IGCSE Biology - Excretion, Coordination, Response, Hormones, and Homeostasis

Vocabulary flashcards covering human excretion, nervous system structures, sense organ anatomy, hormones, homeostasis mechanisms, and plant tropic responses.

Excretion

The removal of metabolic wastes from the body, including carbon dioxide by the lungs, lactic acid by the liver, and urea, excess water, and ions by the kidneys.

Urea

A toxic nitrogenous waste formed in the liver from excess amino acids, containing toxins and excess nutrients.

Assimilation

The uptake and use of nutrients by cells, such as the liver converting amino acids to proteins.

Deamination

The removal of the nitrogen-containing part of amino acids to form urea.

Nephron

The kidney tubule structure beginning in the cortex, passing into the medulla, returning to the cortex, and leading through the medulla to the pelvis.

Ultrafiltration

The process where small molecules such as water, glucose, salts, and urea are squeezed out of the blood into a renal capsule.

Reabsorption (in kidneys)

The reabsorption of all of the glucose, some of the ions, and most of the water back into the blood from the nephron tubule.

Central Nervous System (CNS)

The part of the nervous system comprising the brain and the spinal cord.

Peripheral Nervous System (PNS)

The system comprising all nerves outside of the brain and spinal cord.

Stimulus

A change in the environment that is sensed by receptors.

Sensory Neurons

Specialised nerve cells that transmit electrical impulses from receptors to the central nervous system.

Motor Neurons

Neurons that transmit electrical impulses from the central nervous system to appropriate effectors.

Relay Neurons

Neurons that connect sensory neurons to motor neurons within the central nervous system.

Effector

Muscles or glands that produce a response when receiving nerve impulses from the CNS.

Voluntary Response

A response that requires a person to think about doing the action (e.g. running, lifting).

Involuntary Response

A response controlled without the person thinking about it (e.g. breathing).

Reflex Action

A rapid and involuntary response to a stimulus.

Reflex Arc

The pathway taken by nerve impulses in a reflex: Stimulus -> Receptor -> Sensory neuron -> Co-ordinator -> Motor neuron -> Effector -> response.

Synapse

The junction between two neurons that ensures impulses travel in one direction only by releasing neurotransmitters across the synaptic gap.

Sense Organs

Groups of receptor cells that detect and respond to specific stimuli e.g. light, sound, touch, temperature, and chemicals.

Eye

A sense organ containing light receptors and auxiliary structures that focus light and convert visual input into nerve impulses.

Cornea

The front section of the eye that refracts light.

Iris

The structure that controls how much light enters the pupil through antagonistic circular and radial muscles.

Lens

The structure in the eye that focuses light onto the retina.

Retina

The inner layer of the eye containing light receptors (cones and rods) which respond to light.

Cones

Light receptor cells in the retina that sense high light intensity and provide colour vision.

Rods

Light receptor cells in the retina that sense low light intensity and provide black-and-white vision.

Fovea

A region of the retina containing many cones where perfect sharp vision is attainable, allowing fine detail and colour to be distinguished.

Blind Spot

The area on the retina where the optic nerve leaves the eye, containing no rods or cones.

Optic Nerve

The nerve that carries electrical impulses from the eye to the brain.

Accommodation

The adjustment of the shape of the lens to focus light on the retina as light comes from different distances.

Hormone

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

Endocrine Glands

Organs that produce and secrete hormones directly into the bloodstream, such as the adrenal glands, pancreas, testes, and ovaries.

Adrenaline

A hormone secreted by adrenal glands during a 'Fight' or 'Flight' situation to increase breathing rate, heart rate, pupil diameter, and blood glucose concentration.

Homeostasis

The maintenance of a constant internal environment within set limits.

Negative Feedback

The process where a change in a condition from a norm or set point causes a series of actions that return the condition to the norm/set point.

Insulin

A hormone produced by the pancreas that decreases blood glucose concentration by promoting uptake of excess glucose to form glycogen for storage.

Glucagon

A hormone produced by the pancreas that increases blood glucose concentration by converting stored glycogen into glucose and releasing it into the blood.

Type 1 Diabetes

A disease caused by the death of cells that secrete insulin due to the body's immune system attacking and destroying them.

Vasoconstriction

The narrowing of arterioles supplying skin surface capillaries when cold, reducing blood flow and heat loss.

Vasodilation

The widening of arterioles supplying skin surface capillaries when hot, increasing blood flow so more heat is lost across the skin surface.

Tropism

A growth response by a plant where the direction of growth is affected by the direction of the stimulus.

Gravitropism

A plant response in which parts of a plant grow towards (positive: roots) or away from (negative: shoots) gravity.

Phototropism

A plant response in which parts of a plant grow towards (positive: shoots) or away from (negative: roots) the direction of a light source.

Auxin

A plant hormone that controls shoot growth.