CHAPTER 6PHOTOSYNTHESIS

BIOLOGY LECTURE

ENERGY FOR LIFE PROCESS1. All organisms

require a constant supply

of energy

2. Energy does not recycle;

almost all energy is from

the sun

3. Organisms capture the energy of light and store it in organic compounds

ENERGY FOR LIFE PROCESS

• Classifying Organisms By How They Get Their Energy:– Autotrophs – manufacture their

own food from inorganic

substances and energy– Heterotrophs – cannot

manufacture their own

organic compounds from

inorganic substances

AUTOTROPHS

MAKE FOOD: Use photosynthesis to convert

light energy from the sun into chemical energy

They store the chemical energy

in organic compounds (carbohydrates)

Examples are plants, algae, and

cyanobacteria

HETEROTROPHS

• Take in food• They eat autotrophs or

other heterotrophs– A caterpillar (H) feeds

on grass (A)

– A bird (H) feeds on the caterpillar (H)

• Examples are animals, most bacteria, fungi, and protozoa

All fuel originates with the Autotrophs

Energy Transfer Compounds

Photosynthesis – a biochemical pathway that converts solar energy to chemical energy (STORE ENERGY = FOOD)

Autotrophs manufacture organic compounds from carbon dioxide and water and oxygen is released

6CO2 + 6H2O + LIGHT = C6H12O6 + 6O2

How Do We Get Energy?

Cellular Respiration – A biochemical pathway that breaks down chemical energy for use by the cell (RELEASE ENERGY)

In both autotrophs and heterotrophs, organic compounds are combined with oxygen to produce ATP, carbon dioxide and water

C6H12O6 + 6O2 = 6CO2 + 6H2O + ENERGY (ATP)

Energy Transfer Compounds

Adenosine Triphosphate – molecule of stored energy

Energy stored in bonds between phosphate (A M P ~ P ~ P)

AMP, ADP, ATP

Nicotinamide Adenine Dinucleotide Phosphate - molecule that transports energy

NADP+ to NADPH

Do Now

• 1. What is the difference between autotrophs and heterotrophs?

• 2. What is photosynthesis?

• 3. What is cellular respiration?

• 4. What are the 2 energy transfer compounds we talked about?

LIGHT ABSORPTION IN CHLOROPLASTS

Chloroplasts - membrane bound organelles that contain:

1. the pigment chlorophyll

2. enzymes for photosynthesis

*Both light and dark reactions take place here

Chloroplasts• Inner/outer membrane• Thylakoids: flattened sacs where photosynthesis takes

place• Granum (pl. grana): stack of thylakoids• Stroma: liquid solution that surrounds the thylakoids

CHLOROPLASTS IN PLANT CELL

LightA. White light composed of

visible spectrum– ROY G BIV

B. Light travels in energy waves

C. Wavelength (λ) determines color of light

D. UV → violet → red

Short λ → Long λ

E. Pigment: compound that absorbs light

F. Ex. Green pigment absorbs colors other than green & reflects/transmits green

Chloroplast Pigments

• There are several different

pigments in the thylakoid

membranes• Chlorophyll is a pigment

that absorbs red and blue

light and reflects green light• Chlorophyll a is directly involved with the light reaction

Chloroplast Pigments• Accessory pigments trap wavelengths of light

that can not be absorbed by chlorophyll a (help capture more light)

a. Chlorophyll b – also reflects green, but absorbs more blue than red

b. Carotenoids – reflect orange, yellow, and brown and absorbs green and blue

c. Phycobilins – reflect violet & blue and absorb orange, brown and green

Do Now

• 1. What important process occurs in chloroplasts?

• 2. What are the flattened sacs in chloroplasts called?

• 3. What is a pigment and what important pigment is found in the chloroplast?

Electron Transport Chain (ETC)

• Photosystem: a cluster of pigment molecules found in the thylakoid membrane

• 2 Photosystems – each has different roles in photosynthesis– Photosystem I– Photosystem II

Electron Transport Chain (ETC)• Light Reaction – Photosystem II

1. Light energy absorbed by pigments and transferred to chlorophyl a . Electron from chlorophyl a gets “excited” & enters a higher energy level

2. Electron leaves chlorophyl a & enters primary e- acceptor

3. Primary e- acceptor transfers e- to series of molecules (electron transport chain) & loses

Energy (E used to move p+ into thylakoid)

Electron Transport Chain (ETC)

• Light Reaction – Photosystem I– 4. Light is absorbed by photosystem I, electrons

move from chlorophyll a molecules to another primary electron acceptor. These e- are replaced with those from photosystem II

– 5. e- used to make NADPH from NADP+ (NADP+ & H+ NADPH)

Water’s role

• e- from splitting of H2O replaces lost e- in photosystem II

– 2 H2O → 4 H+ + 4 e- + O2

– O2 leaves plant or used for cellular respiration

– H+ stays in thylakoid → concentration gradient

Electron Transport Chain

E. Biochemical pathways – series of biochemical reactions

Chemiosmosis - Make ATP

• Concentration gradient causes protons (H+) to move from thylakoid (high conc) to stroma (low conc)

• ATP synthase uses movement of protons/change in potential energy to make ATP– Converts potential E to chemical E

• ATP synthase (multifunctional protein)– Carrier protein – carries protons across thylakoid

membrane

– Enzyme – catalyzes synthesis of ATP from ADP

Calvin cycle

• Uses ATP & NADPH from the light reaction as energy to make organic compounds

• Carbon from CO2 “fixed” into organic compounds

• Each cycle uses 3 ATP & 2 NADPH

• Occurs in stroma of chloroplast

• Called the Dark Reaction

Photosynthesis Balance Sheet

• 3 turns of the Calvin Cycle are required to produce each molecule of PGAL

• This uses up 9 molecules of ATP and 6 molecules of NADPH

• Most of the molecules made in the Calvin Cycle are built up into:– Amino Acids

– Lipids

– Carbohydrates

• Heterotrophs use the energy in these organic compounds for living

Photosynthesis Equation

6CO2 + 6H2O + Light Energy = C6H12O6 + 6O2

Do Now

• 1. What is a photosystem?

• 2. What is the electron transport chain?

• 3. What is the purpose of the Calvin cycle?

• 4. What is the equation for photosynthesis?

C3 Plants & Alternative Pathways

•Plants that use Calvin cycle are called C3 plants because they fix CO2 into a 3C compound PGA

•Stomata (pl.) - small pores on the underside of a leaf where water, CO2, and O2 pass through

•Plants can partially close stomata to minimize water loss

•Plants open stomata during day & close @ night

C3 Plants & Alternative Pathways

• When stomata close up, CO2 can’t get into the plant and O2 can’t get out of the plant

• This inhibits carbon fixation by the Calvin Cycle in the plant

• Plants have to find other ways

to fix carbon and make food

C4 Plants

• Partially close stomata during hottest part of day

• Certain cells have enzymes that can fix CO2 into 4C compound even when CO2↓, O2↑

• Lose ½ the amount of water as C3 plants but produce the same amount of carbs

• Ex. Corn, sugar cane, crab grass

CAM Plants

• Open stomata @ night &

close during day

• B/C of this CO2 enters when colder → slower growth, less water loss

• Fix CO2 into a variety of diff. C comp.

at night, use for Calvin Cycle during day

• Cactuses, pineapple, and others with different adaptations to hot climate

Rate of Photosynthesis

• Effected by the Environment:– Light Intensity – as light increases – rate of

photosynthesis increases and then levels off when available electrons are already excited

– CO2 – as CO2 levels increase – rate of photosynthesis increases and then levels off

– Temperature – raising the temp. speeds up chemical reactions and increases the rate of photosynthesis, but soon the temp gets too high and photosynthesis rate decreases

Rate of photosynthesis1. Light, CO2: eventually level off @ maximum

2. Temperature: reach a maximum & decrease– Enzymes begin to become unstable & ineffective

– Stomata close & limit water loss & CO2 entry

Cellular Respiration

Chapter 7

Cellular Respiration Overview

A. Releases energy from organic molecules (sugars) to make ATP (available cell energy)

B. Done by autotrophs and heterotrophsC. Aerobic respiration – organic molecules

broken down with oxygen – yields a lot of ATP

D. Anaerobic respiration – organic molecules broken down without oxygen – little or no ATP.

E. Living organisms could specialize in one, or switch depending on available oxygen.

GlycolysisA. All organisms begin respiration with glycolysis (to break glucose) = small amount of energy

(net 2 ATP produced), but makes energy carrying (electron) molecule NADH and pyruvic acid (organic product)

B. Anaerobic in nature

C. Products can either be fermented (recycle NADH) or aerobically broken (lots of ATP)

D. Takes place in cytoplasm

E. Reactions in the biochemical pathway:

Glycolysis

1. 2 phos. groups attach to glucose from 2 ATPs to form a new 6 C compound

2. 6 C comp. splits into 2 PGAL molecules (3 C)

3. 2 phos. groups attach to PGALs and PGALs oxidized. NAD+ reduced to NADH.

4. Phos. groups removed and combine with ADPs → ATP. 2 pyruvic acid molecules formed.

Do Now

• 1. What is cellular respiration?

• 2. What is anaerobic respiration?

• 3. What is aerobic respiration?

• 4. What is glycolysis?

Fermentation

A. Performed in the absence of oxygen

B. Makes no ATP, occurs in cytoplasm

C. Regenerates NAD+ which can keep glycolysis going

D. Types:

1. Lactic Acid

2. Ethyl alcohol

Lactic Acid Fermentation• Enzyme converts pyruvic acid into lactic acid• Some bacteria & fungi do this → yogurt, cheese• Animal cells (Muscle cells w/o oxygen)

Lactic Acid Fermentation

• Occurs when you are exercising strenuously• Muscle cells use up oxygen faster than you can breathe it in• Muscle cells switch from aerobic

respiration to lactic acid fermentation• Can make muscles sore and cause

cramping• Eventually the lactic acid gets turned

back into pyruvate in the liver

Alcoholic Fermentation• Plants and yeast• Pyruvic acid is broken down and a CO2 is

removed, the resulting 2C compound is ethyl alcohol.

Alcoholic Fermentation

• The basis of the beer

and wine industry

• Yeast cells are added

to either crushed grapes

or grains

• They perform fermentation to produce ethyl alcohol– Regular wine – CO2 is released

– Beer and champagne – CO2 is retained

Anaerobic Energy Yield

• When glucose is broken down anaerobically, only 2 ATPs are produced during glycolysis

• Most of the energy is still trapped in the pyruvic acid

• The efficiency of energy transfer is very low at 3.5%

• This is OK for small, unicellular organisms, but larger organisms need more energy!!

Do Now

• 1. Is fermentation done in the presence or absence of oxygen?

• 2. What are the 2 types of fermentation we talked about?

• 3. Is fermentation efficient for energy transfer?

Aerobic Respiration

• If oxygen is present, pyruvic acid goes from glycolysis to aerobic respiration

• Aerobic respiration produces ~ 20 X as much ATP

• 2 major stages:– 1. Kreb’s Cycle – small amount of ATP– 2. Electron transport chain – large

amount of ATP

Aerobic RespirationOccurs in mitochondria of eukaryotes

(cytoplasm in prokaryotes) 1. Outer membrane

2. Inner membrane (cristae – folds)

3. Matrix – inside inner membrane – contains enzymes needed to catalyze the Kreb’s Cycle

Coenzyme A/Acetyl CoA

1. As Pyruvic acid enters the mitochondrial matrix it bonds with Coenzyme A (CoA) and produces CO2 & Acetyl CoA & a.NAD+ → NADH

2. Acetyl CoA begins the Kreb’s cycle

Kreb’s CycleBreaks down Acetyl CoA producing CO2,

H atoms, and ATP

1. Acetyl CoA rxts w/ oxaloacetic acid → CoA + citric acid

2. 1 glucose does 2 cycles

3. Kreb’s cycle produces 2 CO2,

3 NADH, 1 FADH2 and 1 ATP per cycle

(x2 b/c 2 cycles)

4. NADH & FADH2 used in ETC

Energy So Far• Bulk of the energy released by the oxidation

of glucose is still not in form of ATP

• This will require the NADH and FADH2 that we have made so far– Glycolysis – 2 NADH– Convert Pyruvic Acid to Acetyl CoA – 2 NADH

– Kreb’s Cycle – 6 NADH, and 2 FADH2

• These 10 NADH and 2 FADH2 molecules will enter the electron transport chain and make ATP

Electron Transport Chain1. Electrons for the ETC are supplied by the

splitting of NADH and FADH2

2. Protons from NADH and FADH2 are pumped through the inner mitochondrial membrane away from the matrix by the ETC

3. The pumping of protons across the membrane creates a conc. gradient which is then used to make ATP by ATP synthase.

4. Final e- acceptor is O2. (H20 is produced)

Electron Transport Chain

Energy1. Converted in the ETC

a. 1 NADH = 3 ATP

b.1 FADH2 = 2 ATP

2.

a. 38 ATP (12 kcal)/Glucose (686 kcal)

b. Aerobic Efficiency = 66%

Respiration Equation

• C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy

• This equation is the opposite of the equation for Photosynthesis!