Biology Study Notes: Control and Coordination

Life processes involve controlled and coordinated movements, either growth-related (e.g., seed germination) or non-growth-related (e.g., running, chewing cud, responding to heat).
Movement in living organisms is often a response to environmental triggers used to the organism's advantage.
Multi-cellular organisms use specialized tissues for control and coordination; in animals, these are nervous and muscular tissues.

Neurons (Nerve Cells): Specialized for conducting information via electrical impulses.
Process of Nerve Impulse:
- Information is acquired at the dendritic tip.
- Sets off a chemical reaction creating an electrical impulse.
- Impulse travels: Dendrite $\rightarrow$ Cell body $\rightarrow$ Axon.
- At the axon end, chemicals are released into the Synapse (gap) to start the impulse in the next neuron.
Receptors: Located in sense organs (e.g., Gustatory receptors for taste, Olfactory receptors for smell).
Neuromuscular Junction: The point where a nervous impulse is delivered to a muscle cell or gland.

Reflex Action: A sudden response to an environmental stimulus without conscious thought (e.g., pulling a hand away from a flame).
Reflex Arc: The connection between the input (sensory) nerve and output (motor) nerve through the spinal cord for quick responses.
Central Nervous System (CNS): Comprises the brain and spinal cord; the main coordinating center.
Peripheral Nervous System (PNS): Facilitates communication between the CNS and body via cranial and spinal nerves.
Regions of the Brain:
- Fore-brain: Main thinking part; contains separate specialized areas for hearing, smell, and sight. Interprets sensory information.
- Mid-brain & Hind-brain: Control involuntary actions (e.g., blood pressure, salivation, vomiting).
- Cerebellum (Hind-brain): Responsible for the precision of voluntary actions and maintaining posture and equilibrium.
- Medulla (Hind-brain): Controls involuntary actions.
Protection: The brain is protected by a bony box (skull) and shock-absorbing fluid; the spinal cord is protected by the vertebral column.

Action occurs when muscle cells change their shape by shortening.
Specialized proteins in muscle cells change their shape and arrangement in response to electrical impulses.

Plants lack a nervous system and muscles. They use electrical-chemical means to convey information between cells.
Immediate Response: Non-growth movement (e.g., leaves of Mimosa / chhui-mui folding). Movement is caused by cells changing the amount of water (turgor), leading to swelling or shrinking.
Tropic Movements (Growth-dependent):
- Phototropism: Bending towards light.
- Geotropism: Response to gravity (roots grow down, shoots grow up).
- Hydrotropism: Growth toward water.
- Chemotropism: Growth toward chemicals (e.g., pollen tubes moving toward ovules).

Plant Hormones:
- Auxin: Synthesized at shoot tips; promotes cell elongation on the shady side, causing the plant to bend toward light.
- Gibberellins: Help in stem growth.
- Cytokinins: Promote cell division; found in high concentrations in seeds and fruits.
- Abscisic Acid: Inhibits growth (e.g., wilting of leaves).
Animal Hormones (Endocrine System):
- Adrenaline (Adrenal Gland): Secreted during stress; increases heart rate and oxygen supply to skeletal muscles ("fight or flight").
- Thyroxin (Thyroid Gland): Regulates metabolism; requires Iodine for synthesis (deficiency causes Goitre).
- Growth Hormone (Pituitary Gland): Regulates growth and development (deficiency causes dwarfism).
- Testosterone/Oestrogen: Regulate changes during puberty.
- Insulin (Pancreas): Regulates blood sugar levels (deficiency causes Diabetes).

The timing and amount of hormone release are regulated by feedback mechanisms.
Example: Pancreas cells detect high blood sugar and produce more insulin; secretion reduces as sugar levels fall.

Difference between reflex action and walking: Reflex actions are involuntary, sudden, and managed by the spinal cord, whereas walking is a deliberate voluntary action involving the brain.
Function of receptors: They detect environmental stimuli. Failure in receptors prevents the body from detecting danger (e.g., heat) or essential signals.
Iodised salt importance: It provides Iodine necessary for the thyroid to produce thyroxin, which regulates growth metabolism and prevents Goitre.
Reflexes and Brain: While reflexes occur in the spinal cord for speed, the information is still sent to the brain for processing and memory.
Taste and Smell: Activity $6.1$ shows that blocking the nose affects the ability to fully appreciate flavor, demonstrating the link between olfactory and gustatory receptors.