PHOTOSYNTHESIS Chapter 10. Sunbeams- photons provide the energy to drive photosynthesis. Without...

PHOTOSYNTHESIS

Chapter 10

Sunbeams- photons provide the energy to drive photosynthesis.Without photosynthesis almost all organisms would die. They would have no energy.

Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis.

To begin… the why of photosynthesis.

Growth, reproduction and maintenance of the organization of living systems require free energy and matter.

Organisms must exchange matter with the environment to grow, reproduce and

maintain organization.

a. Molecules and atoms from the environment are necessary to build new molecules. (BIOGEOCHEMICAL CYCLES)

1. Carbon moves from the environment to organisms where it is used to build carbohydrates, proteins, lipids or nucleic acids. Carbon is used in storage compounds and cell formation in all organisms. (atmospheric)

2. Nitrogen moves from the environment to organisms where it is used in building proteins and nucleic acids.

3. Phosphorus moves from the environment to organisms where it is used in nucleic acids and certain lipids.

4. Water. Living systems depend on properties of water that result from its polarity and hydrogen bonding. (Nitrogen & Phosphorus in water- roots)

W

Biogeochemical Cycles

Organisms capture and store free energy for use in biological

processes.a. Life requires a highly ordered system

b. Living systems do not violate the second law of thermodynamics, which states that entropy increases over time.

c. Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway.

d. Organisms use free energy to maintain organization, grow and reproduce.

e. Changes in free energy availability can result in changes in population size.

f. Changes in free energy availability can result in disruptions to an ecosystem.

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis. Organisms capture and store free energy for use in biological processes.

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a. Life requires a highly ordered system

1. Order is maintained by constant free energy input into the system. OPEN SYSTEM NOT CLOSED

2. Loss of order or free energy flow results in death. WITHOUT ATP THE ORGANISM WILL DIE

3. Increased disorder and entropy are offset by biological processes that maintain or increase order. PHOTOSYNTHESIS AND CELL RESPIRATION STORE AND CONVERT ENERGY INTO ATP WHICH CAN MAINTAIN ORDER AND INCREASE IT WHEN NEW PROTEINS AND CELLS ARE BUILT.

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis. Organisms capture and store free energy for use in biological processes.

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b. Living systems do not violate the second law of thermodynamics, which states that entropy increases over time.

1. Order is maintained by coupling cellular processes that increase entropy (and so have negative changes in free energy) with those that decrease entropy (and so have positive changes in free energy).

2. Energy input must exceed free energy lost to entropy to maintain order and power cellular processes. (lost as heat)

3. Energetically favorable exergonic reactions, such as ATP→ADP, that have a negative change in free energy can be used to maintain or increase order in a system by being coupled with reactions that have a positive free energy change.

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis. Organisms capture and store free energy for use in biological processes.

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c. Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway.

Illustrative examples:

• Krebs cycle

• Glycolysis

• Calvin cycle

• Fermentation

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis.

d. Organisms use free energy to maintain organization, grow and reproduce.

1. Organisms use various strategies to regulate body temperature and metabolism.

Illustrative examples:

– Endothermy (the use of thermal energy generated by metabolism to maintain homeostatic body temperatures) REQUIRES GREATER AMOUNTS OF FUEL/FOOD

– Ectothermy (the use of external thermal energy to help regulate and maintain body temperature) REQUIRES LESS FUEL/FOOD

– Elevated floral temperatures in some plant species RESEARCH WHY FOR EXTRA CREDIT

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis.

d. Organisms use free energy to maintain organization, grow and reproduce.

2. Reproduction and rearing of offspring require free energy beyond that used for maintenance and growth. Different organisms use various reproductive strategies in response to energy availability.

Illustrative examples:

– Seasonal reproduction in animals and plants

– Life-history strategy (biennial plants, reproductive diapause)

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis.

d. Organisms use free energy to maintain organization, grow and reproduce.

3. There is a relationship between metabolic rate per unit body mass and the size of multicellular organisms — generally, the smaller the organism, the higher the metabolic rate. HUMMINGBIRD vs. ME

4. Excess acquired free energy versus required free energy expenditure results in energy storage or growth. IF YOU EAT MORE THAN YOU BURN YOU WILL GAIN WEIGHT/GROW.

5. Insufficient acquired free energy versus required free energy expenditure results in loss of mass and, ultimately, the death of an organism. IF YOU DON’T EAT ENOUGH YOUR CELLS WILL TAKE ENERGY FROM APOPTOSIS OF CRUCIAL CELLS- LIKE CARDIAC MUSCLE. PLEASE EAT ENOUGH FOOD- HAVE ENOUGH STORED ENERGY AS MUSCLE & FAT.

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis.

e. Changes in free energy availability can result in changes in population size. (BOOM BUST CYCLES)

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to

maintain dynamic homeostasis.

f. Changes in free energy availability can result in disruptions to an ecosystem.

Illustrative Examples:

– Change in the producer level can affect the number and size of other trophic levels.

– Change in energy resources levels such as sunlight can affect the number and size of the trophic levels.

Rainforest- diverseTundra-notDesert-not

What organisms can do photosynthesis???

Photoautotrophs- plants, kelp, protists, fillametousous algae, cyanobacteria

CYANOBACTERIAALGAEUNICELLULARPROTIST

PLANT

KELP

In plants, where does photosynthesis occur?

Photosynthesis occurs within the :

leaves of plantswithin

mesophyll cellswithin

chloroplasts

LEAF IN CROSS SECTION

(MESOPHYLL CELLS)

CHLOROPLAST

Mesophyll cells filled with chlorplasts…

How is the chloroplast organized? (draw it)

a) Double membrane

b) Stroma

c) Thylakoid

What is the overall reaction for photosynthesis???

What is the overall reaction for photosynthesis???

6 CO2 + 12 H20 + photons --> C6H12O6 + 6 H2O + 6 O2

LIGHT RXNSthylakoid membrane

CALVIN CYCLEstroma

PHOTOSYNTHESIS: A 2 PART BIOCHEMICAL PATHWAY

#1: LIGHT REACTIONS• Occur on/through thylakoid

membrane• Chlorophyll is the light

absorbing pigment• Produces: ATP and NADPH

and O2 gas from H2O and light.

#2: LIGHT INDEPENDENT REACTIONS a.k.a. Dark reactions or Calvin Cycle

• Occur in the stroma• Produces C6H12O6 from CO2 & forms

H2O (condensation rxn) using energy supplied by NADPH and ATP

The Light ReactionsPhotons of lightabsorbed by chlorophylls inPHOTOSYSTEM II & IEnergized electrons travel ETC

e’s PS II PS I power a proton pumppump H+ into thylakoid spaceChemiosmosis ATPe’s PS I NADP+ NADPH(NADP+ is final electron acceptor)PS II’s replacement e’s from H20

The Calvin-Benson CycleC3 cycle/ dark rxns/ light independent rxns

OCCURS IN 3 STEPS:1) Carbon Fixation

6 CO2

2) Reduction12 ATP & 12 NADPH

3) Regeneration of RuBP (the CO2 acceptor)

6 ATP* 1 GLUCOSE

THE DETAILS

During photosynthesis, chlorophylls absorb free energy from light, boosting electrons to a higher energy level in Photosystems I and II.

Photosystems I and II are embedded in the internal membranes of chloroplasts

(thylakoids) and are connected by the transfer of higher free energy electrons through an

electron transport chain (ETC).

In photosynthesis,H2O is the electron donor and

NADP+ is the electron acceptor

O2, H+, and NADPH are produced.

When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical

gradient of hydrogen ions (protons) across the thykaloid membrane is established.

In prokaryotes, the passage of electrons is accompanied by the outward movement of protons

across the plasma membrane.

The formation of the proton gradient is a separate process, but it is linked (through

chemiosmosis) to the synthesis of ATP from ADP and inorganic phosphate via ATP synthase.

The energy captured in the light reactions as ATP and NADPH powers the production of

carbohydrates from carbon dioxide in the Calvin cycle, which occurs in the stroma of the

chloroplast.

QUIZ

What are autotrophs? Heterotrophs?

What are autotrophs?

• “self-feeders”/ producers

• Create chemical energy for self that is later converted to ATP via cellular respiration.

• The amount of sunlight and water available to the ecosystem determines the amount of energy.

• Compare and contrast a tropical rainforest with a desert with tundra biomes.

What are heterotrophs?

• “other-feeders”/ Consumers• Consumes energy trapped in the chemical bonds of autotrophs

or other heterotrophs.

• RAINFORESTS exhibit the greatest biodiversity (large #s and large #s of species)

• H20, sunlight, CO2 is abundant.

• Tundra lacks light and liquid water- low biodiversity

• Desert lacks water- low biodiversity

Where does the oxygen produced by plants come from?

Where does the oxygen produced by plants come from?

• The oxygen plants release comes from breaking water (by the water splitting enzyme) into 2 e-, 2 H+, and 1/2 O2 gas… is called PHOTOLYSIS.

Why does water appear on both sides of the reaction?

Why does water appear on both sides of the reaction?

• Water is used (reactant) to provide replacement electrons to photosystem 2 at the beginning of the electron transport chain.

• Water is released during the Calvin Cycle during the “condensation reactions” that form the glucose from CO2.

I. THE LIGHT REACTIONS

How is light used in the process of photosynthesis?

I. THE LIGHT REACTIONS

How is light used in the process of photosynthesis?

1. Photons drive electrons in ETC of the thylakoid membrane and and are used to make NADPH from NADP+.

2. Moving electrons power a proton pump which creates a concentration gradient. ATP is formed by chemiosmosis from the thylakoid space out into the STROMA.

Figure 10.5 The electromagnetic spectrum

380-750 nmVisible light spectrumis the energy that drives photosynthesis.

Figure 10.7 Determining an absorption spectrum

1) Chlorophyll a absorbs red & purple2) Chlorophyll b absorbs blue & orange3) Carotenoids absorb green & blue

LIGHT CAPTURING PIGMENTS:

Why do leaves change color in the fall?

Chlorophyll ainitiates the light reactions

Chlorophyll b andCarotenoids are accessory pigments

Figure 10.x1 Melvin Calvin

II. THE CALVIN-BENSON CYCLE

GENERATE SUGAR!!!!

DON’T FORGET THAT LAB #4 IS NEXT CLASS…

EXTRA CREDIT (1 QUIZ PT)TO HELP SET UP TOMORROWDURING 7TH PERIOD.

ALL YOU NEED TO KNOW IS THAT ATP & NADPH IS USED TO FORM GLUCOSE FROM CO2 AND H2O IN THIS ENZYME MEDIATED SERIES OF REACTIONS

On a hot dry day…plants reduce water loss (transpiration)

by closing their stomata = problem

PHOTORESPIRATION• Occurs in the light “photo”• Consumes Oxygen “respiration”• Problem: Rubisco binds oxygen as well as carbon dioxide.• Evolutionary relic from a time when the atmosphere lacked/was low in

Oxygen.• On hot days when plants close their stomates to prevent water loss,

CO2 levels drop and O2 levels rise.• Rubisco adds O2 to the Calvin Cycle… a two carbon product splits and

is transported to the peroxisomes where it is broken down into CO2.• Drains away as much as 50% of the carbon fixed by the Calvin cycle.

EVOLUTIONARY ADAPTATIONS TO PREVENT

PHOTORESPIRATION1) C4 Plants- have stomates partially closed during the

day. They preface the Calvin Cycle with an alternate form of carbon fixation that uses a different enzyme to “fix” Carbon dioxide that is more choosey… picks the few CO2 out like a needle from a haystack. It creates a 4 carbon compound (OAA) called the C4 pathway.

2) CAM Plants- use the C4 pathway then Calvin cycle; but also are strict… they have their stomates closed during the day and OPEN at night.

Creates a humid microclimate in an arid climate.

CRYPTSAre pockets on the Underside of the leaf

Biological systems utilize free energy and molecular building blocks to grow, to reproduce

and to maintain dynamic homeostasis.Organisms capture and store free energy for use in biological processes.

1. Different energy-capturing processes use different types of electron acceptors.

Cellular Respiration- Oxygen

Photosynthesis- NADP+

2. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules.

light rxns = H20 + Light ATP & NADPH + (O2) + CO2 glucose

3. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that prokaryotic (bacterial) photosynthesis was responsible for the production of an oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis.

PHOTOSYNTHESIS OUTLINE QUESTIONS:

Biological systems utilize free energy and molecular building blocks to grow, to reproduce

and to maintain dynamic homeostasis.Organisms capture and store free energy for use in biological processes.

a. Autotrophs capture free energy from physical sources in the environment.

b. Heterotrophs capture free energy present in carbon compounds produced by other organisms.

c. Different energy-capturing processes use different types of electron acceptors.

d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules.

e. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that prokaryotic (bacterial) photosynthesis was responsible for the production of an oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis.

f. Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed reactions that harvest free energy from simple carbohydrates.

g. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.