These review questions may not not cover all important objectives

Q1 Define the terms atom and element. Are these terms interchangeable?

The elements are listed in the periodic table: fig. 2.2 - substances that cannot be broken down into simpler substances by ordinary chemical reactions. An atom is the smallest particle that exhibits the characteristics of an element.

Q2 Your body contains vast numbers of carbon atoms.  How is it possible that some of these carbon atoms may have been part of the body of a prehistoric creature?

The principle of conservation of matter says that substances are recycled but not created or destroyed.  Carbon atoms are one of the components of living things. When an organism dies, its carbon (and other elements) are recycled. The carbon atoms that once were in the body of a prehistoric creature are still somewhere on earth and may make up a portion of your body, or the air you breathe, etc.

Q3 In the biosphere, matter follows a circular pathway while energy follows a linear pathway. Explain.

The principle of the conservation of matter says that matter is endlessly recycled.  The laws of thermodynamics, on the other hand, say that while energy is neither created nor destroyed (first law), it dissipates, or is transformed to a lower-intensity form, as it is used (second law). Thus living things require a constant input of energy (from the sun), which is used and re-used by living things until it dissipates, or is lost from the system.

Q4 The oceans store a vast amount of heat, but this huge reservoir of energy is of little use to humans (except for climate moderation). Explain the difference between high-quality and low-quality energy.

Low-quality energy is diffused, dispersed, or low in temperature, so it is difficult to gather and use for productive purposes.  High-quality energy is intense, concentrated, or high in temperature, and it is useful in carrying out work.  But in a fully sustainable world little fossil fuel is used, and mostly use energy from wind, waves, sun, rainfall etc.

Q5 Ecosystems require energy to function. Where does this energy come from? Where does it go?  How does the flow of energy conform to the laws of thermodynamics?

The sun provides the energy for nearly all ecosystems. (Exception: deep ocean thermal vent ecosystems, which derive energy from chemical reactions, called chemosynthesis)  Organisms use this energy to perform chemical reactions to live.  As an organism functions, its cells transform energy by forming and breaking chemical bonds. The first law of thermodynamics describes this energy transformation. And the energy is steadily dissipated into the environment, as in the case of heat released from your body as you work. The second law of thermodynamics describes this loss of energy from ecosystems.

Q6 Heat is released during metabolism. How is this heat useful to a cell and to a multicellular organism? How might it be detrimental, especially in a large, complex organism?

Cells must be warm for respiration and other processes to occur.  Metabolic heat helps maintain necessary warmth. Over-heating can impede cellular processes, however. In large, complex organisms, heat-releasing mechanisms or structures (such as sweating, panting, or an elephant's large, heat-releasing ears), may be essential for survival.

Q7 Photosynthesis and cellular respiration are complementary processes. Explain how they exemplify the laws of conservation of matter and thermodynamics.

Photosynthesis involves capturing the sun's energy and converting it to chemical energy in the bonds of molecules such as glucose. Respiration is the process of releasing that stored energy and providing it to cells that use the energy for movement, reproduction, and other life processes. Respiration and photosynthesis constantly recycle atoms of matter (principle of conservation of matter). Respiration involves the re-use of energy (first law of thermodynamics) and the reduction of the intensity of that energy from chemical energy to heat or kinetic energy (second law of thermodynamics).

Q8 What do we mean by carbon-fixation or nitrogen-fixation? Why is it important to humans that carbon and nitrogen be "fixed?"

Carbon-fixation and nitrogen-fixation mean "capturing" these elements from their gaseous form (CO2 and N2, NOx) and converting them to chemical compounds that are useful to most living organisms.  Humans and other animals cannot fix gaseous elements, so we must acquire the elements we need by consuming organisms that can do so, such as plants and animals that eat plants. Green plants can fix carbon (through photosynthesis), and legumes (bacteria in) and soil bacteria with lightning can fix nitrogen. (See figure 2.21.)

Q9 The population density of large carnivores is always very small compared to the population density of herbivores occupying the same ecosystem. Explain this in relation to the concept of an ecological pyramid.

The concept of an energy pyramid is that, because energy is lost as it passes through an ecosystem, many primary producers are needed to support a consumer. The number of individuals therefore declines at higher and higher levels of a food chain. Large carnivores, at the "top" of the energy pyramid, are fewest in number.

Q10 A species is a specific kind of organism. What general characteristics do individuals of a particular species share? Why is it important for ecologists to differentiate among the various species in a biological community?

Individuals of a common species share all functional traits. Generally a "species" is defined by the ability to interbreed and produce fertile offspring. Differentiating among species in a biological community helps distinguish organisms with different functions, abilities, or niches. These distinctions help an ecologist understand how the components of an ecosystem fit together.