PHOTOSYNTHESIS• Autotrophs: Plants and plant-like organisms make their

energy (glucose) from sunlight or chemical bonds• Phototroph - use light as an energy source

• Chemotroph – obtain energy from chemicals (inorganic)

Video - chemotroph

meansmeans "putting together with light.""putting together with light."

Heterotrophs• Animals and other

organisms that must get energy from food instead of sunlight or inorganic chemicals

• Depend on autotrophs to obtain energy

Why is Photosynthesis important?

Makes organic molecules (glucose) out of inorganic materials (CO2 and H2O)

It begins all food chains/webs. Thus all life is supported by this process.

It also makes oxygen gas!!

Plants use glucose as food for energy and as a building block for growing.

6CO2 + 6H2O + sunlight C6H12O6 + 6O2

Photosynthesis-starts to ecological food webs!

How do we know that plants make carbohydrates from just carbon dioxide

water and light energy?

• Ex: Jan Baptisa van Helmont (1648) planted a willow branch weighing 5 pounds into 200 pounds of soil and then after 4 years the tree weighed 169 lbs. and the soil was still nearly 200 lbs.

Experiments!Experiments!

Photosynthesis

Carbon dioxide + water glucose + oxygensunlightsunlight

absorbed by chlorophyllabsorbed by chlorophyll

66COCO22 + + 66HH22O + energy O + energy C C66HH1212OO66 + + 66OO22

As can be seen from the equation for photosynthesis, the wood, bark, and root came from water and carbon dioxide.

PHOTOSYNTHESIS• 2 Phases

• Light-dependent reaction (Light Reactions)• Light-independent reaction (Calvin Cycle)

• Light-dependent: converts light energy into chemical energy; produces ATP molecules and NADPH to be used to fuel light-independent reaction

• Light-independent: uses ATP, NADPH, and CO2 to make simple sugars.

PHOTOSYNTHESIS• Light-dependent reaction (LIGHT Reaction)

• Requires light• Occurs in chloroplast- which have 2 membranes• Thylakoids –system of membranes inside the inner

membrane; arranged as flattened sacs• Grana – stacks of layered thylakoids• Stroma – solution surrounding the grana• membrane

Chloroplasts make the sugars!

Plant Cells

Elodea leaf x400

Chloroplasts make the oxygen too!

PlantsLeaves are green

because they contain

the pigment:

chlorophyll

Leaves have a Leaves have a large surface area large surface area to absorb as much to absorb as much light as possiblelight as possible

• Pigments: compounds that absorb different colors of white light (ROY G BIV) – visible spectrum

Visible light is only a small part of the electromagnetic spectrum (all forms of light).

When white light strikes an objet, its component colors can be reflected or absorbed by the pigments in the object

Main pigment: Chlorophyll a –directly involved in light reactions - absorbs less blue light but more red light than chlorophyll b Accessory pigments: Chlorophyll b and Carotenoids – enable plants to capture more energy by absorbing colors that chlorophyll a cannot -These pigments absorb all wavelengths (light) BUT green!

Why are plants green? - video

• LIGHT behaves as if it were composed of "units" or "packets" of energy that travel in waves. These packets are photons.

• The wavelength of light determines its color.

• Ted Talks – animation• Photosynthesis - song

PHOTOSYSTEMS• There are 2 photosystems, photosystem II and photosystem I.• They contain chlorophyll a, chlorophyll b, and carotenoids.• They are embedded in the thylakoid membrane.• There is a pair of “chlorophyll a” molecules at the base of each photosystem that harnesses all the energy captured by the

pigments.• Their job (chlorophyll a molecules) is to absorb light energy and pass it on to the electrons.

• Photosystem I and Photosystem II – different roles in the light reactions

Photosynthesis - song

THE LIGHT REACTIONSSTEP 1:•Begins when pigments (PSI and PSII) absorb light•Light energy forces electrons (e-) to enter a higher energy level in a pair of chlorophyll a molecules of PSII•“excited” e- leave chlorophyll a (oxidation reaction)•Each oxidation reaction must be accompanied by a reduction reaction so something has to accept the e-

THE LIGHT REACTIONSSTEP 2:•Primary Electron Acceptor – accepts the e- lost from chlorophyll a

STEP 3:•Primary Electron Acceptor donates the e- the first molecules of the ELECTRON TRANSPORT CHAIN•As e- are passed along the chain, they lose most of the energy the acquired when they were excited•This energy is used to move protons (H+) into thylakoid

NADPH

THE LIGHT REACTIONSSTEP 4:•Light is absorbed into PSI – happens at same time that light is absorbed into PSII

•e- move from a pair of chlorophyll a molecules in PSI to another Primary Electron Acceptor

•The e- lost by these chlorophyll a molecules are replaced by the e- that have passed through the ETC from PSII

NADPH

THE LIGHT REACTIONSSTEP 5:•At the end of the second ETC the electrons will be used to bond NADP+ and H+ to make NADPH an energy storing compound used in the Calvin Cycle.

•This happens in the stroma of the chloroplast.

Replacing Electrons • A special water splitting enzyme exists at the

base of PSII.

• The water splitting enzyme splits water into its parts.• Water (H2O)

• H+: The hydrogen proton will accumulate inside the thylakoids in the lumen.

• O2: The oxygen will be released by the thylakoids and it will end up in our atmosphere.

• The electrons from the hydrogen atom will enter at the base of PSII.

CHEMIOSMOSIS• the process of the movement of protons down their concentration

gradient for the synthesis of ATP• concentration of (H+) is great inside the thylakoid (from the splitting of

water and the H+ that were pumped on by the ETC)

• concentration gradient causes the H+ to diffuse through ATP synthase (an enzyme that helps make ATP by using the energy from the moving H+)

• That energy bonds ADP with a phosphate to make ATP in the stroma.

• Some of the H+ flowing into the stroma can be used to make NADPH.

• Both ATP and NADPH will be used in the Calvin Cycle (The Dark Reactions)

• In plants and simple animals, waste products are removed by diffusion. Plants, for example, excrete O2, a product of

photosynthesis.

PHOTOSYNTHESIS

• What affects photosynthesis?• Light intensity: as light increases, rate of

photosynthesis increases

PHOTOSYNTHESIS

• What affects photosynthesis?• Carbon Dioxide: As CO2 increases, rate of

photosynthesis increases

PHOTOSYNTHESIS

• What affects photosynthesis?• Temperature:

• Temperature Low = Rate of photosynthesis low

• Temperature Increases = Rate of photosynthesis increases

• If temperature too hot, rate drops

StomaThis opening how plants exchange gases!Can you name the two important gases that go in and out of the leaves?

Why are the Why are the stomata stomata located on the located on the underside of underside of leaves?leaves?

"Thanks for the Glucose!“"Thanks for the Glucose!“

LET’S PRACTICE! LET’S PRACTICE! - game

Calvin

Cycle

Calvin

Cycle

The Calvin Cycle –carbon fixingThe Calvin Cycle –carbon fixing1.1. 6 CO6 CO22 molecules enter the cycle. molecules enter the cycle.2.2. Enzyme “RuBisCo” combines six 5-carbon (RuBp) Enzyme “RuBisCo” combines six 5-carbon (RuBp)

molecules with the carbon from COmolecules with the carbon from CO22 and forms and forms them into twelve 3-carbon moleculesthem into twelve 3-carbon molecules

3.3. 12 ATP and 12 NADPH form the twelve 3-carbon 12 ATP and 12 NADPH form the twelve 3-carbon molecules into twelve High-energy 3-carbon molecules into twelve High-energy 3-carbon molecules (G3P)molecules (G3P)

4.4. 2 (G3P)of the twelve 3-carbon molecules are 2 (G3P)of the twelve 3-carbon molecules are combined to form a 6-carbon sugarcombined to form a 6-carbon sugar

5.5. 6 ATP molecules are used to convert the 10 6 ATP molecules are used to convert the 10 remaining 3-carbon molecules back into the six 5-remaining 3-carbon molecules back into the six 5-carbon molecules the cycle began with (RuBp) carbon molecules the cycle began with (RuBp)

Calvin

Cycle

Calvin

Cycle

Types of Photosynthesis

• C3 Photosynthesis

• C4 Photosynthesis

• CAM Photosynthesis

C3 Photosynthesis : C3 plants • Called C3 because the CO2 is first incorporated into a 3-

carbon compound. • Stomata are open during the day. • RUBISCO, the enzyme involved in photosynthesis, is

also the enzyme involved in the uptake of CO2. • Adaptive Value: more efficient than C4 and CAM plants

under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy).

Most plants are C3.

C4 Photosynthesis : C4 plants

• Called C4 because the CO2 is first incorporated into a 4-carbon compound.

• Stomata are partially closed during the hottest parts of the day.

• Have an enzyme that allows CO2 to be taken into the plant very quickly when CO2 levels are low and O2 levels are high.

• Photosynthesizes faster than C3 plants. • Has better water use efficiency because plants do

not need to keep stomata open as much • C4 plants include corn, sugar cane, and many of

our summer annual plants.

CAM Photosynthesis : Crassulacean Acid Metabolism • Named after plant family in which it was first found

(Crassulaceae) & because CO2 is stored as an acid before use in photosynthesis.

• Stomata open at night (evaporation rates are lower) and are closed during day.

• CO2 is converted to an acid and stored during the night. • During the day, the acid is broken down and the CO2 is released to

RUBISCO for photosynthesis • Better water use efficiency than C3 plants under arid conditions

due to opening stomata at night (no sunlight, lower temperatures, lower wind speeds, etc.)

• include many succulents such as cactuses and agaves and also some orchids and pineapples

Videos and other resources:

• Carbon Cycle Ted Talks - video

• Bozeman Science – video

• Crash Course –video

• Calvin Cycle game