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EnglandBiology

3.6 Organisms respond to changes in their internal and external environments

7 dot points across 7 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do the kidneys keep the water potential of the blood constant?

The role of the kidney in osmoregulation and in the excretion of metabolic waste. The detailed structure of a nephron and its associated blood vessels. The processes of ultrafiltration and selective reabsorption, the role of the loop of Henle in producing concentrated urine, and the control of blood water potential by antidiuretic hormone (ADH) through negative feedback.
A focused answer to the AQA 3.6 dot point on osmoregulation. Covers the nephron structure, ultrafiltration and selective reabsorption, the loop of Henle countercurrent multiplier, and the control of blood water potential by ADH through negative feedback.
13 min answer →

How does the body keep blood glucose concentration within narrow limits?

The principles of homeostasis and negative feedback in maintaining a constant internal environment. The control of blood glucose concentration by insulin and glucagon, including the roles of the liver in glycogenesis, glycogenolysis and gluconeogenesis, the action of insulin through the second messenger model involving adenylate cyclase and cyclic AMP, and the causes and control of types 1 and 2 diabetes mellitus.
A focused answer to the AQA 3.6 dot point on homeostasis and blood glucose. Explains negative feedback, the roles of insulin and glucagon, glycogenesis, glycogenolysis and gluconeogenesis, the second messenger model, and types 1 and 2 diabetes.
13 min answer →

How is an electrical signal generated and conducted rapidly along a neurone?

The structure and function of myelinated motor neurones. The establishment of a resting potential in terms of differential membrane permeability, electrochemical gradients and the movement of sodium and potassium ions. Changes in membrane permeability that lead to depolarisation and the generation of an action potential, the all-or-nothing principle, the passage of a wave of depolarisation along a neurone, saltatory conduction in myelinated neurones, and the nature and importance of the refractory period.
A focused answer to the AQA 3.6 dot point on the nerve impulse. Explains the resting potential, the action potential and depolarisation, the all-or-nothing principle, saltatory conduction in myelinated neurones, and the refractory period.
12 min answer →

How do specialised receptor cells convert a stimulus into a nerve impulse?

Receptors are specific to a single type of stimulus and produce a generator potential when stimulated. The Pacinian corpuscle as a receptor that responds to changes in mechanical pressure. The role of rod and cone cells in the retina, the differences in sensitivity and visual acuity, and the distribution of rods and cones across the retina.
A focused answer to the AQA 3.6 dot point on receptors. Explains generator potentials, the Pacinian corpuscle as a pressure receptor, and the differences between rod and cone cells in sensitivity, visual acuity and distribution across the retina.
10 min answer →

How does the structure of a muscle fibre allow it to shorten and generate force?

The gross and microscopic structure of skeletal muscle, including the ultrastructure of a myofibril and the sarcomere. The sliding filament theory of muscle contraction, including the roles of actin, myosin, calcium ions and ATP. The structure, location and general properties of slow and fast skeletal muscle fibres.
A focused answer to the AQA 3.6 dot point on skeletal muscle. Covers the sarcomere ultrastructure, the sliding filament theory and the roles of actin, myosin, calcium ions and ATP, plus the properties of slow and fast twitch fibres.
12 min answer →

How do simple and complex organisms detect and respond to changes in their environment so that they survive?

A stimulus is a detectable change in the internal or external environment of an organism that produces a response. Taxes and kineses as simple responses that maintain a mobile organism in a favourable environment; tropisms as growth responses controlled by indoleacetic acid (IAA); the role of a simple reflex arc in protecting the body from harm.
A focused answer to the AQA 3.6 dot point on stimuli and responses. Distinguishes taxes from kineses, explains tropisms and the role of IAA in phototropism and gravitropism, and traces the simple reflex arc that protects the body from harm.
10 min answer →

How is a nerve impulse passed from one neurone to the next across a gap?

The detailed structure of a synapse and of a neuromuscular junction. The sequence of events involved in transmission across a cholinergic synapse. The roles of summation, both spatial and temporal, and the importance of synapses in ensuring unidirectional transmission. Predicting and explaining the effects of specific drugs on synaptic transmission.
A focused answer to the AQA 3.6 dot point on synaptic transmission. Details the cholinergic synapse step by step, compares it with the neuromuscular junction, explains spatial and temporal summation, and shows why transmission is unidirectional.
11 min answer →