Download Plant Reproduction - Field Natural History - Lecture Notes and more Study notes History in PDF only on Docsity! Field Natural History Plant Reproduction I. Introduction to haploid and diploid life stages. 1. The life cycle of all plants has two stages โ haploid and diploid. a. The diploid stage means that there are two sets of chromosomes. Abbreviated as 2n. b. The haploid stage means that there is only one set of chromosomes. Abbreviated as 1n. c. Eggs (1n) and sperm (1n) are often called gametes. When they join together (fertilization) the newly formed 2n cell is called a zygote. 2. Alternation of generations โ Sequential change in the life cycle of plants between the diploid and haploid stage. 3. Sporophyte - the diploid (2n) generation. a. The sporophyte generation eventually produces spores, which are haploid. 4. Gametophytes โ haploid individuals produced by germinating spores. a. The gametophyte produces haploid gametes, e.g. egg and sperm. b. The gametes fuse to form a diploid zygote โ the sporophyte. 5. The major trend in alternation of generations from primitive plants to the more advanced flowering plants is for plants to spend less time in the gametophyte generation and more time in the sporophyte generation. II. Alternation of Generations. A. Vascular plants with seeds. 1. The sporophyte is the form of plants that you are most familiar with. a. In plants, the growth of the zygote produces an embryo. Encased in what we call a seed. 2. The seed is a very important structure that permitted the successful colonization of land. a. The seed structure serves as a protective, drought-resistant enclosure for the embryo, enabling it to be dispersed to a new locality by wind, water or animals. 3. The pollen grain represents another important adaptation that allowed for the colonization of land by plants. a. The pollen encapsulates the male gametes in watertight packages that frees plants from the need to use water to transport the sperm to the egg for fertilization. B. Seedless, plants without vascular systems โ the mosses. 1. Although mosses live on land, they have never really freed themselves from their dependence upon an aquatic environment. There are 2 main reasons for this. a. Most of the mosses lack well-developed vascular tissue (phloem and xylem). b. They still have flagellated sperm cells which must swim to the eggs. 2. Basic structure of a moss. a. Typical moss is actually the gametophyte generation. b. It is haploid and it dominates the life cycle of mosses. c. The sporophyte is the stalk and capsule. 3. The gametophyte generation is nutritionally independent. a. The sporophyte is usually dependent upon the gametophyte. b. Reverse in flowering plants โ the sporophyte nutritionally independent. c. The gametophytes โ the pollen and egg , are produce by the sporophyte and dependent upon it! 4. The sperm of moss have two flagella. When released, they swim to the egg. a. They swim through a film of moisture provided by rain or a heavy dew. Docsity.com
