TN Board 11th Bio Botany Important Questions Chapter 13 Photosynthesis

Students get through the TN Board 11th Bio Botany Important Questions Chapter 13 Photosynthesis which is useful for their exam preparation.

TN State Board 11th Bio Botany Important Questions Chapter 13 Photosynthesis

Very short answer questions

Question 1.
Who was Stephen Hales?
Answer:
Stephen Hales is the father of plant physiology. He was the person to propound that plants obtain nourishment from air & light.

Question 2.
Give the overall equation of photosynthesis.
Answer:

Question 3.
What happens to water & carbon dioxide during photosynthesis?
Answer:
Water is oxidised to oxygen. CO₂ is reduced to carbohydrates.

Question 4.
Define anaerobic photosynthesis.
Answer:
In some bacteria, oxygen is not evolved and is called non-oxygenic and anaerobic photosynthesis. Examples: Green sulphur, Purple sulphur and green filamentous bacteria.

Question 5.
What is Bioluminescence?
Answer:
Bioluminescence is the production and emission of light by a living organism. Bioluminescence is rare in true plants.

Question 6.
What are Quantasomes?
Answer:
In chloroplast, Inner surface of lamellar membrane consists of a small spherical structure called as Quantasomes.

Question 7.
Define the term photosynthetic pigment.
Answer:
A photosynthetic pigment is a pigment that is present in chloroplasts or photosynthetic bacteria ‘ which captures the light energy necessary for photosynthesis.

Question 8.
Apart from chlorophyll, other pigments are called accessory pigments. Why?
Answer:
Chlorophyll ‘a’ is the primary pigment that acts as a reaction centre and all other pigments act as accessory pigments and trap solar energy and then transfer it to chlorophyll ‘a’.

Question 9.
What is a Phytol tail? Mention its role.
Answer:
a. Phytol tail is the lipophilic tail of chlorophyll molecule,
b. It helps in anchoring the chlorophyll to lamellae.

Question 10.
Mention the minerals used in the biosynthesis of Chlorophyll a.
Answer:
Mg, Fe, Cu, Zn, Mn, K and Nitrogen.

Question 11.
How chlorophyll b differs from chlorophyll a?
Answer:
Chlorophyll ‘b’ differs from Chlorophyll ‘a’ in having CHO (aldehyde) group instead of CH₃ (Methyl) group at the 3rd C atom in II Pyrrole ring.

Question 12.
Carotenoids are shield pigments – Comment.
Answer:
Carotenoids are yellow to orange pigments, mostly tetraterpens and these pigments absorb light strongly in the blue to the violet region of the visible spectrum. These pigments protect chlorophyll from photooxidative damage. Hence, they are called shield pigments.

Question 13.
Give an account of Xanthophylls.
Answer:
Yellow (C₄₀H₅₆O₂) pigments are like carotenes but contain oxygen. Lutein is responsible for the yellow colour change of leaves during the autumn season. Examples: Lutein, Violaxanthin and Fucoxanthin.

Question 14.
Name the two forms of phycobilins and also give an example.
Answer:
Phycobilins exist in two forms. They are:
a. Phycocyanin found in Cyanobacteria.
b. Phycoerythrin found in red algae.

Question 15.
Define Quantum.
Answer:
Light as a particle is called a photon. Each photon contains an amount of energy known as quantum.

Question 16.
How will you define Quantasomes?
Answer:
Quantasomes are the morphological expression of physiological photosynthetic units, located on the inner membrane of thylakoid lamellae.

Question 17.
Mention the events occurring in the photo-oxidation phase of light reaction.
Answer:
Photo-oxidation Phase:

• Absorption of light energy.
• Transfer of energy from accessory pigments to the reaction centre.
• Activation of Chlorophyll ‘a’ molecule.

Question 18.
Mention the events of the Photochemical phase of light reaction.
Answer:
Photo Chemical Phase:

• Photolysis of water and oxygen evolution
• Electron transport and synthesis of assimilatory power.

Question 19.
Define Photophosphorylation.
Answer:
Phosphorylation takes place with the help of light generated electron and hence it is known as
photophosphorylation.

Question 20.
Compare fluorescence with Phosphorescence.
Answer:

Fluorescence	Phosphorescence
Fluorescence is the immediate emission of absorbed radiation.	Phosphorescence is the delayed emission of absorbed radiation.

Question 21.
Draw the diagram representing the oxygen-evolving complex.
Answer:

Question 22.
Compare oxidative phosphorylation with substrate-level phosphorylation.
Answer:
Phosphorylation taking place during respiration is called oxidative phosphorylation and ATP produced by the breakdown of the substrate is known as substrate-level phosphorylation.

Question 23.
State Chemiosmotic theory.
Answer:
The chemiosmotic theory was proposed by P. Mitchell (1966). According to this theory, electrons are transported along the membrane through PS I and PS II and connected by the Cytochrome b6-f complex.

Question 24.
What are the assimilatory powers produced during the light reaction?
Answer:
ATP and NADPH + H⁺

Question 25.
Why PCR cycle is called as C₃ cycle?
Answer:
The first product of the PCR pathway is a 3- carbon compound (Phospho Glyceric Acid) and so it is also called as C₃ Cycle. It takes place in the stroma of the chloroplast.

Question 26.
Name the three stages of dark reaction.
Answer:

1. Carboxylation (fixation),
2. Reduction (Glycolytic Reversal) and
3. Regeneration.

Question 27.
Give an account on RUBISCO.
Answer:
RUBISCO – RUBP Carboxylase Oxygenase enzyme, is the most abundant protein found on earth. It constitutes 16 % of the chloroplast protein. It acts as carboxylase in the presence of CO₂ and oxygenase in the absence of CO₂.

Question 28.
C₄ plants are of ecological benefit – Comment.
Answer:
C₄ plants account for about 30% of terrestrial carbon fixation. Increasing the proportion of C₄ plants on earth could assist the biosequestration of CO₂ and represent an important climate change avoidance strategy.

Question 29.
Compare the features of dimorphic chloroplasts.
Answer:
The characteristic feature of C₄ plants is the presence of dimorphic chloroplast: Bundle sheath chloroplast: Larger chloroplast, thylakoids not arranged in granum and rich in starch. Mesophyll Chloroplast: Smaller chloroplast, thylakoids arranged in granum and less starch.

Question 30.
Define Photorespiration.
Answer:
Photorespiration is the excess respiration taking place in photosynthetic cells due to the absence of CO₂ and an increase of O₂.

Question 31.
What is CO₂ compensation plant?
Answer:
When the rate of photosynthesis equals the rate of respiration, there is no exchange of oxygen and carbon dioxide and this is called a carbon dioxide compensation point.

Question 32.
State Blackman’s law of limiting factor.
Answer:
“At any given point of time, the lowest factor among essentials will limit the rate of photosynthesis”.

Question 33.
List out the external and internal factors that affect photosynthesis.
Answer:

• External factors: Light, carbon dioxide, temperature, water, mineral and pollutants.
• Internal factors: Pigments, protoplasmic factor, accumulation of carbohydrates, anatomy of leaf and hormones.

Question 34.
Enumerate the anatomical features of the leaf that affects photosynthesis.
Answer:
The thickness of cuticle and epidermis, distribution of stomata, presence or absence of Kranz anatomy and relative proportion of photosynthetic cells affect photosynthesis.

Question 35.
Name the photosynthetic apparatus of bacteria.
Answer:
Bacteria have a special type of photosynthetic apparatus called chlorosomes and chromatophores.

Short answer questions

Question 1.
Give an account of the biosynthesis of chlorophyll.
Answer:
Chlorophyll is synthesized from intermediates of respiration and photosynthesis. Succinic acid an intermediate of the Krebs cycle is activated by the addition of coenzyme A and it reacts with a simple amino acid glycine and the reaction goes on to produce chlorophyll ‘a’.
Biosynthesis of chlorophyll ‘a’ requires Mg, Fe, Cu, Zn, Mn, K and nitrogen. The absence of any one of these minerals leads to chlorosis.

Question 2.
List out the types of radiations in the Electromagnetic spectrum.
Answer:
The electromagnetic spectrum consists of 8 types of radiations such as cosmic rays, gamma rays, X rays, U-V rays, Visible light spectrum, infrared rays, electric rays and radio rays.

Question 3.
Write a brief note on Emerson’s Red Drop.
Answer:
Emerson conducted an experiment in Chlorella using only one wavelength of light (monochromatic light) at a time and he measured quantum yield. He plotted a graph of the quantum yield in terms of O, evolution at various wavelengths of light. His focus was to determine at which wavelength the photochemical yield of oxygen was maximum. He found – that in the wavelength of 600 to 680 the yield was constant but suddenly dropped in the region above 680 nm (red region). The fall in the photosynthetic yield beyond the red region of the spectrum is referred to as Red drop or Emerson’s first effect.

Question 4.
Explain the term Emerson’s Enhancement Effect.
Answer:
Emerson found that the monochromatic light of longer wavelength (far red light), when supplemented with a shorter wavelength of light (red light), enhanced photosynthetic yield and recovered red drop. This enhancement of photosynthetic yield is referred to as Emerson’s Enhancement Effect.

Question 5.
Give the conclusions of Hills Reaction.
Answer:
Conclusions of Hill’s Reaction:

1. During photosynthesis, oxygen is evolved from water.
2. Electrons for the reduction of CO₂ are obtained from water.
3. A reduced substance produced, later helps to reduce CO₂.
   2H₂O + 2A → 2 AH₂ + O₂

Question 6.
Define Dark Reaction.
Answer:
Fixation and reduction of CO₂ into carbohydrates with the help of assimilatory power produced during light reaction. This reaction does not require light and is not directly light-driven. Hence, it is called as Dark reaction or Calvin-Benson cycle.

Question 7.
Illustrate S’ state mechanism.
Answer:
S’ State Mechanism consists of a series of 5 states called as S₀, S₁, S₂, S₃ and S₄. Each state acquires a positive charge by a photon (hv) and after the S₄ state, it acquires 4 positive charges, four electrons and the evolution of oxygen. Two molecules of water go back to the S₀. At the end of photolysis 4H⁺, 4e^– and O₂ are evolved from water.

Question 8.
Kranz Anatomy – Define.
Answer:
Kranz Anatomy is a German term meaning a halo or wreath. In C₄ plants vascular bundles are surrounded by a layer of bundle sheath. The bundle sheath is surrounded by a ring of mesophyll cells.

Question 9.
Point out the significances of C₄ cycle.
Answer:
Significance of C₄ cycle

1. Plants having C₄ cycle are mainly of tropical and sub-tropical regions and are able to survive in an environment with low CO₂ concentration.
2. C₄ plants are partially adapted to drought conditions.
3. Oxygen has no inhibitory effect on C₄ cycle since PEP carboxylase is insensitive to O₂.
4. Due to the absence of photorespiration, CO₂ Compensation Point for C₄ is lower than that of C₃ plants.

Question 10.
Point out the significances of photorespiration.
Answer:
Significance of photorespiration

1. Glycine and Serine synthesised during this process are precursors of many biomolecules like chlorophyll, proteins, nucleotides.
2. It consumes excess NADH + H⁺ generated.
3. Glycolate protects cells from Photooxidation.

Question 11.
Mention the role of light intensity in photosynthesis.
Answer:
The intensity of light plays a direct role in the rate of photosynthesis. Under low intensity the photosynthetic rate is low and at higher intensity photosynthetic rate is higher. It also depends on the nature of plants. Heliophytes (Bean Plant) require higher intensity than Sciophytes (Oxalis).

Question 12.
Classify photosynthetic bacteria and give example.
Answer:
Photosynthetic bacteria are classified into three groups:

1. Green sulphur bacteria. Example: Chlorobacterium and Chlorobium.
2. Purple sulphur bacteria. Example: Thiospirillum and Chromatium.
3. Purple non-sulphur bacteria. Example: Rhodopseudomonas and Rhodospirillum.

Long answer questions

Question 1.
Mention the significance of photosynthesis.
Answer:
Significance of Photosynthesis:

1. Photosynthetic organisms provide food for all living organisms on earth either directly or indirectly.
2. It is the only natural process that liberates oxygen in the atmosphere and balances the oxygen level.
3. Photosynthesis balances the oxygen and carbon cycle in nature.
4. Fuels such as coal, petroleum and other fossil fuels are from preserved photosynthetic plants.
5. Photosynthetic organisms are the primary producers on which all consumers depend for energy.
6. Plants provide fodder, fibre, firewood, timber, useful medicinal products and these sources come by the act of photosynthesis.

Question 2.
Describe the structure of chloroplasts.
Answer:
Chloroplasts are the main site of photosynthesis and both the energy-yielding process (Light reaction) and fixation of carbon dioxide (Dark reaction) that takes place in the chloroplast. It is a double-wall membrane-bounded organelle, discoid or lens-shaped, 4 -10 pm in diameter and 1-33 pm in thickness. The membrane is a unit membrane and the space between them is 100 to 200 A. A colloidal and proteinaceous matrix called stroma is present inside.
A sac-like membranous system called thylakoid or lamellae is present in the stroma and they are arranged one above the other forming a stack of a coin-like structure called granum (plural grana). Each chloroplast contains 40 to 80 grana and each granum consists of 5 to 30 thylakoids. Thylakoids found in granum are called grana lamellae and in the stroma are called stroma lamellae. Thylakoid disc size is 0.25 to 0.8 micron in diameter. A thinner lamella called the Fret membrane connects grana. Pigment system I is located on the outer thylakoid membrane facing stroma and Pigment system II is located on the inner membrane facing the lumen of the thylakoid. Grana lamellae have both PS I and PS II whereas stroma lamellae have only PS I. Chloroplast contains 30-35% Proteins, 20-30% phospholipids, 5-10% chlorophyll, 4-5% Carotenoids, 70S ribosomes, circular DNA and starch grains. The inner surface of the lamellar membrane consists of a small spherical structure called as Quantasomes. The presence of 70S ribosome and DNA gives them the status of semi-autonomy and proves the endosymbiotic hypothesis which says chloroplast evolved from bacteria. Thylakoid contains pigment systems that produce ATP and NADPH + H⁺ using solar energy. The stroma contains an enzyme which reduces carbon dioxide into carbohydrates.

Question 3.
Tabulate the different types of photosynthetic pigments.
Answer:

Question 4.
Give an account of Chlorophyll.
Answer:
Chlorophyll ‘ a’ is the primary pigment that acts as a reaction centre and all other pigments act as accessory pigments and trap solar energy and then transfer it to chlorophyll ‘a’. Chlorophyll molecules have a tadpole-like structure. It consists of the Mg-Porphyrin head (Hydrophilic Head) and (Lipophilic tail) Phytol tail. The Porphyrin head consists of four pyrrole rings linked together by C-H bridges. Each pyrrole ring comprises four carbons and one nitrogen atom. Porphyrin ring has several side groups which alter the properties of the pigment. Different side groups are indicative of various types of chlorophyll. The Phytol tail made up of 20 carbon alcohol is attached to carbon 7 of the Pyrrole ring IV. It has a long propionic acid ester bond. A long lipophilic tail helps in anchoring chlorophyll to the lamellae.

Question 5.
Explain the steps involved in paper chromatography.
Answer:
Separation of Chloroplast pigments by paper Chromatography method:
Step 1. Extract chlorophyll pigment from the leaves using 80% Acetone.
Step 2. Allow concentrating by evaporation.
Step 3. Apply few drops on one end above 2 cm from the edge of a chromatographic paper.
Step 4. A solvent with a mixture of Petroleum ether and acetone in the ratio of 9:1 is prepared and poured into the development chamber.
Step 5. Place the strip above the solvent by placing one end of the strip touching the solvent. Observation: After one hour of observing the chromatographic paper. You can find the pigments being separated into four distinct spots.

Question 6.
Enumerate the properties of light.
Answer:
Properties of Light

1. Light is a transverse electromagnetic wave.
2. It consists of oscillating electric and magnetic fields that are perpendicular to each other and perpendicular to the direction of propagation of the light.
3. Light moves at a speed of 3 x 108 ms^-1.
4. Wavelength is the distance between successive crests of the wave.
5. Light as a particle is called a photon. Each photon contains an amount of energy known as quantum.
6. The energy of a photon depends on the frequency of the light.

Question 7.
Differentiate between Photosystem I and Photosystem II.
Answer:

Photosystem I	Photosystem II
The reaction centre is P700.	The reaction centre is P680.
PS I is involved in both cyclic and non-cyclic.	PS II participates in the Non-cyclic pathway.
Not involved in the photolysis of water and evolution of oxygen.	Photolysis of water and the evolution of oxygen takes place.
It receives electrons from PS II during non-cyclic photophosphorylation.	It receives electrons by the photolysis of water.
Located in unstacked region granum facing chloroplast stroma.	Located in the stacked region of the thylakoid membrane facing the lumen of the thylakoid.
The chlorophyll and Carotenoid ratio is 20 to 30:1.	The chlorophyll and Carotenoid ratio is 3 to 7:1.

Question 8.
Explain the various complexes in the Electron transport chain.
Answer:
The electron transport chain in each photosystem involves four complexes:

• Core Complex (CC): CC I in PS I the reaction centre is P700, CC II in PS II the reaction centre is P680
• Light-Harvesting Complex or Antenna complex (LHC):
• Two types: LHC I in PS I and LHC II in PS II.
• Cytochrome b₆ f complex: It is the non-pigmented protein complex connecting PS I and PS II. Plastoquinone (PQ) and Plastocyanin (PC) are intermediate complexes acting as mobile or shuttle electron carriers of the Electron Transport Chain. PQ acts as a shuttle between PS II and Cytochrome b₆– f complex and PC connects
• Cytochrome b₆-f and PS I complex.
• AT Pave complex or Coupling factor: It is found on the surface of the thylakoid membrane. This complex is made up of CF₁ and CF₀ factors. This complex utilizes energy from ETC and converts ADP and inorganic phosphate (Pi) into ATP.

Question 9.
Explain cyclic photophosphorylation.
Answer:
Cyclic photophosphorylation refers to the electrons ejected from the pigment system I (Photosystem I) and again cycled back to the PS I. When the photons activate P700 reaction centre photosystem II is activated. Electrons are raised to a high energy level. The primary electron acceptor is Ferredoxin Reducing Substance (FRS) which transfers electrons to Ferredoxin (Fd), Plastoquinone (PQ), cytochrome b₆-f complex, Plastocyanin (PC) and finally back to chlorophyll P700 (PS I). During this movement of electrons, Adenosine Di Phosphate (ADP) is phosphorylated, by the addition of inorganic phosphate and generates Adenosine Tri Phosphate (ATP). Cyclic electron transport produces only ATP and there is no NADPFI + H⁺ formation. At each step of electron, transport, the electron loses potential energy and is used by the transport chain to pump H⁺ ions across the thylakoid membrane. The proton gradient triggers ATP formation in the ATP synthase enzyme situated on the thylakoid membrane. Photosystem I need the light of a longer wavelength (> P700 nm). It operates under low light intensity, less CO₂ and under anaerobic conditions which makes it considered as earlier in evolution.

Question 10.
Explain the stages occurring during non-cyclic electron transport.
Answer:
In oxygenic species, non-cyclic electron transport takes place in three stages.

1. Electron transport from water to P680: Splitting of water molecule produce electrons, protons and oxygen. Electrons lost by the PS II (P680) are replaced by electrons from the splitting of a water molecule.
2. Electron transport from P680 to P700: Electron flow starts from P680 through a series of electron carrier molecules like pheophytin, plastoquinone (PQ), cytochrome b6 – f complex, plastocyanin (PC) and finally reaches P700 (PS I).
3. Electron transport from P700 to NADP⁺: PS I(P700) is excited now and the electrons pass to a high energy level. When electron travels downhill through ferredoxin, NADP+ is reduced to NADPH + H⁺.

Question 11.
Point out the Bio-energetics of light reaction.
Answer:
Bio energetics of light reaction:

• To release one electron from the pigment system requires two quanta of light.
• One quantum is used for the transport of electron from water to PS I.
• The second quantum is used for the transport of electron from PS I to NADP
• Two electrons are required to generate one NADPH + H⁺.
• During Non-Cyclic electron transport two NADPH + H⁺ are produced and it requires 4 electrons.
• Transportation of 4 electrons requires 8 quanta of light.

Question 12.
Differentiate between Cyclic & Non-cyclic photophosphorylation.
Answer:
Differences between Cyclic Photophosphorylation and Non-Cyclic Photophosphorylation

Cyclic Photophosphorylation	Non-Cyclic Photophosphorylation
PS I only involved.	PS I and PS II involved.
The reaction centre is P700.	The reaction centre is P680.
Electrons released are cycled back.	Electron released are not cycled back.
Photolysis of water does not take place.	Photolysis of water takes place.
Only ATP synthesized.	ATP and NADPH + H+ are synthesized.
Phosphorylation takes place at two places.	Phosphorylation takes place at only one place.
It does not require an external electron donor.	Requires external electron donor like H20 or H2S.
It is not sensitive to dichloro dimethyl urea (DCMI).	It is sensitive to DCMI and inhibits electron flow.

Question 13.
Draw a Flow chart depicting Calvins cycle.
Answer:

Question 14.
Explain the three phases of the Dark reaction.
Answer:
Phase 1- Carboxylation (Fixation)
The acceptor molecule Ribulose 1,5 Bisphosphate (RUBP) a 5 carbon compound with the help of RUBP carboxylase oxygenase (RUBISCO) enzyme accepts one molecule of carbon dioxide to form an unstable 6 carbon compound. This 6C compound is broken down into two molecules of 3-carbon compound phospho glyceric acid (PGA).

Phospho glyceric acid is phosphorylated by ATP and produces 1,3 bis phospho glyceric acid by PGA kinase. 1,3 bis phospho glyceric acid is reduced to glyceraldehyde 3 Phosphate (G-3-P) by using the reducing power NADPH + H⁺. Glyceraldehyde 3 phosphate is converted into its isomeric form dihydroxy acetone phosphate (DHAP).

Phase 3 – Regeneration: Regeneration of RUBP involves the formation of several intermediate compounds of 6-carbon, 5-carbon, 4-carbon and 7- carbon skeleton. Fixation of one carbon dioxide requires 3 ATPs and 2 NADPH + H⁺, and the fixation of 6 CO₂ requires 18 ATPs and 12 NADPH + H⁺ during C₃ cycle. One 6 carbon compound is the net gain to form hexose sugar.

Question 15.
Explain the phases of C₄ pathway.
Answer:
C₄ pathway is completed in two phases, first phase takes place in the stroma of mesophyll cells, where the CO₂ acceptor molecule is a 3-Carbon compound, phosphoenol pyruvate (PEP) to form 4-carbon Oxalo acetic acid (OAA). The first product is a 4-carbon and so it is named as C₄ cycle. Oxalo acetic acid is a dicarboxylic acid and hence this cycle is also known as a dicarboxylic acid pathway. Carbon dioxide fixation takes place in two places one in mesophyll and another in bundle sheath cell (dicarboxylation pathway). It is the adaptation of tropical and subtropical plants growing in warm and dry conditions. Fixation of C02 with minimal loss is due to the absence of photorespiration. C₄ plants require 5 ATP and 2 NADPH + H⁺ to fix one molecule of CO₂.

Oxaloacetic acid (OAA) is converted into malic acid or aspartic acid and is transported to the bundle sheath cells through plasmodesmata.
Stage: II Bundle Sheath Cells: Malic acid undergoes decarboxylation and produces a 3 carbon compound Pyruvic acid and CO₂. The released CO₂ combines with RUBP and follows the Calvin cycle and finally, sugar is released to the phloem. Pyruvic acid is transported to the mesophyll cells.

Question 16.
Differentiate between C₃ & C₄ plants.
Answer:
Differences between C₃ and C₄ plants

C3 Plants	C4 Plants
CO2, fixation takes place in mesophyll cells only.	CO2 fixation takes place mesophyll and bundle sheath.
CO2 acceptor is RUBP only.	PEP in mesophyll and RUBP in bundle sheath cells.
The first product is 3C- PGA.	The first product is 4C- OAA.
Kranz anatomy is not present.	Kranz anatomy is present.
Granum is present in mesophyll cells.	Granum is present in mesophyll cells and absent in bundle sheath.
Normal Chloroplast.	Dimorphic chloroplast.
Optimum temperature 20° to 25°C.	Optimum temperature 30° to 45°C.
Fixation of CO2 at 50 ppm.	Fixation of CO2 even less than 10 ppm.
Less efficient due to higher photorespiration.	More efficient due to less photorespiration.
RUBP carboxylase enzyme used for fixation.	PEP carboxylase and RUBP carboxylase used.
18 ATPs used to synthesize one glucose.	Consumes 30 ATPs to produce one glucose.
Efficient at low CO2	Efficient at higher CO2
Example: Paddy, Wheat, Potato and so on.	Example: Sugar cane, Maize, Sorghum, Amaranthus and so on.

Question 17.
Explain in detail about Crassulacean Acid Metabolism.
Answer:
Crassulacean Acid Metabolism or CAM cycle:
It is one of the carbon pathways identified in succulent plants growing in semi-arid or xerophytic condition. This was first observed in Crassulaceae family plants like Bryophyllum, Sedum, Kalanchoe and is the reason behind the name of this cycle. It is also noticed in plants from other families. Examples: Agave, Opuntia, Pineapple and Orchids. The stomata are closed during the day and are open during the night (Scotoactive). This reverse stomatal rhythm helps to conserve water loss through transpiration and will stop the fixation of CO₂ during the daytime. At night time CAM plants fix CO₂ with the help of Phospho Enol Pyruvic acid (PEP) and produce oxalo acetic acid (OAA). Subsequently, OAA is converted into malic acid like C₄ cycle and gets accumulated in vacuole increasing the acidity. During the daytime stomata are closed and malic acid is decarboxylated into pyruvic acid resulting in the decrease of acidity. CO₂ thus formed enters into Calvin Cycle and produces carbohydrates.
Significance of CAM Cycle

1. It is advantageous for succulent plants to obtain CO₂ from malic acid when stomata are, closed.
2. During the daytime, stomata are closed and CO₂ is not taken but continue their photosynthesis.
3. Stomata are closed during the daytime and help the plants to avoid transpiration and water loss.

Question 18.
State the differences between photorespiration and dark respiration.
Answer:
Differences between Photorespiration and Dark Respiration

Photorespiration	Dark respiration
It takes place in photosynthetic green cells.	It takes place in all living cells.
It takes place only in the presence of light.	It takes place all the time.
It involves chloroplast, peroxisome and mitochondria.	It involves only mitochondria.
It does not involve Glycolysis, Kreb’s Cycle, and ETS.	It involves glycolysis, Kreb’s Cycle and ETS.
The substrate is glycolic acid.	The substrate is carbohydrates, protein or fats.
It is not essential for survival.	Essential for survival.
No phosphorylation and yield of ATP.	Phosphorylation produces ATP energy.
NADH2 is oxidised to NAD+.	NAD+ is reduced to NADH.
Hydrogen peroxide is produced.	Hydrogen peroxide is not produced.
End products are CO2 and PGA.	End products are CO2 and water.

Question 19.
Explain the Internal factors that affect photosynthesis.
Answer:
Internal Factors

1. Photosynthetic Pigments: It is an essential factor and even a small quantity is enough to carry out photosynthesis.
2. Protoplasmic factor: Hydrated protoplasm is essential for photosynthesis. It also includes enzymes responsible for Photosynthesis.
3. Accumulation of Carbohydrates: Photosynthetic end products like carbohydrates are accumulated in cells and if translocation of carbohydrates is slow then this will affect the rate, of photosynthesis.
4. Anatomy of leaf: Thickness of cuticle and epidermis, distribution of stomata, presence or absence of Kranz anatomy and relative proportion of photosynthetic cells affect photosynthesis.
5. Hormones: Hormones like gibberellins and cytokinin increase the rate of photosynthesis.

Question 20.
Compare photosynthesis in plants & bacteria.
Answer:
Differences between Photosynthesis in Plants and Photosynthesis in Bacteria

Photosynthesis in Plants	Photosynthesis in Bacteria
Cyclic and non-cyclic phosphorylation takes place.	Only cyclic phosphorylation takes place.
Photosystem I and II involved.	Photosystem I only involved.
The electron donor is water.	The electron donor is H2S.
Oxygen is evolved.	Oxygen is not evolved.
Reaction centres are P700 and P680.	The reaction centre is P870.
The reducing agent is NADPH + H+.	The reducing agent is NADPH + H+.
PAR is 400 to 700 nm.	PAR is above 700 nm.
Chlorophyll, carotenoid and xanthophyll.	Bacterio chlorophyll and bacterio viridin.
Photosynthetic apparatus – chloroplast.	It is chlorosomes and chromatophores.

Higher Order Thinking Skills (HOTs)

Question 1.
The picture given below is an organelle of a plant cell. Identify the picture and answer the questions.

(a) Name the organelle.
(b) Mention the role of the organelle in the cell.
(c) How do you call the stack of coin-like structures present on it?
(d) Whether it shows semi-autonomy? If yes how? If no, why?
Answer:
(a) Chloroplast.
(b) Chloroplast is the site of photosynthesis.
(c) Grana made of thylakoids.
(d) Yes, the presence of DNA, 70S ribosomes gives them the status of semi-autonomy.

Question 2.
Succulents are known to keep their stomata closed during the day to check transpiration.
How do they meet their photosynthetic CO₂ requirements?
Answer:
Succulents undergo a special carbon pathway called Crassulacean Acid Metabolism (CAM pathway). At night time, CAM plants for CCE with the help of Phosphoenol Pyruvic Acid (PEP) and produce Oxalo Acetic Acid (OAA). Subsequently, OAA is converted into malic acid like C₄ cycle and produces CO₂. The CO₂ thus formed enters the Calvins cycle and produces carbohydrates.

Question 3.
An increase in temperature decreases photosynthetic rale – Justify.
Answer:
In general, the optimum temperature for photosynthesis is 25°C to 35°C. An increase in temperature will lead to the closure of stomata thereby inhibiting the gaseous exchange and also inactivate the enzymes responsible for photosynthesis.

Question 4.
“Photosynthesis is a redox reaction”. Comment.
Answer:
Photosynthesis is an oxidation and reduction process where, water is oxidised to release oxygen and CO₂ is reduced to form carbohydrates.

Question 5.
Carrots, Capsicum, Tomatoes etc are organe/red coloured fruits.
(a) Name the pigment responsible for the colour.
(b) State whether it is a photosynthetic pigment.
(c) Mention its role in plants.
Answer:
(a) Carotenoids are the yellow to orange pigments responsible for fruit colours.
(b) Yes, it is a photosynthetic pigment.
(c) They absorb the light energy and transfer it to the chlorophyll. They also protect chloro¬phyll from photo-oxidative damage. Hence also called shield pigments.

Question 6.
Paddy is a C₃ plant. C₃ plants utilise ATP and NADPH₂ molecules to generate oxygen molecules. How many ATP and NADPH₂ molecules would a C₃ plant consume to generate 12 molecules of oxygen.
Answer:
C₃ plants utilise 3 ATP’s and 2 NADPH₂ molecules to evolve one oxygen molecule. To generate 12 molecules of oxygen, 36 ATP’s and 24 NADPH₂ molecules are utilised.

Question 7.
Give the meaning for the following terminologies:
(a) Decarboxylation (b) Phosphorylation (c) Photolysis
Answer:
(a) Decarboxylation : Removal of C02 from a molecule.
(b) Phosphorylation: Synthesis of ATP by the addition of inorganic phosphate to ADP.
(c) Photolysis: Splitting of water molecules using light energy.

Question 8.

The above equation represents the first step of a cyclic pathway occurring in plant cells.
(а) Name the pathway.
(б) Where does this pathway occur inside the cell?
(c) How many carbon molecules are seen in RUBP & PGA.
(d) State the role of RUBISCO in this step.
(e) Under which condition does this pathway proceed.
Answer:
(a) Photorespiration or C₂ cycle.
(b) C₂ cycle takes place in chloroplast, peroxisome and mitochondrion.
(c) RUBP is a 5C compound and PGA is a 3C compound
(d) RUBISCO plays the role of oxygenase enzyme.
(e) C₂ cycle occurs in photosynthetic cells due to the absence of CO₂ and increased O₂.

Choose the correct answer.

1. Photosynthetic organisms used only percent of solar light.
(a) 0.2
(b) 0.6
(c) 0.1
(d) 0.8
Answer:
(a) 0.2

2. ………… is famously called as father of plant physiology.
(a) Joseph Priestley
(b) Lavoisier
(c) Stephen Hales
(d) Van Helmont
Answer:
(c) Stephen Hales

3. In Green sulphur bacteria, is the hydrogen donor.
(a) H₂O
(b) H₂S
(c) H₂O₂
(d) HCl
Answer:
(b) H₂S

4. Ruben & Kamen used radioactive oxygen to prove the evolution of oxygen from water.
(a) 180
(b) 160
(c) 140
(d) 120
Answer:
(a) 180

5. In photosynthesis ………….. is reduced into carbohydrates.
(a) H₂O
(b) Chlorophyll
(c) CO₂
(d) O₂
Answer:
(c) CO₂

6. Which of the following performs anaerobic photosynthesis?
(a) Green sulphur bacteria
(b) Cyanobacteria
(c) Purple sulphur bacteria
(d) Green filamentous bacteria
Answer:
(b) Cyanobacteria

7. The colloidal proteinaceous matrix of chloroplast is
(a) Thylakoid
(b) Stroma
(c) Grana
(d) Lamellae
Answer:
(b) Stroma

8. Each granum has thylakoids.
(a) 8-30
(b) 40 – 80
(c) 5-30
(d) 40 – 70
Answer:
(c) 5-30

9. Which of the following is a primary pigment?
(a) Chlorophyll a
(b) Carotene
(c) Xanthophyll
(d) Phycoerythrin
Answer:
(a) Chlorophyll a

10. The chlorophyll pigment found in xanthophycean algae is
(a) Chlorophyll b
(b) Chlorophyll c
(c) Chlorophyll d
(d) Chlorophyll e
Answer:
(d) Chlorophyll e

11. The nature of phytol tail in chlorophyll is
(a) Hydrophilic
(b) Lipophilic
(c) Hydrophobic
(d) Lipophobic
Answer:
(b) Lipophilic

12. The porphyrin head of chlorophyll has ………. pyrrole rings.
(a) 1
(b) 2
(c) 3
(d) 4
Answer:
(d) 4

13. Which of the following mineral is NOT required for the biosynthesis of chlorophyll a?
(a) Mn
(b) Mg
(c) Mo
(d) Cu
Answer:
(c) Mo

14. In chlorophyll C, which of the following component is absent?
(a) Porphyrin head
(b) Phytol tail
(c) Pyrrole ring
(d) Methyl group
Answer:
(b) Phytol tail

15. …………. pigments are also called as shield pigments.
(a) Carotenoids
(b) Chlorophyll b
(c) Phycobilins
(d) Phycoerythrin
Answer:
(a) Carotenoids

16. ………….. is responsible for the yellow colour change of leaves during autumn.
(a) Cutin
(b) Lutein
(c) Phycobilin
(d) Carotein
Answer:
(b) Lutein

17. The colour of the light is determined by its …………..
(a) Intensity
(b) Refractive power
(c) Wavelength
(d) Reflection
Answer:
(c) Wavelength

18. Visible spectrum ranges between ………….
(a) 390 – 763 nm
(b) 370 – 700 nm
(c) 450 – 700 nm
(d) 357 – 736 nm
Answer:
(a) 390 – 763 nm

19. Electromagnetic spectrum consists of …………. types of radiation.
(a) 2
(b) 4
(c) 6
(d) 8
Answer:
(d) 8

20. Light as a particle is called …………
(a) Neutron
(b) Quantum
(c) Photon
(d) Quantasome
Answer:
(c) Photon

21. Usually …………… chlorophyll molecules are considered as physiological units of photosynthesis.
(a) 300 – 700
(b) 200-300
(c) 240-750
(d) 200-280
Answer:
(b) 200-300

22. Who coined the term Quantasomes?
(a) Steinmann
(b) Park & Biggins
(c) Emerson & Arnold
(d) Von Mayer
Answer:
(b) Park & Biggins

23. In Emerson’s first effect, the photosynthetic yield was dropped in the region above ………..
(a) 720 nm
(b) 620 nm
(c) 680 nm
(d) 600 nm
Answer:
(c) 680 nm

24. In photosynthetic reactions ………… is considered as assimilatory power.
(a) NADPH
(b) FADPH
(c) ATP
(d) GTP
Answer:
(c) ATP

25. Antenna molecules refers to …………
(a) Light-harvesting complex
(b) Central core complex
(c) PS II
(d) Oxygen evolving complex
Answer:
(a) Light-harvesting complex

26: Chlorophyll and carotenoid ratio in PS II is …………
(a) 3 to 7:1
(b) 20 to 30:1
(c) 7 to 30:1
(d) 10 to 30:1
Answer:
(a) 3 to 7:1

27. Phosphorylation taking place during respiration is called …………
(a) Substrate level phosphorylation
(b) Oxidative phosphorylation
(c) Reductive phosphorylation
(d) Photophosphorylation
Answer:
(b) Oxidative phosphorylation

28. Which of the following statement is NOT true regarding cyclic photophosphorylation?
(a) The primary electron acceptor is FRS
(b) It produces only ATP molecules
(c) It produces only NADPH + H⁺ molecules.
(d) Electrons ejected from PSI again cycled back to PSI
Answer:
(c) It produces only NADPH + H⁺ molecules

29. Chemiosmotic theory was proposed by …………
(a) Mitchell
(b) Hatch & Slack
(c) Calvin
(d) Priestley
Answer:
(a) Mitchell

30. How many ATP molecules are utilized by C₃ plants to evolve one oxygen molecule.
(a) 3
(b) 4
(c) 8
(d) 12
Answer:
(a) 3

31. The first formed product of C₃ cycle is …………
(a) Succinic acid
(b) Phosphoglyceric acid
(c) Oxalo Acetic acid
(d) Malic acid
Answer:
(6) Phosphoglyceric acid

32. RUBP is a ……….. carbon compound.
(a) Three
(b) Four
(c) Five
(d) Seven
Answer:
(c) Five

33. Number of dicot species performing C₄ pathway is …………
(a) 200
(b) 300
(c) 800
(d) 1000
Answer:
(b) 300

34. The CO₂ acceptor molecule in C₃ plants is …………
(a) PEP
(b) PGA
(c) OAA
(d) RUBP
Answer:
(d) RUBP

35. C₂ cycle refers to
(a) CAM cycle
(b) PCO cycle
(c) PCR cycle
(d) DCA cycle
Answer:
(b) PCO cycle

36. Identify the mismatched pair:
(i) Phosphorylation reaction – phosphorous
(ii) Photolysis of water – Manganese & Chlorine
(iii) Plastocyanin formation – Copper and Zinc
(iv) Chlorophyll formation – Magnesium, Iron, Nitrogen
(a) (i) only
(b) (iii) only
(c) Both (i) & (iii)
(d) All the above
Answer:
(b) (iii) only

37. Photosynthetically Active Radiation (PAR) is between
(a) 700 – 760 nm
(b) 400-700 nm
(c) 500-600 nm
(d) 350 – 760 nm
Answer:
(b) 400 – 700 nm

38. In atmosphere the percentage of CO₂ is …………
(a) 0.3%
(b) 0.7%
(c) 0.1%
(d) 0.6%
Answer:
(a) 0.3%

39. The inhibitory effect of oxygen in photosynthesis was first discovered by ……………..
(a) Warburg
(b) Van Helmont
(c) Dutrochet
(d) Desaussure
Answer:
(a) Warburg

40. In general, the optimum temperature for photosynthesis is …………
(a) 26°C to 39°C
(b) 25°C to 40°C
(c) 55°C
(d) 25°C to 35°C
Answer:
(d) 25°C to 35°C