IGCSE Biology: Coordination and Response Vocabulary

A complete set of vocabulary flashcards covering nervous coordination, reflex actions, eye structure, sense organs, hormonal regulation, homeostasis, and plant tropisms based on IGCSE Biology notes.

Central Nervous System (CNS)

The part of the nervous system consisting of the brain and spinal cord that processes information and makes decisions.

Peripheral Nervous System (PNS)

The nerves outside of the brain and spinal cord that carry signals between the central nervous system and the rest of the body.

Neurone

A nerve cell that carries electrical messages; it consists of dendrites to receive signals and an axon to send signals.

Sensory Neurone

A nerve cell that carries electrical signals from sense organs to the central nervous system.

Relay Neurone

A nerve cell located entirely within the brain and spinal cord that connects sensory neurones to motor neurones.

Motor Neurone

A nerve cell that carries electrical signals from the central nervous system to effectors such as muscles or glands.

Stimulus

Any change in the environment that can be detected by an organism, such as heat, light, or sound.

Receptor

A specialized structure or cell that detects a stimulus and initiates a nerve signal.

Effector

A muscle or gland that responds to a signal from the nervous system by contracting or releasing secretions.

Voluntary Response

An action that you consciously choose to perform, which originates in the brain.

Involuntary Response

An automatic and fast action performed without conscious thought or decision-making.

Reflex Action

An automatic and rapid integration and coordination of stimuli with effector responses that protects the body from danger without brain involvement.

Reflex Arc

The pathway taken by electrical impulses during a reflex action: Stimulus -> Receptor -> Sensory Neurone -> Relay Neurone -> Motor Neurone -> Effector -> Response.

Synapse

A junction between two neurones where neurotransmitters are released from vesicles, diffuse across the synaptic gap, and bind to receptor proteins to ensure one-way signal travel.

Sense Organs

Groups of receptor cells that respond to specific environmental stimuli including light, sound, touch, temperature, and chemicals.

Cornea

The transparent front layer of the eye that refracts light as it enters.

Iris

The coloured part of the eye that controls how much light enters the pupil using antagonistic circular and radial muscles.

Pupil

The central opening in the iris through which light passes into the eye.

Lens

The transparent structure behind the pupil that changes shape to focus light onto the retina.

Retina

The light-sensitive layer at the back of the eye containing light receptor cells known as rods and cones.

Optic Nerve

The nerve that carries electrical impulses from the retina of the eye to the brain, leaving a blind spot where it exits.

Pupil Reflex

An involuntary action where the pupil dilates in dim light to admit more light and constricts in bright light to protect the retina.

Accommodation

The adjustment of the shape of the lens (thicker for near objects via ciliary muscle contraction; thinner for distant objects via ciliary muscle relaxation) to focus light on the retina.

Rod Cell

A type of receptor cell in the retina with high sensitivity for vision in dim light (night vision) that cannot distinguish colours.

Cone Cell

A receptor cell in the retina responsible for colour vision in bright light, present in three types absorbing red, green, and blue light.

Hormone

A chemical messenger produced by an endocrine gland, transported in the bloodstream, that alters the activity of specific target organs.

Endocrine Glands

Organs that synthesize hormones and secrete them directly into the blood system.

Adrenaline

A hormone secreted by the adrenal glands during stress or danger that prepares the body for fight or flight by increasing heart rate, breathing rate, and pupil diameter.

Insulin

A hormone produced by the pancreas that decreases blood glucose concentrations by causing liver cells to convert glucose into stored glycogen.

Glucagon

A hormone produced by the pancreas that increases blood glucose concentrations by stimulating the breakdown of glycogen into glucose in the liver.

Glycogen

A complex carbohydrate storage molecule stored primarily in the liver, converted from glucose by insulin.

Homeostasis

The maintenance of a constant internal environment within an organism, including temperature, water levels, and blood glucose concentration.

Negative Feedback

A homeostatic control mechanism where a change away from the optimal set point triggers responses that reverse the change back to normal.

Type 1 Diabetes

A metabolic condition caused by the failure of the pancreas to produce insulin, resulting in uncontrolled high blood glucose levels.

Vasodilation

The widening of blood vessels near the skin surface when body temperature is too high, increasing blood flow and heat loss.

Vasoconstriction

The narrowing of blood vessels near the skin surface when body temperature is too low, reducing blood flow and conserving heat.

Gravitropism

A directional plant growth response to gravity, where roots display positive gravitropism (growing downwards) and shoots display negative gravitropism (growing upwards).

Phototropism

A directional plant growth response to light, where shoots display positive phototropism (growing towards light) and roots display negative phototropism (growing away from light).