Abal Writes

10/08/2021

Tracheophyte:

A vascular plant contains the conducting systems which consist of xylem for conveyance of water and phloem for conveyance of food such as sugar.
Supplement
Tracheophytes are commonly known as vascular plant that contains lignified and non-lignified tissues which includes the angiosperm, clubmosses, ferns, horsetails and gymnosperms. These kinds of plants have vascular tissues that able to grow in large size compare to the non-vascular plants wherein nutrients and water in the form of organic solutes distributed throughout the plant body by the xylem and the organic compound such as sugar produced during photosynthesis in leaves are disseminated by the phloem through sieve tube elements.
Tracheophytes growth starts from principal generation phase sporophytes which are typically diploid with two sets of chromosomes per cell compare to the generation phase of non-vascular plants which begin as gametophyte that are haploid with one set of chromosomes and only the spores, stalk and capsule are diploid.
Herbaceous tracheophytes are plants without wooded stem such as the yearly flowering plants petunias and other perennial ornamental plants like ferns, lavender or aster as well as fruits and vegetables like lettuce, strawberries and tomatoes.
Tracheophyte comprises 260,000 species including all the prominent flora of the Earth and believed to have originated from green algae wherein fossils have been discovered 400,000,000 years ago in

10/08/2021

Bryophytes

BRYOPHYTES

Bryophytes include various mosses and liverworts, commonly grow in moist shaded areas in the hills.

Bryophytes are also called amphibians of the plant kingdom because these plants can live in soil but are dependent on water for s*xual reproduction.

Plant body is thallus-like and prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids.

They lack true roots, stem or leaves and may possess root-like, leaf-like or stem-like structures.

The main plant body of the bryophyte is haploid, produces gametes, and hence is called a gametophyte.

The male s*x organ is called antheridium, which produce biflagellate antherozoids and the female s*x organ called archegonium is flask-shaped, produces a single egg.

The antherozoids are released into water where they come in contact with archegonium and fuses with the egg to produce the zygote.

Zygotes produce a multicellular body called a sporophyte, which is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.

Some cells of the sporophyte undergo reduction division to produce haploid spores, which germinate to produce gametophyte.

The bryophytes are divided into

10/08/2021

Ascent of SAP:

The water after being absorbed by the roots is distributed to all parts of the plant (excess of which is lost through transpiration). In order to reach the topmost parts of the plant, the water has to move upward through the stem. This upward movement of water is called as Ascent of Sap.

Ascent of sap can be studied under the following two heads:

(A) Path of Ascent of Sap, and

(B) Mechanism of Ascent of Sap.

(A) Path of Ascent of Sap:

It is well established that the ascent of sap takes place through xylem.

It can be shown by the fol­lowing experiments:

(i) A leafy twig of balsam plant (it has semi- transparent stem) is cut under water (to avoid entry of air-bubbles through the cut end) and placed in a beaker containing water with some eosin (a dye) dissolved in it. After sometime coloured lines will be seen moving upward in the stem. If sections of stem are cut at this time, only the xylem elements will appear to be filled with coloured water.

10/08/2021

Bohr Atomic Model

A Danish physicist named Neil Bohr in 1913 proposed the Bohr atomic model. He modified the problems and limitations associated with Rutherford’s model of an atom. Earlier in Rutherford Model, Rutherford explained in an atom a nucleus is positively charged and is surrounded by electrons (negatively charged particles).

Learn about Rutherford’s Atomic Model here in detail.

The electrons move around in a predictable path called orbits. Bohr modified Rutherford’s model where he explained that electrons move around in fixed orbital shells. Furthermore, he explained that each orbital shell has fixed energy levels. Therefore, Rutherford basically explained a nucleus of an atom whereas Bohr took the model one step ahead. He explained about electrons and the different energy levels associated with it.

According to Bohr Atomic model, a small positively charged nucleus is surrounded by revolving negatively charged electrons in fixed orbits. He concluded that electron will have more energy if it is located away from the nucleus whereas the electrons will have less energy if it located near the nucleus.



Bohr’s Model of an Atom (Source Credit: Britannica)

Postulates of the Bohr Atomic Model

Electrons revolve around the nucleus in a fixed circular path termed “orbits” or “shells” or “energy level.”

The orbits are termed as “stationary orbit.”

Every circular orbit will have a certain amount of fixed energy and these circular orbits were termed orbital shells. The electrons will not radiate energy as long as they continue to revolve around the nucleus in the fixed orbital shells.

The different energy levels are denoted by integers such as n=1 or n=2 or n=3 and so on. These are called as quantum numbers. The range of quantum number may vary and begin from the lowest energy level (nucleus side n=1) to highest energy level. Learn the concept of an Atomic number here.

The different energy levels or orbits are represented in two ways such as 1, 2, 3, 4…

10/08/2021

Photorespiration
➢ Consumption of oxygen and release of carbon dioxide without production of energy
➢ Occurs commonly in wheat, rice, soybeans (C3 plants)
➢ Oxidation process
➢ Occurs during hot and dry days
➢ Occurs due to less concentration of carbon dioxide inside leaves
➢ Wasteful process, no ATP formation
➢ Reduces photosynthetic output
❖ Reaction
❖ RuBP+O2----------rubisco---------→PGA+Phosphoglycolate
❖ Phosphoglycolate-----------------→serine+CO2+0ATP

10/08/2021

Gaseous exchange in plants
➢ Respiration occurs constantly day and night in all cells
➢ Photosynthesis occurs only in daytime in chloroplast containing cells only
➢ In unicellular gas exchanged through diffusion
➢ Lower plants exchange gases through wet body surface
➢ In higher plants gas exchange through stomata
➢ Each stoma is formed by two modified epidermal bean shaped guard cells
➢ Guard cells bear chloroplast
➢ In Woody stems epidermis is replaced by closely packed cork cells that hamper the diffusion
➢ Woody stems have lenticels (loosely arranged cells having intercellular spaces)
Roots also exchange gases through root hairs and epidermal cells
➢ All living cells constantly respire
➢ But no transport system
➢ Transport of gases only by diffusion
➢ To facilitate transport plant tissues are permeated by air sacs

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