The Watson-Crick Model of DNA (1953) Deoxyribonucleic Acid (DNA) is a double-stranded, helical molecule. It consists of two sugar-phosphate backbones on the outside, held together by hydrogen bonds between pairs of nitrogenous bases on the inside.

Watson and Crick DNA Model
DNA stands for Deoxyribonucleic acid which is a molecule that contains the instructions an organism needs to develop, live and reproduce.
It is a type of nucleic acid and is one of the four major types of macromolecules that are known to be essential for all forms of life.

Mycorrhiza is a mutually beneficial or symbiotic association of fungi Avith roots of higher
plants. Orchids grow as epiphyte on plants, have their roots associated with fungi right from the seedling stage. Many orchids cannot survive without mycorrhizae associations. Many forest trees such as pines appear stunted if mycorrhizal associations are absent. In presence of these associations, these plants absorb 2-3 times more nitrogen, potassium and phosphorus compared to without them.

When you swallow food, it passes from your mouth down into your throat (pharynx). From there, the food moves down through a long tube (the esophagus) and into your stomach. This journey is made possible by a series of actions from the muscles in these areas. Dysphagia happens when there is a disruption in the swallowing process as food and liquids pass through your mouth, throat, and esophagus. 

The pharynx is also part of the system that brings air into your lungs. When you breathe, air enters your mouth and moves into the pharynx. The air then goes down into your main airway (trachea) and into your lungs. A flap of tissue called the epiglottis sits over the top of the trachea. This flap blocks food and drink from going down into the trachea when you swallow. But in some cases, food or drink can enter the trachea causing aspiration. It may go down as you swallow. Or it may come back up from the stomach. A person with dysphagia is much more likely to aspirate.

Dysphagia is more common in older adults. Stroke is a very common cause of both dysphagia and aspiration. About half of people who have had a stroke also have dysphagia. About half of people with dysphagia have aspiration. About one-third of these people will need treatment for pneumonia at some point.

 The functions of centrioles are:

• The main function of centriole is to help with cell division in animal cells.
• The centrioles also help in the formation of the spindle fibers that separate the chromosomes during cell division (mitosis).
• The second function of centrioles that we will focus on is celiogenesis. Celiogenesis is the formation of cilia and flagella on the surface of cells. Cilia and flagella help in the movement of cell.

The vegetable ghee may contain trans fat. Trans fats are said to cause serious health conditions.” In fact, since vegetable ghee is so high in trans fats, it is considered extremely harmful for people, especially those who live sedentary lifestyles. The higher concentration of the nutrients in the ghee is due to its higher concentration of fat. A 2013 study determined that ghee isn't as harmful to heart health as it may appear. Ghee has been blamed for heart disease in Asian Indians populations because of the high amounts of artery clogging saturated fat.

Characteristics of Phylum Chordata

1. (Noton; back and chorda; cord).
2. Kingdom: Animalia
3. Presence of a notochord
4. They are backboned animals (vertebrates),
5. Most of the living chordates are familiar vertebrate animals.
6. Presence of dorsal hollow nerve cord
7. Blood vascular system: Present, closed type
8. Ventral heart, hepatic portal system and RBC are present.
9. Germ layer: Triploblastic.
10. Symmetry: bilateral symmetry body.
11. Coelom: Present. Well developed
12. Presence of gill (pharyngeal) slits
13. Presence of post **** tail

Phylum Chordata is divided into four sub-phylum:

1. Hemichordata,
2. Urochordata,
3. Cephalochordata
4. vertebrata or Craniata

Factors affecting enzyme activity

Enzyme activity can be affected by a variety of factors, such as temperature, pH, and concentration.

Enzymes work best within specific temperature and pH ranges, and sub-optimal conditions can cause an enzyme to lose its ability to bind to a substrate.

• Temperature: Raising temperature generally speeds up a reaction, and lowering temperature slows down a reaction. However, extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working.

• pH: Each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Extreme pH values can cause enzymes to denature.

• Enzyme concentration: Increasing enzyme concentration will speed up the reaction, as long as there is substrate available to bind to. Once all of the substrate is bound, the reaction will no longer speed up, since there will be nothing for additional enzymes to bind to.

• Substrate concentration: Increasing substrate concentration also increases the rate of reaction to a certain point. Once all of the enzymes have bound, any substrate increase will have no effect on the rate of reaction, as the available enzymes will be saturated and working at their maximum rate.

Glycosidic Bond: Certain type of functional group which joins a sugar molecule to another group is called glycosidic bond. Another group may or may not be another carbohydrate.

Peptide Bond: A chemical bond formed between two molecules; when the carboxyl group of one molecule reacts with the amine group of another molecule; is called peptide bond (amide bond). A molecule of water is released during this reaction. This is a dehydration synthesis reaction and usually occurs between two amino acids. This is also known as a condensation reaction. The resulting CO – NH bond is called a peptide bond. The resulting molecule is called an amide. The four atom functional group – C (=O)NH – is called an amide group or a peptide group.

Phospho-diester Bond: A group of strong covalent bonds between a phosphate group and two other molecules over two ester bonds is called a phosphor-diester bond. Phosphodiester bonds make the backbone of the strands of DNA and hence are central to all life on Earth. In DNA and RNA, the phosphodiester bond is the linkage between the 3’ carbon atom of one sugar molecule and the 5’ carbon atom of another.

Nucleic acids

• Nucleic acids are long chain polymers of nucleotides; hence called Polynucleotides
• They are found inside nucleus, hence called Nucleic acids
• 2 types of nucleic acids:
• DNA
  • Deoxyribonucleic Acid
  • Specify order of amino acids in a polypeptide
  • Store genetic information, has capacity to duplicate
  • Double-stranded structure                                                           
• RNA
  • Ribonucleic acid
  • Helps in Polypeptide synthesis
  • Convey genetic information, cannot self replicate
  • Single stranded structure

Polysaccharides

• Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages.
• These are the most commonly encountered carbohydrates in nature.
• They mainly act as the food storage or structural materials.
• Some examples of polysaccharides are:
  • Starch
  • Cellulose
  • Glycogen

Proteins are complex biomolecules that are made up of smaller units known as amino acids. 

Due to different rearrangement of amino acids, the structure of proteins divides into four types:

• Primary- the covalent linkages of the proteins
• Secondary- the linear peptide chains fold either into an alpha-helical structure(coiled) or a beta-pleated structure(sheets) which contain hydrogen bonds.

• Tertiary- The arrangement and interconnection of proteins into specific loops and bends forms the tertiary structures. This structure contains hydrogen, ionic and disulfide bonds.
• Quarternary- this structure is proteins containing more than one peptide chain.

Primary Metabolites

These are the chemical compounds produced during the growth and development, processes. They are also involved in the primary metabolic processes of respiration and photosynthesis. The primary metabolites are formed in the growth phase. They maintain the physiological functions of the body and are known as central metabolites. They are the intermediate products of anabolic metabolism, which are used by the cells for the formation of essential macromolecules.

Secondary Metabolites

These compounds are produced by the organisms that are not required for primary metabolic processes. However, they can be important ecologically or otherwise. Secondary metabolites are considered to be the end products of primary metabolites because they are derived by the pathways in which the primary metabolites involve.

For eg., antibiotics, toxins, pheromones, enzyme inhibitors, etc. Streptomycetes and related actinomycetes are the sources of novel secondary metabolites.

• A nucleotide is an organic molecule with a basic composition of a nitrogenous base, pentose sugar and phosphate.
• DNA and RNA are polynucleotides, which contain a chain of nucleotides monomers with different nitrogenous bases.
• Nucleotides are essential for carrying out metabolic and physiological activities.
• ATP (Adenosine triphosphate) acts as the energy currency of cells. Nucleotides form various coenzymes and cofactors, such as NAD, NADP, FAD, coenzyme A, etc. and are essential for many metabolic processes.

Lipids

• Lipids are Heterogeneous organic compounds. They contain Carbon, hydrogen, less amount of oxygen, phosphorus, nitrogen, sulphur
• These are Water insoluble; therefore they form part of membranes that divide water components in the body
• Lipids perform the following functions:
  • Energy storage in the form of Oils & fats
  • Structural roles in Cell membrane
  • Messenger (steroid hormones)
  • Constituents of Plants pigments chlorophyll, carotene etc, Wax, rubber, Vitamins A, E, K
  • Fat acts as an insulator that conserves body heat in animals
  • Fat underneath the skin also act as shock absorber

Amino acids are normal components of cell proteins (called amino acid). They are 20 in number specified in genetic code and universal in viruses, prokaryotes and eukaryotes. Otherwise amino acids may be termed rare amino acids, which take part in protein synthesis e.g. hydroxyproline and non- protein amino acids do not take part in protein synthesis e.g. Ornithin, citrullin, gama-aminobutyric acid (GABA) a neurotransmitter, etc.

Chemical Composition Tests Available:

1. Chromatography. Gas Chromatography. Ion Chromatography. Liquid Chromatography.
2. Mass Spectroscopy. GC Mass Spectroscopy (GC-MS) Inductively Coupled Plasma (ICP-MS)
3. Spectroscopy. FTIR (Solution & Pellet) X-Ray - EDS & XRF Analysis. Inductively Coupled Plasma (ICP-AES)

One has to perform a chemical analysis in order to find the type of organic compounds are found in living organisms. We can take any living tissue (a vegetable or a piece of liver, etc.) and grind it in trichloroacetic acid (Cl3CCOOH) using a mortar and a pestle. We obtain a thick slurry.

A person lying in comma neither responds to environmental stimuli nor has self-consciousness. He/she is supported by machines to carry out the vital life processes and he/she is brain-dead. Some of these patients never come back to normal life. Such persons can neither be considered as living nor non-living.

A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden. A pteridophyte is a vascular plant that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden. Ferns, horsetails, and lycophytes are all pteridophytes.

The single-celled prokaryotic microorganisms with various range of characteristics are called Eubacteria or true bacteria. These types of microorganisms are found in almost all conditions. They do not consist of membrane nuclei. The cell wall of Eubacteria is made up of peptidoglycans in a cross-linked chain pattern.

Three importance of classification are: 

1. It helps in the identification of living organisms as well as in understanding the diversity of living organisms. 
2. To understand and study the features, similarities and differences between different living organisms and how they are grouped under different categories. 
3. It is essential to understand the inter-relationships among the different groups of organisms.