Class 10 Science • Complete Chapter Notes
Living organisms constantly receive information from their surroundings and respond to changes in the internal and external environment. The coordination of these activities helps an organism maintain proper functioning and respond appropriately to stimuli.
In animals, coordination is mainly carried out through the nervous system and endocrine system. Plants do not have a nervous system, but they show responses through growth, movements and chemical signals.
The nervous system receives information from receptors, processes it and coordinates suitable responses through electrical and chemical signals.
A neuron is a specialised cell that carries nerve impulses from one part of the body to another.
A typical pathway is:
A reflex action is a quick, automatic and involuntary response to a stimulus. It helps protect the body from potentially harmful situations.
The pathway followed by nerve impulses during a reflex action is called a reflex arc.
A synapse is the junction between two neurons or between a neuron and an effector cell.
At a chemical synapse, chemicals called neurotransmitters are released from the ending of one neuron and help transmit the signal to the next cell.
The brain is the main coordinating centre of the nervous system. It receives sensory information, interprets it and coordinates suitable responses.
The forebrain includes the cerebrum and other associated structures. It is involved in interpreting sensory information, thinking, learning, memory and voluntary actions.
The midbrain is involved in certain reflex responses and coordination of movements related to visual and auditory stimuli.
The hindbrain contains structures involved in posture, balance and involuntary activities essential for life.
| Structure | Important Function |
|---|---|
| Cerebellum | Coordinates balance, posture and precision of movement. |
| Medulla | Controls several involuntary activities such as breathing and heartbeat. |
| Pons | Helps coordinate communication between brain regions and contributes to respiratory control. |
The brain is protected by the skull. It is also surrounded by membranes and cerebrospinal fluid, which help provide mechanical protection and cushioning.
The spinal cord is an important part of the central nervous system. It carries information between the brain and the rest of the body and is involved in many reflex actions.
Receptors are specialised structures or cells that detect specific types of stimuli.
| Receptor | Stimulus |
|---|---|
| Photoreceptors | Light |
| Mechanoreceptors | Mechanical stimuli such as pressure or movement |
| Chemoreceptors | Chemicals |
| Thermoreceptors | Temperature changes |
Plants do not possess a nervous system like animals. Their responses occur through growth movements, changes in cell behaviour and chemical signals.
Some plant movements are directional responses to external stimuli, while others are not dependent on the direction of the stimulus.
Tropic movements are directional growth movements of a plant part in response to a stimulus.
| Tropism | Stimulus | Example |
|---|---|---|
| Phototropism | Light | Shoot bends towards light. |
| Geotropism / Gravitropism | Gravity | Roots generally grow in the direction of gravity. |
| Hydrotropism | Water | Roots grow towards regions with greater moisture. |
| Chemotropism | Chemicals | Pollen tube growth towards the ovule. |
Nastic movements are non-directional movements in response to a stimulus.
The folding of leaves of Mimosa pudica after touch is a commonly studied example of a nastic movement.
Auxin is a plant hormone involved in growth. It plays an important role in cell elongation and phototropic responses.
Gibberellins promote growth in plants and are associated with processes such as stem elongation and seed germination.
Cytokinins promote cell division and influence plant growth and development.
Abscisic acid generally acts as a growth-inhibiting hormone and plays an important role in responses to environmental stress. It also contributes to stomatal closure under water-stress conditions.
Ethylene is a plant hormone that is associated with fruit ripening and several other developmental processes.
Hormones are chemical messengers secreted by endocrine glands. They are transported through the blood to target tissues and help coordinate various body functions.
The pituitary gland secretes several hormones and is often called the master endocrine gland because it regulates the activity of several other endocrine glands.
The thyroid gland secretes thyroxine, which plays an important role in regulating metabolism and supporting normal growth and development.
Adrenaline is secreted by the adrenal glands and prepares the body for situations requiring rapid action, often described as the "fight or flight" response.
Insulin is produced by the pancreas and helps regulate blood glucose concentration by promoting uptake and storage of glucose in appropriate tissues.
Testosterone is mainly produced by the testes and contributes to development of male reproductive organs and secondary sexual characteristics.
Oestrogen is mainly produced by the ovaries and plays an important role in development of female reproductive organs and secondary sexual characteristics.
Progesterone is an important hormone involved in the menstrual cycle and maintenance of the uterine lining.
| Hormone | Source | Main Function |
|---|---|---|
| Growth Hormone | Pituitary | Growth and development |
| Thyroxine | Thyroid | Regulation of metabolism |
| Adrenaline | Adrenal glands | Fight-or-flight response |
| Insulin | Pancreas | Regulation of blood glucose |
| Testosterone | Testes | Male reproductive development |
| Oestrogen | Ovaries | Female reproductive development |
| Feature | Nervous Coordination | Hormonal Coordination |
|---|---|---|
| Signal | Electrical impulses and neurotransmitters | Chemical hormones |
| Speed | Generally rapid | Generally slower |
| Effect | Usually focused and immediate | Often longer-lasting and more widespread |
For curriculum-aligned preparation, use the official NCERT textbook resources and current CBSE Academic curriculum.
NCERT Class 10 Science Textbook → CBSE Academic Curriculum 2026-27 → CBSE Assessment Resources →