Photosynthesis and

Cellular Respiration

Outline

I. Energy and Carbon Cycle

II. Photosynthesis

A. Introduction

B. Reactions

II. Cellular Respiration

A. Introduction

B. Reactions

Carbon Cycle

� All organisms require energy to maintain life

� The primary form of cellular energy is in ATP

adenosine triphosphate

adenosine diphosphate -- carrier

Carbon Cycle

� ATP is generated in a process called cellular

respiration

� Cellular respiration requires glucose molecules

(a carbohydrate commonly called sugar)

C6H12O6

Carbon Cycle

� Glucose is an organic compound, which means it

contains carbon

� Glucose must be made by organisms

� Organisms that make glucose are called

autotrophs (auto = self; troph = nourishment)

� Autotroph means self-feeding, or an organism

that can make its own food

� Autotrophs are called producers because they

produce their own food

Carbon Cycle

� Producers create glucose in a process called

photosynthesis

� Producers include plants, algae, and some

bacteria and protists

� Once glucose is created, it can be used to make

the ATP that supplies energy

Carbon Cycle

� Plants get the carbon they need to make glucose

(C6H12O6) from carbon dioxide (CO2)

� This carbon is cycled through photosynthesis

and cellular respiration through a perpetual

process that reuses the carbon to create new

energy

� Thus, it is called the Carbon Cycle – and is also

known as the Energy Cycle

Carbon Cycle

Photosynthesis

� Method of converting sun energy into chemical energy usable by cells

� Autotrophs: self feeders, organisms capable of making their own food– Photoautotrophs: use sun energy e.g. plants

photosynthesis-makes organic compounds (glucose) from light

– Chemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

Photosynthesis

� Photosynthesis takes place in specialized

structures inside plant cells called chloroplasts

– Light absorbing pigment molecules e.g. chlorophyll

Why Plants are Green

� Light is composed of photons

� Photon energy is measured in wavelengths

� Different wavelengths generate different colors of

light

What is Seen

� All wavelengths (colors) together appear as white light

� The white light can be separated into the visible spectrum

– the rainbow…. ROYGBIV

� Other wavelengths are not visible to humans – Infrared

(IR) and Ultraviolet (UV)

Why Plants are Green

� What is seen is what is reflected back

� All other detectable colors are absorbed

� Chloroplasts contain pigments

� The dominant pigment is chlorophyll, which absorbs red

and blue while reflecting green and yellow

The absorbed

wavelengths provide

the energy needed to

power photosynthesis

Overall Reaction

� 6CO2 + 12 H2O + light energy → C6H12O6 + 6O2+ 6H2O

� Water appears on both sides because 12 H2O molecules

are required and 6 new H2O molecules are made

� Water is split into H and O2 so the H can be split further

into protons and electrons

� The e- are used as a source of energy and the H+ are

used to create a concentration gradient

� Both are used to create the energy need to create

glucose

� O2 is released as a byproduct

Photosynthesis

� Most easily understood in two parts:

1. Light dependent reactions

– make the energy needed to connect carbons

2. Light independent reactions

– use the energy to connect the carbons

Light-dependent Reactions

� Light energy is absorbed by chlorophyll molecules

� Energy boosts e- to high energy states

� As the e- fall back down to low energy states, the energy they release is used to create the energy molecules ATP and NADPH

Calvin Cycle (light independent or “dark” reactions)

� ATP and NADPH generated in light reactions

used to fuel the reactions which take CO2 and

break it apart, then reassemble the carbons into

glucose.

� Called carbon fixation: taking carbon from an

inorganic molecule (atmospheric CO2) and

making an organic molecule out of it (glucose)

� Simplified version of how carbon and energy

enter the food chain

Photosynthesis Review

� CO2 + H2O + light energy → C6H12O6 + O2

� Light dependent reactions

– Make the energy needed to drive the Calvin cycle

– ATP and NADPH

� Calvin cycle

– Carbon fixation

– Joins carbons together to make glucose

Photosynthesis Review

� Photosynthesis happens in the chloroplasts of plants

– CO2 from atmosphere

– H2O from soil

– Light from sun

– C6H12O6 created as energy source

– O2 created as waste product

� The glucose can now be converted into energy that cells

can use -- ATP

Harvesting Chemical Energy

� Energy enters the food web via autotrophs when they convert light energy into chemical energy.

� All organisms use this chemical energy (glucose) to create energy molecules (ATP) that fuel their metabolism.

� Heterotrophs – unlike autotrophs they don’t create the fuel they use; they must consume it.

Cellular Respiration Overview

� Transformation of chemical energy in food

(glucose and other macromolecules) into

chemical energy cells can use: ATP

� These reactions proceed the same way in plants

and animals – CELLULAR RESPIRATION

� Overall Reaction:

�C6H12O6 + O2 → CO2 + H2O

Hint – Reverse Photosynthesis

� Cellular Respiration is like photosynthesis in reverse…

sort of.

� The products become reactants and the reactants the

products…

Just switch light energy for ATP

And don’t get any dumb tattoos… it’s

not that hard to remember.

Cellular Respiration Overview

� Breakdown of glucose begins in the cytoplasm --

the liquid matrix inside the cell

� There are two pathways:

– Anaerobic cellular respiration (aka fermentation)

– Aerobic cellular respiration

OR

C.R. Reactions

� Glycolysis

– Series of reactions which break the 6-carbon glucosemolecule down into two 3-carbon molecules called pyruvate

– Process is an ancient one-all organisms from simple bacteria to humans perform it the same way

– Yields 2 ATP molecules for every one glucose

molecule broken down (net)

– Yields 2 NADH per glucose molecule

Glycolosis

C6H12O6

2 NAD

2 NADH

4 ADP

4 ATP

2 ATP

2 ADP

2 pyruvate (3C)

NET GAIN:2 ATP

2 NADH

Anaerobic Cellular Respiration

� Some organisms thrive in environments with little or no oxygen

– Marshes, bogs, gut of animals, sewage treatment ponds

� Results in no more ATP: final steps in these pathways serve ONLY to regenerate NAD+ so it can be recycled to be used in gycolosis again.

an = without

aerobic = oxygen

anaerobic = without oxygen

Ferment yeast, make ethanol, get beer.

Work your muscles, make lactic acid, get sore.

Aerobic Cellular Respiration

� Oxygen present

� 2 more steps, which occur in the mitochondria

1. Kreb’s Cycle2. Electron Transport Chain

Kreb’s Cycle Overview

� Completes the breakdown of glucose

� Occurs in the mitochondria

� Production of only 2 more ATP

� Creates carrier molecules NADH and FADH2

– These molecules will produce most of the ATP later

Kreb’s Cycle

2 Pyruvate

6 NADH

6 NAD

2 ATP

2 ADP

2 FADH2

2 FADCO2

Kreb’sCycle

2 NADH

Electron Transport Chain

� The temporary carriers (NADH and FADH2) enter

the ETC.

� Their high energy e- are used to create more

ATP.

� In the process, the extra electrons and protons

are joined to oxygen to create water.

� Once all the carriers have gone through, a total

of 34 more ATP are produced.

38 total ATP per glucose

Energy Yield

� Anaerobic

– Yields only 2 ATP (net)

– organisms that use this can’t be too energetic

– important microorganisms for carbon recycling

– fermentation

– lactic acid

Energy Yield

• Aerobic Respiration

•Glycolosis…………………….2 ATP

•Kreb’s Cycle………………….2 ATP

•Electron Transport Chain….34 ATP

•Total………………...……38 ATP• Much more efficient

• A little sugar = lots of energy

• A lot of sugar

Energy Cycle

CO2 + H2O + light C6H12O6 + O2

C6H12O6 + O2 → CO2 + H2O + ATP

cellular respiration

photosynthesis

Energy Cycle Revisited