Photosynthesis LightDependent Reactions Calvin Cycle Section 8 2

Photosynthesis Light-Dependent Reactions & Calvin Cycle Section 8. 2

Fig. 10 -2 • Photosynthesis occurs in plants, algae, some prokaryotes • ENDERGONIC PROCESS-stores energy • ANABOLIC PROCESS-Builds up molecules Bio. Flix: Photosynthesis (a) Plants 10 µm (c) Unicellular protist (e) Purple sulfur bacteria (b) Multicellular alga (d) Cyanobacteria 40 µm 1. 5 µm

Structures of Photosynthesis • Leaves are the major locations of photosynthesis • Chlorophyll - the green pigment within chloroplasts • CO 2 enters and O 2 exits the leaf through microscopic pores called stomata

Fig. 10 -3 a Vein • Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf Leaf cross section Mesophyll Stomata Chloroplast CO 2 Mesophyll cell 5 µm

Component of a Chloroplast • Thylakoid – Saclike photosynthetic membranes – Light-dependent reactions occur here • Granum – Stack of thylakoids • Stroma – Region outside thylakoid membrane – Reactions of the Calvin Cycle occur here

DRAW THIS CHLOROPLAST DIAGRAM IN YOUR NOTES

The Photosynthesis Equation 6 CO 2 + 6 H 2 O + Light energy C 6 H 12 O 6 + 6 O 2

The Two Stages of Photosynthesis: A Preview • Photosynthesis consists of the Light Reactions (the photo part) and Calvin Cycle (the synthesis part) • The light reactions (in the thylakoids): – Split H 2 O – Release O 2 – Reduce NADP+ to NADPH – Generate ATP from ADP • The Calvin cycle (in the stroma) forms sugar from CO 2, using ATP and NADPH • The Calvin cycle begins with carbon fixation, incorporating CO 2 into organic molecules (most importantly, glucose)

• Light. Dependent reaction – Occurs in thylakoid – Uses H 2 O and light to produce ATP, NADPH, and O 2 – NADPH is an electron carrier • Calvin cycle (Light-Independent Reaction) – Occurs in stroma – uses carbon dioxide, ATP, and NADPH to produce sugars (aka food, glucose, carbohydrates, etc. )

Light-Dependent Reactions Electron Transport Chain • This stage of photosynthesis includes an electron transport chain (ETC). The molecules of the electron transport chain use highenergy electrons to push H+ ions from the stroma into the inner thylakoid space, producing ATP & NADPH in the process (Don’t worry about the details of the ETC). The ATP & NADPH are then used in the next stage, the light-independent reactions (Calvin Cycle).

Calvin Cycle

Fig. 10 -5 -1 H 2 O Light NADP+ ADP + Pi Light Reactions Chloroplast

Fig. 10 -5 -2 H 2 O Light NADP+ ADP + Pi Light Reactions ATP NADPH Chloroplast O 2

Fig. 10 -5 -3 CO 2 H 2 O Light NADP+ ADP + Pi Light Reactions ATP NADPH Chloroplast O 2 Calvin Cycle

Fig. 10 -5 -4 CO 2 H 2 O Light NADP+ ADP + Pi Light Reactions Calvin Cycle ATP NADPH Chloroplast O 2 [CH 2 O] (sugar)

Fig. 10 -7 The light reactions convert solar (light) energy to the chemical energy of ATP and NADPH Light • Chloroplasts are solar-powered chemical factories – Their thylakoids transform light energy into the chemical energy of ATP & NADPH – ATP &NADPH are then used to power the Calvin Cycle (lightindependent reactions) Reflected light Chloroplast Absorbed light Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings Granum Transmitted light

The Nature of Sunlight • Light is a form of electromagnetic energy • The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation • Visible light consists of wavelengths (including those that drive photosynthesis) that produce colors we can see Wavelength is the distance between crests of waves Wavelength determines the type of electromagnetic energy

Fig. 10 -6 10– 5 nm 10– 3 nm 103 nm 1 nm Gamma X-rays UV 106 nm Infrared 1 m (109 nm) Microwaves 103 m Radio waves Visible light 380 450 500 Shorter wavelength Higher energy 550 600 650 700 750 nm Longer wavelength Lower energy

Light and Pigments • Pigments – light absorbing chemicals • Chlorophyll – principle pigment in plants – – Chlorophyll a Chlorophyll b Carotenoids Xanthophyll

Why do leaves change colors? • Chlorophyll a • Chlorophyll b

Why Do Leaves Change Color?

Why Do Leaves Change Color? • Leaves change color in the Fall because chlorophyll begins to break down and disappear, exposing the other pigments – the carotenoids (orange, yellow, and reds) and xanthophylls (yellows).

Factors Affecting Photosynthesis • Water supply • Amount of sunlight • Temperature

Types of Photosynthesis • C 3 Photosynthesis • C 4 Photosynthesis • CAM Photosynthesis

C 3 Photosynthesis : C 3 plants. • Called C 3 because the CO 2 is first incorporated into a 3 carbon compound. • Stomata are open during the day. • Photosynthesis takes place throughout the leaf. • Adaptive Value: more efficient than C 4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy). . • Most plants are C 3.

C 4 Photosynthesis : C 4 plants. • Called C 4 because the CO 2 is first incorporated into a 4 carbon compound. • Stomata are open during the day. Adaptive Value: • Photosynthesizes faster than C 3 plants under high light intensity and high temperatures • Has better Water Use Efficiency because they do not need to keep stomata open as much (less water lost by transpiration) • C 4 plants include several thousand species in at least 19 plant families. Examples: corn, sugar cane, grasses

CAM Photosynthesis : CAM plants. CAM stands for Crassulacean Acid Metabolism • Stomata open at night (when evaporation rates are usually lower) and are usually closed during the day. • Adaptive Value: – Better Water Use under arid conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc. ). • Examples: succulents such as cacti, pineapple, and also some orchids and bromeliads