Topic 6: Organisms responding to changes in internal or external environment

What is a stimulus?

A stimulus is something that can be detected by an organism, either internal or external.

What is a receptor?

A receptor is an organ or specialized cell that detects changes causing a stimulus.

What is a response in biological terms?

A response is the action taken by an organism as a result of a detected stimulus.

What is a taxis?

A taxis is a directional movement response towards or away from a stimulus.

What is positive taxis?

Positive taxis is movement towards the stimulus.

What is negative taxis?

Negative taxis is movement away from the stimulus.

What is kinesis?

Kinesis is a non-directional movement response that increases the likelihood of encountering favorable conditions.

What is phototropism?

Phototropism is a plant growth response towards light.

What is the role of indoleacetic acid (IAA) in plants?

IAA is an auxin that controls plant growth and tropisms by uneven distribution, causing differential growth.

What happens to auxin distribution when a plant shoot is illuminated from one side?

Auxins move towards the shaded side, causing that side to elongate and the shoot to bend towards the light.

What is gravitropism in roots?

Gravitropism is the growth response of roots towards gravity, with IAA causing faster growth on the upper side.

What is a reflex arc?

A reflex arc is the pathway taken by nerve impulses during a reflex action, bypassing the brain for rapid response.

What is the role of the sensory neurone in a reflex arc?

The sensory neurone carries the nerve impulse from the receptor to the spinal cord.

What does the motor neurone do in a reflex arc?

The motor neurone carries the nerve impulse from the spinal cord to the effector (muscle or gland).

What is the function of the intermediate neurone?

The intermediate neurone relays the nerve impulse from the sensory neurone to the motor neurone within the spinal cord.

What are Pacinian corpuscles?

Pacinian corpuscles are receptors that detect mechanical pressure and vibrations, located deep in the skin.

How do Pacinian corpuscles generate a nerve impulse?

Under pressure, stretch-mediated sodium channels open, allowing sodium ions to enter, depolarizing the membrane and creating a generator potential.

What are the two types of photoreceptors in the retina?

The two types are cones (for color vision) and rods (for monochromatic vision).

What is the function of cone cells?

Cone cells are responsible for color vision and require bright light to function.

What is the function of rod cells?

Rod cells are sensitive to low light conditions and provide monochromatic vision.

What is the sinoatrial node?

The sinoatrial node is the heart's pacemaker that initiates electrical stimulation for heart contractions.

What role do the accelerator and vagus nerves play in heart rate control?

The accelerator nerve increases heart rate, while the vagus nerve decreases it.

What effect does high carbon dioxide concentration have on heart rate?

High CO2 levels lead to increased heart rate due to signals from chemoreceptors to the medulla oblongata.

What do baroreceptors monitor?

Baroreceptors monitor blood pressure and send impulses to adjust heart rate accordingly.

What is the basic structure of a neurone?

A neurone consists of a cell body with a nucleus and organelles, along with an axon and dendrites.

What are the two main components of a neuron involved in impulse conduction?

Dendrites (conduct impulses towards the cell body) and axons (conduct impulses away from the cell body).

What is the resting potential of a neuron?

-70mV

What causes the resting potential in a neuron?

An imbalance between sodium ions (Na+) and potassium ions (K+) across the neuron's membrane.

What is the role of the sodium-potassium pump?

It moves sodium ions out of the axon and potassium ions into the axon, maintaining the resting potential.

What happens during depolarization of a neuron?

Sodium ion channels open, allowing Na+ to enter the axon, making the inside less negative.

What is the threshold potential for an action potential to occur?

-55mV

What is hyperpolarization?

When the potential difference becomes more negative than the resting potential.

What is saltatory conduction?

The process by which action potentials jump between nodes of Ranvier in myelinated axons.

What factors affect the speed of a nerve impulse?

Presence of myelin sheath, diameter of the axon, and temperature.

What is the refractory period in neuronal activity?

A short period during which the neuron cannot be excited again, ensuring action potentials travel in one direction.

What is the all-or-nothing principle in action potentials?

An action potential is either produced or not; it must reach a threshold value to occur.

What is a synapse?

A junction between two neurons that transmits signals.

How do synapses prevent action potentials from going in the wrong direction?

Neurotransmitters are only made in the presynaptic neuron and receptors are only on the postsynaptic neuron.

What are the two types of summation in synaptic transmission?

Temporal summation (single presynaptic neuron releases neurotransmitter multiple times) and spatial summation (multiple presynaptic neurons release neurotransmitter).

What happens to acetylcholine after it stimulates the postsynaptic neuron?

It is hydrolyzed by acetylcholinesterase into choline and ethanoic acid, preventing continuous action potential generation.

What is the function of tendons?

Connect muscles to bones.

What is the function of ligaments?

Join bones together and determine the amount of movement possible at a joint.

What are antagonistic muscle pairs?

Pairs of muscles that pull in opposite directions, such as biceps and triceps.

What are myofibrils made of?

Thick filaments (myosin) and thin filaments (actin).

What is required for muscle contraction?

A large amount of ATP.

What role does myoglobin play in muscle function?

It helps maintain a good supply of oxygen for aerobic respiration.

What is phosphocreatine's role in muscle contraction?

It supplies phosphate for ADP phosphorylation to continue ATP production.

What happens during the process of repolarization?

Sodium channels close and potassium channels open, allowing K+ to exit the neuron and restore the resting potential.

What is the significance of the banded appearance of myofibrils?

It results from the overlapping arrangement of thick and thin filaments.

What is the effect of increased temperature on nerve impulse conduction?

It increases the rate of ion diffusion and affects ATP production for the sodium-potassium pump.

What is the function of calcium ions in synaptic transmission?

They trigger the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters.

What are the two types of muscle fibers?

Slow twitch fibers and fast twitch fibers.

What are slow twitch fibers specialized for?

Slow contractions and long periods of exercise such as marathon running.

What adaptations do slow twitch fibers have?

Large store of myoglobin, rich supply of blood vessels, and numerous mitochondria.

What are fast twitch fibers adapted for?

Rapid release of energy during intense exercise such as sprinting.

What adaptations do fast twitch fibers have?

Thick and numerous myosin filaments, high concentration of glycogen, high concentration of enzymes for anaerobic respiration, and a store of phosphocreatine.

What is homeostasis?

The maintenance of a constant internal environment despite changes in the external environment.

Why is homeostasis important for enzymes?

Changes in body temperature and pH can denature enzymes.

What is negative feedback?

A mechanism that counteracts changes in internal conditions to restore optimum levels.

What role do sensory receptors play in homeostasis?

They detect changes in internal conditions and send messages to effectors.

What is an example of negative feedback in blood glucose regulation?

When blood glucose falls, hormones are released to convert glycogen to glucose.

What is positive feedback?

A mechanism that increases the original change in conditions, such as cervix dilation during childbirth.

What is the normal range for blood glucose concentration?

About 70-99 mg/dl.

What happens when blood glucose concentration is too high?

It is excreted in urine, meaning it cannot be stored as glycogen or fat.

What are the three processes the liver uses to regulate blood glucose?

Glycogenesis, glycogenolysis, and gluconeogenesis.

What triggers insulin secretion from the pancreas?

A rise in blood glucose concentration detected by beta cells.

What is the function of insulin in blood glucose regulation?

It increases the permeability of cells to glucose, promoting glucose uptake.

What happens when blood glucose concentration is too low?

Alpha cells secrete glucagon, stimulating the conversion of glycogen to glucose.

How does adrenaline affect blood glucose levels?

It activates a secondary messenger system that catalyzes the conversion of glycogen into glucose.

What is Type 1 diabetes?

Insulin-dependent diabetes occurring early in life, often due to the immune system destroying beta cells.

What is Type 2 diabetes?

Non-insulin dependent diabetes that often develops later in life, associated with decreased insulin production or unresponsive receptors.

What is the structure of the human kidney?

It consists of an outer fibrous capsule, cortex, medulla, and renal pelvis.

What is ultrafiltration in the kidneys?

The process where blood is filtered in the glomerulus, forcing water and soluble components out.

What is selective reabsorption in the kidneys?

The reabsorption of glucose and other necessary substances from the glomerular filtrate back into the blood.

What role does the Loop of Henle play in water reabsorption?

It acts as a counter-current multiplier to reabsorb water through sodium ion transport.

How does ADH affect the collecting duct?

It increases the permeability of the collecting duct to water, enhancing reabsorption.