Biology: Photosynthesis Quiz

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Questions and Answers

Converts light energy to a usable form: [blank]

photosynthesis

What does respiration do and what does it facilitate?

Respiration releases stored energy from glucose and is broken into individual carbon dioxide molecules, development and reproduction.

[blank] is the sum of all interrelated biochemical processes in living organisms.

metabolism

Animals rely on green plants for oxygen, food, shelter, and other products.

True Signup and view all the answers

Which of the following processes are regulated by enzymes? (Select all that apply)

Anabolism Signup and view all the answers

What does anabolism do?

Builds chemical bonds from simpler molecules Signup and view all the answers

Which of the following processes breaks chemical bonds?

Catabolism Signup and view all the answers

Photosynthesis involves the respiration cycle that transfers

energy and carbon dioxide into glucose and oxygen Signup and view all the answers

What is the difference between oxidation and reduction?

Oxidation is the loss of electrons, while reduction is the gain of electrons. Signup and view all the answers

[blank] is lost during oxidation and gained during reduction

hydrogen Signup and view all the answers

What is the final acceptor of an electron?

Oxygen Signup and view all the answers

Where is respiration initiated and completed?

Cytoplasm and mitochondria Signup and view all the answers

Aerobic respiration can be completed without oxygen.

False Signup and view all the answers

The cellular respiration equation is...

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + ATP (energy) Signup and view all the answers

What is a key difference between anaerobic respiration and fermentation?

Anaerobic respiration produces more energy than fermentation. Signup and view all the answers

Which of the following are types of fermentation?

Lactic acid fermentation Signup and view all the answers

Which of the following statements about glycolysis is true?

Glycolysis converts glucose to pyruvic acid. Signup and view all the answers

What is the primary function of chlorophyll in photosynthesis?

It captures light energy. Signup and view all the answers

Which factor can limit the rate of photosynthesis?

Temperature Signup and view all the answers

What happens during photorespiration in plants?

It consumes oxygen and releases carbon dioxide. Signup and view all the answers

How do plants primarily obtain carbon dioxide for photosynthesis?

Via diffusion through stomata Signup and view all the answers

What is a consequence of too high light intensity on photosynthesis?

Destruction of chlorophyll due to photooxidation Signup and view all the answers

What is the primary role of chlorophyll b in photosynthesis?

To transfer light energy to chlorophyll a Signup and view all the answers

Where do the light-dependent reactions of photosynthesis occur?

In the thylakoid membranes of chloroplasts Signup and view all the answers

During the light-independent reactions, what molecule combines with carbon dioxide to help form sugars?

RuBP Signup and view all the answers

Which statement accurately describes the process of photosynthesis?

It involves light-dependent and light-independent reactions. Signup and view all the answers

What type of pigment absorbs blue or red light in certain algae and cyanobacteria?

Phycobilins Signup and view all the answers

What is the primary purpose of chlorophyll when it absorbs light?

To elevate electrons to a higher energy state Signup and view all the answers

What happens to the electrons lost from P680 in Photosystem II?

They are replaced by electrons extracted from water Signup and view all the answers

Which reaction occurs immediately after light photons are absorbed by P680?

Photolysis of water Signup and view all the answers

What is the role of pheophytin in Photosystem II?

It accepts electrons from P680 Signup and view all the answers

Which statement correctly describes the relationship between photosystem I and photosystem II?

Photosystem II events occur before those of photosystem I. Signup and view all the answers

How is ATP formed in the electron transport system of photosynthesis?

Via chemiosmosis across the thylakoid membrane Signup and view all the answers

What is the result of the electron transport chain involving cytochromes and plastocyanin?

Generation of a proton gradient for ATP production Signup and view all the answers

What defines fluorescence as it relates to chlorophyll?

Energy is released immediately as light Signup and view all the answers

What kind of molecules primarily accept electrons during the light-dependent reactions?

Iron-sulfur proteins Signup and view all the answers

What key product results from the water-splitting reaction in photosystem II?

Oxygen Signup and view all the answers

Study Notes

Photosynthesis

Photosynthesis is the process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen
Photosynthesis takes place in chloroplasts and other green parts of plants
The chemical equation for photosynthesis is: 6CO2 + 12H2O + light → C6H12O6 + 6O2 + 6H2O
Photosynthesis is essential for life on Earth as it provides the energy and oxygen necessary for all living organisms

Carbon Dioxide

Carbon dioxide reaches chloroplasts in mesophyll cells by diffusing through stomata into the leaf interior
Human activities like burning fossil fuels and deforestation are adding more carbon dioxide to the atmosphere than is being removed
Increased carbon dioxide in the atmosphere can lead to global increases in temperature
Increased carbon dioxide can enhance photosynthesis

Water

Less than 1% of all water absorbed by plants is used in photosynthesis, most is transpired or incorporated into plant materials
Water is the source of electrons in photosynthesis and oxygen is released as a byproduct
When water is in short supply or light intensities are too high, plants close their stomata to reduce the supply of carbon dioxide available for photosynthesis

Light

About 40% of the radiant energy received on Earth is in the form of visible light
Violet to blue and red-orange to red wavelengths of light are used most extensively in photosynthesis
Green light is reflected by plants

Optimal Rates and Limiting Factors

Plants vary considerably in light intensities needed for optimal photosynthetic rates
Temperature and amount of carbon dioxide can also be limiting factors for photosynthesis

### Effects of Changing Light and Temperature

If light and temperatures are too high, the ratio of carbon dioxide to oxygen inside leaves may change
Photorespiration occurs when the ratio of carbon dioxide to oxygen inside leaves changes, which uses oxygen and releases carbon dioxide
Photorespiration can help some plants survive under adverse conditions
If light intensity is too high, photooxidation occurs, which results in the destruction of chlorophyll

Chlorophyll

Chlorophyll is a green pigment found in plants that absorbs light energy for photosynthesis
There are several types of chlorophyll molecules, but chlorophyll a (blue-green) and chlorophyll b (yellow-green) are the most prevalent
Chlorophyll b transfers energy from light to chlorophyll a, which makes it possible for photosynthesis to occur over a broader spectrum of light
The magnesium end of a chlorophyll molecule captures light energy
The lipid tail of a chlorophyll molecule anchors it into the thylakoid membrane

Photosynthetic Pigments

Photosynthetic pigments other than chlorophyll include carotenoids (yellow and orange), phycobilins (blue or red), and other types of chlorophyll
About 250-400 pigment molecules are grouped in a light-harvesting complex = photosynthetic unit
Two types of photosynthetic units work together in light-dependent reactions

### The Two Phases of Photosynthesis

Light-dependent reactions: occur in the thylakoid membranes of chloroplasts and produce ATP and NADPH
Light-independent reactions: occur in the stroma of chloroplasts and use ATP and NADPH to make sugars

Light-Dependent Reactions

Water molecules are split apart, releasing electrons and hydrogen ions, and oxygen gas is released
Electrons pass along an electron transport system
ATP is produced
NADP is reduced, forming NADPH (used in light-independent reactions)

Light-Independent Reactions

ATP and NADPH are used to form sugars
The Calvin cycle: carbon dioxide combines with RuBP (ribulose bisphosphate), and the combined molecules are converted to sugars (glucose).

A Closer Look at Photosynthesis

1772: Joseph Priestley noted that photosynthesis “restored” oxygen
1779: Jan Ingen-Housz showed that air is only restored when the green parts of plants received sunlight
1782: Jean Senebier discovered that photosynthesis requires carbon dioxide
1796: Ingen-Housz showed that carbon is a plant nutrient
1804: Theodore de Saussure showed that water is required for photosynthesis

Light-Dependent Reactions Reexamined

Each pigment has its own distinctive pattern of light absorption called the pigment’s absorption spectrum
Shorter wavelengths of light carry higher amounts of energy
Chlorophylls absorb light in the violet to blue and red wavelengths.

When Pigments Absorb Light

When a pigment absorbs light, the energy levels of some of the pigment’s electrons are elevated
These electrons are said to be in an excited state
Energy from an excited electron is released when it drops back to its ground state
Fluorescence: energy is immediately released as light
Phosphorescence: energy is emitted as light after a delay
Energy may otherwise be converted to heat.
In photosynthesis, energy is stored in chemical bonds.

The Light-Dependent Reactions Reexamined

Two types of photosynthetic units: photosystem I and photosystem II
Events of photosystem II come before those of photosystem I
Both can produce ATP
Only organisms with both photosystem I and photosystem II can produce NADPH and oxygen as a consequence of electron flow.

Photosystems I and II

Photosystem I = chlorophyll a, small amount of chlorophyll b, carotenoid pigment, and P700
- P700 = reaction-center molecule - Only one that actually can use light energy
- Remaining pigments = antenna pigments
- Gather and pass light energy to the reaction center
- Iron-sulfur proteins - Primary electron acceptors, first to receive electrons from P700
Photosystem II = chlorophyll a, B-carotene, small amounts of chlorophyll b, and reaction-center molecule: P680
- Pheophytin (Pheo) - Primary electron acceptor

The Light-Dependent Reactions of Photosynthesis

Photolysis - Water-splitting, occurs in Photosystem II
- Light photons absorbed by P680, which boosts electrons to a higher energy level.
- Electrons are passed to the acceptor molecule, pheophytin, then to PQ (plastoquinone), then along the electron transport system to photosystem I.
- Electrons extracted from water replace electrons lost by P680.
- One molecule of oxygen, 4 protons, and 4 electrons are produced from two water molecules.

Electron Flow and Photophosphorylation

The electron transport system consists of cytochromes, other electron transfer molecules, and plastocyanin.
Photons move across the thylakoid membrane by chemiosmosis.
Phosphorylation - ATP is formed from ADP

Photosystem I

Light is absorbed by P700, which boosts electrons to a higher energy level.
Electrons are passed to the iron-sulfur acceptor molecule, Fd (ferredoxin), then to FAD (flavin adenine dinucleotide).
NADP is reduced to NADPH.
Electrons removed from P700 are replaced by electrons from Photosystem II

Chemiosmosis

Net accumulation of protons in the thylakoid lumen occurs from the splitting of water molecules and electron transport.
The proton gradient gives ATPase (special proteins in the thylakoid membrane) the potential to move protons from the lumen to the stroma.
The movement of protons across the membrane = source of energy for the synthesis of ATP

Calvin Cycle

Six molecules of CO2 combine with six molecules of RuBP (ribulose 1,5-bisphosphate) with the aid of rubisco.
This eventually results in twelve 3-carbon molecules of 3PGA (3-phosphoglyceric acid).
NADPH and ATP supply energy and electrons that reduce 3PGA to GA3P (glyceraldehyde 3-phosphate).
Ten of the twelve GA3P molecules are restructured, using 6 ATP, into six 5-carbon RuBP molecules.
Net gain of 2 GA3P, which can be converted to carbohydrates or used to make lipids and amino acids.

### Photorespiration

Photorespiration - Competes with carbon-fixing role of photosynthesis
- Rubisco fixes oxygen instead of carbon dioxide.

CAM and C4 Plants

CAM photosynthesis - Similar to C4 photosynthesis in that 4-carbon compounds are produced during light-independent reactions, however:
- Converted back to CO2 during the day for use in the Calvin cycle (stomata closed)
- Allows plants to function well under limited water supply, as well as high light intensity.

Other Significant Processes that Occur in Chloroplast

Reduction of sulfate to sulfide
- Sulfides are used to make amino-acids
Nitrates converted to ammonia
- Ammonia is used to make amino-acids, for eg-glutamine which is stored in roots and specialized stems

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Description

Test your knowledge on the process of photosynthesis and how plants convert light energy into chemical energy. This quiz covers key concepts and terminology related to this fundamental biological process.