Principles of Biology 2 Exam 2 (Follow-up Questions)

Choose two ways animals (humans) are different from plants. For each difference, explain how/why this difference could contribute to differences in their homeostatic systems.

1. Humans have brains while plants don’t

2. Humans have three different body systems that communicate with each other to maintain homeostasis (nervous, sensory, endocrine); plants don’t have this

   • The brain utilizes neurotransmitters to help control homeostasis, in which plants cannot utilize them from lack thereof

   • Having multiple systems working with each other could increase efficiency with communication in homeostasis in humans, while plants solely rely on one unit of communication throughout their body

In your own words, describe the three main parts of animal homeostatic systems, their roles, and their connections.

1. Sensors: Cells/organs that detect internal and external conditions and sends signals to integrating center

2. Integrating Centers: Part of brain that receives/interprets messages from sensors and communicates messages to effectors only if response is necessary

3. Effectors: Cells that receive messages from integrating centers and alter behavior to carry out response

Regulation of blood sugar levels is an example of negative feedback. In general terms, describe what would happen if you miss lunch and your blood sugar falls too low. Now describe what would happen if you ate 10 candy bars and your blood sugar rose too high.

• If your blood sugar falls too low, your body has fallen below the “ok range” and will attempt to increase blood sugar to return to the “set point”

• If your blood sugar rises too high, your body has risen above the “ok range” and will attempt to decrease blood sugar to return to the “set point”

Humans lack sensors capable of detecting the amount of vitamin D in the body. Based on that information, can the levels of vitamin D be regulated in your body? Why or why not?

No, without sensors detecting vitamin D levels, there is nothing that can communicate within your body saying whether you are high or low in vitamin D.

In one sentence, summarize the role of the nervous system in maintaining homeostasis.

The nervous system processes external/internal environments, and then carries out an appropriate response to those conditions through motor commands.

In what direction(s) does information flow through the different parts of the nervous system, the CNS and the two divisions of the PNS?

Information flows from the PNS (sensory division) up to the CNS (through the spinal cord and into the brain). After processing, the CNS sends commands down through the spinal cord to the PNS (motor division).

Based on what we’ve discussed, describe/explain how the different parts of your nervous system might work together to allow you to catch a pen that rolls off your desk

As the pen rolls off the desk, your eyes witness this and send sensory information from the sensory division (PNS) to your brain up the spinal cord (CNS). This information is interpreted in the brain and then sends a command down to the motor division (PNS) towards the nerves in your hand, in which the rapid reflex of catching the pen occurs.

Explain the role of glial cells in the nervous system.

Glial cells function as a neuron support system by accelerating the speed at which neuron communication occurs.

What are the two kinds of ions important for nerve signals? Indicate their charges.

• Na+ (Sodium Ions)

• K+ (Potassium Ions)

Explain what selective permeability means. What does it mean that membrane proteins are specific?

Selective permeability means that only certain things can move in and move out of something. When a membrane protein is specific, the protein only lets certain particles in and out of the neuron.

Describe the difference between voltage-gated ion channels and chemically gated ion channels.

• Voltage-Gated Ion Channels: Channels that open/close in response to changes in the relative charge inside vs. outside of the neuron

• Chemically Gated Ion Channels: Channels that open/close in response to interaction of molecules

How is the sodium-potassium pump different from gated ion channels? Describe what the sodium-potassium pump does (i.e. how many of each type of ion does it move and in what direction).

• Sodium-Potassium Pump: Moves three Na+ ions out for every two K+ ions moved in

• Key Difference: The sodium-potassium is always functioning, while gated ion channels operate based on certain responses.

In your own words, define resting potential.

Resting Potential: The membrane potential of a neuron when it’s not sending signals (gated ion channels are closed, but the sodium-potassium pump is always functioning).

When gated sodium ion channels in the membrane of a resting neuron open, in which direction will ions move? What if gated potassium ion channels open? Explain your answers

When gated sodium channels open, sodium ions (Na+) move into the neuron, and when gated potassium channels open, potassium ions (K+) move out of the neuron

If a neuron is treated with a drug that inhibits sodium-potassium pumps, do you predict that the neuron will be able to generate action potentials normally?

No, if the sodium-potassium pumps were inhibited, then the charges outside and inside of the neuron will never change, meaning that membrane potential will never change and the threshold for action potentials won’t be reached.

Which type of ion channel, voltage-gated or chemically gated, open and close during an action potential?

During an action potential, voltage-gated ion channels open (both Na+ and K+).

If voltage-gated ion channels were not specific (i.e. allowed many different types of molecules through a membrane), would a neuron be able to generate an action potential? Explain your answer.

No, if this were the case, there wouldn’t be any control of the amount of Na+ and K+ inside/outside the neuron, disrupting the membrane potential reversal that’s essential for an action potential.

What does it mean that action potentials are local events?

This means that action potentials occur at a specific place in the membrane.

Explain why action potentials are described as “all-or-nothing” events.

Action potentials have a certain threshold that the membrane potential must reach. If it goes above the threshold, then an action potential occurs. If not, then the action potential doesn’t occur.

If two drugs are added simultaneously to a neuron, one that opens voltage-gated Na+ channels and one that opens voltage-gated K+ channels, do you think that the neuron will generate an action potential? Explain your answer.

No, the membrane potential would be prevented from reaching the threshold as the influx of Na+ in the neuron would be counteracted by the efflux of K+ from the neuron.

A neuron is stimulated so that its membrane potential is just above the threshold. Later, the same neuron is stimulated so that its membrane potential is significantly above the threshold. Compare what will happen after the first and second stimulation events in terms of action potential generation.

There would be no difference upon action potential generation as it’s an “all-or-nothing” event.

Describe how a signal is transmitted along the length of an axon. Explain why signals are always transmitted from axon hillock to the synaptic terminals.

A signal is transmitted along the axon in one direction. This explains why signals are always transmitted from axon hillock to synaptic terminal.

Although it is frequently used, explain why the statement “An action potential moves down an axon” is NOT the best way to describe how a signal gets from the cell body to the synaptic terminals of a neuron.

An action potential doesn’t move down an axon, rather it triggers another action potential in an adjacent location, creating a wave of action potentials that are transmitted along the axon.

What’s a myelin sheath? Explain the role/importance of myelin sheaths in nervous system signaling.

A myelin sheath is a set of surrounding cells in the axon that accelerates transmitting an action potential across the axon, as well as prevents transmission of a signal to a different neuron if their axons touch each other.

Why do action potential signals travel more rapidly along myelinated versus unmyelinated axons?

In myelinated axons, the action potentials can only be generated at the nodes of the Schwann cells, resulting in less action potentials generated in sooner time.

Describe the differences between signal transmission at chemical vs. electrical synapses.

Electrical synapses have directly transmitted action potentials, rapid transmission, and cannot modify signaling, while chemical synapses have a gap between sending/receiving cells, slower transmission, and can modify signaling

In your own words, describe what happens when an action potential reaches the synaptic terminal of a neuron at a chemical synapse. Now do the same thing for an electrical synapse.

• Chemical Synapse: The synapse dumps the neurotransmitters into the synaptic cleft for the receiving neuron’s receptors to interact with.

• Electrical Synapse: The synapse directly sends the ions to the receiving neuron through ion channels that connect the membranes.

At some chemical synapses, dopamine acts as an excitatory neurotransmitter. At other chemical synapses, it’s inhibitory. Describe dopamine’s effects on the receiving neuron in each situation, then propose one explanation for how dopamine can function both as an excitatory and an inhibitory neurotransmitter.

When excitatory, dopamine will make action potential more likely; when inhibitory, dopamine will make action potential less likely. This is because neurotransmitters can have different effects when interacting with different receptors.

What type of gated channel that we discussed, voltage-gated or chemically gated, is important for signal transmission from one neuron to another?

Chemically gated channels

Describe signal integration in your own words and explain why it is important. If a neuron receives multiple excitatory stimuli simultaneously, can you be sure that it will generate an action potential? Why or why not?

• Signal Integration: A neuron receives many different signals, causing local changes in the membrane potential depending on the sum total of excitatory and inhibitory signals

• Yes, having multiple excitatory signals with no inhibitory signals will generate a threshold change in membrane potential that will create an action potential.

Describe two ways in which a drug could decrease signaling at a chemical synapse. Describe two ways a drug could increase signaling at a chemical synapse.

• Decrease: If the drug blocks receptor proteins or inhibits neurotransmitter release

• Increase: If the drug disables reuptake or mimics effects of neurotransmitter

In your own words, describe the role of the sensory system in maintaining homeostasis.

The sensory system senses information from both internal and external stimuli and sends communication signals to the CNS (brain) to interpret.

Explain why your perception of the world around you is determined by the types/locations of sensory receptors and the communication links they form with interneurons in your CNS. Use an example to illustrate your description.

Our perception of the world is determined by whether or not our sensory receptors can detect stimuli and communicate the signal to our CNS or not. For example, if a tree were cut down in a forest, we would perceive the tree hitting the ground if we were nearby the tree and could detect the noise that it made; we wouldn’t perceive it if we weren’t nearby the tree to detect the noise it made.

The same amount of pressure is applied to two different sensory receptor neurons that detect touch in your skin. One generates action potentials and one does not. Propose a hypothesis to explain this observation. Hint – Think about what determines whether or not a sensory receptor neuron generates action potentials.

The pressure that was applied to the sensory receptor neuron that generated action potential has a lower membrane potential threshold than the other sensory receptor neuron.

You drop your textbook on the floor and it makes a loud noise. A minute later you drop your pen on the floor and it makes a much softer sound. Explain how the messages sent by the sensory receptor cells in your ear are different when you drop your textbook versus your pen, and how their messages are interpreted as noise rather than, say, the color orange.

• The stimulus strength from dropping the textbook is much stronger than the strength from dropping the pen, resulting in more membrane potential from dropping the textbook, which creates more action potentials.

• We interpret these messages as noise rather than color as the sensory receptor cells that detect noise are specific for only noise (they cannot detect other stimuli, such as color).

You walk into your apartment and notice that it smells like the toast you burned in the morning. Propose an explanation for why, after a few minutes, you do not notice a burnt toast smell.

After a few minutes, you don’t notice a burnt toast smell because you begin to adjust to the stimuli in the environment through sensory adaptation (your receptors decrease response from the continuous stimuli).

Compare the structures and properties of rods and cones.

• Rods: Very sensitive to light, have one type of opsin protein

• Cones: Less sensitive to light, three kinds that detect different wavelength (red, green, blue), has different kind of opsin protein for each type of cone

Explain why all rods detect the same wavelengths of light. Explain why rod signals are all interpreted as shades of gray.

Rods have one type of opsin protein, in which that protein determines which wavelengths of light retinal can absorb. Rod signals are not interpreted as colors, rather as shades of gray based on how strong the signal is.

What allows blue cones, red cones, and green cones to detect different wavelengths of light? What determines that blue cone signals are interpreted as blue, red cone signals as red, and green cone signals as green?

Interpretation/integration of cone signals allows us to perceive a wide range of colors, and each type of cone (color) has a different opsin protein that determines which wavelength it detects.

Foods high in vitamin A (e.g. carrots) are often said to improve your ability to see at night. Explain why consuming more vitamin A could improve your ability to see in the dark AND in brighter light.

Retinal is made from vitamin A, in which vitamin A is used to repair straight retinal. Consuming more vitamin A could improve your ability to see in both light and dark as retinal is replenished with more vitamin A available.

Describe the steps from when light enters your eyes to when signals from a photoreceptor reach interneurons in your brain (i.e. which cells detect the light, which cells they then communicate to, etc.).

Photoreceptors absorb light, which decreases inhibitory neurotransmitter release as a result of change in membrane potential. This decrease in inhibitory neurotransmitter alters the membrane potential of bipolar cells, which releases excitatory neurotransmitter. The excitatory neurotransmitter then reverses membrane potential of ganglion cells and sends an action potential to the brain IF the change reaches threshold.

You leave a brightly lit hallway and enter a dark room. Explain why you can’t see very well right away, but over time you are able to see more clearly.

When in the brightly lit hallway, your retina becomes used up (straight) and is unable to absorb light. As the retina repairs into the bent form, you are able to see better over time in the dark room as retina can absorb light again.

Why do objects appear sharper and more distinct in bright light, but fuzzier in dim light?

Objects appear sharper in bright light as signals from few cones are transmitted to one bipolar cell; objects appear fuzzier in dim light as signals from many rods are transmitted to one bipolar cell.

Find someone you know who hasn’t learned about the human sensory system and explain the cause of color blindness to them.

Individuals who have color blindness lack the functional cones that are needed to detect those colors (for example, if someone is red-green colorblind, they don’t have functional red or green cones).

How are chemoreceptors similar to photoreceptor cells? How are they different?

• Similarities: Both are sensory receptor cells that has receptor proteins that interact to alter the membrane potential and create action potentials

• Differences: Chemoreceptors interact with chemicals, while photoreceptors interact with light wavelengths

What determines which chemicals a chemoreceptor can detect?

Specific chemical detection is based on the receptor proteins of the chemoreceptors and what specific chemical matches with the receptor protein.

You put a piece of lemon in your mouth. In general terms, explain why your reaction is “sour!” rather than “sweet!”

Our reaction is “sour” rather than “sweet” because the chemicals within the lemon are specific towards chemicals our taste buds detect that determine the type of taste (sour, sweet, etc.). Our “sour” taste buds detect the “sour” chemical and send a signal to our brain that says we are tasting something sour.

Humans can detect many different bitter-tasting chemicals, but cannot distinguish between them. Use what you know about chemoreceptors, receptor proteins, and perception to propose a reasonable hypothesis to explain why.

Humans can’t distinguish between different bitter-tasting chemicals because our taste processing region can only receive/interpret signals that determine the type of taste, not the particular chemical to name.

Many spicy foods cause people to experience a burning sensation. Propose a hypothesis to explain this observation.

Spicy foods cause people to experience a burning sensation because the strength of the chemical stimulus pushes the membrane potential well above the threshold and results in several action potentials that create a burning sensation.

Review the experiment we discussed that assessed the ability of individual papillae to detect chemicals associated with different tastes. Explain why it was important to determine whether droplets of solution applied to individual papilla spread on a person’s tongue in order to test their hypothesis.

It was important to determine whether multiple papilla were detecting the solution or not.

In the taste experiment, participants rinsed their mouths with distilled water and there was a one minute pause between each solution application. Every 10 trials, participants took a five minute break. Thinking about what we’ve discussed related to the human sensory system, explain why these breaks were important. Hint – Think about what might happen if a taste receptor was repeatedly stimulated over a long period of time.

These breaks were important so that participants could cleanse their taste palette with water and make sure that multiple solutions weren’t being tasted at the same time.

You identify a papilla that’s only able to detect chemicals associated with one taste (e.g. sour). Propose a reasonable hypothesis to explain why the papilla can only detect one taste.

The papilla can only detect one taste because it has receptor proteins that can only detect one chemical that corresponds to that particular taste.

Why can humans detect a much wider range of smells than tastes?

We have more unique receptor proteins in our olfactory receptor cells than our papillae.

What’s the role of hormones in maintaining homeostasis?

Hormones serve as signaling molecules to communicate to our brains if we need more or less of something, or if we’re all good.

Write a sentence that explains why it is important that a particular type of hormone receptor is specific for a certain kind of hormone rather than interacting with many different types of hormones.

To ensure a particular response occurs within the cell, it’s important that a particular type of hormone receptor is specific for a certain kind of hormone.

Your liver and muscle cells respond differently to the hormone insulin. Based on what we’ve discussed, what’s the most reasonable hypothesis to explain why insulin causes different responses in your muscle vs. your liver cells.

Insulin causes different responses in your muscle vs. liver cells because it responds differently when interacting with different receptors on different cells (excitatory on one, while inhibitory on another).

Heart muscle cells and skeletal muscle cells (the ones attached to your bones) both respond to thyroid hormones. Thinking about what we’ve discussed, what does that tell you about both heart and skeletal muscle cells?

Both of these cells have receptor proteins for thyroid hormones.

Describe the differences between a neuron, a neurosecretory cell, and an endocrine cell.

• Neuron: Receives/sends nervous system signals

• Neurosecretory Cell: Receives/sends BOTH nervous and endocrine system signals

• Endocrine Cell: Produces/releases hormones in response to specific signals

Make a list of observations that would allow you to determine whether a chemical should be classified as a hormone or a neurotransmitter. What observations would not be helpful (i.e. what would you expect to see for both a neurotransmitter and a hormone)?

• Helpful: Hormones are found in the bloodstream, while neurotransmitters are not

• Not Helpful: Both must interact with a receptor protein to cause a response in a cell, and both communicate to cells that are not neurons

Why is it important that mechanisms exist to remove hormone signals from your bloodstream?

A particular hormone would not want to be utilized when not necessary, so removing the hormone signals from our bloodstream is important to eliminate unnecessary signaling that could interfere with other signals.

Explain the difference between synergistic and antagonistic hormones. Use an example if it helps.

• Synergistic: Two hormones that create the same response

• Antagonistic: Two hormones that create opposite/counteracting responses

What allows the hypothalamus to act as the communication link between your nervous and endocrine systems?

The hypothalamus integrates/transmits both nervous and endocrine system signals, allowing communication between both systems.

Identify at least two ways control of hormone signaling by your hypothalamus and pituitary gland is different from how your nervous system control center (brain and spinal cord) works.

• Signals for hormones travel through the bloodstream while signals for neurotransmitters travel through synapses/synaptic cleft

• The hypothalamus (brain) signals the pituitary gland while the nervous system signals the brain

Describe the relationship between your hypothalamus, anterior pituitary, and posterior pituitary (i.e. how and in what directions is information communicated between them).

The hypothalamus communicates information relating to the endocrine system to both the anterior and posterior pituitary. The anterior pituitary releases hormones controlled by hypothalamus hormone signals that communicate to endocrine organ cells and other body cells. The posterior pituitary releases hormones in response to nervous system signals from the brain.

Describe how insulin and glucagon regulate blood glucose levels, and explain why glucagon and insulin are an example of antagonistic hormones.

Insulin and glucagon regulate blood glucose levels by negative feedback loops (insulin decreases blood glucose and glucagon increases blood glucose). These two hormones are antagonistic since they produce opposite/counteracting responses.

If the alpha cells of your pancreas could no longer produce glucagon, how would that affect the ability of your body to regulate blood glucose levels? What if target cells lost the ability to respond to glucagon signals? Now answer the same questions for beta cells and insulin.

• Glucagon: Blood glucose will continue to fall and target cells will not produce/release glucose

• Insulin: Blood glucose will continue to rise and target cells will not store glucose from bloodstream

Propose a reasonable hypothesis to explain why liver, muscle, and adipose (fat) cells respond to insulin, but only liver cells respond to glucagon.

Only liver cells respond to glucagon because liver cells have receptor proteins for glucagon, while muscle and adipose cells don’t.

Explain why regulation of insulin by blood glucose levels is an example of negative feedback, then do the same thing for glucagon.

For both hormones, the response leads to a change in blood glucose levels to returnInsl levels back to normal.

Find someone who is not in the class and explain to them why virtually all type 1 diabetics are treated with insulin injections, while insulin injections are less effective at treating type 2 diabetes.

Insulin injections are less effective for treating type 2 than type 1 because type 2 has cells that are resistant to insulin, making insulin injections less impactful for an effective response (type 1 can’t produce insulin entirely).

In what way(s) are the adrenal gland and pituitary gland similar? Identify at least one difference between the adrenal gland and pituitary gland.

• Similarities: Both are split into two different sections and produce hormones in response to signaling

• Differences: Pituitary responds directly from hypothalamus while adrenal doesn’t (responds from PNS neuron or hormones from pituitary)

Compare the signals involved and the changes that occur during your short-term vs. long-term stress responses.

• Short-Term: Nervous system signaling is involved, and results in increased heart rate, airways opening, and increased blood glucose levels

• Long-Term: Hormone signaling is involved, and results in liver cells releasing glucose, immune system cells reducing activity, and inhibited growth

Explain why hormones released by cells in your adrenal medullae function in your short-term stress response and hormones released by cells in your adrenal cortices are important for your long-term stress response.

Epinephrine (from adrenal medullae) functions for immediate action by increasing heart rate and blood glucose levels while cortisol (from adrenal cortices) function for long-term glucose availability by reducing activity.

A drug prevents cells in your hypothalamus from detecting cortisol. How would the levels of CRH (the releasing hormone that promotes ACTH release), ACTH, and cortisol during long-term stress be different in the presence of the drug vs. without the drug? What if cells in your anterior pituitary could no longer respond to cortisol? What if cells in your anterior pituitary could no longer respond to CRH?

• If drug is present: More CRH will be released as hypothalamus thinks no cortisol is present, which would increase release in ACTH, and then increase release in cortisol

• If cells can’t respond to cortisol: More ACTH will be released, with more cortisol being released, but more cortisol would decrease release of CRH

• If cells can’t respond to CRH: Less ACTH will be released, with less cortisol being released, but less cortisol would increase release of CRH

Describe the roles/functions of each of the endocrine system organs we discussed (hypothalamus, pituitary gland, pancreas, and adrenal glands).

• Hypothalamus: Main control center of the endocrine system as it integrates/transmits endocrine system hormone signals

• Pituitary Glands: Releases hormones in response to hypothalamus signals, which communicate to other cells in the body

• Pancreas: Regulates blood glucose levels in response to high or low levels

• Adrenal Glands: Triggers and regulates many of the changes that occur in stress response

Give one example of a hormone we discussed whose release is controlled by hypothalamus signals. Give one example of a hormone we discussed whose release is NOT controlled by hypothalamus signals.

• Controlled: CRH (releasing hormone controlled by neurosecretory cells receiving hypothalamus signals that’s important for the production of ACTH in long-term stress)

• Not Controlled: Insulin (hormone controlled by beta cells that’s important for lowering blood glucose levels)