Which of the following substances protects the skin from ultraviolet radiation?

 

Control.

A control group is a group in an experiment that does not receive the treatment or manipulation being tested and is used as a benchmark to measure how the other tested subjects do.

The control group is used to minimize the effects of all variables except the independent variable.

This allows researchers to determine if changes in the dependent variable are due to the manipulation of the independent variable or if they are due to some other factor.

Choice A.

Responding is not the correct answer because it refers to the dependent variable, which is the variable that is being measured in an experiment.

Choice B.

Manipulated is not the correct answer because it refers to the independent variable, which is the variable that is being manipulated in an experiment.

Choice D.

Variable is not the correct answer because it refers to any factor that can change in an experiment and can include both independent and dependent variables.

The approximate threshold value for mammalian neurons is -55 mV.

The threshold potential is the critical level to which a membrane potential must be depolarized to initiate an action potential.

Most often, the threshold potential is a membrane potential value between –50 and –55 mV

The membrane potential of a neuron is determined by the distribution of ions across the cell membrane.

At rest, the inside of a neuron is more negative than the outside due to the presence of negatively charged proteins and other molecules.

The movement of ions across the cell membrane can change the membrane potential.

For example, when sodium ions enter the cell, they make the inside of the cell more positive (less negative), causing depolarization.

Choice B is incorrect because -80 mV is below the typical threshold value for mammalian neurons.

Choice C is incorrect because +35 mV is above the typical threshold value for mammalian neurons.

Choice D is incorrect because 0 mV is above the typical threshold value for mammalian neurons.

The pH scale is a logarithmic scale that measures the acidity or alkalinity of a solution.

A solution with a pH of 7 is neutral, while a solution with a pH less than 7 is acidic and a solution with a pH greater than 7 is alkaline.

Because the pH scale is logarithmic, each whole number change in pH represents a tenfold change in acidity or alkalinity.

Therefore, a substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4.

Choice A.

A substance with a pH of 3 is two times more alkaline than a substance with a pH of 4 is not correct because it incorrectly states that the substance with a lower pH is more alkaline and also incorrectly states the magnitude of the difference in acidity or alkalinity.

Choice B.

A substance with a pH of 3 is two times more acidic than a substance with a pH of 4 is not correct because it correctly states that the substance with a lower pH is more acidic but incorrectly states the magnitude of the difference in acidity.

Choice D.

A substance with a pH of 3 is 10 times more alkaline than a substance with a pH of 4 is not correct because it incorrectly states that the substance with a lower pH is more alkaline.

The pleura is a double-layered serous membrane that covers each lung and lines the thoracic cage

The pleura is a vital part of the respiratory tract.

Its role is to cushion the lung and reduce any friction that may develop between the lung, rib cage, and chest cavity.

Each pleura (there are two) consists of a two-layered membrane that covers each lung.

The layers are separated by a small amount of viscous (thick) lubricant known as pleural fluid.

The pleura is comprised of two distinct layers: the visceral pleura and the parietal pleura.

The visceral pleura is the thin, slippery membrane that covers the surface of the lungs and dips into the areas separating the different lobes of the lungs (called the hilum).

Proteins.

Proteins are made up of amino acids which are organic molecules that contain both an amine functional group (–NH2) and a carboxylic acid functional group (– COOH).

Choice A, Lipids, is not the correct answer because lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, phospholipids, and others.

They do not contain both an amine and carboxyl group.

Choice B, Chitin, is not the correct answer because chitin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose.

It does not contain both an amine and carboxyl group.

Choice C, Cellulose, is not the correct answer because cellulose is an organic compound with the formula (C6H10O5)n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units.

It does not contain both an amine and carboxyl group.

Triple covalent bonds.

Nitrogen gas (N2) is an extremely stable molecule because it consists of two nitrogen atoms bonded together by a triple covalent bond.

A covalent bond is a type of chemical bond where atoms share electrons to form a molecule.

In a triple covalent bond, three pairs of electrons are shared between the two atoms, resulting in a very strong bond that makes the molecule extremely stable.

Choice A.

Ionic bonds is not correct because ionic bonds involve the transfer of electrons from one atom to another to form ions, which are then attracted to each other due to their opposite charges.

Nitrogen gas does not contain ions and is not held together by ionic bonds.

Choice B.

Hydrogen bonds is not correct because hydrogen bonds are weak electrostatic attractions between molecules that contain hydrogen atoms bonded to highly electronegative atoms such as oxygen or nitrogen.

Nitrogen gas does not contain hydrogen atoms and is not held together by hydrogen bonds.

Choice C.

Resonance bonds is not correct because resonance refers to the delocalization of electrons in a molecule where multiple Lewis structures can be drawn to represent the molecule.

Nitrogen gas has a single Lewis structure and does not exhibit resonance.

The polarity of water molecules explains its solvent abilities for certain substances.

Water is a polar molecule because it has a partial positive charge on one end and a partial negative charge on the other end due to the unequal sharing of electrons between the oxygen and hydrogen atoms.

This polarity allows water to dissolve other polar substances and ionic compounds.

Choice A.

Kinetic energy of liquid water molecules is not the correct answer because kinetic energy refers to the energy of motion and does not directly explain water’s solvent abilities.

Choice B.

High specific heat is not the correct answer because specific heat refers to the amount of heat required to raise the temperature of a substance and does not directly explain water’s solvent abilities.

Choice C.

High surface tension is not the correct answer because surface tension refers to the cohesive forces between liquid molecules and does not directly explain water’s solvent abilities.

The pulmonary veins are the vessels that carry oxygenated blood from the lungs to the left atrium of the heart.

Choice A is not correct because the superior vena cava carries deoxygenated blood from the upper body to the right atrium of the heart.

Choice B is not correct because the inferior vena cava carries deoxygenated blood from the lower body to the right atrium of the heart.

Choice C is not correct because the pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs.

Antidiuretic hormone (ADH), also known as vasopressin, is a hormone that helps regulate the amount of water in your body.

It works to control the amount of water your kidneys reabsorb as they filter out waste from your blood.

Choice A is not correct because an increase in the concentration of calcium in the glomerulus is not a physiological response caused by the release of antidiuretic hormone.

Choice C is not correct because a decrease in the concentration of calcium in the glomerulus is not a physiological response caused by the release of antidiuretic hormone.

Choice D is not correct because a decrease in water reabsorption in the collecting duct is not a physiological response caused by the release of antidiuretic hormone.

A catalyst is a substance that increases the rate of a chemical reaction without being consumed by the reaction.

As a result, the reaction is completed in a shorter amount of time.

Choice B is not correct because using a catalyst does not necessarily result in the formation of a more desirable product.

Choice C is not correct because using a catalyst does not necessarily result in the release of a greater amount of heat energy by the reaction.

Choice D is not correct because using a catalyst does not necessarily increase the yield of product.