A unicellular organism is an organism that consists of a single cell. This means all life processes, such as reproduction, feeding, digestion, and excretion, occur in one cell. Amoebas, bacteria, and plankton are just some types of unicellular organisms. All single-celled organisms contain everything they need to survive within their one cell. These cells are able to get energy from complex molecules, to move, and to sense their environment. The ability to perform these and other functions is part of their organization. Living things increase in size.

Human evolution is the lengthy process of change by which people originated from apelike ancestors. Scientific evidence shows that the physical and behavioral traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years. The earliest known life-forms on Earth are putative fossilized microorganisms, found in hydrothermal vent precipitates, that may have lived as early as 4.28 Gya, relatively soon after the oceans formed 4.41 Gya, and not long after the formation of the Earth 4.54 Gya.

Nucleotides are small complex molecules made of:
(1) Njicleotide : Each nucleotide consist of 3 units - a nitrogenous base, a pentose sugar and phosphate group.
(2) Nitrogenous base: Nitrogenous base are the purine (adenine or guanine) or pyrimidine (thymine, cytosine or uracil).
(3) The nucleotides are mono or di or triphosphates of nucleosides, e.g., Adenosine monophosphate (AMP), Adenosine diphosphate (ADP) and Adenosine triphosphate (ATP).
 

Since it is nearly impossible to study all the living organisms , it is necessary to devise some means to make this possible . so, on this basis modern classification  is  made up..  
and CLASSIFICATION -  classification is the process by which anything is grouped into convenient categories based on some easily observable characters.
For example , we can recognize groups such as plants or animals .

Lacuna is a Latin word derived from lacus meaning lake. Thus, in biology, it is a term pertaining to a small depression or cavity and supposedly containing a nucleate cell. In histology or anatomy, lacuna (plural: lacunae) refers to the small cavity in the substance of the bone containing an osteocyte. In histology, a lacuna is a small space containing an osteocyte in bone or chondrocyte in cartilage.

Alkaloids are nitrogenous compounds of low molecular weight. They are mainly produced by plants and animals for defense. Examples of alkaloids include morphine, codeine, coniine, quinine, scopolamine, hyoscamine, atropine, caffeine, sangunarine, berberine, etc.

Totipotency is the ability of living cells to form the whole organism unless and until they have become extremely specialized

Obligate intracellular parasite composed of: Nucleic acid - either DNA or RNA
Protein coat is present.
Single type of nucleic acid - DNA or RNA Protein coat, or capsid.
some have envelopes.
Multiply inside of living cells using the host cell machinery.
Direct the synthesis of structures to transfer viral nucleic acid to other cells.

Sexual Reproduction in Bacteria is usually carried out in three ways:

1. Transformation – In this process, the DNA from the capsulated bacteria is transferred into a non-capsulated bacteria.
2. Transduction – In this process, the DNA is transferred from one bacterial cell into another bacterial cell with the help of a bacteriophage. This process is known to occur in several bacterial species such as Escherichia, Micrococcus, Salmonella, etc.
3. Conjugation – It is a process in which the genetic material of a bacterial cell of a particular strain is transferred from a donor or male into that of another bacterial cell recipient or female of a different strain. The donor cells are known to possess a *** factor or F factor and the recipient cell does not have this factor and hence it is described as F- strain.

Viroids are different from viruses in the following ways:

• Its RNA does not code for protein
• It exists within the cells as RNA particles only with no envelope or capsid
• It possesses only one circular RNA strand comprising of very few nucleotides
• Contrary to viruses, viroids require no help of viruses to infect cells
• Contrary to viruses of which the RNA can be copied in the nucleus or cytoplasm, the RNA of viroids are copied in the nucleus only
• To detect the presence of viroids in the plant tissues, special techniques are used 

• Species represents the basic taxonomic category while the taxon represents any level of taxonomic category.
• Species is always monophyletic while a taxon may be monophyletic or polyphyletic.
• Species, being a rank, is an abstract term while a taxon represents a group of various living beings.

 In animals, metamerism is defined as a mesodermal event resulting in serial repetition of unit subdivisions of ectoderm and mesoderm products. Endoderm is not involved in metamerism. Segmentation is not the same concept as metamerism. Segmentation can be confined only to ectodermally derived tissue, e.g., in the Cestoda tapeworms. Metamerism is far more important biologically since it results in metameres, also called somites, that play a critical role in advanced locomotion.

Phylogenetic classification system is based on the evolutionary ancestry. It is based on the evolution of life and shows the genetic relationships among organisms. It generates trees called cladograms, which are groups of organisms that include an ancestor species and its descendants. Classifying organisms on the basis of descent from a common ancestor is called phylogenetic classification.

Taxonomy is the science of naming, describing and classifying organisms and includes all plants, animals and microorganisms of the world. axonomy is the science of naming, describing and classifying organisms and includes all plants, animals and microorganisms of the world. Using morphological, behavioural, genetic and biochemical observations, taxonomists identify, describe and arrange species into classifications, including those that are new to science. Taxonomy identifies and enumerates the components of biological diversity providing basic knowledge underpinning management and implementation of the Convention on Biological Diversity. Unfortunately, taxonomic knowledge is far from complete. In the past 250 years of research, taxonomists have named about 1.78 million species of animals, plants and micro-organisms, yet the total number of species is unknown and probably between 5 and 30 million.
 

Ganglia is a mass of nerve tissue or a group of nerve cell bodies. They are collections of nerve cells forming a nerve center, especially one located outside the brain or spinal cord. ganglia are given specific names which indicate their function or location, such as acoustic, cardiac, carotid, jugular, etc

Gas vacuoles are aggregates of hollow cylindrical structures called gas vesicles. They are located inside some bacteria. The inflation and deflation of the vesicles provides buoyancy, allowing the bacterium to float at a desired depth in the water.

• Homo sapiens– After Homo erectus came, the Homo sapiens who separated into two types:

1) Homo sapiens neanderthelensis

They had a brain size larger than modern man and were gigantic in size. Also, they had a large head and jaw and were very powerful and muscular . They were carnivores and the tools from the era indicate they were hunters. They were also cave dwellers but their caves were more comfortable and they lived in groups and hunted for food gathering.

2) Homo sapiens sapiens

Also known as ‘modern-day man’ is what we are today. Compared to the Homo sapiens neanderthelensis, they became smaller in size and the brain size reduced to 1300cc. There was also a reduction in the size of the jaw, rounding of the skull and chin. Cro- Magnon was the earliest of the Homo sapiens. They spread wider from to Europe, Australia, and the Americas. They were omnivores, had skilful hands, developed the power of thinking, producing art, more sophisticated tools and sentiments.

Algae are mainly classified on the basis of their pigments. Flagellation, storage products and chemistry of cell wall are also taken into account. The three classes of algae are Chlorophyceae (green algae), Phaeophyceae (brown algae) and Rhodophyceae (red algae).

1. Chlorophyceae: The members of Chlorophyceae are commonly called green algae. The pigments, chlorophyll-a, chlorophyll-b, carotene and xanthophyll are present in them. They are usually grass green in colour due to the dominance of pigments i.e.chlorophyll a and b.
2. Phaeophyceae: The members of Phaeophyceae are commonly called brown algae. Brown algae are found primarily in marine habitats. They possess the pigments chlorophyll a and c, carotenoids and xanthophylls.
3. Rhodophyceae: The members of Rhodophyceae are commonly called Red Algae. The pigments present in them are r-phycoerythrin, r-phycocyanin, chlorophyll-a and chlorophyll-d. The characteristic red colour is due to the predominance of the red pigment r-phycoerythrin.

Cytoskeleton is the network of protein filaments and microtubules in the cytoplasm that controls cell shape, maintains intracellular organization, and is involved in cell movement. Through a series of intercellular proteins, the cytoskeleton gives a cell its shape, offers support, and facilitates movement through three main components: microfilaments, intermediate filaments, and microtubules. 

Humans have 23 pairs of chromosomes. Out of these 23 pairs, 22 pairs are Autosomes and only one pair is the ‘*** Chromosome’, which actively takes part in the process of *** determination.