Organisms respond to changes in their internal and external environments (A-level only) – A Level AQA Biology revision notes
Choose a subtopic. Organisms respond to changes in their internal and external environments (A-level only) covers Stimuli, both internal and external, are detected and lead to a response (A-level only), Nervous coordination (A-level only), Skeletal muscles are stimulated to contract by nerves and act as effectors (A-level only), and Homeostasis is the maintenance of a stable internal environment (A-level only) in A Level AQA Biology. 22 lessons in 4 subtopics.
Revise Organisms respond to changes in their internal and external environments (A-level only) for A Level AQA Biology. 22 lessons across 4 subtopics.
22
Lessons
4
Subtopics
What this topic covers
Organisms respond to changes in their internal and external environments (A-level only) has 4 subtopics:
Stimuli, both internal and external, are detected and lead to a response (A-level only)
Nervous coordination (A-level only)
Skeletal muscles are stimulated to contract by nerves and act as effectors (A-level only)
Homeostasis is the maintenance of a stable internal environment (A-level only)
Organisms respond to changes in their internal and external environments (A-level only) lessons by subtopic
22 lessons, grouped by subtopic.
Stimuli, both internal and external, are detected and lead to a response (A-level only)
Survival and Plant Growth Responses: Explain how responding to environmental changes increases an organism's chance of survival; Describe how growth factors move from growing regions to other tissues in flowering plants; Explain the effect of different concentrations of indoleacetic acid (IAA) on cell elongation in roots and shoots
Simple Responses and Reflexes: Explain how taxes and kineses act as simple responses that maintain a mobile organism in a favourable environment; Compare taxes and kineses in terms of direction, mechanism, and adaptive advantage; Describe the sequence of events in a three-neurone simple reflex arc
Myogenic Heart Stimulation: Explain what is meant by myogenic stimulation of the heart; Describe the roles of the sinoatrial node (SAN), atrioventricular node (AVN), and Purkyne tissue in coordinating the cardiac cycle; Explain how the wave of electrical activity spreads through the heart in the correct sequence
Chemo- and Pressure Receptors in Heart Rate Control: Describe the locations and roles of chemoreceptors and pressure receptors in detecting changes in blood chemistry and pressure; Explain how the autonomic nervous system coordinates heart rate responses via the cardiovascular centre; Compare the roles of the sympathetic and parasympathetic divisions in accelerating and decelerating heart rate
Receptor Specificity and Potentials: Explain why receptors respond only to specific stimuli, using the concept of receptor specificity; Describe how stimulation of a receptor leads to the establishment of a generator potential; Compare the sensitivity, habituation, and resolution of touch receptors in human skin
Pacinian Corpuscle Structure and Function: Describe the basic structure of a Pacinian corpuscle, including the arrangement of lamellae and the sensory neurone ending; Explain how deformation of stretch-mediated sodium ion channels leads to the establishment of a generator potential; Analyse how the Pacinian corpuscle acts as a mechanoreceptor that converts a mechanical stimulus into an electrical signal
Sensitivity to light, sensitivity to colour and visual acuity: Explain how differences in the optical pigments of rods and cones account for differences in sensitivity to light and colour; Compare the connections rods and cones make in the optic nerve and explain how these connections determine visual acuity; Analyse how the distribution of rods and cones across the retina relates to their functions
Nervous coordination (A-level only)
Neurone Structure & Resting Potential: Describe the structure of a myelinated motor neurone, naming all key components and their functions; Explain how differential membrane permeability to sodium and potassium ions establishes a resting potential; Analyse the roles of electrochemical gradients and the sodium-potassium pump in maintaining the resting potential
Action Potential Generation & Propagation: Explain how changes in membrane permeability lead to depolarisation and the generation of an action potential; Describe the all-or-nothing principle and its significance for nerve signalling; Compare the propagation of action potentials along non-myelinated and myelinated axons
Refractory Period & Conduction Speed: Explain the nature and importance of the refractory period in producing discrete nerve impulses; Analyse how the refractory period limits the maximum frequency of impulse transmission; Compare the effects of myelination, axon diameter, and temperature on the speed of nerve impulse conduction
Synaptic Structure and Function: Describe the detailed structure of a cholinergic synapse and a neuromuscular junction; Explain the sequence of events involved in transmission across a cholinergic synapse; Compare the structure and function of a cholinergic synapse with a neuromuscular junction
Synaptic Properties and Drug Effects: Explain why synaptic transmission is unidirectional and describe the structural basis for this property; Explain how temporal and spatial summation allow a postsynaptic neurone to integrate signals from multiple sources; Describe how inhibitory synapses can prevent or reduce the likelihood of an action potential being generated
Skeletal muscles are stimulated to contract by nerves and act as effectors (A-level only)
Muscle Structure and Antagonistic Action: Describe the gross and microscopic structure of skeletal muscle, including the ultrastructure of a myofibril; Explain how muscles act in antagonistic pairs against an incompressible skeleton; Compare the arrangement of actin and myosin filaments within a sarcomere and relate this to the banding pattern seen under electron microscopy
Myofibril Contraction: The Sliding Filament Model: Describe the roles of actin, myosin, calcium ions and ATP in myofibril contraction; Explain the cycle of actinomyosin bridge formation, including the roles of calcium ions and tropomyosin; Analyse the sequence of molecular events that produce the sliding filament mechanism
Energy Sources and Muscle Fibre Types: Explain the roles of ATP and phosphocreatine in providing energy for muscle contraction; Describe the structure and location of slow and fast skeletal muscle fibres; Compare the properties of slow-twitch and fast-twitch muscle fibres in relation to their function
Homeostasis is the maintenance of a stable internal environment (A-level only)
Insulin, Glucagon and Blood Glucose Regulation: Explain how insulin and glucagon act on target cells via surface receptors to regulate blood glucose concentration; Describe the roles of glycogenesis, glycogenolysis, and gluconeogenesis in the liver; Compare the actions of insulin and glucagon in terms of the enzymes they activate and the metabolic conversions they trigger
Diabetes: Types, Control, and Glucose Concentration Measurement: Explain the causes of type I and type II diabetes and how each is controlled; Evaluate the positions of health advisers and the food industry regarding the increased incidence of type II diabetes; Describe and carry out the production of a dilution series of a glucose solution
Homeostasis: Maintaining a Stable Internal Environment: Explain what homeostasis is and why physiological control systems are necessary to maintain the internal environment within restricted limits; Explain the importance of maintaining a stable core temperature and stable blood pH in relation to enzyme activity; Explain the importance of maintaining a stable blood glucose concentration in terms of respiratory substrate availability and blood water potential
Negative Feedback: Restoring Balance: Explain how negative feedback restores a physiological variable to its original set point; Describe how separate negative feedback mechanisms control departures in opposite directions, providing greater precision; Compare negative and positive feedback in terms of their effects on the original stimulus
Filtration & Reabsorption in the Nephron: Explore the key processes in the nephron, including glomerular filtration, reabsorption in the proximal convoluted tubule, and the role of the loop of Henle.
Fine-Tuning Water Balance: Distal Tubule & ADH: Describe the structure of the nephron and identify the roles of the distal convoluted tubule and collecting duct in water reabsorption; Explain osmoregulation as the control of water potential of the blood; Explain the roles of the hypothalamus, posterior pituitary gland, and ADH in osmoregulation
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What is Organisms respond to changes in their internal and external environments (A-level only)?
Organisms respond to changes in their internal and external environments (A-level only) covers Stimuli, both internal and external, are detected and lead to a response (A-level only), Nervous coordination (A-level only), Skeletal muscles are stimulated to contract by nerves and act as effectors (A-level only), and Homeostasis is the maintenance of a stable internal environment (A-level only) in A Level AQA Biology. 22 lessons in 4 subtopics.
What is the normal blood glucose range?
Normal blood glucose concentration is about 4–6 mmol per litre. The Insulin, Glucagon and Blood Glucose Regulation notes cover this in full.
What is homeostasis?
Homeostasis is the maintenance of an organism's internal environment within restricted limits using physiological control systems. The Homeostasis: Maintaining a Stable Internal Environment notes cover this in full.
What are the stages of a reflex arc?
A three-neurone reflex arc runs from a receptor along a sensory neurone to a relay neurone in the spinal cord, then to a motor neurone and an effector. The Simple Responses and Reflexes notes cover this in full.
What is insulin resistance?
Insulin resistance is when target cells, particularly in the liver and muscles, become less sensitive or completely unresponsive to insulin. The Diabetes: Types, Control, and Glucose Concentration Measurement notes cover this in full.
What causes type 2 diabetes?
Type 2 diabetes is caused by insulin resistance: beta cells still produce insulin, often in normal or raised amounts, but target cells in the liver and muscles become less sensitive or unresponsive to it. The Diabetes: Types, Control, and Glucose Concentration Measurement notes cover this in full.
How does the sliding filament model work?
In the sliding filament model, myosin heads bind to actin filaments and pull them towards the centre of the sarcomere, so the actin and myosin filaments overlap more. The Myofibril Contraction: The Sliding Filament Model notes cover this in full.
What is the difference between type 1 and type 2 diabetes?
In type I diabetes, the immune system destroys the beta cells in the islets of Langerhans, so no insulin is produced; onset is usually in childhood or early adulthood. The Diabetes: Types, Control, and Glucose Concentration Measurement notes cover this in full.
What are the islets of Langerhans?
The islets of Langerhans are clusters of endocrine cells in the pancreas. The Insulin, Glucagon and Blood Glucose Regulation notes cover this in full.