal cord (relay neuron) -> Motor neuron -> Effector (muscle). The signal is processed at the spinal cord, not the brain, which is why reflexes are so fast.
Q. What is a synapse, and what is its function?
A synapse is the junction between two neurons. When an electrical impulse reaches the end of a neuron, it triggers the release of chemicals that cross the synapse and set off a new electrical impulse in the next neuron, allowing one-way transmission of nerve signals.
The human brain has three main parts: the forebrain (thinking, voluntary actions), the midbrain, and the hindbrain (which includes the medulla, controlling involuntary actions like blood pressure, salivation and vomiting).
Q. How does chemical coordination occur in plants?
Plants use hormones such as auxin, gibberellin, cytokinin, abscisic acid and ethylene for chemical coordination. These hormones control growth, movement (tropisms), and responses to light, gravity and water, without a nervous system.
Which plant hormone promotes growth and is responsible for phototropism (bending towards light)?
Correct answer: (A) Auxin
The gland that secretes insulin to regulate blood sugar is the _______.
Pancreas
Hormones act only on the gland that secretes them.
False — hormones are secreted by endocrine glands directly into the bloodstream and travel throughout the body, acting on specific target organs or tissues, not just the gland of origin.
Why is the gap between two neurons called a synapse important for the nervous system to function correctly, in terms of signal direction?
The synapse ensures nerve impulses travel in only one direction, since the chemical signal can only be released from the end of one neuron and received by receptors on the next, preventing signals from flowing backward and keeping the nervous system's communication orderly.