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