Passage III

Amphiprion percula, a species of clownfish, are kept in many home aquariums. Two experiments were conducted to determine how diet and stocking density (number of fish per liter of seawater, fish/L) affect the specific growth rate (SGR; percent increase in length per day, percent/day) in A. percula.

Experiment 1

Each of 12 identical 15 L tanks received 10 L of seawater having a salinity of 33 parts per thousand (ppt), a temperature of 27°C, and a pH of 8.2. Salinity, temperature, and pH were kept constant over the course of the experiment. A. percula of similar lengths were selected, and their lengths were measured, in cm, with a ruler. Then they were equally distributed among the tanks at a stocking density of 1 fish/L. The tanks were then divided equally into 4 groups.

For 4 months, each group was fed a different diet (Diets Q–T). Each group was fed the same mass of food 3 times daily. At the end of 4 months, the length of each fish was measured, in cm, with a ruler, and the SGR of each fish was calculated. The average SGR was then determined for each group (see Table 1).

Table 1

Experiment 2

The procedures for Experiment 1 were repeated except that each group was kept at a different stocking density, 0.5 fish/L, 1 fish/L, 2 fish/L, or 3 fish/L, and all fish were fed Diet T. At the end of 4 months, the average SGR was determined for each group (see Table 2).

Table 2

Tables adapted from João Champeil et al., "Effect of Stocking Density and Different Diets on Growth of Percula Clownfish, Amphiprion percula (Lacepede, 1802)." 2015 by Springer.

Passage IV

Scientists hypothesized that heating tomatoes affects the concentration of nutrients such as vitamin C and lycopene (a red pigment) in the tomatoes. They conducted 2 experiments to test their hypothesis.

Experiment 1

Two kilograms of a particular variety of raw tomatoes were sliced and then blended in a food processor until a homogeneous (uniform) tomato mixture was produced. The mixture was divided into 4 equal samples (Samples 1−4). Each sample was placed in a separate plastic bag, and the bags were sealed. The bag containing Sample 1 was immediately frozen at −40°C. The bags containing Samples 2−4 were each incubated in a water bath at 88°C for a different period of time (see Table 1) and then frozen at −40°C.

Then, 2 days later, Steps 1−3 were performed for each sample.

1. The sample was thawed, and then 100 g of the sample was placed in a beaker containing 200 mL of Solvent A.

2. The contents of the beaker were mixed for 5 min at 25°C and then filtered using a paper filter. The filtered liquid was collected.

3. The filtered liquid was analyzed to determine the vitamin C concentration in micromoles per gram of tomato (μmol/g tomato).

The results for each sample are shown in Figure 1.

Experiment 2

Experiment 1 was repeated except that in Step 3 the filtered liquid was analyzed to determine the lycopene concentration in milligrams per gram of tomato (mg/g tomato). The results for each sample are shown in Figure 2.

Figures 1 and 2 adapted from Veronica Dewanto et al., “Thermal Processing Enhances the Nutritional Value of Tomatoes by Increasing Total Antioxidant Activity.” 2002 by American Chemical Society.

Passage V

A molten alloy (a mixture of 2 or more metallic elements) can be poured into a cylindrical mold and cooled to form an ingot. Crystals form inside the ingot as it cools. The average crystal length, L, in micrometers (μm), determines how brittle the ingot will be. A method for reducing L using rotating magnetic fields was applied to Alloy Q as it cooled in the molds. Table 1 shows the elemental composition of Alloy Q. Figure 1 shows the effect of the relative magnetic stirring force, F, on L for ingots formed from molten Alloy Q that had an initial temperature of either $280$°C or $550$°C.

Table 1

Figure 1

Figure 1 is adapted from S. Denisov, et al., “The Effect of Traveling and Rotating Magnetic Fields on the Structure of Aluminum Alloy During Its Crystallization in a Cylindrical Crucible.” 2014 by Institute of Physics, University of Latvia.

Passage IV

In a lake, water leaches (dissolves out) soluble organic compounds from decaying tree leaves, producing dissolved organic carbon (DOC). DOC is subsequently removed from the water if it is adsorbed by (becomes adhered to the surface of) clay mineral particles that are suspended in the water. Three studies done at a lake examined DOC adsorption by 3 clay minerals—CM1, CM2, and CM3—found in the lake’s sediment.

Green leaves were collected from 5 types of trees around the lake (maple, oak, pine, magnolia, and rhododendron). A 5 L volume of lake water was filtered to remove all solid particles. The following procedures were performed for each type of leaf: A 100 g sample of the leaves was mixed with a 1 L volume of the filtered lake water. The mixture was then placed in the dark for 10 weeks at 4°C while leaching occurred. At 10 weeks, the mixture was filtered to remove all solid particles. The resulting liquid (the leachate) was analyzed for DOC.

Study 1:

The following procedures were performed for each leachate: A 100 mL volume of the leachate was mixed with 10 g of CM1. The mixture was stirred continuously for 2 hr, then filtered to remove all solid particles. The resulting liquid (the filtrate) was analyzed for DOC. The percent of leachate DOC that had been adsorbed by CM1 was calculated (see Figure 1).

Study 2: Study 1 was repeated, substituting CM2 for CM1 (see Figure 2).

Study 3: Study 1 was repeated, substituting CM3 for CM1 (see Figure 3).

Figures and table adapted from Todd Teitjen, Anssi Vähätalo, and Robert Wetzel, "Effects of Clay Mineral Turbidity on Dissolved Organic Carbon and Bacterial Production." 2025 by the Swiss Federal Institute for Environmental Science and Technology.

Passage VII

When light shines on a metal plate, electrons can be ejected from the plate. An electron will be ejected if the energy, E, of a photon (particle of light) striking the plate is greater than the minimum energy, M, required for the electron to be removed from the plate. The maximum kinetic energy of the ejected electron, K, is the difference between E and M as shown in the equation:

K = E - M

Students conducted 2 experiments to examine how differences in the light striking a metal plate affect K. The setup included a light source, a removable filter, a circuit with an ammeter to measure current, a power supply that could be adjusted to measure K, and a vacuum tube containing a metal plate and an electrode (see Figure 1).

Experiment 1

A filter was placed between the metal plate and the light source, and the K of the ejected electrons was measured. This procedure was repeated with each of 4 additional filters. Each filter transmitted light of only one frequency. Table 1 lists the following:

• color of light transmitted by the filter

• frequency of light in hertz, Hz

• E in electron volts, eV

• K in electron volts

Table 1

*N.A. - Not Available; no electrons were ejected

Experiment 2

With the same setup as in Experiment 1 except without a filter, the current, in milliamperes (mA), and K were measured as the intensity of the light was varied. Table 2 shows the current and K for 4 different relative light intensities, each given as a percent of maximum intensity.

Table 2