3 Biology -- Photosynthesis

The source of oxygen in photosynthesis is the water but not the carbon dioxide. Explain with reasons. Briefly describes the hill reaction.

1 Answers

In photosynthesis, the source of oxygen is indeed water, but carbon dioxide (CO2) also plays a crucial role, the process and clarify the relationship between water and carbon dioxide in photosynthesis.

Photosynthesis is the biochemical process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose. It occurs in the chloroplasts of plant cells, specifically in the thylakoid membranes.

During the light-dependent reactions of photosynthesis, also known as the Hill reaction, light energy is absorbed by chlorophyll and other pigments present in the thylakoid membranes. This energy is then used to split water molecules (H2O) into hydrogen ions (H+), electrons (e-), and molecular oxygen (O2).

The reaction can be represented as follows:

2H2O + 2NADP+ + 3ADP + 3Pi + light energy → O2 + 2NADPH + 3ATP

The water molecules are the source of the oxygen released during photosynthesis. Water molecules provide the necessary electrons to replace the ones lost by chlorophyll when it absorbs light energy. This process is called photolysis, and it occurs in a complex called the Photosystem II (PSII).

In addition to water, carbon dioxide (CO2) is also an essential component of photosynthesis. During the light-independent reactions, also known as the Calvin cycle or dark reactions, carbon dioxide is incorporated into organic molecules to produce glucose. This process occurs in the stroma of the chloroplasts and utilizes the energy and reducing power (NADPH and ATP) generated during the light-dependent reactions.

The overall equation for photosynthesis can be summarized as:

6CO2 + 12H2O + light energy → C6H12O6 + 6O2 + 6H2O

As you can see, both water and carbon dioxide are involved in photosynthesis. Water is the source of oxygen, released as a byproduct, while carbon dioxide is the source of carbon atoms that are used to build glucose molecules.

So, to clarify, both water and carbon dioxide play essential roles in the process of photosynthesis, with water serving as the source of oxygen and carbon dioxide as the source of carbon atoms for glucose synthesis.

What is photosynthesis?

The synthesis of complex organic compounds from simple organic compounds like water and carbondioxide by green plants in the presence of chlorophyll using sunlight is called photosynthesis.

6CO₂+ 6H₂O CHO+6O

Write the importance of photosynthesis.

The importance's of photosynthesis are as follows:-

It provides food for the plants and oxygen which makes environment clean
It utilizes carbondioxide from the atmosphere which helps to reduce global warming to some extent.
Food produced by plants by the process of photosynthesis is utilized by many organisms. So, it serves as a source of food.
Fuels in the form of coal, wood, petroleum products, etc. are the indirect product of photosynthesis.
It serves as the primary energy process for most...

What are photosynthetic pigments?

The pigments present in the plant cell that absorb sunlight and are responsible for photosynthesis are called photosynthetic pigments. For example:- chlorophyll, xanthophyll, carotene, etc.

What is light reaction? Where does it occur

Light reaction also called Light-dependent reaction or Hill's reaction is the first phase of photosynthesis in which production of chemical energy like NADPH2 and ATP take place in the presence of light. This reaction takes place in the grana membranes of the chloroplast.

What is dark reaction? Where does it occur?

Dark reaction, also called calvin cycle is an anabolic process in which 3-Carbon sugar called glyceraldehyde-3-phospate is produced. This is a light independent process.

Differentiate between cyclic and non-cyclic photophosphorylation.

Differences between cyclic and non-cyclic photophosphorylation are given below:-

cyclic photophosphorylation

non-cyclic photophosphorylation

1. In this process, electron released from the reaction centre passes through different different ways and return back to the same centre.

2. Only PSI system is involved in it.

3. Last electron acceptor in it is P (PSI) itself.

4. It produces ATP only.

5. First electron donor in it is P.

6. It takes place in all plants and bacteria.

1. In this...

Explain the C3 pathway of photosynthesis.

It is the reaction which occurs in the stroma of chloroplast in absence of light or in dark condition. In this ATP and NADPH₂produced during light reaction are utilized as source of energy. It is studied in the following steps:-

1. Assimilation of carbondioxide or carboxylation:- It is the fixation of carbondioxide by RuBP in presence of RuBISCO enzyme. When RuBP reacts with carbondioxide, 6-carbon compound is formed which is unstable and converted into 3-carbin compound PGA phosphoglyceric...

What is photorespiration?

When during hot, arid days, stomata opens only a little, enough carbon dioxide is not taken, so rubisco takes up oxygen and uses it in the Calvin cycle instead of carbon dioxide, this process of light dependent uptake of carbon dioxide and release of oxygen is called photorespiration.

Explain the mechanism of photorespiration.

The utilization of oxygen and release of carbondioxide in presence of light during high temperature and low concentration of CO₂is called photorespiration.

It proceed in the following mechanism:-

1. During high temperature, high concentration of O₂and low concentration of CO₂, the affinity of Ribulose bi-phosphate (RuBP) carboxylase for CO decreases and for O increases and form oxyɡenase which catalyse the oxidation of RuBP to form 3-PGA(3-phospgoglyceric acid) and 2-phosphoglycolate.

RuBP +O...

Differentiate between C3 and C4 cycle.

Differences between C3 cycle and C4 cycle are as follows:-

C3 cycle	C4 cycle
1. It's CO₂acceptor molecule is Ribulose bi-phosphate.	1. It's CO₂acceptor molecule is phosphoenol pyruvic acid.
2.The first stable compound produced in it is phosphoglyceric acid which is 3 carbon compound	2. The first stable compound produced in it is oxalo acetic acid which is 4 carbon compound.
3. Only one type of chlorophyll is found in such plants	3. Two types of chlorophyll are found in such plants...

Decribe role of light in photosynthesis.

The major role of light during photosynthesis is toprovides energy for the synthesis of glucose from carbon dioxide and water. During light reaction, the chlorophyll entraps light and the solar energy is converted into chemical energy in the form of ATP molecules.

Decribe C4 cycle.

It is also a pathway for fixation and reduction of carbondioxide. It was discovered by Hatch and Slack in 1977. The first acceptor of CO₂is phosphoenol pyruvic acid and the first stable compound is oxalo acetic acid which is 4-carbon compound. So, this cycle is called C4 cycle. The anatomy of leaf of C4 plants is called krantz anatomy.

It is completed in the following ways:-

1. Fixation of CO takes place in mesophyll cell. In mesophyll cell, the affinity of PEP carboxylase (Phosphoenol pyruvic...

List down the significance of C4 plants

The significances of C4 plants are as follows:-

1. C4 plants have very low photorespiration.

2. C4 plants are more efficient in fixation of CO in low concentration of CO, because of high affinity of PEP.

3. Concentric arrangement of mesophyll cells produces a smaller area in relation to volume for better utilization of available water and reduces intensity of light.

4. They are adapted to high temperature (30 - 45C), intense radiation and saline condition.

5. Generally their product is higher than...

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