Chapter – 3A : Plant Physiology | Chapter Solution Class 9

(c) Glucose

Explanation: Photosynthesis produces glucose as the main product, which stores energy. It is formed using carbon dioxide and water in the presence of sunlight and chlorophyll. Oxygen is released as a byproduct of this process.

(b) Glucose

Explanation: During the dark reaction of photosynthesis, CO₂ is reduced (gains hydrogen) to form glucose (C₆H₁₂O₆) with the help of ATP and NADPH produced in the light reaction.

(c) Chlorophyll + CO₂ + H₂O + Sunlight

Explanation: Photosynthesis requires chlorophyll to absorb light, CO₂ from the air, H₂O from the soil, and sunlight as the energy source to produce glucose and oxygen.

(d) Glucose

Explanation: It is an anabolic process because it involves the building up of complex molecules (glucose) from simpler ones (CO₂ and H₂O), storing energy in the process.

(b) Mesophyll tissue

Explanation: The mesophyll tissue of leaves (especially palisade and spongy parenchyma) contains many chloroplasts, which are the actual organelles where photosynthesis takes place.

(d) ATP

Explanation: Photophosphorylation is the process in which ATP is formed using light energy in the light reaction of photosynthesis. ATP stores energy used in the dark reaction.

(d) All of them

Explanation: Light, temperature, and CO₂ concentration all affect the rate of photosynthesis. Light provides energy, temperature influences enzyme activity, and CO₂ is a raw material.

(d) Age of the leaf

(b) Mn

Explanation: Manganese (Mn) is an essential micronutrient involved in the photolysis of water during the light reaction. It plays a role in enzyme activation in plants.

(d) B

Explanation: (d) B, as Boron (B) is a micronutrient that plants require but is not considered a non-essential nutrient for humans or other animals.

(a) Essential elements

Explanation: Essential elements like nitrogen, potassium, magnesium, and phosphorus are necessary for plant growth, photosynthesis, and development. Without them, the plant cannot complete its life cycle.

Essential elements

Explanation: These are nutrients required for growth and metabolic functions. Their absence prevents plants from maturing and reproducing.

pH

Explanation: Hydrogen ions (H⁺) control the pH of cells and solutions. A balanced pH is crucial for enzyme activity and physiological processes in plants.

Protoplasm

Explanation: Protoplasm is the living content of a cell (nucleus + cytoplasm), responsible for all vital activities.

ATP

Explanation: ATP, NADPH, and O₂ are produced in the light reaction. ATP and NADPH store energy for use in the dark reaction.

Enzyme

Explanation: Enzymes like RuBisCO catalyze steps of the dark reaction, especially carbon fixation in the Calvin cycle.

PGA (Phosphoglyceric acid)

Explanation: In the Calvin cycle, PGA is the first stable product formed after CO₂ fixation by RuBP.

Tinospora

Explanation: In some plants like Tinospora, roots contain chlorophyll and can perform photosynthesis.

ATP

Explanation: Photophosphorylation is the process of making ATP from ADP and Pi using light energy during the light phase.

True

Explanation: Manganese is required in small amounts for photosynthesis and enzyme activation, thus classified as a micronutrient.

True

Explanation: Chlorophyll contains carbon, hydrogen, oxygen, nitrogen, and a central magnesium (Mg) ion crucial for capturing light energy.

False

Explanation: Carbon is a non-mineral nutrient. It is absorbed from CO₂ in the air, not from the soil like minerals.

True

Explanation: Sunlight provides the energy needed to activate chlorophyll, drive photolysis, and produce ATP and NADPH.

True

Explanation: In the light reaction, light energy splits H₂O into H⁺ and OH⁻ through photolysis, releasing oxygen as a byproduct.

True

Explanation: The balanced chemical equation for photosynthesis uses 6CO₂ to form 1 glucose (C₆H₁₂O₆), along with water and light.

True

Explanation: The oxygen released during photosynthesis comes from H₂O, not CO₂, as shown in the photolysis step.

False

Explanation: While photosynthesis is the main natural method, glucose can also be produced industrially or through chemosynthesis in some organisms.

Oxygen

Explanation:

CO₂, chlorophyll, and sunlight are all essential components required for photosynthesis to occur.

Zinc (Zn)

Explanation:

Nitrogen (N), Phosphorus (P), and Potassium (K) are considered macronutrients — needed in large quantities by plants.

In the leaves of plants, between the upper and lower epidermis.

Explanation: Mesophyll tissue is located in the middle part of the leaf and contains chloroplast-rich cells like palisade and spongy parenchyma, where photosynthesis mainly occurs.

To perform photosynthesis.

Explanation: Mesophyll cells contain chloroplasts that capture sunlight and carry out photosynthesis, producing food for the plant.

Yes.

Explanation: ATP is used during the synthesis of glucose in the dark reaction and also released when glucose is broken down during respiration for energy.

Sunlight, chlorophyll, carbon dioxide, and water.

Explanation: These four components are essential for photosynthesis to occur, leading to the production of glucose and oxygen.

Photosynthesis maintains oxygen and carbon dioxide balance of nature.

Explanation: Photosynthesis absorbs CO₂ and releases O₂, maintaining the gas balance in the atmosphere and supporting life on Earth.

Photosynthesis stops at night due to absence of sunlight.

Explanation: Light is necessary for the light-dependent reactions of photosynthesis, so in the absence of sunlight, the process halts.

Photosynthesis takes place in the chloroplast.

Explanation: Chloroplasts contain chlorophyll and are the organelles where all photosynthetic reactions take place.

Solar energy is stored in the form of chemical energy in glucose molecules.

Magnesium (Mg).

Explanation: Magnesium is a key element in chlorophyll molecules and is essential for capturing light energy during photosynthesis.

Photosynthesis is called carbon assimilation because plants absorb carbon dioxide (CO₂) from the atmosphere and convert its carbon into organic compounds like glucose.

It is called an anabolic process because it involves the synthesis of complex molecules like glucose from simple molecules such as carbon dioxide and water. Energy is stored during this process, and it increases the plant’s dry weight.

Photosynthesis occurs mainly in the mesophyll tissue of the leaf, especially in palisade and spongy parenchyma cells. These cells contain chloroplasts, the organelles where photosynthesis takes place.

Photosynthesis is an oxidation-reduction (redox) process because water is oxidized (loses electrons and hydrogen), and carbon dioxide is reduced (gains electrons and hydrogen) to form glucose.

Photosynthesis is the process by which green plants prepare glucose using CO₂, H₂O, and sunlight in presence of chlorophyll.

It is called carbon assimilation because carbon from CO₂ is absorbed and converted into organic matter like glucose.

Photophosphorylation is the process in which ATP is formed from ADP and inorganic phosphate (Pi) using light energy during the light-dependent phase of photosynthesis. This ATP is used in the dark reaction to form glucose.

The Hill reaction is the light-dependent splitting of water molecules in the presence of chlorophyll, releasing oxygen, protons (H⁺), and electrons. This process takes place in the grana of chloroplasts.

ATP is called the energy currency of the cell because it stores and supplies energy for various biochemical reactions. It is easily broken down to release energy needed for cell functions like synthesis, transport, and movement.

Blackman’s reaction refers to the dark reaction of photosynthesis, where carbon fixation takes place using ATP and NADPH formed in the light reaction. It is controlled by enzymes and is not directly dependent on light.

The Calvin Cycle is a series of enzyme-catalyzed reactions in the stroma of chloroplasts where CO₂ is fixed into glucose using ATP and NADPH. It was discovered by Melvin Calvin and is also called the C₃ pathway.

Photosynthetic quotient (PQ) is the ratio of volume of O₂ evolved to CO₂ absorbed during photosynthesis. For carbohydrate formation, PQ = 1 (i.e., 6O₂/6CO₂ = 1).

Micronutrients are essential elements required by plants in very small amounts (less than 0.1 mg/g dry matter), but they are vital for growth and metabolism.

Examples – Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Chlorine (Cl).

Carbon assimilation is the process by which green plants absorb carbon dioxide (CO₂) from the atmosphere and convert its carbon into organic compounds like glucose during photosynthesis. This takes place in the dark reaction (Calvin cycle) of photosynthesis inside the stroma of chloroplasts.

Components required and their sources:

Carbon dioxide (CO₂):

• Source: Atmosphere
• Role: Provides the carbon needed to form glucose.

Water (H₂O):

• Source: Absorbed from the soil through root hairs.
• Role: Supplies hydrogen for glucose formation and releases oxygen.

Sunlight:

• Source: The sun
• Role: Provides energy needed for the light reaction and drives the overall process.

Chlorophyll:

• Source: Present in chloroplasts (mostly in mesophyll cells of leaves)
• Role: Absorbs light energy to initiate photosynthesis.

Short notes on various importance of photosynthesis

1. Food Production: Photosynthesis is the primary source of food for all living organisms. Plants produce glucose, which is used directly or stored as starch and transferred through the food chain.
2. Oxygen Release: During photosynthesis, oxygen (O₂) is released as a byproduct, which is essential for the respiration of all aerobic organisms.
3. Maintains CO₂–O₂ Balance: Photosynthesis helps maintain the balance of carbon dioxide and oxygen in the atmosphere, which is crucial for life on Earth.
4. Energy Conversion: It converts solar energy into chemical energy and stores it in glucose molecules, which is later used by organisms for growth and activity.

Photosynthesis is a biochemical process in which green plants prepare glucose using carbon dioxide, water, and sunlight in the presence of chlorophyll, releasing oxygen as a byproduct.

Equation:

6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O

Benefits to the living world:

1. Provides food directly to herbivores and indirectly to carnivores.
2. Releases oxygen, essential for respiration in animals and humans.
3. Maintains CO₂–O₂ balance in the atmosphere.
4. Acts as the base of the food chain and supports life.
5. Stores solar energy in chemical form for all organisms.

Photosynthesis is the process by which green plants convert CO₂ and H₂O into glucose using sunlight and chlorophyll, releasing oxygen.

It is called carbon assimilation because the carbon from CO₂ is absorbed and converted into organic compounds like glucose. This is the way atmospheric carbon becomes part of living organisms.

Blackman’s reaction refers to the dark phase of photosynthesis, named after F. F. Blackman (1905). It includes enzyme-controlled reactions that fix carbon dioxide and form glucose using ATP and NADPH produced in the light phase.

It occurs in the stroma of chloroplasts and is not directly dependent on light, but cannot occur without the products of the light reaction. This reaction forms the Calvin cycle, also called the C₃ pathway.

Functions of essential mineral elements :

1. Formation of Protoplasm and cell walls : Major component of protoplasm and cell walls are formed by the carbon, hydrogen, oxygen and nitrogen. Along with these nutrients S, P, Mg and Fe are also required for synthesis of protein, nucleic acid, hormone, vitamin etc.
2. Formation of Chlorophyll : Major component of chlorophyll is C, H, O, N and Mg. All these are macronutrients. Mg also helps in formation of chlorophyll.
3. Enzyme activator : Mg, Ca, Mn, K are used as activator of enzyme at different biochemical process of plants.
4. Co-enzyme activities : Fe, Cu, Zn are required in very small quantities as act as prosthetic groups or coenzyme of certain enzyme system.
5. Oxidation-reduction system : Fe and Cu⁺⁺ act as electron carrier in different bio-chemical reaction.
6. Catalytic function : Cu, Zn, Fe, Mg etc. are acted as catalysts in various enzymatic reaction.
7. Opening and closing of Stomata : Potassium plays an important role in opening and closing movement of guard cell of the stomatal pore.

The light phase of photosynthesis occurs in the grana (thylakoid membranes) of chloroplasts and requires sunlight. It involves a series of oxidation-reduction reactions that convert solar energy into chemical energy in the form of ATP and NADPH, and it also releases oxygen (O₂) as a byproduct.

Steps of Light Phase Reaction:

(i) Activation of Chlorophyll: When photon (light) particles strike the chlorophyll molecule, its electrons become excited and move to a higher energy level. This creates activated chlorophyll which starts the chain of reactions.

Reaction: Photon + Chlorophyll → Activated Chlorophyll*

(ii) Photolysis of Water: In the presence of light and activated chlorophyll, water molecules are split into H⁺ (protons), OH⁻ (hydroxyl ions), and electrons (e⁻). This is called photolysis.

Reaction: H₂O → H⁺ + OH⁻; 4OH⁻ → 2H₂O + O₂ ↑

• The electrons replace those lost by excited chlorophyll.
• The O₂ is released as a byproduct.

(iii) Evolution of Oxygen:

Oxygen (O₂) is released into the atmosphere as a byproduct of photolysis. It comes from the splitting of water, not from CO₂.

(iv) Formation of NADPH (Reduced NADP):

The electrons released during photolysis are transferred to NADP⁺, along with H⁺ ions, to form NADPH.

Reaction: NADP⁺ + 2e⁻ + H⁺ → NADPH

NADPH is used later in the dark reaction (Calvin cycle) for reducing CO₂.

(v) Photophosphorylation (ATP Formation): The energy from excited electrons is used to convert ADP + Pi (inorganic phosphate) into ATP. This process is called photophosphorylation.

Reaction: ADP + Pi → ATP

This ATP is also used in the dark reaction for synthesizing glucose.