Problem 171 - Objective Biology for NEET

Question

Assertion: Photosynthesis occurs only in green parts of plants. Reason: Green part of plant contains chlorophyll.

Step-by-Step Solution

Answer

The assertion and reason are correct. Photosynthesis primarily occurs in the green parts of plants because these parts contain chlorophyll, which is crucial for the conversion of sunlight into chemical energy during photosynthesis.

Step 1: Understand Photosynthesis

Photosynthesis is a process by which green plants, algae and some bacteria convert sunlight energy into chemical energy stored as glucose. This process primarily happens in the leaves (the green part) of the plants.

Step 2: Role of Chlorophyll

Chlorophyll is a pigment found in the chloroplasts of the green parts of plants. This pigment absorbs sunlight, especially in the blue and red light wavelengths, and the energy is then used to combine carbon dioxide and water to produce glucose. This is why photosynthesis primarily happens in the green part of the plant.

Step 3: Connecting Photosynthesis and Chlorophyll

Without the chlorophyll to absorb and convert the sunlight into chemical energy, photosynthesis would not occur. Therefore, the statement 'Photosynthesis occurs only in green parts of plants' is generally true because those are the areas where chlorophyll is present. The reason 'Green part of plant contains chlorophyll' is directly related to the assertion and is definitely a main cause why photosynthesis typically occurs in green parts of plants.

Key Concepts

Chlorophyll

In plants, chlorophyll plays a crucial role in the process of photosynthesis. This green pigment is located within the chloroplasts, which are the specialized structures in plant cells responsible for photosynthesis. Chlorophyll specifically absorbs light most efficiently in the blue and red parts of the electromagnetic spectrum. By capturing sunlight, chlorophyll acts like a solar panel, setting in motion the process of converting light energy into chemical energy.
Chlorophyll's unique structure enables it to excite electrons when it absorbs sunlight, a vital step in the photosynthesis process. This excitation of electrons drives the synthesis of energy-rich molecules that eventually lead to the production of glucose, the plant's source of energy. Due to its ability to absorb light, chlorophyll imparts the characteristic green color to plants and is a primary reason why photosynthesis occurs mainly in the plant's green areas. Without chlorophyll, plants would not be able to harness solar energy efficiently to fuel their growth.

Chloroplasts

Chloroplasts are often referred to as the 'powerhouses' of plant cells. These structures are where photosynthesis takes place. From an anatomical standpoint, chloroplasts have a unique, double-membraned structure that houses the photosynthetic machinery. Inside chloroplasts are thylakoids, disc-shaped structures stacked in piles called grana, where chlorophyll resides.
The role of chloroplasts in photosynthesis is to create the environment for chlorophyll to efficiently capture sunlight. This energy is subsequently used to convert water and carbon dioxide into glucose. Chloroplasts, thanks to their organized layout, facilitate the conversion of light to chemical energy in an efficient manner.

• They provide a controlled environment for the photosynthetic reactions.
• Organize components necessary for light absorption and glucose production.
• Transport energy carriers like ATP and NADPH, crucial for the synthesis of glucose.

Chloroplasts are indispensable for photosynthesis, enabling plants to utilize sunlight effectively to produce their own food.

Glucose production

The culmination of photosynthesis is the production of glucose, a simple sugar that serves as an essential energy source for plants. The process begins with absorbing sunlight energy through chlorophyll, located in the chloroplasts. With this energy, plants convert carbon dioxide from the air and water from the soil into glucose through a series of reactions known as the Calvin cycle.
Glucose is vital for plants because it acts as a building block for growth and development. It can be used right away to fuel cellular activities or stored as starch for later use. This capacity to produce glucose gives plants the energy to perform various functions crucial for survival and growth. Additionally:

• Glucose contributes to the synthesis of cellulose, a structural component of plant cell walls.
• It is a precursor to numerous other organic molecules, such as amino acids and lipids.
• Plants utilize glucose for respiration, releasing energy required for metabolic processes.

The production of glucose exemplifies the efficiency and self-sustainability of plants within the ecosystem, showcasing the importance of photosynthesis.