Photosynthesis: Light and Dark Reactions

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Questions and Answers

What is produced during the light stage of photosynthesis?

PGAL

NADP⁺

ATP (correct)

Carbon dioxide

Which component is required during the dark stage of photosynthesis?

Sunlight

NADPH (correct)

Water

Chlorophyll

How are chloroplasts and mitochondria similar in terms of energy conversion?

Both have a smooth inner membrane

Both utilize chemiosmotic mechanisms (correct)

Both have a double outer membrane

Both utilize the same type of transport proteins

Which of the following accurately describes the structure of chloroplasts?

They have a highly permeable outer membrane. Signup and view all the answers

What is the main purpose of the energy released as protons flow down their gradient in the mitochondria?

To synthesize ATP Signup and view all the answers

Which of the following best describes the role of chlorophyll a in the light-dependent reactions?

It is the only pigment capable of transferring an excited electron. Signup and view all the answers

What happens to the energy absorbed by chlorophyll molecules during the light-dependent reactions?

It is converted into chemical potential energy. Signup and view all the answers

In which part of the chloroplast do the light-dependent reactions take place?

Thylakoid membranes Signup and view all the answers

What is the primary function of the antenna complex in photosystems?

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

How does the concentration gradient of protons contribute to ATP production in the chloroplast?

It powers ATP synthase to produce ATP. Signup and view all the answers

Which statement accurately describes the energy change in the light-dependent reactions?

Light energy becomes chemical potential energy. Signup and view all the answers

What is the maximum absorbance wavelength of chlorophyll a in Photosystem I?

700 nm Signup and view all the answers

During the light-dependent reactions, which complex is responsible for pumping protons into the thylakoid lumen?

Cytochrome b6/f complex Signup and view all the answers

What is the main function of photosynthetic organisms in the ecosystem?

They convert light energy into chemical energy. Signup and view all the answers

Which term describes the process of photosynthesis?

Endergonic process Signup and view all the answers

How is the energy content of photons related to their wavelength?

Inversely proportional Signup and view all the answers

Which of the following is NOT a characteristic of chlorophyll?

Exclusively absorbs infrared light Signup and view all the answers

What percentage of solar radiation that reaches Earth's surface is visible light?

42% Signup and view all the answers

What role do carotenoids play in photosynthesis?

They act as accessory pigments. Signup and view all the answers

Where does the absorption of photons occur in a plant cell?

In the thylakoid membranes Signup and view all the answers

Which characteristic of chlorophyll allows it to be positioned in the thylakoid membrane?

It has a polar head and non-polar tail. Signup and view all the answers

What is the primary reason chlorophyll appears green?

It reflects green light. Signup and view all the answers

Which accessory pigment is primarily responsible for the pink to purple colors in foliage during autumn?

Anthocyanins Signup and view all the answers

What happens to electrons in chlorophyll after they absorb a photon?

They are boosted to a higher energy state. Signup and view all the answers

What is photo-oxidation in the context of chlorophyll?

Electrons are removed by a primary electron acceptor. Signup and view all the answers

Which pigment is less abundant than chlorophyll in green leaves but can become more visible in autumn?

Carotenoids Signup and view all the answers

What is the outcome of photo-excitation in chlorophyll?

Electrons return to their ground state. Signup and view all the answers

What role do accessory pigments play in the process of photosynthesis?

They absorb light that chlorophyll absorbs poorly. Signup and view all the answers

What triggers the process of photosynthesis?

Absorption of light by chlorophyll molecules. Signup and view all the answers

Study Notes

4.1 Capturing Solar Energy!

Photosynthesis is the process by which photosynthetic organisms serve as the ultimate source of food for life.
Photosynthesis is an endergonic process.
Photosynthesis transforms light energy into chemical energy stored in glucose.
Photosynthesis is an anabolic process.

Photosynthesis Overview

Sunlight provides energy for photosynthesis.
Photosynthetic organisms are the base of food chains.
The process of photosynthesis converts carbon dioxide and water into glucose and oxygen.
The balanced chemical equation summarizing the process is: 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
It is an endergonic process, meaning it requires energy input.
It is an anabolic process, meaning it builds complex molecules from simpler ones.

Where Does Photosynthesis Take Place?

Photosynthesis primarily takes place in the leaves of plants.
Leaves contain chloroplasts.
Chloroplasts are the site of photosynthesis.
A chloroplast is composed of an outer membrane, inner membrane, stroma, and grana.
Grana is made of thylakoid membranes.
Thylakoids contain chlorophyll molecules.
Each cell in a leaf contains many chloroplasts, from 40-300 per cell.

Photosynthesis Background Information

Solar radiation is described by wavelength.
Photons are discrete packets of radiant energy.
Visible light, part of the electromagnetic spectrum, is captured by plants for photosynthesis.
The portion of visible light useful for photosynthesis is called PAR (photosynthetically active radiation).
Only 42% of solar radiation reaches the earth's surface. most as visible light

Light May Be

Transmitted: Passed through matter.
Reflected: Bounced off matter.
Absorbed: Changed from light energy into another form.
Pigments absorb certain wavelengths of visible light, then reflect other colors, determining the color we observe.

Chlorophyll Structure

Chlorophyll is a pigment found in chloroplasts.
It has a "porphyrin ring" and a "phytol tail".
The "phytol tails" are non-polar, and the heads are polar, accounting for chlorophyll's position in the thylakoid membrane.
Magnesium is at the center of the chlorophyll molecule, contributing to its instability.

Photosynthetic Pigments

Chlorophyll a is the primary pigment in photosynthesis, absorbing red and blue-violet light and reflecting green light.
Chlorophyll b is an accessory pigment, absorbing light in different wavelengths than chlorophyll a to extend the spectrum that can drive photosynthesis.
Carotenoids are accessory pigments, that absorb light in different wavelengths than chlorophyll a and b.
Different plants may have different combinations and amounts of accessory pigments based on their surroundings.

Light-Dependent Reactions of Photosynthesis

These reactions occur in the thylakoid membranes of chloroplasts.
They require two photosystems (Photosystem I and Photosystem II).
Photosystems are collections of accessory pigments.
Chlorophyll a is a pigment located in the reaction center of a photosystem.
A photon of light excites an electron in chlorophyll a.
The excited electron is passed to a primary electron acceptor.
The electron acceptor is a protein containing a PEA.

Photosystems I and II

Photosystem II (PSII) absorbs light at 680nm.
Photosystem I (PSI) absorbs light at 700nm.
Chlorophyll b and carotenoids, which help absorb other wavelengths, act like antennae to capture sunlight and transfer energy to chlorophyll a.

Light-Dependent Summary

Light energy is converted into chemical energy as ATP and NADPH.
A series of redox reactions and an electron transport chain (ETC) "package" the energy.

Chemiosmosis in the Chloroplast

The gradient of H+ ions, formed by the ETC, is used to power the synthesis of ATP.
The process of ATP synthesis is called photophosphorylation.

Light Stage (Requirements & Products)

Requirements: Sunlight, water, chlorophyll, NADP+, ADP+P
Products: Oxygen, NADPH, ATP

Dark Stage (Requirements & Products)

Requirements: NADPH from light, ATP, CO₂
Products: PGAL (a form of glucose) , ADP+P, NADP+

Chloroplast vs. Mitochondria

Both use chemiosmosis but differ structurally and in function.
Chloroplasts have a highly permeable outer membrane, a less permeable inner membrane, and a narrow intermembrane space.

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Description

Test your knowledge on the light and dark stages of photosynthesis. This quiz covers key concepts such as energy production, chlorophyll function, and the structural similarities between chloroplasts and mitochondria. Perfect for students studying plant biology.