Photosynthesis in Higher Plants - Class 11 Biology - Chapter 11 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Photosynthesis in Higher Plants | NCERT | Biology | Class 11
Middle lamella is composed mainly of:
A) Phosphoglycerides
B) Hemicellulose
C) Muramic acid
D) Calcium pectate
The correct answer is Option D: Calcium pectate.
The middle lamella serves as the glue-like cementing layer between adjacent plant cells. It is primarily composed of calcium and magnesium pectates, which help in holding the plant cells together effectively.
Plastids that are white in color (pigment-free) are known as:
A. chromoplast
B. lysosome
C. leucoplast
D. chloroplast
The correct option is C. leucoplast.
Leucoplasts are white or colorless plastids that lack pigments and are typically located in non-photosynthetic tissues of plants. They are specialized for the bulk storage of substances like proteins, lipids, or starch. In contrast, chromoplasts contain colored pigments, and chloroplasts are characterized by the green pigment chlorophyll, which is essential for photosynthesis.
Identify the given figures of algae and select the correct option:
A) A - Fucus B - Polysiphonia
B) A - Dictyota B - Polysiphonia
C) A - Dictyota B - Porphyra
D) A - Porphyra B - Polysiphonia
The correct option is B: A - Dictyota, B - Polysiphonia.
Dictyota is described as a ribbon-shaped dichotomous and marine brown algae that thrives in shallow water.
Polysiphonia is a marine red algae known for being attached to the substratum by rhizoids and holdfast.
Which of the following molecules is not required for photosynthesis?
A $\mathrm{CO}_{2}$
B $\mathrm{H}_{2}\mathrm{O}$
C $\mathrm{O}_{2}$
D Chlorophyll
The correct answer is C $(\mathrm{O}_{2})$.
Photosynthesis is a process that plants use to create food, which involves turning carbon dioxide $(\mathrm{CO}{2})$ and water $(\mathrm{H}{2}O)$ into glucose and oxygen, using sunlight and chlorophyll. Oxygen $(\mathrm{O}_{2})$, as mentioned, is not used in the process but is instead produced as a byproduct of photosynthesis. Thus, oxygen is not required for photosynthesis to occur.
Stomata of desert plants remain closed during the daytime. How do they take up carbon dioxide and perform photosynthesis?
Desert plants employ a specialized form of photosynthesis referred to as CAM photosynthesis. They open their stomata at night to take in carbon dioxide (CO2). This CO2 is then stored in the form of an intermediate compound which is utilized during the day when the stomata are closed.
This adaptation is crucial because keeping the stomata closed during the daytime helps to minimize water loss through transpiration in the harsh desert environment. Additionally, in many desert plants, the chlorophyll is located in the stems since leaves are reduced to spines. This allows the stem to undertake the functions of photosynthesis.
In summary, desert plants perform photosynthesis during the day by using the CO2 accumulated at night. This mechanism allows them to survive in extreme conditions by conserving water while still obtaining the necessary carbon dioxide for photosynthesis.
Assertion: Mitochondria and chloroplast are semi-autonomous cell organelles. Reason: Mitochondria and chloroplast have their own DNA and protein synthesizing machinery.
A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true but R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.
The correct option is A: Both A and R are true and R is the correct explanation of A.
Mitochondria and chloroplasts are referred to as semi-autonomous organelles because they possess their own DNA, mRNA, tRNA, ribosomes, and they replicate independently through binary fission. This setup suggests that they are to some extent self-governing or autonomous. These organelles are involved in a symbiotic relationship with the cell, indicating their evolution and integration into the cellular environment, thereby supporting the assertion of their semi-autonomous nature.
The stomatal pore opens when:
A. Guard cells swell up
B. Chloroplast of guard cells shrink
C. Guard cells shrink
D. Chloroplast of guard cells swell up
The correct answer is A. Guard cells swell up.
The stomatal pore opens when the guard cells surrounding it absorb water and swell up. This swelling causes the stomata to open, allowing for gas exchange needed for photosynthesis.
The algae like Ulothrix and Spirogyra take essential minerals and water by
A. Holdfast
B. nucleus
C. chloroplast
D. general body surface
The correct answer is D. general body surface.
In algae like Ulothrix and Spirogyra, essential minerals and water are absorbed through the general body surface of the organism. These algae do not use specialized structures like roots for absorption; instead, the entire surface of their bodies is involved in the uptake of nutrients and water from their surrounding environment.
Nitrogen & Sulphur are required by the plant for
A Stomatal movement
B Rigidity of the cell wall
C Enzyme action
D Chlorophyll synthesis
The correct answer is C. Enzyme action.
Nitrogen (N) and Sulphur (S) are crucial constituents of coenzymes, which play a vital role in facilitating enzyme actions within the plant. These elements are essential in the biochemical processes that allow enzymes to function effectively.
"Explain why plants have lower energy needs compared to animals."
Plants generally have lower energy needs compared to animals due to several fundamental differences in their biological functions and lifestyles:
Lack of Locomotion: Plants are sessile, meaning they do not move from one place to another. This immobility removes the necessity for energy expenditure on activities such as searching for food, seeking shelter, or finding mates, which are common in animals.
Static Location: Plants obtain their nutrients and energy primarily through photosynthesis from a fixed position, usually rooted in the soil. They do not need to move to acquire their sustenance, unlike animals that must often travel or hunt for their food, expending considerable energy in the process.
Structural Simplicity: Many of a plant's cells are non-living, contributing to less overall metabolic activity compared to animals. Animals, however, possess complex organ systems that require constant energy input to maintain homeostasis and support various life processes.
These factors collectively contribute to the reduced energy demands of plants compared to the more active and complex systems observed in animals.
Which product is initially formed during photosynthesis?
A. Starch
B. Glucose
C. Glycogen
D. Ribose
The correct answer is B. Glucose.
During photosynthesis, the primary product formed is glucose, which is a simple sugar. It serves as a key molecule for energy production. Any glucose that is not immediately used by the plant is converted into starch, which is essentially a polymer composed of multiple glucose units, and is used for storage.
Describe briefly the mechanism of stomatal movement. [4 MARKS]
The mechanism of stomatal movement was elucidated by Levitt in 1967. He explained that starch produced during photosynthesis is converted into organic acids, leading to a decrease in the concentration of potassium ions in the guard cells. This conversion increases the concentration of organic acids within the guard cells, elevating the osmotic concentration of the cell sap. As a result, water is absorbed by the guard cells, causing them to swell and thus open the stomata.
Conversely, in the absence of light (during the night), photosynthesis ceases and the concentration of $\mathrm{CO}_2$ increases. This prompts the conversion of organic acids back into starch, which decreases the osmotic concentration of the cell sap. Consequently, water moves out of the guard cells, reducing their turgor and leading to the closure of the stomata.
In summary, stomata open during the daytime due to the conversion of starch to organic acids and water absorption, and close at night due to the reverse process, demonstrating a diurnal rhythm in response to light and carbon dioxide levels.
Assertion: The plant biomass, which serves as the food of herbivores and decomposers, is said to result from the gross primary productivity. Reason: Gross primary productivity is the rate at which consumers convert the chemical energy of their food into their own biomass.
A. Both assertion and reason are true, and the reason is the correct explanation of the assertion. B. Both assertion and reason are true, but the reason is not the correct explanation of the assertion. C. Assertion is true, but the reason is false. D. Assertion and reason are false.
The correct option is D. Assertion and reason are false.
Gross Primary Productivity (GPP) is the total rate of photosynthetic production of organic matter. The biomass that is available for heterotrophs (herbivores and decomposers) to consume is actually the Net Primary Productivity (NPP), not GPP. NPP is the portion of GPP that remains after plants have used some of this productivity for their own respiration. Thus, the assertion that plant biomass, serving as the food for herbivores and decomposers, results from the gross primary productivity is false.
The reason states that Gross Primary Productivity is the rate at which consumers convert the chemical energy of their food into their own biomass. This statement is also false. The correct term for this process is Secondary Productivity, which refers to the rate at which consumers (herbivores and carnivores) transform the chemical energy of their food into their own new biomass.
Therefore, both the assertion and the reason are incorrect.
These plants store water in their stems in order to:
A) Survive in dry conditions
B) Increase transpiration
C) Attract insects
D) Survive in aquatic habitat
The correct answer is A) Survive in dry conditions.
Plants like the cactus have adapted to arid environments by evolving thick, fleshy stems that store water. These adaptations allow them to minimize water loss and endure prolonged periods of drought. Unlike normal leaves, a cactus has spines (modified leaves) that help reduce transpiration and preserve its stored water, ensuring its survival in harsh, dry conditions.
The following are the properties of plastids except:
A. they are found only in plants
B. they help in giving shape to the cell
C. contain colored pigments called chlorophylls
D. have double-layered membrane
The correct answer is B - they help in giving shape to the cell.
Plastids are indeed only found in plants and are characterized by their double-layered membrane. A well-known plastid, the chloroplast, imparts the green color to leaves due to the presence of green-colored pigments called chlorophylls. However, the property of giving shape to a cell is mainly attributed to the cell wall in plant cells, rather than to plastids. Thus, the statement in option B is an incorrect attribution to plastids.
Name the pigment that imparts green colour to plant parts?
A Chloroplast
B Xanthophyll
C Chlorophyll
D Chromoplast
The correct answer is C Chlorophyll.
Chlorophyll is the pigment responsible for the green color of plant parts. Chloroplasts and chromoplasts are types of plastids, which are organelles found in plant cells. Xanthophyll, on the other hand, is a pigment that imparts a yellow color.
Keratin is the skin pigment that protects it against ultraviolet light.
A) True
B) False
The correct answer is B) False.
Keratin is actually a type of protein found in the skin, hair, and nails, and is not responsible for protecting the skin from ultraviolet (UV) light. Instead, the skin pigment known as melanin plays a crucial role in protecting the skin by absorbing UV radiation. This absorption helps prevent damage to the DNA in skin cells, which can lead to skin cancer. Keratin provides structure and protects cells from physical and mechanical damage, not UV radiation.
Which of the following activities do not help in increasing the content of water vapor in air?
A) Transpiration
B) Evaporation
C) Respiration
D) Condensation
The correct answer is D) Condensation.
Transpiration involves the evaporation of water from plants, leading to an increase in water vapor content in the air.
Evaporation occurs when water is heated and transforms from a liquid to a gas state, adding water vapor to the air.
Respiration is the process where food is broken down in the presence of oxygen, releasing both carbon dioxide and water, contributing vapor to the air.
Condensation, however, refers to the conversion of water vapor back into liquid form, reducing the amount of water vapor in the air. Thus, condensation does not help in increasing the content of water vapor in the air.
Which of the following plant products do we take in while breathing?
A. Carbon dioxide
B. Oxygen
C. Glucose
D. Nitrogen
The correct answer is B. Oxygen.
During the process of photosynthesis, plants consume water and carbon dioxide and harness sunlight to produce oxygen and glucose. While breathing, humans and other animals inhale oxygen and exhale carbon dioxide. Oxygen is crucial for the survival of most living organisms on Earth.
During which stage of photosynthesis is oxygen produced?
A) Cyclic photophosphorylation
B) Non-cyclic photophosphorylation
C) Carbon fixation
D) Calvin cycle
The correct answer is B) Non-cyclic photophosphorylation.
Oxygen production in photosynthesis occurs due to water molecules splitting. This process primarily takes place during non-cyclic photophosphorylation, where the electrons given off from Photosystem II (PS-II) migrate to Photosystem I (PS-I). These electrons are replenished by the splitting of water, hence filling the electron deficit in PS-II. The byproduct of this water-splitting process includes protons, electrons, and notably, oxygen, which is released into the atmosphere.
Contrastingly, during cyclic photophosphorylation, no new electrons are needed as the electrons from PS-I are redirected back to the same system through the electron transport chain, thus bypassing the need for water splitting and eliminating oxygen release.
Meanwhile, the Calvin cycle, or carbon fixation, primarily involves the incorporation of carbon dioxide into organic molecules like glucose, and does not involve the release of oxygen.
In photosynthesis, the light energy (from the sun) is converted to chemical energy, which can be used to perform the activities of the organism. This is an example of $\qquad$ reaction.
A) Endothermic
B) Exothermic
C) Combination
D) Substitution
The correct answer is A) Endothermic.
Endothermic reactions are those in which energy, typically in the form of heat, is absorbed. During photosynthesis, plants absorb light energy from the sun, enabling them to convert carbon dioxide and water into glucose and oxygen. This absorption of light energy classifies photosynthesis as an endothermic reaction.
Ribbon-shaped chloroplasts occur in
A. Spirogyra
B. Ulothrix
C. Riccia
D. Chlamydomonas
The correct answer is A. Spirogyra.
Spirogyra is known for its distinctive spiral-shaped chloroplasts, which is where the genus derives its name from. Thus, ribbon-shaped chloroplasts are a characteristic feature of Spirogyra.
Which wavelength gives maximum photosynthetic output?
A) None of these
B) Violet
C) Blue
D) Red
The correct option is D) Red.
Light serves as the primary energy source for photosynthesis, which predominantly utilizes wavelengths within the visible spectrum (ranging from 380 to 760 nm). When using monochromatic light sources, red light maximizes photosynthetic efficiency, followed by blue light. Green light, however, supports notably poor photosynthesis. It's important to note that polychromatic light, which combines multiple wavelengths, typically yields the highest rates of photosynthesis.
Floridean starch occurs in:
A) Rhodophyceae B) Phaeophyceae C) Myxophyceae D) Chlorophyceae
Correct Answer: A) Rhodophyceae
Floridean starch is the storage form of food in Rhodophyceae (also known as red algae). Notably, the grains of floridean starch are stored outside the chloroplast in these organisms. Thus, option A) Rhodophyceae is the correct choice.
In Spirogyra, pyrenoids occur in
A) Nucleus
B) Cell wall
C) Cytoplasm
D) Chloroplast
The correct answer is D) Chloroplast.
Spirogyra is a type of filamentous green algae, known for its uniquely spiral-shaped chloroplasts. Within these chloroplasts, you can find multiple small, round structures known as pyrenoids. These pyrenoids are typically located along the edges of the chloroplasts in Spirogyra.
Photosynthesis takes place in the membranes of small sacs called:
A. thylakoids B. grana C. photosystems D. photons
The correct answer is A. thylakoids.
Thylakoids are the specific structures within chloroplasts where the light-dependent reactions of photosynthesis occur. These reactions are crucial for the synthesis of energy, thereby supporting the plant's ability to convert light energy into chemical energy.
Which pair is wrong?
A. $\mathrm{C}_{3}$ - Maize
B. $\mathrm{C}_{4}$ - Kranz anatomy
C. Calvin cycle - PGA
D. Hatch and Slake cycle - O.A.A
The incorrect pair is Option A: $\mathbf{C_3}$ - Maize.
Maize is actually a $\mathbf{C_4}$ plant, characterized by Kranz anatomy and it utilizes the Hatch and Slack pathway.
The first stable product in the Hatch and Slack pathway is Oxaloacetic Acid (O.A.A), which correctly corresponds to Option D.
The Calvin cycle, mentioned in Option C, correctly begins with the formation of 3-phosphoglyceric acid (PGA).
Hence, the pair that is incorrectly matched is Option A.
A green leaf is often compared to a factory. Match the items in Column A with those in Column B according to this comparison.
Column A | Column B |
---|---|
(i) Chloroplast | (a) Power |
(ii) Oxygen and water | (b) Raw material |
(iii) Sunlight | (c) Machinery |
(iv) CO2 and water | (d) End products |
(v) Glucose (sugar) | (e) Workrooms |
(vi) Cells in the leaf | (f) Byproducts |
The correct matches for each item in Column A to the corresponding item in Column B, in the context of comparing a green leaf to a factory, are:
(i) Chloroplast is matched to (c) Machinery because chloroplasts are the sites where photosynthesis occurs, similar to machinery that produces products in a factory.
(ii) Oxygen and water are matched with (f) Byproducts since these are substances produced during the process of photosynthesis, not unlike how factories might generate byproducts during the manufacturing process.
(iii) Sunlight corresponds to (a) Power because it provides the energy required for photosynthesis, analogous to how power runs factory machinery.
(iv) CO$_2$ and water are connected to (b) Raw Materials because these are the basic inputs used in the photosynthesis process, like raw materials used in manufacturing.
(v) Glucose (sugar) is identified with (d) End Products as it is the main product of photosynthesis, just as factories have end products.
(vi) Cells in the leaf align with (e) Workrooms reflecting their role as the basic structural and functional units where all the essential processes take place, similar to workrooms or sections in a factory where different parts of the production occur.
Thus, the associations are correctly marked as:
(i) - (c)
(ii) - (f)
(iii) - (a)
(iv) - (b)
(v) - (d)
(vi) - (e)
Assertion [A]: Food chains start with photosynthesis and end with decomposition. Reason [R]: In an ecosystem, plants produce food and decomposers help in the decay of dead matter.
A. Both A and R are true and R explains A.
B. Both A and R are true, but R does not explain A.
C. A is true and R is false.
D. Both A and R are false.
The correct option is A: Both A and R are true and R explains A.
Explanation: In an ecosystem, plants, or producers, are the primary source of food as they can synthesize their own nutrients through photosynthesis, distinguishing them as autotrophs. Thus, every food chain commences at this first trophic level with plants. As the chain progresses, energy and matter flow through different organisms until it reaches the end of the chain, where decomposition occurs.
Decomposers, including bacteria and fungi, play a pivotal role at this terminal stage of a food chain. They break down dead organisms, returning valuable nutrients to the environment. These nutrients are then available to be reused by producers, thereby facilitating nutrient cycling in the ecosystem. This essential process directly relates to how the food chain operates, from inception (photosynthesis) to conclusion (decomposition), which is why R provides a clear explanation of A.
Supply of oxygen to the biogas plant will have:
A) Positive effect
B) Negative effect
C) No effect
D) Positive or negative effect depending on the temperature
The correct answer is B) Negative effect
Biogas production involves the breakdown of organic matter in the absence of oxygen, an anaerobic process. Introducing oxygen into this environment disrupts the process, negatively affecting biogas yield. Thus, the supply of oxygen to the biogas plant will indeed have a negative effect.
Give two ways in which carbon dioxide is fixed.
(i) Green plants fix carbon dioxide ($\mathrm{CO}_2$) through the process of photosynthesis. In this process, they convert $ \mathrm{CO}_2 $ into glucose, using energy from sunlight.
(ii) Marine animals, such as mollusks and corals, utilize carbonates dissolved in seawater to construct their shells. This process effectively fixes carbon dioxide from the environment into a solid, calcareous form.
Match List-I with List-II and select the correct answer using the codes given below the lists.
List I | List II |
---|---|
A. The amount of energy accumulation in green plants through the process of photosynthesis | 1. Gross primary productivity |
B. The total organic matter synthesized by the producers in the process of photosynthesis per unit of time and area | 2. Primary productivity |
C. Rate of storage of organic matter in plant tissues in excess of the respiratory utilization during the measurement period | 3. Secondary productivity |
D. Rate of energy storage at the consumer level | 4. Net primary productivity |
A) A-1 B-2 C-3 D-4
B) A-2 B-1 C-3 D-4
C) A-1 B-3 C-4 D-2
D) A-1 B-2 C-4 D-3
The correct answer is D, with matching as follows:
A-1: The amount of energy accumulation in green plants through the process of photosynthesis corresponds to Gross primary productivity.
B-2: The total organic matter synthesized by the producers in the process of photosynthesis per unit of time and area aligns with Primary productivity.
C-4: The rate of storage of organic matter in plant tissues in excess of the respiratory utilization during the measurement period describes Net primary productivity.
D-3: The rate of energy storage at the consumer level is referred to as Secondary productivity.
Explanation:
Primary productivity represents the rate at which biomass or organic matter is produced per unit area over a time period by plants through photosynthesis. This can be quantified as either gross or net primary productivity.
Gross Primary Productivity (GPP) is the total rate of photosynthetic energy production by green plants.
Net Primary Productivity (NPP) is the portion of energy that remains after accounting for the plants' respiratory losses (energy used by plants in metabolism) and is stored as organic matter.
Secondary productivity refers to the amount of biological production at the consumer level, that is, the energy transferred to consumers and stored in their bodies.
The option D accurately matches the concepts in List I with those defined in List II.
Leaves appear green due to the presence of
A) sunlight
B) chlorophyll
C) carbon dioxide
D) nutrients
The correct answer is Option B: chlorophyll.
Leaves appear green primarily due to the presence of chlorophyll. This pigment is crucial for absorbing light necessary for photosynthesis, the process through which plants produce their food. Chlorophyll specifically absorbs red and blue wavelengths of light effectively, but reflects green light, which is why leaves appear green to our eyes. Thus, the presence of chlorophyll not only aids in food production but also imparts the characteristic green color to the leaves.
Compared to a dry day, how would the rate of transpiration be affected on a humid day?
A) There would be no difference between the rate of transpiration on a dry or a humid day.
B) Higher rate of transpiration on a dry day compared to a humid day.
C) Higher rate of transpiration on a humid day compared to a dry day.
D) On a dry day there would be no transpiration at all, while on a humid day there would be maximum transpiration.
The correct answer is B) Higher rate of transpiration on a dry day compared to a humid day.
Transpiration largely depends on the amount of water vapor already present in the atmosphere. On a dry day, the air has less water vapor, which results in a greater difference in water vapor concentration between the inside of the leaf and the outside environment. This difference drives more diffusion of water vapor from the leaves into the air, leading to a higher rate of transpiration.
Conversely, on a humid day, the air contains more water vapor. This reduces the concentration difference between the leaf and the atmosphere. As a result, less water vapor diffuses out of the leaves, and thus there is a reduced rate of transpiration.
What is the ultimate source of energy for all living organisms?
A) Wind
B) Soil
C) Water
D) Sun
The correct answer is D) Sun.
The Sun is the primary and ultimate source of energy for all living organisms on Earth. This is because virtually all food chains and food webs begin with plants or other autotrophs that create organic matter from sunlight through the process of photosynthesis. Hence, the Sun's energy is fundamental to sustaining life on the planet.
What precautions would you take to set up a potometer?
To properly set up a potometer and ensure its accurate functioning, consider the following essential precautions:
(a) Cutting and Watering the Twig: The twig must be cut obliquely under water to prevent air from entering the xylem. This process keeps the pathway for water transportation intact.
(b) Ensuring Airtight Joints: It is crucial that all connections within the potometer are airtight. This precaution prevents any air leaks which could disrupt the measurement of water uptake.
(c) Adjusting the Air Bubbles: The air bubbles in the apparatus should be carefully adjusted to the zero point by delicately manipulating the reservoir. This setting is important for obtaining a clear starting point for any measurements of transpiration rates.
(d) Placement of the Capillary Tube: The free end of the capillary tube must be fully submerged in water. Proper immersion ensures that the tube measures the transpiration rate accurately without any interference from air.
Which of the following are the functions of a plastid?
A) Trap solar energy for photosynthesis.
B) Impart color to leaves and fruits.
C) Store fats, proteins, and starch.
D) All of the above.
The correct answer is D) All of the above.
Plastids are specialized organelles within plant cells that serve various functions:
Chloroplasts: These are responsible for trapping solar energy to perform photosynthesis and give leaves their green color.
Chromoplasts: These contain red and yellow pigments and are primarily involved in imparting color to flowers and fruits.
Leucoplasts: These plastids are found in seeds where they store fats, proteins, and starch.
All the choices given in the question are valid functions of the different types of plastids present in plant cells.
Leaves in desert plants are modified into spines. Why?
A) To bear more flowers
B) To minimize water loss through transpiration
C) To absorb more water
D) To reduce the rate of photosynthesis
The correct answer is B) To minimize water loss through transpiration.
In desert environments, where water is scarce, the adaptation of plants to preserve water is crucial. Leaves typically have stomata (tiny pores used for gas exchange), which can lead to significant water loss through transpiration. By modifying leaves into spines, desert plants drastically reduce the number of stomata and subsequently the surface area susceptible to water loss. This adaptation is essential for survival in arid conditions, as it minimizes unnecessary water expenditure.
What would happen if plants stop consuming carbon dioxide?
If plants were to stop consuming carbon dioxide (CO2), the impact on the ecosystem and life on Earth would be catastrophic. Plants play a crucial role in photosynthesis, where they convert CO2 and sunlight into oxygen and carbohydrates. This process is essential not only for the survival of plants but also for providing the primary energy source for nearly all other life forms on Earth.
Should this CO2 uptake by plants cease entirely, plants would no longer be able to photosynthesize, leading to their eventual death. This would result in the collapse of the food chain, as all organisms, directly or indirectly, depend on plants for food and oxygen. Initially, humans and animals might survive on existing food reserves, but this would only be a temporary solution.
The death of plant life would lead to severe food shortages and starvation. Social structures would likely disintegrate, leading to chaos and lawlessness, often depicted as food riots and societal collapse. As food sources become scarce, the competition for remaining resources would intensify, possibly leading to increased violence and a breakdown of moral and social norms.
Moreover, the halt in oxygen production by plants would not immediately affect the oxygen levels in the atmosphere, but the absence of food production would pose a much more immediate threat to human survival. In such extreme scenarios, some might resort to unsustainable measures like eating livestock, game, or even other humans as traditional food sources dwindle.
Ultimately, if plants stopped consuming CO2 and ceased their role in photosynthesis and oxygen production, life on Earth as we know it would face extreme challenges with potential for widespread extinction events.
Green plants convert solar energy to ______ energy by the process of photosynthesis.
A. mechanical
B. electrical
C. solar
D. chemical
Correct Answer: D. chemical
Explanation:
Green plants use their chlorophyll, a green pigment, to capture solar energy from the sun. During photosynthesis, this solar energy is used to produce simple sugars, such as glucose. Consequently, the transformation happening in photosynthesis is from light (solar) energy to chemical energy. Hence, the answer is chemical energy.
Is it correct to say that photosynthesis occurs only in leaves of a plant? Besides leaves, what are the other parts that may be capable of carrying out photosynthesis? Justify.
Photosynthesis is primarily known to occur in the leaves of green plants, as leaves are structured specifically to capture solar radiation and effectively convert it into chemical energy. However, it is not exclusive to leaves; there are several exceptional cases involving other plant parts capable of photosynthesis.
Alternate Photosynthetic Plant Parts:
Root as Photosynthetic Organ:
In some plants, roots can develop chlorophyll and begin photosynthesis, termed assimilatory roots. Examples include Trapa and Tinospora.
Stem as Photosynthetic Organ:
In the case of plants like Opuntia, the stem modifies itself to take on the functions of leaves. These stems become flattened, thick, and succulent, performing photosynthesis. Such structures are called phylloclades.
Petiole as Photosynthetic Organ:
In Australian Acacia, the petiole adapts to perform photosynthesis after the leaf lamina falls off early, assuming both the shape and function of the leaf in photosynthesis.
These adaptations showcase the versatility and diversity of plant structures in adapting photosynthetic functions beyond just the leaves.
Mention four factors which are essential for photosynthesis.
Each factor is critical for the process of photosynthesis, earning 0.5 Marks for each correct mention.
Water: Essential for providing electrons and protons which are used in the synthesis pathways.
Carbon dioxide: Acts as a carbon source for producing glucose.
Sunlight: Provides the energy required to drive the chemical reactions of photosynthesis.
Chlorophyll: The primary pigment responsible for absorbing light energy to initiate the process.
In photosynthesis, solar energy is captured by the pigment called _______.
In photosynthesis, solar energy is captured by the pigment called chlorophyll.
Additional Information:Chlorophyll is the green pigment present in the leaves of plants. It plays a crucial role in photosynthesis by capturing solar energy, which is essential for converting water and carbon dioxide into carbohydrates. This process is vital for the plant's food production and growth.
Which of the following plants are low carbon dioxide compensation plants, i.e., thrive well even at low carbon dioxide concentrations?
A) C3-plants
B) C4-plants
C) C2-plants
D) Alpine plants
The correct answer is B) C4-plants.
C4 plants utilize a distinctive mechanism called the Hatch-Slack cycle or the C4 cycle, which enables them to thrive even at low carbon dioxide concentrations. This process is particularly advantageous because it helps these plants to efficiently avoid the issues associated with photorespiration. Photorespiration occurs when the enzyme RuBisCO starts fixing oxygen instead of carbon dioxide, which can be wasteful.
In C4 plants, the process is optimized by creating an environment around RuBisCO that is enriched with carbon dioxide and depleted of oxygen. This adaptation makes C4 plants particularly effective at carbon fixation under conditions such as drought, high temperatures, and low availability of nitrogen or carbon dioxide.
The two-pigment system theory of photosynthesis was proposed by:
A) Hill
B) Arnon
C) Ruben and Kamen
D) Emerson
The correct answer is D) Emerson.
Two-pigment system theory of photosynthesis was proposed by Robert Emerson. This theory is essential for understanding how plants use different pigments to absorb light effectively during photosynthesis.
Other scientists mentioned have contributed differently:
Hill discovered that the evolution of oxygen during photosynthesis occurs in the light reaction.
Arnon elucidated the process by which green plants transfer energy from light to form chemical energy and produce oxygen.
Ruben and Kamen found that the oxygen released during photosynthesis is derived from water, not carbon dioxide.
The process of production of energy takes place in the:
A. mitochondria
B. nucleus
C. vacuole
D. chloroplast
The correct answer is A. mitochondria.
Mitochondria are often referred to as the powerhouses of the cell. They play a crucial role in generating energy in the form of ATP (Adenosine Triphosphate). This is primarily achieved through the process of aerobic respiration, which converts glucose into ATP, thus supplying the cell with the necessary energy it needs to function.
The substrate which undergoes oxidation and phosphorylation in glycolysis is:
A) Glyceraldehyde-3-phosphate
B) 1,3-bisphosphoglyceric acid
C) Dihydroxyacetone phosphate
D) 2-phosphoglyceric acid
The correct option is A:
Glyceraldehyde-3-phosphate
In glycolysis, Glyceraldehyde-3-phosphate (G-3-P) undergoes a critical transformation where it is converted into 1,3-bisphosphoglyceric acid. This conversion is facilitated by the enzyme glyceraldehyde-3-phosphate dehydrogenase. During this biochemical reaction, the cofactor NAD^+ is reduced to NADH and H^+. Additionally, an inorganic phosphate (Pi), originally sourced from H_3PO_4, is incorporated into the product. This step is a clear example of both oxidation (loss of electrons) and phosphorylation (addition of phosphate group), positioning Glyceraldehyde-3-phosphate as the substrate for these processes in glycolysis.
Absorption of water is associated with:
A Root apex
B Root hairs
C Bark of roots
D All of these
Let's understand the role of different parts of a plant's root system:
Root hairs: This is the primary site for water and mineral absorption. Root hairs are unicellular structures that extend from the root and are mainly responsible for absorbing essential nutrients and water from the soil.
Root apex: Also known as the root tip, the root apex is primarily involved in growth through its meristematic activity. It is not directly involved in water absorption.
Bark of roots: This part of the root primarily provides protection and is not specialized for the absorption of water.
Given these roles, root hairs (Option B) are correctly associated with the absorption of water in plants. Hence, the correct answer to the question is:
B Root hairs
The xylem in plants is responsible for:
A. Transport of water
B. Transport of oxygen
C. Transport of food
D. Transport of amino acid
The xylem in plants is a complex tissue composed of more than one type of cells, designed for the specific purpose of conduction. The primary role of xylem is the transportation of water and minerals absorbed from the soil, distributing them throughout the plant. This makes xylem crucial for the plant’s hydration and mineral nutrition.
In summary, the correct answer to the role of xylem in plants is: A. Transport of water.
Reserve food product of most algae is:
A. Glycogen
B. Fat
C. Cellulose
D. Starch
The reserve food product in most algae is starch, as indicated by option D. Starch is a form of carbohydrate that gets stored in algae primarily in two forms: amylose and amylopectin. These serve as key energy reserves and are synthesized by algae to be used when needed.
In contrast to other options:
Glycogen (option A) is mainly a storage form of glucose in animals, including humans.
Fat (option B) also serves as a storage form in some organisms, but it is not the primary reserve food in most algae.
Cellulose (option C) is a structural component of the cell walls of plants and algae, not a storage form of energy.
Thus, the correct answer is D. Starch. This highlights the importance of carbohydrates like starch in biological energy storage, specifically in algae.
In plants, transport of soluble products in the process of photosynthesis occurs in:
A. xylem
B. phloem
C. both of these
D. none of these.
In plants, the transport of soluble products resulting from the process of photosynthesis mainly involves the component called glucose. This glucose is synthesized in the leaves (the primary site for photosynthesis) and needs to be distributed to other parts of the plant.
To handle this transportation, phloem tissues play a crucial role. Phloem is responsible for transporting the synthesized food, primarily in the form of glucose, from the leaves to various parts of the plant where it is needed. This transport mechanism is vital for distributing energy resources to all parts of the plant.
It’s important to differentiate between phloem and xylem roles:
Xylem is primarily involved in the transportation of water and minerals from the roots to other parts of the plant.
Phloem, on the other hand, specifically handles the distribution of the products of photosynthesis, which includes organic food materials like glucose.
Given the options:
A. xylem
B. phloem
C. both of these
D. none of these,
The correct answer to the question concerning the transport of soluble products of photosynthesis in plants is B. phloem.
Suppose a mutant of a photosynthetic alga has dysfunction in mitochondria. It would affect its ability to perform:
A. glycolysis
B. anaerobic respiration
C. aerobic respiration
D. photosynthesis
Glycolysis occurs in the cytoplasm and not in the mitochondria. Therefore, mitochondrial dysfunction would not affect the alga's ability to perform glycolysis.
Anaerobic respiration also takes place in the cytoplasm. This process similarly remains unaffected by any issues in the mitochondria.
Aerobic respiration, however, occurs in the mitochondria where glucose and oxygen are used to produce energy (ATP), along with carbon dioxide as waste. The mitochondria's primary role is crucial here because they facilitate oxidative phosphorylation, a key energy-releasing step in aerobic respiration. Hence, dysfunction in the mitochondria will directly impair the alga's capacity for aerobic respiration.
Photosynthesis predominantly occurs in chloroplasts, not mitochondria. Therefore, mitochondrial dysfunction does not typically interfere with photosynthetic processes.
Given this clarification, the likely correct answer to which process would be affected by mitochondrial dysfunction in a photosynthetic alga is:
C. Aerobic Respiration
This answer is chosen because aerobic respiration requires a properly functioning mitochondrion to generate energy efficiently.
Food synthesized in leaves is transported by:
A. Xylem
B. Phloem
C. Cambium
D. Epidermis
In plants, the transportation of synthesized food from the leaves to other parts of the plant occurs through specialized tissues known as vascular tissues. These include two primary types: xylem and phloem.
Xylem is responsible for the transport of water and minerals from the roots to the other parts of the plant.
Phloem, however, is crucial for the movement of photosynthetically produced food (or sugars) throughout the plant.
When we consider the food synthesized in leaves, which mainly results from photosynthesis, it's the phloem that carries this food to various parts of the plant where it is needed. This process is essential for distributing energy resources across the plant, enabling growth and development.
Hence, for the question asking which tissue transports food synthesized in leaves, the correct answer is:
B. Phloem
Here’s a brief clarification on the other options:
A. Xylem: Transports only water and minerals.
C. Cambium: Involved in secondary growth, not in the transportation of food.
D. Epidermis: Serves as an outer protective layer and is not involved in the transport of nutrients.
What is the storage form of glucose in plants?
Starch
Cellulose
Carbohydrates
None of the above
The correct option is A. Starch.
During photosynthesis, a plant absorbs light energy using the pigment chlorophyll. This process allows the plant to convert carbon dioxide and water into glucose. The glucose produced is either:
Transported to the growing parts of the plant for use in respiration, or
Converted and stored as starch.
Thus, starch serves as the primary storage form of glucose in plants.
A diagram of stomatal apparatus is given alongside. Select the option where the alphabets correctly indicate the parts:
A. A = subsidiary cells, $\mathrm{B}=$ guard cells, $\mathrm{C}=$ nucleus, $\mathrm{D}=$ stomatal aperture
B $\mathrm{A}=$ guard cells, $\mathrm{B}=$ vacuoles, $\mathrm{C}=$ chloroplast, $\mathrm{D}=$ cell sap
C $\mathrm{A}=$ subsidiary cells, $\mathrm{B}=$ guard cells, $\mathrm{C}=$ chloroplast, $\mathrm{D}=$ stomatal pore
D $\mathrm{A}=$ guard cells, $\mathrm{B}=$ subsidiary cells, $\mathrm{C}=$ chloroplast, $\mathrm{D}=$ vacuole
The correct option is D
A = Guard Cells
B = Subsidiary Cells
C = Chloroplast
D = Vacuole
This representation accurately depicts the stomatal apparatus commonly found in a typical dicot plant with reniform (kidney-shaped) guard cells.
Who demonstrated that photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidisable compound reduces carbon dioxide to carbohydrates?
Jan Ingenhousz
Joseph Priestly
Cornelius van Niel
Von Mayer
Cornelius van Niel (1897-1985) is recognized for demonstrating that photosynthesis is primarily a light-dependent reaction. His research, particularly on green and purple bacteria, revealed the process where hydrogen from a suitable oxidizable compound is used to reduce carbon dioxide to carbohydrates.
The general equation provided by Cornelius van Niel to describe this process is:
$$ 2 \mathrm{H}_{2} \mathrm{~A} + \mathrm{CO}_{2} \rightarrow 2 \mathrm{~A} + \mathrm{CH}_{2} \mathrm{O} + \mathrm{H}_{2} \mathrm{O} $$
Here, $\mathrm{H}_{2} \mathrm{~A}$ represents the hydrogen donor, and in the presence of light, it facilitates the reduction of $\mathrm{CO}_{2}$ (carbon dioxide) to $\mathrm{CH}_{2} \mathrm{O}$ (carbohydrates), releasing $\mathrm{H}_{2} \mathrm{O}$ (water) in the process.
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By looking at a plant externally can you tell whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$ ? Why and how?
No, it is not possible to determine whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$ just by looking at it externally. The distinction between $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ plants is based on internal physiological and anatomical differences that are not visible externally. Here are some key points to explain why:
Internal Leaf Anatomy: $\mathrm{C}_{4}$ plants have a special leaf anatomy called Kranz anatomy, which includes distinct bundle sheath cells and mesophyll arrangement, whereas $\mathrm{C}_{3}$ plants do not.
Biochemical Pathways: $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ plants use different biochemical pathways for the fixation of CO₂. $\mathrm{C}_{3}$ plants use the Calvin cycle directly, whereas $\mathrm{C}_{4}$ plants have an additional CO₂ fixation step that takes place in the mesophyll cells.
To determine whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$, microscopic examination of leaf cross-sections or biochemical tests to check for the presence of specific enzymes (e.g., PEP carboxylase in $\mathrm{C}_{4}$ plants) is required.
By looking at which internal structure of a plant can you tell whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$ ? Explain.
You can determine whether a plant is $\mathrm{C}_{3}$ or $\mathrm{C}_{4}$ by examining the internal anatomy of the leaf, specifically the arrangement of mesophyll cells and bundle sheath cells.
$\mathrm{C}_{3}$ Plants:
Mesophyll Cells: The Calvin cycle or $\mathrm{C}_{3}$ cycle takes place in the mesophyll cells.
Leaf Anatomy: Typically, $\mathrm{C}_{3}$ plants do not have a distinctive separation of mesophyll and bundle sheath cells.
$\mathrm{C}_{4}$ Plants:
Kranz Anatomy: These plants show a characteristic leaf anatomy termed "Kranz anatomy".
Bundle Sheath Cells: These form a wreath-like structure around the vascular bundles and contain chloroplasts. These cells are involved in the Calvin cycle or $\mathrm{C}_{3}$ pathway.
Mesophyll Cells: $\mathrm{CO}_{2}$ is initially fixed into a 4-carbon compound in the mesophyll cells.
In summary, the distinctive Kranz anatomy with well-developed bundle sheath cells surrounding the vascular bundles is a clear indicator of $\mathrm{C}_{4}$ plants. In contrast, $\mathrm{C}_{3}$ plants will lack this specific structural arrangement.
Even though a very few cells in a $\mathrm{C}_{4}$ plant carry out the biosynthetic - Calvin pathway, yet they are highly productive. Can you discuss why?
$\mathrm{C}_{4}$ plants are highly productive despite fewer cells carrying out the Calvin pathway for several reasons:
Efficient Carbon Fixation: The primary CO(_2) acceptor in $\mathrm{C}_{4}$ plants is phosphoenol pyruvate (PEP), which has a higher affinity for CO(_2) than RuBisCO. This reduces the occurrence of photorespiration, a wasteful process that occurs in $\mathrm{C}_{3}$ plants.
Kranz Anatomy: $\mathrm{C}_{4}$ plants possess a special leaf anatomy known as Kranz anatomy, which allows spatial separation of the initial CO(_2) fixation and the Calvin cycle. This leads to an increased concentration of CO(_2) at the site of the Calvin cycle, enhancing its efficiency.
Reduced Photorespiration: In $\mathrm{C}_{4}$ plants, the release of CO(_2) within the bundle sheath cells ensures high levels of CO(_2) around RuBisCO, thereby significantly reducing photorespiration. This leads to more efficient carbon fixation.
Adaptation to High Light and Temperature: $\mathrm{C}_{4}$ plants are better adapted to high light intensities and higher temperatures. These conditions favor the $\mathrm{C}_{4}$ pathway, making these plants more efficient in converting light energy to chemical energy.
Water Use Efficiency: $\mathrm{C}_{4}$ plants tend to have better water use efficiency because they minimize water loss by keeping their stomata partially closed, which can still facilitate the Calvin cycle due to their CO(_2) concentrating mechanism.
These factors collectively contribute to the high productivity of $\mathrm{C}_{4}$ plants.
RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in $\mathrm{C}_{4}$ plants?
In C₄ plants, RuBisCO carries out more carboxylation due to a specialized mechanism that increases the concentration of $\mathrm{CO}_{2}$ at the enzyme site. This occurs because:
Spatial Separation: The initial fixation of $\mathrm{CO}_{2}$ happens in the mesophyll cells, where it combines with PEP to form a $\mathrm{C}_{4}$ acid. This $\mathrm{C}_{4}$ acid is then transported to the bundle sheath cells.
Release of $\mathrm{CO}_{2}$ in Bundle Sheath Cells: In the bundle sheath cells, the $\mathrm{C}_{4}$ acids are broken down to release $\mathrm{CO}_{2}$, which increases the local concentration of $\mathrm{CO}_{2}$ around RuBisCO.
High $\mathrm{CO}_{2}$: $\mathrm{O}_{2}$ Ratio: The elevated concentration of $\mathrm{CO}_{2}$ in the bundle sheath cells ensures that RuBisCO acts more as a carboxylase (fixing $\mathrm{CO}_{2}$) rather than an oxygenase (fixing $\mathrm{O}_{2}$). This minimizes photorespiration and promotes carboxylation.
Thus, RuBisCO functions mainly as a carboxylase in C₄ plants due to the higher concentration of $\mathrm{CO}_{2}$ at the site of the enzyme, resulting from the unique biochemical pathway in these plants.
Suppose there were plants that had a high concentration of Chlorophyll $b$, but lacked chlorophyll $a$, would it carry out photosynthesis? Then why do plants have chlorophyll $b$ and other accessory pigments?
Plants that lacked chlorophyll $a$ would not be able to carry out photosynthesis effectively. Chlorophyll $a$ is the chief pigment responsible for trapping light, and it is essential for the photosynthetic process.
However, plants have chlorophyll $b$ and other accessory pigments like xanthophylls and carotenoids because:
Accessory pigments broaden the spectrum of light that a plant can use by absorbing different wavelengths of light that chlorophyll $a$ does not absorb efficiently.
They transfer the absorbed light energy to chlorophyll $a$, making photosynthesis more efficient.
These pigments help protect chlorophyll $a$ from photo-oxidation by dissipating excess light energy.
In summary, while chlorophyll $a$ is essential for the fundamental process of photosynthesis, chlorophyll $b$ and other accessory pigments enhance the efficiency and flexibility of the photosynthetic apparatus.
Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?
The color of a leaf kept in the dark turns frequently yellow or pale green because the chlorophyll, which gives the leaf its green color, degrades in the absence of light. This degradation leads to the loss of green color faster than the other pigments.
The pigments xanthophylls and carotenoids, which are yellow to yellow-orange in color, are more stable compared to chlorophyll. This is why, when chlorophyll degrades, the remaining pigments make the leaf appear yellow or pale green.
Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green ? Why?
Leaves on the shady side or potted plants kept in the shade generally have darker green leaves. This is because plants increase the production of chlorophyll in low light conditions to maximize the capture of available light for photosynthesis. Thus, these leaves appear darker green compared to those exposed to more sunlight.
Figure 11.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:
(a) At which point/s (A, B or $\mathrm{C}$ ) in the curve is light a limiting factor?
(b) What could be the limiting factor/s in region A?
(c) What do C and D represent on the curve?
(a) Point(s) where Light is a Limiting Factor
In Figure 11.10, points A and B represent regions where light is a limiting factor. This is because, in these regions, as light intensity increases, the rate of photosynthesis also increases.
(b) Limiting Factors in Region A
In Region A, possible limiting factors could be:
Light intensity: Due to insufficient light, photosynthesis cannot proceed as efficiently.
Availability of carbon dioxide: Low levels of $\mathrm{CO}_{2}$ could also limit the rate of photosynthesis if not enough carbon dioxide is available for fixation.
Temperature: The temperature might be too low for the enzymes involved in photosynthesis to function effectively.
(c) Representation of C and D on the Curve
Point C: Represents the light saturation point, where increasing light intensity no longer results in an increase in the rate of photosynthesis. At this point, other factors such as $\mathrm{CO}_{2}$ availability, temperature, or enzyme activity may become limiting.
Point D: Represents the maximum rate of photosynthesis which is achieved when light is no longer a limiting factor. Beyond point D, further increases in light intensity do not increase the rate of photosynthesis due to the other limiting factors mentioned.
Give comparison between the following:
(a) $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ pathways
(b) Cyclic and non-cyclic photophosphorylation
(c) Anatomy of leaf in $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ plants
(a) Comparison between $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ pathways
Characteristics | $\mathrm{C}_{3}$ Pathway | $\mathrm{C}_{4}$ Pathway |
---|---|---|
First stable product | 3-phosphoglyceric acid (PGA), a 3-carbon compound | Oxaloacetic acid (OAA), a 4-carbon compound |
Primary carbon acceptor | Ribulose bisphosphate (RuBP), a 5-carbon compound | Phosphoenol pyruvate (PEP), a 3-carbon compound |
Enzyme for $\mathrm{CO}_{2}$ fixation | RuBisCO | PEP carboxylase and RuBisCO |
Sites/Cells involved | Occurs in mesophyll cells | Occurs in mesophyll and bundle sheath cells |
Photorespiration | Photorespiration is present | Photorespiration is negligible |
Adaptation | Common in temperate plants | Common in tropical plants |
Light and temperature | Lower temperature optimum, low light optima | Higher temperature optimum, high light optima |
(b) Comparison between Cyclic and Non-cyclic photophosphorylation
Characteristics | Cyclic Photophosphorylation | Non-cyclic Photophosphorylation |
---|---|---|
Photosystems involved | Only Photosystem I (PSI) | Both Photosystem I (PSI) and Photosystem II (PSII) |
Electron flow | Electrons cycle back to PSI | Electrons travel from PSII to PSI |
ATP and NADPH production | Only ATP is produced | Both ATP and NADPH are produced |
Involvement of water | No splitting of water | Splitting of water occurs, releasing $\mathrm{O}_{2}$ |
Type of phosphorylation | Cyclic | Non-cyclic (Z-scheme) |
(c) Comparison of leaf anatomy in $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ plants
Characteristics | $\mathrm{C}_{3}$ Plants | $\mathrm{C}_{4}$ Plants |
---|---|---|
Cell type for Calvin cycle | Mesophyll cells | Bundle sheath cells |
Cell type for initial carboxylation | Mesophyll cells | Mesophyll cells (initial), Bundle sheath cells (Calvin cycle) |
Mesophyll cells | Have chloroplasts, large intercellular spaces | Have chloroplasts, close to each other |
Bundle sheath cells | Few chloroplasts | Large cells with many chloroplasts, forming a "Kranz" anatomy (wreath) around vascular bundles |
Leaf anatomy | Less differentiated between mesophyll and bundle sheath | Kranz anatomy, distinct bundle sheath cells around vascular bundles |
These comparisons highlight the major differences and similarities between the pathways and anatomical features of $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ plants, as well as the types of photophosphorylation in photosynthesis.
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Comprehensive Notes on Photosynthesis in Higher Plants for Class 11
Introduction to Photosynthesis
What is Photosynthesis in Higher Plants?
Photosynthesis is a biochemical process in which green plants, algae, and certain bacteria convert light energy into chemical energy. In higher plants, it involves the synthesis of organic compounds (like glucose) using carbon dioxide, water, and sunlight absorbed by chlorophyll.
Why is Photosynthesis Important for Higher Plants and Other Organisms?
Photosynthesis is crucial because it is the primary source of all food on Earth and is responsible for releasing oxygen into the atmosphere, which is essential for the respiration of living organisms.
Early Experiments in Photosynthesis
Joseph Priestley’s Experiment
Joseph Priestley (1733–1804) conducted experiments in the 1770s that demonstrated the essential role of air in the growth of green plants. He discovered that plants could "restore" the air that had been "damaged" by burning candles or respiration.
Contributions of Jan Ingenhousz
Jan Ingenhousz showed that sunlight is essential to the process by which plants produce oxygen, a discovery made through experiments with aquatic plants.
Studies by Julius von Sachs
Julius von Sachs provided evidence that glucose is produced during photosynthesis and stored as starch. He also discovered that chlorophyll is located in chloroplasts within plant cells.
T.W Engelmann’s Prism Experiment
Using a prism to split light into its spectral components, Engelmann demonstrated that photosynthesis is most efficient under blue and red light, which corresponds with chlorophyll absorption.
Melvin Calvin and the Calvin Cycle
Who was Melvin Calvin?
Melvin Calvin was an American chemist who received the Nobel Prize in 1961 for his research on the Calvin Cycle, the series of biochemical reactions that occur in the light-independent phase of photosynthesis.
Calvin’s Contribution to Photosynthesis Research
Calvin mapped the path of carbon during photosynthesis and demonstrated how plants convert light energy into chemical energy, significantly enhancing the understanding of photosynthesis.
The Photosynthetic Machinery
Where Does Photosynthesis Take Place in Higher Plants?
Photosynthesis occurs in the chloroplasts within the green parts of plants, primarily the leaves.
Chloroplasts are the sites within mesophyll cells where light energy is converted into chemical energy.
Structure of Chloroplasts
Chloroplasts contain a membranous system (thylakoids arranged in grana) and stroma. The thylakoid membranes house the pigments and are where the light reactions occur.
Pigments Involved in Photosynthesis
Types of Pigments Involved
There are four main pigments involved in photosynthesis: chlorophyll a, chlorophyll b, xanthophylls, and carotenoids.
Role of Chlorophyll and Accessory Pigments
Chlorophyll a is the chief pigment responsible for capturing light energy. Accessory pigments like chlorophyll b, xanthophylls, and carotenoids expand the range of light that plants can use and protect chlorophyll a from photo-oxidation.
The Light Reactions
What are Light Reactions in Higher Plants?
Light reactions include light absorption, water splitting, oxygen release, and the formation of ATP and NADPH.
The Electron Transport Chain
The electron transport chain involves the transfer of electrons from water through photosystems II and I, culminating in the production of NADPH and ATP.
The Z Scheme of Light Reactions
The Z Scheme describes the electron flow from water to NADP+ through the two photosystems, creating a characteristic "Z" shape.
Splitting of Water and Its Significance
Water is split in photosystem II, releasing oxygen, protons, and electrons, which replenish those lost by chlorophyll in photosystem II.
Photophosphorylation
Cyclic Photophosphorylation
Cyclic photophosphorylation involves only photosystem I and produces ATP without producing NADPH or oxygen.
graph TB
PS1[Photosystem I]
Acceptor[Primary Electron Acceptor]
CEA(Cyclic Electron Flow)
PS1 -->|Light| Acceptor
Acceptor --> CEA --> PS1
Non-cyclic Photophosphorylation
Non-cyclic photophosphorylation involves both photosystems and produces ATP, NADPH, and oxygen.
graph TD
PS2[Photosystem II]
PS1[Photosystem I]
Acceptor2[Primary Electron Acceptor PSII]
CEA2(Cyclic Electron Flow PSII)
Acceptor1[Primary Electron Acceptor PSI]
NADP[NADP+]
PS2 -->|Light| Acceptor2
Acceptor2 --> PS1 --> Acceptor1 --> NADP -->|NADPH| CalvinCycle[Calvin Cycle]
Chemiosmotic Hypothesis and ATP Synthesis
Mechanism of ATP Synthesis in Chloroplasts
ATP synthesis in chloroplasts is driven by a proton gradient created by the movement of electrons through the electron transport chain.
graph LR
ThylakoidMembrane[Thylakoid Membrane]
PSII --> Q --> PC --> PSI --> Fd --> NADP --> ATPsynthase[ATP Synthesis]
ATPsynthase --> ThylakoidLumen[Thylakoid Lumen]
The Dark Reactions
Where are ATP and NADPH Used?
ATP and NADPH produced in the light reactions are used in the Calvin cycle to fix carbon dioxide into glucose.
The Calvin Cycle: Process and Significance
The Calvin cycle, consisting of carboxylation, reduction, and regeneration steps, converts atmospheric CO2 into glucose and regenerates RuBP.
The C4 Pathway
What is the C4 Pathway?
The C4 pathway is an adaptation in some plants that enables them to efficiently fix CO2 in hot, dry environments.
Difference Between C3 and C4 Plants
C4 plants have a unique leaf anatomy known as Kranz anatomy, where the initial CO2 fixation occurs in mesophyll cells, and the Calvin cycle takes place in bundle sheath cells.
Photorespiration
What is Photorespiration?
Photorespiration is a process in C3 plants where oxygen is consumed and carbon dioxide is released, which reduces the efficiency of photosynthesis.
Photorespiration in C3 vs. C4 Plants
Photorespiration does not occur in C4 plants due to their ability to concentrate CO2 in bundle sheath cells, enhancing photosynthetic efficiency.
Factors Affecting Photosynthesis
Internal Factors
Internal factors include the number, size, age, and orientation of leaves, chlorophyll content, and internal CO2 concentration.
External Factors
External factors include light intensity, CO2 concentration, temperature, and water availability.
Law of Limiting Factors
Blackman's Law of Limiting Factors states that the rate of a physiological process is limited by the factor that is closest to its minimum value.
Conclusion
Summary of Photosynthesis
Photosynthesis is the process by which green plants produce food and oxygen using sunlight, carbon dioxide, and water. It occurs in chloroplasts and involves both light-dependent and light-independent reactions. Understanding the intricacies of photosynthesis is crucial for appreciating how life on Earth is sustained.
Importance in the Ecosystem
Photosynthesis forms the foundation of the food chain and is vital for the survival of almost all living organisms by maintaining atmospheric oxygen levels and providing food.
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