Mastering Biology

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Which of these extracellular signal molecules could diffuse through a plasma membrane and bind to an intracellular receptor?


A(n) _____ is an example of a signal molecule that can bind to an intracellular receptor and thereby cause a gene to be turned on or off.


Thyroid hormones bind to _____ receptors.


Which of these is a logical signal transduction pathway?

A G-protein-linked receptor activates G protein, which activates phospholipase C, which cleaves a membrane lipid to form IP3, which binds to a calcium channel on the ER, which opens to release calcium ions into the cytoplasm, which bind to an intracellular enzyme that carries out a response.

What role does a transcription factor play in a signal transduction pathway?

By binding to DNA it triggers the transcription of a specific gene.

Which of the following, when activated by a signal transduction pathway, moves from the cytoplasm to the nucleus of a cell?

Transcription factor

A signal transduction pathway is initiated when a _____ binds to a receptor.

signam molecule

Which of these acts as a second messenger?

Cyclic AMP

Calcium ions that act as second messengers are stored in _____.

endoplasmic reticula

_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell’s cytoplasm.

Phospholipase C … IP3 …. Ca2+

A protein kinase activating many other protein kinases is an example of _____.


Which type of hormone is lipid soluble?


Which molecules determine the tissue specificity of hormones?


True or false? Lipid-insoluble hormones affect their target cells by binding to receptors inside the cell.


Which of the following statements about lipid-soluble hormones is true?

They act by affecting the transcription of genes.

Which of the following is a structure that allows hormone-receptor complexes to bind to specific DNA sequences?

Zinc finger

What is the role of cAMP in the signal transduction pathway activated by epinephrine?

It binds to and activates protein kinase A, which then phosphorylates other enzymes.

True or false? For a signal transduction pathway to be activated, hormones must be present in the bloodstream at very high concentrations.


Vertebrates have two major communication and control systems: the endocrine system and the nervous system. Choose the correct statement describing the coordination of these systems.

Epinephrine functions as a hormone in the endocrine system and as a neurotransmitter in the nervous system.

Select the correct statement about feedback regulation in endocrine systems.

Some homeostatic control systems rely on pairs of negatively regulated hormone pathways, each counterbalance the other.

A neuron’s nucleus is located in its _____.

cell body

A nerve impulse moves toward a neuron’s cell body along _____.


A nerve impulse moves away from a neuron’s cell body along____.


An impulse relayed along a myelinated axon "jumps" from _____ to _____.

node of Ranvier … node of Ranvier

Axons insulated by a(n) _____ are able to conduct impulses faster that those not so insulated.

myelin sheath

What type of cell makes up the myelin sheath of a motor neuron?

Schwann cells

What part of a neuron relays signals from one neuron to another neuron or to an effector?

synaptic terminal

Which term describes the difference in electrical charge across a membrane?

Membrane potential

Resting neurons are most permeable to which of the following ions?


True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.


Which channel is mainly responsible for the resting potential of a neuron?

Potassium leak channel.

Which term describes an electrical signal generated by neurons?

Action potential

Which channel maintains the concentration gradients of ions across a neuronal membrane?

The sodium-potassium pump moving Na+ ions out and K+ ions in.

What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?

The sodium channel opens, and Na+ ions flow in.

Which of the following is true of a target cell?

It must have a receptor for the chemical signal.

A compound that is secreted in one part of the body and travels through the bloodstream to another part of the body where it has an effect is called a(n)


Protein signal molecules are not permeable to the cell membrane but can affect their target cells because

the target cells have cell membrane bound receptors specific to the signal molecule.

In a normal cell which of the following statements is correct.

The membrane potential is negative
The concentration of negative ions is greater outside than inside
The concentration of Na+ inside the cell is greater than outside
The concentration of K+ outside the cell is greater than inside

The membrane potential is negative.

In a portal system how many capillary beds does the blood flow through as it travels from the heart back to the heart?


Which structure is not part of a neuron?

Myelin sheath

Which of the following statements about action potentials in a given neuron is false?

They are propagated down the length of the dendrite.

True or false? Action potentials travel in only one direction down an axon because potassium channels in the neuron are refractory and cannot be activated for a short time after they open and close.


Which event triggers the creation of an action potential?

The membrane depolarizes above a certain threshold potential.

Which of the following terms describes how a neuronal membrane’s potential is altered in the presence of inhibitory signals?


Where in the neuron do action potentials begin?

Axon hillock

How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron’s membrane?

Sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon.

Which of these causes the release of neurotransmitter molecules?

an action potential reaching the end of the axon

The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____.

synaptic cleft

Neurons store neurotransmitter molecules in vesicles located within _____.

synaptic terminals

Which part of the eye is the opening through which light initially passes?


Which of the following statements does not describe a vertebrate eye?

It contains many light-sensing columns called ommatidia.

True or false? The "blind spot" in vertebrate eyes is a region of the retina that contains no photoreceptors.


Which part of the eye contains the densest concentration of cone cells?


Which part of the eye bends light to focus it on the retina?


Which of the following statements about photoreception is true?

The retinal molecule changes shape when it absorbs light.

True or false? Cone cells are color photoreceptors that use different retinal molecules to absorb different wavelengths of light.


Identify the correct statement(s) about the resting membrane potential of a cell.

1. Neurons are the only cells that have a charge difference across their membranes.
2. Potassium (K+) and sodium (Na+) gradients are maintained by active transport in a resting mammalian neuron.
3. Concentration gradients of potassium (K+) and sodium (Na+) across the plasma membrane represent potential energy.

2. Potassium (K+) and sodium (Na+) gradients are maintained by active transport in a resting mammalian neuron. 3. Concentration gradients of potassium (K+) and sodium (Na+) across the plasma membrane represent potential energy.

If the membrane potential of a neuron decreases, the membrane potential _____.

becomes more positive

Why is an action potential an all-or-none response to stimuli?

Because voltage-gated ion channels open when membrane potential passes a particular level

The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels?

Membrane depolarization first opens sodium channels and then opens potassium channels.

What causes the falling phase of the action potential?

Inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels

In a normal cell which of the following statements is correct

The membrane potential is negative

A membrane depolarization is generally caused by:

Na+ flowing into a cell

Excitable cells differ from other cells in that they have___in their membranes

voltage-gated Na+ and K+ channels

While membrane depolarizations can be variable, all action potentials are the same.


Action potentials in myelinated axons propagate:

using salutatory motion

Voltage gated Na+ channels have gates.


The portion of a neuron that transmits membrane potentials to the cell body is usually the:


A single neuron can synapse with other neurons


Post-synaptic cells respond to neurotransmitters through the neurotransmitter:

binding to a receptor

An EPSP is caused by the movement of and results in __________.

Na+, depolarization

The thick filaments of sarcomeres are composed of _____.


The thin filaments of sarcomeres are composed of _____.


A single muscle cell is referred to as a _____.

muscle fiber

During the course of muscle contraction the potential energy stored in ATP is transferred to potential energy stored in _____.

the myosin head

The release of _____ ions from the sarcoplasmic reticulum is required for skeletal muscle contraction.


Myosin heads bind to _____, which they then pull and cause to slide toward the center of the sarcomere.

thin filaments

Of these events, the first to occur when a motor neuron stops sending an impulse to a muscle is _____.

the pumping of calcium ions out of the cytoplasm and back into the sarcoplasmic reticulum

In the post-synaptic neuron with a resting potential of -70mV and a threshold of -50mV. Two EPSPs decrease the membrane potential by 15mV each and one IPSP increases the membrane potential by with a 15mV.
Does this post-synaptic cell fire an action potential?


True or false? The horizontal cells are involved in the integration of sensory information.


True or false? The rods and cone are involved in sensory transduction


True or false? The amacrine cells are responsible for amplifying the stimulus energy


During sensory adaptation your response to a stimulus___


The Central nervous System (CNS) consists of:

the brain and spinal cord

The somatic division_____

is under conscious control

If muscles can only shorten when stimulated how is it possible for you to move your limbs in at least two directions (flexed and extended):

by using pairs of muscles working in opposition to one another

The binding of actin to myosin during muscle contraction is regulated by


True or false? During a muscle contraction the space between the Z-lines will decrease.


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