Biology Chapter 5 - Photosynthesis

light dependant reaction equation

(An Overview of Photosynthesis)

H₂O + NADP⁺+ ADP + P_i → O₂ + ATP + NADPH

light independant reaction equation

(An Overview of Photosynthesis)

ATP + NADPH + CO₂ →NADP⁺ + ADP + P_i + G3P

Grana

(An Overview of Photosynthesis)

a stack of thylakoids

Lamellae

(An Overview of Photosynthesis)

unstacked thylakoids between grana

Thylakoid Membrane

(An Overview of Photosynthesis)

the photosynthetic membrane within a chloroplast that contains light-gathering pigment molecules and electron transport chains

Thylakoid Lumen

(An Overview of Photosynthesis)

the fluid filled space inside a thylakoid

How many grana in a typical chloroplast?

(An Overview of Photosynthesis)

60How many

chloroplast ancestors

(An Overview of Photosynthesis)

cyanobacteria

how are chloroplasts similar to cyanobacteria?

(An Overview of Photosynthesis)

they contain their own DNA and replicate by binary fission

How do chloroplasts replicate?

(An Overview of Photosynthesis)

by binary fission

Chlorophylls

(Photosynthetic Pigments)

major photosynthetic pigments in plants, green algae, and cyanobacteria

Where is bacteriochlorphyll present?

(Photosynthetic Pigments)

in prokaryotes other than cyanobacteria

The two types of chlorphylls

(Photosynthetic Pigments)

chlorphyll A and chlorophyll B

Difference between chlorphyll A and chlorophyll B

(Photosynthetic Pigments)

they are both exactly the same except for the functional groups

Porphyrin head

(Photosynthetic Pigments)

light absorbing head

Why is Mg present in chlorophyll?

(Photosynthetic Pigments)

to stabilize the chlorophyll molecule

phytol tail

(Photosynthetic Pigments)

hydrophobic tail that anchors the pigments to the thylakoid membrane

Where are carotenoids present?

(Photosynthetic Pigments)

in plants, algae, and cyanobacteria

What do carotenoids do?

(Photosynthetic Pigments)

serve as accessory pigments helping to capture additional light energy

Effect of carotenoids on fruits and vegetables

(Photosynthetic Pigments)

produce bright orange, red, and yellow fruits and vegetables

Effect of carotenoids on humans

antioxidants

What does the antenna complex ensure?

(Photosynthetic Pigments)

the max harvesting of light

At what point in the antenna complex is light captured?

(Photosynthetic Pigments)

Photons → Carotenoids →Chlorophyll B → Chlorophyll A

At what point in the antenna complex is light transformed into chemical energy?

(Photosynthetic Pigments)

the reaction centre

Describe Joseph Priestly's experiments and explain the contribution this made to our understanding of photosynthesis.

(Photosynthetic Pigments)

• Joseph Priestley conducted two experiments related to gases and combustion.

• First Experiment:

  • A candle and a mouse were placed in a sealed glass dome.

  • The candle extinguished, and the mouse died.

  • Priestley believed this was due to a noxious gas called "phlogiston."

• Second Experiment:

  • A candle, a mouse, and a plant were placed in a sealed glass dome.

  • The candle remained lit, and the mouse survived.

  • Priestley believed the plant removed "phlogiston."

• Contribution to Photosynthesis Understanding:

  • Demonstrated that plants release a substance (later identified as oxygen) that supports combustion and respiration.

  • Showed that in a closed system, plants replenish atmospheric oxygen.

  • Indicated that plants and animals maintain an equilibrium of oxygen and carbon dioxide.

  • Helped establish the role of plants in supporting life by producing oxygen.

Pigment molecules do not float freely within thylakoid membranes; where are they located?

(Pigments and Photosystems)

they are bound very precisely to different proteins, which are organized into photosystems

What is the antenna complex also known as?

(Pigments and Photosystems)

a light harvesting complex

What makes up a reaction centre?

(Pigments and Photosystems)

a small number of proteins, each bound to a pair of specialized chlorophyll ‘A’ molecules, as well as the primary electron acceptor

Why does photosystem 2 appear before photosystem 1 in diagrams?

(Pigments and Photosystems)

the actions of photosystem 2 happen before photosystem 1

differences between photosystems 1 and 2

(Pigments and Photosystems)

photosystem 1:

• reaction centre contains P700 molecules

• discovered first

photosystem 2:

• reaction centre contains P680 molecules

• actions occur first

When do photosystems have lots of redox reactions?

(Pigments and Photosystems)

when the pigments in the large antennae complex absorb the light of a range of wavelengths and efficiently transfer the energy to the reaction centre

Oxidation of P680

(Light Dependent Reactions)

Photosystem II absorbs light, exciting its chlorophyll molecules (P680) to a higher energy state (P680*). This excited P680* molecule quickly loses an electron, becoming oxidized and passing the high-energy electron to the primary electron acceptor.

Oxidation-Reduction of Plastoquinone (PQ)

(Light Dependent Reactions)

The electron from the primary acceptor is transferred to plastoquinone, a mobile electron carrier. PQ accepts electrons and protons (H⁺) from the stroma, then transports them through the thylakoid membrane to the cytochrome complex. When PQ donates electrons to the cytochrome complex, it releases protons into the lumen, increasing the proton concentration there.

Electron Transfer and Shuttling by Plastocyanin

(Light Dependent Reactions)

Electrons move from the cytochrome complex to plastocyanin, a mobile carrier that transfers electrons to Photosystem I.

Oxidation-Reduction of P700

(Light Dependent Reactions)

Photosystem I absorbs light, exciting its chlorophyll molecules (P700) to a higher energy state (P700*). P700* transfers its electron to its primary electron acceptor. The oxidized P700 (P700⁺) is then reduced back to P700 by accepting an electron from plastocyanin.

Electron Transfer to NADP⁺ by Ferredoxin

(Light Dependent Reactions)

Electrons from P700* are passed through a series of carriers, eventually reaching ferredoxin, an iron-sulfur protein. Ferredoxin transfers electrons to NADP⁺, reducing it to NADPH.

Formation of NADPH

(Light Dependent Reactions)

A second electron, along with a proton from the stroma, is transferred to NADP⁺, forming NADPH. This decreases the proton concentration in the stroma.

Chemiosmotic Synthesis of ATP

(Light Dependent Reactions)

The proton gradient across the thylakoid membrane, established by the oxidation-reduction of plastoquinone, the splitting of water, and the formation of NADPH, drives ATP synthesis. Protons move from the lumen to the stroma through ATP synthase, which harnesses this movement to convert ADP and inorganic phosphate (P) into ATP.

How many times does the Calvin Cycle need to turn to make 1 glucose molecule?

(Understanding The Calvin Cycle)

6 times

By the time 1 glucose molecule is made, how many ATP and NADPH are also produced?

(Understanding The Calvin Cycle)

18 ATP and 12 NADPH

Rubisco Full Name

(Understanding The Calvin Cycle)

Riulase bisphosphate carboxylase

What sort of protein is Rubisco?

(Understanding The Calvin Cycle)

an enzyme

What is the most abundant protein on Earth?

(Understanding The Calvin Cycle)

Rubisco

Describe Rubisco’s role in carbon fixation

(Understanding The Calvin Cycle)

It incorporates CO₂ from the atmosphere into RuBP, producing 2 molecules of 3-PGA, which are then further processed into organic compounds

What are the 3 phases of the Calvin Cycle?

(The Calvin Cycle)

1. carbon fixation

2. reduction

3. regeneration of the starting molecule

What is Carbon Fixation?

(The Calvin Cycle)

The process where plants and algae convert atmospheric inorganic carbon into organic matter for biological building blocks and cellular respiration.

most common metabolic pathway for carbon fixation

(The Calvin Cycle)

C₃ photosynthesis

How is 3-PGA formed?

(The Calvin Cycle)

by spontaneous scission of an unstable 6-C molecule

Summarize what happens in Phase 2 of the Calvin Cycle

(The Calvin Cycle)

ATP and NADPH are used to convert the 3-PGA molecules into G3P molecules

How do G3P molecules arrange into RuBP?

(The Calvin Cycle)

they use ATP and are arranged into RuBP

In order to produce one G3P molecule, how many molecules of ATP and NADPH are used?

(The Calvin Cycle)

9 ATP and 6 NADPH

Why is photosynthesis said to be self-sufficient?

(The Calvin Cycle)

because it enables plants, algae, and certain bacteria to produce their own food and energy without relying on organic nutrients from external sources

What percentage of plants are C3 plants?

(Alternative Methods of Carbon Fixation)

89%

Why are C3 plants called C3 plants?

(Alternative Methods of Carbon Fixation)

because during fixation 2x (3C) PGA molecules are formed

What is the alternative fixation to carbon fixation?

(Alternative Methods of Carbon Fixation)

photorespiration

What is photorespiration?

(Alternative Methods of Carbon Fixation)

a process that occurs in plants when the enzyme Rubisco binds to oxygen (O₂) instead of carbon dioxide (CO₂).

What can Rubisco bind to?

(Alternative Methods of Carbon Fixation)

CO₂ and O₂

In lab conditions, what does Rubisco have a higher affinity for?

(Alternative Methods of Carbon Fixation)

CO₂ (80x more)

In the natural atmosphere (where O₂ concentration is 21% and CO₂ concentration is 0.04%), what does Rubisco bind to?

(Alternative Methods of Carbon Fixation)

it binds to CO₂ 75% of the time and O₂ 25% of the time

Conditions that Increase Photorespiration

(Alternative Methods of Carbon Fixation)

High O₂/Low CO₂ ratios, and hot and dry conditions

Process of Photorespiration

(Alternative Methods of Carbon Fixation)

When Rubisco binds to O₂, it attaches it to RuBP, producing one molecule of 3-PGA and one other uselesss molecule that cannot directly be used in the Calvin Cycle, and must be processed through a series of reactions to be converted back into a useful form, such as 3-PGA.

Why is photorespiration bad for plants?

(Alternative Methods of Carbon Fixation)

it consumes ATP and NADPH, releases CO₂, and slows down the Calvin cycle, making it energy-intensive and wasteful.

C4 Plants

(Alternative Methods of Carbon Fixation)

• have several thousand species, including corn

• usually live in hotter, dryer climates

• have an internal leaf structure that minimizes photorespiration

CAM plants

(Alternative Methods of Carbon Fixation)

• tend to live in very hot, very dry environments

Cellular Respiration inputs

(Photosynthesis and Cellular Respiration: A Comparison)

oxygen and glucose

Photosynthesis inputs:

(Photosynthesis and Cellular Respiration: A Comparison)

carbon dioxide, light, and water

Cellular Respiration products:

(Photosynthesis and Cellular Respiration: A Comparison)

carbon dioxide, water, energy (ATP)

Photosynthesis products

(Photosynthesis and Cellular Respiration: A Comparison)

oxygen, water, glucose

Types of Cells Cellular Respiration Occurs In:

(Photosynthesis and Cellular Respiration: A Comparison)

all cells

Types of Cells Photosynthesis Occurs In:

(Photosynthesis and Cellular Respiration: A Comparison)

plants, some protists, and bacteria

Where does Cellular Respiration Occur In Cells?

(Photosynthesis and Cellular Respiration: A Comparison)

cytoplasm (anaerobic) and mitochondria (aerobic)

Where Does Photosynthesis Occur In Cells?

(Photosynthesis and Cellular Respiration: A Comparison)

chloroplasts

Where cellular respiration energy comes from

(Photosynthesis and Cellular Respiration: A Comparison)

carbon compounds (chemical breakdowns)

Where photosynthetic energy comes from?

(Photosynthesis and Cellular Respiration: A Comparison)

light

Cellular respiration role of ATP

(Photosynthesis and Cellular Respiration: A Comparison)

end product

Photosynthesis role of ATP

(Photosynthesis and Cellular Respiration: A Comparison)

carries energy of light reactions into dark reactions

Names of Reactions in Cellular Respiration

(Photosynthesis and Cellular Respiration: A Comparison)

glycolysis, fermentation, krebs cycle, ETC

names of reactions in photosynthesis

(Photosynthesis and Cellular Respiration: A Comparison)

light reactions - photosystems I and II, ETC

dark reactions - calvin cycle