Coordination and response

Tropism

A growth response by a plant, in which the direction of the growth is affected by the direction of the stimulus.

Auxin

Type of plant hormone that promotes cell growth or elongation

Gravitropism/Geotropism

A response in which a plant grows towards or away from gravity

Phototropism

A response in which a plant grows towards or away from the direction from which light is coming

Stimulus

A change in an organism's surroundings that causes the organism to react

Receptors

Special structures that allow living organisms to sense the conditions of their internal or external environment.

Effectors

Causes responses that alter conditions in the internal environment

Examples of effectors

Muscles and glands

Nervous system

The body's communication network, consisting of all the nerve cells (receptors, nerves) of the peripheral and central nervous systems

Nerve impulses

Electrical signals from other neurones

Endocrine system

The body's chemical communication system; a set of glands that secrete hormones into the bloodstream

Neurones

Basic cells of the nervous system that carry minute electrical impulses around the body

Structure of neuron

Central Nervous System (CNS)

Consists of the brain and spinal cord

Peripheral Nervous System (PNS)

All of the parts of the nervous system except for the brain and the spinal cord, made up of nerves and receptors

Reflex Arc

- stimulus detected by receptors

- sensory neurones carry impulses to relay neurones in CNS

- relay neurones carry impulses to motor neurones

- motor neurones carry impulses to effectors

- effectors carry out response

Sensory Neurone

A neurone that sends impulses (from a sensory receptor) to a relay neurone in the spinal cord/CNS

Relay Neurone

Carries impulses from sensory neurone to motor neurone

Motor Neurone

Sends impulses from the spinal cord/CNS to the effector (muscle or gland)

Reflex action

An immediate response to a specific stimulus without conscious control

Synapse

A junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter

Retina

The part of the eye that contains the receptor cells, and is therefore the part that is sensitive to light

Sclera

A very tough coat surrounding the part of the eye inside the orbit, in order to protect this part of the eye

Fovea

Part of the retina where light is focused

Blind spot

A spot near where the optic nerve leaves the retina where there are no receptor cells

Choroid

Jelly-like liquid which nourishes eye

Rod cells

A type of receptor cell that is sensitive to dim light, but doesn't respond to colour, found in the retina

Cone cells

A type of receptor cell that is able to distinguish between different colours of light, found in fovea

Iris

A circular piece of tissue in front of the lens, contains muscles to control diameter of the pupil

Pupil

A gap in the middle of the iris which lets light in

Circular muscles

When they contract, they make the pupil constrict, or get smaller

Radial muscles

When they contract, they make the pupil dilate, or get larger

Cornea

The clear tissue that covers the front of the eye and is responsible for most of the bending of the light

Lens

The transparent structure behind the pupil that changes shape to help focus images on the retina

Accomodation

The process by which the eye's lens changes shape to focus/adjust near or far objects on the retina

Suspensory ligaments

A fibrous membrane that holds the lens of the eye in place

Ciliary muscle

A smooth muscle portion of the ciliary body, which contracts to assist in near vision

Object far away

- relaxed ciliary muscles

- tightened suspensory ligaments

- thinner lens

Objects close by

- contracted ciliary muscles

- slack suspensory ligaments

- thicker lens

Hormones

A chemical substance produced by a gland, carried by the blood, which alters the activity of one or more specific target organs

Adrenaline

A hormone released into the bloodstream in response to a situation where the body may be in danger, 'fight or flight'