Taxon is the basic unit of taxonomy. It is defined as a group of one or more populations of a living being which is seen by taxonomists to form an unit. A classic example is African elephants from the genus Loxodonta which is widely accepted as a taxon. Species is considered as basic taxonomic category because individuals of a species have same morphological features and they can also interbreed. This is the only taxonomic category which shows these two characteristics.

Characteristics of Bryophyta:

1. Bryophytes are small multicellular green land plants. These <a name="_Hlk41157034">simple land plants are confined to shady damp places. </a>
2. A true vascular system is absent in them.
3. The *** organs are multicellular.
4. An embryo is formed upon fertilisation.
5.  They are also called amphibians of the plant kingdom. Example: Riccia and Marchantia.

Earthworm mating occurs on the surface, most often at night. Earthworms are hermaphrodites; that is, they have both male and female sexual organs. The sexual organs are located in segments 9 to 15. Earthworms have one or two pairs of testes contained within sacs. The two or four pairs of seminal vesicles produce, store and release the sperm via the male pores. Ovaries and oviducts in segment 13 release eggs via female pores on segment 14, while sperm is expelled from segment 15. One or more pairs of spermathecae are present in segments 9 and 10 (depending on the species) which are internal sacs that receive and store sperm from the other worm during copulation. As a result, segment 15 of one worm exudes sperm into segments 9 and 10 with its storage vesicles of its mate. Some species use external spermatophores for sperm transfer.

Alternation of generations, also called metagenesis or heterogenesis, in biology, the alternation of a sexual phase and an asexual phase in the life cycle of an organism. The two phases, or generations, are often morphologically, and sometimes chromosomally, distinct. The fern is an example of alternation of generations, in which both a multicellular diploid organism and a multicellular haploid organism occur and give rise to the other. ... The large, leafy fern is the diploid organism. On the undersurface of its fronds or leaves, its cells undergo meiosis to create haploid cells.

Hypoxic hypoxia occurs when the <i>P</i>_O2 of arterial blood falls. This could occur because inspired <i>P</i>_O2 is lower than normal (high altitude) or it could be due to a respiratory problem (e.g., hypoventilation, diffusion impairment caused by pulmonary edema, ventilation–perfusion mismatch, or anatomic shunt of blood past the gas exchange region). In terms of O₂ transport, decreased arterial blood oxygenation (hypoxemia) is the primary limitation, and thus, the problem resides with the respiratory system. Oxygen delivery is abnormal since [O₂]_a is less than normal. The circulatory system responds in two ways to improve tissue oxygenation.

Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. ... In trees pith is generally present in young growth, but in the trunk and older branches the pith often gets replaced - in great part - by xylem. Because monocots have vascular bundles throughout their ground tissue, their stems do not have a discernible pith; the parenchyma cells in monocot stems are referred to simply as ground tissue.

Systematics is the science which deals with the diversity of organisms and their comparative and evolutionary relationships based on comparative anatomy, comparative biochemistry and physiology.

 Systematics helps in

1. Providing knowledge about the evolutionary tree of life

2. Identification of new organisms