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The Plants. The Origin of Plants. Plants are believed to have originated on the Earth about half a billion years ago. They evolved from early algal ancestors and adapted to the wide variety of landforms, transforming the land into soil that would be suitable for its offspring.
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The Origin of Plants • Plants are believed to have originated on the Earth about half a billion years ago. • They evolved from early algal ancestors and adapted to the wide variety of landforms, transforming the land into soil that would be suitable for its offspring.
General Characteristics • Eukaryotic organisms. • Autotrophs – they carry out photosynthesis. • Cell wall made of cellulose. • Mostly terrestrial – land-dwelling. • Embryos are protected by tissues of the parent plant. (Like an apple.) • Lifecycles include an alternation of generations. This sees the cycling between a diploid and haploid form.
Alternation of Generations • The plants alternate between a diploid form and a haploid form – sometimes within the same structure. • The diploid form – called the sporophyte – produces haploid spores which are the reproductive cells of the plants. Sporophytes tend to be the plants that you see when you are walking around. • The spores will grow into plants called gamteophytes that will be haploid (like the spore). • The gametophytes will eventually produce gametes – sex cells – that will fuse and form a diploid zygote. This diploid zygote will become the next sporophyte.
Who Are These Plants? • Plants can be divided into four major divisions/phyla – the bryophytes, ferns, conifers and flowering plants. The Bryophytes • Bryophytes include mosses, liverworts and hornworts. • They do not have any vascular tissue so they are small and must live near the water. A wet environment is key to them. • To reproduce, bryophytes must release sperm cells into the water so they can swim to the female reproductive structures and fertilize the eggs. • Bryophytes are important because they form such substances as peat – which can be used as a fertilizer or fuel. The peat bogs are also huge storage areas for atmospheric carbon dioixde.
Vascular Plants • Vascular Plants are also known as tracheophytes. They have conducting tissues called xylem and phloem that carry water and food respectively. • The tracheophytes can be broken down into three groups: • Spore producers (ferns) • Gymnosperms (“Naked Seeds” - Cones) • Angiosperms (Flowers & Seed in Fruit)
Spore ProducingVascular Plants • These plants have vascular tissue and produce spores. • Ferns, club mosses and horsetails are prime examples. • These plants must grow close to water or where water gathers. Roots are not long and water is needed to reproduce. • Reproductive structures called sporangia produce spores – these small cases can be found on the underside of the ferns leaves. • Ferns are a food source for many forest creatures. They also look nice.
Gymnosperms • Gymnosperms are seed producing plants that produce a “naked” seed that is in the form of a cone. • The cones can be female seed cones or male pollen cones. The pollen grains are carried in the wind to he female cones. • Gymnosperms are large trees and are found pretty much everywhere. • They are important in that they are a major food source, provide shelter and look pretty at Christmas.
Angiosperms • Angiosperms are flowering plants with their seeds encased in a fruit. The fruit is actually the ripened ovary of the plant. • They are the most successful plants on Earth and dominate most habitats that plants are able to exist within. • Flowers are the sexual organs of angiopserms. Flowers can be either male or female but many of them contain both sexual organs. • Angiosperms also provide a major food source for living things as well as flowers. They may also be used for aesthetic purposes.
