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 uses glucose molecules (a

carbohydrate commonly called sugar)

C6H12O6

Carbon Cycle

Glucose is an organic compound, which means it

contains carbon-hydrogen bonds

Glucose must be made by organisms

Organisms that make glucose are called

autotrophs (auto = self; troph = feed)

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

Human Influence

Human civilization has a very

significant influence on the

carbon cycle.

Burning of fossil fuels (oil,

coal, natural gas) releases

CO2 into the atmosphere.

CO2 is a greenhouse gas and

traps heat in the atmosphere.

This has a warming effect on

the earth.

Human Influence

Human activity began releasing CO2 into the atmosphere

in unprecedented amounts starting with the Industrial

Revolution

In the last 150 years, the amount of CO2 in the

atmosphere has increased by more than 30%.

This is a major contributing factor to global warming.

2014, 2015, 2016, 2017, and 2018 rank as the 5 warmest

years (globally) on record.

125,000 years ago was the last time the Earth was this

warm. Sea levels were 18-27 feet higher at that time.

The last time CO2 levels were this high was 3-5 million years ago

during the warmest part of the Pliocene.

Global temperatures were 3-4 C (5-7 F) higher and temperatures at

the poles were 10 C (18 F) higher.

Ice caps were small and sea levels were as much as 90 feet higher

than today.

There was a cooling trend toward the end of this epoch, but

scientists are unclear what caused it.

Human Influence

Impacts of human caused global warming:

– Temperatures rise glaciers melt oceans warm more

glaciers melt temperatures rise further

– Sea levels rise

New Orleans, Miami, Boston, L.A., and New York City are among

the U.S. cities predicted to be underwater in the coming decades

– Ocean currents disrupted

Superstorms, hurricanes’ and

blizzards become more common

and more severe

– Desertification

Forests and grasslands

become arid deserts

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

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

Chloroplast Structure

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

Important carrier molecules are used

– ADP ATP

– NADP NADPH

Light Dependent Reactions

Three important components

1. Harnesses sunlight

2. Splits water

3. Creates energy molecules

Composed of two separate processes

1. Photosystems – creates NADPH

2. Chemiosmosis – creates ATP

Both of these occur in the thylakoid membrane

Both use peripheral and integral proteins

Splitting Water

Water is split into H+, e-, and O2

– H+ and e- are used elsewhere

– O2 is a waste product

Photosystems

• Light energy is absorbed by

chlorophyll molecules

• Energy boosts e- to high energy

states

• As the e- fall back down to low

energy states, NADPH is created

*The H+ and e- come

from the split water

Chemiosmosis

Photosystems also create H+

concentration gradient

H+ diffuses back through ATP

synthase to create ATP

Light-dependent Reactions

Overview

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

Calvin Cycle

Takes place in stroma

Single C m-cules cycled through to

create C3 m-cules

C3 m-cules made into glucose later

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 + 6O2 → 6CO2 + 6H2O

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 glucose

molecule 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

3 more steps, which occur in the mitochondria

1. Link Reaction

2. Kreb’s Cycle

3. Oxidative Phosphorylation

Mitochondrial Structure

Link Reaction

Preps the 3C pyruvate for the Kreb’s cycle and

brings it into the mitochondria

Happens in matrix

Coenzyme A used, CO2 given off

NADH produced

Kreb’s Cycle Overview

Completes the breakdown of glucose

– Takes the Acetyl CoA (2-carbons) and breaks it down,

the carbon and oxygen atoms end up in CO2

– Hydrogens and electrons are stripped and loaded onto

NAD+ and FAD to produce NADH and FADH2

Occurs in the mitochondrial matrix

Production of only 1 more ATP (per Acetyl CoA)

– but loads up the carriers NAD+ and FAD to produce

large quantities of ATP in the final stage.

Kreb’s Cycle

Acetyl CoA

(2C)

3 NADH

3 NAD

1 ATP

1 ADP

1 FADH2

1 FADCO2

Kreb’s

Cycle

YIELD*: 1 ATP

3 NADH

2 FADH2

*REMEMBER: 2x

Oxidative Phosphorylation

The temporary carriers (NADH and FADH2) enter

the ETC (electron transport chain) in the cristae.

Their high energy e- are used to pump protons

(H+) across the cristae membrane to create a

concentration gradient.

The H+ then diffuse back through ATP synthase

to create ATP. (chemiosmosis again!)

In the process, the extra electrons and protons

are joined to oxygen to create water.

Electron Transport Chain

1 NADH creates 3 ATP

1 FADH2 creates 2 ATP

BIG PICTURE

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

Gycolosis

Acetyl CoA

Kreb’s Cycle

ETC2 ATP

18 ATP

6 ATP

6 ATP

2 ATP

4 ATP

2 NADH

1 NADH x2

3 NADH x2

1 FADH2 x2

1 ATP x2

4 ATP -2

x3

x3

x3

x2

1 C6H12O6

Energy Cycle

6CO2 + 6H2O + light → C6H12O6 + 6O2

C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

cellular respiration

photosynthesis