Question

An experiment using two leaves, a variegated leaf or a leaf that was covered with black paper and one that was exposed to light on testing these leaves for starch shows that photosynthesis occurs only in _________ part of leaf in the_________ of sunlight (a) non-green, presence (b) green, presence (c) non-green, absence (d) green, absence

Short answer

Therefore, the correct answer is (b) the green part of leaf in the presence of sunlight.

Step-by-step solution

Understand Photosynthesis

Photosynthesis is a process that converts light energy into chemical energy in plants. This process occurs in the chloroplasts, found predominantly in the cells of the green parts of leaves.

Identify the Conditions for Photosynthesis

To take place, photosynthesis requires light, water, and carbon dioxide. Light is absorbed by chlorophyll in the chloroplasts. When a leaf is covered with black paper or when it is variegated (non-green), photosynthesis cannot occur because light cannot be absorbed.

Relate This Knowledge to the Choices Given

A leaf that was covered with black paper, or non-green areas of a variegated leaf cannot perform photosynthesis as they cannot absorb light. This process occurs in the green parts of the leaf in the presence of sunlight.

Key concepts

Chloroplasts

Chloroplasts are tiny organelles found mostly in the green parts of plants, especially in leaves. These organelles are critical to the process of photosynthesis. They contain pigments like chlorophyll, which is responsible for capturing light energy. Once the light energy is absorbed, chloroplasts initiate a series of reactions to convert this energy into chemical energy in the form of glucose.
Plants rely heavily on chloroplasts to perform photosynthesis efficiently. These organelles are like tiny factories, taking in sunlight and using it to produce food. It's important to remember that without chloroplasts, plants wouldn't be able to produce their own energy and would not survive for long. Chloroplasts are highly concentrated in the green tissues of a plant because these areas capture the most light.

• Chlorophyll inside chloroplasts captures light energy.
• Photosynthesis creates glucose and releases oxygen.
• Chloroplasts are especially concentrated in leaf cells.

Variegated Leaf

A variegated leaf has distinct areas of different colors, generally green and white or yellow. The green parts contain chlorophyll and, therefore, chloroplasts, which allow photosynthesis to occur. On the other hand, the non-green areas lack chlorophyll and cannot participate in photosynthesis.
In the context of studying photosynthesis, variegated leaves provide a unique opportunity to understand how chlorophyll impacts a plant's ability to produce energy from light. Because only the green sections of a variegated leaf can perform photosynthesis, these leaves are effective in demonstrating which parts of the leaf are active in energy conversion.

• Green areas contain chloroplasts and can perform photosynthesis.
• Non-green areas lack chlorophyll and do not photosynthesize.
• Variegated leaves are useful for experiments on photosynthesis.

Starch Test

The starch test is a simple experiment used to show if photosynthesis has occurred in leaves. Since starch is a byproduct of photosynthesis, finding it in leaf tissue indicates that photosynthesis happened. The test typically involves boiling the leaf in water, immersing it in alcohol to remove chlorophyll, and then applying iodine, which will turn blue-black in the presence of starch.
This method is particularly revealing when using variegated leaves. It shows that only the green sections of the leaf, which perform photosynthesis, contain starch. It’s an excellent hands-on way to visually confirm photosynthesis activity in the leaf.

• Starch indicates photosynthesis has taken place.
• Involves iodine test after removing chlorophyll.
• Non-green areas will not turn blue-black, indicating no starch.

Light Absorption

Light absorption is vital for photosynthesis, as plants use light energy to transform carbon dioxide and water into glucose. The pigment chlorophyll, found in chloroplasts, plays a crucial role by absorbing light, mainly in the blue and red wavelengths. This absorbed light energy drives the photosynthetic reactions.
Leaves designed to maximize light absorption tend to be broad and flat to capture as much sunlight as possible. Each variegated leaf illustrates how essential light absorption is, as the green, chlorophyll-rich parts of the leaf can absorb sufficient light to trigger photosynthesis. Without light absorption, a plant cannot generate energy to grow and reproduce.

• Light energy is absorbed by chlorophyll within the chloroplasts.
• Blue and red wavelengths are most efficiently absorbed.
• Leaf structure supports maximum light absorption for energy conversion.