Starting out as simple waterborne green algae, plants now cover the earth in their many forms. Ferns and mosses were among the earliest plants to venture out of the lakes and streams, able to live on land but still needing abundant water sources for reproduction. Flowering plants are the most evolved and it is their adaptations that have created the most diversity in the plant world.
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Being a water plant, algae rarely had the problem of having enough moisture to survive. They also didn't have to worry so much about gravity since water gave them buoyancy. Plants trying to take hold on land needed to develop a support structure that could withstand the pull of gravity and keep them hydrated at the same time.
The answer was to develop cell walls. Early land plants, such as mosses don't have these supportive tissues so they grow low to the ground. Ferns have a primitive type of cell wall, so most species grow to less than 3 feet in height. Trees and flowering plants have the most developed cell wall structures.
Nutrient Transport System
Flowering plants can live almost anywhere because they have an internal system for transporting water and nutrients throughout their systems. Water plants absorb their nutrients directly from the surrounding waters. Land plants have developed a root system that pulls water and nutrients from the soil and draws both up and through the organism.
Plant parts became more specialised. The leaves would take carbon dioxide from the air and sunlight and with the help of the chemical chlorophyll make sugars to nourish the plants and starches to be stored for future use. Stems and branches not only provided support, but a vascular transport system both to and from the roots.
Flowering plants have a self-contained reproductive system. Most flowers contain male sex organs, the stamen, which hold pollen, and a female sex organ, the carpel, which hold the eggs. The flower's bright colours and sweet scents attract bees, birds and other insects. Bees, for example, visit flowers for nectar and honey. As they fly from flower to flower, some of the pollen caught on their hairy bodies gets transferred to the stigma, the female sex organ.
Fruit and Seeds
Once the pollen grains reach the eggs, the flower is fertilised and the ovary that surrounds the future seeds swells to provide a protective covering. Flowering plants that depend on animals to disperse their seeds form enticing fruits or nuts, like apples or walnuts. Some flowering plants that depend on wind dispersal develop light, airy seeds, such as the dandelion. Seeds also provide a protective covering and a source of nutrition for the new plant when it is time for the seed to germinate.
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