Problem 149 - Objective Biology for NEET

Question

Assertion: Actinomorphic flowers show radial symmetry. Reason: Zygomorphic flowers have bilateral symmetry.

Step-by-Step Solution

Answer

The assertion and reason are both true, but the reason is not the correct explanation for the assertion.

Step 1: Understanding Actinomorphic Flowers

Actinomorphic refers to a type of flower that can be divided into two equal halves in any radial plane about the center, i.e., they display radial symmetry.

Step 2: Understanding Zygomorphic Flowers

Zygomorphic flowers, on the other hand, can only be divided into two mirror-image halves by a single plane, i.e., they display bilateral symmetry.

Step 3: Analyze the Assertion and Reason

The given assertion states that actinomorphic flowers show radial symmetry, which is accurate according to the definition of actinomorphic flowers discussed in Step 1. The reason provided is also true, as zygomorphic flowers do display bilateral symmetry. However, the reason does not justify or elaborate on the assertion as they are talking about two different types of flowers.

Key Concepts

Actinomorphic Flowers

Actinomorphic flowers are nature's intricate designs that exhibit a remarkable form of symmetry. These flowers, often referred to as 'radially symmetrical', can be split into two equal halves through multiple planes that pass through the central axis. This means, much like the spokes of a wheel, any slice through the middle results in mirror-image halves.

Examples of actinomorphic flowers include the cheerful daisy and the vibrant sunflower. One can imagine cutting these blossoms like a pizza, where each 'slice' would look the same. This type of floral structure is advantageous for plants because it allows for a greater range of pollinators, like wind or multiple species of insects, to access the reproductive organs without a specific approach.

Zygomorphic Flowers

In contrast, zygomorphic flowers present a unique type of floral symmetry known as 'bilateral symmetry'. This specific form means that you can only divide the flower into two mirror-image halves along one plane, similar to how one would slice a symmetrical heart in half down the middle.

Orchids and sweet peas are classic examples of zygomorphic flowers. These types of flowers are often evolved in conjunction with specific pollinators, which is why their distinct shape can be crucial for the survival of both the flower and its pollinator partners. For instance, a bee might be attracted to a certain zygomorphic flower, the shape and size of which perfectly caters to its body during the act of pollination.

Radial Symmetry

Radial symmetry is a characteristic seen in various forms of life, including many flowers as we have noted with actinomorphic species. It is defined by the ability to divide an organism into similar halves through more than one plane passing through the central axis.

This concept can be pictured if one visualizes sea stars or jellyfish, where multiple planes of division result in similar halves. In the plant world, the concept of radial symmetry refers to a layout that's arranged around a central point, and it provides advantages such as offering multiple opportunities for pollinators to land and access the nectar or pollen.

Bilateral Symmetry

Bilateral symmetry, on the other hand, is a sophisticated type of design in both flora and fauna where only a single divisional plane will produce two mirrored halves. It's a common characteristic in the animal kingdom, evident in the human body, where our left and right sides reflect each other.

In the botanical realm, plants with bilateral symmetry, like zygomorphic flowers, attract certain pollinators which have co-evolved with them. This symmetry often leads to specialized interactions, where specific body parts of the pollinator come into contact with the reproductive parts of the flower, enhancing the effectiveness of pollination.