Photosynthesis In Higher Plants Module

Q 1. As a result of photorespiration, glycolate is converted into serine and carbon dioxide in the following ways:

1. Mitochondria
2. Chloroplasts
3. Vacuoles
4. Peroxisomes

Answer: d, Peroxisomes
Explanation: Photorespiration involves converting glycolate into serine and carbon dioxide in peroxisomes. Plants undergo photorespiration through the oxygenation of ribulose-1,5-bisphosphate (RuBP) instead of the desired carboxylation reaction, which is the outcome of photorespiration. Consequently, glycolate is formed, which needs to be salvaged to prevent carbon and energy loss.

In the peroxisomes, glycolate is metabolized through a series of reactions known as the glycolate pathway. This pathway involves several enzymatic steps, leading to the conversion of glycolate into serine and carbon dioxide. After producing serine, it is transported to the mitochondria and converted into glycine, which can then be returned to the chloroplasts for further metabolism.

While mitochondria, chloroplasts, and vacuoles play essential roles in plant metabolism, glycolate is primarily converted into serine and carbon dioxide in the peroxisomes during photorespiration.

Q 2. Which molecules combine with carbon dioxide in the C4 pathway?

1. glyceraldehyde phosphate
2. ribulose biphosphate
3. phosphoenol pyruvic acid
4. citric acid

Answer: c, phosphoenol pyruvic acid
Explanation: Known as the Hatch-Slack pathway, the C4 pathway combines phosphoenolpyruvate (PEP) with carbon dioxide. Plants use this pathway to reduce photorespiration and improve carbon fixation efficiency.

Phosphoenolpyruvate carboxylase (PEPC) catalyzes the carboxylation of PEP in mesophyll cells, forming oxaloacetate – a four-carbon compound.

It can be further reduced to malate or transferred to bundle sheath cells for decarboxylation – releasing carbon dioxide. C4 plants can minimize photorespiration and maximize carbon dioxide levels around Rubisco in bundle sheath cells by optimizing the separation of initial carbon fixation and subsequent carbon release.

Q 3. Dark reactions of photosynthesis are not independent of light:

1. The first reaction takes place in the presence of light.
2. The presence of light inhibits this reaction.
3. It can also occur during the day.
4. They utilize the products of light reactions.

Answer: d, They utilize the products of light reactions
Explanation: Photosynthetic dark reactions, also called Calvin cycles or light-independent reactions, are not entirely light-independent because they depend on the effects of the photoreaction.

In photosynthetic photoreaction, light energy is converted by light into chemical energy, ATP, and NADPH. Dark reactions use these products along with carbon dioxide (CO2) to synthesize organic molecules, especially glucose. The light response produces ATP and NADPH, providing the energy and reducing the power needed to fix carbon dioxide and produce carbohydrates in the Calvin cycle.

Therefore, the dark reaction depends on the product of the light reaction. Without these products, or if the photoreaction is blocked, the photoreaction will not occur. Although the dark response does not directly depend on light energy, it can occur during the day even when it does not directly depend on light energy. These are called dark reactions because they do not require direct light energy.

Q 4. Except for the following, all of the next is correct regarding xanthophylls and carotenoids in photosynthesis:

1. They act as auxiliary pigments
2. Maximum absorption is in the VIBGYOR blue and red range.
3. It enables a broader wavelength range of incident light for photosynthesis.
4. They protect chlorophyll through a form of photooxidation.

Answer: b, Their peak absorption is in the blue and red regions of VIBGYOR
Explanation: Xanthophylls and carotenoids are accessory pigments that play essential roles in photosynthesis. Light energy is absorbed by them and transferred to chlorophyll, the primary stain involved in photosynthesis. The absorption spectrum of xanthophylls and carotenoids is complementary to that of chlorophyll a, as they absorb light in regions where chlorophyll a has lower absorption.

Xanthophylls and carotenoids absorb light primarily in the blue and green regions of the visible spectrum rather than the blue and red regions, as mentioned in the statement. As chlorophyll absorbs light most efficiently in the blue and red areas of the range, xanthophylls and carotenoids also absorb light in the green region.

Q 5. Chlorophyll can be described as a pigment that differs from retinal that has a

1. narrow absorption range but high efficiency
2. limited absorption range but low efficiency
3. wide absorption range but high efficiency
4. wide absorption range but low efficiency
    

Answer: a, narrow absorption range but high efficiency
Explanation: Chlorophyll has a narrow absorption range but high efficiency. It can absorb most of the visible light spectrum and convert it to chemical energy. Chlorophyll is more efficient than retinal but has a much narrower absorption range. It does not absorb as many wavelengths as retinal, but it is still very efficient at converting light into energy.

Q 6. As part of the electron transport chain during terminal oxidation, what is the cytochrome that donates electrons to oxygen?

1. Cytochrome-b
2. Cyto-C
3. Cyto-a3
4. Cyto-f

Answer: c, Cyto – a3
Explanation: The cytochrome that donates electrons to oxygen is Cytochrome-a3. Cytochrome-a3 is part of the electron transport chain during terminal oxidation and is responsible for transferring electrons from the cytoplasm to the final acceptor, usually oxygen.

Q 7. Do they not produce hexose When isolated thylakoids are suspended in a culture medium containing CO2 and H2O?

1. ATP
2. Enzyme
3. Proteins
4. Hill reagent

Answer: a, ATP
Explanation: Due to the absence of ATP, isolated thylakoids suspended in CO2 and H2O do not produce hexose. ATP is vital for photosynthesis as it provides energy for the electron transport chain and other processes involved in making hexose. Without ATP, none of these processes can occur, meaning no hexose can be produced.

Q 8. four pyrrole rings are attached to Mg through _ atom in chlorophyll structure.

1. N
2. C
3. H
4. O

Answer: a, N
Explanation: Magnesium atoms are attached to the four pyrrole rings in chlorophyll structure through Nitrogen atoms.

Q 9. Which family has many plants that are C4 type?

1. Malvaceae
2. Solanaceae
3. Cruciferae
4. Graminae

Answer: d, Graminae
Explanation: Grass or C4 plants include corn, sugarcane, and sorghum.

Q 10. The process making the significant difference between C3 and C, four plants are

1. respiration
2. Calvin cycle
3. photorespiration
4. Glycolysis

Answer: c, photorespiration
Explanation: The significant difference between C3 and C4 plants is photorespiration. Photorespiration is the process in which oxygen is used, rather than carbon dioxide, during respiration. It reduces the efficiency of photosynthesis in C3 plants but not in C4 plants.

Q 11. It was Emerson’s enhancement effect and Red drop that led to the discovery of

1. two photosystems operating simultaneously
2. oxidative phosphorylation
3. photophosphorylation and cyclic electron transport
4. photophosphorylation and non-cyclic electron transport

Answer: a, two photosystems operating simultaneously
Explanation: In addition to Emerson’s enhancement effect, Red drop has been instrumental in identifying two photosystems operating simultaneously: oxidative phosphorylation (photophosphorylation) and cyclic electron transport (photophosphorylation) and non-cyclic electron transport (photophosphorylation). With Emerson’s work, we better understood photosynthesis by showing that both systems work together.

Q 12. Light-independent reactions in photosynthesis takes place at

1. thylakoid lumen
2. photosystem II
3. photosystem I
4. stromal matrix

Answer: d, stromal matrix
Explanation: The light-independent photosynthesis reactions occur at the thylakoid lumen, within a photosystem, and in the stromal matrix. During these reactions, carbon dioxide (CO2) is turned into usable energy for the plant. The process begins with the fixation of CO2 by enzymes called RuBisCO into molecules called 3-phosphoglycerates. These molecules are then used to produce sugars such as glucose through a process known as the Calvin cycle.

Q 13. Which of the following best represents the components that are necessary for photosynthesis to take place?

1. Mitochondria, accessory pigments, visible light, water, and carbon dioxide.
2. Chloroplasts, accessory pigments, visible light, water, and carbon dioxide.
3. Mitochondria, chlorophyll, visible light, water, and oxygen.
4. Chloroplasts, chlorophyll, visible light, water, and carbon dioxide.

Answer: d, chloroplasts, chlorophyll, visible light, water, and carbon dioxide.
Explanation: The correct answer is chloroplasts, chlorophyll, visible light, water, and carbon dioxide. Photosynthesis is a process that uses the energy from sunlight to convert carbon dioxide and water into glucose (sugar) and oxygen. Chloroplasts contain chlorophyll which acts as an accessory pigment capturing the energy from the sun for photosynthesis. Carbon dioxide and water are also necessary components for photosynthesis to occur.

Q 14. What is/are the function(s) of accessory pigments?

1. They enable a more comprehensive range of wavelengths of incoming light to be utilized for photosynthesis.
2. They absorb light and transfer the energy to the reaction center.
3. They protect the reaction center from photo-oxidation. |
4. All of the above

Answer: d, All of the above
Explanation: Accessory pigments are present in addition to photosynthetic pigments and have multiple functions – they enable a more comprehensive range of wavelengths of incoming light to be utilized for photosynthesis, absorb light and transfer the energy to the reaction center, and protect reaction centers from photo-oxidation.

Q 15. Crops such as tomatoes and bell pepper, allowed to grow in a carbon dioxide-rich environment, show higher yields because:

1. They show an increased rate of photosynthesis at higher carbon dioxide concentrations.
2. They can respond to high carbon dioxide conditions even in low light conditions.
3. They show C4 pathway for carbon fixation at high carbon dioxide is the limiting factor in such plants.
4. Only carbon dioxide is the limiting factor in such plants.

Answer: a, They show an increased rate of photosynthesis at higher carbon dioxide concentrations.
Explanation: The statement that correctly explains why crops such as tomatoes and bell peppers show higher yields when grown in a carbon dioxide (CO2) rich environment is:

“They show an increased rate of photosynthesis at higher carbon dioxide concentrations.”

Increased carbon dioxide levels in the surrounding atmosphere can stimulate photosynthesis in many plants, including crops like tomatoes and bell peppers. This phenomenon is known as the CO2 fertilization effect.

During photosynthesis, plants capture carbon dioxide from the air and use it with water and sunlight to produce glucose and other organic compounds. When the concentration of carbon dioxide in the environment is increased, it can enhance the rate of photosynthesis. It occurs because carbon dioxide is one of the essential reactants required for photosynthesis, and higher levels of CO2 can lead to increased carbon fixation and production of sugars.

As a result, crops grown in a carbon dioxide-rich environment often exhibit higher rates of photosynthesis, which can translate into increased growth and yield. However, it’s important to note that other factors, such as light availability, nutrient availability, and temperature, can also impact crop productivity, so they should be considered in conjunction with elevated carbon dioxide levels.