Systems, Energy, and Matter Flashcards

A sealed terrarium containing plants, soil, and insects is left in a sunny location. While the terrarium can be considered a closed system regarding matter, it is an open system for energy. After several weeks, the total biomass of the plants has increased. According to the laws of thermodynamics, what must also have happened within and outside the system?

Answer: To decrease entropy (increase order) inside the terrarium by building biomass, a greater amount of entropy (disorder) in the form of waste heat was released to the surroundings.

This scenario demonstrates the Second Law of Thermodynamics in a biological context. Living organisms, like the plants in the terrarium, are highly ordered systems. To create this order (low entropy) by growing, they must process energy. Photosynthesis captures light energy, but the process is not 100% efficient. Energy transformations result in the release of heat (a less ordered form of energy) into the surroundings. Therefore, to achieve a local decrease in entropy (the plant's growth), the total entropy of the universe (terrarium + surroundings) must increase by releasing a larger amount of disordered energy (heat).

A student creates a mixture of cornstarch and water, known as oobleck. When the student slowly pushes their finger into the mixture, it acts as a liquid. However, when they tap the surface sharply, it feels solid. This substance is best classified as which of the following?

Answer: A non-Newtonian fluid whose viscosity changes with applied stress.

Oobleck is a classic example of a non-Newtonian fluid. Unlike Newtonian fluids (like water), whose viscosity is constant regardless of the force applied, non-Newtonian fluids change their viscosity under stress. Oobleck is a shear-thickening fluid, meaning its viscosity increases with increased stress (like a sharp tap), causing it to behave like a solid. When stress is low (a slow push), it flows like a liquid.

In a biogeochemical cycle, such as the nitrogen cycle, human activities like the industrial production of fertilizers have dramatically increased the amount of fixed nitrogen entering terrestrial and aquatic systems. This massive influx is considered an alteration of which component of the cycle?

Answer: The 'flux' of nitrogen from the atmospheric pool to the terrestrial pool.

Biogeochemical cycles involve 'pools' (reservoirs where elements are stored) and 'fluxes' (the processes that move elements between pools). The atmosphere is a massive pool of N2 gas. The industrial Haber-Bosch process 'fixes' this atmospheric nitrogen into usable forms like ammonia for fertilizers. This human activity dramatically increases the rate of movement—the flux—of nitrogen from the atmospheric pool to the terrestrial (soil) and aquatic pools, far exceeding natural fixation rates.

A 'mesoscale convective system' (MCS) is a large, organized complex of thunderstorms that can persist for several hours. How does an MCS, as a system, primarily interact with the larger-scale environment (the atmosphere)?

Answer: It is an open system that exchanges both energy (e.g., releasing latent heat of condensation) and matter (e.g., drawing in moist air, producing rain).

A mesoscale convective system is a classic example of an open thermodynamic system in meteorology. It actively exchanges both matter and energy with its surroundings. It draws in vast amounts of water vapor (matter) from the surrounding atmosphere, and through condensation and precipitation, it releases enormous amounts of latent heat (energy), which in turn fuels the storm and alters the temperature and pressure of the surrounding environment.

A self-heating meal pack uses an exothermic chemical reaction to heat food. From a systems perspective, which statement accurately describes the energy transfer?

Answer: The food (surroundings) gains thermal energy, while the chemical reactants (system) lose chemical potential energy.

In thermodynamics, we define the 'system' as the process being studied (the chemical reaction) and the 'surroundings' as everything else (the food, the container, the air). In an exothermic reaction, chemical potential energy stored in the bonds of the reactants is converted into thermal energy. This energy is released from the system to the surroundings. Therefore, the system (the chemicals) loses energy, and the surroundings (the food) gain that energy as heat, causing its temperature to rise. This adheres to the First Law of Thermodynamics (Conservation of Energy).

The Second Law of Thermodynamics states that the total entropy of an isolated system can only increase over time. How can complex, highly-ordered biological organisms exist and grow without violating this fundamental law?

Answer: Organisms are not isolated systems; they maintain internal order by increasing the entropy (disorder) of their surroundings.

This is a key concept in understanding life from a thermodynamic perspective. An organism is an open system, not an isolated one. It takes in energy and matter from the environment (e.g., food, sunlight) and uses it to build and maintain its complex, low-entropy structure. However, the metabolic processes involved are not perfectly efficient and release waste products and a significant amount of heat (a high-entropy form of energy) into the surroundings. This increase in the entropy of the surroundings is always greater than the decrease in entropy within the organism, so the total entropy of the universe (organism + surroundings) increases, satisfying the Second Law.