Question

Which of the following are chemical changes? Which are physical changes? a. the cutting of food b. interaction of food with saliva and digestive enzymes c. proteins being broken down into amino acids d. complex sugars being broken down into simple sugars e. making maple syrup by heating maple sap to remove water through evaporation f. DNA unwinding

Short answer

Physical changes: a. the cutting of food, e. making maple syrup by heating maple sap to remove water through evaporation, and f. DNA unwinding. Chemical changes: b. interaction of food with saliva and digestive enzymes, c. proteins being broken down into amino acids, and d. complex sugars being broken down into simple sugars.

Step-by-step solution

a. the cutting of food

The cutting of food involves changing the size and shape of the food without altering its chemical composition. Therefore, it is a physical change.

b. interaction of food with saliva and digestive enzymes

The interaction of food with saliva and digestive enzymes involves chemical reactions that break down the food into simpler substances. This process changes the chemical composition of the food. Thus, it is a chemical change.

c. proteins being broken down into amino acids

The breakdown of proteins into amino acids involves chemical reactions that transform the proteins into different substances (amino acids). This means the chemical composition of the substances has changed, so it is a chemical change.

d. complex sugars being broken down into simple sugars

The process of breaking down complex sugars into simple sugars involves chemical reactions that change the substances' chemical composition. Therefore, it is a chemical change.

e. making maple syrup by heating maple sap to remove water through evaporation

Making maple syrup by heating maple sap involves removing water through evaporation, which results in a change in physical appearance and state but not in the chemical composition of the maple sap. As a result, it is a physical change.

f. DNA unwinding

DNA unwinding is a process where the double helix structure of DNA temporarily separates into two single strands. This unwinding does not involve any chemical change in the DNA's composition; instead, it involves a change in its physical structure. Thus, it is a physical change.

Key concepts

Chemical Reactions

Chemical reactions involve processes where substances undergo changes in their chemical composition. When food interacts with saliva and digestive enzymes, chemical reactions take place. These reactions help in breaking down the food into simpler substances, making nutrients easier for the body to absorb. During these reactions, bonds between molecules are broken and new bonds are formed, resulting in new substances being created.

For example, when proteins in food break down into amino acids, it's a chemical change. This involves an alteration to the molecular structure as the proteins are turned into entirely different molecules known as amino acids. Similarly, complex sugars undergo chemical reactions to transform into simple sugars, allowing the body to easily use them as energy.

Physical Changes

Physical changes refer to modifications that affect the form of a substance, but not its chemical identity. When you cut food, you're changing its size and shape, but its chemical structure remains unchanged. This is a typical physical change. Likewise, when DNA unwinds, it simply alters its physical structure temporarily, without changing its chemical composition.

The making of maple syrup by heating maple sap is another example of a physical change. Here, the water in the sap is removed by evaporation, leaving behind a more concentrated syrup. The sap's chemical composition remains unchanged during this physical process.

Digestive Enzymes

Digestive enzymes play a crucial role in the breakdown of food into smaller, absorbable components. These enzymes are biological catalysts that speed up chemical reactions in the digestive system. When food comes into contact with saliva, enzymes like amylase start breaking down starches into simpler sugars.

This interaction represents a chemical change, as the enzymes alter the chemical bonds within the food molecules. Without digestive enzymes, the body wouldn't be able to efficiently convert food into the essential nutrients it needs for energy and growth.

Protein Breakdown

Protein breakdown is a process that involves converting proteins into amino acids through chemical reactions. This occurs in the stomach and small intestine, aided by digestive enzymes such as pepsin and trypsin. These enzymes break the peptide bonds between amino acids, altering the protein's chemical structure into smaller units.

This chemical change is vital since amino acids are necessary for numerous bodily functions including building and repairing tissues, producing hormones, and supporting immune function. Without this breakdown, proteins wouldn't be in a usable form for the body.

Evaporation

Evaporation is a physical process where a liquid turns into vapor. During the making of maple syrup, evaporation is used to remove water from the maple sap. As the sap is heated, water molecules escape into the air as steam, leaving behind a more concentrated syrup. This change affects the physical state and concentration of the sap but does not alter its chemical structure.

Evaporation is a common method for concentrating liquids or separating components based on their boiling points, making it an essential technique in numerous food production and industrial processes.