Biology 224- Chapter 8- Photosynthesis

What is the conversion of light energy to chemical energy?

Photosynthesis

What are organisms which can not manufacture their own food from simple carbon compounds?

Heterotrophs

What are organisms which can manufacture their own food from simple carbon compounds?

Autotrophs

What are the parts/structures of photosynthesis?

Plant parts, basic reactants and products, light, pigments, and photosystems

What are the reactants of photosynthesis?

Carbon dioxide, water, and light (energy)

What are the products of photosynthesis?

Food (carbohydrates, oxygen)

Photosynthesis formula

H2O + CO2 —→ C6H12O6

How does water enter the plant?

Through the roots traveling up the stem, through the Xylem, into the vascular bundles.

How does Carbon Dioxide enter the plant?

Through the atmosphere (only 0.3%) through microscopic pores known as stomata on the underside of leaves.

How does water enter roots and how does carbon dioxide enter leaf cells?

Diffusion

Light comes in particles called _____.

Photons

How does light travel?

Through waves

What is the distance from one wave peak to the next?

Wavelength

What are all forms of radiant energy, including the visible light spectrum?

Electromagnetic radiation

What are the parts of the visible light spectrum?

Gamma rays, X-rays, UV, infrared, microwaves, radio waves

What type of relationship occurs between wavelengths and energy? This means that _______ wavelengths have less ______.

Inverse relationship, longer, energy

What is the wavelength of the visible spectrum?

400-700 nm

What has the smallest waves and highest energy content?

Purple light

What has the biggest waves and lowest energy content?

Red

What is the composition of white light?

All wavelengths (colors) of light

What are molecules capable of absorbing some wavelengths (colors) of light but not others?

Pigments

Pigments produce color because only the wavelengths ___ absorbed by a pigments are _______ or transmitted so they can be seen.

Not, reflected

Why is red, red?

Blues and Greens are absorbed, Orange and Red are not, they are transmitted (seen).

Why is blue, blue?

Pigment absorbs green, yellow, orange and red, so only blue is reflected (seen).

Why is green, green?

Blue, orange and red wavelengths are absorbed, so only green is reflected (seen).

What is a graph for a pigment, plotting the amount of light absorbed vs, wavelength?

Absorption spectrum

What is a graph for the entire plant, plotting the photosynthetic activity (action) vs. wavelength?

Action spectrum

What does a plant do with the light absorbed?

Photosynthesis

What does chlorophyll’s hydrophobic hydrocarbon tail do?

It inserts chlorophyll into the thylakoid membrane.

What is the function of the alternating double and single bonds in chlorophyll’s head?

They help chlorophyll pick up and give off extra electrons.

What are Photosystems I and II?

Groups of 250–400 chlorophyll a and b molecules, plus carotene and xanthophyll accessory pigments.

How is light energy passed through a photosystem?

Light energy is passed from pigment to pigment in the antenna complex.

What is the role of the special pair of chlorophyll a molecules in the reaction center?

They receive energy from the other pigments and are involved in transferring electrons.

What is chlorophyll As maximum absorbance in Photosystem 1?

P700

What is chlorophyll As maximum absorbance in Photosystem 2?

P680

In photo systems, chlorophyll a has special associations with the Photosystem’s ________.

Protiens

What do photo systems do?

They pass the high energy electrons generated by the Photosystem absorbing light, to molecules outside the Photosystem (electron transport chain).

What are the two photosynthetic reactions called?

Energy transduction reactions (light dependent) and carbon fixation (light independent)

What are light reactions OR light-dependent reactions; and transfer energy?

Energy transduction reactions

What are dark reactions OR light-independent reactions; CO2 “fixed” to OR enzymatically combined with OR covalently bonded to RuBP?

Carbon fixation reactions

What are the main functions of the photosynthetic light reactions?

Produce ATP and NADPH to provide energy and reducing power for carbon fixation reactions.

What happens to ADP during the light reactions?

ADP is converted to ATP

What happens to NADP⁺ during the light reactions?

NADP⁺ is converted into NADPH.

What is ATP used for in photosynthesis?

Provides energy for carbon fixation reactions.

What is NADPH used for in photosynthesis?

Provides high-energy electrons and reducing power for carbon fixation reactions.

What happens when water is split during the light reactions?

Water splits into electrons, hydrogen ions, and oxygen.

What is the equation for splitting water?

H₂O → 2e⁻ + 2H⁺ + ½ O₂

Where does water splitting occur?

At Photosystem II in the thylakoid membrane. Hydrogen ions are released into the thylakoid space.

What is the role of light energy in the light reactions?

Excites electrons and provides energy to drive the light reactions.

Where do the light reactions occur?

In the thylakoid membranes of chloroplasts.

What is the overall purpose of the photosynthetic light reactions?

Convert light energy into chemical energy stored in ATP and NADPH, which power carbon fixation reactions.

What are the four main processes of the light-dependent reactions?

Noncyclic photophosphorylation

Photolysis (splitting water)

Chemiosmosis (making ATP)

Cyclic photophosphorylation

What is the process that transfers light energy and electrons to produce NADPH and ATP, while releasing oxygen from water splitting?

Noncyclic photophosphorylation

What is the splitting of water molecules into electrons, hydrogen ions (H⁺), and oxygen using light energy?

Photolysis

What is the process in which hydrogen ions (H⁺) flow through ATP synthase, providing energy to make ATP?

Chemiosmosis

What is a process in which electrons cycle back through the electron transport system to produce additional ATP? It does not produce NADPH or oxygen?

Cyclic photophosphorylation

What is the overall purpose of noncyclic photophosphorylation?

To use light energy and water to produce ATP, NADPH, and oxygen.

What happens in Step 1 of noncyclic photophosphorylation?

Light hits Photosystem I, transferring photon energy to an electron in one of the pigment molecules.

What happens when light energizes Photosystem I (P700)?

Electrons pass to ferredoxin, then NADP⁺ reductase, which helps convert NADP⁺ into NADPH.

What happens if Photosystem I runs out of electrons?

It cannot continue functioning, so it needs replacement electrons from Photosystem II.

What happens when light hits Photosystem II (P680)?

Light energizes electrons, which pass through the electron transport chain to Photosystem I.

What is photolysis, and why is it important?

Photolysis splits water into electrons, H⁺ ions, and oxygen. It replaces the electrons lost by Photosystem II.

What happens to the H⁺ ions and oxygen produced during photolysis?

H⁺ ions help build up inside the thylakoid space for ATP production, while oxygen is released as a byproduct.

How does chemiosmosis help make ATP during photosynthesis?

Electrons moving through the electron transport chain provide energy to pump H⁺ ions from the stroma into the thylakoid lumen.

How do hydrogen ions help ATP synthase make ATP?

H⁺ ions flow down their concentration gradient through ATP synthase, providing energy to make ATP from ADP.

What happens when H⁺ ions pass through ATP synthase?

H⁺ ions flow into the stroma through ATP synthase, providing energy to make ATP.

What type of protein is ATP synthase?

multimeric

How does ATP synthase use H⁺ ions to make ATP?

H⁺ flow causes ATP synthase to rotate, providing energy to join ADP with phosphate to make ATP.

What does ATP synthase consist of?

A base embedded in the thylakoid membrane, a rotating shaft, and a stationary head

In ATP synthase, the shaft rotates as ____ ions pass between the….

H+, a and c subunits in the base

In ATP synthase, how much does the shaft rotate?

120 degrees, which causes conformational changes in the head.

In ATP synthase, in one conformation, the ___ subunit binds what?

B, ADP and Phosphate

What are the major products of light-dependent reactions?

ATP, NADPH, and Oxygen

What happens during cyclic photophosphorylation?

Light energizes electrons in Photosystem I (P700), and the electrons cycle back through the electron transport chain to produce extra ATP.

What does cyclic photophosphorylation produce?

ATP only. It does not produce NADPH or oxygen.

What are the two other names for light-independent reactions?

Calvin Benson Cycle and C3 photosynthesis

What happens in Step 1 of the Calvin Cycle?

CO₂ combines with RuBP (Ribulose Bisphosphate) to produce 2 molecules of 3PG (3-Phosphoglycerate).

What enzyme catalyzes Step 1 of the Calvin Cycle?

RuBisCo

Where do light dependent reactions occur?

Thylakoid membrane

Where do light independent reactions occur?

Stroma

What happens in Step 2 of the Calvin Cycle?

3PG is converted into G3P using ATP and NADPH.

What do ATP and NADPH provide during Step 2 of the Calvin Cycle?

ATP: Provides energy.

NADPH: Provides electrons for reduction.

What is G3P, and what molecule is it made from?

G3P (Glyceraldehyde 3-Phosphate) is a 3-carbon sugar produced from 3PG during the Calvin Cycle.

What happens in Step 3 of the Calvin Cycle?

G3P is used to regenerate RuBP so the Calvin Cycle can continue.

Which molecule is regenerated in Step 3 of the Calvin Cycle?

RuBP

What pathway helps regenerate RuBP from G3P?

The Pentose Phosphate Pathway.

Net Yield: For every ___ Carbon Dioxide entering the cycle, ___ net Carbons of carbohydrate or ___ Glucose equivalent are produced.

6,6,1

How are other organic molecules synthesized after photosynthesis?

Other organic molecules are made from the carbohydrates produced during photosynthesis.

What can the carbohydrates produced during photosynthesis be used to make?

Other organic molecules, such as fats, proteins, and other carbohydrates.

What happens during photorespiration?

When CO₂ is limited, RuBisCO adds O₂ to RuBP instead of CO₂.

What enzyme causes the reaction during photorespiration?

RuBisCo

Why does photorespiration occur?

When CO₂ levels are low, RuBisCO binds to O₂ instead of CO₂ and adds it to RuBP. This causes the plant to waste energy and reduces sugar production.

What are the two products formed when RuBisCO adds O₂ to RuBP during photorespiration?

One molecule of 3PG (3-Phosphoglycerate) and one molecule of glycolate.

Does photorespiration produce ATP?

No. Glycolate is broken down using oxygen, but this process produces no ATP.

How does photorespiration affect the plant's carbohydrate supply?

It reduces the amount of carbohydrates available in the cell, leaving fewer sugars for storage.

Why is photorespiration considered wasteful for the plant?

It uses resources and reduces sugar production instead of helping the Calvin-Benson Cycle produce carbohydrates.

What environmental conditions increase photorespiration?

Hot, dry, or still conditions

Why do plants close their stomata in hot, dry conditions?

To prevent excessive water loss.

Why does closing the stomata increase photorespiration?

It concentrates CO₂ around RuBisCO, reducing the chance that RuBisCO will bind to O₂.

How does C4 photosynthesis help prevent photorespiration?

It concentrates CO₂ around RuBisCO, reducing the chance that RuBisCO will bind to O₂.