PhotosynthesisPhotosynthesisChapter 8Chapter 8

Autotrophs vs. HeterotrophsAutotrophs vs. Heterotrophs

Autotrophs: Plants and some other types of organisms that use light energy from SUNLIGHT to make their own food. These organisms undergo photosynthesis!! – EX: Trees, grass, algae, plants

Heterotrophs: Organisms that CANNOT use the sun’s energy to make food– they obtain energy from the foods they consume – EX: Deer, rabbits, bear, fish, insects, etc…

The Photosynthesis EquationThe Photosynthesis Equation

Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high energy sugars and oxygen

6CO2 + 6H2O + light→C6H12O6 + 6O2

(carbon dioxide + water + light → sugars + oxygen)

Plants then use the sugars to produce complex carbohydrates such as starches

Plants obtain CO2 from the air or water in which they grow

PhotosynthesisPhotosynthesis

Light Energy

CO2 + H2O Sugars + O2

Chloroplast

Inside a ChloroplastInside a Chloroplast

Chloroplast= Filled with chlorophyll and are where photosynthesis takes place in plants and other photosynthetic eukaryotes – Thylakoids= saclike photosynthetic membranes

arranged into stacks known as grana. Area where light-dependent reactions take place

– Photosystems= clusters of chlorophyll and other pigments that are organized by the thylakoids

– Stroma= Area outside the thylakoid membranes where light- independent reactions

Light-dependent ReactionsLight-dependent Reactions

Absorption of Light byChlorophyll a and Chlorophyll b

V B G YO R

Chlorophyll b

Chlorophyll a

Section 8-2

Figure 8-5 Chlorophyll Light Absorption

Electron CarriersElectron Carriers

Electron Transport= The transfer of a pair of high energy electrons & their energy to another molecule

Electron Carriers= The “bucket” or carrier that moves electrons and their energy from molecule to the next EX: NADP+: Accepts and holds a pair of high-energy electrons

and an H+ ion, converting NADP+ into NADPH turning energy from the sun into chemical energy .

An analogy would be a pan carrying hot coals like the NADP+ carries two electrons and a H+ ion.

ATP FormationATP Formation

Adenosine Triphosphate (ATP)Adenosine Triphosphate (ATP)

Adenine Ribose 3 Phosphate groups

ADP and ATP (Electron Carriers)ADP and ATP (Electron Carriers)

ATPADP

Energy

Adenosine diphosphate (ADP) + PhosphateEnergy

Adenosine triphosphate (ATP)

Partiallychargedbattery

Fullychargedbattery

Light-Dependent ReactionsLight-Dependent Reactions

Light-Dependent Reactions: Use energy from sunlight to produce the energy carriers ATP and NADPH and oxygen. – Reactions occur within the thylakoid

membranes of chloroplasts

Light-dependent ReactionsLight-dependent Reactionshttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/

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HydrogenIon Movement

Photosystem II

InnerThylakoidSpace

ThylakoidMembrane

Stroma

ATP synthase

Electron Transport Chain Photosystem I ATP Formation

Chloroplast

Section 8-3

Figure 8-10 Light-Dependent Reactions

PhotosynthesisPhotosynthesis

Steps in PhotosynthesisSteps in Photosynthesis

Photosynthesis: Has five major steps that occur within the thylakoid membrane of the chloroplast – 1. Photosystem II: Light absorbed by photosystem

II is used to break up water molecules into energized electrons, hydrogen ions (H+) and oxygen.

– 2. Electron Transport Chain: High-energy electrons from photosystem II move through the electron transport chain into photosystem I.

Steps in PhotosynthesisSteps in Photosynthesis

– 3. Photosystem I: Electrons released by photosystem II are energized again in photosystem I. Enzymes in the membrane use these electrons to make NADPH/

– 4. Hydrogen Ion Movement: The inside of the thylakoid membrane is charged with H+ ions. This causes the outside of the thylakoid membrane to be negatively charged and the inside of the membrane to be positively charged.

Steps in PhotosynthesisSteps in Photosynthesis

– 5. ATP Formation: As hydrogen ions pass through ATP synthase, their energy is used to convert ADP into ATP. As it rotates ATP synthase (enzyme) binds ADP and P+ group to create ATP. Because of this, light-dependent transport produces high energy electron AND ATP.

SUMMARY: Light dependent reactions use water, ADP and

NADP+ to produce oxygen, ATP and NADPH (Water, ADP, NADP+ Oxygen, ATP, NADPH)

ATP and NADPH then provide energy to build energy containing sugars from low-energy compounds.

Light-independent ReactionsLight-independent Reactions

Calvin Cycle: Energy stored in the ATP and NADPH formed during photosynthesis, is used to build high-energy sugars that can be stored for a long period of time. – Does not require light and is called light

independent reaction – Takes place in the stroma of the

chloroplasts

Calvin CycleCalvin Cyclehttp://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.htmlhttp://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html

Steps in the Calvin CycleSteps in the Calvin Cycle

The Calvin Cycle has four major steps: – 1. C02 Enters the Cycle: 6 CO2 molecules are

combined with six 5- carbon molecules to produce three 12-carbon molecules

– 2. Energy Input: Energy from ATP and electrons from NADPH convert the twelve 3-carbon molecules into higher-energy forms

– 3. 6-Carbon Sugar Produced: two 3-carbon molecules are removed to produce sugars, lipids, amino acids, and other compounds

Steps in the Calvin CycleSteps in the Calvin Cycle

– 4. 5-Carbon Molecules Regenerated: the 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to start the next cycle : )

ChloropIast

CO2 Enters the Cycle

Energy Input

5-CarbonMoleculesRegenerated

Sugars and other compounds

6-Carbon SugarProduced

Section 8-3

Figure 8-11 Calvin Cycle

Photosynthesis

includes

of

take place intakes place in uses

to produce to produce

use

Light-dependentreactions

Calvin cycle

Thylakoidmembranes Stroma NADPHATPEnergy from

sunlight

ATP NADPH O2 Chloroplasts High-energysugars

Section 8-3

Concept Map

Chloroplast

Light

O2

Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPH

ATP

ADP + PNADP+Chloroplast

Section 8-3

Figure 8-7 Photosynthesis: An Overview

Factors Affect PhotosynthesisFactors Affect Photosynthesis

Various Factors Affect the Rate of Photosynthesis.

Some of these factors are:1. Amount of available water

– EX: Plants in dry areas have waxy leaves to prevent water loss

2. Temperature – EX: Enzymes work best between 0° and 35°C. Temps

above or below this range may slow down photosynthesis or stop it entirely

3. Light Intensity 1. EX: The higher the intensity the higher the rate of

photosynthesis. There is a maximum limit however. This varies from plant to plant