Photosynthesis

Photosynthesis

A process that converts solar energy to chemical energy

Light

A component of electromagnetic radiation. Can be described via wave characteristics or as particles of energy (photons).

Spectroscope

Separates individual wavelengths of the Sun.

Chlorophyll.

Green pigment that absorbs light. Color of pigment comes from wavelengths of reflected light.

Chlorophyll “a”

In all photosynthetic organisms; mainly where photosynthesis takes place.

Chlorophyll “b” (“c”, “d), Xanthophylls, and Carotenoids.

Accessory pigments that absorb the light chlorophyll “a” doesn’t. Light green, yellow, and orange respectively. When it gets cooler, there’s less sunlight, and therefore chlorophyll a and b break down, leaving behind carotenoids (and xanthophylls), which is why leaves are yellow and orange in autumn.

Spectrophotometer

Instrument that determines the wavelength of light absorbed or reflected by a pigment. Chlorophyll “a” reflects green light waves, and absorbs red & blue.

Chloroplasts

Organelles in leaves that performs photosynthesis. Has chlorophyll, which captures light for food production.

Leaf structure

Xylem & Phloem - transports water and food (respectively). Stomata -point of entry/exit for gases. Waxy cuticle & epidermis - protects plant from water loss. Palisades-houses the chloroplasts.

Chloroplast anatomy

Outer & inner membrane.

Stroma- (where carbon cycle happens) rich, semi liquid material inside of chloroplast.

Thylakoid- (where light reactions happen) system of interconnected flattened membranes sacs that form separate compartments with the stroma.

Thylakoid membrane- photosynthetic membrane in the chloroplast, contains chlorophyll and the electron transport chain.

Thylakoid lumen- fluid filled space inside the thylakoid.

• Photosynthesis occurs in the stroma and thylakoid membrane.

• Thylakoid system designed to have max. Surface area, and the chloroplasts replicate via division.

Paper chromatography

Method for separating different compounds in a solution. The solvents move up the paper in such a way that the smaller & more soluble you are, the farther you will travel up.

Reaction for photosynthesis

6H2O + 6CO2 + light — C6H12O6 + O2

What is ATP?

Adenosine triphosphate- a molecule that provides an immediate source of energy for cellular processes. It is formed by the addition of ADP and Pi (phosphate). The energy is stored when ATP is formed. But when it’s needed, it’s released, and ATP reverts back to ADP + Pi.

NADPH (nicotinamide dinucleotide phosphate)

This molecule is involved in energy transfers, and is in several places during photosynthesis. It is formed when NADP+ accepts 1 hydrogen ion, and 2 electrons. NADPH is an electron donor, so it eventually becomes NADP+ again.

Glucose

Transport molecule (blood sugar)

REDOX

ADP is reduced to form ATP (gains Pi and an electron). ATP is oxidized to form ADP (loses Pi and an electron)

REDOX pt.2

NADP+ is reduced when a hydrogen ion is added to it. It then becomes NADPH which is stable and cane be used to release energy to the next electron acceptor. (NADP+ + H — NADPH)

NADPH is oxidized when the hydrogen ion is taken away. It becomes NADP+ which can be reused in future reduction reactions. ( NADPH — NADP+ + H

3 stages of photosynthesis

1.) Capture solar energy and transfer it to electrons

2.) Use solar energy to make ATP; energized electrons are transferred to NADP+; NADPH is then used as a high energy electron carrier.

3.) Energy stored in ATP and NADPH is used to form energy-rich molecules (like glucose) from CO2.

Light dependant reactions

Location -inside thylakoid across thylakoid membrane.

Requirements - Sunlight, H2O, chlorophyll

Products - ATP, NADPH, O2.

In light dependent reactions, solar energy is trapped by chlorophyll molecules and used to make tow high energy compounds: ATP and NADPH

Light independent reactions (Calvin cycle)

Location - stroma

Requirements- ATP, CO2, NADPH, RuBP,

Product - G3P (glucose), NADP+, ADP.

In light independent reactions, energy of ATP and reducing power of NADPH are used to reduce carbon dioxide and make glucose. Therefore, both ATP and NADPH are oxidized in this reaction.

Photosystems (Stage 1 of photosynthesis (capturing solar energy))

Cluster of chlorophyll and other pigments packed into thylakoid membranes. Photosystems one and two use different forms of chlorophyll “a” ( p700 & p680 respectively), allowing for a wider range of wavelengths to be used for photosynthesis. All pigments in a photosystem capture and absorb photons.

• Solar energy is captured when an electron in a chlorophyll molecule in photosystem two absorbs a photon. Before said photon is absorbed, the chlorophyll has low energy. After it strikes, the chlorophyll absorbs it and the electron has high energy, transforming the photon to chemical energy.

• Two energized electrons are then removed from photosystem two, oxidizing the chlorophyll molecule while the electron enter the Electron Transport Chain (ETC). The electron is passed from one molecule to the next.

• Electron deficient p680 molecules (type of chlorophyll “a” in PS two) replace electrons by taking them from H2O via photolysis (breaking apart). Photolysis occurs in the thylakoid lumen and the chlorophyll is reduced after the fact. The solar energy that was absorbed by the chlorophyll is what facilitates photolysis. The oxygen is released out of the leaves or used later to make water. The hydrogen is used later to make ATP.

Stage 2:Electron Transfer and ATP Synthesis

High energy electrons from P680 travel down the ETC (which is often compared to a set of stairs) and gradually release built up energy. This same energy is later used in the production of ATP. Therefore energy derived from electrons is used to pull hydrogen ions across the membrane into the lumen, creating a high concentration of said hydrogen. By the time electrons reach the end of the ETC, they have lost almost all of their energy, and are then transferred to photosystem one and re-energized by photons. Thereafter, the electrons are transferred to NADP+ which takes in both those 2 electrons, and one hydrogen ion. The NADP+ is then reduced to NADPH.

• The two sources of hydrogen ions in the light dependant reaction are the ETC and photolysis. Due to the build up of hydrogen ions in the lumen, the concentration of positive ions increase, which in turn create an electrical gradient. They move from high concentration to low concentration through ATP Synthase, releasing potential energy from the hydrogen ions. This energy drives the synthesis of ATP (ADP + Pi — ATP). This process is called chemiosmosis.

• After all is said and done, oxygen leaves through the stomata of the leaves, and the newly formed ATP and NADPH are sent to stage three (Calvin cycle).