Chapter 8

The Working Cell:

Energy from Sunlight

8.1 Photosynthesis uses light

chloroplast: organelle where photosynthesis takes place chlorophyll: chemical compound that gives

green colorGreen parts of plantsChloroplasts concentrated in mesophyll cells mesophyll: inner layer of tissue of a leaf

stomata: pores found on surface of leaf that allows gas and liquid exchange

CO2 enters; O2 exitsVeins carry water to leaves

Chloroplast

Similar to mitochondriaInner and outer membranes

stroma: thick fluid in inner membrane thylakoids: many disk-shaped sacs

Each has a membrane surrounding an interior space

grana:stacks of thylakoids

2 Stages of Photosynthesis

1. Light Reaction• Convert energy in

sunlight to chemical energy

2. Calvin Cycle• “Light-independent”• Makes sugar from

CO2

8.2 Light Reactions electromagnetic energy: travels in waves that can be compared to ocean waves onto a beach

Sunlight

wavelength: distance between 2 adjacent waves

Different in each formLongest=radio (weakest)Shortest= gamma rays

Electromagnetic Spectrum

electromagnetic spectrum: range of types of EM energy

Visible light between 400nm(violet) and 700nm(red)

UV has enough energy to damage cells

Specifically proteins and nucleic acids

Pigments

pigments: a substances color due to chemical compounds

Light can be absorbed, transmitted or reflected

A chloroplast’s pigments absorb blue-violet and red-orange very well

Does not absorb greenReflected or transmitted

Paper ChromatographyUsed to observe pigments in a green leaf chlorophyll a: absorbs mainly blue-violet and red-orange and reflects mostly green

Major role in photosynthesis

chlorophyll b: “helper” absorbs mainly blue and orange and reflects yellow-green. carotenoids: “helper”- absorbs mainly blue-green and reflects yellow-orange

Ex. carotein

Stages of Photosynthesis

The Light ReactionsConvert energy in sunlight to chemical energy1. Chlorophyll molecules(membrane of thylakoid) capture light energy2. Captured energy used to remove electrons from water which splits into oxygen and hydrogen3. Water’s electrons and H+ ions are used to make NADPH4. Captured energy used to make ATP

Photosystems

photosystems: clusters of chlorophyll and other molecules in the thylakoid

Each contain a few hundred pigment molecules

Acts like a solar panel

The Calvin Cycle

“Light- independent reactions”

Makes sugar from CO2 and H+ and electrons carried by NADPHEnzymes located in stromaATP from light reactions provides energyRequires ATP and NADPH