Cell Biology Answers

27
Which of the following statements describes saltatory conduction?
Conduction occurs exclusively at nodes of Ranvier.
Voltage-gated sodium channels open, depolarizing unmyelinated axons.
Voltage-gated potassium channels open, depolarizing myelinated axons
Conduction occurs along unmyelinated axons, decreasing conduction velocity.

28
What is temporal summation?
combination of postsynaptic potentials due to the repeated stimulation of a single synapse
predisposition for a neuron to be excited due to previous stimuli shifting the baseline potential towards threshold
addition of postsynaptic potentials due to the simultaneous stimulation of multiple synapses
interaction between inhibitory postsynaptic potentials and excitatory postsynaptic potentials

23.
What is an equilibrium potential
the potential across a membrane at which flow of a specific ion into the cell equals the flow out of the cell
the difference in positive and negative charge across the membrane of an unstimulated, resting cell
the transmembrane potential at which there is no movement of any individual ions into or out of the cell



26
Action potentials in neurons involve opening and closing of voltage-gated Na and K ion channels. Place the events of an action potential in order, starting and ending with a cell at its resting membrane potential.
1. K rushes out the cell, causing repolarization 2. a graded potential brings the membrane to threshold potential. 3. K channels fully open, and Na channel inactivation gates close. 4. Na rushes into cell, causing membrane depolarization. 5. Fast Na and slow K channels are activated. 6. K channels close slowly resulting in hyperpolarization Na channel gate reset

19.
Which of the following describes how neurons use neurotransmitters to communicate with one another?
The axons of one neuron connect to the axons of another neuron to relay information through neurotransmitter release.
At synapses, dendrites release neurotransmitters that are recognized by proteins on axons.
Axons fuse with dendrites to produce a continuous cellular body that allows neurotransmitters to flow from one neuron to another.
At synapses, axons release neurotransmitters that are recognized by proteins on dendrites.

21.
Select the descriptions that apply to the sodium-potassium pump. More than one answer
Sodium ions and potassium ions move into and out of the plasma membrane by osmosis.
The pump helps to maintain the concentration of sodium and potassium ions in living cells.
The pump is an active mechanism for transporting ions through the plasma membrane.
The concentration gradient of the ions determines the direction of movement through the pump.

What is the primary benefit for an animal to excrete nitrogenous waste as uric acid?
Uric acid requires less energy to synthesize than urea.
Uric acid is highly toxic to predators.
Uric acid increases efficiency of kidney function.
Uric acid improves gastric absorption of nucleic acids.
Uric acid helps an animal to conserve water.


The kidney of a given land animal has particularly short loops of Henle. Predict the type of environment in which this animal lives.
a. temperate forest
b. arid mountain range
c. desert
d. wetland

Which of the following statements describes saltatory conduction?
Voltage-gated sodium channels open, depolarizing unmyelinated axons
Voltage-gated potassium channels open, depolarizing myelinated axons.
Conduction occurs exclusively at nodes of Ranvier.
Conduction occurs along unmyelinated axons, decreasing conduction velocity.

What is temporal summation?
addition of postsynaptic potentials due to the simultaneous stimulation of multiple synapses
interaction between inhibitory postsynaptic potentials and excitatory postsynaptic potentials
combination of postsynaptic potentials due to the repeated stimulation of a single synapse
predisposition for a neuron to be excited due to previous stimuli shifting the baseline potential towards threshold

Select the descriptions that apply to the sodium-potassium pump. (more than one answer)
The concentration gradient of the ions determines the direction of movement through the pump.
The pump helps to maintain the concentration of sodium and potassium ions in living cells.
Sodium ions and potassium ions move into and out of the plasma membrane by osmosis.
The pump is an active mechanism for transporting ions through the plasma membrane.

What is an equilibrium potential?
the state at which positive and negative charge distribution for an ion across a membrane is equal, therefore there is no net ion movement
the potential across a membrane at which flow of a specific ion into the cell equals the flow out of the cell
the transmembrane potential at which there is no movement of any individual ions into or out of the cell
the difference in positive and negative charge across the membrane of an unstimulated, resting cell

The Cambrian explosion was
a sudden increase in new species that challenges the fundamental correctness of evolution.
the asteroid impact near the Yucatan Peninsula that likely caused a mass extinction of dinosaurs and other species.
the sudden diversification of animal life from simple organisms to all the basic body types known today
the sudden appearance of dinosaurs in the fossil record during the Cambrian period.

Which of the following describes how neurons use neurotransmitters to communicate with one another?
At synapses, dendrites release neurotransmitters that are recognized by proteins on axons.
At synapses, axons release neurotransmitters that are recognized by proteins on dendrites.
Axons fuse with dendrites to produce a continuous cellular body that allows neurotransmitters to flow from one neuron to another.
The axons of one neuron connect to the axons of another neuron to relay information through neurotransmitter release.

The study of biology can be understood through the organizational hierarchy of life. Each level of life builds upon the next level, and this increasing complexity is what leads from molecules up to an entire ecosystem. How is the tissue level different from the other levels of life?
A tissue is an individual living thing, such as a bacterium, fungus, protist, plant, or animal.
A tissue is a group of similar cells that work together to perform a function.
A tissue is a group of multiple organs that work together to perform vital functions for the organism.
A tissue is a collection of molecules and reactions that form the basic unit of all living things.

What is the function of Hox genes during development?
maintain pluripotency in embryonic stem cells
promote cleavage in the early embryo
encode enzymes that provide cellular energy for the developing embryo
direct the formation of the appropriate structure at a given location in the embryo

After an mRNA strand has been transcribed from DNA, it must be processed before translation can take place. Which of the following statements are true about the RNA editing process?
Additional amino acids are added before translation occurs,
noncoding segments are removed and exons are joined together,
a cap is added to one end of the mRNA,
editing occurs in the cytosol as the new mRNA strand leaves the nucleus. (more than one answer)


Which statement describes an operon?
Heritable changes in gene expression that occur without altering the DNA sequence,
mRNA modifications, such as the addition of a 5\'-cap and 3\' poly-A tail and the removal of introns,
a gene cluster controlled by a single promoter that transcribes to a single mRNA strand,
the processing of exons in mRNA that results in a single gene coding for multiple proteins,
protein modifications, such as the addition of a functional group, or alternate folding of the protein

Intracellular receptors are located in either the cytoplasm or the nucleus. Which type of ligands binds to intracellular receptors? small hydrophobic molecules, large water soluble molecules, small water soluble molecules, or large polar molecules.

Select the description of an exon - noncoding portion of a DNA sequence that is removed from pre mRNA, altered guanine nucleotide added to the front of pre-mRNA, portion of a DNA sequence that is not removed from pre-mRNA and is expressed in the protein, or sequence of adenine nucleotides added onto the end of pre-mRNA.