Railway Science (Biology – Plant Kingdom)

Excretion - The removal of the waste products of metabolism from living organisms. In plants, waste products are removed by diffusion. Plants excrete oxygen (a waste product of photosynthesis).
Waste products may be stored in vacuoles or may be stored in leaves which fall off. Waste products are also stored in resins and gums.
Resins and gums are stored in xylem which are harmless to trees. Plants also excrete some waste substances into the soil around them.

Sclerenchyma - Composed of dead cells, cell walls are uniformly thickened and are made up of complex polymer lignin, gives strength, rigidity, flexibility and elasticity to the plant body. This tissue is found in roots, veins of leaves and hard covering of seeds and nuts.
In the transverse section the cells are also polygonal with uniform thickening. Cell walls are very much thickened due to deposition of lignin leaving a narrow lumen. In the longitudinal section, the cells are long, narrow and pointed.

In a plant waste materials are often stored in old xylem in the form of gums and resins. Vacuole:- membrane-bound cell organelle. Intercellular space of tissues is usually filled with interstitial fluid. Xylem carries water and minerals from the roots to the leaves. Phloem carries the food prepared by the leaves to different parts of the plant.

Plants produce a wide variety of waste products as a result of their metabolic processes, such as cellular respiration, photosynthesis, and other reactions. Acacias tree - a diverse group of trees and shrubs with over 1,000 species. It grows in both deserts and tropical climates.
Plant parts like bark, stems, leaves, etc. store waste products like gums, oils, latex, resins, etc. and over time, plants are able to discard these components. Waste product of aerobic respiration in plant cells is Carbon dioxide and waste product of photosynthesis is Oxygen.

Plants respire through stomata in leaves, lenticels, and root hairs. Photosynthesis - It is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.

Xylem fibres (wood fibres) are non-living sclerenchyma cells which provide mechanical support to the plant. Xylem parenchyma are living cells with the cellulose cell wall that helps to distribute water and minerals throughout the plant. Xylem vessels are long, tube-like cells that are connected end-to-end to form long columns.
They are the most efficient water-conducting cells in plants. Xylem tracheids are elongated cells with tapering ends. They have thick, lignified walls, but they also have pits (pores) in their walls that allow water to flow from one cell to the next.

Plumule (a baby plant) is the embryonic shoot that gives rise to the shoot system. Radicle is the first to appear from the seed, followed by the plumule. Plumule grows on to become the shoot of the plant, into its stem and leaves. The radicle grows to become the root system. Plant Structure - Roots, Stems, Leaves, Flowers, Fruits and seeds.

Sieve tubes are long, the tube-like structure arranged longitudinally and are associated with companion cells and lack a nucleus. Companion cells are specialized parenchymatous cells that help in maintaining the pressure gradient in the sieve tube.
Phloem parenchyma is made of elongated, tapering cylindrical cells which have dense cytoplasm and nucleus. Phloem fibers are sclerenchymatous cells and are found in secondary phloem are elongated, unbranched and pointed needle-like.

Metabolism is the chemical reactions in the body's cells that change food into energy. Gum is extracted from larch wood chips. Use of gum - Cosmetics, pharmaceuticals, and foods. Xylem is used for transportation of water and Phloem for sugars and amino acids dissolved in water.

Chlamydomonas are motile and unicellular green algae found in both freshwater and seawater. In the life cycle of Chlamydomonas, both sexual and asexual reproduction has been observed. Asexual reproduction is by zoospores. Sexual reproduction is by formation of gametes.