Botany Quiz - Photosynthesis Light Reactions

What does Photosynthesis do?

Produces the basic organic molecules a plant needs in order to survive and reproduce 

What are the 2 stages of Photosynthesis?

1. Light Dependent

2. Light - Independent (Calvin Cycle)

Where does photosynthesis occur?

Occurs in the chloroplasts of plants 

Where does light dependent photosynthesis occur?

The thylakoid membrane

Where does the Calvin Cycle occur?

The Stroma

What is the thylakoid system?

The green colored pigments called chlorophyll are found in the thylakoid membrane

What are Light Reactions and what do they produce?

• "photo" part of photosynthesis, captures light 

• uses light energy water to generate chemical energy (ATP, NADPH) 

• releases O2

What is the Calvin Cycle

"synthesis" part of photosynthesis, assembles simple sugars using energy from the light reaction

How do you summarize photosynthesis

Photosynthesis can be summarized in terms of the amount of CO2, and H2O needed to produce one molecule of glucose (C6H12O6)

Chemical Equation of Photosynthesis

6CO2 + 6H2O + light energy -> C6H12O6 + 6O2

Differentiate photosynthesis and respiration

1. Photosynthesis : Photosynthesis by itself does not sustain life, while it produces food, it does not describe how energy is extracted from the food

2. Respiration : Respiration harvests energy from the food produced by photosynthesis

Photosynthesis and respiration are interdependent, each process relies on each other | Photosynthesis uses CO2 and H20 resp uses sugars and O2

What happens and is produced in light reactions?

• Light energy is absorbed by chlorophyll pigments to make two energy-rich compounds:

  • ATP ~ Adenosine Triphosphate 

  • NADPH ~ Nicotinamide adenine dinucleotide phosphate

What are the main types of chlorophyll in plants and green algae?

chlorophyll a and chlorophyll b

What structure in chlorophyll absorbs light?

 the porphyrin ring system

What is Chlorophyll A and what does it do?

• In plants, chlorophyll a is the only pigment directly involved in the light reactions

• It primarily absorbs light from the blue violet and red ranges of the spectrum mainly reflects green light

What is Chlorophyll B and what does it do?

• Chlorophyll b does not take part directly in the light reactions

• Absorbs light and then transmits it to chlorophyll a

• Chlorophyll b therefore is an accessory pigment

Why do plants need accessory pigments

Chlorophyll A only makes up 1% of all pigments, other pigments are needed to absorb the light and help chlorophyll a

What is carotenoid and what does it do?

1. An accessory pigment which will primarily absorb blue-green light and reflect yellow

2. Carotenoids help dissipate excess energy as heat instead of letting it form harmful reactive oxygen species (ROS)

What are Photosystems

• Chlorophyll pigments cluster along associated protein molecules

• Light reactions are triggered by one chlorophyll a molecule which absorbs energy of a photon

What occurs after a chlorophyll a molecule absorbs a photon?

• It then ejects an electron that is then absorbed by a molecule known as a primary electron acceptor

The combination of chlorophyll a molecule and the primary electron acceptor is called what?

a reaction center

What is the function of a reaction center

• The reaction center and accessory pigments work together as a light harvesting unit known as a photosystem

Is chlorophyll a directly hit by protons often?

No | Chlorophyll a represents less than 1% of the pigments in a photosystem → Accessory pigments funnel the energy from photons to the chlorophyll a

What are the 2 types of photosystems and where do they occur?

1. photosystem I 

2. photosystem II

They occur repeatedly throughout the membrane

What molecule may be found in photosystem 2?

• The chlorophyll a molecule in the reaction center in photosystem II is called P680

  • P stands for pigment

  • The number means that it absorbs light best at 680nm

What molecule may be found in photosystem 1?

• The chlorophyll a molecule in the reaction center in photosystem I is called P700

What are the two light-absorbing photosystems are linked together in a zigzag pattern called?

a Z-scheme

What does a Z-scheme represent?

shows the unidirectional flow of electrons from photosystem II ultimately to NADP+

What occurs in the first 2 steps of the photo system 2 process

1. Photosystem II absorbs light energy

2. When light energy reaches the chlorophyll a it energizes an electron in the chlorophyll a molecule

In photosystem 2 when light energy reaches Chlorophyll a, and an electron is energized what happens to that electron?

This electron is transferred to the primary electron acceptor, pheophytin

After an electron is transferred to pheophytin in photosystem 2 what occurs next?

1. Each ejected electron is quickly replaced by an electron from H2O, after an enzyme splits a molecule into 2 electrons, 2 H ions (H+), and one O atom

2. Excited electrons (2e-) are passed to pheophytin, plastoquinone, cytochrome b6f complex, plastocyanin, and then to photosystem I
   

What occurs in the electron transport chain?

1. Electrons gradually lose energy by transfer through the electron transport chain

2. The energy that is released by the flow of electrons is indirectly used to power the synthesis of ATP

3. Each electron that passes through the ETC neutralizes the positively charged chlorophyll a in the reaction center of photosystem I

What occurs in photosystem 1?

1. This chlorophyll pigment is positively charged because the absorption of a photon has ejected a reenergized electron

2. The reenergized electron is transferred to a primary electron acceptor, chlorophyll A0

3. Each electron ejected from photosystem I passes through another electron transport chain

4. Passed to membrane sulfur proteins, ferredoxin, and finally to NADP+ reductase, which reduces NADP+ to NADPH

What occurs in Light Reactions ?

1. the light reactions use the energized electrons ejected from photosystem II in producing ATP

2. use the reenergized electrons ejected from photosystem I in producing NADPH

What does the Electron Transport Chain power and cause?

1. The energy that is released by the flow of electrons is indirectly used to power the synthesis of ATP

2. This energy lost in ETC is used to pump protons from the stroma into the thylakoid compartment

3. This causes a concentration difference in H+ ions across the thylakoid membrane

What do excited electrons pass in the electron transport chain (name every acceptor in order)

1. Pheophytin

2. Plastoquinone

3. Cytochrome b6f complex

4. Plantacyanin

5. Eventually Photosystem 1

What are harmful Reactive Oxygen Species and give an example of 1?

1. some are free radicals

2. are taken care of by Peroxisomes

3. can cause damage to various cellular organelles

Example : Hydrogen Peroxide (H2O2)