Photosynthesis

Photosynthesis

Middle School

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Learning Objectives

• Describe the process of photosynthesis, including its reactants and products.

• Explain how photosynthesis helps cycle matter and move energy through ecosystems.

• Trace the transfer of matter and energy from the sun to plants to animals.

• Interpret the chemical equation that is used to represent photosynthesis.

Key Vocabulary

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Photosynthesis

A process where plants use sunlight, water, and carbon dioxide (CO₂) to create their own food, glucose.

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Autotroph

An autotroph is an organism that can produce its own food, usually through the process of photosynthesis.

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Heterotroph

A heterotroph is an organism that gets its energy by consuming other living things in the food chain.

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Chlorophyll

Chlorophyll is the green pigment inside chloroplasts that absorbs the sunlight needed for photosynthesis to occur.

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Chloroplast

The chloroplast is the specific part of a plant cell where the entire process of photosynthesis takes place.

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Reactant

A reactant is a substance that is present at the start of and participates in a chemical reaction.

Key Vocabulary

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Product

A product is a new substance that is formed when a chemical reaction takes place.

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Glucose

A simple sugar, C₆H₁₂O₆, that is made during photosynthesis and provides energy for living cells.

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Cycling of Matter

The continuous movement of matter, such as carbon and nitrogen, within and between different ecosystems.

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Flow of Energy

The one-way path of energy transfer from the sun through various organisms in an ecosystem.

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Organic Molecules

Carbon-based molecules, such as sugars and proteins, that are primarily made by living organisms.

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Algae

Simple, plant-like aquatic organisms that perform photosynthesis to create their own food from sunlight.

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Producers and Consumers

• All living things need energy, which flows from the sun to producers.

• Producers, or autotrophs, make their own food called glucose through photosynthesis.

• Consumers, or heterotrophs, get their energy by eating other living organisms.

• This energy flows to consumers when they eat producers or other consumers.

Multiple Choice

What is the fundamental difference between how producers and consumers obtain energy?

• Producers make their own food, while consumers get energy by eating other organisms.

• Producers get energy from eating other organisms, while consumers make their own food.

• Producers are only plants, while consumers are only animals.

• Producers live on land, while consumers live in the water.

Multiple Choice

How do producers, like plants and algae, make energy available to an entire ecosystem?

• They convert sunlight into glucose, which provides energy to the ecosystem.

• They absorb energy directly from the soil and water.

• They create energy by breaking down other dead organisms.

• They get all of their energy by eating consumers.

Multiple Choice

If a large number of producers, such as algae and microorganisms, were removed from an ecosystem, what would be the most likely consequence for the consumers?

• The consumers would have less available food because their energy source is connected to producers.

• The consumers would learn to make their own food through photosynthesis.

• The consumers would not be affected because they do not eat microorganisms.

• The producers would grow larger because there are fewer consumers.

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What Is Photosynthesis?

Multiple Choice

What is the primary purpose of photosynthesis?

• To use light energy to make food.

• To release oxygen into the atmosphere.

• To absorb water through the roots.

• To help the plant grow taller.

Multiple Choice

Which statement best describes the chemical change that occurs during photosynthesis?

• Carbon dioxide and water are converted into glucose.

• Glucose and oxygen are converted into water.

• Light energy and water are converted into carbon dioxide.

• Oxygen and water are converted into light energy.

Multiple Choice

If all plant and algae cells suddenly lost their chloroplasts, what would be the most significant consequence for the ecosystem?

• The production of glucose would stop, limiting the matter available to the ecosystem.

• The plant would adapt to use oxygen instead of carbon dioxide.

• The amount of water in the ecosystem would increase.

• The chloroplasts would start producing their own carbon dioxide.

The Two Stages of Photosynthesis

• Chlorophyll traps sunlight to split water, releasing oxygen.

• The cell uses this energy to make food from hydrogen and carbon dioxide.

• This process creates the sugar glucose (C₆H₁₂O₆) for the plant.

Multiple Choice

What is the main outcome of the entire process of photosynthesis?

• To create the sugar glucose for the plant to use as food.

• To release carbon dioxide into the atmosphere.

• To help the plant absorb more water from the soil.

• To break down chlorophyll in the leaves.

Multiple Choice

What is the specific function of chlorophyll in the first stage of photosynthesis?

• It captures sunlight to split water molecules and release oxygen.

• It combines hydrogen and carbon dioxide to make sugar.

• It stores glucose molecules for later use by the plant.

• It converts sugar into a usable form of chemical energy.

Multiple Choice

If a plant has plenty of sunlight and water but is in an environment with no carbon dioxide, what would be the most likely result?

• The plant could not make food because it needs carbon dioxide to create sugar.

• The plant would not be able to release oxygen.

• The plant would not be able to trap sunlight.

• The plant would produce more water instead of using it.

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The Photosynthesis Equation

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

• The reactants are the starting materials: carbon dioxide (CO₂) and water (H₂O).

• The products are the substances made: glucose (C₆H₁₂O₆) and oxygen (O₂).

• Light energy is not matter but provides the power for the reaction.

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Multiple Choice

Which statement best describes the overall process of photosynthesis shown in the equation?

• A process that uses light energy to convert carbon dioxide and water into glucose and oxygen.

• A process that breaks down glucose with oxygen to release energy.

• A process that combines glucose and carbon dioxide to create light energy.

• A process that uses water to create light energy and oxygen.

Multiple Choice

What is the role of carbon dioxide (CO₂) and water (H₂O) in the photosynthesis equation?

• They are the starting materials that are converted into products.

• They are the substances that are created at the end of the reaction.

• They are the energy source that powers the chemical change.

• They are forms of energy released when the reaction is complete.

Multiple Choice

If a plant has access to plenty of carbon dioxide and water but is moved into a completely dark room, what is the most likely outcome for the photosynthesis reaction?

• The production of glucose and oxygen would stop.

• The plant would start making more carbon dioxide.

• The reaction would continue, but at a much slower rate.

• The plant would use oxygen and glucose as reactants instead.

How Plants Use Their Food

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For Energy

• Plants use glucose for immediate energy through a process called cellular respiration.

• This energy powers all of the plant's essential life functions daily.

• This process ensures the plant has the fuel it needs to live.

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For Growth

• Glucose molecules link together to form a strong material called cellulose.

• Cellulose is the main building block for creating new, strong cell walls.

• This allows the plant to grow taller and develop new leaves.

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For Storage

• Plants convert extra glucose into starch for long-term energy storage.

• This starch is often kept in the plant's roots, seeds, or fruits.

• Stored energy helps plants survive winter and produce new offspring later.

Multiple Choice

What is the primary way a plant uses the glucose it produces?

• To provide the immediate energy needed for daily life functions.

• To create the building blocks for the plant's stem and leaves.

• To store energy in the roots for use during winter.

• To absorb water and nutrients from the soil.

Multiple Choice

What is the relationship between glucose and cellulose in a plant?

• Glucose is used to create cellulose, which forms strong cell walls for growth.

• Glucose is converted into starch, which is then used to build cell walls.

• Cellulose is broken down to release glucose for immediate energy.

• Cellulose and glucose are both stored in the roots for winter survival.

Multiple Choice

A plant had a successful summer with plenty of sunlight. As winter approaches, which stored resource will be most critical for its survival until spring?

• The starch stored in its roots from the extra glucose made during the summer.

• The cellulose that makes its cell walls strong and tall.

• The glucose being produced daily through cellular respiration.

• The energy used to grow new leaves during the fall.

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Cycling of Matter & Flow of Energy

Flow of Energy

• ​Energy enters the ecosystem as sunlight, which is then captured by plants.

• ​​Photosynthesis converts light energy into chemical energy that is stored in glucose.

• ​This energy is transferred to animals when they eat plants for food.

Cycling of Matter

• ​Photosynthesis uses simple matter like carbon dioxide (CO₂) and water (H₂O).

• ​​It rearranges them into complex organic molecules like sugar, storing the matter.

• ​When organisms decompose, matter returns to the soil and atmosphere to be reused.

Multiple Choice

What is the fundamental difference in 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 within the ecosystem.

• Both energy and matter enter the ecosystem and are then destroyed.

Multiple Choice

What is the combined role of photosynthesis in the ecosystem?

• To convert light energy into chemical energy and simple matter into complex molecules.

• To transfer energy from animals to plants and break down matter.

• To release energy into the atmosphere and create simple matter like water.

• To help dead organisms decompose and return energy to the soil.

Multiple Choice

Based on the relationships described, what would be the most likely long-term consequence if decomposition stopped happening?

• The matter needed by plants would become trapped in dead organisms and unavailable.

• The flow of energy from the sun to plants would stop immediately.

• Animals that eat plants would no longer be able to get energy.

• Energy would stop flowing, but matter would continue to cycle normally.

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Common Misconceptions

Misconception	Correction
Plants get their food from the soil.	Plants create their own food through photosynthesis. Soil provides nutrients, not food.
Photosynthesis is how plants breathe.	Photosynthesis makes food. Plants “breathe” using cellular respiration to get energy.
Sunlight is a physical ingredient (reactant).	Sunlight is the energy source. The reactants are water and carbon dioxide.

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Summary

• Photosynthesis drives the flow of energy and cycling of matter.

• It converts light energy, water, and CO₂ into glucose and oxygen.

• This process occurs in the chloroplasts of autotrophs like plants and algae.

• The equation is: light energy + 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Poll

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