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Photosynthesis in Higher Plants

Photosynthesis in Higher Plants

Action PlanNotesQuestionsMock-Test
Study Action Plan (Sorted by Difficulty)
Blackman’s Law and Limiting Factors Graphs
Accuracy: 0%
Total Attempted1
Total Correct0
Total Incorrect1
Difficulty Level:
High
Cyclic and Non-Cyclic Photophosphorylation
Accuracy: 0%
Total Attempted4
Total Correct0
Total Incorrect4
Difficulty Level:
High
Photosystems and Light Harvesting Complex
Accuracy: 0%
Total Attempted5
Total Correct0
Total Incorrect5
Difficulty Level:
High
Photorespiration
Accuracy: 17%
Total Attempted6
Total Correct1
Total Incorrect5
Difficulty Level:
High
C4 Pathway (Hatch-Slack Pathway)
Accuracy: 33%
Total Attempted3
Total Correct1
Total Incorrect2
Difficulty Level:
High
Photosynthesis in Higher Plants
Accuracy: 33%
Total Attempted12
Total Correct4
Total Incorrect8
Difficulty Level:
High
Calvin Cycle
Accuracy: 38%
Total Attempted16
Total Correct6
Total Incorrect10
Difficulty Level:
High
Chemiosmotic Hypothesis
Accuracy: 38%
Total Attempted8
Total Correct3
Total Incorrect5
Difficulty Level:
High
Early Experiments in Photosynthesis
Accuracy: 56%
Total Attempted9
Total Correct5
Total Incorrect4
Difficulty Level:
Medium
Light Reactions and Electron Transport
Accuracy: 60%
Total Attempted10
Total Correct6
Total Incorrect4
Difficulty Level:
Medium
Factors Affecting Photosynthesis
Accuracy: 62%
Total Attempted13
Total Correct8
Total Incorrect5
Difficulty Level:
Medium
Pigments in Photosynthesis
Accuracy: 67%
Total Attempted9
Total Correct6
Total Incorrect3
Difficulty Level:
Medium
C3 and C4 Plants Comparison
Accuracy: 71%
Total Attempted7
Total Correct5
Total Incorrect2
Difficulty Level:
Medium
Site of Photosynthesis and Chloroplast Organisation
Accuracy: 75%
Total Attempted4
Total Correct3
Total Incorrect1
Difficulty Level:
Low
Water Splitting and Oxygen Evolution
Accuracy: 80%
Total Attempted5
Total Correct4
Total Incorrect1
Difficulty Level:
Low

Learning Objectives

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Learning Objectives

  • Understand the process of photosynthesis in plants.
  • Identify the role of chlorophyll and other pigments in photosynthesis.
  • Explain the significance of light reactions and dark reactions in photosynthesis.
  • Describe the structure and function of chloroplasts in photosynthesis.
  • Compare and contrast C₃ and C₄ pathways in plants.
  • Analyze early experiments that contributed to the understanding of photosynthesis.
  • Discuss factors affecting the rate of photosynthesis.

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Revision Notes & Summary

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Chapter 11: Photosynthesis in Higher Plants

11.1 What do we Know?

  • All animals, including humans, depend on plants for food.
  • Green plants synthesize their own food through photosynthesis and are called autotrophs.

11.2 Early Experiments

  • Simple experiments have shown that chlorophyll, light, and CO₂ are required for photosynthesis.
  • Joseph Priestley discovered oxygen and demonstrated the role of air in plant growth.
  • Jan Ingenhousz showed that sunlight is essential for the process of photosynthesis.

11.3 Where does Photosynthesis take place?

  • Photosynthesis occurs in the green parts of plants, primarily in the leaves.
  • Mesophyll cells contain chloroplasts that align to optimize light absorption.

11.4 How many Pigments are involved in Photosynthesis?

  • Chlorophyll and accessory pigments (like chlorophyll b, xanthophylls, and carotenoids) absorb light and transfer energy to chlorophyll a.

11.5 What is Light Reaction?

  • Light reactions include:
    • Light absorption
    • Water splitting
    • Oxygen release
    • Formation of ATP and NADPH
  • Photosystems I and II play crucial roles in these reactions.

11.6 The Electron Transport

  • Electrons are excited in Photosystem II and transferred through an electron transport chain.
  • This process creates a proton gradient that drives ATP synthesis.

11.7 Where are the ATP and NADPH Used?

  • ATP and NADPH produced in light reactions are used in the biosynthetic phase to synthesize sugars.
  • The first product of CO₂ fixation in the Calvin cycle is 3-phosphoglyceric acid (PGA).

11.8 The C₄ Pathway

  • C₄ plants fix CO₂ into a 4-carbon compound in mesophyll cells before entering the Calvin cycle in bundle sheath cells.

11.9 Photorespiration

  • RuBisCO can catalyze a wasteful oxygenation reaction in C₃ plants, leading to photorespiration.

11.10 Factors affecting Photosynthesis

  • Factors include light intensity, CO₂ concentration, and temperature.

Important Comparisons

C₃ vs C₄ Plants

CharacteristicsC3 PlantsC4 Plants
Cell type for Calvin cycleMesophyllBundle sheath
Initial carboxylationMesophyllMesophyll
Primary CO2 acceptorRuBPPEP
CO2 fixation productPGAOAA
Temperature optimum20-25°C30-40°C

Important Diagrams

Diagram of Chloroplast Structure

  • Guard Cells: Flank the stoma, regulate gas exchange.
  • Thylakoid Membrane: Site of light reactions, contains photosystems.
  • Stroma: Site of the Calvin cycle, contains enzymes for sugar synthesis.
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Practice Test – MCQs, True/False

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Multiple Choice Questions

A.

To perform the light-dependent reactions of photosynthesis.

B.

To store excess water and nutrients.

C.

To carry out the Calvin cycle and minimize photorespiration.

D.

To transport CO2CO_2 from the roots to the leaves.
Correct Answer: C

Solution:

In C₄ plants, the bundle sheath cells are specialized for carrying out the Calvin cycle and minimizing photorespiration by maintaining a high concentration of CO2CO_2.

Chapter Concept:

Photorespiration

A.

By reducing photorespiration through concentrating CO2CO_2 in bundle sheath cells

B.

By increasing the surface area for light absorption

C.

By enhancing water uptake through deeper root systems

D.

By increasing chlorophyll concentration in mesophyll cells
Correct Answer: A

Solution:

In C₄ plants, the spatial separation of the initial CO2CO_2 fixation and the Calvin cycle reduces photorespiration by concentrating CO2CO_2 in the bundle sheath cells, where RuBisCO is located.

Chapter Concept:

C4 Pathway (Hatch-Slack Pathway)

A.

Cyclic photophosphorylation involves only Photosystem I and results in the production of ATP but not NADPH.

B.

Non-cyclic photophosphorylation involves both Photosystem I and II and results in the production of ATP, NADPH, and O2O_2.

C.

Cyclic photophosphorylation produces O2O_2 as a byproduct, while non-cyclic does not.

D.

Non-cyclic photophosphorylation occurs only in the absence of light, whereas cyclic occurs in the presence of light.
Correct Answer: A

Solution:

Cyclic photophosphorylation involves only Photosystem I and results in the production of ATP without the production of NADPH or O2O_2. Non-cyclic photophosphorylation involves both Photosystem I and II, producing ATP, NADPH, and O2O_2 as a byproduct.

Chapter Concept:

Cyclic and Non-Cyclic Photophosphorylation

A.

To perform the Calvin cycle using concentrated CO2CO_2

B.

To transport water and nutrients

C.

To store excess glucose

D.

To initiate the light-dependent reactions
Correct Answer: A

Solution:

In C₄ plants, bundle sheath cells are the site where the Calvin cycle occurs, utilizing CO2CO_2 concentrated by the C₄ pathway to efficiently produce sugars.

Chapter Concept:

C4 Pathway (Hatch-Slack Pathway)

A.

They are the primary electron donors in Photosystem II and Photosystem I, respectively.

B.

They are responsible for the synthesis of glucose in the Calvin cycle.

C.

They act as primary electron acceptors in the electron transport chain.

D.

They are involved in the cyclic photophosphorylation process.
Correct Answer: A

Solution:

P680 and P700 are the reaction center chlorophyll molecules in Photosystem II and Photosystem I, respectively, and are responsible for donating electrons to the electron transport chain.

Chapter Concept:

Photosystems and Light Harvesting Complex

A.

Chlorophyll a; accessory pigments extend the range of light absorption and protect chlorophyll a from photo-oxidation.

B.

Chlorophyll b; accessory pigments only protect chlorophyll b from photo-oxidation.

C.

Carotenoids; accessory pigments do not play any significant role.

D.

Xanthophylls; accessory pigments are the main light absorbers.
Correct Answer: A

Solution:

Chlorophyll a is the chief pigment associated with photosynthesis, absorbing light primarily in the blue and red regions. Accessory pigments like chlorophyll b, xanthophylls, and carotenoids help in extending the range of light absorption and also protect chlorophyll a from photo-oxidation.

Chapter Concept:

Pigments in Photosynthesis

A.

Increased synthesis of sugars.

B.

Release of CO2CO_2 and utilization of ATP.

C.

Increased production of ATP and NADPH.

D.

Enhanced photosynthetic efficiency.
Correct Answer: B

Solution:

When RuBisCO binds with O2O_2, it leads to photorespiration, which results in the release of CO2CO_2 and utilization of ATP without the synthesis of sugars.

Chapter Concept:

Photorespiration

A.

Light is the limiting factor

B.

Photosynthesis rate is decreasing

C.

Other factors become limiting

D.

Photosynthesis stops
Correct Answer: C

Solution:

The plateau region in the graph indicates that the rate of photosynthesis does not increase further with increasing light intensity because other factors, such as CO₂ concentration or temperature, become limiting.

Chapter Concept:

Blackman’s Law and Limiting Factors Graphs

A.

Ribulose bisphosphate (RuBP)

B.

Phosphoenolpyruvate (PEP)

C.

3-phosphoglycerate (PGA)

D.

Oxaloacetic acid (OAA)
Correct Answer: A

Solution:

The primary acceptor of CO2CO_2 in the Calvin cycle is Ribulose bisphosphate (RuBP), a 5-carbon compound.

Chapter Concept:

Photosynthesis in Higher Plants

A.

Photosystem I (PS I)

B.

Photosystem II (PS II)

C.

Both PS I and PS II

D.

Neither PS I nor PS II
Correct Answer: A

Solution:

Photosystem I (PS I) has a reaction center chlorophyll a with an absorption peak at 700 nm, known as P700.

Chapter Concept:

Light Reactions and Electron Transport

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Photosynthesis in Higher Plants

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True or False

Correct Answer: True

Solution:

The Calvin cycle is divided into three stages: carboxylation, where CO2CO_2 is fixed into an organic intermediate; reduction, where carbohydrates are formed using ATP and NADPH; and regeneration, where the CO2CO_2 acceptor molecule RuBP is regenerated. RuBisCO is the enzyme responsible for the carboxylation step, making it essential for the cycle.

Chapter Concept :

Calvin Cycle

Correct Answer: True

Solution:

The chemiosmotic hypothesis describes how ATP synthesis in chloroplasts is driven by a proton gradient across the thylakoid membrane, similar to the process in mitochondria.

Chapter Concept :

Chemiosmotic Hypothesis

Correct Answer: True

Solution:

In cyclic photophosphorylation, electrons are cycled back to Photosystem I, resulting in the production of ATP only, without the formation of NADPH.

Chapter Concept :

Cyclic and Non-Cyclic Photophosphorylation

Correct Answer: True

Solution:

Photosystem II (PS II) is characterized by its reaction center chlorophyll a, which absorbs light most efficiently at a wavelength of 680 nm, hence it is called P680.

Chapter Concept :

Photosystems and Light Harvesting Complex

Correct Answer: True

Solution:

Photosynthesis takes place in the green parts of plants, mainly the leaves, where chloroplasts are abundant in the mesophyll cells.

Chapter Concept :

Site of Photosynthesis and Chloroplast Organisation

Correct Answer: True

Solution:

The chemiosmotic hypothesis describes the mechanism of ATP synthesis in chloroplasts, which involves the creation of a proton gradient across the thylakoid membrane. This gradient is established by the movement of protons into the thylakoid lumen and is utilized by ATP synthase to generate ATP.

Chapter Concept :

Chemiosmotic Hypothesis

Correct Answer: False

Solution:

Photorespiration does not occur in C₄ plants because they have a mechanism that increases the concentration of CO2CO_2 at the enzyme site, ensuring that RuBisCO functions primarily as a carboxylase, minimizing oxygenase activity.

Chapter Concept :

Photorespiration

Correct Answer: False

Solution:

In C₄ plants, the Calvin cycle takes place in the bundle sheath cells, not in the mesophyll cells.

Chapter Concept :

Photosynthesis in Higher Plants

Correct Answer: True

Solution:

Photosynthesis is affected by several internal factors such as the number, size, age, and orientation of leaves, as well as external factors like the availability of sunlight, temperature, CO2CO_2 concentration, and water.

Chapter Concept :

Factors Affecting Photosynthesis

Correct Answer: True

Solution:

Priestley's experiments showed that plants could restore the air that had been 'damaged' by burning candles or breathing animals, indicating the role of plants in replenishing oxygen.

Chapter Concept :

Early Experiments in Photosynthesis

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