What is the purpose of using PCR (polymerase chain reaction) in the laboratory?

Neurons communicate with each other through both electrical and chemical signals.

The electrical signal, or action potential, runs from the cell body area to the axon terminals, through a thin fiber called axon.

Neurons also communicate with one another at junctions called synapses.

At a synapse, one neuron sends a message to a target neuron—another cell.

Most synapses are chemical; these synapses communicate using chemical messengers.

Choice A is incorrect because neurons communicate not only through electrical signals but also through chemical signals.

Choice B is incorrect because neurons communicate not only through chemical signals but also through electrical signals.

Choice D is incorrect because neurons do not communicate through mechanical signals.

The correct answer is choice A. Golgi apparatus.

The Golgi apparatus is a membrane-bound organelle that is responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations.

Choice B is incorrect because mitochondria are responsible for energy production.

Choice C is incorrect because ribosomes are responsible for protein production.

Choice D is incorrect because the endoplasmic reticulum is responsible for lipid production and protein production, but not for modifying, sorting and packaging proteins and lipids.

Innate immunity represents the first line of defense to an intruding pathogen.

The innate immune system is a series of nonspecific defenses that make up the innate immune system.

These defenses are not directed against any one pathogen but instead provide a guard against all infection.

Choice A is incorrect because adaptive immunity is activated when pathogens are able to bypass innate immune defenses.

Choice B is incorrect because antibodies are part of the adaptive immune system and are produced by B cells.

Choice D is incorrect because T cells are part of the adaptive immune system and assist B cells or directly kill infected cells.

In a well-designed experiment, all variables apart from the treatment should be kept constant between the control group and treatment group.

This means researchers can correctly measure the entire effect of the treatment without interference from confounding variables.

Choice B) Independent variable and dependent variable is incorrect because these are not groups but rather variables.

The independent variable is manipulated by the experimenters while the dependent variable is measured to see if it changes as a result of the manipulation.

Choice C) Experimental group and non-experimental group is incorrect because a non-experimental group is not a term used in experimental design.

The correct term for the group that does not receive the treatment is control group.

Choice D) High level and low level of the independent variable is incorrect because these are levels of the independent variable, not groups.

In an experiment, there can be multiple levels of the independent variable, but they are applied to different groups (e.g.

control group, treatment group).

Immunologic memory is the hallmark of adaptive immunity.

Immunologic memory enables the host to mount a more rapid and efficient immune response upon subsequent exposure to the antigen.

Choice A is incorrect because rapid recruitment of immune cells to sites of infection and inflammation is a characteristic of innate immunity.

Choice B is incorrect because antigen-independent defense mechanisms are characteristic of innate immunity.

Choice D is incorrect because non-specific host-defense mechanisms are characteristic of innate immunity.

Atomic mass is very close to mass number but with some deviation in the decimal places.

Atomic mass is also known as atomic weight and is the weighted average mass of an atom of an element based on the relative natural abundance of that element’s isotopes.

The mass number, on the other hand, is a count of the total number of protons and neutrons in an atom’s nucleus.

Choice A is incorrect because atomic mass and mass number do not mean the same thing.

Choice B is incorrect because atomic mass is not always greater than mass number.

Choice C is incorrect because atomic mass and mass number are related.

The correct answer is choice D.

Genes that regulate cell division can become oncogenes when mutated.

Oncogenes are mutated genes that can contribute to the development of cancer.

In their non-mutated state, everyone has genes which are referred to as proto- oncogenes.

When proto-oncogenes are mutated or increased in numbers due to DNA damage, the proteins produced by these genes can affect the growth, proliferation, and survival of the cell, and potentially result in the formation of a malignant tumor.

Choice A is incorrect because mutations in oncogenes do not always result in the inhibition of cell division.

Instead, they can contribute to the development of cancer by affecting cell growth.

Choice B is incorrect because oncogenes are not only found in human cells but can be present in other organisms as well.
Choice C is incorrect because genes that regulate cell division can be found in viruses.

Ionization is the process in which an atom loses or gains electrons to form an ion.

An ion is an atom or molecule that has a net electrical charge due to the loss or gain of one or more electrons.

Choice B is not the best answer because oxidation refers to the loss of electrons from an atom or molecule.

Choice C is not the best answer because reduction refers to the gain of electrons by an atom or molecule.

Choice D is not the best answer because isotopic decay refers to the process in which an unstable atomic nucleus loses energy by emitting radiation

Hydrogen bonding is an interaction involving a hydrogen atom located between a pair of other atoms having a high affinity for electrons.

One atom of the pair (the donor), generally a fluorine, nitrogen, or oxygen atom, is covalently bonded to a hydrogen atom, whose electrons it shares unequally; its high electron affinity causes the hydrogen to take on a slight positive charge.

The other atom of the pair (the acceptor), also typically F, N, or O, has an unshared electron pair, which gives it a slight negative charge.

Mainly through electrostatic attraction, the donor atom effectively shares its hydrogen with the acceptor atom, forming a bond.

Choice B) The repulsion between the positive and negative charges of two molecules is incorrect because hydrogen bonding involves attraction, not repulsion.

Choice C) The attraction between two nonpolar molecules is incorrect because hydrogen bonding involves polar molecules.

Choice D) The attraction between two ionic molecules is incorrect because hydrogen bonding involves polar molecules and not ionic molecules.

The correct answer is choice A.

The superior vena cava is the largest vein in the human body that returns deoxygenated blood from the upper half of the body to the right atrium of the heart.

Choice B is incorrect because the inferior vena cava returns deoxygenated blood from the lower half of the body to the right atrium of the heart.

Choice C is incorrect because the pulmonary vein carries oxygenated blood from the lungs to the left atrium of the heart.

Choice D is incorrect because the renal vein carries deoxygenated blood from the kidneys to the inferior vena cava.