Grade 11 Botany Note

Introduction To Biology (Biomolecules)

1. Life component (biochemical important molecule)

Those chemical components required for cellular activities. Those molecules can be organic or inorganic.

(A) Organic compounds:

A chemical compound containing carbon is called organic compound. Carbon, hydrogen, oxygen and nitrogen are joining in the various combinations to form several organic compounds. The organic compounds are macromolecules and micromolecules.

Micromolecules: those molecule having low molecular weight and simple in structure are called micromolecule. For e.g. monosaccharides, fatty acids, lipids etc.

Macromolecules: those molecule having higher molecular weight and complex in structure is called macromolecules..For e.g. polysaccharides, nucleic acid etc.

     a. Carbohydrates

Carbon hydrogen and oxygen is the main constituent of the carbohydrates. Where hydrogen and oxygen are present in the ratio of 2:1 as in water. Carbohydrate divides in 3 types.

i) Monosaccharides: it is the simplest form of the carbohydrate. The general formula is CnH2nOn. For e.g. glucose, fructose etc. they are soluble in water and usually sweet in taste.

ii) Disaccharides:Disaccharides are formed by two molecules of the monosaccharides. For e.g. maltose, sucrose, lactose. They are also soluble in water and sweet in taste.

iii) Polysaccharides

Polysaccharides are formed by the large number of monosaccharides and having several million molecular weights. They are insoluble in water and not sweet in taste. The common polysaccharides are starch, glycogen and cellulose. Starch is the reserved food material in plant.


b.  Proteins

Proteins are the macromolecules of amino acids. The amino acids are the building blocks of protein. Several amino acids join together by the peptide bond to form a proteins hence the protein is also known as poly peptides. Protein found in every part of the body. It mainly found in skin, muscles, and in glands. Proteins can be classified into three types. They are

i) Simple protein: Proteins formed by amino acids only, e.g. albumin

ii) Conjugate protein: Protein which contain amino group as well as some prosthetic group in addition, e.g. hemoglobin.

iii) Derived proteins: Those proteins formed due to other unbiological activities. Such as denaturation. E.g. proteoses


      c. Amino acids

Amino acids are building blocks of proteins. They are micromolecule having carbon, hydrogen and oxygen group. Each amino acid is a nitrogenous compound having an acidic carboxyl (-COOH) and a basic amino (-NH2)group. About 20 amino acids are occurring naturally. According to the body which synthesis amino acid it can be divided into two types, i.e. essential and non-essential.

      Essential protein

  Non-essential protein

1. These amino acids cannot besynthesized by our body.

2. These amino acids must be supply through diet.

3. These include Isoleucine, leucine, lysine, threonine, valine.

1. These amino acids can be synthesized by our body.

2. These amino acid are abundant in our body.

3. These include glutamic acid, aspartic acids, glycine, tyrosine, arginine, ornithine, taurine, histidine, serine, proline, asparagine, alanine


d. Lipids

The lipids are an important constituents of the diet because of their high energy value and also because of the fat soluble vitamins and the essential fatty acids found with the fat of the natural foodstuffs.

                        The lipids are a heterogeneous group of compound related to fatty acids and include fats, oils, waxes and other related substance. These are oily and greasy organic substance, relatively insoluble in water and soluble in organic solvents like ether, chloroform and benzene. Thus, they are hydrophobic in nature. They are classified into three types.

1. Simple lipids: these are ester of fatty acid with various alcohols.

a. Fats and oils: these are ester of fatty acid with a trihydroxy alcohol, glycerol. A fat is solid at ordinary room temperature whereas oil is liquid.

b. Waxes: these are esters of fatty acid with high molecular weight monohydroxy alcohols. 

2. Compound lipids: these are ester of fatty acids with alcohol and possess additional groups also. i.e.

Glycolipids: carbohydrate and lipid

Phospholipid: phosphoric acid and lipid

Lipoprotein: lipid and protein

3. Derived lipids: these are the substance derived from simple and compound lipids by hydrolysis. These includes fatty acids, alcohols, mono and di-saccharide etc. e.g. Cholesterol. 

Importance: It is a precursor molecule of many sex hormones like testosterone, progesterone etc. It is not bad but not useful as well.


Function of Lipids

1. They are found abundantly in seeds as reserve food.

2. They make insulating membrane beneath the skin.

3. The soap can be made by the lipids by hydrolysis.


    e. Nucleic Acids

    The nucleic acid is the molecular repositories for genetic information and are jointly referred to as the “molecules of heredity”. The structure of every protein, and ultimately of every cell constitute, is a product of information programmed into the nucleotide sequence of a cell’s nucleic acids. The nucleic acids have been the subject of biochemical investigation since 1869 when F. Miescher, a 25-year old Swiss chemist, isolated nuclei from pus cells.

 Living organisms contain two types of nucleic acids in the form of DNA and  RNA. These are long chain macromolecules of nucleotide with high molecular weight.

Deoxyribonucleic Acid (DNA): DNA is mainly found in the nucleus of eukaryotic cell, but also found in mitochondria  and chloroplast in little amount. It is formed by the end to end polymerization of a large number of repeated units called nucleotides. Those nucleotides are formed by i) deoxy-ribose sugar ii) Phosphate and iii) nitrogenous base.

i) Deoxy-ribose sugar: It is a pentose sugar having 5 carbon atoms. Due to the deoxyribose sugar it is called deoxyribose nucleic acid.

ii) Phosphate: the phosphate in the DNA is present as phosphoric acid (H3PO4).

iii) Nitrogenous Bases: the nitrogenous bases are of two types- Purine and pyrimidine. Purine bases comprise mainly adenine (A) and guanine (G) while pyrimidine bases comprise cytosine (C) and thymine (T).

Nucleoside: nitrogenous base + sugar

Nucleotide: nucleoside + phosphate


Watson and crick’s model of DNA

J.D. Watson and F. crick (1953) combined the physical and chemical bata generated by early work and purposed a double helix model for DNA molecule. This model is widely accepted. According to this model, the DNA molecule consists of two strands, which are connected together by hydrogen bonds and helically twisted. Each step on the one strand consists of a nucleotide of purine base which alternate with that of pyrimidine base. Thus, a strand of a DNA molecule is a polymer of four nucleotide i.e. A, G, T, C. the two strand join together to form double helix. Bases of two nucleotide form hydrogen bond i.e. A combines with T by two H-bond (A=T) and G combines with C by three hydrogen bond. However, the sequence of bonding is such that for every A.T.G.C. On one strand there would be T.A.C.G. on the other strand. Therefore, the two strands are complementary to each other. The two strands of double helix run in antiparallel direction, i.e. they have opposite polarity.

                     Fig: Structure of DNA (Watson and Crick Model)


The hydrogen bonds between the two strands are such that maintain a distance of 20A0. The double helix coils in right hand direction. The turning of double helix results in the formation of a deep and wide groove called major groove. The major groove is the site if bonding of specific protein. The distance between two strands forms a minor groove. The DNA model also suggested a copying mechanism of the genetic material. DNA replication is the fundamental and unique event underlying growth and reproduction in all living organism ranging from the smallest viruses to the most complex of all creatures including man. DNA replicates by semiconservative mechanism.


Structure of RNA: The RNA is usually single stranded except viruses such as TMV, yellow mosaic virus, reovirus etc. RNA is found both in the nucleus and in the cytoplasm. The single strand of the RNA is folded either at certain regions or entirely to form hairpin shaped structure. The RNA dose not possess equal purine-pyrimidine ratio, as is found in the DNA.

                                               Fig: Structure of RNA.

       Like DNA, the RNA is also the polymer of four nucleotides each one contains D-ribose, phosphoric acid and a nitrogenous base. The bases are two purines (A,G) and two pyrimidines (C,U). Thyamine is not found in RNA. Pairing between bases occurs as A-U and G-C.

If the RNA is involved in genetic mechanism, it is called genetic RNA as found in plant, animal, and bacterial viruses. The DNA acts as genetic material and RNA follows the order of DNA, In such cells the RNA dose not have genetic role. Therefore, it is called non-genetic RNA. The non- genetic RNA is of three types:

1. m-RNA(messenger RNA): it constitutes about 5% - 10% of the total RNA present in the cell, m-RNA  carries the genetic information from DNA for Protein synthesis.

2. r- RNA(Ribosomal RNA): It makes about 80% of the total RNA in the cell. It is the major component of ribosomal.

3. t RNA (Transfer RNA): it is also known as soluble RNA. It forms about 10% - 15% of the total RNA. It used to transfer amino acid molecule to the site of protein synthesis.

A nucleotide is made up of three molecules. These are

a) Pentose sugar: the pentose sugar is ribose.

b) Nitrogenous bases:  i) Purine = Adenine And Guanine ii) Pyrimidine=Cytosine And Uracil

c) Phosphoric Acid



Minerals are the inorganic substances that are essential for the growth and development of the living organism. Those minerals which are essential for the growth and survival of organism are called essential elements. Some minerals are required in high amount for the growth and are called macronutrient. The macronutrients are calcium, nitrogen, phosphorus, sodium, chlorine, magnesium and sulphur. Some minerals are required in small amount and they are called as micronutrient. The micronutrients are iron, copper, cobalt, zinc, manganese, molybdenum, fluorine, iodine and selenium.

 Water (H2O):

Water is the mother liquor of all forms of life. It is the vital essence, miracle of nature, and the great sustainer of life. The essentiality of water for living system is quite evident a without water, there is no life. In human adult total body water accounts for about 70% of the lean body mass. In plant it makes about 70%-90% of the living matter of active cells. In many hydrophytes and fruits, water appears in even high percentage. A greater portion of water is found in free form that means the water which is available for the metabolic process.

General properties of water:

1.Expansion on freezing: most substance decreases in volume and hence increases in density as their temperature decrease. But in case of water, there is a temperature at which its density exceeds that at higher or lower temperature. This temperature is 40C. In fact, water just above the freezing point is heavier than water at the freezing point. Which make easier to live those organism at the bottom of the lake.

2. Uniquely high surface tension: like a stretched membrane, the surface of a liquid tends to contract as much as possible. This phenomenon is called surface tension. Water has the highest surface tension of 72.8 of any known liquid. And it is reason why water rises to unusually high levels in narrow capillary tubes. This has great significance in physiology.

3.High solvent power:water is a solvent for a great number of molecule which form ionized solutions in water. It may, thus, be called a universal solvent which facilitates chemical reaction both outside of and within biological systems.

4. Uniquely high heat capacity: There occurs a smaller temperature rise in water as compared to most other substance, when a given amount of heat is applied. Thus, water acts as a temperature buffer. It maintains its temperature more successfully than most other substance. 

Function of water

i)Water is a universal solvent.

ii) It is used as a raw material in photosynthesis.

iii) It also helps in transpiration due to turgor pressure.

Iv) It also maintain the turgidity of cells and their organelles.

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