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.

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.

Alternation of Generations

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.

Mosses

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: 1.Spore producers (ferns) 2.Gymnosperms (“Naked Seeds” - Cones) 3.Angiosperms (Flowers & Seed in Fruit)

Spore Producing Vascular 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.

Ferns & Horsetails

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.

Gymnosperms

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.

Angiosperms

Flower Anatomy

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