Railway Science (Biology – Plant Kingdom) (Part-III)

In plants with a thallus, functions such as photosynthesis, reproduction, and nutrient absorption occur directly through the flattened, undifferentiated body.

Rhizoids are root-like structures found in some non-vascular plants, such as mosses, liverworts, and hornworts. In bryophytes, they are bulges growing from the lower epidermal cells. In the liverworts, they are absent or unicellular, but multicelled in mosses.

Permanent tissues are derived from meristematic tissue once. They lose the ability to divide. They are classified as simple and complex tissues. Xylem and phloem are examples of such complex tissues. They are both conducting tissues and constitute a vascular bundle.

Phototropism : Induced by light e.g. bending of stems towards light. Geotropism : Induced by gravity e.g. growth of roots towards gravity. Thigmotropism : Movement caused by contact e.g., twining stem and tendril and the drooping of leaves of sensitive plants by touch. Hydrotropism : Induced by water i.e., growth of roots towards source of water.

These are thin, hair-like structures that help anchor the bryophyte to the substrate, absorb water and nutrients, and facilitate gas exchange. They originate from the lower epidermal cells of the plant body.

Angiosperms are flowering plants. Structure of a Dicotyledonous Seed: The outermost covering of a seed is the seed coat. The seed coat has two layers, the Testa and the Tegmen. The Dicotyledonous plants have tap roots while Monocotyledonous plants have fibrous roots.

Parenchyma is the simple permanent tissue. It consists of relatively unspecialised cells with thin cell walls. They are living cells. This tissue stores food. Collenchyma - It provides flexibility in plants and mechanical support.
It allows bending of various parts of a plant like tendrils and stems of climbers without breaking. Sclerenchyma - It is the tissue which makes the plant hard and stiff. Example - Coconut husk.

Phototropism - The light induced growth response in plants. Negative phototropism - It refers to the growth or movement of a plant organ away from the light source.

Non-vascular plants are plants without a vascular system consisting of xylem and phloem. Instead, they may possess simpler tissues that have specialized functions for the internal transport of water. Example - Mosses.

Gymnosperms are commonly known as "exposed-seeded" plants. This term reflects the characteristic feature of gymnosperms where their seeds are not enclosed within a fruit or ovary. Instead, the seeds are typically borne naked or exposed on the surface of specialized reproductive structures, such as strobili.