Problem 2 - Campbell Biology

Question

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

Step-by-Step Solution

Answer

D) alternation of multicellular generations

Step 1: Identify the characteristics of plants

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

Step 2: Compare with charophyte algae

Charophyte algae share several traits with plants, including chlorophyll b (A), cellulose in cell walls (B), and sexual reproduction (C).

Step 3: Identify the unique characteristic

The trait that is present in plants but absent in charophyte algae is alternation of multicellular generations (D). Charophyte algae do not exhibit this trait as they do not alternate between multicellular haploid and diploid stages in their life cycle.

Key Concepts

chlorophyll b

Chlorophyll b is one of the essential pigments found in plants, algae, and cyanobacteria. This pigment serves as an accessory pigment, meaning it assists chlorophyll a in capturing light energy during photosynthesis. While chlorophyll a is the primary pigment, chlorophyll b extends the range of light wavelengths a plant can use.

Specifically, chlorophyll b absorbs light in the blue and red-orange parts of the electromagnetic spectrum, channels this energy to chlorophyll a, thereby optimizing the plant's ability to perform photosynthesis efficiently. It's noteworthy that charophyte algae also contain chlorophyll b, which highlights their close evolutionary relationship with plants.

cellulose in cell walls

Cellulose is an integral component of the cell walls in plants and certain algae, including charophyte algae. This polysaccharide provides structural support and rigidity to the cells by forming a fibrous network. In plants, cellulose allows cell walls to maintain their shape while still being flexible enough to support growth.

The cell wall's role in maintaining cellular integrity and plant uprightness is crucial. By comparison, charophyte algae also have cellulose in their cell walls. This shared feature is one reason charophyte algae are considered the closest relatives of land plants.

alternation of generations

The alternation of generations is a distinctive and complex life cycle seen in plants but not in their close relatives like charophyte algae. This process involves alternating between two multicellular stages: the haploid gametophyte and the diploid sporophyte.

• The haploid gametophyte produces haploid gametes (egg and sperm) through mitosis.
• When these gametes fuse during fertilization, they form a diploid zygote that develops into the diploid sporophyte.
• The sporophyte then undergoes meiosis to produce haploid spores, which grow into new gametophytes, completing the cycle.

This alternation between different stages allows plants to adapt to various environments, ensuring their survival and reproduction. Charophyte algae do not exhibit such a life cycle, which marks a significant evolutionary advancement in plants.

charophyte algae

Charophyte algae are a group of green algae that share several significant traits with land plants, making them the closest living relatives to plants. Among these shared traits are chlorophyll b and cellulose in their cell walls.

However, although charophyte algae and plants share these characteristics, there are essential differences as well. For example, charophyte algae do not undergo alternation of multicellular generations, a life cycle feature unique to plants. This evolutionary split allowed plants to adapt more precisely to terrestrial life.

Understanding charophyte algae also helps scientists trace the evolutionary steps that led to the rise of complex plant life from simpler algal ancestors.