Problem 2 - Campbell Biology

Question

Which of the following characteristics of plants is absent in their closest relatives, the charophyte algae? (A) chlorophyll \(\underline{b}\) (B) cellulose in cell walls (C) sexual reproduction (D) alternation of multicellular generations

Step-by-Step Solution

Answer

(D) alternation of multicellular generations

Step 1: Identify Plant Characteristics

List the given characteristics of plants mentioned in the question: (A) chlorophyll \(b\), (B) cellulose in cell walls, (C) sexual reproduction, (D) alternation of multicellular generations.

Step 2: Examine Charophyte Algae

Research and understand the characteristics of charophyte algae, which are the closest relatives to terrestrial plants. Note that charophytes have chlorophyll \(b\), cellulose in cell walls, and engage in sexual reproduction.

Step 3: Determine the Absent Characteristic

Compare the plant characteristics with the characteristics of charophyte algae. The alternative of multicellular generations (alternation of generations) is a distinctive feature of plants that is absent in charophyte algae.

Step 4: Conclude

The characteristic of plants that is absent in their closest relatives, the charophyte algae, is the alternation of multicellular generations.

Key Concepts

Charophyte Algae

Charophyte algae are the closest living relatives of terrestrial plants. These green algae share many characteristics with plants, making them an interesting subject of study for understanding plant evolution. They inhabit freshwater environments and display some complex features that bridge the gap between true multicellular plants and their simpler ancestors. While charophyte algae have some plant-like properties, they lack certain key characteristics that are unique to land plants. Notably, charophytes contain chlorophyll b, have cellulose in their cell walls, and can reproduce sexually. However, they do not possess the alternation of multicellular generations, a distinguishing feature of true plants.

Alternation of Generations

The alternation of generations is a significant life cycle found in all land plants but absent in their closest relatives, the charophyte algae. This process involves two distinct multicellular stages: the haploid gametophyte and the diploid sporophyte. Each generation alternates between producing gametes (sex cells) and spores.

In detail:

• The gametophyte produces haploid gametes via mitosis.
• When gametes from two different plants fuse, they form a diploid zygote.
• The zygote grows into a diploid sporophyte.
• The sporophyte undergoes meiosis to produce haploid spores, which grow into new gametophytes.

This cycle is crucial for plant life as it allows for genetic variation and adaptation to changing environments.

Chlorophyll B

Chlorophyll b is one of the essential pigments responsible for photosynthesis in plants. It assists in capturing light energy, which is necessary for the production of glucose and oxygen. Chlorophyll b complements chlorophyll a by absorbing light in different wavelengths, allowing plants to utilize a broader spectrum of sunlight.

Interestingly, chlorophyll b is also found in charophyte algae. This shared trait suggests an evolutionary connection between charophytes and land plants. The presence of chlorophyll b in both groups highlights their similar photosynthetic processes, even though they diverge in other fundamental characteristics.

Cellulose in Cell Walls

Cellulose is a robust carbohydrate that forms the primary structural component of plant cell walls. It provides rigidity and strength, allowing plants to grow upright and withstand various environmental pressures. The production of cellulose is a key characteristic of land plants and their closest relatives, the charophyte algae.

• In plants, cellulose fibers are synthesized by enzyme complexes that move along the cell membrane.
• This network of cellulose fibers creates a flexible yet strong framework, essential for plant structure.

The presence of cellulose in both plants and charophytes underscores their close evolutionary relationship. However, despite this similarity, plants have evolved additional structural complexities that are not found in charophyte algae.