Photosynthesis in Higher Plants: Overview, Topics, MCQs, Books, Tips
Photosynthesis in higher plants is the process by which green plants use sunlight, chlorophyll, water and carbon dioxide. It converts sunlight into chemical energy, producing glucose and oxygen. This photosynthesis process is the foundation of plant growth. Sunlight energy helps plants produce glucose and release oxygen. Without photosynthesis in higher plants, life on Earth cannot survive.
This Story also Contains
- Photosynthesis in Higher Plants: Introduction
- Chloroplast Structure and Photosynthetic Pigments
- Process of Photosynthesis in Higher Plants
- Photosynthesis in Higher Plants: Light Reaction
- Photophosphorylation and ATP Formation in Plants
- Photosynthesis in Higher Plants: Dark Reaction
- Photorespiration: Oxygen Fixation and Energy Loss
- Factors Affecting Photosynthesis in Higher Plants
- Photosynthesis Importance
- Photosynthesis in Higher Plants NEET MCQs (With Answers & Explanations)
- Recommended Video on Photosynthesis in Higher Plants
Early experiments proved that photosynthesis in higher plants depends on sunlight and chlorophyll. Plants absorb light energy, fix carbon dioxide and release oxygen. This photosynthesis in higher plants chapter explores the structure of chloroplasts, light and dark reactions, C3, C4, and CAM pathways, and factors influencing photosynthesis—core concepts for NEET Biology.
Photosynthesis in Higher Plants: Introduction
The Early experiments on photosynthesis by Joseph Priestley and Jan Ingenhousz proved that photosynthesis in higher plants releases oxygen. They use sunlight and chlorophyll for this process. Plants absorb light energy and fix carbon dioxide. Sunlight is used for synthesising organic compounds by this physicochemical process.
The process of photosynthesis in higher plants uses light energy to synthesise organic compounds in green plants. It is an enzyme-controlled anabolic process. Life on Earth depends on photosynthesis as it is the primary source of food, and it is responsible for releasing oxygen into the atmosphere. Life on Earth depends on photosynthesis in higher plants because it provides food and maintains oxygen levels in the atmosphere.
It can be represented by the equation: 6CO2 + 6H2O + Light → C6H12O6 + 6O2
Chloroplast Structure and Photosynthetic Pigments
Chloroplasts are found in the mesophyll cells of the leaves, where photosynthesis in higher plants occurs. Photosynthesis involves the four biological pigments in plants:
Chlorophyll a
Chlorophyll b
Xanthophylls
Carotenoids
All these pigments participate in the process of photosynthesis in higher plants. Hence, they are also called photosynthetic pigments. While chlorophyll traps the light energy for photosynthesis, xanthophylls and carotenoids act as accessory pigments.
Process of Photosynthesis in Higher Plants
Photosynthesis in higher plants converts sunlight into chemical energy. It uses chlorophyll, water, and carbon dioxide. It mainly takes place in the chloroplasts of leaf cells and is vital for plant growth and oxygen production. Photosynthesis in higher plants involves the following phases:
Light Reaction
Dark Reaction
Photosynthesis in Higher Plants: Light Reaction
The light-dependent reaction occurs in the presence of light. Light wavelengths are absorbed by pigments, and ATP is produced. Key steps:
Absorption of light, splitting of water, oxygen release, and formation of ATP and NADPH are all involved in the process.
A pigment molecule attached to a protein in the light-harvesting complex is found in both types of photosystems, where it helps capture light energy for photosynthesis.
Antennae containing accessory pigments are attached to each photosystem's reaction centre, which consists of chlorophyll.
Photosystems: P-700 for PS-I, as chlorophyll a has an absorption peak of 700 nm, while it is P-680 for PS-II, as chlorophyll a has an absorption peak of 680 nm.
Photophosphorylation and ATP Formation in Plants
Photophosphorylation is the process by which light energy is used to produce ATP during photosynthesis. It occurs in the thylakoid membranes of chloroplasts.
The two types of photophosphorylation are:
Non-cyclic Photophosphorylation
The table shows the difference between cyclic and non-cyclic photophosphorylation:
| Features | Non-cyclic Photophosphorylation | Cyclic Photophosphorylation |
|---|---|---|
Photosystems Involved | Both PS-II and PS-I are involved | Only PS-I is involved |
Light Absorption | PS-II absorbs light at 680 nm; PS-I absorbs light at 700 nm | PS-I absorbs light at 700 nm |
Electron Flow | Electrons flow from PS-II to PS-I, then to NADP+ | Electrons circulate within PS-I |
Products | Produces ATP, NADPH+ H⁺, and O₂ | Produces only ATP |
Electron Return | Electrons lost by PS-II do not return (non-cyclic) | Electrons return to PS-I (cyclic) |
Final Electron Acceptor | NADP+ (reduced to NADPH+ H⁺) | No external electron acceptor; electrons return to PS-I |
Oxygen Production | Oxygen is produced as a byproduct | No oxygen is produced |
Type of Flow | Linear (non-cyclic) | Cyclic |
Photosynthesis in Higher Plants: Dark Reaction
When there is no light, this process takes place in the stroma of the chloroplast. The process involves the following cycles:
Calvin Cycle (C3 Cycle)
The steps of the Calvin cycle include:
In a carbon-fixation process, ribulose-1, 5-bisphosphate combines with carbon dioxide to form 3-phosphoglyceric acid, a 3-carbon compound. In this process, a protein enzyme called RuBisCO is involved.
Glyceraldehyde-3-phosphate is formed by the reduction of one molecule of carbon dioxide with two molecules of ATP and NADPH.
A series of reactions occurs to form glucose from glyceraldehyde-3-phosphate molecules, and RuBP regenerates to continue the cycle.
C4 Cycle (Hatch and Slack Pathway)
The pathway follows a cycle, where mesophyll cells and bundle sheath cells contain enzymes involved in the C4 pathway. It involves:
Pathway where plants produce a chemical compound containing four carbons from atmospheric carbon dioxide.
Carbon dioxide is taken up by phosphoenolpyruvate located in the mesophyll cells. Phosphoenolpyruvate carboxylase is responsible for the reaction.
In the resulting mesophyll cells, aspartic acid and malic acid are formed and transported to the bundle sheath cells. Three-carbon molecules are released, and carbon dioxide is released as a result of the breakdown of C4 acids.
They are then converted into phosphoenolpyruvate in the mesophyll cells at the end of the cycle.
The cycle is completed when carbon dioxide enters the bundle sheath cells.
The difference between the C3 pathway and C4 pathway is given below-
Feature | C3 Pathway | C4 Pathway |
|---|---|---|
First stable product | 3-carbon compound (PGA) | 4-carbon compound (OAA) |
Site of photosynthesis | Mesophyll cells only | Mesophyll and bundle sheath cells |
Photorespiration | High | Very low or absent |
Efficiency in hot climates | Less efficient | More efficient due to the CO₂ concentration |
CAM Pathway (Crassulacean Acid Metabolism)
CAM is a special photosynthetic adaptation seen in some desert plants where stomata open at night to reduce water loss. Carbon dioxide is fixed into organic acids at night and used during the day for photosynthesis, helping the plant conserve water.
CAM plants are adapted to arid conditions and open their stomata at night to minimise water loss, unlike C3 and C4 plants, which open their stomata during the day.
In the CAM pathway, CO2 is fixed at night into a 4-carbon acid (like malic acid), which is stored in vacuoles and later used during the day for photosynthesis.
The C4 and CAM pathways have processes such as the carbon fixation into a 4-carbon compound, but are in different times. C4 separates processes by organellar space, and CAM separates the CO₂ fixation by time.
In the day, CAM plants close their stomata and use the stored CO2 for the Calvin cycle, allowing photosynthesis to occur without any water loss.
Examples of such plants are cacti, pineapple, and Agave.
Photorespiration: Oxygen Fixation and Energy Loss
Photorespiration is a light-dependent process that occurs when the enzyme RuBisCO fixes oxygen instead of carbon dioxide. It leads to the loss of energy and carbon for the plant and typically happens under high light intensity and low carbon dioxide levels.
Photorespiration is a phenomenon in plants where, instead of using carbon dioxide for photosynthesis. The plant uses oxygen.
It occurs when there is more oxygen and less carbon dioxide, typically in hot and dry conditions.
The plant will, therefore, emit carbon dioxide but cannot produce any energy or sugar from the process; hence, the whole process is inefficient and wasteful for the plant.
Factors Affecting Photosynthesis in Higher Plants
Several factors influence the rate of photosynthesis, including light intensity, carbon dioxide concentration, temperature, and availability of water. These factors determine how efficiently a plant can produce food and grow. The following list the factors affecting photosynthesis in higher plants:
| Factors | Description |
|---|---|
Light intensity | Higher light intensity increases the rate of photosynthesis up to a certain point, as it provides the energy needed for the reaction. |
Carbon dioxide concentration | Carbon dioxide is a raw material for photosynthesis, and increasing its concentration usually hastens the process until other factors become limiting |
Water availability | Water is essential for the photolysis step in the light reactions. Lack of water can slow down or even stop photosynthesis and lead to stomatal closure. |
Temperature | Photosynthesis is enzyme-driven, so the rate increases up to an optimum point and then declines. |
Chlorophyll content | The presence of chlorophyll is important as it captures light energy. Less chlorophyll means reduced photosynthesis. |
Photosynthesis Importance
Photosynthesis is essential for life on Earth. There are several ecological implications, but photosynthesis also derives some practical benefits for the living world.
It has a vital role in the carbon cycle; CO2 is converted into organic compounds, leading to a decrease in atmospheric CO2.
It maintains the levels of CO2 and O2 in the ecosystems.
It serves as the basic source of energy for all trophic levels.
In agriculture, improved crop yields and artificial photosynthesis are being researched as a means of sustainable energy production.
Photosynthesis in Higher Plants NEET MCQs (With Answers & Explanations)
Important topics for NEET are:
Stages of photosynthesis
Factors affecting Photosynthesis
Practice Questions for NEET
Q1. Which among the following has the greatest energy in its quantum?
Red light
Blue light
Green light
Yellow light
Correct answer: 2) Blue light
Explanation:
According to the equation E = hc/λ, energy is inversely proportional to wavelength. Blue light has the greatest energy in its quantum compared to longer wavelengths because it has a shorter wavelength (450–495 nm). According to the wave-particle duality of light, energy is inversely proportional to wavelength. This means that shorter wavelengths like blue light carry more energy per photon than longer wavelengths, such as red or infrared light.
Hence, the correct answer is Option (2) Blue light.
Q2. Oxygen is not produced during photosynthesis by
Cycas
Nostoc
Green sulphur bacteria
Chara
Correct answer: 3) Green sulphur bacteria
Explanation:
Photosynthesis -
Enzyme-regulated anabolic process of manufacture of organic compounds inside the chlorophyll-containing cells.
Since Charan Cycas come under the plant kingdom, they perform oxygenic photosynthesis. Green sulfur bacteria utilize H2S instead of H2O and perform anoxygenic photosynthesis or do not evolve oxygen.
Hence, the correct answer is Option (3) Green sulfur bacteria.
Q3. Greatest proportion of photosynthesis in the world is carried out by:
trees in the rain forests of the world
trees in the temperate forests of the world
algae in oceans
irrigated crop fields
Correct answer: 3) Algae in oceans
Explanation:
Algae are the largest oxygen-producers in the world through photosynthesis, in the oceans, and these organisms are very significant in the production of oxygen. Estimates have suggested that marine plants, particularly unicellular photosynthetic algae, produce about 70% to 80% of the oxygen produced in the atmosphere. These kinds of organisms, such as Prochlorococcus, play an important role in the aquatic ecosystem and, because of photosynthesis, play a crucial role in affecting the balance of oxygen in the environment.
Hence, the correct answer is Option (3) algae in oceans.
Also Read:
Recommended Video on Photosynthesis in Higher Plants
Frequently Asked Questions (FAQs)
In photosynthesis (Class 11 Biology, Higher Plants), the antenna complex is a group of pigment molecules (chlorophyll a, chlorophyll b, carotenoids) that capture light energy and transfer it to the reaction centre.
Photosynthesis occurs in the chloroplasts of mesophyll cells in leaves. The grana carry out light reactions, while the stroma is the site of dark reactions (Calvin cycle).
- Light reactions: Occur in thylakoid membranes, produce ATP, NADPH, and oxygen.
- Dark reactions (Calvin cycle): Occur in stroma, use ATP and NADPH to fix CO2 into glucose.
