Experimental Design Practice Test

PASSAGE V

BIOLOGY: This passage is adapted from a study on the metabolic rates of vertebrates.

Introduction

Metabolism is the set of chemical reactions that occur in living organisms to maintain life. The metabolic rate is often measured by the amount of oxygen ($O_2$) consumed per gram of body mass per hour.

Animals can be classified based on how they regulate body temperature:

•Endotherms (e.g., mammals, birds) generate their own body heat to maintain a constant internal temperature.

•Ectotherms (e.g., reptiles, amphibians) rely on external heat sources to regulate their body temperature.

Students conducted two studies to compare the metabolic rates of a Mouse (Endotherm) and a Lizard (Ectotherm) of similar body mass.

Study 1

The students placed the mouse and the lizard in separate metabolic chambers. They varied the environmental temperature from 5°C to 35°C in 10°C increments. The animals were kept at rest. The rate of oxygen consumption ($mL \ O_2 / g \cdot hr$) was measured after the animals had acclimated to each temperature for 30 minutes. Findings were reported in Figure 1.

Study 2

The students investigated the effect of activity level on metabolic rate. They maintained the environmental temperature at 25°C for both animals. They measured the oxygen consumption while the animals were at rest and while they were running on a treadmill at 1.0 km/hr. Findings were reported in Table 1.

Study 3

To determine if body mass affects metabolic rate within the same group, students measured the resting metabolic rate of three different lizards at 25°C. Findings were reported in Table 2.

PASSAGE II

BIOLOGY: This passage is adapted from a study on the factors affecting the rate of photosynthesis in aquatic plants.

Introduction

Photosynthesis is the process by which green plants use sunlight to synthesize nutrients from carbon dioxide ($CO_2$) and water ($H_2O$). The process releases oxygen ($O_2$) as a byproduct according to the following chemical equation: $$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$$ Students conducted three studies to investigate how different environmental factors affect the rate of photosynthesis in Elodea, an aquatic plant. The rate was measured by counting the number of oxygen bubbles produced by a cut stem of Elodea submerged in water over a 5-minute period.

Study 1

To test the effect of light intensity, students placed a 10 cm sprig of Elodea into a test tube filled with a 0.5% sodium bicarbonate ($NaHCO_3$) solution (a source of $CO_2$). A light source was placed at various distances from the test tube. The temperature was maintained at 25°C. The number of bubbles produced in 5 minutes was recorded.

Study 2

To test the effect of light color (wavelength), students used the same setup as in Study 1. The light source was kept at a constant distance of 10 cm. Colored filters were placed between the light and the plant to isolate specific wavelengths. Clear cellophane was used as a control.

Study 3

To test the effect of $CO_2$ availability, students prepared five test tubes with different concentrations of sodium bicarbonate ($NaHCO_3$). A 10 cm sprig of Elodea was placed in each. The light source was kept constant at 10 cm (white light).