Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration

Middle School

​

Learning Objectives

• Describe how photosynthesis uses sunlight to create food, cycling matter and energy.

• Explain how cellular respiration breaks down food to release energy for life.

• Explain the movement of matter and energy between photosynthesis and cellular respiration.

• Model how atoms in food are rearranged into new molecules during chemical reactions.

Key Vocabulary

​

Photosynthesis

Converting light energy, water, and CO₂ into glucose and oxygen to be used for energy.

​

Cellular Respiration

A series of reactions that release the stored energy from food molecules like glucose.

​

ATP

Adenosine triphosphate, or ATP, is a usable form of energy that powers all cellular processes.

​

Cycling of Matter

The movement of essential atoms and molecules, such as carbon and nitrogen, within an ecosystem.

​

Flow of Energy

This describes the transfer and transformation of energy through the different levels of an ecosystem.

​

Chloroplasts

These are special organelles that are found inside plant cells where photosynthesis takes place.

Key Vocabulary

​

Mitochondria

Mitochondria are the organelles inside a cell where the second step of cellular respiration takes place.

​

Glucose

Glucose is a simple sugar molecule that provides and stores chemical energy for the cell's activities.

​

Chemical Reaction

A chemical reaction is a process that involves the rearrangement of the atoms within molecules.

​

Molecule

A molecule is the smallest particle of a substance, made up of two or more atoms.

Photosynthesis: Capturing Light Energy

• Plants use sunlight, water, and carbon dioxide to create their food, called glucose.

• The chemical equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

• Glucose is used for energy or stored for growth and later use.

Multiple Choice

What is the main purpose of photosynthesis in plants?

• To create food (glucose) for energy

• To release water vapor into the air

• To absorb nutrients from the soil

• To provide shade for the plant's roots

Multiple Choice

What three things does a plant need to take in to perform photosynthesis?

• Sunlight, water, and oxygen

• Sunlight, water, and carbon dioxide

• Oxygen, glucose, and water

• Carbon dioxide, soil, and sunlight

Multiple Choice

If a healthy plant in sunlight is moved into an environment with no carbon dioxide, what would be the most likely result?

• The plant would start producing more oxygen.

• The plant would not be able to produce glucose.

• The plant would use water and sunlight to grow faster.

• The plant would convert oxygen into carbon dioxide.

​

​

The Flow of Energy & Cycling of Matter

Flow of Energy

• Photosynthesis captures light energy from the sun, bringing it into the ecosystem.

• This light energy is converted and stored as chemical energy in sugar molecules.

• The stored energy is transferred to animals when they consume the plants for food.

Cycling of Matter

• Plants take in simple inorganic molecules like carbon dioxide (CO₂) and water (H₂O).

• The atoms of these molecules are rearranged to create complex organic sugar molecules.

• This process is essential for building the basic matter that all organisms need.

Multiple Choice

What is the initial source of energy that is brought into the ecosystem?

• The sun's light

• The sugar in plants

• The water in the soil

• The carbon dioxide in the air

Multiple Choice

What is the role of photosynthesis in both the flow of energy and the cycling of matter?

• It converts light energy into chemical energy and rearranges simple molecules into complex ones.

• It transfers energy from animals to plants and creates new atoms.

• It releases light energy for animals to use and breaks down sugar molecules.

• It uses chemical energy to create water and releases simple inorganic molecules.

Multiple Choice

What is the primary difference between how energy and matter move through an ecosystem?

• Energy flows in one direction, while matter is cycled and reused.

• Matter flows in one direction, while energy is cycled and reused.

• Both energy and matter are cycled and reused by plants.

• Both energy and matter are lost after being transferred to animals.

​

​

Cellular Respiration: Releasing Stored Energy

• Cellular respiration converts food energy into a usable form of energy called ATP.

• This essential process occurs in the cells of both plants and animals.

• It starts in the cytoplasm and finishes in the cell’s mitochondria.

• The process creates carbon dioxide (CO₂), water (H₂O), and usable energy (ATP).

​

Multiple Choice

What is the primary purpose of cellular respiration?

• To convert food energy into a usable form called ATP.

• To create oxygen for the cell to breathe.

• To store sunlight energy in the form of sugar.

• To absorb water and nutrients from the soil.

Multiple Choice

Which statement correctly describes the outcome of cellular respiration?

• The process produces carbon dioxide, water, and usable energy (ATP).

• The process uses carbon dioxide to create food and oxygen.

• The process happens only in the cytoplasm of animal cells.

• The process converts ATP directly into food for the cell.

Multiple Choice

Given that cellular respiration finishes in the mitochondria, what would be the most likely consequence if a cell's mitochondria were damaged?

• The cell would not be able to complete the process of releasing usable energy.

• The cell would start the process in the nucleus instead.

• The cell would produce more ATP than it normally does.

• The cell would release oxygen instead of carbon dioxide.

​

​

Rearranging Molecules for Growth & Energy

• Atoms are not created or destroyed in reactions, only rearranged into new molecules.

• Glucose (C₆H₁₂O₆) and oxygen (O₂) atoms form carbon dioxide (CO₂) and water.

• The breakdown of food provides smaller molecules that are used as building blocks.

• Organisms rearrange these blocks to build new molecules for growth and repair.

​

Multiple Choice

What happens to atoms during a chemical reaction?

• They are rearranged to form new molecules.

• They are completely destroyed during the reaction.

• New atoms are created to build different substances.

• They are converted into pure energy.

Multiple Choice

According to the law of conservation of matter, why do organisms need to break down food?

• To provide building blocks for growth and repair.

• To increase the number of atoms in the organism.

• To eliminate all waste materials from the body.

• To store large food molecules for later use.

Multiple Choice

When an organism's cells use glucose (C₆H₁₂O₆) and oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O), what conclusion can be drawn?

• The atoms in the original molecules were rearranged to form the new molecules.

• Some atoms were destroyed, while new atoms were created.

• The reaction converted all the glucose directly into energy.

• The oxygen atoms were eliminated from the organism as waste.

​

​

The Relationship Between Photosynthesis & Respiration

• Photosynthesis stores energy using CO₂ and H₂O to make glucose (C₆H₁₂O₆).

• Cellular respiration releases energy by breaking down glucose with O₂.

• The products of one process are the reactants for the other process.

• This creates a cycle for matter and a one-way flow of energy.

Multiple Choice

What is the primary purpose of photosynthesis?

• To store energy from sunlight by building a sugar called glucose.

• To release energy for the cell by breaking down the glucose molecule.

• To produce carbon dioxide and water for the plant to use.

• To create a waste product called oxygen for the plant to release.

Multiple Choice

How are the reactants and products of photosynthesis and cellular respiration related?

• The products of photosynthesis are the reactants of cellular respiration.

• Both processes use the exact same reactants and create the same products.

• The reactants of photosynthesis are also the reactants of cellular respiration.

• Photosynthesis creates ATP, and cellular respiration uses that ATP.

Multiple Choice

If a plant performs photosynthesis to create glucose, what would happen if its cells could not perform cellular respiration?

• The plant would not be able to release the energy stored in the glucose molecules for its use.

• The plant would stop being able to produce its own glucose and oxygen.

• The plant would not be able to absorb carbon dioxide from the atmosphere.

• The plant would immediately run out of water and carbon dioxide.

​

Common Misconceptions

Misconception	Correction
Plants only photosynthesize and do not perform cellular respiration.	Plants perform both to create food and release energy.
Photosynthesis's main purpose is to create oxygen for other animals.	Its main purpose is making glucose for the plant. Oxygen is a byproduct.
Animals create the matter for their bodies from scratch.	Matter comes from rearranging atoms from the food they eat.
Photosynthesis and respiration are the same process, just in reverse.	They are separate processes; one stores energy, and the other releases it.

​

Summary

• Photosynthesis uses light, water, and CO₂ to create glucose and oxygen.

• Cellular respiration breaks down glucose to release ATP energy, CO₂, and water.

• Matter is conserved as atoms in food are rearranged to release energy.

• These two processes form a continuous cycle of matter in ecosystems.

• All energy in food webs originates from the sun through photosynthesis.

• This cycle is vital for balancing oxygen and CO₂ in the atmosphere.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4