Problem 43 - Objective Biology for NEET

Question

Phyllotaxy is usually of three types, namely, (a) Alternate (b) Whorled (c) Opposite (d) All of these

Step-by-Step Solution

Answer

The correct answer is (d) All of these.

Step 1: Understanding the Question

The question asks to select the types of phyllotaxy from the given options. Phyllotaxy refers to the arrangement of leaves on an axis or stem of a plant.

Step 2: Analyze Each Option

Let's analyze each option. (a) Alternate phyllotaxy: In this type, a single leaf arises at a node in alternate manner along the stem. (b) Whorled phyllotaxy: In this type, more than two leaves arise at a node and form a whorl. (c) Opposite phyllotaxy: In this type, a pair of leaves arise at each node and lie opposite to each other. (d) All of these: This option indicates that all the previously mentioned options are types of phyllotaxy.

Step 3: Select the Correct Option

The correct answer would be (d) All of these, as all the mentioned types are valid types of phyllotaxy.

Key Concepts

Leaf Arrangement

Leaf arrangement, also known as phyllotaxy, refers to how leaves are systematically positioned on the stem of a plant. This arrangement plays a crucial role in maximizing sunlight exposure for photosynthesis, ensuring efficient water drainage, and optimizing space. This strategic positioning helps to avoid shading one leaf with another, allowing each leaf to capture the optimal amount of light. There are three main types of leaf arrangement, or phyllotaxy: alternate, opposite, and whorled. Understanding these types can give insight into plant identification and their adaptation strategies.

Alternate Phyllotaxy

Alternate phyllotaxy is characterized by a single leaf growing at each node, with each leaf alternating one after another along the stem. This pattern is seen in plants such as sunflowers and oaks.

• This type creates a spiral or staggered arrangement as you move up the stem, optimizing light exposure and minimizing overlap.
• Such an arrangement is common in many plant species and is specifically beneficial for light orientation and efficient water runoff.

The alternate pattern can sometimes appear helical, enhancing the plant's overall ability to withstand various environmental stresses.

Whorled Phyllotaxy

In whorled phyllotaxy, more than two leaves are attached at a single node, forming a ring or whorl around the stem. Known examples include plants like oleander and Alstroemeria.

• This symmetrical arrangement maximizes light capture and surface area for photosynthesis, especially in environments where light is limited.
• This type can give plants a bushy or full appearance, which can enhance their visual appeal and functional efficiency in photosynthesis.

As the leaves are equidistant, this arrangement can help balance the plant's structural weight along the stem.

Opposite Phyllotaxy

Opposite phyllotaxy involves a pair of leaves growing at each node, positioned directly across from one another. This type can be observed in plants like maples and mint.

• Such an arrangement ensures that leaves are not shading each other while maintaining structural balance.
• It often results in a highly efficient exposure of leaves to sunlight, essential for optimal photosynthesis.

In some species, opposite phyllotaxy can pair with a decussate pattern, where each successive pair of opposite leaves is rotated 90 degrees from the previous pair, forming an X-shape when viewed from above.