Question

Which of the following is not a source of energy for at least some forms of life on Earth? (a) inorganic chemical reactions; (b) energy release from plutonium; (c) consumption of preexisting organic compounds.

Short answer

(b) Energy release from plutonium.

Step-by-step solution

Identify the Forms of Energy

Start by identifying the types of energy sources provided in the multiple choice options. These are: (a) inorganic chemical reactions, (b) energy release from plutonium, and (c) consumption of preexisting organic compounds.

Evaluate Each Source

- **Inorganic Chemical Reactions**: Certain life forms, especially some bacteria and archaea, utilize inorganic chemical reactions, such as those in chemosynthesis, to gain energy. This makes option (a) a source of energy for life. - **Energy Release from Plutonium**: Plutonium is a radioactive element, and while it releases energy through radioactive decay, this type of energy is not utilized by any known living organisms on Earth directly as a source for life processes. This makes it a likely candidate for the correct answer. - **Consumption of Preexisting Organic Compounds**: Many life forms on Earth, including humans, rely on consuming preexisting organic compounds for their energy source, making option (c) a valid energy source.

Determine the Correct Answer

Based on the evaluations above, only option (b), energy release from plutonium, is not a source of energy for any forms of life known on Earth. Life on Earth does not directly use energy from radioactive decay processes like those involving plutonium for sustaining biological activities.

Key concepts

Inorganic Chemical Reactions

Inorganic chemical reactions are fascinating sources of energy for different life forms on Earth. This type of energy is particularly significant for organisms that do not rely on sunlight. Life forms, like certain bacteria and archaea, tap into these reactions. This process is used especially in environments where sunlight is absent, such as deep-sea vents.

In a process known as chemosynthesis, these organisms derive energy from chemical reactions involving inorganic molecules. For instance, hydrogen sulfide and methane are common inorganic substrates used in such reactions.

Chemosynthetic organisms form the base of the food chain in such extreme environments, supporting a diverse ecosystem even in the absence of sunlight. This highlights how inventive life can be in tapping into available resources for survival.

• Inorganic chemicals often serve as initial fuels for chemosynthetic processes.
• Inorganic chemical reactions allow organisms to thrive in darkness.

Radioactive Energy and Life

While radioactive energy can release a substantial amount of energy through decay, it is not a usual source for life forms as we know them. Plutonium is a radioactive element, and its decay is known to emit radiation.

However, this energy type is generally too intense and hazardous for biological systems to exploit effectively. The radiation could cause more harm than good, potentially damaging DNA and other essential biological molecules.

Some bacteria, known as radiotrophic fungi, have been found to potentially harness radiation indirectly, but this does not equate to using radioactive energy to fuel basic life processes. These exceptions aside, radioactive elements like plutonium do not provide a reliable or safe energy source for life on Earth.

• Radioactive energy is generally not sustainable for biological life.
• Radiotrophic fungi are tiny exceptions but do not directly use radioactive energy.

Organic Compounds as Energy Sources

Organic compounds are among the most common and straightforward energy sources for life on Earth. This includes carbohydrates, proteins, and fats, which organisms break down to release energy.

Through metabolic processes like cellular respiration, organisms convert these compounds into usable forms of energy, such as ATP (adenosine triphosphate). This process is crucial for supporting life activities, from cellular maintenance to movement and reproduction.

Most life forms, including humans, rely heavily on this type of energy to function. The consumption of organic compounds not only provides energy but also essential nutrients that are necessary for growth and repair.

• Energy from organics supports complex life processes.
• Organic compounds provide both energy and nutrients.