AP Bio Mid-Term

The carbohydrates glucose, galactose, and fructose have the same chemical formula (C6H12O6) but different structural formulas, as represented in the figure.

sugar structure

Which of the following statements about glucose, galactose, and fructose is most likely true?

• They are all proteins.
• They have different chemical formulas.
• The carbohydrates have different properties because they have different arrangements of carbon, hydrogen, and oxygen atoms.

• They are all liquids at room temperature.

Which of the following statements best describes how organisms such as rabbits obtain the carbon necessary for building biological molecules?

• By breathing in carbon dioxide from the air
• By absorbing carbon from the soil
• By converting nitrogen into carbon
• Rabbits eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules.

Researchers compared similar proteins from related organisms in different habitats. They found that the proteins from organisms living in harsh environments had a greater number of cysteine amino acids than did proteins from organisms not living in harsh environments. The structure of cysteine is shown. Bonds can form between the sulfur atom of different cysteine amino acids (S-S bonds).

• S-S bonds
• The change leads to increased protein stability because of an increased number of S-S bonds in the tertiary structure of the proteins.

• O-O bonds
• H-H bonds

Figure 1 represents a nucleic acid fragment that is made up of four nucleotides linked together in a chain.

nucleic acid fragment

Which of the following characteristics of Figure 1 best shows the fragment is RNA and not DNA?

• The identity of each nitrogenous base

• The presence of adenine (A) instead of cytosine (C)
• The presence of thymine (T) instead of uracil (U)
• The presence of uracil (U) instead of thymine (T)

Water and ammonia interact to form hydrogen bonds, as represented in the figure.

hydrogen bond

Which statement best helps explain the formation of the hydrogen bond represented in the figure?

• Water and ammonia molecules repel each other, causing the formation of hydrogen bonds.
• The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge.

• The partially positive and partially negative charges on water and ammonia molecules allow them to form hydrogen bonds.
• The hydrogen bond is formed due to the strong covalent bond between water and ammonia molecules.

The figure shows a model of the exchange of matter between the organisms that live together in an aquarium. The model includes matter exchange between plants, fish, and bacteria. The bacteria are represented as rod-shaped organisms living in the gravel at the bottom of the aquarium.

exchange of matter

Which of the following statements best describes how molecules released by the fish become nutrients for the plants?

• The ammonia molecules released by the fish are converted by the bacteria to nitrates, which are used by the plants to make proteins and nucleic acids.

• The fish eat the molecules released by the plants, and then the plants absorb the nutrients from the fish waste.
• The molecules released by the fish are broken down by the water in the aquarium, and the resulting nutrients are absorbed by the plants.
• Bacteria in the gravel break down the molecules released by the fish, and the resulting nutrients are absorbed by the plants.

Figure 1 represents a common process that occurs in organisms.

structural formula for a common biological reaction

Which of the following is an accurate description of the process shown in Figure 1?

• A common biological reaction
• A process that does not occur in organisms
• A chemical reaction in a non-living system
• The formation of a covalent peptide bond in a dehydration synthesis reaction

Which of the following best describes the structures of carbohydrates?

• Composed of nitrogen, hydrogen, and oxygen
• They occur as monomers, chains of monomers, and branched structures.

• Composed of carbon, hydrogen, and nitrogen
• Composed of carbon, hydrogen, and oxygen

The sequences for two short fragments of DNA are shown above. Which of the following is one way in which these two segments would differ?

• Temperature of the DNA
• Color of the DNA
• Segment 1 would become denatured at a lower temperature than would segment 2 because A-T base pairs have two hydrogen bonds whereas G-C base pairs have three.

• Nucleotide sequence

Which of the following correctly illustrates a dipeptide and an amino acid in the optimal position to form a tripeptide?

• Option D
• 
• Option B
• Option A