Brief Summary
The session introduces teridophytes, a category of plants with dominant leafy structures, and discusses their classification, characteristics, and life cycle. It covers the three types of leaves found in teridophytes: microphylls, megaphylls (or macrofills), and sporophylls. The lecture also explains the general characteristics of teridophytes, including their vascular tissue and reproduction through spore formation. The life cycle of teridophytes, involving alternation of generations between sporophyte and gametophyte phases, is explained in detail, along with the concepts of homospory and heterospory.
- Teridophytes are the first terrestrial plants with vascular tissue.
- They reproduce via spore formation, not seeds.
- The life cycle involves alternation of generations, with both sporophyte and gametophyte phases being photosynthetic.
Introduction to Teridophytes
The class is starting with a discussion on teridophytes, a plant category distinguished by its dominant leafy structures. Unlike algae and bryophytes, teridophytes are characterized by leaves as their most prominent feature. The instructor shows diagrams of various teridophytes, highlighting their leafy nature and noting that these plants are often used as ornamental plants in offices and gardens.
Types of Leaves in Teridophytes
Teridophytes have three types of leaves: microphylls, megaphylls (or macrofills), and sporophylls. Microphylls are small leaves, exemplified by Selaginella. Megaphylls are large leaves, commonly found in ferns. Sporophylls are reproductive leaves with small, brown structures called sporangia on their surface. Sporophylls are involved in reproduction, as teridophytes do not have flowers. Sporophylls come together to form cones or strobili, which are the reproductive structures of teridophytes. Sporangia within the sporophylls produce spores, which are essential for reproduction.
General Characteristics of Teridophytes
Teridophytes are more advanced than bryophytes and are the first terrestrial plants to possess vascular tissue (xylem and phloem). They are also known as vascular cryptogams because they are vascular and non-flowering. The dominant phase in their life cycle is the sporophyte, and they are typically found in cool, damp, shady places. Xylem in teridophytes lacks vessels. Reproduction in teridophytes occurs through spore formation inside sporangia, which are present on sporophylls within cones.
Life Cycle of Teridophytes
The life cycle of teridophytes involves alternation of generations, with both diploid (2n) sporophytic and haploid (n) gametophytic phases. The sporophyte, which is the main plant body, has sporophylls that produce spores. These spores germinate into a young gametophyte called prothallus. The prothallus has male (antheridium) and female (archegonium) sex organs, which produce male and female gametes, respectively. Water is required for fertilization, leading to the formation of a zygote, which develops into an embryo and then into a sporophyte. Both gametophytes and sporophytes are photosynthetic and independent of each other.
Homospory vs. Heterospory
Most teridophytes are homosporous, producing only one type of spore. However, some teridophytes, like Selaginella and Salvinia, are heterosporous, producing two types of spores: microspores (male) and megaspores (female). Heterospory is significant because it marks the beginning of seed evolution. While teridophytes do not have seeds, the development of heterospory is a crucial step in that evolutionary direction. Bryophytes are homosporous, while teridophytes can be either homosporous or heterosporous.
Examples and Identification of Teridophytes
The lecture provides examples of teridophytes, categorized under groups like psilopsida, lycopsida, sphenopsida, and teropsida. Examples include Selaginella, Psilotum, Lycopodium, Equisetum, Dryopteris, Pteris, and Adiantum. Teropsida is commonly known as ferns. Equisetum is also called walking fern. Diagrams from NCERT textbooks are shown to help identify these plants.
Assertion Reason Questions
The session includes assertion-reason questions to reinforce understanding. One question asserts that teridophytes are the first vascular plants, with the reason being their well-developed xylem and phloem. Another question addresses Selaginella's heterospory and spore morphology.
