Obtaining Energy via Photosynthesis

Why is Photosynthesis important? #1 One of the most important processes on Earth. Chemical energy that is produced from photosynthesis directly or indirectly supplies energy to all organisms. Therefore crucial for the survival of all organisms on Earth. First step in the food chain.

Why is Photosynthesis important? #2 Only source of organic matter (Carbon) which is the building block for all carbon-based life forms, including humans. Produces and maintains all of world’s Oxygen required for animals & humans to survive.

What is Photosynthesis? The process by which light energy from sun is used to convert carbon dioxide & water to chemical energy stored in simple carbohydrates or sugars (e.g glucose) & oxygen. Equation: 6 CO2 + 6 H2O C6H12O6 + 6 O2 Light Energy

How does Photosynthesis provide energy to all organisms on Earth? Plants, algae & some bacteria able to produce their own energy from sun through process of Photosynthesis Thus known as Autotrophs. Animals obtain their energy by directly or indirectly feeding on energy-rich molecules that originated in plants Thus are known as Heterotrophs.

Where does Photosynthesis occur? Some occurs on land (in plants) and some in ocean (in algae). In plants, photosynthesis occurs in leaves. Leaf like a solar sugar factory. In microscopic structures called Chloroplasts.

Area where most photosynthesis occurs Leaf Structure Area where most photosynthesis occurs

Chloroplast Structure Chloroplasts contain the green pigment called Chlorophyll which absorbs the solar energy and triggers photosynthesis. Inner membrane called the Thylakoid membrane. Thickened regions called thylakoids. A stack of thylakoids is called a granum. (Plural – grana) Stroma is a liquid surrounding the thylakoids.

Chloroplast Structure Thylakoid membrane Contains chlorophyll Site of light reactions of photosynthesis electron transfer O2 evolution energy production Stroma Contains enzymes of the carbon fixation cycle Contains complete genetic machinery sugar and starch synthesis

Pigments Chlorophyll A most important photosynthetic pigment. Other pigments called antenna or accessory pigments are also present in leaf. Chlorophyll B Carotenoids (orange / red) Xanthophylls (yellow / brown) These pigments are embedded in membranes of chloroplast in groups called Photosystems.

Two Main Stages of Photosynthesis Light reactions “Photo” part of photosynthesis. Light absorbed by chlorophyll. Involves splitting of water which requires light. Forms ATP. Dark reactions “Synthesis” part of photosynthesis. Does not require light but can happen any time of day. Trapped energy from sun is converted to the chemical energy of sugars

Light Reactions Occur on the thylakoid membranes. Light & water required for this process. Energy storage molecules are formed (ATP and NADPH) Oxygen gas is made as a “waste” product.

Dark Reactions Light-independent Occur in stroma. Carbon dioxide is “fixed” into the sugar glucose. ATP & NADPH molecules created during light reactions power production of this glucose.

The dark reactions: capturing CO2 Atmospheric CO2 is 0.035% (and rising!) Total CO2 in atmosphere 700 x 109 tonnes Photosynthesis fixes ~100 x 109 tonnes per year ~15% of total atmospheric CO2 moves into photosynthetic organisms each year!

How do organisms extract & use energy stored in carbohydrates produced by Photosynthesis? Metabolic process of Cellular Respiration used to retrieve energy stored in the chemical bonds of carbohydrates. Convert energy into a molecule, called adenosine triphosphate (ATP) that is able to do work in the cell. The general equation for cellular respiration is: C6H12O6 + 6 O2 6 CO2 + 12 H2O