Photosynthesis

Energy & Life Photosynthesis is the process of capturing and transforming the energy of sunlight into chemical energy. (What type of organisms can make their own food?) a. Autotrophs – organisms that can make their own food make their own food b. Heterotrophs – organisms that obtain energy from the food they obtain energy from the food they consume consume

Energy & Life Chemical Energy and ATP a. ATP – energy molecule used by cells (Fig. 8-2) b. Energy is stored in the bonds between phosphate c. When these bonds are broken energy is released c. When these bonds are broken energy is released

Energy & Life

Using Biochemical Energy a. Active Transport Transport Transport b. Motor proteins move organelles throughout the cell throughout the cell c. Synthesize various molecules

Photosynthesis: An Overview I.Understand the significance of Helmont’s, Priestley’s, and Ingenhousz’s experiments. II.6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 C 6 H 12 O 6 + 6O 2

Photosynthesis: An Overview III.Light and Pigments (Fig. 8-5) A. Wavelength – distance between crests; shorter wavelengths have higher energy than longer wavelengths

Photosynthesis: An Overview

Photosynthesis: An Overview III.Light and Pigments (Fig. 8-5) B. Photon – a particle of light C. In photosynthetic organisms, absorbed energy is used to make chemical energy (glucose) D. Photosynthetic pigment – molecule that absorbs light (color you see is the color being reflected) 1. chlorophyll a - primary pigment; converts light energy to chemical energy

Photosynthesis: An Overview III.Light and Pigments (Fig. 8-5) D. Photosynthetic pigment (con’t) 1. chlorophyll a - (con’t) a. reflects green light b. absorbs red & blue light c. normally hides other pigments pigments 2. Chlorophyll b – accessory pigment; absorbs light and transfers the energy to chlorophyll a

Photosynthesis: An Overview III.Light and Pigments (Fig. 8-5) D. Photosynthetic pigment (con’t) 3. carotenes & xanthophylls – accessory pigment; colors can be seen in autumn when chlorophylls start to break down E. Absorption spectrum – the different colors (wavelengths) of light absorbed by each pigment

Reactions of Photosynthesis I.Inside a chloroplast – organelle in which photosynthesis occurs

Reactions of Photosynthesis I.Inside a chloroplast A. Thylakoids – flattened sacs of photosynthetic membranes; pigments and proteins are organized into photosystems in order for light energy to be captured & stored as chemical energy B. grana – stacks of thylakoids C. stroma – region between grana

Reactions of Photosynthesis II. Electron Carriers – molecules that can accept a pair of high-energy electrons and protons and transfer them to another molecule (NADP + )

Reactions of Photosynthesis There are two sets of reactions that take place within the chloroplasts: The light dependent reactions & the Calvin Cycle (also know as the light independent or the dark cycle)

Reactions of Photosynthesis III.Light Dependent Reactions A. Takes place only in the presence of light B. Occurs on membranes of thylakoids C. Produces high energy compounds that are used in the dark reaction: ATP and NADPH D. Photosystem II 1. pigments absorb light energy and electrons are boosted to a higher energy level

Reactions of Photosynthesis III.Light Dependent Reactions D. Photosystem II (con’t) 2. lost electrons are replaced by the splitting of H 2 O into 2 e-,2 p +, and O 2 a. electrons are picked up by NADP b. protons (H + ) are pumped into inner thylakoid space

Reactions of Photosynthesis III.Light Dependent Reactions D. Photosystem II (con’t) c. Flow of hydrogen ions down their gradient provides the energy necessary to synthesize ATP: ATP is used to power the Calvin cycle c. Flow of hydrogen ions down their gradient provides the energy necessary to synthesize ATP: ATP is used to power the Calvin cycle

Reactions of Photosynthesis III.Light Dependent Reactions E. Photosystem I 1. pigments use energy from light to re-energize the elctrons from photosystem II 2. produces NADPH which also powers the Calvin Cycle

Reactions of Photosynthesis III.Light Dependent Reactions L6MI L6MI

Reactions of Photosynthesis IV.The Calvin Cycle – (light independent, dark reaction) – uses ATP and NADPH from the light dependent reactions to produce high energy sugars (Fig. 8-11) A. Takes place with or without the presence of light as long as ATP and NADPH are available B. Occurs in the stroma chloroplast C. 6CO 2 molecules enter the cycle from the atmosphere and combine with 6 five carbon molecules

Reactions of Photosynthesis IV.The Calvin Cycle (con’t) D. The resulting 12 three carbon molecules use the energy from ATP and NADPH to produce 12 high energy three carbon molecules E. 2 of these molecules are used to synthesize sugar and other compounds F. The remaining 10 molecules are used to produce more of the “starting” 6 carbon molecule of the cycle

The Calvin Cycle

Reactions of Photosynthesis V.Factors Affecting Photosynthesis A. Light intensity – as intensity increases the rate of photosynthesis increases (up to a point) B. Temperature – photosynthesis occurs rapidly at specific temp.; extreme temps. are damaging to enzymes C. H2O – decrease in water slows rate of photosynthesis D. Minerals – must be present in certain amounts