Introduction to Photosynthesis Chapter 10 (Part 1) Introduction to Photosynthesis Ms. Day AP Biology www.campbellbiology.com
The Process That Feeds the Biosphere Photosynthesis the process that converts solar energy into chemical energy Light + CO2 + water food Who or What? Plants and other autotrophs They are producers of the biosphere
2 Types of Autotrophs Chemoautotrophs Use chemosynthesis to make “food” Photoautotrophs Use photosynthesis to make “food”
Plants, some bacteria and algae are photoautotrophs Use energy of sun to make organic molecules from H2O and CO2 Some worms and bacteria are chemoautotrophs Use energy from chemicals to make organic molecules
(b) Multicellular algae (c) Unicellular protist Photosynthesis Occurs in plants, algae, certain other protists, some **prokaryotes These organisms use light energy to drive the synthesis of organic molecules from carbon dioxideand (in most cases) water. They feed not onlythemselves, but the entire living world. (a) On land, plants are the predominant producers of food. In aquatic environments, photosynthetic organisms include (b) multicellular algae, such as this kelp; (c) some unicellular protists, such as Euglena; (d) the prokaryotes called cyanobacteria; and (e) other photosynthetic prokaryotes, such as these purple sulfur bacteria, which produce sulfur (spherical globules) (c, d, e: LMs). (a) Plants (b) Multicellular algae (c) Unicellular protist 10 m 40 m (d) Cyanobacteria 1.5 m (e) Pruple sulfur bacteria Figure 10.2
Autotrophs vs. Heterotrophs Obtain their organic material from other organisms They are consumers of the biosphere
Chloroplasts: The Sites of Photosynthesis in Plants The leaves of plants-THEY’RE GREEN!! major sites of photosynthesis VeinH2O Leaf cross section Figure 10.3 Mesophyll (leaf tissue) CO2 O2 Stomata 30-40 chloroplats Stomata; Stoma (pl) CO2 O2
Leaf Anatomy
Organelle where photosynthesis occurs Chloroplasts Organelle where photosynthesis occurs Stroma Dense fluid within chloroplast Dark reaction occurs here Thylakoids Membranous sac (or “coin”) in stroma Inside space called thylakoid space Light reactions occur here Grana (granum = singular) Stack of thylakoids (“coins”)
The Equation for Photosynthesis Photosynthesis converts light energy to the chemical energy of food Overall chemical equation **almost opposite of cell respiration 6 CO2 + 6 H2O + Light energy C6H12O6 + 6 O2
Photosynthesis as a Redox Process Photosynthesis is an endergonic redox process Water is oxidized carbon dioxide (CO2) is reduced What is the source of energy? Light The light boosts the energy of e-s as they are moved from H20 C6H12O6 (glucose)
The Nature of Sunlight Light A form of electromagnetic energy Travels in waves and particles Particles are called photons Wavelength Distance between crests of waves Determines type of energy light has (wavelength & energy are inversely proportionate)
The electromagnetic spectrum The entire range of electromagnetic energy, or radiation Gamma rays X-rays UV Infrared Micro- waves Radio 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 1 m 103 m 380 450 500 550 600 650 700 750 nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy
The visible light spectrum Includes the colors of light we can see (ROYGBV) Includes the wavelengths that drive photosynthesis When light hits matter it is: Absorbed Reflected Transmitted
BLACK all colors are absorbed Color we SEE = color most reflected by pigment; other colors (wavelengths) are absorbed BLACK all colors are absorbed Light Reflected Chloroplast Absorbed light Granum Transmitted
How do the light reactions capture solar energy? Photosynthetic Pigments molecules that absorb visible light different pigments absorb different wavelengths of light Different pigments used in photosynthesis
Primary vs. Accessory Pigments Primary Pigment Chlorophyll a (most abundant) Accessory (Antennae) Pigments Chlorophyll b Anthocyanins Xanthophylls Cartenoids
Photosynthetic pigments Primary pigment = chlorophyll a takes direct part in light reactions Accessory pigments protect chlorophyll a from UV damage absorb light at wavelengths that are not absorbed by chlorophyll a Funnel e-s to chlorophyll a help broaden absorption spectrum for photosynthesis (act as “antennae”)
The Two Stages of Photosynthesis: A Preview The Light reactions NEEDS LIGHT A.k.a- Light Dependent Reactions The Calvin cycle A.k.a- Dark Reactions Light Independent Reactions C3 pathway DOES NOT NEED LIGHT
GOAL= Convert solar energy to chemical energy (ATP & NADPH) The Light Reactions Occur in the grana (& thylakoids) GOAL= Convert solar energy to chemical energy (ATP & NADPH) Chlorophyll absorbs solar energy Splits water release O2 (a by-product) produce ATP (using chemiosmosis) Forms NADPH from NADP+ (an e- acceptor/carrier) Temporarily stores high energy e-’s “Electron shuttle bus”
The Calvin Cycle GOAL= Use ATP & NADPH to convert CO2 into sugar Occurs in the stroma Forms SUGAR from carbon dioxide Carbon fixation occurs (CO2 fixed carbon into sugars) **Uses ATP and NADPH from light reactions
An overview of photosynthesis https://www.youtube.com/watch?v=6jQ6rzala0g http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/index.html http://dendro.cnre.vt.edu/forestbiology/photosynthesis.swf H2O CO2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH2O] (sugar) NADPH NADP ADP + P O2 ATP G3P