Problem 1 - Campbell Biology

Question

Three of the following are evidence that charophytes are the closest algal relatives of plants. Select the exception. \begin{equation} \begin{array}{l}{\text { (A) similar sperm structure }} \\ {\text { (B) the presence of chloroplasts }} \\ {\text { (C) similarities in cell wall formation during cell }} \\ {\text { division }} \\ {\text { (D) genetic similarities in chloroplasts }}\end{array} \end{equation}

Step-by-Step Solution

Answer

Option (B) the presence of chloroplasts is the exception.

Step 1: Understand the Question

Identify the task of selecting the exception from the list of evidence that suggests charophytes are the closest algal relatives of plants.

Step 2: Evaluate Option (A)

Determine if similar sperm structure between charophytes and plants is evidence of close relation. Yes, it is evidence because both have flagellated sperm.

Step 3: Evaluate Option (B)

Check if the presence of chloroplasts is evidence of a close relationship. Note that chloroplasts are present in a wide range of algae, not only charophytes, so this is not strong evidence specific to charophytes.

Step 4: Evaluate Option (C)

Examine similarities in cell wall formation during cell division. Charophytes and plants share similar patterns of cell wall formation during cytokinesis (cell division), indicating a close relationship.

Step 5: Evaluate Option (D)

Review genetic similarities in chloroplasts between charophytes and plants. This is a strong piece of evidence, as genetic similarities in chloroplast DNA indicate a close evolutionary connection.

Step 6: Identify the Exception

Based on the evaluations, identify that Option (B), the presence of chloroplasts, is the exception because it is a common feature in many types of algae, not just charophytes and plants.

Key Concepts

charophytes

Charophytes are a group of green algae that are considered to be the closest relatives to land plants. Understanding their features helps us to see why scientists believe charophytes and land plants share a common ancestor. These features include:
1. **Flagellated Sperm**: Both charophytes and plants, especially in primitive forms like mosses, have sperm with flagella that swim to reach the egg.
2. **Apical Growth**: Charophytes exhibit growth at the tips (apically), similar to land plants.
3. **Sporopollenin**: This is a tough polymer found in the walls of plant spores and charophyte zygotes, protecting them from desiccation. These similarities make charophytes key to studying plant evolution.

plant evolution

Plant evolution traces the origin and diversification of plants from a common ancestor shared with charophytes. Initial evidence suggests that complex plants evolved through several significant changes.
1. **Water to Land Transition**: Plants adapted to live on land, developing structures to manage water and reproduce without water.
2. **Development of Vascular Tissue**: This allowed plants to transport water and nutrients, facilitating greater size and complexity.
3. **Adaptations**: These include stomata for gas exchange, roots for anchoring and absorbing water, and seeds to protect and nourish the embryo. Studying plant evolution gives insight into the successful strategies plants used to colonize various environments.

chloroplasts

Chloroplasts are essential organelles in plant cells that conduct photosynthesis, converting light energy into chemical energy stored in glucose. These organelles have their own DNA, which is similar to the DNA found in cyanobacteria, suggesting an ancient symbiotic origin.
1. **Pigments**: Chloroplasts contain chlorophyll and other pigments that capture light energy.
2. **Energy Production**: The light reactions occur in the thylakoid membranes, producing ATP and NADPH.
3. **Carbon Fixation**: The Calvin cycle in the stroma converts CO2 into organic molecules like glucose. The presence of chloroplasts is common across many algae, not just charophytes, which is why it is not a definitive link between charophytes and plants.

cell wall formation

Cell wall formation during cell division is a crucial process that is remarkably similar in charophytes and land plants, indicating their close relationship.
1. **Cytokinesis**: Both groups form a cell plate during cytokinesis, which is guided by a structure called the phragmoplast.
2. **Cellulose Synthesis**: Both charophytes and plants use similar cellulose-synthesizing complexes to construct their cell walls.
3. **Structural Integrity**: The cell wall provides structural support and protection, facilitating growth and development. These similarities in cell wall formation underscore the evolutionary ties between charophytes and land plants.

genetic similarities

Genetic similarities, especially within the chloroplast DNA, provide strong evidence for the close relationship between charophytes and plants.
1. **Chloroplast DNA**: Sequencing of chloroplast genomes reveals that charophytes and plants share significant genetic sequences.
2. **Nuclear DNA**: There are also noteworthy similarities in certain genes found in the nuclear DNA of both groups.
3. **Evolutionary Insights**: These genetic markers help scientists trace back the evolutionary lineage and understand how land plants evolved from their aquatic ancestors. The genetic link serves as a crucial piece of evidence supporting the theory that charophytes are the closest algal relatives to plants.