Photosynthesis

Essential Question:

How is photosynthesis carried out?

How Energy is Stored?

• The first way that the energy can be stored is by NADP– This is an electron transport molecule and when the electron is

added it becomes NADPH– This is a very temporary storage solution – use it or lose it

• The second way is as ATP• Both these chemicals are used in the light independent

reaction to create glucose which is long term storage of energy for the cell

ATP

• This is the chemical that is used to store energy for use by plants and animals

• Made of a 5 carbon sugar and three phosphate groups – A = the sugar– T = tri = 3– P = phosphate

• Energy is stored on the molecule by making bonds between the sugar and the phosphates and released by breaking the bonds between the sugar and the phosphates

• Starts as AMP (m=mono=1) add a little energy and get ADP (d=di=2) add a little more energy and get ATP

Some ATP Uses

• Used to fuel the membrane pumps we learned about earlier

• Also used to help make proteins and other chemical messengers

• Used to make animals bioluminescent (like dinoflagellate plankton)

Light and Pigments

• Light is actually a form of energy that travels in waves

• Each color has a different wavelength and therefore a different amount of energy

• White light is a combination of all different wavelengths of light

• Plants use different pigments to harvest this energy by attracting specific wavelengths of light– The main pigment is chlorophyll – absorbs blue green

and red wavelength and reflects green wavelengths– Plants also contain accessory pigments to capture

other wavelengths of light

Structure of a Chloroplast

• Composed of sac-like membranes called thylakoids

• Stacks of thylakoids are called grana

• Inside the thylakoids the chlorophyll is organized into photosystems to harvest the energy from the sun

• Only the light reaction occurs within the thylakoid

Introduction to Photosynthesis

• Plants are able to transform the energy from the sun to produce the energy that allows the plants to grow and reproduce

• This energy is passed onto other animals and eventually to us– Plants are the base of our food chain

• The leaves of plants use the chlorophyll to attract certain wavelengths of light

The chemical reaction

• 6CO2 + 6H2O C6H12O6 + 6O2

• Simply stated carbon dioxide combines with water in the presence of light to form glucose and oxygen

Light Dependent Reaction

• The sunlight hits the photoreception area supercharging the electrons

• These electrons are then converted to NADPH and ATP

• These two compounds are then used in the light independent reaction

The Process

• Light strikes the chloroplast and the energy from the sun excites the electrons in photosystem II and they move to a higher orbit– The electrons come from the splitting of water into hydrogen and

oxygen

• The electron is then passed on the electron transport chain to photosystem I

• The initial electrons create a chemical known as NADPH• Eventually enough inside of the thylakoid membrane has

a positive charge because of all the hydrogens and the outside has a negative charge

• The differences in charges allows ATP to be made

HydrogenIon Movement

Photosystem II

InnerThylakoidSpace

ThylakoidMembrane

Stroma

ATP synthase

Electron Transport Chain Photosystem I ATP Formation

Chloroplast

Light-Dependent Reactions

Light Independent Reaction

• Called this because light is no longer needed• AKA the Calvin cycle• The purpose of the Calvin cycle is to create

glucose for long term storage• All plant cells do both the light dependent and

the light independent reactions• The independent reaction cannot occur without

the light dependent reaction

ChloropIast

CO2 Enters the Cycle

Energy Input

5-CarbonMoleculesRegenerated

Sugars and other compounds

6-Carbon SugarProduced

Calvin Cycle

The Process

• Carbon dioxide enters the cycle and uses ATP and NADPH to energize existing molecules.

• One molecule leaves the cycle to make glucose.• The rest are recycled to keep the cycle going.• Two turns of the cycle are needed to make one

glucose molecule.

Chloroplast

Light

O2

Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPH

ATP

ADP + PNADP+Chloroplast

Photosynthesis: An Overview

Factors Affecting Photosynthesis

• Shortage of water– Water is needed to donate hydrogens to the light

cycle

• Temperature– If the temperature falls than the enzymes that allow

photosynthesis to occur no longer function

• Intensity of light– Plants need the correct wavelength of light to perform

photosynthesis– As the intensity changes leaves will change colors to

capitalize on the light available