Chapter 8

Energy From SunlightEnergy From Sunlight

Photosynthesis / Cellular Respiration

Recycle a common set of chemicals:

• Water

• Carbon Dioxide

• Oxygen

• Glucose (Organic Compounds)

Food and Chemical Energy Energy – The ability to do work

• Work = whenever an object is moved

versus an opposing force

Two Types of Energy

1. Kinetic Energy – energy in motion• Anything Moving

• Although, energy can’t be created or destroyed it can be converted from one form to another

• Stop moving

Two Types of Energy2. Potential Energy – Energy that is

stored due to an objects position or arrangement

• The higher you go against the force of gravity the more potential energy your body has.

• As you fall; that is kinetic energy

Abby Wambach U.S Soccer

Potential Energy

Thermal EnergyThe total amount of energy associated

with the random movement of atoms and molecules in a sample of matter

• The transfer of energy from a warmer object to a colder one

Chemical Energy• The potential to perform work is due to

the arrangement of the atoms within the molecules

• So structure and chemical make-up = energy

• Rearrangement of atoms during a chemical reaction releases potential energy.• After this breakdown; smaller molecules

have less energy than the original molecule.

Chemical EnergyNote: Some energy is lost as heat

• Easy to see in a car; “internal combustion” engine

• In our bodies our cells are more efficient plus some heat is used by our bodies to maintain a constant body temperature.

Calories: Unit of Energy• The amount of energy required to raise the

temperature of 1 gram of water by 1° C• When measuring calories in food is actually

measure in kilocalories because one calorie is SO small.

• Calories are measured in a lab by burning foods and measuring the increase in temperature in water.

The Energy in Food

ATP – Adenosine Triphosphate • Cells in plants and animals use ATP as

their main energy supply

ATPAdenosine Triphosphate

Adenosine – A Nitrogen Compound

+

RiboseRibose – a five carbon sugar

+

Triphosphate tail Triphosphate tail – 3 phosphate groups

• This is where energy is taken from

ATP

• Each Phosphate group is negatively charged• Bonded by a Phosphate Bond• Remember “like” charges repel; that “forced” bond

acts like a coiled spring = potential energy• Break the phosphate bond (release) spring energy

is released.

ATP Cycle• In most cases: one phosphate bond is

broken• Left with two phosphate groups

• Adenosine Diphosphate (ADP)

ATP Cycle

ATP can be recycled; Requires energy

• A working muscle recycles all its ATP in one minute• Break between sets when working out.

Cellular Work

• During a chemical reaction that breaks one of the ATP’s bonds, the phosphate group is transferred from ATP to another molecule• Specific enzymes enable this transfer• Molecule that accepts phosphate undergoes a

change; driving the work

3 Types of work that Cells Perform

1. Chemical Work

• Building large molecules like proteins• ATP provides energy for Dehydration Dehydration

Synthesis

3 Types of work that Cells Perform

2. Mechanical Work• Muscle Contraction

• ATP causes change in shape of protein which then opens the door for Potassium (K) and Calcium (Ca) to cause the binding of Actin and Myosin.

3 Types of work that Cells Perform

3. Transport Work

• Pumping Ions across a membrane

Pigments

Sunlight is a form of electromagnetic energy• Electromagnetic energy travels in wavesWavelength – The distance between two adjacent waves• Different forms of electromagnetic energy have

their own wavelength.

Electromagnetic Spectrum

• The range of types of electromagnetic energy; from the very short wavelength (gamma rays) to the very long wavelength (radio waves) TV Show Alphas

Pigment and Color

• Chloroplast DO NOT absorb green very well• Green light bounces off leaf• Leaf is green because green light is not

absorbed

Visible Light

ROYGBIV

Visible Light

• Those wavelength that your eyes can see as different colors

• Make a small fraction of the electromagnetic spectrum

• Shorter wavelengths have more energy than longer wavelengths (violet/indigo)

• Actually shorter wavelengths can damage organic molecules like proteins and nucleic acids

• This is why U.V. rays cause sunburns and can lead to skin cancer

Pigment and Color

Pigment – chemical compounds in a substance that

determines color

Three Things That Happen to Wavelengths

1. Absorbed

2. Transmitted

3. Reflected

• Pigments in the leaf’s chloroplast absorb blue-violet and red very well

Photosynthesis

The process by which plants and other producers convert the energy of sunlight into the energy stored in organic

molecules.

Leaf Structure

Design allows leaf to act like a solar panel

Chloroplast

• The organelle where photosynthesis takes place

Chlorophyll – A chemical found in

chloroplast, that gives green

color.

• In a plant when you see green; photosynthesis is occurring.• Most plants it is in their leaves.

Types of Chlorophyll Pigments

Chlorophyll a – absorbs mainly blue-violet and red

light; reflects green light• Plays a major role in photosynthesis

Chlorophyll b – (helper pigment) absorb mainlyChlorophyll b – (helper pigment) absorb mainly

blue and orange light; reflects blue and orange light; reflects

yellow-greenyellow-green

Carotenoids – (many types) absorb mainly blue-

green light; reflect yellow-orange

Types of Chlorophyll Pigments

Chloroplast

Mesophyll – areas where chloroplast are

concentrated (on a leaf); inner layer of

tissue• Palisade Mesophyll – layer on the top side of the

leaf to collect as much

sunlight as possible• Spongy Mesophyll - A leaf tissue consisting of

loosely arranged,

chloroplast-bearing, usually

lobed cells. 

Chloroplast

Chloroplast

Stomata – (stoma singular) are tiny pores found at

the surface of the leaf.• CO₂ enters; O₂ leaves these sites, along with H₂O.

• Veins carry water and other nutrients from the plant roots to the leaves

• Veins also carry organic molecules made on the leaf to where it is needed.

Mesophyll & Stomata

Chloroplast• structure is key to function

Stroma – thick fluid enclosed by inner

membrane• Look at Sroma like a thick version of cytoplasm

Thylakoids – disk shaped sacs in stroma• Each thylokoid has membrane surrounding an interior

space

Grana – (singular granum) stacks of Thylakoids.• These structures all organize the series of

chemical reactions that make up photosynthesis• Like in cellular respiration some happen interior

(thylakoid) while other occur in the stoma; outside

Chloroplast

Photosystems – in the thylakoid membrane; clusters

of chlorophyll and other molecules• Contain a few hundred pigments chlorophyll a/b

and carotenoids• Cluster of pigments acts like a light gathering panel

• Like a mini-solar panel.

Chloroplast

Photosynthesis

• Opposite reaction of cellular respiration

• eˉ form water go “uphill” using energy from the Sun.

• Chloroplast use these electrons with carbon dioxide and H ions to produce sugar molecules.

PhotosynthesisTwo Main Stage

Stage I Light Reaction• Convert the energy in sunlight to chemical energy

1st – Chlorophyll molecules in the membrane

capture light energy

2nd – Chloroplast use energy to remove eˉ

from water• This splits H⁺ + O₂• O₂ is the “waste product” for photosynthesis

Light Reaction

• O₂ escape into the atmosphere via the stoma (on leaves)

3rd – Chloroplast use H₂O e and H⁺ ions to ˉ (make energy rich molecules) NADPH4th – (finally) ATP is made in chloroplast

Results of Light Reaction – NADPH + ATP

Light Reaction

Harvesting Light Energy

• Each time a pigment absorbs light energy 1 of the pigments eˉ gains energy• eˉ goes from a low energy state to a high enegry state.

• This “excited” state is unstable

• Almost immediately the excited eˉ fall back down to a low energy state transferring the energy to a neighboring molecule• And so on to the next

• And so on to the next

Harvesting Light Energy

• Energy continues to jump from molecule to molecule till it reaches the reaction center of the photosystem • Contains chlorophyll a and PEA

Harvesting Light Energy

Primary Electron Acceptor – a molecule (located in

the reaction center)

that traps the excited

electron from the

chlorophyll a molecule• Now other molecules in the thylakoid membrane

can use trapped energy to make ATP/NADPH

Products of Light Reactions

• Two photosystems are involved in light reactions• The First photosystem traps light energy and

transfers the light excited eˉ to an electron transport chain.

• AKA – Water – Splitting Photosystem• Released O₂ as waste and release H ions

Products of Light Reactions

• The eˉ transport chain connecting the two photosystems releases energy which chloroplast use to make ATP• It is very similar reaction to cellular respiration

• An electron transport chain pumps hydrogen ions across a membrane• In mitochondria it is the inner membrane

(cellular respiration)• In the thylakoid membrane in photosynthesis

Products of Light Reactions

• The second photosystem produces NADPH by transferring excited eˉ and H ions to NADP⁺

Light Reactions Produce – ATP and Light Reactions Produce – ATP and NADPHNADPH

NADPHNADPH

ATP

Products of Light Reactions

• Main difference is that in respiration food provides the eˉ for the electron transport chain• In photosynthesis lightlight-excited eˉ for the

electron transport from chlorophyll travel down the chain. (P680/P700 are pigments)

Photosynthesis

Stage II The Calvin Cycle• Makes sugar from the atoms in CO₂ + the H ions

and high-energy e carried by NADPH ˉ• Enzymes for the Calvin Cycle are located outside

the thylakoids and are dissolved in the stoma• ATP made in Light Reaction provides energy to

make sugar• Calvin Cycle AKA “Light Independent Reactions”

because it does not require light to begin reaction

The Calvin Cycle

• Material is regenerated each time the process occurs

• 5 Carbon sugar: RuBP• It’s the compound that gets regenerated

1st – Carbon enters the cycle as 3CO₂; an enzyme adds a molecule to a RuBP molecule – forming 3 unstable 6 Carbon molecules2nd – The (3) 6 C molecules break immediately into 6 3-carbon molecules called 3-PGA

The Calvin Cycle

3rd – At this point: ATP/NADPH (from light

reaction) provides energy and eˉ that are used to

convert the 3-PGA to G3P the Direct Product of

Photosynthesis.

4th – Carbon exits in one molecule of G3P to make

glucose and other compounds

5th – 15 Carbon atoms remain in 5-G3P molecules

6th – ATP provides the energy used to rearrange G3P

molecules and Regenerate RuBP and ADP and

NADP → sent back to the light reaction

Calvin Cycle

The Calvin Cycle

Photosynthesis Summary

Light Reaction – takes place in the thylakoid

membrane

• Convert light energy to chemical energy (ATP) and NADPH

Calvin Cycle – takes place in the stroma; uses ATP and NADPH to convert CO₂ to sugar.

Photosynthesis Summary

First Step in the Flow of Energy in a Ecosystem

Factors that affect PhotosynthesisFactors that affect Photosynthesis

• Carbon dioxide uptake

• pH

• Temperature

• Water