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

Understanding a chemical change is essential when studying the nature of matter. A chemical change is a process that alters the chemical composition of a substance, leading to the formation of one or more new substances with different properties. These changes are also referred to as chemical reactions. Common indications of a chemical change include a change in color, the production of gas (bubbles), the formation of a precipitate (a solid from a liquid solution), or a change in temperature or light.

For example, the interaction of food with saliva and digestive enzymes is a chemical change. Saliva contains enzymes like amylase and lipase, which start the breakdown of certain nutrients. This results in the formation of new substances, such as glucose from starches, fundamentally changing the chemical nature of the food consumed. Similarly, proteins that are broken down into amino acids during digestion represent a chemical change. The large, complex protein molecules are dismantled into smaller, simpler amino acid units, creating an entirely different substance in terms of chemical composition.

In contrast, a physical change involves a change in the physical appearance or state of a substance without affecting its chemical identity. This means that the substance undergoing a physical change maintains its original properties despite its new form. Physical changes are often reversible, and no new substance is produced. Examples of physical changes include changes in the state of matter, such as freezing, melting, or boiling, as well as changes in size or shape.

When you cut food into smaller pieces, this represents a physical change - the food's size and shape are altered, but its chemical makeup remains the same. Another instance is the unwinding of DNA. DNA molecules may uncoil or unwind as part of natural biological processes, but the sequence of nucleotides – the chemical composition – does not change. Therefore, DNA unwinding is classified as a physical change. The extraction of maple syrup through evaporation is also a physical process; while water is removed and the syrup is concentrated, the sugar composition doesn't change.

Digestive enzymes play a crucial role in the body's process of breaking down food into nutrients that can be absorbed and utilized. These enzymes are biological catalysts that speed up the chemical reactions involved in digestion. There are several types of enzymes, and each one is specific to the substrates it works on.

• Proteases break down proteins into amino acids.
• Lipases break down fats into fatty acids and glycerol.
• Carbohydrases, such as amylase, break down carbohydrates into simple sugars like glucose.

These enzymes are mainly secreted by the pancreas and the lining of the small intestine. Their activity results in chemical changes as they break down complex molecules into simpler ones, enabling the body to absorb and assimilate these smaller units as needed. Without these enzymes, our bodies would not be able to process the food we eat.

Amino acids are the building blocks of proteins, one of the most critical macromolecules in living organisms. Proteins are made up of long chains of amino acids that are folded into specific three-dimensional structures essential for function. There are twenty different amino acids found in proteins, and the sequence in which they are linked determines the protein's structure and function.

Amino acids are organic compounds composed of an amino group (-NH2), a carboxyl group (-COOH), and a characteristic side chain that gives each amino acid its unique properties. When we ingest proteins, digestive enzymes called proteases cleave the peptide bonds between amino acids, resulting in a chemical change where the large protein molecules are decomposed into the smaller, absorbable amino acids. These are then transported throughout the body and reassembled into new proteins that support growth, repair tissues, and perform various other vital functions.