Problem 32 - Objective Biology for NEET

Question

Photosynthesis occurs in (a) Green leaf (b) Green stem (c) Guard cells (d) All of these

Step-by-Step Solution

Answer

All of the given components - a green leaf, a green stem, and guard cells - can perform photosynthesis. Therefore, the correct answer is (d) All of these.

Step 1: Green leaf

Photosynthesis primarily occurs in the leaves of plants. This is because leaves are packed with chloroplast-containing cells. These chloroplasts contain chlorophyll, the pigment which gives leaves their green appearance and captures the light energy necessary for photosynthesis.

Step 2: Green stem

While stems are not the primary site of photosynthesis, green stems do contain chlorophyll and can carry out photosynthesis.

Step 3: Guard cells

Guard cells are specialized plant cells in the epidermis of leaves, stems, and other organs that are used to control gas exchange. They contain chloroplasts, so they can perform photosynthesis. However, their main function is to regulate the opening and closing of stomata to control the water movement.

Key Concepts

Chloroplasts

Chloroplasts are small, but mighty organelles found in plant cells. They are the main site where photosynthesis happens. It is in these chloroplasts that sunlight is converted into chemical energy, which is then used by the plant. This process involves

• Capturing sunlight using chlorophyll
• Converting light energy into glucose and oxygen

Chloroplasts contain a fluid known as the stroma and a set of membranes called thylakoids. The thylakoids stack up to form structures known as grana.
These components work together to make the magic of photosynthesis possible. Chloroplasts are abundant in the cells of green leaves and, to a lesser extent, in some green stems and guard cells.
Despite their small size, chloroplasts can hold large amounts of chlorophyll, which is essential for absorbing the energy from sunlight.

Chlorophyll

Chlorophyll is the green pigment found within chloroplasts. It plays a vital role in photosynthesis by absorbing light energy, particularly from the blue and red parts of the light spectrum.
This energy absorption is crucial as it powers the conversion of water and carbon dioxide into glucose and oxygen. While the most common type of chlorophyll in plants is chlorophyll a, other types like chlorophyll b also play supporting roles.
Chlorophyll is what gives leaves their green color. It's highly efficient at capturing solar energy, making it a fundamental participant in the life-sustaining process of photosynthesis. Without chlorophyll, plants wouldn't be able to convert solar energy into the chemical energy needed for growth and survival.

• Found in chloroplasts
• Absorbs blue and red light
• Essential for photosynthesis

Guard cells

Guard cells are an essential part of the leaf's anatomy, controlling the exchange of gases with the environment. They surround stomata, which are small openings on the surface of leaves and stems. By regulating the opening and closing of stomata, guard cells manage the intake of carbon dioxide and release of oxygen.
They are also key to controlling water loss through a process called transpiration.
Although their main job is to control gas exchange, guard cells do contain chloroplasts. These chloroplasts enable guard cells to perform photosynthesis to some degree, although it is not as much as the leaf cells do.

• Regulate stomatal opening and closing
• Contain chloroplasts for limited photosynthesis
• Critical for gas exchange and water control

Guard cells are always at work to ensure the plant maintains balance in its gas and water exchange with the environment, helping to safeguard the plant’s overall health.