Photosynthesis Part I (Photosystem II)

What is the overall reaction for photosynthesis?

Carbon dioxide+Water---->(sunlight) glucose +Oxygen

Describe the structure of a chloroplast

Has two membranes, Stroma,and Thylakoids

Thylakoid

Thylakoids are membranous sacs. There are 2 types-Grana and Lamellae

Grana (Granum)

Stacks of round thylakoids. They look like "stacks of pancakes"

Stroma

Fluid-filled space between the thylakoid and inner membrane

Lamellae

Linking a thylakoid within one granum to one in another. They are the sites of photosystem I.

What are the two main steps of photosynthesis and what are the reactions associated with each?

Light Reactions and Calvin Cycle.

Light reactions form oxygen from water and produce ATP+NADPH. Calvin Cycle uses carbon dioxide, ATP, and NADPH to make glucose.

What are the light reactions?

Photosystem II and photosystem I

What are the photosystems composed of?

Pigments and Proteins

What are chlorophyll molecules composed of?

A "head" containing Magnesium and a lipid "tail" to anchor in the thylakoid membrane.

What do chlorophyll molecules do?

Absorb blue, violet, and red light

Why do plants need Magnesium?

So that the chlorophylls are continually made.

Describe the structure of a photosystem.

The outer portion of the the photosystem are chlorophylls, accessory pigments, and protein. The inner part contains special pigments, called PED and PEA.

What is the antennal complex?

The part of the photosystem that captures the photons.

What does the antennal complex do?

The photons are absorbed by the chloroplasts and the excited electron gets passed from chloroplast to chloroplast until it reaches the reaction center.

What is in the reaction center?

The reaction center is where the energized electron leaves the antennal complex.

What are accessory pigments and what do they do?

Accessory pigments are Carotenoids, xanthophyll, and others. They absorb green and other colors.

Why do leaves change color in the fall?

Because the accessory pigments are shown through as the chloroplasts die.

Describe what happens in the antennal complex and the reaction center in photosystem II.

In the antennal complex, electrons are passed from chloroplast to chloroplast to excite the electron. In the reaction center, the electron leaves in the PEA.

What are the primary electron donor and primary electron acceptor in photosystem II?

The primary electron donor is P680. The primary electron acceptor is pheophytin.

How and why is oxygen generated by photosystem II?

The four electrons removed from the water molecules are transferred by an electron transport chain which is formed hydrogen ions and molecular oxygen to plastoquinone2. By obtaining these electrons from water, photosystem II provides the electrons for all of photosynthesis to occur

Describe how energy is collected and transferred by the antennal complex.

Photons are captured by the chlorophyll and accessory pigments. The energy is passed from chlorophyll to chlorophyll until it reaches the reaction center.

What does it mean when we say an electron in chlorophyll is "excited"?

The electron has a lot of energy.

What happens to the electron from the reaction center chlorophyll in photosystem II?

It is passed from chlorophyll to chlorophyll until it reaches the reaction center. It then gets accepted by the PEA.

How are the photosystem II reaction center chlorophyll regenerated after they lose an electron?

Chlorophyll splits a water molecule to make up for the electron it just lost making hydrogen ions and oxygen.

What are the primiary electron acceptor and primary electron donor composed of?

The PEA is chlorophyll without magnesium. The PED is a chlorophyll dimer

What are the primary electron acceptor and primary electron donor's role in photosynthesis?

When the electron is added to the PED, it breaks apart a water molecule. Then the electron is transferred to the PEA so that it can go on to the electron transport chain.

What is the electron transport chain used for in photosystem II reactions?

It pumps the hydrogen ion from the stroma to the thylakoid interior

How is a hydrogen ion gradient generated?

When the electron is transfered to the Electron Transport Chain, hydrogen ions are pumped from a low concentration of H+ to a high [H+]

What is this hydrogen ion gradient used for and how is it used?

They hydrogen ion gradient is used to spin the ATP synthase to make ATP.

What is the output of photosystem II?

ATP