ACT Science Practice Test 8

Sylvatic, or jungle, Yellow Fever is caused by a virus transmitted by mosquitoes from monkeys to humans. Figure 1 shows the life cycle of the mosquitoes who carry this disease. These mosquitoes' eggs do not hatch unless there is enough water for the next two stages of their life cycles. Yellow Fever is passed when an adult of these mosquitoes first bites a monkey that is infected with the virus and then bites a human.

Figure 1

A study was done on a group of ecologists who went into a jungle where the monkeys carrying the Yellow Fever virus live. These ecologists were divided into groups based on how frequently they went into the jungle. The ecologists were tested monthly for Yellow Fever. Figure 2 shows the number of new cases of Yellow Fever and the amount of rainfall in the jungle. For each group, Table 1 shows the number of ecologists in each group, number of mosquito bites, and percent of each group with Yellow Fever.

Figure 2

Ethanolamines are compounds that contain both alcohol (-OH or HO-) and amine (-NH₃, -RNH₂, -R₂NH, or -R₃N) subgroups. They remove weakly acidic gases from the atmosphere of enclosed spaces such as on a submarine. An example is the use of monoethanolamine (MEA) to remove CO₂ from the atmosphere as shown in Figure 1.

2 MEA(liquid) + CO²(gas) (MEA)COO^-(aqueous) + (MEA)H ⁺(aqueous) + heat

Figure 1

If the temperature rises sufficiently, ethanolamines will release any absorbed acidic gases back into the environment, creating a potential hazard.

Scientists studied the absorption properties of 2 ethanolamines (MEA and DEA).

Experiment 1

At 0°C and 1 atmosphere (atm) pressure, 1 mole (6.02 × 10²³ molecules) of MEA was spread at the base of a reaction vessel containing CO₂ gas at a concentration of 1,000 parts per million (ppm). As the CO₂ was absorbed, its ambient concentration decreased. The scrub time (time for CO₂ concentration to drop to at least 10 ppm) was measured. Longer scrub times indicate a slower rate of absorption. The experimental procedure was repeated at varying temperatures and for DEA, with results recorded in Table 1.

Experiment 2

The scrub times of MEA for different acidic gases were measured using the procedures of Experiment 1 at 26°C (see Table 2). Each of the gases listed is toxic and poses a significant safety hazard if its concentration becomes elevated within an enclosed space.

Taraxicum, the common dandelion, can reproduce both through spreading seeds and through vegetative reproduction. To spread its seeds, the dandelion grows seed pods shaped like globes, in which the seeds are loosely attached to a central ball; each seed grows a parachute-like tuft that lets it travel long distances on the wind (or when blown upon by humans). In vegetative reproduction, a new dandelion stalk and leaves can grow up from an existing root system. Two students discuss the spread of dandelion populations.

Student 1

In Taraxicum, vegetative reproduction and seed distribution make up the only means of growing new plants. Each accounts for 50% of the growth of new dandelions.

Taraxicum grows throughout North America. In many places there is very little wind. Therefore, Taraxicum must have a non-wind-based means of spreading itself. While blowing dandelion seeds is a common pastime among humans, this human influence is very recent in evolutionary terms; it is very unlikely that Taraxicum evolved to rely on humans to distribute its seeds.

The way Taraxicum grows in a typical field shows that both vegetative reproduction and seed distribution are at work. While seeds scatter over the whole field, the dandelions tend to grow together in clumps. This suggests that individual seeds sprout the first new dandelions, which then grow several more through vegetative reproduction.

Student 2

Seed distribution is the main way Taraxicum spreads itself. Without seed distribution, there are very few new dandelions. Taraxicum does use vegetative reproduction, sending new stalks from existing roots, but this is mainly to replace the above-ground plant if it has been cut or eaten. This allows the plant to survive threats in the environment but does not allow for the growth of new plants.

Plant studies show that plants which rely on vegetative reproduction to spread themselves tend to have large, complex root networks or underground root clusters. Taraxicum plants, however, each have a single large, deep taproot. This makes them very difficult to uproot, but it also means that their roots do not spread out underground, so any new plants growing from the roots would compete with each other for sunlight. Even a slight breeze or the brush of a passing animal is enough to spread dandelion seeds to a new area. Additionally, all known types of Taraxicum produce seed globes. If half the new dandelions grew from vegetative reproduction, then a seedless dandelion should not be at a competitive disadvantage and should be commonly observed in the wild.

Experiment

The students proposed 3 trials using an introduced Taraxicum population in three fields in a windy area where Taraxicum can naturally thrive (see Table 1).

Three studies were conducted to analyze the content of cake mix.

Study 1

Samples of 3 different cake mixes (X, Y, and Z) weighing 500.0 g were desiccated (thoroughly dried) in a 350°F oven for 36 hours and then passed through a sieve with 0.045 cm holes. Each sample was evenly spread in a trough 0.100 cm deep with a fan at one end and a secured piece of dark colored paper at the other end, downwind from the fan, as shown in Figure 1. Fan speed was slowly increased from 0 m/s until cake mix particles could be seen on the paper. This speed is called the maximum immovable speed. The maximum immovable speed was recorded for each sample.

Figure 1

This procedure was repeated with 35.0 g of cornmeal, a heavier ingredient, added to the cake mix prior to drying. The results are shown in Table 1.

Study 2

Samples of each cake mix were prepared as in Study 1. Each sample was mixed with 500 mL of water then allowed to rest for 6 hours to ensure equal saturation of all particles in the sample. The samples were then evenly spread in a trough in an apparatus identical to that of Study 1. The fan was set to 10 m/s. Once the fan had dried the sample sufficiently, particles began to appear on the dark paper. At this point, the water content of the sample was calculated. This procedure was repeated with the 16 m/s fan speed. This set of procedures was then repeated with samples of each cake mix to which 35.0 g of cornmeal had been added. Figure 2 displays the results.

Figure 2

Study 3

Samples of each cake mix, without any preparation, were analyzed for flour particle, sugar particle, gelatin particle, and water content. The results are shown in Table 2.