Photosynthesis and Chloroplasts Overview

Photosynthesis Overview

• Photosynthesis converts light energy, carbon dioxide, and water into high-energy compounds like glucose.
• The general equation for photosynthesis is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
• Photosynthesis is essentially the reverse of cellular respiration.
• Autotrophs, like plants and algae, perform photosynthesis to create their own food.
• Without autotrophs, heterotrophs (organisms that eat other organisms) would not have a food/energy source.
• Photosynthesis happens in the chloroplast.

Chloroplast Structure

• Chloroplasts contain internal membranes called thylakoid membranes, organized into stacks called grana.
• The fluid-filled space around the thylakoids is called the stroma.
• Chloroplasts contain two main membranes: outer and inner.
• The chloroplast contains chlorophyll, which traps light energy.

Chlorophyll and Pigments

• Chlorophyll primarily absorbs red and blue light wavelengths, reflecting green light, causing leaves to appear green.
• Other pigments, like carotenoids and xanthophylls, absorb different wavelengths, contributing to colors like yellow and orange.
• These accessory pigments absorb colors that chlorophyll doesn't absorb for more efficient light capture.
• Pigments are molecules that absorb light; their color depends on the light they reflect.

Parts of a Leaf and their Functions

• Cuticle: Protective waxy layer on the leaf surface.
• Epidermis: Transparent layer of cells below the cuticle.
• Mesophyll: Cells forming the bulk of the leaf; contains chloroplasts.
• Vascular Bundle (Vein): Transports water and nutrients, including sugars.
• Guard Cells: Regulate the opening and closing of stomata (pores) to control gas exchange.
• Stoma: Pores on the leaf surface where gases (carbon dioxide, oxygen) exchange between the leaf and atmosphere.

Photosynthesis Raw Materials

• Light: Enters leaves through the upper epidermis and is absorbed by chlorophyll in the mesophyll.
• Water: Taken up by roots and transported to leaves through vascular bundles.
• Carbon Dioxide: Enters leaves through stomata.

Photosystem

• A photosystem is a protein complex in the thylakoid membrane containing pigments (e.g., chlorophyll) that capture light.
• These pigments capture light energy, exciting electrons that are passed along to power photosynthesis.
• Photosystems I and II are the primary photosystems.

Cyclic and Noncyclic Photophosphorylation

• Both are processes in the light-dependent reactions that generate ATP.
• Noncyclic photophosphorylation creates ATP and NADPH, producing oxygen (O2).
• Cyclic photophosphorylation creates ATP without producing NADPH or oxygen.

Calvin Cycle

• The Calvin cycle uses ATP and NADPH from light-dependent reactions to fix carbon dioxide into carbohydrates (sugars).
• The Calvin cycle occurs in the stroma of the chloroplast.
• The Calvin cycle is also known as the light-independent reactions.