Outline Overview Photosynthesis I III IV V Properties

Outline • • Overview Photosynthesis I. III. IV. V. • Properties of light and pigments Chloroplast structure and function Light reactions “Dark” or Carbon reactions Summary and conclusions Respiration I. Processes II. Energy and food chains III. Carbon Cycle

Photosynthesis and Cellular Respiration Photosynthesis and respiration are complementary processes in the living world. Photosynthesis uses the energy of sunlight to produce sugars and other organic molecules. These molecules in turn serve as food for other organisms that carry out respiration to obtain the chemical bond, a process that uses O 2 to form CO 2 from the same carbon atoms that had been taken up as CO 2 and converted into sugars by photosynthesis.

PHOTOSYNTHESIS 6 CO 2 + 6 H 2 O SUNLIGHT 6 O 2 + CHLOROPLASTS 1 C 6 H 12 O 6

RESPIRATION 1 C 6 H 12 O 6 + 6 O 2 6 H 2 O + 6 CO 2 + ATP MITOCHONDRIA

What came first, photosynthesis or respiration? The first cells on the earth are thought to have been capable of neither photosynthesis nor respiration. However, photosynthesis must have preceded respiration on the earth, since there is strong evidence that billions of years of photosynthesis were required before O 2 had been released in sufficient quantity to create an atmosphere rich in this gas. (The earth's atmosphere presently contains 20% O 2. )

Introduction to photosynthesis • From the Greek PHOTO = produced by light SYNTHESIS = a whole made of parts put together. Definition: PHOTOSYNTHESIS is the process whereby plants, algae, some bacteria, use the energy of the sun to synthesize organic compounds (sugars) from inorganic compounds (CO 2 and water).

WHY IS PHOTOSYNTHESIS SO IMPORTANT? PHOTOSYNTHESIS is one of the most important biological process on earth! • Provides the oxygen we breathe • Consumes much of the CO 2 • Food • Energy • Fibers and materials

GENERAL FORMULA FOR PHOTOSYNTHESIS * light * 6 CO 2 + 12 H 2 O -----> C 6 H 12 O 6 + 6 O 2 + 6 H 2 O pigments, enzymes • Oxygen on earth allowed for the evolution of aerobic respiration and higher life-forms. • Respiration: extracting energy from compounds (sugars) C 6 H 12 O 6 + O 2 6 CO 2 + ATP

PROPERTIES OF LIGHT Virtually all life depends on it! • Light moves in waves, in energy units called PHOTONS • Energy of a PHOTON inversely proportional to its wavelength • Visible light (between UV and IR) occurs in a spectrum of colors

Visible light contains just the right amount of energy for biological reactions

Light is absorbed by pigments • The primary pigment for photosynthesis is chlorophyll a • It absorbs blue and red light, not green (green light is reflected back!) Absorption spectrum of chlorophyll a

Chlorophyll a is the primary photosynthetic pigment that drives photosynthesis. Accessory pigments absorb at different wavelengths, extending the range of light useful for photosynthesis.

• Absorption spectrum of chlorophyll a: BLUE & RED • Action spectrum of photosynthesis closely matches absorption spectrum of chlorophyll a, but not perfectly (due to accessory pigments)

Chloroplast structure • • Football shaped Double membrane Stroma Thylakoid membrane • Grana (stacks) • Lumen (inside thylakoid) stroma Grana lumen thylakoids

Chloroplast structure and function: solar chemical factory

Chloroplast Membrane Structure • The thylakoid is the structural unit of photosynthesis containing photosynthetic chemicals. • Thylakoids are stacked like pancakes in stacks known collectively as grana. The areas between grana are referred to as stroma. • While the mitochondrion has two membrane systems, the chloroplast has three, forming three compartments.

Chloroplast Structure & Function • The chloroplast has three membranes: inner, outer, and thylakoid. It has three compartments: stroma, thylakoid space, and inter-membrane space. • These compartments and the membranes that separate them serve to isolate different aspects of photosynthesis. – Dark reactions take place in the stroma. – Light reactions take place on the thylakoid membranes.

Inside a Chloroplast • Remember: Structure correlates to function!

Overview of photosynthesis: Note: The Light and “Dark”or Carbon reactions happen at different sites in the chloroplast H 2 O light CO 2 LIGHT REACTIONS (Thylakoids) O 2 ATP “DARK” or CARBON REACTIONS NADPH (Stroma) (ENERGY) (OXYGEN GAS) C 6 H 12 O 6 (GLUCOSE)

The Light Reactions 1. Light dependent 2. Occur in the thylakoid membrane of chloroplast 3. Water is split into oxygen gas (O 2) and H+ 4. Use light energy (photons) to generate two chemical energy compounds: ATP & NADPH

The“Dark” or Carbon Reactions 1. Light independent (can occur in light or dark; some enzymes require activation by light) 2. Occur in the stroma of chloroplasts 3. Use the chemical energy produced in Light Reactions (ATP; NADPH) to reduce CO 2 to carbohydrate (sugar). 4. CO 2 is converted to sugar by entering the Calvin Cycle

Efficiency & Photosynthesis • Photosynthesis is not perfect. • Depending upon the plant type, it ranges from being only 1 - 4 % efficient to having 7% efficiency

Summary of Photosynthesis: 1. Light energy absorbed by chlorophyll a drives the reactions of photosynthesis. 2. Converts light energy into chemical energy to make organic compounds. 3. CO 2 and H 2 O used to produce C 6 H 12 O 6 (glucose) and O 2 (gas).

4. Light Reactions occur in thylakoids of the chloroplasts; ATP and NADPH are formed; water is split to O 2 (gas) and protons. 5. Carbon Reactions occur in stroma – Calvin Cycle fixes CO 2 to produce C 6 H 12 O 6 (glucose). 6. Low efficiency, about 1 - 7% 7. Nevertheless, PHOTOSYNTHESIS is still the most important biological process on earth!

Without photosynthesis, virtually all plants and animals would become extinct.

RESPIRATION • Process of making energy of food available in the cell… • Involves breaking down • Complicated molecules into simple molecules (C 6 H 12 O 6, sugars) (CO 2, water)

Chloroplast –vs- Mitochondria • Both are surrounded by a double membrane with an intermembrane space. • Both have their own DNA. • Both are involved in energy metabolism. • Both have membrane reticulations filling their inner space to increase the surface area on which reactions with membrane-bound proteins can take place.

Mitochondria Structure • The outer membrane to protect the organelle • The intramembranous space of the mitochondria (the space between the inner and outer membranes) • The inner membrane is folded into a series cristae or long folds that greatly increase the surface area of the inner membrane allowing more area for energy production.

RESPIRATION The energy held by complicated molecules is held temporarily as ATP (energy currency) C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + 36 ATP (glucose) (energy) Respiration occurs mainly in Mitochondria and Cytoplasm

Stages of Respiration Cellular Respiration has three main stages: • Glycolysis • Krebs Cycle • Electron transport system

3 Stages of cellular respiration • Glycolysis: Splitting of glucose – 2 net ATP generated • Krebs Cycle: Energy of glucose molecule is harvested as ATP (2) – it occurs in the mitochondria (matrix) • Electron Transport System: also happens in the mitochondria, more ATP are generated (32). • For each glucose molecule, total ATP = 36 • Only 39% efficient, rest is lost as heat.

Photosynthesis • • Reaction: Respiration CO 2+H 2 O+sun C 6 H 12 O 6+O 2+H 2 O C 6 H 12 O 6+O 2 CO 2+H 2 O+36 ATP Reactants: Carbon dioxide, water, sun Glucose, oxygen Products: Glucose By-products: Oxygen Cellular location: Chloroplasts Energetics: Requires energy Energy Chemical paths: Light reactions & Calvin cycle • Summary: Sugar synthesized using energy from the sun Carbon dioxide, water Cytoplasm, mitochondria Releases energy Glycolysis, Krebs cycle & Electron Transport Syst. Energy released from sugar breakdown

Photosynthesis and respiration • Photosynthesis and respiration are complimentary reactions…

PHOTOSYNTHESIS CO 2 + H 2 O O 2 + SUGARS O 2 H 2 O RESPIRATION SUGARS + O 2 H 2 O + CO 2 PLANTS, ALGAE, BACTERIA Sunlight energy SUGARS O 2 MOST LIVING ORGANISMS USEFUL CHEMICAL ENERGY (ATP) H 2 O

Respiration, Energy & Carbon Cycle • • Energy Virtually all organisms require energy of food for: Making chemicals (proteins, carbs, etc. ) Movement Cell division Heat, electricity and light production The way living organisms obtain energy is through Cell respiration

ENERGY: ability to do work Newton’s First Law of Thermodynamics: (1701) “Energy cannot be created or destroyed, it can only be transformed from one form to another” • Once a cell has used energy to do work, it cannot be used again by any organism.

ENERGY FLOW IS LINEAR Sun Earth Producers 1 o consumers 2 o consum heat resp, heat Energy flows into ecosystem from the sun Energy travels in a straight line by way of food chains.

ENERGY However, much energy is lost as heat along the way – as a result of respiration. Approximately 90% energy is lost on each step! • Newton’s Second Law of Thermodynamics: “In any transfer of energy there is always a loss of useful energy to the system, usually in the form of heat”

Food Chains Food chains demonstrate linear nature of energy • Producers are the base of the food chain, they include photosynthetic organisms like: • Plants • Algae • Certain bacteria

Food chains • Primary consumers – all plant eaters (herbivores). Secondary consumers – Eat primary consumers, (carnivores)

Food chains • Decomposers – obtain energy by breaking down remaining organic material of the other members of the food chain. • Fungi and bacteria.

Matter • All important elements move in cycles; Environment Organisms Cycles called biogeochemical cycles: Water cycle Carbon cycle Nitrogen cycle

The Carbon Cycle • Carbon from the atmosphere (CO 2) enters the biosphere by way of plants! – CO 2 used in photosynthesis – Carbon moves into food chain • Carbon is released to the physical environment by respiration – Release CO 2 during respiration – Amount CO 2 fixed in photosynthesis = the amount released by respiration

Carbon Cycle • Carbon moves from atmosphere to plants to animals and back to atmosphere.

“Look deep into nature, and then you will understand everything better. ” Albert Einstein

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