Photosynthesis

Schreiber

Honors Biology

Who does it??• Photoautotrophs

• Plants• Algae• Protists• Bacteria

• **In Plants• Primarily Leaves• Mesophyll/

Parenchyma

Leaf Anatomy Review• Stomata

• Allow gas exchange

• Vein = Xylem and Phloem

Chloroplast Structure• Double Membrane

• Thylakoid – membrane bound compartment, site of the light dependent reactions of Photosynthesis

• Grana – Stacks of Thylakoids

• Stroma – Fluid surrounding thylakoids, site of light independent reactions

Light = electromagnetic wave made of photons (packets of energy)

Wavelength, Frequency, Energy

Light

Reflected

Transmitted

AbsorbedLight Granum

Absorption Spectrum of Chlorophyll

Light Absorbing Pigments• Chlorophylls are chemicals that have

lose electrons easily, so they provide energized electrons to other molecules. This is the fundamental process by which chlorophyll "captures" the energy of sunlight.

• There are several kinds of chlorophyll, the most important being chlorophyll "a". This is the molecule which makes photosynthesis possible, by passing its energized electrons on to molecules which will manufacture sugars. A second kind of chlorophyll is chlorophyll "b", which occurs only in "green algae" and in the plants.

Continued• Carotenoids are usually red,

orange, or yellow pigments, and include the familiar compound carotene, which gives carrots their color.

• Carotenoids cannot transfer sunlight energy directly to the photosynthetic pathway, but must pass their absorbed energy to chlorophyll. For this reason, they are called accessory pigments.

Hydrocarbon tailAnchors molecule to thylakoids

HYDROPHOBIC

Equation• Reactants = carbon dioxide and water

• Products = glucose, water, and oxygen

6 CO2 + 12 H2O C6H12O6 + 6 O2 + 6 H2O

6 CO2 + 6 H2O C6H12O6 + 6 O2

6

Overview

6 CO2 12 H2O

C6H12O6 6 H2O 6 O2

• Water Split – Releasing O2

• Electrons and hydrogen ions transferred to carbon dioxide, reducing it to sugar

• Light Dependent Reactions

• Convert Solar Energy to Chemical Energy, Split Water, Release O2, Produce ATP + NADPH

• Calvin Cycle – Light Independent Reactions

• Incorporation of carbon into organic molecules (carbon fixation), uses ATP

Reactants

Products

ATP

Adenosine tri phosphate

Ribose

3 phosphates

Adenine

High energy bondCells recycle

ATP

ADP + Pi ↔ ATP

Light Dependent Reactions

Overview of Light Reactions

1. Light energy energizes electrons from chlorophyll.

2. The electron travels through Photosystem II and I losing energy, the energy is used to pump H+ into the thylakoid space.

3. NADP+ accepts the electron and is REDUCED to form NADPH (goes to Calvin Cycle).

4. Water is split in this process, replenishing the electron to chlorophyll, generating H+ ions and oxygen.

5. Some ATP made (photophosphorylation) (goes to CC)

6. No sugars produced

Light Reactions

• http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html

LE 10-14

ATP

Photosystem II

e–

e–

e–e–

Millmakes

ATP

e–

e–

e–

Ph

oto

n

Photosystem I

Ph

oto

n

NADPH

Overview of Calvin Cycle/Light Independent RXNs

1. Carbon dioxide is incorporated into organic molecules. This process is called carbon fixation

2. Compounds then reduced to sugars by adding electrons

3. Requires energy provided by light reactions (ATP& NADPH)

4. Sometimes called the dark reactions Careful!!! This only means that these reactions do not need light, but they still happen during the DAY!

Light Independent Reactions

• http://www.science.smith.edu/departments/Biology/Bio231/calvin.html

https://www.youtube.com/watch?v=sQK3Yr4Sc_k

www.youtube.com/watch?v=g78utcLQrJ4