Module 5 - Communication, Homeostasis & Energy

• Abscisic acid (ABA):

  • A plant hormone that stimulates stomatal closing, maintains seed dormancy and triggers cold protective responses
• Abscission:

  • The shedding of leaves in plants
• Acetylcholine:

  • A type of neurotransmitter used for communication between neurones
• Actin:

  • A type of protein filament found in myofibrils, forming thin filaments consisting of two long twisted chains
• Actin-myosin binding site:

  • A site on actin normally blocked by tropomyosin, exposed during muscle contraction for myosin head attachment
• Actin-myosin cross-bridge:

  • Formed when a myosin head attaches to the myosin binding site on an actin filament
• Adenylyl cyclase:

  • An enzyme that catalyses the conversion of ATP to cAMP
• Adrenal glands:

  • Located on top of the kidneys, producing adrenaline and steroid hormones
• Adrenaline:

  • A hormone secreted by the adrenal glands under stressful conditions, serving as a 'primary messenger' activating adenylyl cyclase
• Afferent arteriole:

  • The larger diameter arteriole carrying blood to the glomerulus for ultrafiltration
• Alkaloids:

  • A group of bitter-tasting nitrogenous compounds found in plants affecting the metabolism of animals or insects
• All-or-nothing principle:

  • Describes how any generator potential reaching or exceeding the threshold potential will produce an action potential of equal magnitude
• Alpha cells (α cells):

  • Pancreatic cells secreting glucagon to raise glucose concentration
• Anisotropic (A) bands:

  • The darker bands in a myofibril consisting of overlapping actin and myosin filaments
• Anabolic steroids:

  • Performance-enhancing drugs structurally similar to testosterone used illegally by athletes to promote muscle growth
• Anterior pituitary gland:

  • Region of the pituitary gland producing and secreting hormones
• Antidiuretic hormone (ADH):

  • Hormone released from the posterior pituitary gland increasing water reabsorption in kidney tubules
• Aquaporin:

  • A membrane channel for selective water transport in and out of the cell
• Autonomic nervous system:

  • Branch of the nervous system carrying nerve impulses to muscles and glands, controlling involuntary activities with sympathetic and parasympathetic divisions
• Auxins:

  • Plant hormones controlling cell elongation, producing tropisms, preventing abscission, maintaining apical dominance, and stimulating ethene production
• Axon:

  • Nerve cell extension carrying impulses away from the cell body
• Beta cells (β cells):

  • Pancreatic cells secreting insulin to lower glucose concentration
• Bile canaliculi:

  • Vessels collecting bile produced by hepatocytes
• Blinking reflex:

  • Involuntary blinking of the eyelid when an object is held close to the eye, the last reflex to be lost
• Cardiac muscle:

  • Myogenic muscle found in the heart walls
• Central nervous system (CNS):

  • The brain and spinal cord
• Cerebellum:

  • Brain region controlling muscle coordination and non-voluntary movement like balance and posture
• Cerebrum:

  • Largest brain region receiving sensory information and sending motor responses, responsible for voluntary and some involuntary actions
• Cholinergic synapse:

  • Synapse using acetylcholine as the neurotransmitter
• Creatine phosphate:

  • Compound stored in muscles for ATP regeneration
• Cutting:

  • A small section of the root or stem of an adult plant
• Cyclic AMP (cAMP):

  • A 'second messenger' in adrenaline action activating protein kinase
• Dendron:

  • Nerve cell extension carrying impulses towards the cell body
• Depolarisation:

  • Rapid influx of sodium ions into the cell causing loss of negative charge and membrane potential increase
• Ectotherm:

  • Organism dependent on the environment for body temperature maintenance
• Effector:

  • Organ, tissue, or cell producing a response to a stimulus
• Efferent arteriole:

  • Smaller diameter arteriole carrying blood away from the glomerulus after ultrafiltration
• Endocrine signalling:

  • Signalling using hormones secreted into the blood by endocrine cells affecting receptors
• Endotherm:

  • Organism regulating its body temperature without external heat sources
• Ethene:

  • Plant hormone stimulating fruit ripening and promoting abscission in deciduous trees