Biochemical Cycle

What is the primary source of oxygen for living organisms on Earth?

• Photosynthesis

• Respiration

• Combustion

• Evaporation

Answer explanation

Photosynthesis is the primary process by which plants, algae, and some bacteria convert sunlight into energy, producing oxygen as a byproduct. This oxygen is essential for the survival of most living organisms on Earth.

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What do plants release into the atmosphere as a byproduct of photosynthesis?

• Carbon Dioxide

• Oxygen

• Nitrogen

• Methane

Answer explanation

During photosynthesis, plants convert carbon dioxide and water into glucose and oxygen. The oxygen produced is released into the atmosphere as a byproduct, making it the correct answer.

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Which process involves plants using sunlight to convert carbon dioxide and water into glucose and oxygen?

• Respiration

• Photosynthesis

• Fermentation

• Decomposition

Answer explanation

Photosynthesis is the process where plants use sunlight to convert carbon dioxide and water into glucose and oxygen, making it essential for energy production in plants.

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What do animals and other organisms release when they use oxygen to break down food for energy?

• Oxygen

• Nitrogen

• Carbon Dioxide

• Hydrogen

Answer explanation

When animals and other organisms use oxygen to break down food for energy, they produce carbon dioxide as a waste product. This process is known as cellular respiration.

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What is the role of respiration in the oxygen cycle?

• It releases oxygen and absorbs carbon dioxide.

• It consumes oxygen and releases carbon dioxide.

• It only releases water as a byproduct.

• It does not affect the oxygen cycle.

Answer explanation

Respiration is a process where organisms consume oxygen to break down glucose for energy, resulting in the release of carbon dioxide as a byproduct. Thus, it plays a crucial role in the oxygen cycle by consuming oxygen.

What is decomposition?

• The process of photosynthesis in plants.

• The breakdown of dead plants, animals, and organic waste.

• The formation of new plants from seeds.

• The process of respiration in animals.

Answer explanation

Decomposition refers to the breakdown of dead plants, animals, and organic waste, returning nutrients to the soil. This process is essential for ecosystem health, unlike photosynthesis, seed formation, or respiration.

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How does oxygen dissolution and release in water affect the oxygen cycle?

• It prevents oxygen from dissolving in water.

• It balances oxygen levels between the atmosphere and water.

• It only affects oxygen levels in the atmosphere.

• It increases carbon dioxide levels in water.

Answer explanation

Oxygen dissolution and release in water helps maintain a balance of oxygen levels between the atmosphere and aquatic environments, ensuring that both ecosystems can thrive. This is why the correct answer is that it balances oxygen levels.

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What is oxidation?

• A process where substances lose oxygen.

• A chemical reaction where substances combine with oxygen.

• A process that only occurs in living organisms.

• A method of producing oxygen in the atmosphere.

Answer explanation

Oxidation is defined as a chemical reaction where substances combine with oxygen, making the second answer choice correct. The other options misrepresent the process or its context.

What is the carbon cycle?

• The process by which carbon moves between the atmosphere, living organisms, oceans, and the Earth's crust.

• The process by which water circulates between the Earth's oceans, atmosphere, and land.

• The process by which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems.

• The process by which oxygen is exchanged between the atmosphere and living organisms.

Answer explanation

The carbon cycle describes how carbon is exchanged among the atmosphere, living organisms, oceans, and the Earth's crust, making it essential for life and climate regulation.

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How do plants contribute to the carbon cycle?

• By releasing carbon dioxide during photosynthesis.

• By taking in carbon dioxide from the air during photosynthesis.

• By converting carbon dioxide into nitrogen.

• By releasing oxygen and nitrogen into the atmosphere.

Answer explanation

Plants contribute to the carbon cycle by taking in carbon dioxide from the air during photosynthesis, which they use to produce glucose and oxygen, thus playing a crucial role in regulating atmospheric carbon levels.

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