INTRODUCTION: Some organisms are living e.g. Bacteria, animals whereas some organisms are non-living. e.g. bricks ,stones. The main difference between the two is of ‘life’. Defining ‘life’ is difficult. Example of virus supports it. A virus doesn't have a life but when it is inside a cell, it becomes active and multiplies showing that it has life.
(1.1) ORGANISMS SHARE SOME BASIC AND UNIFIED CHARACTERISTICS :
Living organisms differ from each other in many aspects but they have many things in common like all are built up of cells, which have same structure and function. All have same basic characteristics governed by same physical laws like order, energy utilization, regulation, growth, development, reproduction etc.
Common feature of living organisms:
* Have fixed shape and size.
* Are highly organized. It is because of this organization that living being is called ‘organism’. Cell is the basic structure of organization and there are different levels of organization.
* All show metabolism i.e. series of biochemical reactions keep going inside cell. Reactions involving breakdown of compounds are ‘catabolic reactions. Reactions involving synthesis of compounds are ‘anabolic reactions’.
* Use energy for metabolism and growth.
* Show development and reproduce.
* Maintain constant body temperature (Homeostasis)
* Adapt to environmental changes.
* Gradually evolve into new species.
(1.2) ANALYSING THE LIVING THINGS :
All living organisms have organized structure. Lower organisms have simpler
Structure and higher organisms have complex structural level. Plants don’t have similar organization as that of animals.
Levels of Biological organization: Organization can be defined as the manner in which smaller units are arranged into larger ones and each level co-ordinates with each another.
In living organisms, lowest unit of organization is ‘Atom’. Atoms combine to from ‘Molecules’. Molecules undergo chemical reactions and form ‘organelles’ which are contained in a ‘Cell’. Organisms can have single cell (unicellular) or many cells (multicellular). Group of cells performing common function is ‘Tissues’. Many tissues combined together form ‘Organs’ (stomach, lungs). Many organs together, performing a specific function forms ‘Organ System’ (e.g. digestive system). Such living things with higher levels of organization are called ‘Individuals/ Organisms’. Group of individuals, which can interbreed sexually form ‘Species’. Group of organisms belonging to same species forms ‘Population’. Population of different species in an area is ‘Community’. Community with its abiotic (non-living) environment forms ‘Ecosystem’. All the ecosystems of world interact and form ‘Biosphere’.
Molecular organization: A shift in approach
In early days, when techniques were not advanced, the knowledge of living organism was based only on its morphology. But now, when scientists have advanced techniques, they study finer details of organism up to molecular level. Their observation tells-
-Basically, all living organisms are made up of similar atoms and molecules.
-Life is governed by same physical and chemical laws as seen in non-living things.
-There is interaction between living things of Biosphere and non-living things in land, water and air.
All living and non-living things are made up of matter. ‘Matter’ is something, which has, mass and occupies space. It is made up of atoms. Similar atoms form ‘Elements’. There are more than 100 elements in nature. 25 are essential to life. Six elements (C, H, O N, P, S) form 98% of the mass of living organism. Other elements are required in small amounts and are called ‘Trace Elements’ (K, Ca, Mg, I, Na). These are also very important e.g. Iodine is very important for normal functioning of Thyroid gland.
Chemical bonds:
Covalent Bond – Two or more atoms link together to form a molecule. The linkage is due to chemical bonds. When pair of valence electron is shared between two atoms, it forms covalent bond.
If single electron pair is shared – Single bond e.g. H-H
If two electron pair is shared - Double bond e.g. O=O
If many electron pair is shared - Multiple bond e.g. in CH2
Hydrogen Bond – when molecules show separate charges, these are called ‘Polar molecules’. e.g.H2O (water). It has two atoms of hydrogen and one atom of oxygen. H has positive charge and O has negative charge. In liquid water, negative oxygen atom of one water molecule is attracted to positive hydrogen atom of another water molecule. This force of attraction is called Hydrogen bond. It is a weak bond and has only 10% strength of a covalent bond. Weak H-bonds are very important in biological systems because:
--Contact between molecules remains brief.
--Molecules separate after interacting.
Importance of weak H- bonds can be explained by a situation- Transmission of chemical signals to molecules in brain. Molecules send signals to brain using weak bonds. After this, they separate (because of weak H-bonds). Receiving cells in brain receive signal and initiate reaction.
If, there is a strong covalent bond instead of weak H- bond, the receptor cells will keep responding for a long time even after the signal cells have stopped sending signals (because strong bond will not let them separate faster.)
Ionic Bonds: Ions are charged particles when atom gains/ looses electrons to attain stability. Ions with positive charge are called cations. Ions with negative charge are Anions. A bond formed due to attraction between these two oppositely charged ions is known as Ionic Bond.
e.g. in NaCl , Na atom has 11 electrons ( 2 in inner energy level, 8 in next level and 1 in outermost i.e. valence level). It is unstable because of unpaired outer electron. To become stable, it should loose this electron and then it becomes positively charged ion i.e. Na+.
Cl has 17 electrons (2 in inner energy level, 8 in next and 7 in outermost valence level). To become stable, it should gain 1 electron to make total of 8 electrons. In doing so, it becomes a negatively charged ion i.e. Cl‾ .Electro negativity of Cl atom is more (3.1) than Na atom (0.9), so electrons will be closer to Cl nucleus. Na donates electrons to Cl forming Na+ and Cl- ions, which link by ionic bond to form NaCl crystals.
Importance of NaCl: -
(i) It is given as saline drip to patients with low B.P. as it retains water in body.
(ii) Na+ and Cl- help in transportation of materials into cell membrane.
(iii) Na+ is important for conduction of nerve impulse.
(iv) NaCl maintains R.B.C.
(v) Cl- are important constituents of blood plasma.
Water is cradle of life- It is the only molecule existing as liquid at low temp.
Importance of H2O :-
* 70-80% of cells and 70% of human body is made up of water.
* Life originated in water and evolved in it for 3 billion years.
* It speeds up metabolic reactions.
* In most biochemical reactions, water is either substrate or product.
* It maintains turgidity of cells.
* It is a natural solvent for most nutrients. This can be explained by dissolving salt in water. H2O molecules form H-bond very fast. They gather around charged molecule (NaCl). The electrical attraction of H2O molecule breaks the forces/ bond between Na+ and Cl‾. Then it forms H-bonds around individual Na+ and Cl‾ ions, forming Hydration Shell around each so that they cannot reassociate.
Carbon :-
It is the main structural element of the cell. Source of C is inorganic CO2. Our atmosphere has only 0.003% of CO2. To take part in a chemical reaction, it should dissolve in water. All cells have film of water, which is enough to dissolve CO2 and form Carbonic acid.
Oxygen :- It is essential for life .Our atmosphere has 21% of oxygen.
Importance of oxygen:
* Most animals and plants need O2 to get energy.
* It accepts electrons.
* Efficiency of cell decreases in absence of O2 (are only 5% efficient of their normal efficiency)
* It is weakly soluble in water but for aquatic organisms, this small amount of O2 is enough.
Building Blocks of Life :- All the living organisms are made up of C, H ,O and N. These elements can group to form smaller molecules called ‘Micro molecules’.
Micro molecules can group further to form a bigger molecule called ‘Macromolecule’. Life depends on both the molecules.
e.g. Micro molecules – water , salt , sugar.
Macromolecules- Lipids, Proteins etc.
* Carbohydrates – These are compounds containing C, H & O in the ratio of 1: 2:1. These can be sub-divided into –
* Monosaccharides- (single sugars) these are simple sugars. e.g. Glucose
* Disaccharides- (double sugars) When two monosaccharides join by bonds, they form disaccharides. e.g. Sucrose, Lactose.
* Polysaccharides- when many monosaccharides join, they form polysaccharides. e.g. Starch, Cellulose. These molecules join by C-H or C=O bonds, which store a lot of energy. When these bonds break, energy is released. So these are ‘energy storage molecules.’
* Lipids – These are the esters of fatty acid and alcohol. Lipids:-
* Have –COOH group (carboxyl).
* Are hydrophobic i.e. insoluble in water.
* Are soluble in organic solvents like ether.
* Act as shock absorbers of the body.
* Provide insulation.
* Store a lot of energy.
* Form structural element of cell membrane e.g. phospholipids.
* Act as hormones e.g. Steroids.
* Constitute biological pigments. e.g. Chlorophyll.
* Act as local chemical messengers in the cell. e.g. Prostaglandin
* Proteins- is made up of amino acids, which have amino group (-NH2) and a carboxyl group (-COOH). There are 20 different amino acids which link by peptide bonds to form proteins.20 different amino acids can arrange in any sequence. Amino acids are also called ‘Peptides’, so when many peptides link together, we call it as ‘Polypeptide chain’ also. Proteins are formed of many polypeptide chains.
Proteins-
* Are structural and functional components of the cell.
* Collagen in bone cells is made up of proteins.
* Helps in muscle contraction. e.g. Actin, Myosin.
* All enzymes are proteins.
* Help in defense system of the body e.g. Antibodies which fight diseases are proteins.
* Act as oxygen transporters. e.g. Hemoglobin.
iv) Nucleic Acids – are also called as ‘Polynucleotides’. Many nucleotides join together by phosphodiester bonds. Each nucleotide contains-
(1.3) ENERGY TRANSFER DEVICES OF LIFE :
Energy is the capacity to do work and is essential requirement of all the organisms. All the activities like growth, transport etc. going on in the cell need energy. Cells cannot manufacture energy on their own but get it from outside. Then they transform (change) it into the form in which they need it.
e.g. .In Plants, they take solar energy and transform it into chemical energy for their activities.
E.g. In Animals, they take food from outside and break it down to release energy.
Energy Flow takes place through chemical reactions. In chemical reactions, electrons are transferred from one atom to another. Energy is captured in the electrons. When electron is lost, reaction is called ‘Oxidation’. When electron is gained, reaction is called ‘Reduction’.
Enthalpy: The total energy in the biological system is called ‘enthalpy’. It includes the usable energy as well as the unusable energy. Usable energy is used for performing work and unusable energy is lost to disorder.
Free Energy: The amount of usable energy, which can perform work at constant temperature and pressure, is called ‘Free energy’.
Activation Energy: The minimum amount of energy required to initiate a chemical reaction by destabilizing the bonds is called ‘Activation Energy’.
Spontaneous Reactions: Reactions, which occur on their own, release energy and perform work, are ‘Spontaneous reactions’.
Exergonic reactions: Reactions, which release energy and do not need energy from outside, are called ‘Exergonic Reactions’.
Endergonic Reactions: Reactions, which require energy from outside to start are termed as ‘Endergonic Reactions’.
Energy Flow: Chemical reactions are important for constant flow of energy. Energy can neither be created nor destroyed but can be changed from one form to another (energy transformation). All daily activities like running etc. involve energy transformation. This energy change is explained by LAWS OF THERMODYNAMICS.
First law of thermodynamics- The total amount of energy in the universe is constant. It can neither be created nor destroyed but can be changed from one form to another.
Explanations:-
a) In plants,
Second law of thermodynamics- For any process, physical or chemical to occur, there is increase in entropy (disorder) and decrease in free energy of the system.
Explanation: - This is because energy flows from higher energy area to lower energy area. During this, molecules collide, which increases disorder. When disorder increases, energy is lost in the form of heat, which cannot be restored.
Open System: Systems in which materials and energy are freely exchanged with the surroundings.
e.g. Living organisms. In living organisms, energy and materials are freely exchanged between cells and surroundings. If this will not happen, entropy will increase and organism will die.
Closed System : Systems in which materials and energy are not exchanged with the surroundings.
e.g. Non living materials like Thermos Flask.
In Thermos flask, exchange cannot take place with the surroundings. So energy remains same for a certain period of time (depending upon the efficiency of flask) and liquid remains warm.
(1.4) METABOLISM : All living things need continuous supply of energy and materials. Energy keeps flowing from one cell to another and from one organism to another. Metabolism can be defined as sum total of all the chemical reactions, which occur due to molecular interactions in a cell of an organism.
Enzymes – A catalyst is a substance that speeds up a chemical reaction but remains unchanged itself at the end of the reaction. Cells also require catalysts for specific reactions. These specialized catalysts are called as ‘Enzymes’. An organism has thousands of enzymes. Reactions in a cell occur in a sequence called ‘Biochemical pathway’. A particular enzyme acts on a particular substrate. Most enzymes are protein molecules with pockets on their surface. These pockets are called ‘Active Sites’ and a particular substrate binds here. Enzyme-Substrate complex is formed which forms products.
 
Regulation of Biochemical Pathways:
Anabolic reactions and catabolic reactions never occur simultaneously otherwise there would be chaos. Lot of energy and material would be wasted. Cells have regulatory system to control biochemical reactions. All biochemical reactions need enzymes, which bind to particular substrate. Activity of enzymes depends upon specific substances also which bind to it. A substance which binds and decreases its activity is called an ‘Inhibitor’. A substance which binds and increases the activity is called an ‘Activator’.
In a biochemical pathway, product of one reaction can serve as substrate for next reaction. So, enzymes selectively accelerate a reaction when necessary. The product itself becomes an inhibitor and stops enzyme activity. This regulatory mechanism is called ‘Feedback Mechanism’. (Enzymes have active sites where substrates attach& have ‘allosteric sites’ where an inhibitor attaches. this inhibitor then changes the shape of active sites and enzyme cannot bind to the substrate and the reaction stops.) So, regulation of biochemical reaction depends upon allosteric site of an enzyme.
Homeostasis :
Organisms need to maintain a constant internal condition so that biochemical reactions go on. They themselves regulate and adjust to the fluctuations in the external environment. So, such a self-regulated mechanism of maintaining a steady internal environment by an organism despite changes in external environment is called as ‘Homeostasis’.
e.g. Vigorous exercise raises the body temperature. Sweating brings it back to normal.
Thermoregulation:
Regulation of body heat by an organism is called Thermoregulation.
* Some animals like vertebrates and plants loose their thermal energy to the environment. Such animals are called ‘Ectothermic animals’. They are also called ‘Poikilothermous’ as they depend upon environment for its temp. regulation. If their environment is warm, their skin will be warm. If environment is cold, their skin will be cold.
* Some animals like mammals, birds, fish don’t loose but retain their thermal Energy for use. These animals have fats, feathers, furs, hairs etc. which act
as insulators. Such animals are called ‘Endothermic’. They are also called As ‘Homeothermous’ as their body temp. remains constant. If outside is very cold, their superficial vessels contract and warm blood stays in deeper vessels. If outside is very hot, the superficial vessels dilate and extra warmth of blood is lost by radiation.
Homeothermy in Humans:
Humans are endothermic and homeothermic. Their constant body temp. is 37 degrees Celsius. Our skin has two types of sensory neurons, which are sensitive to temp. outside. These are called ‘Thermoreceptors’and occur in skin and brain.
In brain- Receptors are present in hypothalamus. These monitor blood temp. and send message to brain whenever there is change in temperature.
How thermoregulation works: It can be explained with the help of example below:-
This is called negative feedback loop because temperature is regulated by negative reaction i.e. cooling of the body.
(1.6) GROWTH, DEVELOPMENT AND REPRODUCTION :
All organisms grow, develop and reproduce. Growth is the result of metabolic reactions. Energy transfer takes place. If rate of anabolism is more, growth occurs. If rate of catabolism is more, degrowth occurs. If anabolism is equal to catabolism, no growth occurs.
So, Growth is increase in mass/overall size of an organism.
Growth is a part of development.
Reproduction is the production of similar copies of an organism. It is necessary for continuation of life. Organisms reproduce sexually as well as asexually.
In sexual reproduction, there are sperms (male sex cells) and ova (female sex cells).
Asexual reproduction can occur by Binary fission, multiple fission, fragmentation etc.
(1.7) ADAPTATION:
It is the characteristic of an organism, which makes it better suited to its environment. When organism possesses inherited features, which increase its survival and ability to reproduce, they are best adapted. Adaptation can be structural, physiological and behavioral. These can be temporary or permanent.
E.g. (i) Narrow and elongated beak of Humming Bird: -
This helps the bird to suck flower nectar without sitting on them as there is
no place to sit.
(ii) Shapes of Orchids: -
Some orchids have shapes like female bees or female flies. So male flies/bees get attracted to it and try to copulate. In doing so, they transfer pollens from flower to flower.
iii) Night flowers are white to attract insects.
(1.8) DEATH :
Death is a permanent feature of all living organisms. A living organism is born as a young one, grows in size, becomes adult, reproduces its own kind. Undergoes ageing, grows old and ultimately dies.
Significance of death: -
i) It maintains balance in population thus avoiding overcrowding.
ii) It maintains biological cycle because when an organism dies, it increases organic matter. Decomposers attack organic matter, break complex organic matter into simpler forms which further transform into inorganic C, H, O, N, S, P by mineralization. These, then return to soil.
iii) Some dead cells or derivatives are important structures of body. e.g. nails, horns, hooves, claws etc. |
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