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Photosynthesis in Higher plants involves more additional processes but it remains basically the same as photosynthesis. Plants generally use light energy to drive the synthesis of organic compounds in a physicochemical process known as photosynthesis. It's an anabolic process that's controlled by enzymes. Oxygen is released as a by-product of photosynthesis along with water and glucose. Photosynthesis in higher plants involves two processes namely Light Reaction and Dark Reaction. The light reaction occurs in the presence of light whereas the dark reaction occurs in the absence of light in the stroma of the chloroplasts.
Process of Photosynthesis
Very Short Answer Questions (1 Mark Questions)
Ques. Identify the steps of the Calvin cycle.
Ans. There are three steps to the Calvin cycle: carboxylation, reduction, and regeneration.
Ques. Chlorophyll has which metal ion as a component?
Ans. A chlorine ring surrounds a magnesium ion in the structure of chlorophyll pigment.
Ques. What are the kinds of pigments present in plants?
Ans. Chlorophyll a (bright or blue-green), chlorophyll b (yellow-green), xanthophyll (yellow), and carotenoids are four pigments present in plants (yellow to yellow-orange).
Ques. Name the cell organelle that performs photosynthesis.
Ans. Chloroplast is the cell organelle where photosynthesis takes place.
Ques. Which pigment converts light energy straight into chemical energy?
Ans. Chlorophyll A converts light energy straight into chemical energy.
Ques. Which PSII reaction is influenced by sunlight?
Ans. Photolysis of water is controlled by sunlight in PSII.
Read More: Photochemical Reactions
Ques. In the C3 pathway, how many ATP molecules are required for the creation of one molecule of glucose?
Ans. For the creation of one molecule of glucose, 18 ATP molecules are required.
Ques. What does NADP stand for in its entire form?
Ans. Adenine Dinucleotide Phosphate is the full form of NADP.
Ques. What types of photosynthetic reactions take place in the grana and stroma of chloroplasts?
Ans. Light reaction of Grana and Stroma dark reaction.
Read More: Cyclic Photophosphorylation
Light Reaction and Dark Reaction
Short Answer Questions (2 Marks Questions)
Ques. Is moonlight beneficial to photosynthesis?
Ans. The light energy from the moonlight is insufficient to stimulate the chlorophyll molecules. As a result, photosynthesis cannot occur in the presence of moonlight.
Ques. In both a symbol and a text equation, write the complete balanced equation for Photosynthesis.
Ans. In textual format, the balanced photosynthesis reaction is
Carbon dioxide + Water → Glucose + oxygen.
In symbol form, the balanced photosynthesis reaction is
6CO2 + 6H2O \( \to \)C6H12O6 + 6O2 + 6H2O
Ques. Explain the importance of photosynthesis.
Ans. The importance of photosynthesis can be attributed to two factors:
- It is the world's primary source of all food.
- It's also responsible for green plants that release oxygen into the atmosphere.
Ques. The "Kitchen of the Cell" refers to which organelle. Why.
Ans. The chloroplast is known as the kitchen of the cell because it produces food for the plant in the presence of sunshine, carbon dioxide, and water.
Ques. Chloroplasts are absent in cyanobacteria and in several other photosynthetic microorganisms. What method do they use to carry out photosynthesis?
Ans. Cyanobacteria and other organisms lack chloroplasts. Photosynthesis takes place in the folds of these organisms’ inner membranes. The bluish pigment phycocyanin absorbs solar energy and uses it to carry out the photosynthesis process.
Ques. Why does photosynthesis slow down when the temperature rises?
Ans. The rate of photosynthesis slows down in high-temperature environments. Because photosynthesis is an enzyme-mediated reaction, this is the case. These enzymes perform best when the temperature is just right. The process is affected when the temperature range exceeds the optimum value.
Ques. Other than chlorophyll, what are the two main roles of pigments in green leaves?
Ans. Other than chlorophyll, pigments have the following functions:
- Absorb light energy and transfer it to chlorophyll in order to perform photosynthesis
- To prevent photooxidation of the chlorophyll molecule
Read More: Separation of Plant Pigments Using Chromatography
Long Answer Questions (3 Marks Questions)
Ques. What distinguishes the anatomy of a typical C4 leaf from that of a C3 leaf?
Ans. In a typical C3 leaf, the photosynthetic parenchyma cells are divided into two tissues: an upper layer of tightly packed palisade cells and a lower layer of loosely distributed spongy mesophyll cells enclosing wide intercellular spaces. There is only one type of mesophyll cell in C4 leaves. The leaves of C4 plants are typically narrower than those of C3. The presence of firmly packed, thick-walled bundle sheath cells all around the vascular bundle distinguishes C4 leaves.
Ques. Is photosynthesis a ‘dark reaction’ that requires light? Explain.
Ans. Carbohydrate synthesis takes place during the dark reaction. Because the dark reaction does not require the presence of light, it is called the dark reaction. The dark reaction can occur during the day and does not necessitate complete darkness. As a result, the dark reaction requires sun energy but can also function without it.
Ques. Describe the relationship between photosynthesis and respiration.
Ans. Carbohydrate oxidation occurs during respiration to release energy. The process of photosynthesis is used to create such sugars. As a result, it's clear that the two processes are related. Furthermore, respiration necessitates the use of oxygen, which is produced as a by-product of photosynthesis. Similarly, the carbon dioxide ingested during respiration is important for photosynthesis to occur.
Read More: Difference between Photosynthesis and Respiration
Ques. What is the significance of water splitting?
Ans. The significance of water splitting is as follows:
- Photosystem II electrons that were transmitted must be replenished.
- Electrons released as a result of water splitting are used to accomplish this.
- Water splitting is linked to the PS II; water is split into 2H+, [O], and electrons.
- Oxygen is one of the primary processes of photosynthesis. The electrons necessary to replace those wasted in the photosystem are provided by photosystem II.
Ques. Why does photorespiration not occur in C4 plants?
Ans. Photorespiration is linked to the C3 cycle, in which plants lose carbon dioxide fixing due to an increase in oxygen concentration and a change in the type of RuBP carboxylase oxygenase activity. C4 plants have devised a technique to prevent carbon dioxide loss. There is no direct contact with RuBP carboxylase oxygenases as the C3 cycle functions in bundle sheath cells. Carbon dioxide is fixed by the enzyme PEP carboxylase in mesophyll cells, which produces oxaloacetate, which is transformed to malic acid, which is then transmitted to bundle sheath cells, where carbon dioxide is used in the Calvin cycle in C3 plants’ bundle sheath cells.
Read More: Excretion Plants
Very Long Answer Questions (5 Marks Questions)
Ques. RuBisCo is a carboxylase and oxygenase enzyme that works in together. Why do you suppose RuBisCo performs more carboxylation in C4 plants than in other plants?
Ans. C4 plants lack the enzyme RuBisCo in their mesophyll cells. It's found in the cells that surround the vascular bundles, called bundle-sheath cells. The Calvin cycle occurs in the bundle sheath cells of C4 plants. Phosphoenol pyruvate, a three-carbon molecule, is the major CO2 receiver in mesophyll cells. It is transformed into oxaloacetic acid, a four-carbon molecule (OAA). Malic acid is formed after OAA has been transformed. The Calvin cycle transports malic acid to the bundle sheath cells, where it conducts decarboxylation and CO2 fixation. The enzyme RuBisCo can no longer function as an oxygenase as a result of this.
Read More: Difference Between Xylem And Phloem
Ques. Why is it that when a leaf is stored in the dark, it often turns yellow or pale green? Which pigment do you believe is the most durable?
Ans. As leaves need light to accomplish photosynthesis, their colour changes from a darker to a lighter shade of green when they are kept in the dark. It can also turn yellow at times. The amount of light available determines the amount of chlorophyll pigment produced, which is required for photosynthesis. Chlorophyll-a molecule creation ceases in the absence of light, and they slowly degrade. The leaf progressively turns light green as a result of this. The xanthophyll and carotenoid pigments become prominent during this process, turning the leaf yellow. As light is emitted, these pigments become more stable.
Ques. Explain the Hatch and Slack pathways, as well as the C4 pathway, in brief.
Ans. Hatch and Slack pathway, also known as the C4 pathway, consists of the following steps:
- Inside mesophyll cells, phosphoenolpyruvic acid takes CO2 and converts it to oxaloacetic acid. Phosphoenolpyruvate carboxylase is present in the presence of this enzyme.
- In the presence of the enzyme malate dehydrogenase, NADPH2 reduces oxaloacetic acid to malic acid.
- In the presence of the enzyme transaminase, oxyaloacetic acid creates aspartic acid via a transamination process.
- Malic acid is delivered to bundle sheath cells, where it is decarboxylated by NADP and a particular malic enzyme, resulting in pyruvic acid and CO2. The Calvin cycle fixes carbon dioxide once more inside the bundle sheath cells.
- Pyruvic acid is returned to mesophyll cells and converted to phosphoenolpyruvate with the help of ATP. As a result, instead of ADP, AMP (adenosine monophosphate) is formed (adenosine diphosphate).
Read More: Kranz Anatomy: C4 Plants, Mesophyll & Bundle-Sheath Cells
Ques. What are the key events and outcomes of the light reaction?
Ans. The key events and outcomes of the light reaction are outlined here.
- Light absorption is done with the use of a light-harvesting complex, also known as the LHC. The antennas of the photosystem are made up of several pigments. The pigments aid in the absorption of various wavelengths of light. The chlorophyll in a molecule serves as the reaction's focal point.
- The sun energy collected by the plant aids in the splitting of water molecules, releasing oxygen and hydrogen ions. The NADP ion uses the electrons produced during this process to generate NADPH.
- The oxygen that is produced as a result of the water-splitting process is released through the stomatal opening.
- The light reaction results in the formation of ATP and NADPH.
- ATP and NADPH are formed as a result of the light reaction, which produces two high-energy intermediate molecules, ATP and NADPH.
Ques. Is photosynthesis limited to leaves? If not, what are the other sections of the plant that can perform photosynthesis? Justify.
Ans. Photosynthesis is largely carried out in the leaves of all green plants. The leaves are shaped in such a way that they effectively capture sunlight and convert it into chemical energy. Photosynthesis is carried out by modified components other than leaves in some plants. Assimilatory roots are those that generate chlorophyll and initiate photosynthesis in some plants. Tinospora and Trapa are two examples. Some plants, such as Opuntia, have their stems modified and adapted to perform the functions of leaves, such as becoming thick, succulent, and flattened, and performing photosynthesis. These structures are known as phylloclade.
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