Module 8: Energy for life

What is photosynthesis?

The process by which plants, algae, and some bacteria use sunlight to make food (glucose).

Why is photosynthesis important for life on Earth?

It provides energy (food) and oxygen for most living organisms.

What type of organisms perform photosynthesis?

Autotrophs (like plants, algae, and cyanobacteria).

What are heterotrophs?

Organisms that cannot make their own food and must consume other organisms.

Where does most energy in ecosystems originate?

Sunlight.

How do humans depend on photosynthesis?

Directly (eating plants) and indirectly (eating animals that eat plants).

Why is photosynthesis the base of food chains?

It converts solar energy into chemical energy stored in food.

What are the reactants of photosynthesis?

Carbon dioxide (CO₂), water (H₂O), and sunlight.

What are the products of photosynthesis?

Glucose (C₆H₁₂O₆) and oxygen (O₂).

What is the overall equation for photosynthesis?

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

Where does photosynthesis mainly occur in plants?

In the leaves.

What layer of the leaf contains most photosynthesis?

The mesophyll.

What are stomata?

Small openings that allow gas exchange (CO₂ in, O₂ out).

What organelle carries out photosynthesis?

The chloroplast.

What pigment captures light energy?

Chlorophyll.

What are thylakoids?

Disc-shaped membranes where light reactions occur.

What is a granum?

A stack of thylakoids.

What is the stroma?

The fluid surrounding thylakoids where the Calvin cycle occurs.

What are the two stages of photosynthesis?

Light-dependent reactions and the Calvin cycle.

Where do light-dependent reactions occur?

In the thylakoid membranes

What do light-dependent reactions produce?

ATP, NADPH, and oxygen.

Where does the Calvin cycle occur?

In the stroma.

What does the Calvin cycle produce?

Glucose (sugar).

What happens if stomata close on a hot day?

Less CO₂ enters, so photosynthesis slows down.

Why is chlorophyll important?

It absorbs sunlight to start photosynthesis.

How is photosynthesis connected to cellular respiration?

Photosynthesis makes glucose and oxygen, which respiration uses to produce ATP.

Why are autotrophs essential to ecosystems?

They produce energy that supports all other organisms.

Why is photosynthesis considered the foundation of nearly all ecosystems?

Because it converts solar energy into chemical energy, which is then transferred through food chains to all organisms.

How would life on Earth change if photosynthesis suddenly stopped?

Food chains would collapse, oxygen levels would decrease, and most organisms would eventually die.

Why are autotrophs essential even for organisms that never eat plants?

Because energy in all food ultimately traces back to autotrophs via photosynthesis.

Why is glucose considered an energy-rich molecule?

It contains high-energy bonds that release energy when broken during cellular respiration.

Why is oxygen released as a byproduct in photosynthesis?

It comes from the splitting of water molecules during light-dependent reactions.

Why can’t the Calvin cycle occur without the light-dependent reactions?

Because it depends on ATP and NADPH produced during the light-dependent stage.

How does the structure of the leaf maximize photosynthesis efficiency?

Large surface area, mesophyll cells packed with chloroplasts, and stomata for gas exchange

Why are chloroplasts concentrated in mesophyll cells?

Because this layer receives the most light, maximizing photosynthesis.

How does the structure of thylakoid membranes support their function?

They provide a large surface area for light absorption and contain chlorophyll and electron transport chains.

What would happen to photosynthesis if there were no water available?

Light reactions would stop, no oxygen or energy carriers would form, and the entire process would halt.

Why is carbon dioxide necessary for photosynthesis?

It provides the carbon atoms needed to build glucose molecules.

How does photosynthesis demonstrate energy transformation?

It converts light energy into chemical energy stored in glucose.

Why might plants close stomata during hot, dry conditions, even though it reduces photosynthesis?

To prevent water loss, even though it limits CO₂ intake.

How does deforestation impact global photosynthesis

It reduces the number of autotrophs, decreasing oxygen production and carbon dioxide absorption.

How are photosynthesis and cellular respiration interdependent?

Photosynthesis produces glucose and oxygen, which respiration uses; respiration produces CO₂ and water, used in photosynthesis.

Why is photosynthesis important for maintaining atmospheric balance?

It removes CO₂ and releases O₂, helping regulate climate and support life.

If a mutation prevented chlorophyll from absorbing light, what would happen?

Photosynthesis would stop because light energy couldn’t be captured.

Why is photosynthesis less efficient than it appears from the equation?

Because many intermediate steps lose energy as heat and not all light is absorbed.

How does the concept of limiting factors apply to photosynthesis?

The rate is limited by whichever factor (light, CO₂, water) is in shortest supply.