BACKGROUND:
Gymnosperms are the non-flowering seed
plants such as cedar, pine, redwood, hemlock, and firs. Gymnosperms are woody
plants that bear "naked seeds." They are called naked because their
seeds develop exposed on the upper surfaces of cone scales, such as in pine
cones. A pollen grain is carried by wind currents to the appropriate
"egg" where the growth of the pollen tubes through this tissue
brings the sperm to the egg. Gymnosperms are usually of large size with much
secondary growth, the leaves are usually evergreen needles or scales.
Angiosperms have flowers and bear seeds
enclosed in a protective covering called a fruit. Angiosperms are the dominant
types of plants today. Angiosperms are further divided into monocots and
dicots. Monocots have one seed leaf. Dicots have two seed leafs. There are at
least 250,000 species of angiosperms ranging from small flowers to enormous
wood trees. Pollination is accomplished by wind, insects, and other animals.
The male part is the pollen grain, and the female part is the ovary. The ovary
goes through meiosis to produce an "egg", which is them fertilized
by the "sperm" carried by the pollen. The sperm of the male part
travels down the pollen tube in the style. Two sperm enter the micropyle of
the ovary. After the process of mitosis, it turns into a seed with an embryo.
The seed may be inside a fruit.
PROCEDURE:
- Discuss how angiosperms and gymnosperms
reproduce. You may want to review the different parts of the plants.
- In angiosperms, the pistil is the female
reproductive structure found in flowers, and consists of the stigma, style,
and ovary. There are two parts to an angiosperm: a male part and a female
part. The male gametophyte consists of 2_3 cells contained within a pollen
grain; the female gametophyte consists of eight cells contained within an
ovule. The stamen is the male reproductive structure of a flower; usually
consisting of slender, thread_like filaments topped by anthers, which contain
the pollen.
- In gymnosperms the cone is the female
reproductive part and the pollen is the male reproductive part. Pine trees and
other gymnosperms produce two types of cones. The male cone is called the
pollen cone. The larger female cone is the seed cone. A single tree usually
produces both pollen and seed cones. Spore_producing structures are found on
the scales of cones.
- Give students flowers, fruits, seeds,
and cones. The kit contains seeds and cones, but you will have to get some
flowers and fruit. Have the students dissect the flowers and fruit so they can
see the different parts of the fruit. Have reference material available so
that students can identify the different parts easily or use the recommended
web site. You may want students to identify male and female species.
http://home.thezone.net/~gosse/asperm.html
Goes through the life history of
angiosperms and gymnosperms.
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