capturing solar energy: photosynthesis - miamifig.cox.miami.edu/~ddiresta/bil101/lec10.pdfcapturing...

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Capturing Solar Energy:

Photosynthesis

(a)

(b) internal leaf structure

chloroplast in mesophyll cell

mesophyllcells

chloroplastsstomavein

channelinterconnectingthylakoids

(c)

outer membraneinner membranethylakoidstroma

Photosynthesis

• Complex series of chemical reactions involving a transition in forms of energy

• Uses light energy to make food and is a process by which some organisms can make organic compounds from simple inorganic compounds using energy from the sun

Photosynthesis

• Light energy captured and stored as chemical potential energy in the covalent bonds of carbohydrate molecules

6 CO2 + 6 H2O + light → C6H12O6 + 6 O2

Life depends on photosynthesis

• A. Foundation of energy for most ecosystems

• B. Source of oxygen

• C. Key component of the carbon cycle

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The mechanism of photosynthesis

• Solar energy and light

• The electromagnetic spectrum

– Pigment molecules absorb some wavelengths of light and reflect others

• Chlorophyll—a green photosynthetic pigment associated with the thylakoid membranes of chloroplasts

(a)

(b)

chlorophyll

carotenoids phycocyanin

(c)The mechanism of

photosynthesis

• Chloroplasts are the sites of photosynthesis

– Have a membrane system within internal space (stroma)

– Arranged in disk-shaped sacks (thylakoids)

• The thylakoids contain light-harvesting photosynthetic pigments & enzymes

• Internal membranes define space (lumen) that is separate from the rest of the stroma

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electron transport system

chloroplast

thylakoids

light- harvestingcomplex

reactioncenter


Photosynthesis occurs in two steps

1. Light-dependent reactions

• a. Provides the energy necessary to fix carbon

• b. Occurs in the thylakoid membranes

• c. Generates ATP

• d. Photolysis—light, electrons and water

2

1

3

4

5

6

7

8

9

electron transportsystem

energy to drive

photosystem II

photosystem I

reactioncenter

reactioncenter

synthesis


Energy carriers ATP and NADPH transport energy from the light-dependent reactions to the light-independent reactions

energy from sunlight

Light-dependentreactions occur in thylakoids.

Light-independentreactions (C3cycle)occur in stroma.


2. Light-independent reactions

a. Uses energy of the light-dependent reaction to make sugar from CO2

b. Occurs in the stroma

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2 G3P availablefor synthesis oforganic molecules.

3 RuBPregeneration uses energy and 10 G3P.

2 G3P synthesisuses energy.

1 Carbon fixationcombines CO2with RuBP. C4 plants utilize an alternate

pathway to make sugars in dry environments

• Closing stomata to conserve water results in photorespiration in C3plants

Much photorespirationoccurs under hot,dry conditions.

CO2 is capturedwith a highlyspecific enzyme.

Almost nophotorespirationoccurs in hot,dry conditions.Much glucose

synthesis occurs.

mesophyll cell in C4 plant

mesophyll cell in C3 plant

bundle-sheath cell in C4 plant

bundle-sheath cells

C3 plants use the C3 pathway

C4 plants use the C4 pathway

In a C3 plant, most chloroplasts are in mesophyll cells.

In a C4 plant, both mesophylland bundle-sheath cells contain chloroplasts.

(a)

(b)

The History of Life on Earth

When did life arise on Earth?

• The Earth is thought to be approximately 4.6 billion years old, but life is believed to have occurred approximately 4 billion years ago (bya)

•How did life begin???

The Origin of Life: Early Ideas

• Spontaneous Generation– idea popular in the 1600-1700’s– living things come from the nonliving– evidence: beetles and other insect larvae arise from

cow dung; frogs emerge from mud

• In 1688, the Italian Francisco Redi In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars. He demonstrated that meat that was covered did not produce maggots

• This may have been the first true scientific experiment…

Francesco Redi experiment with flies and wide-mouth jars

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The Origin of LifeSpontaneous generation

• Mid-1800s—disproved by Louis Pasteur and John Tyndall

Broth in flask is boiled to kill preexisting microorganisms.

Condensing water collectsas the broth cools, sealing

the mouth of the flask.

If neck is later broken off,outside air can carry

microorganisms into broth.

no growth growth

Other Ideas: Life from a Biblical Creation?

Christian Creationism states that the world, including all life, was created about 6,000 years ago in six literal days by a God.

…But how does one accurately and fairly test for this?...What’s the observation, hypothesis, test…?

This idea does not really fit into the confines of a Science course.

Like the study of French Impressionist painters, Religion is not part of, nor adequately covered in, a Science course.

Origin of Life:Another idea Biogenic-looking features in

ALH84001 Martian meteorite

http://ares.jsc.nasa.gov/astrobiology/biomarkers/images.html

In 1969, a meteorite (left-over bits from the origin of the solar system) landed near Allende, Mexico. The AllendeMeteorite (and others of its sort) have been analyzed and found to contain amino acids, the building blocks of proteins.

This idea of panspermia hypothesized that life originated out in space and came to earth inside a meteorite. The amino acids recovered from meteorites are in a group known as exotics: they do not occur in the chemical systems of living things. The ET theory is now discounted by most scientists, although the August 1996 discovery of the Martian meteorite and its possible fossils have revived thought of life elsewhere in the Solar System.

Anyway….This only moves the problem to elsewhere!

Extra-terrestrial OriginsThe Latest on Extra-terrestrial Origins…

The Raelians

• Raelians believe that humanity was created from the DNA of superior alien scientists

• Follow the teachings of a former French magazine sportswriter and wannabe race-car driver Claude Vorilhon, 56. He took the name "Rael" after he claimed a close encounter of the third kind….

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Origin of Life: Current Theory• Chemical Evolution• .....The idea that long ago complex

collections of chemicals formed the first cells.

• Life began in the oceans 4 bya from simple chemicals joining together in a “primordial soup”

• Complex chemicals evolved into living cells

What were the conditions like on Earth when life arose?

• Up to about 4 bya, asteroid impacts and volcanic eruptions resulted in the release of various gases that began to form an atmosphere

• It consisted mainly of CO2, with some nitrogen, water vapor and sulfur gases; hydrogen quickly escaped into space

• CO2 in the atmosphere trapped solar radiation, making the Earth’s surface rather warm

• Earth was cool enough to form a crust, and water vapor condensed to form oceans

• Oceans in turn helped to dissolve CO2 from the atmosphere and deposit it into carbonate rocks on the seafloor

What were the conditions like on Earth when life arose?

• Organic molecules were undoubtedly being formed on the Earth’s surface

• Lightening and ultraviolet radiation from the Sun acted on the atmosphere to forms small traces of many different gases, including ammonia (NH3), methane (CH4), carbon monoxide (CO) and ethane

• Also, cyanide (HCN) probably formed easily in the upper atmosphere, from solar radiation and then dissolved in raindrops

The Origin of Life

The possible origin of organic molecules

• a. 1953—the Stanley Miller experiment

What is the simplest living cell that one can imagine?

A universal minimal cell must contain the following::

• Cell membrane • Cytoplasm • DNA and RNA • Proteins • Enzymes • Ribozymes

The Origin of LifeEarly Speculations

• More circumstantial evidence accumulated

– Astronomers found simple organic compounds in meteorites

– They were convinced that Earth’s initial atmosphere could not have matched Oparin-Haldane’s model

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• More circumstantial evidence– Fossils of ancient bacteria (3.5 billion years old)

were found in Australia– Suggested life may have evolved rapidly in less

than a billion years


• What are the possible scenarios?

– When ocean tidal pool evaporates• Salts get highly concentrated

– Could have happened in ancient oceans• Concentrating aminos, may allow

protein to form


• Phospholipids arrange themselves into bubbles– Chemicals could be concentrated in bubbles (might

contain protein, etc.)

– These bubbles would persist aided by natural selection

– If they burst, spew contents into air where other reactions occur

– Over hundreds of millions of years, similar processes could have filled oceans with proteins, carbohydrates, phospholipids, nucleotides


• Phospholipids arrange themselves into bubbles

– Eventually they reach a level of complexity

• Called protocells (not living)

• Still can’t reproduce, no DNA


• Is DNA essential?

– Scripps Institute, 1993 found small molecules of synthetic RNA that within an hour began making copies of itself & the copies made more copies

– Then copies began to change - evolve-acquiring new chemical characteristics, but not alive


• Is DNA essential?– Protocells might qualify as the first cells if they have

RNA that:

• Can make copies of itself & evolve

• Could synthesize enzymes capable of breaking down other organic compounds

• Could synthesize enzymes capable of building and maintaining cell membranes

– Later DNA could have evolved as method of conveniently & safely

• Storing vital chemical info contained in cell RNA

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The First Cells

• Age of microbes—3.5 billion years ago

• 1. The earliest living cells—anaerobic prokaryotes

• 2. Photosynthetic bacteria and the evolution of an oxygen-rich environment

• 3. Development of aerobic metabolism

II. The first cells

• The rise of eukaryotes—about 1.4 billion years ago

• 1. Endosymbiotic hypothesis

• 2. The origin of the nucleus

1. Anaerobic, predatoryprokaryotic cell engulfsan aerobic bacterium.

2. Descendants of engulfedbacterium evolve intomitochondria.

3. Mitochondria-containingcell engulfs a photosyntheticbacterium.

4. Descendants of photosyntheticbacterium evolve into chloroplasts.

aerobicbacterium

First Cell Types

• Heterotrophic cells– Incapable of producing their own food

• Autotrophs– Can produce chemicals to store energy

• Chemoautotrophs– Store energy found in certain inorganic chemicals

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First Cell Types• Most organisms found free oxygen intolerable

– In oceans

• Organisms that built simple and complex organic compounds

• Removed CO2 from the atmosphere

• More advanced autotrophs removed most of the rest & replaced it with oxygen

• The excess oxygen changed forever chemical nature of atmosphere to today’s

Further Evolution of First Cells

• First cells, prokaryotes, were always simple in structure

• 2 - 1.5 billion years ago– A new cell appeared – eukaryotes– Had membranes to isolate certain chemical

reactions

• Cellular life then evolved into what we know today

Archaea & Bacteria Domains

• Directly related to oldest organisms on earth– Have had lots of time to evolve & differentiate

• Thrive nearly everywhere – Depths of oceans & Earth, all surfaces

Multicellular organisms

• A. Advantages of multicellularity

• B. Challenges of multicellularity

• C. The first multicellular organisms

• 1. Plants—primitive marine algae • 2. Animals—marine invertebrates

• D. The transition to land • 1. Advantages of terrestrial living • 2. Challenges of terrestrial living

III. Multicellular organisms

• The transition to land

• The evolution of land plants

• a. The first land plants • 1) Mosses and ferns • 2) Continued water dependency

• b. Conifers—the invasion of dry habitats

• c. Flowering plants • 1) The dominant plant form today • 2) Pollination by insects

•


• D. The transition to land

• The evolution of terrestrial animals • a. Arthropods

• b. Lobefin fish to amphibians

• c. Amphibians to reptiles • 1) The age of the dinosaurs • 2) Reptiles and maintenance of body temperature

• d. Birds • 1) Insulating feathers retain body heat • 2) Evolution of feathers for flight

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The evolution of terrestrial animals

• e. Mammals

• 1) Insulating hair retains body heat

• 2) Live births and mammary glands

Ordovician: 50% of animal families, including many trilobites

Devonian: 30% of animal families, including agnathan and placodermfishes and many trilobites.

Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.

Triassic: 35% of animal families, including many reptiles and marine mollusks.

Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.

Current extinction crisis causedby human activities. Many speciesare expected to become extinctwithin the next 50–100 years.

Species and families experiencing mass extinction

Bar width represents relative number of living species

Extinction

Millions ofyears ago

PeriodEra

Pale

ozoi

cM

esoz

oic

Cen

ozoi

c Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Today

65

180

250

345

500Extinction

Extinction

Extinction

Extinction

Extinction

IV. Human evolution

• A. Primate evolution •

• 1. Grasping hands—precision grip and power grip

• 2. Binocular and color vision with overlapping fields of view

• 3. Large brain—allows fairly complex social systems

Ardipithecusramidus

Australopithecusafarensis

H. heidel-bergensis

A. boisei

A. africanus

A. robustus

H.habilis

H.sapiens

H. erectus

Homo ergaster

H. neanderthalensis

IV. Human evolution

• Hominid evolution • 1. The evolution of dryopithecines—between

20 and 30 million years ago

• 2. Australopithecines—the first true hominids • a. Appeared 4 million years ago as evidenced by

fossils • b. Walked upright • c. Large brains

IV. Human evolution

• 3. Homo habilis—2 million years ago • a. Larger body and brain • b. Ability to make crude stone and bone tools

• 4. Homo erectus—1.8 million years ago • a. Face of modern human • b. More socially advanced • c. Sophisticated stone tools aided in hunting • d. Used fire

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IV. Human evolution

5. Homo sapiens—200,000 years ago

• a. Neanderthals evolved 100,000 years ago •

• 1) Similar to humans–muscular, fully erect, dexterous, large brains

• 2) Developed ritualistic burial ceremonies

• b. Cro-Magnons evolved 90,000 years ago

• 1) Direct descendants of modern humans

• 2) Were artistic and made precision tools

capturing solar energy: photosynthesis - miamifig.cox.miami.edu/~ddiresta/bil101/lec10.pdfcapturing...

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