WBBSE Class 9 Life Science Solutions Chapter 3.1A Plant Physiology: Photosynthesis

Detailed explanations in West Bengal Board Class 9 Life Science Book Solutions Chapter 3.1A Plant Physiology: Photosynthesis offer valuable context and analysis.

WBBSE Class 9 Science Chapter 3.1A Question Answer – Plant Physiology: Photosynthesis

Very Short Questions and Answers : (1 mark for each question)

Question 1.
Name the scientist who coined the term ‘photosynthesis’.
Answer:
Barnes coined the term ‘photosynthesis’.

Question 2.
Name a vascular land plant, which photosynthesises through its roots.
Answer:
Stylites andicola is a vascular land plant, which photosynthesises through its roots.

Question 3.
What does NADP stand for?
Answer:
NADP stands for Nicotinamide Adenine Dinucleotide Phosphate.

Question 4.
From which of the raw materials does glucose get its oxygen during photosynthesis?
Answer:
Glucose, the end product of photosynthesis, gets its oxygen from CO₂

Question 5.
Which element is taken up by green plants from environment in the form of an oxide?
Answer:
Carbon is absorbed by green plants from the environment in the form of an oxide, namely carbon dioxide.

Question 6.
Which biocatalyst is essential for photosynthesis?
Answer:
Chlorophyll is the biocatalyst, which is essential for photosynthesis.

Question 7.
Which pigments are necessary for photosynthesis, other than chlorophyll?
Answer:
Other than chlorophyll, carotenoids are the pigments which are necessary for photosynthesis.

Question 8.
Name two members under kingdom Protista, which are capable of synthesising their own food by photosynthesis.
Answer:
Euglena sp. and Chrysamoeba sp. are the two members under kingdom Protista, which are capable of synthesising their own food by photosynthesis.

Question 9.
Name an enzyme, necessary for the assimilation of carbon during the lightindependent phase of photosynthesis.
Answer:
The enzyme RuBisCO is necessary for the assimilation of carbon during the lightindependent phase of photosynthesis.

Question 10.
What is the full form of the enzyme RuBisCO?
Answer:
The full form of RuBisCO is Ribulose Bisphosphate carboxylase/oxygenase.

Question 11.
Which of the raw materials of photosynthesis is oxidised during the process?
Answer:
Water molecule is oxidised during the process of photosynthesis.

Question 12.
Which of the raw materials of photosynthesis is reduced during the process?
Answer:
Carbon dioxide is reduced during photosynthesis.

Question 13.
In case of terrestrial plants, which process reduces the content of CO₂ and increases the content of O₂ in the atmosphere?
Answer:
In case of terrestrial plants, the process of photosynthesis reduces the content of CO₂ and increases the content of O₂ in the atmosphere.

Question 14.
Where do plants generally store their food?
Answer:
Plants generally store their food in roots, stems and fruits.

Question 15.
What are the end products of photosynthesis?
Answer:
Glucose, oxygen and water are the end products of photosynthesis.

Question 16.
Name the following reaction:
Answer:
This reaction is named as photolysis of water.

Question 17.
Name the following reaction:
Answer:
This reaction is called photophosphorylation.

Question 18.
Who discovered that oxygen, evolved during photosynthesis, comes from water?
Answer:
British scientist Robin Hill discovered that oxygen, evolved during photosynthesis, comes from water.

Question 19.
Who discovered the reaction path of carbon assimilation?
Answer:
Scientist Blackman discovered the reaction path of carbon assimilation.

Question 20.
Who discovered the reaction path of glucose synthesis and regeneration of RuBP from PGA?
Answer:
Scientist Melvin Calvin and his co-workers discovered the cyclic reaction path of glucose synthesis and regeneration of RuBP from PGA.

Question 21.
How many phosphoglyceraldehyde (PGAld) molecules are required to produce a glucose molecule?
Answer:
Two phosphoglyceraldehyde (PGAld) molecules are required to produce one molecule of glucose.

Question 22.
Which co-enzyme carries hydrogen for the reduction of PGA?
Answer:
NADP carries hydrogen for the reduction of PGA.

Question 23.
Which compound supplies chemical energy for the reduction of PGA?
Answer:
Adenosine triphosphate (ATP) supplies chemical energy for the reduction of PGA.

Question 24.
Out of 12 PGAld molecules, how many take part in the synthesis of RuBP in Calvin cycle?
Answer:
Out of 12 PG.Ald molecules, 10 molecules take part in the synthesis of RuBP in Calvin cycle.

Question 25.
Which are the end products of light-dependent phase of photosynthesis?
Answer:
Oxygen, ATP and NADPH+H⁺ are the end products of light-dependent phase of photosynthesis.

Question 26.
Which of the end products of light-dependent phase take part in the reactions of light-independent phase of photosynthesis?
Answer:
ATP and NADPH+H⁺ are the end products of light-dependent phase, which take part in the reactions of light-independent phase of photosynthesis.

Question 27.
Which reactant of light-independent phase of photosynthesis is received from the environment?
Answer:
CO₂ is the only reactant of the light-independent phase of photosynthesis which is received from the environment.

Question 28.
Which are the essential components, necessary for light-independent reactions of photosynthesis?
Answer:
CO₂, ATP, NADPH₂, and RuBP are the essential components, which are necessary for the light independent reactions of photosynthesis.

Question 29.
Which instrument is used to measure the absorption spectrum of chlorophyll?
Answer:
The absorption spectrum of chlorophyll is measured with the help of spectrophotometer.

Question 30.
Due to excessive heat from the sun, the process of photosynthesis stops. What is this condition called?
Answer:
The condition, in which the process of photosynthesis stops due to excessive heat from the sun, is called solarisation.

Question 31.
Under what temperature does photosynthesis occur at its best?
Answer:
Photosynthesis occurs at its best at an optimum temperature ranging between 25°C – 35°C

Question 32.
Name a bacteria which can prepare its own food without performing photosynthesis.
Answer:
Thiobacillus sp, is a bacteria which can prepare its own food without performing photosynthesis.

Question 33.
In green plants, what percentage of the total stored water is used during photosynthesis?
Answer:
During photosynthesis, only 1% of the total stored water is used up by green plants.

Question 34.
Name the co-pigment present in green plants which helps in photosynthesis.
Answer:
In green plants, carotenoids act as co-pigment, which help in photosynthesis.

Question 35.
What is the absorption spectrum of carotenoid?
Answer:
Absorption spectrum of carotenoid is blue-green.

Question 36.
Name two carotenoids.
Answer:
Carotene and xanthophyll are two carotenoids.

Question 37.
Why photosynthesis does not occur in animal cells?
Answer:
Photosynthesis does not occur in animal cells because they lack chloroplast and hence the photosynthetic pigment chlorophyll.

Question 38.
Which compound is both a raw material and a by-product, in the process of photosynthesis?
Answer:
Water is both a raw material as well as a byproduct, in the process of photosynthesis.

Question 39.
How do completely submerged aquatic plants absorb necessary CO₂ for photosynthesis?
Answer:
Completely submerged aquatic plants absorb necessary CO₂ through their entire body surface by the process of diffusion.

Question 40.
Give an example of a natural and an artificial Hill reagent?
Answer:
An example of natural Hill reagent is NADP, and an example of artificial Hill reagent is potassium ferric oxalate.

Question 41.
What are the two types of photophosphorylation?
Answer:
The two types of photophosphorylation are-

• cyclic photophosphorylation and
• non-cyclic photophosphorylation.

Short Questions and Answers : (2 marks for each question)

Question 1.
Define photosynthesis.
Answer:
Photosynthesis is a photochemical process in which green plants and certain chlorophyll containing organisms utilise water and carbon dioxide as raw materials to synthesise monosaccharide (glucose) in their body by entrapping light energy (especially sunlight) within it and releasing oxygen as a by-product in the environment.

Question 2.
Mention the components, necessary for photosynthesis.
Answer:
The materials required for photosynthesis are as follows-

• Raw material- Water and carbon dioxide,
• Pigments – Chlorophyll and carotenoids (carotene and xanthophyll),
• Energy- Light (sunlight or bright artificial light).

Question 3.
Where does photosynthesis occur?
Answer:
Photosynthesis occurs in the chloroplast-containing parenchyma (chlorenchyma) tissues known as mesophyll tissue of higher green plants. These tissues are distributed in leaves and all other green parts of the plants, like stems (in herbs), sepals of flowers, petals (water lily and custard apple flower), bracts (vasak plant), stipule (pea plant), root (orchid, Tinospora) etc.

Question 4.
How do plants absorb water for photosynthesis?
Answer:
Terrestrial plants absorb water from the soil with the help of their roots. Aquatic plants absorb water from the surrounding water medium through their body surface by the process of simple diffusion. Epiphytes (plants growing on other plants) like orchids, have aerial roots, called velamen, with thick hygroscopic outer coating, which absorb rain water and moisture from air to fulfill the plant’s need of water.

Question 5.
How do plants absorb CO₂ for photosynthesis?
Answer:
All terrestrial plants absorb CO₂ from the atmosphere through stomata of the leaves. Aquatic plants absorb dissolved CO₂ from surrounding water by simple diffusion through body surface. Partially submerged plants absorb CO₂ through stomata of the aerial portion of their body and the submerged portion get it by diffusion from the surrounding water medium.

Question 6.
What do photosynthetic pigments in plants do?
Answer:
In plants, there are two types of photosynthetic pigments, namely, chlorophyll and carotenoids. Chlorophyll helps in the dissociation of water and formation of energy packed ATP molecules. Carotenoids (carotene and xanthophyll) trap light energy and transfer it to chlorophylls for further reaction.

Question 7.
What is meant by absorption spectrum of photosynthesis?
Answer:
The specific wavelength of visual spectrum, which is absorbed by certain plant pigments and used in photosynthesis, is called absorption spectrum of that particular pigment.

Question 8.
What is meant by action spectrum of chlorophyll?
Answer:
Out of the seven colours of the visible spectrum of light, chlorophyll molecules strongly absorb red (650-760nm) and blue (430-470nm) light which is most effective for photosynthesis. Therefore, this region of the visible spectrum denotes the action spectrum of chlorophyll.

Question 9.
Mention the events occurring during the light-dependent phase of photosynthesis.
Answer:
Five different events occur during the light dependent phase of photosynthesis. These are–

• activation of chlorophyll,
• ionisation of water (photolysis of water),
• reduction of NADP⁺
• production of oxygen and
• photosynthetic phosphorylation.

Question 10.
What is meant by activation of chlorophyll?
Answer:
Light from the sun comes to earth in the form of energy-rich particles, called photons. When photons hit a chlorophyll molecule, it gets excited and releases an energised electron. This event is known as activation of chlorophyll.

Question 11.
What is meant by photolysis or ionisation of water?
Answer:
Being hit by photons, chlorophyl molecules get excited and dissociates water molecules into protons H⁺ and hydroxyl ions OH^–. This lightdependent dissociation of water molecule is called photolysis of water. This reaction is popularly known as Hill reaction.

Question 12.
What is meant by reduction of NADP⁺ ?
Answer:
NADP⁺ is a proton acceptor, which is present in chloroplast. During light-dependent phase of photosynthesis, proton (H⁺) is produced during photolysis of water, electron (e^–) is released from an excited chlorophyll molecule and NADP⁺, present in the photosynthetic cells, react to produce NADPH+H⁺. This reaction step is known as reduction of NADP⁺.
\(\mathrm{NADP}^{+}+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{NADPH}+\mathrm{H}^{+}\)

Question 13.
How is O₂ produced during photosynthesis?
Answer:
During photolysis of water, protons (H⁺) and hydroxyl ions (H^–) are produced. These hydroxyl ions then release one electron each and are transformed into hydroxyl radicals [OH]. These radicals combine to form water H₂O and oxygen O₂ molecules. Thus, O₂ is produced during light-dependent phase of photosynthesis, which is a by-product.
\(4 \mathrm{OH}^{-} \rightarrow 4[\mathrm{OH}]+4 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2 \uparrow\)

Question 14.
What is meant by photophosphorylation?
Answer:
During light-dependent phase of photosynthesis, the energised electrons released from photon hit chlorophylls, help to combine adenosine diphosphate (ADP) and inorganic phosphate (IP) to produce an energy-rich compound, adenosine triphosphate (ATP). This reaction is known as photosynthetic phosphorylation or photophosphorylation.

Question 15.
Why is it better to designate the second phase of photosynthesis as light-independent phase rather than dark phase?
Answer:
The term dark phase apparently indicates events occurring in dark, but reactions of photosynthesis never occur in the absence of light. The second phase of photosynthesis does not need direct light but some by-products of light phase like ATP and NADPH₂, come to act here. Therefore, it is better to designate this phase as light-independent phase rather than dark phase.

Question 16.
Which reactions take place in the light-independent phase of photosynthesis?
Answer:
During light-independent phase of photosynthesis four different reactions occur. These are

• carbon assimilation,
• reduction of PGA,
• resynthesis of RuBP and
• glucose synthesis.

Question 17.
What is meant by carbon assimilation?
Answer:
The CO₂ absorbed by photosynthetic plants from the atmosphere, reacts with RuBP, a five carbon compound, present in the stroma of chloroplast, to produce phosphoglyceric acid (PGA) in the presence of an enzyme, called RuBisCO. In this reaction, carbon atom of CO₂ is assimilated within the cellular organic compounds. This reaction is known as carbon assimilation. Here, 2 molecules of PGA are produced.

Question 18
How does reduction of PGA occur in lightindependent phase of photosynthesis?
Answer:
After the production of PGA during the assimilation of carbon, two products of light-dependent phase, namely NADPH+H⁺ and ATP come into action. NADPH+H⁺ reacts with PGA and reduces it to produce phosphoglyceraldehyde (PGAld). ATP supplies the necessary chemical energy for this reaction.

Question 19.
How is glucose synthesised in the lightindependent phase of photosynthesis?
Answer:
During the light-independent phase of photosynthesis, RuBP is carboxylated to form PGA, which is reduced to phosphoglyceraldehyde (PGAld) with the help of NADPH+H⁺ and ATP. Out of the total PGAld, 5/6th part undergoes a cycle of reactions and resynthesises RuBP. And the rest 1/6th portion of the total PGAld produced, then undergoes a series of reactions to produce glucose. Two molecules of PGAld produce 1 molecule of glucose.

Question 20.
Why are green plants considered as the food producers of the environment?
Answer:
By the process of photosynthesis, inorganic materials like water and carbon dioxide combine to produce a monosaccharide, called glucose. It is the basic component of all food matters on earth. From this glucose, all other carbohydrates, proteins and lipids are produced through various metabolic processes within the plant body, which is consumed by the other organisms. This is why, green plants are considered as food producers of the environment.

Question 21.
How does solar energy enter in the living organisms?
Answer:
During photosynthesis, light energy from the sun is trapped by the chlorophyll molecules. This energy is then transformed into chemical potential energy by the formation of glucose. At the end, this energy is transferred to different consumers or heterotrophic organisms and decomposers through food chain. This is how solar energy enters in the living organisms.

Question 22.
What are the sources of the components of carbon assimilation?
Answer:
The sources of the components of carbon assimilation are-

• CO₂ – Source of CO₂ is air,
• RuBP- Source of RuBP is the mesophyll tissue of leaf,
• NADPH+H⁺ Source of NADPH+H⁺ is NADP⁺ present in chlorophyll of leaf.
  NADP+ reacts with the H⁺ ion produced by the photolysis of water to form NADPH +H⁺and
• ATP – ATP is formed by the combination of ADP and inorganic phosphate in leaf during photophosphorylation.

Question 23.
Write the differences between light-dependent and light-independent phase of photosynthesis.
Answer:

Features	Light-dependent phase.	Light-independent phase
1. Role of sunlight	Sunlight is necessary	Sunlight is not necessary
2. Site of occurrence	It takes place in the grana of chloroplast	It takes place in the stroma of chloroplast
3. Production of oxygen	Oxygen is given out during this phase	Oxygen is not given out during this phase
4. Fate of NADP	NADP+ is reduced in this process, to form NADPH + H+	NADPH+ + H+ is oxidised in this process, to form NADP+

Long Questions and Answers : (5 marks for each question)

Question 1.
Briefly describe the reactions of light-dependent phase of photosynthesis.
Answer:
Reactions of light-dependent phase of photosynthesis
The reactions of light-dependent phase of photosynthesis occur in the stroma of chloroplastids. Five different reactions occur in this phase, which are mentioned below.

1. Activation of chlorophyll: Light from sun reaches the earth in the form of energy-packed particles, called photons. When these photons hit the chlorophyll molecules present in the chloroplast of green leaves, they get excited and release energised electrons. This event is known as activation of chlorophyll.

2. Photolysis of water: Activated chlorophyll dissociates water molecules into protons H⁺ and hydroxyl ions H^–. This light-dependent dissociation of water molecule is called photolysis or ionisation of water.

3. Reduction of NADP+ NADP⁺ is a proton acceptor, present in the chloroplasts. Proton H⁺ produced during the photolysis of water, reacts with NADP⁺and reduces it to NADPH+H⁺. In this reaction, necessary electrons for the subsequent reactions are emitted from the excited chlorophylls.

4. Production of oxygen: Hydroxyl ions H^–, produced during the dissociation or lysis of water, release electrons and are transformed into hydroxyl radicals OH. These radicals combine to form water H₂O and oxygen O₂ molecules.

5 Photosynthetic phosphorylation: The energised electrons, released from the photon-hit chlorophylls, help to combine adenosine diphosphate (ADP) and inorganic phosphate (iP) to produce an energy-rich compound, called adenosine triphosphate (ATP). This reaction is known as photosynthetic phosphorylation or photophosphorylation.

Question 2.
‘Green plants entrap solar energy and convert it into potential energy’- explain the sentence along with a diagram.
Answer:
Entrapping of solar energy and its conversion to potential energy by green plants. The source of every form of energy on earth is sunlight. The chlorophyll present in palisade cells of green plants absorbs the photon particles of the sunlight and stores it in the form of chemical energy in ATP through various chemical reactions.

This is known as the ‘entrapping of solar energy’. Later, the chemical energy of ATP is converted into the potential energy which remains stored within the glucose which is formed by the combination of CO₂ and H₂. This is known as the ‘conversion of solar energy into potential energy’.

Question 3.
Briefly describe the steps of light-independent phase of photosynthesis along with a diagram.
Answer:
The steps of light-independent phase of photosynthesis:

The reactions of light-independent phase occurs in stroma of chloroplastids. Four different reactions occur in this phase of photosynthesis. These are as follows-

1. Carbon assimilation: Photosynthetic plants absorb CO₂ from the atmosphere. This CO₂ reacts with RuBP in the stroma of chloroplast to produce phosphoglyceric acid (PGA). The enzyme RuBisCO catalyses this reaction. In this reaction, carbon atom (C) of CO₂ is assimilated within the cellular organic compounds. This reaction is known as carbon assimilation.

2. Reduction of PGA: In this step, two products of light-dependent phase, namely NADPH+H⁺and ATP come into action. NADPH + H⁺reacts with phosphoglyceric acid and reduces it to produce phosphoglyceraldehyde (PGAld). ATP supplies the necessary chemical energy for this reaction.

3. Re-synthesis of RuBP: Out of the total PGAld produced, 5/6th part undergoes a cycle of reactions and resynthesises RuBP. This reaction cycle is named Calvin cycle. In this cycle, several intermediate compounds are produced in subsequent steps.

4. Glucose synthesis: Out of the total PGAld produced, 1/6th part takes part in the synthesis of glucose. Within the stroma of chloroplasts, PGAld molecules undergo a series of reactions to synthesise glucose.

Question 4.
Write the significance of light-dependent phase of photosynthesis. What is the significance of light-independent phase of photosynthesis?
Answer:
Significance of light-dependent phase of photosynthesis:

The significance of light-dependent phase of photosynthesis are as follows-

• During photophosphorylation of the light-dependent phase, solar energy is converted into chemical energy and is stored as ATP.
• ATP, produced during photophosphorylation and NADPH₂, produced during reduction of NADP⁺, in the light-dependent phase, help in the reduction of PGA to PGAld, later in the light-independent phase.
• During the photolysis of water, it gets dissociated to liberate oxygen. This oxygen helps in respiration of all living organisms present in the environment.

Significance of light-independent phase of photosynthesis
The significance of light-independent phase of photosynthesis are as follows –

• Solar energy gets stored in glucose as potential energy. This energy helps the living world, either directly, or indirectly, to perform all metabolic functions.
• The CO₂ released into the environment by all organisms during respiration, is taken up by plants during the light-independent phase. As a result, the balance of CO₂ and O₂ is maintained in the environment.
• During this phase, assimilation of carbon takes place and carbohydrate, in the form of glucose, is produced as an end product. This glucose, either actively, or passively, forms the source of food for all living organisms.

Question 5
What are the significance of photosynthesis?
Answer:
Significance of photosynthesis
The significance of photosynthesis are mentioned below.

1. Trapping and transformation of solar energy: Light energy from the sun is trapped by chlorophyll and transformed into chemical potential energy by the synthesis of glucose. This energy is then passed on from the plants to the consumers through food chain.

2. Production of food: By photosynthesis, inorganic materials like water and CO₂ combine to produce glucose, which is the basic component of all food matters on earth. Not only plants but other animals also obtain this food, either directly or indirectly, to survive.

3. Maintenance of O₂ and CO₂ balance in the environment: During respiration, all living organisms release CO₂ and absorb O₂ .On the other hand, green plants release O₂ and absorb CO₂ during photosynthesis. Thus, photosynthesis along with respiration, helps to maintain the balance between O₂ and CO₂ in the environment.

4. Production of fuel: Due to natural disasters, like earthquake, plants get trapped under the soil and in due course of time get converted into coal and mineral oils. The energy obtained from these coal and mineral oils, is the solar energy which was entrapped by the plants in the past. This is how photosynthesis helps in the production of fuel.

5. Source of human welfare: We get different types of important materials from plants, like food, wood, paper, cloth, rubber, gum, paint etc. Apart from these, we get different alkaloids like morphine, quinine, reserpine etc. and various medicines from plants. Therefore, plants, more specifically photosynthesis, is very important for human welfare.

Question 6.
Write the role of chlorophyll in photosynthesis. How is photosynthesis related to the flow of energy in the environment?
Answer:
Role of chlorophyll in photosynthesis:
Chlorophyll gets excited by the absorption of photon particles of sunlight and dissociates the water absorbed by the root hairs into H⁺ and OH^– ions. Chlorophyll also converts the solar energy into the chemical energy which remains stored within ATP in the form of potential energy.

Relation of photosynthesis with energy flow in the environment The green plants trap solar energy and store it within ATP in form of chemical energy by photosynthesis. Later, this energy is converted to potential energy and remains stored within glucose, which is the end-product of photosynthesis.

On the other hand, a large part of potential energy, stored in glucose, is used up for performing various metabolic activities and is released as heat energy. The remaining potential energy enters the body of the primary consumers (herbivores), then secondary consumers carnivores. In this way, the energy reaches the ultimate consumers.

Decomposers, like various bacteria, fungi etc. act on the dead bodies of these consumers and the energy, thus, is recycled back into the environment through their decomposing activities. Thus, the solar energy returns to the environment after passing through producers and various consumers and decomposers. In this way, photosynthesis is related with energy flow in the environment.