Photosynthesis

Properties of Light White light from the sun is composed of a range of wavelengths. All colors

Chlorophyll Chlorophyll is the main pigment that absorbs sunlight. Chlorophyll absorbs blue light and to a lesser extent, red light. It reflects green light

What do chlorophyll and fireworks have in common?

Introduction Autotrophs: Photoautotrophs : Chemoautotrophs

thylakoid compartment Chloroplast two outer membranes thylakoid membrane system Organelle of photosynthesis in plants and algae stroma thylakoid compartment

Important structures Chloroplast Thylakoids: Grana: Stroma:

a A look inside the leaf b One of the photosynthetic cells inside leaf leaf’s upper epidermis photosynthetic cell in leaf leaf vein Leaf Structure leaf’s lower epidermis

Photosynthesis: Light-Dependent Photosystems - chlorophyll a molecule....

What does Chlorophyll absorb?

Figure 4-15 (part 1) Capturing light energy with excited electrons. Chlorophyll electrons are excited to a higher energy state by light energy. 14

Photosynthesis: Light-Dependent pigment absorbs light energy

Two Potential Fates of Excited Electrons Electron returns to resting, unexcited state. Excited electrons are passed to other atoms. An electron in a photosynthetic pigment that is excited to a higher energy state generally has one of two fates (refer to the next two slides also): (1) The electron returns to its resting, unexcited state. In the process, energy is released, some of which may be transferred to a nearby molecule, bumping electrons on that molecule to a higher energy state (and the rest of the energy is dissipated as heat) or (2) The excited electron itself is passed to another molecule. 16

Figure 4-15 (part 2) Capturing light energy with excited electrons. Chlorophyll electrons are excited to a higher energy state by light energy. 17

Photosynthesis: Light-Dependent electrons in the pigments become excited energy (but not the electrons) is transferred excites the electrons in a chlorophyll a molecule at the center of the photosystem.

Photosynthesis: Light-Dependent

The Passing of Electrons in Their Excited State Molecules that gain electrons always carry greater energy than before receiving them The passing of electrons from molecule to molecule is one of the chief ways that energy moves through cells. Many molecules carry or accept electrons during cellular activities. All that is required is that the acceptor have a greater attraction for electrons than the molecule from which it accepts them. 20

Photosynthesis: Light-Dependent chlorophyll that is the reaction center Splits water

Photosynthesis: Light-Dependent

Photosynthesis: Light-Dependent chlorophyll a continually loses its excited electrons to a nearby molecule, replacement electrons come from water.

ATP Adenine Ribose 3 Phosphate groups

ATP ATP Adenosine diphosphate (ADP) + Phosphate Energy Adenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP) Partially charged battery Fully

Photosynthesis: Light-Dependent

Photosynthesis: Light-Dependent Protons rush out of the thylakoid sacs with great force—to build energy-storing ATP molecules

Light-Dependent

Photosynthesis: Light-Dependent Product #1 of the “Photo” Portion of Photosynthesis: ATP Product #2: NADPH Product #3 (waste): O2

Photosynthesis Equation LIGHT ENERGY 6H2O + 6CO2 6O2 + C6H12O6 6 water + 6 carbon dioxide 6 oxygen + glucose

Suppose a large meteor hit the earth Suppose a large meteor hit the earth. How could smoke and soot in the atmosphere wipe out life far beyond the area of direct impact?

Photosynthesis Two stages:

Light-dependent Reactions require light to work

smoke and soot

smoke and soot

smoke and soot

Light-independent Reactions do not require light

Two Steps in Photosynthesis sunlight H2O O2 CO2 Where the two stages of photosynthesis occur inside the chloroplast NADPH, ATP light-dependent reactions light-independent reactions NADP+, ADP sugars

Photosynthesis: Light-inDependent Calvin Cycle whether or not light is present. Occur in the stroma

Light-inDependent take the energy from ATP + energized ions from NADPH + carbon dioxide to make glucose or sugar. carbon dioxide into CH2O.

Photosynthesis: Light-inDependent

Summary of Photosynthesis sunlight Light Dependent Reactions 12H2O 6O2 ATP ADP + Pi NADPH NADP+ 6CO2 Light Independent Reactions Calvin- Benson cycle 6 RuBP 12 PGAL 6H2O P phosphorylated glucose end products (e.g., sucrose, starch, cellulose)

Photosynthesis: Light-inDependent

C3 Plants

C4 Plants

CAM Plants

Factors that Affect Rates 3 factors can limit the speed of photosynthesis: light intensity, CO2 concentration, temperature Without enough light, a plant cannot photosynthesize very quickly, even if there is plenty of water and CO2 .

Factors that Affect Rates Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesize if there is insufficient carbon dioxide.

Factors that Affect Rates If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesize if it gets too hot.

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

Photosynthesis: The Movie Animation Movie