Problem 29 - Objective Biology for NEET

Question

The organism which contain chlorophyll 'a'and 'b' cup-shaped chloroplast and is unicellular is (a) Spirogyra (b) Chlamydomonas (c) Volvox (d) Ulothrix

Step-by-Step Solution

Answer

The correct answer is (b) Chlamydomonas.

Step 1: Understanding the Characteristics

Firstly, one needs to understand the various properties of the different classes of algae mentioned. Spirogyra, for instance, is filamentous, Chlamydomonas and Volvox are both unicellular but only Chlamydomonas has a cup-shaped chloroplast. Ulothrix, on the other hand, is a filamentous alga and hence not unicellular.

Step 2: Comparison of Characteristics

You are meant to find which of the microorganisms given in the multiple choice options are unicellular and possess both chlorophyll 'a' and 'b' and a cup-shaped chloroplast. On comparison, we see that Chlamydomonas matches the criteria completely.

Step 3: Choosing the Correct Option

Finally, after understanding the properties of each organism and comparing them to the given criteria, you can conclude that the unicellular organism that contains both chlorophyll 'a' and 'b' and has a cup-shaped chloroplast is Chlamydomonas.

Key Concepts

Unicellular Algae

Algae are diverse and fascinating organisms, ranging from single-celled to large multicellular forms. Among them, unicellular algae are some of the most intriguing. A classic example of unicellular algae is **Chlamydomonas**.

Unlike Spirogyra or Ulothrix, which are filamentous, Chlamydomonas is a singular green algal cell. This means that it functions as a complete organism on its own.

• Unicellular algae like Chlamydomonas can perform all the necessary functions of life within one cell.
• They are often found in freshwater and damp soils, thriving in various environments.
• Unicellular algae play an essential role in aquatic ecosystems as they contribute to the oxygen supply through photosynthesis.

Their simplicity and adaptability make them vital players in their ecosystems, and also excellent subjects for scientific study.

Chlorophyll Types

Chlorophyll is crucial for photosynthesis, allowing plants and algae to absorb energy from light. Chlamydomonas contains two types of chlorophyll: **chlorophyll 'a' and 'b'**.

Chlorophyll 'a' is the primary pigment in photosynthesis, essential for transferring light energy. It's present in all photosynthetic organisms, including Chlamydomonas.
Chlorophyll 'b', on the other hand, is considered an accessory pigment, which means it assists by broadening the spectrum of light absorbed. Some key points about these chlorophyll types include:

• Chlorophyll 'a' absorbs light primarily in the blue-violet and red wavelengths.
• Chlorophyll 'b' helps capture light in a broader range, especially the blue light spectrum.
• Both chlorophylls work together, increasing the efficiency of photosynthesis in Chlamydomonas.

The presence of both chlorophyll types in Chlamydomonas allows it to maximize sunlight use, which is vital for its growth and energy production.

Algal Characteristics

Algae possess diverse characteristics that enable them to adapt to different environments. Chlamydomonas exhibits specific algal features that make it distinct:

**Cup-shaped Chloroplast**: This is a unique feature of Chlamydomonas, setting it apart from other algae. The cup-shaped chloroplast efficiently captures light, which is crucial for photosynthesis.
**Flagella**: Chlamydomonas has two flagella which it uses for propulsion through its aquatic environment. This mobility aids in locating optimal conditions for light and nutrients.
Other fascinating characteristics include:

• Presence of a cell wall, primarily composed of cellulose, that offers protection and structural support.
• A light-sensitive eyespot, or stigma, that helps the algae move towards light.

These features make Chlamydomonas not only efficient in surviving but also in adapting to changing environmental conditions, ensuring its continued role in natural ecosystems.