IB Bio Photosynthesis - C1.3

Out of IB bio textbook 🌳

What is photosynthesis?

Conversion of light energy to chemical energy using light and simple organic substances.

What is the equation for photosynthesis?

6CO2+6H2O→C6H12O6 + O2

What is chlorophyll?

A type of pigment that absorbs different wavelengths of light. Reflects green light which is why we see plants as green. Pigments absorb photons if their wavelength excites an electron within the pigment.

What is an absorption spectrum?

A graph showing the percentage of light absorbed at each wavelength by a certain pigment. X-axis shows wavelength in nanometers, y-axis shows the absorption of light as a percentage or arbitrary unit.

What is a limiting factor of photosynthesis?

CO2 levels, light levels, temperature

What is a photosystem?

Protein complex that contains chlorophyll and is located in the thylakoid membrane of chloroplasts. In light-harvesting complexes, excited electrons pass their energy to another electrons, effectively transferring energy across the complex.

What are the advantages of photosystems?

1. Increased numbers of photons absorbed per second.

2. Contains multiple types of pigments, so more wavelengths of light can be absorbed.

3. Excited electrons are close to each other so they can pass on their energy.

Where are H2O molecules split and what is the process called?

Water molecules are split through photolysis in photosystem II. (2H2O → O2 +4H+ + 4e-)

Where do electrons give their energy before they reach PSI?

Electrons give their energy to electron transport chains. Their energy is used to pump protons into the thylakoid, creating a gradient that is later used for ATP synthesis.

What does ATP synthase do?

ATP synthase utilizes the proton gradient to synthesize ATP from ADP and P through a process called chemiosomosis.

Where is NADP reduced?

NADP is reduced in photosystem I. Electrons that have traveled through the electron transport chain are transferred to NADP.

What is the system of thylakoids?

Thylakoid membranes make the concentration gradient possible. ATP synthase uses this gradient to make ATP. PSII provides electrons to the system through the photolysis of water. PSII excites these electrons through absorbed light. Proton pumps use energy from the excited electrons to pump protons, creating a concentration gradient. PSI excites the electrons again to reduce NADP, which is used in the calvin cycle later on.

What is carbon fixation?

Carbon dioxide is prevented from diffusing out of the cell due to carbon fixation. CO2 is converted to a complex carbon compound in the stroma. CO2 reacts with a 5-carbon compound to produce 2 glycerate 3-phosphate molecules (catalyzed by rubisco).

What is RuBP and why does it need to be replenished?

5-carbon compound that is used during the calvin cycle. It reacts with CO2 to form glycerate 3-phosphate, which is then reduced and forms a carbohydrate when hydrogen is added. It needs to be replenished because it is used up in the cycle.

How many turns of the calvin cycle does it take to make one glucose molecule?

6

What can be made in photosynthetic organisms?

sucrose, starch, triglycerides, all 20 amino acids

How do light independent and light dependent reactions depend on each other?

Light dependent reactions produce ATP and NADPH, which is used in the calvin cycle to convert CO2 to glucose.