Understanding adaptations in the evolution of plants
Plants, ranging from the simple liverwort (a bryophyte) to the flowering plants (angiosperms), have evolved structures enabling them to colonize the land of almost any habitat.
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Transcript
The evolution of plants began in the water; however, over time some plants developed structures to help them with life on land. Flowering plants, or angiosperms, achieved the greatest success in terrestrial environments, accounting for 80 percent of the known green plants now living.
Several adaptations can be observed. The plant has roots that anchor it to the ground and seek out water and minerals. It has a stem, which is rigid enough to stand upright and support the leaves but also flexible enough to bend without breaking. The leaves contain stomata for respiration and chloroplasts for photosynthesis.
The vascular system, which resembles a vast network of pipes, distributes water and nutrients to all parts of the plant. The plant has bright flowers and nectar, which attract insects, birds, and bats. As these creatures collect nectar from the plant, they also pick up some of the plant's pollen. When these creatures fly from one plant to another, they can deliver this pollen to other individuals in the same plant species. In this way these animals facilitate cross-pollination and cross-fertilization between different plants.
Some plants, however, do not contain elaborate vascular systems or need to use animal pollinators. Bryophytes—the group of seedless plants containing mosses, hornworts, and liverworts—often live in wetter habitats. They do not have to search far for water and nutrients, so they do not need very complex roots. Water loss does not present a large problem, so they do not need a waxy surface to retain water. Instead, bryophytes can absorb water over their whole surface, eliminating the need for a vascular system. In addition, flowers and nectar are not necessary for reproduction in these plants, because the gametes they produce are designed to travel through the water. It is thought that similar adaptations developed during the earliest stages of plant colonization of the land, which would make bryophytes among the simplest and most ancient forms of terrestrial plants.
Several adaptations can be observed. The plant has roots that anchor it to the ground and seek out water and minerals. It has a stem, which is rigid enough to stand upright and support the leaves but also flexible enough to bend without breaking. The leaves contain stomata for respiration and chloroplasts for photosynthesis.
The vascular system, which resembles a vast network of pipes, distributes water and nutrients to all parts of the plant. The plant has bright flowers and nectar, which attract insects, birds, and bats. As these creatures collect nectar from the plant, they also pick up some of the plant's pollen. When these creatures fly from one plant to another, they can deliver this pollen to other individuals in the same plant species. In this way these animals facilitate cross-pollination and cross-fertilization between different plants.
Some plants, however, do not contain elaborate vascular systems or need to use animal pollinators. Bryophytes—the group of seedless plants containing mosses, hornworts, and liverworts—often live in wetter habitats. They do not have to search far for water and nutrients, so they do not need very complex roots. Water loss does not present a large problem, so they do not need a waxy surface to retain water. Instead, bryophytes can absorb water over their whole surface, eliminating the need for a vascular system. In addition, flowers and nectar are not necessary for reproduction in these plants, because the gametes they produce are designed to travel through the water. It is thought that similar adaptations developed during the earliest stages of plant colonization of the land, which would make bryophytes among the simplest and most ancient forms of terrestrial plants.
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