biology unit 1

In vascular plants, water flows from root to leaf via specialized cells called xylem. Xylem cells are hollow cells stacked together like a straw. A student explains that evaporation of water from the leaf pulls water up from the roots through the xylem, as shown in Figure 1 Which statement describes how water is pulled up through the xylem to the leaves of the plant?

As water exits the leaf, hydrogen bonding between water molecules pulls more water up from below.

Which of the following best describes a structural similarity between the two molecules shown in Figure 1 that is relevant to their function?

Both molecules contain nucleotides that form base pairs with other nucleotides, which allows each molecule to act as a template in the synthesis of other nucleic acid molecules.

A student wants to modify model 1 so that it represents an RNARNA double helix instead of a DNADNA double helix. Of the following possible changes, which would be most effective in making model 1 look more like RNARNA than DNADNA? A

Changing the deoxyriboses to riboses by adding −OH groups

A researcher measured the temperature at which two different samples of double-stranded DNADNA denature (separate into single strands). Sample 11 denatured at a significantly lower temperature than sample 22 did. Based on the data, the researcher claims that the DNADNA in sample 22 is composed of a higher percentage of guanine and cytosine than the DNADNA in sample 11 is. Which of the following best supports the researcher's claim?

Guanine-cytosine pairs denature at a higher temperature because they have more hydrogen bonds between them than adenine-thymine pairs do.

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

Rabbits eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules.

Figure 1. A short segment of a double-stranded nucleic acid molecule Which of the following statements is correct about the molecule shown in Figure 1 ?

It is DNA because of the nucleotides present.

Polypeptides are continuously being formed and degraded. One of these processes is shown. Which statement is the most accurate description of the reaction shown in Figure 1?

It represents a polypeptide chain that is broken down through a hydrolysis reaction.

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?

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.

Which of the following describes a key difference among the 20 amino acids that are used to make proteins?

Some amino acids are hydrophobic.

Figure 1 shows three amino acids that are part of a polypeptide chain. Figure 2 shows the same section of the chain after a mutation has occurred. How might this change affect the structure and function of the protein?

The R-groupR-group of the new amino acid, valine, has different chemical properties than the R-groupR-group of cysteine. This will cause the protein to misfold and not function properly in the cell.

The figure shows the results of an experiment to investigate the effects of an enriched CO2CO2 environment on plant growth. Identical plants were separated into different groups and grown either in a standard CO2CO2 environment (400 ppm CO2CO2) or in an enriched CO2CO2 environment (700 ppm CO2CO2). Of the plants in each environment, half were grown under ideal conditions and half were grown under stressed conditions. Based on the figure, which statement best describes the observed relationship between atmospheric CO2CO2 enrichment and plant growth under ideal and stressed conditions?

The increase in atmospheric CO2CO2 resulted in a greater increase in plant growth under stressed conditions than under ideal conditions.

A mutation in the gene coding for a single-polypeptide enzyme results in the substitution of the amino acid serine, which has a polar R group, by the amino acid phenylalanine, which has a nonpolar R group. When researchers test the catalysis of the normal enzyme and the mutated enzyme, they find that the mutated enzyme has much lower activity than the normal enzyme does. Which of the following most likely explains how the amino acid substitution has resulted in decreased catalytic activity by the mutated enzyme?

The substitution altered the secondary and tertiary structure of the enzyme so that the mutated enzyme folds into a different shape than the normal enzyme does.

Which of the following is common feature of the illustrated reactions showing the linking of monomers to form macromolecules?

Monomers are joined by a covalent bond, and a water molecule is produced.

The molecular structures of linoleic acid and palmitic acid, two naturally occurring substances, are shown in the figure. Based on the molecular structures shown in the figure, which molecule is likely to be solid at room temperature?

Palmitic acid, because the absence of carbon-carbon double bonds allows the molecules to pack closely together.

A polypeptide is polymer of amino acids held together by peptide bonds. The process of dehydration synthesis creates these peptide bonds, as shown in Figure 1. As shown in Figure 1, an amino acid must have which of the following properties in order to be incorporated into a polypeptide?

The ability to form a covalent bond with both its NH2NH2 group and its COOH group

The carbohydrates glucose, galactose, and fructose have the same chemical formula (C6H12O6)(C6H12O6) but different structural formulas, as represented in the figure. Which of the following statements about glucose, galactose, and fructose is most likely true?

The carbohydrates have different properties because they have different arrangements of carbon, hydrogen, and oxygen atoms.

Which feature of model 1 best illustrates how biological information is coded in a DNADNA molecule?

The linear sequence of the base pairs

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

The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge.

Phosphorous (P) is an important nutrient for plant growth. Figure 1 shows Arabidopsis thaliana plants grown under phosphorus‐sufficient (left) and phosphorus‐starved (right) conditions for six weeks. Which of the following is the most likely reason for the difference in leaf growth?

The phosphorus-starved plant was unable to synthesize both the required nucleic acids and lipids, limiting growth.

As shown in the diagram, when environmental temperatures drop below freezing, a layer of ice typically forms on the surface of bodies of freshwater such as lakes and rivers. Which of the following best describes how the structure of ice benefits the organisms that live in the water below?

The water molecules in ice are farther apart than those in liquid water, so the ice floats, maintaining the warmer, denser water at the lake bottom.

The diagram shows how water can adhere to the xylem in the stems of plants, which contributes to water movement in the plant. Which of the following best explains how water is able to move upward from the roots of a plant, through its xylem in the stem, and out to the leaves?

Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.

A small protein is composed of 110 amino acids linked together in a chain. As shown in Figure 1, the first and last five amino acids in the chain are hydrophobic (have nonpolar and uncharged RR-groups), whereas the remaining 100 amino acids are hydrophilic (have charged or polar RR-groups). The nature of the RR-group determines if the amino acid is hydrophobic or hydrophilic. A mutation results in the production of a version of the small protein that is only 105 amino acids long, as shown in Figure 2. Five of the hydrophobic amino acids are missing from one end of the chain. Which of the following best depicts the tertiary structures of the two proteins in water? The diagrams in the options are not drawn to the same scale as those in Figure 1 and Figure 2.

when the hydrophobic acids are in the middle