Anything that occupies space and has mass is called matter.
Missing Word
matter
Matter is any substance that takes up space and has mass. All matter, living or nonliving, is made of elements.
Category: Atoms and Ions
Question 2
The smallest unit of an element that still has that element's chemical properties is an atom.
Missing Word
atom
An atom is the smallest piece of an element that keeps the element's identity and chemical behavior. Atoms are made of protons, neutrons and electrons.
Category: Atoms and Ions
Question 3
The time needed for half of a sample of a radioactive isotope to decay is called its half-life.
Missing Word
half-life
Half-life is the time it takes for half of the unstable nuclei in a sample to decay. Each isotope has a characteristic half-life, which allows it to be used to date materials.
Category: Atoms and Ions
Question 4
A substance that dissolves other substances, as water dissolves table salt, is called a solvent.
Missing Word
solvent
A solvent is the substance in which another substance dissolves. Water's polarity makes it an excellent solvent for ions and polar molecules.
Category: Properties of Water
Question 5
The attraction of water molecules to one another, which produces surface tension, is called cohesion.
Missing Word
cohesion
Cohesion is the attraction between molecules of the same substance, which in water comes from hydrogen bonding. It creates surface tension strong enough to support a floating needle.
Category: Properties of Water
Question 6
Carbon can form 4 covalent bonds, which lets it build chains, branches and rings.
Missing Word
4
Carbon has four electrons in its outer shell and needs four more to fill it, so it forms 4 covalent bonds. This bonding flexibility is why carbon is the backbone of biological molecules.
Category: Carbon and Polymers
Question 7
The chemical reaction that breaks a polymer into its monomers by adding water is called hydrolysis.
Missing Word
hydrolysis
Hydrolysis splits a bond between monomers by adding a water molecule. It is the reverse of the dehydration reaction that builds polymers, and it is how food molecules are broken down during digestion.
Category: Carbon and Polymers
Question 8
Single-unit sugars like glucose and fructose, the monomers of carbohydrates, are called monosaccharides.
Missing Word
monosaccharides
Monosaccharides are the simplest carbohydrates and cannot be broken into smaller sugars. They join together to form disaccharides and polysaccharides.
Category: Carbohydrates
Question 9
Table sugar is the disaccharide sucrose, made of glucose joined to fructose.
Missing Word
sucrose
Sucrose is a disaccharide formed when glucose and fructose are joined by a dehydration reaction. It is the sugar commonly refined from sugarcane and sugar beets.
Category: Carbohydrates
Question 10
Plants store energy in their roots and seeds in the form of the polysaccharide starch.
Missing Word
starch
Starch is the energy-storage polysaccharide of plants, built from glucose units. Potatoes and grains are rich in it, and human digestive enzymes can break it down.
Category: Carbohydrates
Question 11
The tough polysaccharide that gives plant cell walls their strength is cellulose.
Missing Word
cellulose
Cellulose is a structural polysaccharide made of glucose units linked in a way that forms strong fibers. It is a major component of plant cell walls.
Category: Carbohydrates
Question 12
A single chain of amino acids, which folds on its own or together with other chains to form a working protein, is called a polypeptide.
Missing Word
polypeptide
A polypeptide is one continuous chain of amino acids joined by peptide bonds. A finished protein is made of one or more polypeptides folded into a specific shape that gives it its function.
Category: Proteins and Nucleic Acids
Question 13
Biological catalysts, which are usually proteins and act on specific substrates, are called enzymes.
Missing Word
enzymes
Enzymes speed up chemical reactions in cells without being used up. Each one is specific to the substrate it acts on, such as salivary amylase breaking down starch.
Category: Proteins and Nucleic Acids
Question 14
The molecule that stores the genetic information in all living organisms is DNA.
Missing Word
DNA
DNA, or deoxyribonucleic acid, is the hereditary material of all living organisms. It is a double helix of two strands of nucleotides.
Category: Proteins and Nucleic Acids
Question 15
Proteins are built from 20 different kinds of amino acids, each with its own side chain, or R group.
Missing Word
20
Proteins are assembled from a set of 20 amino acids. All share a central carbon bonded to an amino group, a carboxyl group and a hydrogen, and they differ only in their R group, which gives each amino acid its chemical character.
Category: Proteins and Nucleic Acids