Question

Match Column-I with Column-II and select the correct option from the codes given below. Column-I Column-II A. \(C_{4}\) plants (i) Succulents B. Chlorophyll \(b\) (ii) Accessory photosynthetic C. PS II pigment (iii) Photo-oxidation of \(\mathrm{H}_{2} \mathrm{O}\) D. CAM (iv) Kranz anatomy (a) \(\mathrm{A}\)-(iv), B-(ii), \(\mathrm{C}-(\) iii), \(\mathrm{D}\)-(i) (b) \(\mathrm{A}\)-(iii), B-(ii), C-(iv), D-(i) (c) \(\mathrm{A}\)-(i), B-(iii), C-(ii), D-(iv) (d) \(A\)-(i), B-(ii), C-(iii), D-(iv)

Short answer

The correct option is (a) A-(iv), B-(ii), C-(iii), D-(i).

Step-by-step solution

Identify Features of C4 Plants

The distinctive feature of C4 plants is Kranz anatomy, which is an anatomical structure in leaves consisting of tightly packed sheath cells around the leaf veins, surrounded by mesophyll cells where the C4 pathway occurs. Therefore, A must be paired with (iv), eliminating options (b) and (c).

Determine the Role of Chlorophyll b

Chlorophyll b is an accessory photosynthetic pigment that helps in capturing light energy for photosynthesis. It complements chlorophyll a by absorbing different wavelengths of light, thus B should match with (ii), which supports option (a) and excludes (d).

Investigate the Function of PS II

Photosystem II (PS II) is involved in the photo-oxidation of water, splitting water molecules and releasing oxygen during the light-dependent reactions of photosynthesis. This means C correlates with (iii).

Connect CAM with its Main Characteristic

CAM plants are a type of succulent that uses Crassulacean Acid Metabolism (CAM) for photosynthesis. They open their stomata during the night to minimize water loss, which associates D with (i).

Key concepts

Kranz Anatomy

Kranz anatomy refers to a unique physical structure found in C4 plants. It stems from the German word 'Kranz', meaning 'wreath', and aptly describes the arrangement of cells in the leaves of these plants. In C4 plants, around the veins of the leaf, there are concentric circles of two different types of photosynthetic cells: the bundle sheath cells and mesophyll cells.

This adaptation is significant as it allows these plants to minimize photorespiration, a wasteful process that occurs when the enzyme RuBisCO oxygenates RuBP, wasting energy. The Kranz anatomy facilitates a division of labor; initial carbon fixation takes place in the mesophyll cells, and the Calvin cycle takes place in the bundle sheath cells. This efficient system is particularly advantageous in hot, dry environments where plants need to conserve water and still perform photosynthesis efficiently. The presence of this anatomical trait is what distinguishes C4 plants from other photosynthetic plants.

Chlorophyll b

Chlorophyll b is a type of pigment found in the chloroplasts of green plants and is an essential component in the process of photosynthesis. It acts as an accessory pigment, complementing the absorptive spectrum of chlorophyll a, the primary pigment responsible for capturing light energy.

Chlorophyll b helps in harvesting light by absorbing a different range of light wavelengths, mainly blue and red-orange light, which chlorophyll a does not absorb as efficiently. By doing so, it broadens the range of light that a plant can use for photosynthesis. This pigment is crucial because it transfers the light energy it captures to chlorophyll a, which then uses the energy to synthesize carbohydrates. Additionally, it's important to note that the presence of chlorophyll b is an indicator of the plant's ability to adapt to varying light conditions.

Photosystem II

Photosystem II, or PS II, is an essential complex in the light-dependent reactions of photosynthesis. Located in the thylakoid membranes of chloroplasts, it is the starting point of the electron transport chain. PS II is responsible for absorbing photons and using the energy to extract electrons from water molecules, a process called photolysis.

During this reaction, two water molecules are split, generating four protons, four electrons, and one molecule of oxygen, thus contributing to the oxygen in our atmosphere. It is also the step that generates the proton gradient used to produce adenosine triphosphate (ATP), a key energy molecule for the plant. Without PS II, the light-dependent reactions could not occur, making it a vital component in sustaining the photosynthetic process.

Crassulacean Acid Metabolism

Crassulacean Acid Metabolism, commonly referred to as CAM, is a photosynthetic adaptation found in many desert plants and succulents such as cacti. Unlike most plants, which open their stomata during the day, CAM plants open their stomata at night to take in carbon dioxide. This adaptation minimizes water loss in arid conditions, as cooler nighttime temperatures lead to reduced rates of evaporation.

The carbon dioxide is then converted into an acid and stored during the night. During the day, when the stomata are closed to conserve water, the acid is broken down, and the released carbon dioxide is used in the photosynthetic process. This strategy is highly water-efficient and enables CAM plants to thrive in environments that would be inhospitable to other plant types, showcasing the incredible diversity and adaptability of plant photosynthetic strategies.