Section 10: Overview of Photosynthesis, The Light-Dependent Reactions of Photosynthesis, and The Calvin Cycle

examines the process of photosynthesis that converts light energy into sugars. Photosynthesis consists of the light-dependent reactions and the Calvin cycle. You'll find that the chemical equation of photosynthesis is the opposite of the Cellular respiration equation.

What is The Calvin Cycle?

the set of light-independent chemical reactions that occur in the stroma of chloroplasts during photosynthesis. It converts atmospheric carbon dioxide () and energy carriers (ATP and NADPH) into organic sugar molecules (carbohydrates) that plants use for growth and energy.

What is the overall chemical equation for photosynthesis?

6CO2 +12H2O → light → C6H12O6 + 6O2
(Reactants: Carbon dioxide and water. Products: Glucose and oxygen).

What are the two main stages of photosynthesis, and where inside the chloroplast does each occur?

1. Light-dependent reactions: Occur in the thylakoid membrane.

2. Calvin cycle (Light-independent reactions): Occurs in the stroma.

What is the difference between a photoautotroph and a heterotroph?

Photoautotrophs (like plants, algae, and cyanobacteria) use light energy to manufacture their own food, Heterotrophs (like animals and fungi) must consume other organisms for food and energy.

What are stomata, and what is their role in photosynthesis?

are microscopic pores on the underside of leaves that allow CO_2 to enter and O_2 and water vapor to exit.

What is the main goal of the light-dependent reactions, and what byproduct is released?

To convert solar energy into chemical energy stored in ATP and NADPH Oxygen is released as a byproduct from splitting water.

What molecule absorbs light energy in the chloroplast, and where is it housed?

Chlorophyll (primarily chlorophyll a), which is located inside protein complexes called photosystems (Photosystem II and Photosystem I) within the thylakoid membrane.

How is ATP generated during the light-dependent reactions?

As high-energy electrons pass down the electron transport chain, hydrogen ions H+ are pumped into the thylakoid space, creating a concentration gradient. As H+ ions flow through ATP synthase back into the stroma, ATP is synthesized (photophosphorylation).

What is carbon fixation, and what enzyme catalyzes it in the Calvin cycle?

Carbon fixation is the conversion of inorganic carbon (CO2) into organic compounds. It is catalyzed by the enzyme RuBisCO (which attaches CO2 tp RuBP)

What three ingredients are required for the Calvin cycle to produce sugar?

1. CO2 (from the atmosphere)

2. ATP (from the light-dependent reactions)

3. NADPH (from the light-dependent reactions)

What 3-carbon sugar molecule is directly produced by the Calvin cycle to build glucose?

G3P (glyceraldehyde-3-phosphate). It takes two molecules of G3P to form one molecule of glucose.

How do the overall equations of photosynthesis and cellular respiration relate to each other?

They are exact biological opposites. The products of photosynthesis (glucose +O2) are the reactants for cellular respiration, and the products of cellular respiration (CO2 +H2O) are the reactants for photosynthesis.