Table of Contents
- Light reaction And Dark reaction
- Difference between Light and Dark Reaction
Overview |
| Light Reaction– Discover its definition and significance |
| Dark Reaction– Explore its meaning and implications |
| Difference between Light and Dark Reaction– Learn how these two processes vary from each other |
Photosynthesis is the process of conversion of light energy into chemical energy which can then be utilized by living organisms.It is a rather complex process which is carried out through various stages.
Photosynthesis comprises two phases:
- The first phase is the photochemical phase or light-dependent process. This phase is commonly known as the light reaction.
- The second phase is the biosyntheticphase of the dark reaction of photosynthesis. This phase is thelight-independent process.
The whole process of photosynthesis takes place within the chloroplast.
Steps Carried out in Light Reaction and Dark Reaction
Light reaction And Dark reaction
As stated above, photosynthesis occurs in two phases – light reaction and dark reaction.
Light Reaction
The light reaction is a light-dependent process which includes a series of events such as light absorption, hydrolysis, the release of oxygen, formation of ATP and NADPH.
The light reaction of photosynthesis initiates only when it is supplied with light energy.
The photosystem is the arrangement of pigments, including chlorophyll within thylakoids.
There are two photosystems in plants:
- Photosystem I (PS-I)
- Photosystem II (PS-II)
Photosystem I absorbs light at a wavelength of 700 nm, whereas Photosystem II absorbs light at a wavelength of 680 nm.
The light reaction occurs in the thylakoids of the chloroplast. When the light hits, chlorophyll-a gets excited to a higher energy state followed by a series of reactions. This energy is converted into energy molecules ATP and NADPH by using PS I and PS II. Also, hydrolysis occurs and releases oxygen.
Also Read:Cyclic and non-cyclic photophosphorylation
DarkReaction
Dark reaction is also called carbon-fixing reaction. It is a light-independent process in which sugar molecules are formed from the carbon dioxide and water molecules.
The dark reaction occurs in the stroma of the chloroplast, where they utilize the products of the light reaction.
Plants capture the carbon dioxide from the atmosphere through stomata and proceed to the Calvin cycle.
In the Calvin cycle, the ATP and NADPH formed during light reaction drives the reaction and convert six molecules of carbon dioxide into one sugar molecule, i.e. glucose.
Also Refer:Photosynthesis in Higher plants
Difference between Light and Dark Reaction
Following are the important differences between light and dark reaction:
Light Reaction | Dark Reaction |
It takes place only in the presence of light. | It can take place in the presence or absence of sunlight. |
It is a photochemical phase. | It is a biochemical phase. |
It takes place in the grana of the chloroplast. | It takes place in the stroma of the chloroplast. |
NADP utilizes H+ ions to form NADPH. | The hydrogen of NADPH combines with CO2. |
The end products are ATP and NADPH. | Glucose is the end product. ATP and NADPH help in the formation of glucose. |
The water molecules split into hydrogen and oxygen. | Glucose is produced. Co2 is utilized in the dark reaction. |
Photolysis occurs in PS-II. | Photolysis does not occur. |
Also Read: Difference betweenCyclic and non-cyclic photophosphorylation
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Frequently Asked Questions
Q1
What is a light reaction?
The light reaction takes place in the thylakoid membranes. In the light reaction, the light is absorbed and energy is used to drive electrons from water to generate NADPH and to drive protons across the membrane.
Q2
What is a dark reaction?
In the dark reaction, plants use carbon dioxide with ATP and NADPH from the light reactions to produce glucose. It takes place in the stroma of the chloroplast.
Q3
What are the end products of light reactions?
The end products of the light reaction are ATP and NADPH, also known as assimilatory powers.
Q4
What is the end product of the dark reaction?
Glucose is the end product of the dark reaction.
Q5
What is the difference between light and dark reaction?
The light reaction is the initial stage of photosynthesis which traps light energy to produce ATP and NADPH, whereas dark reaction is the second step of photosynthesis which utilizes the energy from ATP and NADPH to produce glucose.
Q6
Does the dark reaction occur at night?
No, the dark reaction does not occur at night. It occurs during the day, but the reaction does not use the light directly. Therefore, it is known as the dark reaction.
Q7
How does a plant make energy without light?
Plants make ATP from other sources such as metal ions and turn carbon dioxide into glucose. The anaerobic photosynthetic bacteria use light energy but do not have the light reactions as in plants and produce no oxygen.
Q8
How does light affect the growth of plants?
Light provides energy to plants through a process called photosynthesis. This energy helps the plant to grow. This is how plant growth is affected by light.
Also Read:Light-dependent reaction
FAQs
What is the difference between light and dark reaction? The light reaction is the initial stage of photosynthesis which traps light energy to produce ATP and NADPH, whereas dark reaction is the second step of photosynthesis which utilizes the energy from ATP and NADPH to produce glucose.
What is the difference between the light reaction and the dark reaction brainly? ›
The first phase is the photochemical phase or light-dependent process. This phase is commonly known as the light reaction. The second phase is the biosynthetic phase of the dark reaction of photosynthesis. This phase is the light-independent process.
How do the light and dark reactions balance one another out? ›
The so‐called 'light reactions' of the photosynthetic electron transport chain (PETC) convert light into chemical energy, supplying ATP and NADPH. This energy is used to drive the carbon dioxide reduction and fixation processes known as the 'dark reactions'.
How are light and dark reactions similar? ›
The light reactions and dark reactions of photosynthesis are similar in that they both contribute to the process of carbohydrate synthesis in plants. They differ in that light reactions need sunlight to produce ATP and NADPH, while dark reactions do not, using these molecules to fix CO₂ into carbohydrates.
What are the differences between the light reactions and the Calvin cycle? ›
Unlike the light reactions, which take place in the thylakoid membrane, the reactions of the Calvin cycle take place in the stroma (the inner space of chloroplasts). This illustration shows that ATP and NADPH produced in the light reactions are used in the Calvin cycle to make sugar.
Where is light reaction and dark reaction? ›
(i) Light reactions occur in grana thylakoids whereas dark reactions occur in stroma of chloroplasts. (ii) Light reactions generate ATP and NADPH2 whereas dark reactions consume ATP and NADPH2. (iii) Oxygen is released as a by-product during the light reactions as well as dark reactions.
What is the difference between the light reaction and the dark reaction on the basis of the end products? ›
- At the end of light reaction ATP and NADPH are produced which are used in the dark reaction to produce glucose from carbon dioxide. - The dark reaction is a carbon- fixing reaction.
What is the difference between the reaction and the dark reaction? ›
The light reaction is the first stage of photosynthesis, during which light energy is captured and used to produce ATP and NADPH, whereas the dark reaction is the second stage of photosynthesis, during which light energy is captured and used to produce ATP and NADPH, during which the energy from ATP and NADPH is used ...
How is the light and dark reaction connected? ›
ATP and NADPH These two products are together called Assimilatory Power. These two products are utilized in the dark reaction for the purpose of Carbon Fixation and hence can be called as Connecting link between Light and Dark reactions.
What are the 2 steps of dark reactions? ›
The Calvin cycle, which is another name for the dark reactions of photosynthesis, consists of three steps: carbon fixation, reduction, and regeneration. The Calvin cycle is used to convert atmospheric CO2 into glucose, which is a sugar that plants use to store energy.
Dark reactions are also known as the Calvin Cycle, the Calvin-Benson cycle, and light-independent reactions. The point is that they do not require sunlight to complete their process.
Why are light and dark reactions important? ›
The importance of the light and dark reactions of photosynthesis is that they combine to make it possible for organic molecules to be created from inorganic precursors.
What is another name for the dark reaction? ›
The Calvin cycle is also called dark reactions or light-independentreactions because it's the part that doesn't need energy from the sun to happen. ... This reaction creates a 6-carbon molecule which then splits into two 3-carbon molecules. This part of the cycle is called carbon fixation.
What are the products of the dark reaction? ›
The dark reaction occurs outside of the thylakoids. In this reaction, the energy from ATP and NADPH are used to fix carbon dioxide (CO2). The products of this reaction are sugar molecules and other organic molecules necessary for cell function and metabolism.
Why are plants green? ›
Chlorophyll gives plants their green color because it does not absorb the green wavelengths of white light. That particular light wavelength is reflected from the plant, so it appears green. Plants that use photosynthesis to make their own food are called autotrophs.
What are two cycles in photosynthesis? ›
Photosynthesis, a process vital for life, involves two main stages: light-dependent reactions and the Calvin cycle. Light-dependent reactions use light energy and water to produce ATP, NADPH, and oxygen. The Calvin cycle then uses ATP, NADPH, and carbon dioxide to create sugar.
What is the difference between the light reaction and the light dependent reaction? ›
In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. In the light-independent reactions, the chemical energy harvested during the light-dependent reactions drives the assembly of sugar molecules from carbon dioxide.
What is the difference between the light-dependent reactions and the dark light-independent reactions? ›
The light-dependent reactions occur in the presence of light while the light-independent reactions can occur in the light or dark.
What is the difference between the dark reactions and the Calvin cycle? ›
The dark reactions use the ATP and NADPH produced during the light reactions for energy, since these reactions do not use any energy from sunlight. The Calvin cycle, which is another name for the dark reactions of photosynthesis, consists of three steps: carbon fixation, reduction, and regeneration.
What are the basics of light reactions and dark reactions What are the reactants and the products? ›
Answer and Explanation:
The dark reactions occur in the stroma and requires carbon dioxide and the products of light reactions (ATP and NADPH) as reactants to produce glyceraldehyde 3-phosphate, which is later used to form glucose and regenerate ribulose bisphosphate (RUBP).
