Photosynthesis Chapter 8 p. 222

Overview All energy on earth comes from the sun. We depend on: –Plants autotrophic To provide this energy to us! To provide us with oxygen!

Photosynthesis Equation 6H 2 O + 6CO 2 6O 2 + C 6 H 12 O 6 WaterCarbon Dioxide OxygenGlucose LIGHT ENERGY

Overview

Chloroplasts Have TWO membranes –A “bi-bilayer!” The inner membrane is called the thylakoid. The thylakoid is folded and looks like stacks of coins called granum (grana singular). The stroma is the space surrounding the granum Image source:

Chloroplasts Chlorophyll molecules are embedded in the thylakoid membrane Act like a light “antenna” These molecules can absorb sunlight energy. Image from Biology 11: College Preparation. Pg 73. Nelson, Toronto

Pigments Chlorophylls – major light absorbing pigments –chlorophyll a and chlorophyll b Absorb violet-blue region of light and reflect green –This is why plants look green

Why do leaves change color in the fall? It’s all about pigments! Plants also have accessory pigments –Absorb blue green light and reflect red, yellow, and orange In the fall the trees get ready to lose their leaves, the chloroplasts break down and reflect other colors. –Conserve energy

Two Stages of Photosynthesis sunlightwater uptakecarbon dioxide uptake ATP ADP + P i NADPH NADP + glucose P oxygen release LIGHT- INDEPENDENT REACTIONS LIGHT- DEPENDENT REACTIONS new water

Photosynthesis Phase One: Light Dependent Reactions  The absorption of light is the first step in photosynthesis.

Phase I: Light (dependent)Reactions Happens ONLY in sunlight Uses water and energy (light) 1.Light is absorbed by chlorophyll molecules 2.Electron Transport- splits water molecule 3.Oxygen is released from water 4.The electrons are picked up to generate ATP and NADPH Occurs in thylakoid membrane

Phase Two: Light Independent (Dark) Reactions The Calvin Cycle  In the second phase of photosynthesis, called the Calvin cycle, energy is stored in organic molecules such as glucose.

Light Independent Reactions (formerly the “dark reactions”) Happen in sunlight, and in the dark. –Hence “independent of light” 1.ATP generated by the light reaction drives the Calvin Cycle 2.Uses carbon dioxide to make PGAL 1.Precursor to make important biological molecules such as glucose, cellulose, starch, amino acids, lipids or other sugars Occurs in stroma

Recap Video

Light Independent Reactions

Overall Reaction What is the equation for photosynthesis? carbon dioxide + water  glucose + oxygen + energy 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 + energy Photosynthesis Song

Summary Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto

Linked Processes Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide

Overview Carbon dioxide and water are taken in by plants Plants absorb light energy and convert it to a usable form. –ATP - Energy –NADPH – Electron Carrier Energy is used to “fix” carbon dioxide into sugar molecules –Chemical energy Sugar is converted to starch and stored for use by the plant, and by animals when they eat plants.