Answer and Explanation: 1. The correct response is b. The development of a pollen tube eliminated the requirement for water in sperm transport to the egg. Terrestrial plants can reproduce. See answer in full below.
How did seeded plants evolve to reproduce in the absence of water?
By the conclusion of this section, you will have accomplished the following learning objectives: Describe the emergence of seed plants and the rise of gymnosperms as the main plant group Describe the two developments that made it possible for seed plants to multiply without water.
- Examine the function of pollen grains and seeds.
- Explain the relevance of flowering and fruiting angiosperms Approximately 500 million years ago, it is believed that the first land-dwelling plants were closely linked to present bryophytes (mosses).
- They were succeeded by liverworts (also bryophytes) and early vascular plants, the pterophytes, which are the ancestors of contemporary ferns.
As with gymnosperms and angiosperms, the lifecycle of bryophytes and pterophytes is defined by the alternating of generations; what distinguishes bryophytes and pterophytes from gymnosperms and angiosperms is their reproductive need for water. The completion of the bryophyte and pterophyte life cycle requires water, since the male gametophyte produces sperm that must swim to reach and fertilize the female gamete or egg, pushed by their flagella.
After fertilization, the zygote develops into a sporophyte, which produces sporangia or “spore vessels.” In sporangia, mother cells undergo meiosis in order to create haploid spores. In a favorable setting, the release of spores will result in germination and a new generation of gametophytes. The evolutionary tendency in seed plants resulted in a dominating sporophyte generation and a systematic reduction in the size of the gametophyte, from a prominent structure to a microscopic cluster of cells encased inside the sporophyte tissues.
All spermatophytes are heterosporous, but most lower vascular plants, such as club mosses and ferns, are homosporous (create just one type of spore). They produce both megaspores (female) and microspores (male) (male). Megaspores mature into female gametophytes that create eggs, whilst microspores evolve into male gametophytes that produce sperm.
- They are not free-living, like the gametophytes of other seedless vascular plants, because they develop within the spores.
- Heterosporous seedless plants are considered the evolutionary predecessors of seed plants.
- Seeds and pollen separate seed plants from other (seedless) vascular plants; they are two crucial adaptations to dryness and reproduction that does not require water.
Both modifications were essential for the bryophytes’ and their predecessors’ colonization of land. According to fossil evidence, the earliest unique seed plants appeared around 350 million years ago. The earliest trustworthy record of gymnosperms dates to the Pennsylvanian epoch, around 319 million years ago (Figure 1).
Approximately 380 million years ago, progymnosperms, the earliest seedless plants, appeared. Progymnosperms were a transitional group of plants that superficially resembled conifers (cone-bearing plants) because they formed wood from the secondary development of the vascular tissues; nevertheless, they reproduced similarly to ferns by releasing spores into the environment.
During the Triassic and Jurassic periods of the Mesozoic, gymnosperms dominated the landscape. By the middle of the Cretaceous (about 100 million years ago) in the late Mesozoic period, angiosperms had superseded gymnosperms as the dominant plant group in most terrestrial biomes.
- Various plant species evolved over time, as seen in Figure 1.
- Attribution: U.S.
- Geological Survey) Pollen and seeds were revolutionary structures that enabled seed plants to overcome their need on water for reproduction and embryo development and to conquer dry land.
- Pollen grains are male gametophytes, which contain the plant’s sperm (gametes).
The little haploid (1 n) cells are protected from desiccation and mechanical damage by a protective coating. Pollen grains can travel far from their initial sporophyte, therefore dispersing the DNA of the plant. The seed provides the embryo with protection, nutrition, and a method to maintain dormancy for tens or even thousands of years, guaranteeing that germination may occur under ideal growth circumstances.
What adaptations led to seed plants’ success?
Numerous adaptations to the terrestrial environment led to the success of seed plants. These adaptations, which include the seed, the decrease of the gametophyte production, heterospory, ovules, and pollen, equipped seed plants with new strategies for coping with terrestrial circumstances like as dehydration and exposure to UV light.
Fertilization of seedlings needs water?
In seed plants, fertilization occurs when the male and female sex cells merge. However, water is not required for the fusion of male and female gametes since, in most situations, the male and female gametes are carried to the site of fertilization by other agents.