AQA Bio A Level Unit 6

Question 1

What is a stimulus?

Answer 1

A stimulus is a detectable change in the internal or external environment that evokes a response in an organism.

Question 2

How do organisms respond to stimuli?

Answer 2

Organisms respond to stimuli through receptors detecting the stimulus, a coordination centre processing the information, and effectors producing a response to restore balance or adjust to the change.

Question 3

What is the role of sensory receptors in the nervous system?

Answer 3

Sensory receptors detect changes in the environment (stimuli) and convert them into electrical impulses to be transmitted to the central nervous system.

Question 4

What is the difference between the central nervous system (CNS) and the peripheral nervous system (PNS)?

Answer 4

The CNS consists of the brain and spinal cord, processing and coordinating information. The PNS consists of all the nerves outside the CNS, transmitting signals between the CNS and the rest of the body.

Question 5

What are the roles of the sympathetic and parasympathetic nervous systems?

Answer 5

The sympathetic nervous system prepares the body for “fight or flight” responses by increasing heart rate and releasing energy, while the parasympathetic system promotes “rest and digest” functions, such as slowing the heart rate and enhancing digestion.

Question 6

Describe the structure of a motor neuron.

Answer 6

A motor neuron has a cell body located in the CNS, dendrites to receive signals, a long axon to transmit impulses, and terminal branches which synapse to and communicate with with effectors like muscles (neuromuscular junction) or glands.

Question 7

What is the resting potential of a neuron?

Answer 7

The resting potential is the electrical charge difference across the neuron membrane when it is not transmitting an impulse, typically around -70 mV.

Question 8

What is an action potential?

Answer 8

An action potential is a rapid, temporary reversal of the membrane potential in a neuron, where the inside of the cell becomes positively charged compared to the outside due to ion movements. Around +40mV

Question 9

What is saltatory conduction?

Answer 9

Saltatory conduction is the process by which action potentials jump from one node of Ranvier to the next along a myelinated axon, increasing the speed of nerve impulse transmission.

Question 10

What is the function of synapses?

Answer 10

Synapses are junctions between neurons where neurotransmitters are released to transmit the nerve impulse from one neuron to another or to an effector.

Question 11

How is an impulse transmitted across a synapse?

Answer 11

When an action potential reaches the synaptic terminal, it triggers the release of neurotransmitters into the synaptic cleft. These bind to receptors on the postsynaptic neuron, triggering an action potential in the next neuron.

Question 12

What is homeostasis?

Answer 12

Homeostasis is the maintenance of a stable internal environment despite changes in external conditions, involving regulation of factors like body temperature, blood glucose, and water balance.

Question 13

How does negative feedback regulate homeostasis?

Answer 13

Negative feedback mechanisms work by detecting a change in a physiological factor and initiating responses to reverse the change, bringing the factor back to a set point.

Question 14

What is the role of insulin in blood glucose regulation?

Answer 14

Insulin lowers blood glucose levels by promoting the uptake of glucose into cells and stimulating the liver to convert glucose to glycogen (glycogenesis).

Question 15

What is the role of glucagon in blood glucose regulation?

Answer 15

Glucagon raises blood glucose levels by stimulating the liver to break down glycogen into glucose (glycogenolysis) and to produce glucose from non-carbohydrate sources (gluconeogenesis).

Question 16

What is the role of the kidney in osmoregulation?

Answer 16

The kidney regulates water and solute concentrations in the blood through processes like filtration, reabsorption, and excretion, ensuring the balance of water and electrolytes.

Question 17

How does ADH (antidiuretic hormone) regulate water balance?

Answer 17

ADH increases the permeability of the the DCT and collecting duct to water, inserting more aquaporins into their allowing more water to be reabsorbed back into the blood, thus reducing urine volume and conserving water.

Question 18

What are the roles of actin and myosin in muscle contraction?

Answer 18

Actin and myosin are proteins involved in muscle contraction. Myosin heads bind to actin filaments, pulling them inward, which shortens the muscle fiber and produces contraction.

Question 19

How does the sliding filament theory explain muscle contraction?

Answer 19

The sliding filament theory states that during muscle contraction, myosin filaments slide over actin filaments, pulling them closer together, which shortens the muscle without the filaments themselves changing length.

Question 20

What is the role of the medulla oblongata in controlling heart rate?

Answer 20

The medulla oblongata controls heart rate by sending signals through the autonomic nervous system. The sympathetic nervous system increases heart rate, while the parasympathetic nervous system decreases it.

Question 21

How do baroreceptors and chemoreceptors regulate heart rate?

Answer 21

Baroreceptors detect changes in blood pressure, and chemoreceptors detect changes in blood CO₂, O₂, and pH levels. They send signals to the medulla, which adjusts heart rate via the sympathetic or parasympathetic pathways to maintain homeostasis.

Question 22

What is a tropism?

Answer 22

A tropism is a growth response of a plant toward or away from a stimulus, such as phototropism (response to light) or gravitropism (response to gravity).

Question 23

What is the role of auxins in plant growth?

Answer 23

Auxins are plant hormones that promote cell elongation. In phototropism, auxins accumulate on the shaded side of a plant, causing those cells to elongate more and bending the plant towards the light.

Question 24

What is depolarisation in the context of an action potential?

Answer 24

Depolarisation is the process during an action potential when sodium ion channels open, allowing Na⁺ ions to enter the neuron, making the inside of the membrane more positive compared to the outside.

Question 25

What is repolarisation in the context of an action potential?

Answer 25

Repolarisation occurs after depolarisation, when potassium ion channels open and K⁺ ions move out of the neuron, restoring the negative charge inside the membrane and returning it to its resting potential.

Question 26

What is spatial summation in synaptic transmission?

Answer 26

Spatial summation occurs when multiple presynaptic neurons release neurotransmitters simultaneously at different synapses on the same postsynaptic neuron, combining their effects to trigger an action potential.

Question 27

What is temporal summation in synaptic transmission?

Answer 27

Temporal summation occurs when a single presynaptic neuron releases neurotransmitters repeatedly in quick succession, building up enough stimulation to trigger an action potential in the postsynaptic neuron.

Question 28

How do the pancreas and liver work together to regulate blood glucose levels?

Answer 28

The pancreas secretes insulin to lower blood glucose and glucagon to raise it. The liver stores excess glucose as glycogen or breaks glycogen down into glucose depending on the hormone released.

Question 29

What is the role of the hypothalamus in thermoregulation?

Answer 29

The hypothalamus detects changes in body temperature and initiates responses like sweating (cooling) or shivering (warming) to maintain a stable internal temperature through homeostasis.

Question 30

What is the role of calcium ions in synaptic transmission?

Answer 30

When an action potential arrives at the synaptic terminal, calcium ion channels open, allowing Ca²⁺ ions to enter the neuron, which stimulates the migration of vesicles containing neurotransmitters to the pre-synaptic membrane where they fuse and release neurotransmitters into the synaptic cleft.

Question 31

What is the role of the sodium-potassium pump in maintaining the resting potential?

Answer 31

The sodium-potassium pump actively transports 3 Na⁺ ions out of the neuron and 2 K⁺ ions in, maintaining the resting potential by keeping the inside of the cell more negative than the outside.

Question 32

What is the refractory period in neurons?

Answer 32

The refractory period is the time after an action potential during which a neuron cannot fire another action potential, ensuring impulses travel in one direction and limiting the frequency of nerve impulses.

Question 33

What is the role of the Pacinian corpuscle?

Answer 33

The Pacinian corpuscle is a sensory receptor that detects mechanical pressure and vibration. When stimulated, it generates an action potential that is transmitted to the central nervous system.

Question 34

What are antagonistic muscles, and how do they work in pairs?

Answer 34

Antagonistic muscles are pairs of muscles that work against each other. For example, the biceps contract to bend the arm, while the triceps contract to straighten it, ensuring controlled movement

Question 35

What is the role of tropomyosin in muscle contraction?

Answer 35

Tropomyosin blocks the myosin-binding sites on actin filaments when a muscle is at rest. During contraction, calcium ions bind to troponin, causing tropomyosin to move and expose the binding sites, allowing myosin to attach and initiate contraction.

Question 36

What is the role of rod cells in the retina?

Answer 36

Rod cells are photoreceptor cells in the retina that are highly sensitive to low light levels and allow vision in dim light, but they do not detect color.

Question 37

What is the role of cone cells in the retina?

Answer 37

Cone cells are photoreceptor cells responsible for detecting color and are most effective in bright light. There are three types of cones, each sensitive to red, green, or blue light.

Question 38

What is the function of the fovea in the eye?

Answer 38

The fovea is a small pit in the retina that contains a high concentration of cone cells, providing sharp, detailed central vision and the clearest images.

Question 39

What is the role of rhodopsin in rod cells?

Answer 39

Rhodopsin is a light-sensitive pigment in rod cells. When exposed to light, rhodopsin breaks down, triggering a nerve impulse in the rod cell that is transmitted to the brain for vision in low light.

Question 40

What is the role of calcium ions (Ca²⁺) in muscle contraction?

Answer 40

Calcium ions are released from the sarcoplasmic reticulum in muscle cells during contraction. They bind to troponin, causing tropomyosin to move and expose the myosin-binding sites on actin, allowing cross-bridge formation.

Question 41

What is ATP’s role in muscle contraction and relaxation?

Answer 41

ATP provides the energy for the myosin heads to detach from the actin filaments after contraction and is hydrolysed to reset the myosin heads for the next contraction. It is also required for actively pumping calcium ions back into the sarcoplasmic reticulum, allowing muscle relaxation.

Question 42

What is a reflex arc?

Answer 42

A reflex arc is the neural pathway that controls a reflex, consisting of a receptor, sensory neuron, relay neuron, motor neuron, and effector. It allows for a rapid, involuntary response to a stimulus.