Photosynthesis

Chapter 7

Photosynthesis

Almost all plants are photosynthetic autotrophs As are some bacteria and protists Generate their own organic matter through photosynthesis

Photosynthesis Occurs in chloroplasts Energized electrons are added to carbon dioxide to make

sugar Converts solar energy into the chemical energy of a

carbohydrate Sunlight provides the energy

Anatomy of a Plant

Carried out by the green portions of plants

Leaves contain mesophyll tissue specialized for photosynthesis

Water taken up by roots and transported to leaves by veins

Anatomy of a Plant

Carbon dioxide enters through openings in the leaves called stomata

Light energy absorbed by chlorophyll and other pigments in thylakoids of chloroplasts Main organelle that

carries out photosynthesis!!!!

Chloroplasts Are found in the interior cells of leaves Contain stroma, a thick fluid Contain thylakoids, membranous sacs

Photosynthetic Reaction

Glucose and oxygen are the products of photosynthesis Oxygen given off comes from water

CO2 gains hydrogen atoms and becomes a carbohydrate Reaction written as:

Two Steps…..

1. Light reactions convert solar energy to chemical energy Light-dependent

reactions take place only in presence

of light produce ATP and NADPH

2. Calvin cycle makes sugar from carbon dioxide Light-independent

reactions do not need light to occur result in the formation of

organic molecules

Light Reactions

An Overview of Photosynthesis

Photosystem Starting point of photosynthesis Network of pigments in the membrane of the

thylakoid molecules that absorb light energy primary pigment of a photosystem is chlorophyll pigments act as an antenna to capture energy from

sunlight individual chlorophyll pigments pass the captured energy

between them

How Plants Capture Energy from Sunlight

Light comprised of packets of energy called photons Sunlight has photons of varying energy levels

possible range of energy levels is represented by an electromagnetic spectrum

Human eyes only perceive photons of intermediate energy levels this range of the

spectrum is known as visible light

Chloroplasts absorb select wavelengths of light that drive photosynthesis

The light reactions of photosynthesis Two types of photosystems

cooperate in the light reactions Photosystem II

captures a photon of light and releases an excited electron to the electron transport system (ETS)

Photosystem I absorbs another photon of

light and releases an excited electron to another ETS

Electron transport chain

Connects the two photosystems Releases energy that the chloroplast uses to

make ATP

Calvin Cycle

Calvin Cycle

Light-independent These reactions are the second stage of

photosynthesis Functions like a sugar factory within a chloroplast Regenerates the starting material with each turn NADPH and ATP produced in light reactions used to

reduce carbon dioxide to a carbohydrate

Overview of Photosynthesis

Photosynthesis Versus Cellular Respiration Both plant and animal cells carry out cell respiration

Only plant cells photosynthesize Both processes utilize an electron transport chain

and chemiosmosis for ATP production Photosynthesis reduces CO2 to carbohydrates and

releases O2

Respiration utilizes O2 and gives off CO2

Photosynthesis and Respiration Compared

Environmental Impacts Photosynthesis has an enormous

impact on atmosphere. swaps O2 for CO2

Greenhouses used to grow plant indoors Trap sunlight that warms the air

inside The greenhouse effect

Warms the atmosphere Caused by atmospheric CO2

Greenhouse gases are the most likely cause of global warming Slow but steady rise in the Earth’s

surface temperature Destruction of forests may be

increasing this effect