Problem 4 - Campbell Biology

Question

Which of the following is not a characteristic that distinguishes gymnosperms and angiosperms from other plants? (A) dependent gametophytes (B) ovules (C) pollen (D) alternation of generations

Step-by-Step Solution

Answer

The characteristic that does not distinguish gymnosperms and angiosperms from other plants is (D) alternation of generations.

Step 1 - Understand the Question

The question asks which characteristic does not distinguish gymnosperms and angiosperms from other plants. This means we must identify which of the listed characteristics are common to all plants, not just gymnosperms and angiosperms.

Step 2 - Analyze Each Option

Let's look at each option in the context of various plant groups: (A) Dependent gametophytes: Check if all plants have dependent gametophytes or if this is unique to gymnosperms and angiosperms. (B) Ovules: Determine if ovules are unique to gymnosperms and angiosperms or if other plants also have ovules. (C) Pollen: See if pollen is a characteristic exclusive to gymnosperms and angiosperms or common in other plants as well. (D) Alternation of generations: Check if all plant types exhibit the alternation of generations life cycle.

Step 3 - Assess Alternation of Generations

Alternation of generations is a life cycle that occurs in all plants, including non-vascular plants like mosses and liverworts. Therefore, it is not unique to gymnosperms and angiosperms.

Key Concepts

dependent gametophytes

In gymnosperms and angiosperms, the gametophyte stage is reduced and entirely dependent on the sporophyte for nutrition and shelter. The gametophytes develop within the reproductive structures of the sporophytes. In contrast, in non-vascular plants like mosses, the gametophyte stage is the dominant life stage and can live independently.
Gymnosperms and angiosperms have thus adapted to a more complex structure where the larger sporophyte takes on more responsibility, allowing the gametophyte to become smaller and more specialized.

ovules

Ovules are structures within seed plants where megaspores are produced and develop into female gametophytes. In both gymnosperms and angiosperms, ovules are crucial as they eventually form seeds after fertilization.
However, the manner of ovule protection varies:

• In gymnosperms, ovules are exposed on cones.
• In angiosperms, ovules are enclosed within the ovary of a flower.

This difference aids in the key distinction of these two groups within seed plants, compared to non-seed plants.

pollen

Pollen grains are the male gametophytes of seed plants, and they represent a significant adaptation for terrestrial life as they do not require water for fertilization.
In gymnosperms and angiosperms, pollen allows the transfer of sperm to ovules over long distances via wind or animal pollinators. This adaptation is particularly crucial for reproduction in varied environments. Other plant groups, such as ferns and mosses, rely on water for sperm motility, making pollen a distinctive feature of gymnosperms and angiosperms.

alternation of generations

Alternation of generations is a life cycle involving two distinct phases: a multicellular haploid gametophyte and a multicellular diploid sporophyte. This cycle is universal to all plants, from mosses to angiosperms.
The significance of alternation of generations varies among plant groups:

• In non-vascular plants like mosses, the gametophyte is the dominant stage.
• In vascular plants, including gymnosperms and angiosperms, the sporophyte is dominant.

This cycling allows for genetic variation and adaptation, essential for the survival of plant species in fluctuating environments.