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

a. Physical change b. Chemical change c. Chemical change d. Chemical change e. Physical change f. Physical change

Step-by-step solution

a. The cutting of food

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

b. Interaction of food with saliva and digestive enzymes

This process occurs during digestion when enzymes in saliva break down food chemically into smaller molecules. The chemical composition of the food changes in this process. Hence, it is a chemical change.

c. Proteins being broken down into amino acids

Breaking down proteins into amino acids involves breaking chemical bonds within the protein molecules and forming new bonds to create amino acid molecules. This process alters the chemical composition of the proteins, making it a chemical change.

d. Complex sugars being broken down into simple sugars

In this process, complex sugar molecules (such as starch) are broken down into simpler sugar molecules (such as glucose) through hydrolysis, which involves breaking chemical bonds and changing the chemical composition of the sugar molecules. Thus, it is a chemical change.

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

Heating maple sap to remove water through evaporation only separates the water from the maple syrup, not changing the chemical composition of the maple syrup or the water. This process is a physical change since it involves a change in state (from liquid to vapor) but not a change in chemical properties.

f. DNA unwinding

DNA unwinding involves the separation of the double-stranded DNA helix structure without breaking the chemical bonds responsible for the base pairing and without altering its nucleotide sequence; it doesn't change the chemical composition of the DNA molecule. This process is a physical change, as it involves changes in the shape and structure of DNA but not in its chemical properties.