Test 2 Practice

1. Compare and contrast the dew collectors and the stillsuit in terms of (1) purpose, (2) how they work, (3) energy source, (4) their use in real life.

Dew collectors are designed to collect water that condenses from the air at night, when the air cools below the saturation level of water vapor. A dew collector is made of material that conducts heat efficiently so that the warm air reaching it cools quickly and releases water. In a stillsuit, the purpose is also to collect water. A stillsuit is a personal device built into clothing, whereas dew collectors are fixed to the ground or a building. The stillsuit condenses water from air exhaled by the wearer, rather than from the ambient atmosphere. A stillsuit functions during the day, not at night.

The energy source for a dew collector is passive solar energy, since the water in the air comes from evaporation of water during the day when air is heated by the sun. For a stillsuit, the energy comes from physical motions of the wearer: Kinetic energy is converted into refrigeration and pumping water through filters to purify it. In real life, dew collectors work and are used in dry climates to supplement water supplies. Stillsuits however are not yet practical because we cannot obtain sufficient energy from a person's motion to reclaim enough water for survival.

2. Compare and contrast the sandworm and the camel in terms of desert adaptation. Include (1) water use, (2) heat avoidance, (3) digestive chemistry.

The camel adapts to water scarcity by storing large quantities of water in its hump. After the hump is exhausted, if the camel finds a water hole it can drink several hundred liters of water in a few minutes, and thus replenish the hump. By contrast, the sandworm is poisoned by excess water. It must have evolved an altered biochemistry that minimizes use of water in chemical reactions.

The camel avoids excess heat by maintaining its body perched on long thin legs, which hold the body at a height above the ground. The air a few feet above is much cooler than the air at the surface of the ground. By contrast, the sandworm avoids excess heat by burrowing under the sand.

Both camel and sandworm have digestive systems that include extensive bacteria fermenting their food. Bacterial fermentation breaks down complex plant fibers which cannot be digested by the animal's own enzymes. The products of fermentation are organic acids such as acetic acid and lactic acid, which the animal's own enzymes can digest further, eventually combining the molecules with oxygen to release carbon dioxide. The camel inhales oxygen to combine with the fermentation products. By contrast, the sandworm's digestive microbes are said to release oxygen to the atmosphere of Dune. The source of energy is not explained; this reaction cycle cannot work in real life.

3. Based on your graph of water saturation: Suppose air that is raining at 40 degrees F warms up to 80 degrees F. What is the percent water saturation? How does the air feel?

At 40 degrees F, the rain means that the air is saturated (relative humidity = 100%). The saturation level of absolute humidity (actual amount of water in the air) is 0.7% water. The air feels very humid or "muggy." As the air warms up to 80 degrees F, it still contains the same amount of water (absolute humidity, 0.7%). However, the warmed air can now hold much more water, up to 2.4%. So the relative humidity = 0.7%/2.4% = 0.30 or 30%. A relative humidity of 30% feels somewhat dry but comfortable.

4. Sketch the main carbon cycle in Earth's biosphere. Include cycling of carbon dioxide, water, and other necessary components. Explain how the cycle differs from that proposed for Dune.

Photosynthesis (by plants and by photosynthetic microbes) uses solar energy to split water, releasing oxygen gas (O₂). The hydrogens are added to carbon dioxide (CO₂ fixation) to build biomass (sugars, proteins, etc.). Consumers then break down biomass by oxidation, a process that spends energy and releases CO₂. Consumers include grazers (herbivores) that eat the plants and photosynthetic microbes, and predators (carnivores) that eat the grazers. Decomposers break down the bodies of plants and consumers, returning CO₂ to the atmosphere where it can be fixed by plants and microbes.

On Dune, the problem is that there is not enough water to support plants or photosynthetic microbes. So it's not clear where the energy comes from to drive the cycles of the biosphere. The sandworm's digestion is proposed to be the main source of oxygen (O₂). But the digestive processes that release organic acids require a source of energy; they cannot release oxygen without consuming energy.

5. Suppose Dr. Wu measures the phylogeny of the dinosaurs he has cloned. The table shows the percent relatedness of all pairs of dinosaur species. If the dinosaur mutation rate is 0.13% per million years, draw a tree of phylogeny (divergence) including all the species.

	Dinosaur species	A	B	C	D	E	F
A	Dilphosaurus	100	70	90	70	85	85
B	Hadrosaurus	70	100	70	80	70	70
C	Procompsognathus	90	70	100	70	85	85
D	Stegosaurus	70	80	70	100	70	70
E	Tyrannosaurus	85	70	85	70	100	95
F	Velociraptor	85	70	85	70	95	100

6. Compare and contrast the ocean ecosystems of the upper water layers versus the ocean floor. How do they compare with respect to (1) available nutrients, (2) source of energy, (3) producers and consumers, (4) source of oxygen?

The upper ocean has plenty of CO₂ and O₂ available for photosynthesis and respiration, respectively. Photosynthetic algae produce most of the oxygen. There is plenty of energy coming in from the sun. On the other hand, inorganic minerals such as iron and phosphorus are in short supply. The ocean floor has plenty of minerals such as iron and phosphorus, and some oxygen arrives from above. However, there is no sunlight for energy. At thermal vents, there is CO₂ coming up which can be fixed by bacteria that oxidizs hydrogen sulfide from the vent. These bacteria grow in symbiosis with vent worms and clams, which do not need to eat because their bacteria metabolize the hydrogen sulfide.

7. Explain how the Sharers used lifeshaping of animals and plants to accomplish aims that we accomplish with machines.

8. Suppose you measure the hydrogen ion concentration of a soil sample (1.2 x 10^-5 Molar) and of lemon juice (8.3 x 10^-2 Molar). Are they acidic or basic? Which has greater acidity?

pH of soil = -log10(1.2 x 10^-5) = pH 4.9

pH of lemon juice = -log10(8.3 x 10^-2) = pH 1.1 Both are acidic, but the lemon juice is a much stronger acid. (Actually, lemon juice is usually not quite that strong, closer to the soil pH above.)

10. Compare and contrast the adaptation of Fremen and of Sharers to their respective environments. Which adaptations are genetic, and which are cultural? Which adaptations involve cooperation with other life forms? How do the Fremen and the Sharers use their adaptations to resist foreign invasion?

It might be expected that Fremen would have evolved genetic adaptations seen on Earth in desert-adapted people, such as increased dehydration tolerance and down-pointing noses that avoid sand. However, such adaptations are not described for Fremen. Fremen do show physiological adaptations; that is, adaptations of the body such as small body size and tolerance for water loss, which result from growing in a dry climate but are not inheritable. On the other hand, Sharers have extensive genetic adaptations, including webbed feet and fingers, and inner eyelids. They evolved whitetrance, an ability to attain a form of inner privacy when living surrounded by other people on rafts of limited size.

Fremen have cultural and technological adaptations that conserve water, such as the stillsuit, and traditions of saving all traces of water, which are shared among the tribe members. When people die, their water is immediately conserved for the tribe. Sharers have plenty of water, but limited living space; and the ocean has scarce nutrients, because of lack of access to minerals. Thus, Sharers must limit their population by the regulation of their own fertility, and through tight cooperative social systems that enforce this regulation.

Fremen cooperate with sandworms to maintain the spice flow and provide transport and defense against outsiders. Sharers cooperate with breathmicrobes for oxygen; with rocket squid and starworms for transport; with seaswallowers for maintaining a steady raft population; and with clickflies for communication.

Both Sharers and Fremen have highly cohesive social structures that limit individual freedoms--but promote freedom of the group from oppression by outsiders. The Fremen use their desert adaptations to live secretly in parts of the planet where outsiders cannot survive. They also manipulate the sandworms to interfere with spice mining. Sharers use their enhanced swimming ability to evade the soldiers and maintain long witnesses. They also manipulate the seaswallowers to resume their migration, which disrupts the soldiers’ base.

12. Describe three different kinds of desert ecosystem. How do they relate to the desert ecology of Dune?

13. Explain how ecosystems function. How do they recycle nutrients? How do they maintain energy?

14. Explain how symbiosis works in ecosystems. How does evolution favor symbiosis? How do symbionts maintain their partnership without each destroying the other?

15. Explain how water is used by the human body. How much is consumed, and in what forms is it excreted? Where does all the water we excrete end up? Where does the water we drink come from?

16. The Fremen face a problem in the "watering" of Arrakis. Where does the water come from? What will happen if they succeed? How do their problems relate to ours in our use of water in agriculture?

17. Explain why and how evolution generates many divergent species of a given class of life form. Why does evolution not produce the "one" fittest species?

18. Explain two different ways that nonreproductive sexual behavior (in mammals and birds) can contribute benefits that indirectly increase fitness of an individual (that is, lead to increased propagation of one’s genes).

19. Explain the advantages and drawbacks of each behavioral strategy for a mammal or a bird:

· A male kills offspring fathered by other males.

· A male mates with one female for life and cares for the offspring.

· A female mates only with the strongest or “most fit” male in a group.

· A female mates with all the males of a group.