All living things are made up of four classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids.

All living things are made up of four classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Macromolecules are large molecules composed of thousands of covalently connected atoms, also called polymers. A polymer is a long molecule consisting of many similar building blocks; the small building-block molecules are called monomers. All cells have thousands of different macromolecules, that vary among cells of an organism, vary more within a species, and vary even more between species. A huge variety of polymers can be built from a small set of monomers. What statements are true about the biological macromolecules. All biomolecules could be called carbon-based molecules. The monomers of DNA are nucleotides. Ready cellular energy comes in the form of lipids. Carbohydrates contain nitrogen and therefore differ from the other macromolecules Cell membranes are made, in part, from phospholipids. The monomers of of starch are monosaccharides.

The Correct Answer and Explanation is:

The following statements are true about biological macromolecules:

1. All biomolecules could be called carbon-based molecules: This is true because carbon is the central element in organic compounds. The four classes of biological macromolecules—carbohydrates, lipids, proteins, and nucleic acids—are all carbon-based, meaning they are primarily composed of carbon atoms bonded to hydrogen, oxygen, nitrogen, and sometimes sulfur or phosphorus. Carbon’s ability to form four covalent bonds allows it to serve as a backbone for a vast variety of molecules.
2. The monomers of DNA are nucleotides: This is correct. DNA (deoxyribonucleic acid) is a polymer made of repeating units called nucleotides. Each nucleotide consists of a phosphate group, a sugar molecule (deoxyribose), and one of four nitrogenous bases (adenine, thymine, cytosine, or guanine). These nucleotides are covalently linked together to form long chains that make up the DNA molecule.
3. Ready cellular energy comes in the form of lipids: This statement is somewhat misleading. Lipids, especially triglycerides, are used for long-term energy storage, not immediate energy. The primary source of quick, readily available energy for cells comes from carbohydrates, especially glucose. Carbohydrates are broken down rapidly during cellular respiration to release energy. Lipids, while important for energy storage and insulation, are not typically the immediate source of energy.
4. Carbohydrates contain nitrogen and therefore differ from the other macromolecules: This statement is false. Carbohydrates do not contain nitrogen. Carbohydrates are composed of carbon, hydrogen, and oxygen, with the general formula CnH2nOnC_nH_{2n}O_nCn​H2n​On​. The presence of nitrogen is characteristic of proteins and nucleic acids, not carbohydrates.
5. Cell membranes are made, in part, from phospholipids: This is true. Phospholipids are a major component of cell membranes. These molecules have a hydrophilic (water-attracting) “head” and two hydrophobic (water-repelling) “tails.” The arrangement of phospholipids in a bilayer forms the fundamental structure of cell membranes, providing a barrier that separates the cell from its environment.
6. The monomers of starch are monosaccharides: This is correct. Starch is a polysaccharide, and its monomers are simple sugars, specifically glucose molecules. Starch is composed of long chains of glucose units linked by glycosidic bonds. When plants need energy or need to store sugar, they store it in the form of starch.

In summary, biological macromolecules are diverse and play essential roles in living organisms, with each class of macromolecule having its own structure and function, as seen in the above examples.