Unit 2 Topic 1 Homeostasis

Question 1

What is the endocrine system?

Answer 1

Collection of glands that produce hormones that regulate metabolism, growth and development.

The endocrine system plays a crucial role in maintaining homeostasis.

Question 2

What is a neuron?

Answer 2

A cell that carries electrical impulses; the basic units of the nervous system.

Neurons communicate with each other through synapses.

Question 3

Define hormone.

Answer 3

A hormone is a chemical substance produced by glands, transported in the bloodstream, and responsible for stimulating specific effector cells or tissues into action or response.

Hormones can have various effects on the body, including growth, metabolism, and mood regulation.

Question 4

What is homeostasis?

Answer 4

the process by which living organisms maintain a stable internal environment, despite changes in the external environment.

This stability is crucial for the body’s cells to function properly. For example, humans need to keep things like:

Body temperature (around 37°C)

Blood glucose levels

Water balance

pH of blood and tissues

within narrow, healthy ranges.

Question 5

What are abiotic factors?

Answer 5

Non-living chemical and physical parts of the environment that affect living organisms.

Examples include sunlight, temperature, water, soil, and minerals.

Question 6

Describe the first step in the stimulus-response model.

Answer 6

Stimulus:
A detectable change in the environment (e.g. light, temperature, sound, pressure, chemicals).

Question 7

Describe the second step in the stimulus-response model.

Answer 7

Receptor:
A cell or organ that detects the stimulus (e.g. sensory neurons, photoreceptors, thermoreceptors) and sends the information to the control centre.

Question 8

Describe the third step in the stimulus-response model.

Answer 8

Control Centre:
Usually the brain or spinal cord (the CNS). It processes the information and decides on the appropriate response, which is then relayed to the effector.

Question 9

Describe the fourth step in the stimulus-response model.

Answer 9

Effector
A muscle or gland that carries out the response (e.g. a muscle contracting or a gland releasing a hormone).

Question 10

Describe the final step in the stimulus-response model.

Answer 10

Response:
The action or change in behaviour that occurs as a result of the stimulus (e.g. pulling hand away from something hot).

Depending on the type of feedback loop, this response could counteract or amplify the original stimulus.

Question 11

Describe a negative feedback loop.

Answer 11

A negative feedback loop is a type of stimulus-response model in which the response counteracts changes (stimuli) in a living system to help maintain homeostasis.

Negative feedback is crucial in biological systems to ensure homeostasis. E.g temperature, pH, blood glucose level, etc.

Question 12

Describe a positive feedback loop.

Answer 12

A positive feedback loop is a type of stimulus-response model in which the response to a stimulus amplifies or reinforces the original change rather than reversing it. This creates an increasing effect until a specific outcome is achieved, at which point the loop typically stops.

It is rare to find positive feedback loops in living systems.

Examples in biology:
Childbirth

The hormone oxytocin is released to increase uterine contractions.

More contractions → more oxytocin → stronger contractions → until the baby is delivered.

Blood clotting

When a vessel is injured, platelets stick to the site and release chemicals.

These chemicals attract more platelets → rapid accumulation → clot forms.

Question 13

What are the different types of sensory receptors?

Answer 13

Chemoreceptors, thermoreceptors, mechanoreceptors, photoreceptors, nociceptors

These receptors are specialised to respond to specific types of stimuli.

Question 14

What do chemoreceptors respond to?

Answer 14

Chemical stimuli

Chemoreceptors are involved in detecting taste and smell as well as detecting the blood glucose level.

Question 15

What stimuli do thermoreceptors detect?

Answer 15

Temperature changes

Thermoreceptors help the body sense hot and cold conditions.

Question 16

What type of stimuli do mechanoreceptors respond to?

Answer 16

Mechanical forces

Mechanoreceptors are involved in touch, pressure, and vibration sensations (sound).

Question 17

What do photoreceptors detect?

Answer 17

Light stimuli

Photoreceptors are essential for vision and are found in the retina.

Question 18

What type of stimuli do nociceptors respond to?

Answer 18

Painful stimuli

Nociceptors signal potential harm or injury to the body.

Question 19

What type of stimuli do olfactory receptors respond to?

Answer 19

smell (or olfaction) stimuli

Olfactory receptors are examples of chemoreceptors.

Question 20

What do sensory (afferent) neurons do?

Answer 20

Detect stimuli and transmit nerve impulses from sensory receptors to the central nervous system (CNS).

Sensory neurons are essential for processing external and internal stimuli.

Question 21

What is the function of inter or relay neurons?

Answer 21

Transmit impulses between sensory neurons and motor neurons within the central nervous system (CNS).

Relay neurons play a critical role in processing information within the CNS.

Question 22

What is the function of motor (efferent) neurons?

Answer 22

carry nerve impulses from the central nervous system (CNS) to effectors such as muscles or glands.

Motor neurons are responsible for initiating a response in the body.

Question 23

Name the structure in the diagram and state its function.

Answer 23

Dendrites.

Receive signals (from the environment or other cells nearby)

Question 24

Name the structure in the diagram and state its function.

Answer 24

Cell body (Soma)
It contains various organelles (nucleus, mitochondria, R.E.R, etc) that carry out essential metabolic processes to support the cell.

It also processes incoming signals from the dendrites and, if the signal is strong enough, initiates a nerve impulse.

Question 25

Name the structure in the diagram and state its function.

Answer 25

Axon The function of the axon is to transmit electrical impulses (action potentials) away from the cell body to the axon terminals.

Question 26

Name the structure in the diagram and state its function.

Answer 26

Myelin sheath The function of the myelin sheath is to insulate the axon and increase the speed at which electrical impulses travel along the neuron. ## Footnote It is produced by specialised cells (e.g. Schwann cells).

Question 27

Name the structure in the diagram and state its function.

Answer 27

Nodes of Ranvier: are small gaps between segments of the myelin sheath along an axon. They contain voltage-gated ion channels.

Question 28

What is an electrical impulse?

Answer 28

The flow of charged particles (i.e. +ve) along the axon, towards the axon terminals. ## Footnote Electrical impulses are crucial for transmitting signals in the nervous system.

Question 29

In which parts of a neuron are sodium/potassium pump proteins found?

Answer 29

Along the membranes of dentrites, cell body, axon and axon terminals.

Question 30

Describe the function of sodium/potassium pump proteins.

Answer 30

Using ATP, Sodium/Potassium pump proteins transport 3 Na+ ions out of the cell for every 2 K+ ions that are transported into the cell.

Question 31

Would the cytoplasm of a neuron become more positive or more negative (in terms of electrical charge) as sodium-potassium pumps carry out their function?

Answer 31

The cytoplasm of the neuron becomes more negative overall because the Na⁺/K⁺ pumps export a net of one positive charge from the cell. ## Footnote Three positive charges (Na⁺ ions) leave the cell while two positive charges (K⁺ ions) enter. This means the cell is losing a net of one positive charge, making the inside less positive and therefore more negative.

Question 32

Describe the function of voltage-gated sodium ion channels

Answer 32

Allow sodium ions to move into the cell from a region of high concentration (outside of the cell) to low concentration (the cytoplasm) when triggered*. ## Footnote Voltage-gated sodium ion channels open when the membrane potential reaches a certain threshold level (~ - 55 mV).*

Question 33

In which parts of a neuron are voltage-gated sodium channel proteins found?

Answer 33

Along the axon membrane and axon terminals

Question 34

Is this a myelinated neuron or an unmyelinated neuron?

Answer 34

Myelinated - you can see the myelin sheath surrounding the axon.

Question 35

Is this a myelinated neuron or an unmyelinated neuron?

Answer 35

Unmyelinated - there is no myelin sheath surrounding the axon. The axon is naked. | The axon terminals are not included in the diagram.

Question 36

In which parts of a neuron are voltage-gated potassium channel proteins mostly found?

Answer 36

Along the axon membrane and axon terminals

Question 37

In which parts of a neuron are voltage-gated calcium ion channel proteins mostly found?

Answer 37

Along axon terminals

Question 38

Describe the function of voltage-gated potassium ion channels.

Answer 38

Allow potassium ions to move out of the cell from a region of high concentration (cytoplasm) to low concentration (outside of the cell) when triggered*. ## Footnote Voltage-gated potassium ion channels open when the membrane potential reaches a certain level (~ 55 mV).* But the timing of their opening is slightly delayed, so they open soon after the volatage gated sodium ion channels open.

Question 39

Would the cytoplasm of a neuron become more positive or more negative (in terms of electrical charge) as voltage-gated sodium ion channels carry out their function?

Answer 39

More positive - there will be an influx of sodium ions into the cell when the sodium ion channels open up. ## Footnote It is important to remember that the concentration of sodium ions is higher outside the cell than inside.

Question 40

Would the cytoplasm of a neuron become more positive or more negative (in terms of electrical charge) as voltage-gated potassium ion channels carry out their function?

Answer 40

More negative - there will be an exodus of potassium ions leaving the cell when the potassium ion channels open up. ## Footnote It is important to remember that the concentration of potassium ions is higher inside the cell than outside.

Question 41

What is the resting membrane potential of a neuron?

Answer 41

about - 70 mV

Question 42

What is another term that is used interchangeably with 'action potential'?

Answer 42

Electrical impulse/nerve impulse