Biology · Unit 1 · Paper 1

Chemistry of Life unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1 Paper 2 Paper 3

Each paper is built from this unit’s 34 terms and is the same for everyone, so a teacher can assign “Unit 1, Paper 1” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.

Suggested time 36 min 33 points0/17 attempted

Starch vs cellulose

Antiparallel strands

Phospholipid amphipathicity

R group

Capillary action

High specific heat of water

DNA vs RNA

Saturated vs unsaturated fat

Functional groups

Chargaff's rules

Denaturation

Evaporative cooling

Short answer 1. Define or explain: Buffer

3 pts

Short answer 2. Define or explain: Disulfide bridge

3 pts

Short answer 3. Define or explain: Lipid structure

3 pts

Short answer 4. Define or explain: Nucleotide structure

3 pts

Free response

9 pts

Catalase breaks hydrogen peroxide (H₂O₂) down into water and oxygen gas. Researchers investigating catalase from beef liver measured the initial reaction rate at a range of substrate concentrations, first with the enzyme alone and then with two compounds, X and Y, each added at a fixed concentration. TABLE 1. INITIAL REACTION RATE (μmol O₂ produced per minute) [H₂O₂] (mM) Enzyme alone + Compound X + Compound Y 2 18 6 9 5 36 13 18 10 54 25 27 20 70 43 35 40 78 64 39 80 82 77 40 The researchers also measured the rate of the enzyme alone at 10 mM H₂O₂ across a range of pH values: 12 μmol/min at pH 3, 41 at pH 5, 54 at pH 7, 30 at pH 9, and 4 at pH 11.

(a)(i) Identify the independent variable in the experiment summarized in Table 1.

(a)(ii) Describe the relationship between substrate concentration and reaction rate for the enzyme alone.

(b)(i) Explain why the reaction rate of the enzyme alone levels off at high substrate concentrations.

(b)(ii) Based on Table 1, identify which compound, X or Y, is acting as a competitive inhibitor.

(b)(iii) Justify your identification in (b)(ii) using the data.

(c)(i) Calculate the percent decrease in reaction rate caused by Compound Y at 40 mM H₂O₂ compared with the enzyme alone.

(c)(ii) Explain how a noncompetitive inhibitor changes an enzyme’s function at the molecular level.

(d)(i) Using the pH data, predict the reaction rate of the enzyme alone at 10 mM H₂O₂ in a solution at pH 10.

(d)(ii) Provide reasoning to justify your prediction in (d)(i).