Chapter: LIFE PROCESSES (Part-I) | JKBOSE Class 10th Biology Notes | www.kashmirstudent.com
What are Life Processes?
Life Processes are those basic functions of living beings which are essential for their survival. They are the same in all types of living forms whether unicellular or multicellular, plants or animals.
1. Maintenance:- All living beings are made of protoplasmic structures. They have to be kept in functional state whether an organism is active or inactive. Functional state of protoplasmic structures is maintained only if they are kept in dynamic state with breakdown and build-up processes going on simultaneously.
2. Metabolism:- It is the sum total of all chemical reactions which occur in a living being due to interaction amongst its molecules. All functions of organisms are due to metabolism. Metabolism has two components, anabolism and catabolism. Anabolism or constructive metabolism consists of build-up reactions where complex molecules are formed from simpler ones, e.g., formation of glycogen from glucose or proteins from amino acids. Energy is required for anabolic reactions. Catabolism or destructive metabolism consists of breakdown reactions where complex substances are broken down into simpler substances, e.g., respiration (breaks glucose into carbon dioxide and water).
3. Nutrition:- It is required by all living beings for providing energy and body building materials. Body building materials are usually carbon based so that food sources are also carbon based. Plants manufacture their own food in the process of photosynthesis. Animals obtain food from outside. Food obtained from outside is first broken down into simpler soluble substances for absorption. Inside the cells, the simple substances are converted into various complex bio-chemicals to form components of protoplasm.
4. Respiration:- Every living being requires energy for working of body machinery, its maintenance, repair, replacement and biosynthesis. Energy is obtained by break down of carbon based molecules in the process of respiration. Oxidation-reduction reactions are common chemical reactions involved in respiratory break down of molecules. Most organisms use oxygen obtained from outside for the process of respiration.
5. Growth:- It is irreversible increase in body cells that occurs in young organisms prior to reaching maturity. Plants have the ability to continuously grow. Growth is possible if buildup reactions (Anabolism) are more abundant than break down reactions (Catabolic reactions). For this, the organisms must prepare or obtain food materials more than their requirement for maintenance.
6. Exchange of materials:- There is a regular exchange of materials between the living organisms and their environment. Living beings obtain nutrients, water and oxygen from their environment. They give out undigested materials, carbon dioxide and waste products. Single-celled organisms have the entire surface in direct contact with the environment. They do not possess any specific structures for intake and explosion of materials. Diffusion, facilitated transport and active transport are involved for movement of substances across the cell membrane.
In multicellular organisms specialized structures have been formed for different functions e.g., ingestion, egestion, exchange of gases.
7. Transportation:- In multicellular organisms, all the cells are not in direct contact with the environment. They have specific structures for exchange of gases, ingestion and digestion of food materials. However, every cell of the body has to be provided with food, water and oxygen. Similarly, carbon dioxide and wastes have to be taken away from every cell. Therefore, a mechanism of transportation is found. It is circulatory system in animals and vascular tissues in plants.
8. Excretion:- A number of waste products are formed as byproducts of metabolism. They are usually toxic and are removed from the body. The process of removal of waste products from the body is called excretion.
9. Irritability:- Every living organism is aware of its surroundings. It responds to changes in the environment.
NUTRITION:- may be defined as a collective phenomenon in which an organism is capable of capturing food essential not only for maintaining vital life processes, but also for repair and growth of tissues. The whole process of nutrition involves introduction of food, its digestion by various juices and enzymes and break down into smaller simpler and soluble molecules, absorption of the soluble food and lastly expulsion of undigested matter formed during the process.
MODES OF NUTRITION: - The nutrition of all the organisms may broadly be grouped into three categories, which are:-
a) Autotropic Nutrition Or Holophytic:- It is a mode of nutrition in which organisms are able to build up their own organic food from inorganic raw materials with the help of energy. The organisms performing Autotropic nutrition are called Autotrops, Auto meaning self and trophe meaning nourishment. Autotropic nutrition is a characteristic feature of all the green colored pigments called as chlorophyll. These plants have an ability to synthesize all the essential organic compounds. From inorganic compounds like CO2 and H2O in presence of sunlight with the help of a process called Photosynthesis. Some animals, that contain chlorophyll in their bodies also, show this property of synthesizing their own food material eg; Euglena and some green bacteria like sulphur and methane bacteria.
b) Heterotrophic Nutrition: - It is a mode of nutrition in which organisms obtain readymade organic food from outside source. The organisms that depend upon outside sources for obtaining organic nutrients are called heterotrophs, (hetero or heteros and trophe meaning nourishment). It is a characteristic feature of all animals and non green plants, that are unable to utilize carbon and synthesis organic compounds necessary for life, but depends upon organic sources of carbon. They are thus dependent upon autotropic organisms (Plants) and are called as heterotrophs. It is of the following types:-
1) Saprophytic Nutrition:- In this type of nutrition, an organism lives upon dead organic sources such as dead plants and dead animals. These usually secrete dissolving and digesting enzymes and absorb the liquified molecules so formed e.g.; yeast, bread moulds and dung moulds etc.
2) Parasitic Nutrition:- In this type of nutrition, an organism lives totally at the expense of others and derives its food material and shelter from the other .These organisms which derive food material are called parasites and the organism from which food is derived is called as host. This type of nutrition is termed as parasitic or holozoic nutrition .It is also known as parasite-host relationship e.g. Cuscuta, Ascaris etc.
3) Holozoic Nutrition:- It is a mode of heterotrophic nutrition which involves intake of solid pieces of food. Since solid food is taken in, Holozoic nutrition is also called ingestive nutrition. Holozoic nutrition (GK. Holo-Whole, Zoon-Animal) is found in animals and protozoan protists. The food may consist of another animal, plant or its parts. Depending upon the source of food, Holozoic organisms are of three types- Herbivores, Carnivores, Ominivores.
Steps in Holozoic Nutrition :-
There are five steps in Holozoic nutrition- ingestion, digestion, absorption, assimilation and egestion.
1. Ingestion (L. ingestus-taken in.):- It is taking in of solid food with the help of temporary or permanent mouth. Different animals use different organs for catching, holding and putting the food into mouth. Cutting and tearing the solid food into small pieces is common for ingestion.
2. Digestion:- The ingested food consists of complex insoluble organic substances. The conversion of complex insoluble food ingredients into simple absorbable form is called digestion. It is a catabolic process which occurs with the help of digestive enzymes.
3. Absorption:- The digestive food is absorbed from the digestive tract and transported to all body parts. It is picked up by all the living cells.
4. Assimilation:- Inside the living cells, the absorbed food materials are used in obtaining energy and formation of new components for repair and growth of cells. Assimilation is an anabolic process as it takes part in synthesis of proteins, polysaccharides, fats and other macromolecules.
5. Egestion:- (L.egestus-discharge) The whole of ingested food is seldom digested. The undigested components of food are thrown out of the body as faecal matter. The process is called egestion.
Digestion:- Digestion may be defined as hydrolysis of complex organic molecules with the help of enzymes into their simpler and diffusible component which can be absorbed in the gastrointestinal tract for further utilization. Thus it includes both mechanical and chemical breakdown of the ingested food material. It starts in the mouth and continues into small intestines.
TYPES OF Digestion
Digestion is of two types: - Intracellular and Extracellular
1) Intracellular Digestion: - In unicellular organisms like Amoeba the food is taken through its surface (Endocytosis) and the digests it within the cell. This type of digestion occurring with in the cell is known as Intracellular Digestion.
2) Extracellular or Intercellular Digestion:- In higher multicellular organisms the food is put into a cavity or canal called alimentary canal or digestive tract or Gut or GIT where food is digested and then absorbed into the blood to reach the different parts of the body for proper utilization. The undigested food if any is passed out of the body through the other end of the alimentary canal. This type of digestion (outside the cell) is known as Extracellular or Intercellular digestion.
DIGESTION IN MAN
Digestion of food material ingested by a man does not takes place in a particular region of the digestive tract or alimentary canal .It is completed in different parts which may be described as under:
1. Digestion of food in mouth:- (buccal cavity) In man the process of digestion starts in the mouth which prepares food material for the digestion. In mouth, the teeth start breaking down food by the process of mastication. During this process the food is thoroughly mixed with saliva secreted by the salivary glands .It contains large number of enzymes, of which salivary amylase (ptyalin) is of great importance, causing chemical digestion of starch .The masticated and partially digested food is then rounded off in a form of small ball called as bolus with the help of tongue and is passed through the esophagus or food pipe or gullet into the stomach by the peristaltic movements of the esophagus.
2. Digestion in stomach:- In the stomach, the partially digested food material is acted upon by gastric juice secreted by gastric glands, containing HCL, pepsin, rennin, and gastric lipase enzymes. The gastric juice is a composite secretion of at least three different types of cells - parietal cells, chief cells and mucous cells. The parietal cells secrete HCL, The chief cells supply pepsin and other enzymes like rennin etc. and the mucous cells secrete mucin in the stomach pepsin breaks down the proteins into smaller molecules known as peptidase. The process is aided by the addition of HCL, which not only activates the various enzymes but also turns the food into soup called chyme. This chyme passes into the duodenum for further action.
3. Digestion in small intestine:- In the anterior part of the small intestine called duodenum, the food (chyme) is mixed with the bile juices from liver, pancreatic juice from pancreas and intestinal juice from the intestinal glands. The combined effect of these juices causes the chief chemical changes of the intestinal digestion. These juices contain enzymes, which digest carbohydrates, proteins and fats of the food material. The broken food material is then diffused through the epithelial cells of the intestinal villi (finger like projections of the intestine) into the blood vessels which carries it to the cells.
4. Digestion in large intestine:- The process of the digestion does not take place in this region. It simply secrets mucus, which serves as a lubricant for easy passage of the undigested matter in the form of faeces. The intestinal walls also absorb water from the undigested food material passed into it which is ultimately egested through the anus.
Dental Caries: - It is localized softening and destruction of enamel and dentine of teeth forming cavities that reach the pulp. Dental caries is also called dental decay. It is caused by bacterium streptococcus mutans. It feeds on food particles especially sugars and produces acids. The acids are growing on food particles streptococcus mutans multiplies rapidly and forms a dental plaque. The plaque covers the teeth. Its bacteria secrete the acids that cause dental caries. Saliva which normally neutralises the acid and kills the bacteria is unable to protect the teeth because of the plaque. Brushing of teeth after meals removes the plaque. Bacteria are unable to multiply and produce acids. However, if plaque formation is allowed to persist, softening of enamel and dentine will allow the microorganisms to reach the pulp of the teeth. This results in inflammation and infection resulting in acute pain, total decay and falling of teeth.
Photosynthesis (Photos-Light, Synthesis-putting together)
Photosynthesis may be defined as an anabolic process in which green plants manufacture complex organic food substances (carbohydrate) from simple inorganic compounds like carbon dioxide and water in presence of sunlight with the aid of chlorophyll and evolve out oxygen as a byproduct of the process. Thus photosynthesis is a process in which radiant energy is converted into chemical energy.
In other words photosynthesis is a series of oxidation- reduction reaction in which C02 is reduced and H20 is oxidized to produce carbohydrates and oxygen.
Mechanism of Photosynthesis:- Photosynthesis is formation of organic food from carbon dioxide and water with the help of sunlight inside chlorophyll containing cells. Oxygen is produced as by-products.
Oxygen comes from water. Hydrogen of water is used to reduce carbon dioxide to form carbohydrate.
Actually, photosynthesis occurs in two steps, photochemical and biochemical.
1. Photochemical phase (Light or Hill Reaction)
The reactions of this phase are driven by light energy. They are of two steps- photolysis of water and formation of assimilatory power.
a. Photolysis of water:- Light energy splits up water into two components. The step requires an oxygen evolving complex (formerly called z-complex) having manganese ions. Calcium and chlorine are also required.
b. Formation of Assimilatory power:- Electrons released by photolysis of water are picked up by chlorophyll a molecules. On absorption of light energy, each chlorophyll a molecule throws out an electron with gain of energy. This is primary reaction of photosynthesis which converts light energy into chemical energy. Electrons travel along an electron transport system, releasing energy in the process. The energy is used in the formation of ATP (adeno sine triphosphate) from ADP and inorganic phosphate. Synthesis of ATP and ADP and inorganic phosphate (pi) with the help of light energy is called Phototophosphory lation.
ADP + Pi + energy ►ATP
The electrons ultimately activate NADP (nicotinamide di nucleotide phosophate) and makes it combine with hydrogen to form NADPH2.
Both ATP and NADPH2 together form assimilatory power.
2. Biosynthetic phase (Dark or Blackman's Reaction):- It is actually light independent reaction which can occur both in light as well as in dark. It requires the energy and reducing power contained in assimilatory power of light reaction. Common pathway of biosynthetic phase is calvin cycle. Carbon dioxide combines with ribulose biphosphate in the presence of enzyme ribulose biphosphate carboxylase or rubisco. It produces two molecules of phosphoglyceric acid (PGA). + 2 In the presence of ATP, phosphoglyceric acid is reduced by NADPH2 to form glyceraldehydes phosphate (GAP).
In the presence of ATP, phosphoglyceric acid is reduced by NADPH2 to form glyceraldehydes phosphate (GAP).
A part of glyceraldehydes phosphate is changed into dihydroxyacetone phosphate. The two condense and form glucose. Ribulose biphosphate is regenerated to combine with carbon dioxide again. Glucose undergoes condensation to form starch. To sum up, the dark phase of photosynthesis or calvin cycle comprises of three types of reactions: carboxylation, reduction and regeneration (of RuBP).
The below figure depicts the dark phase of photosynthesis also called Calvin cycle.
Raw material of the photosynthesis:-
The process of photosynthesis require various raw materials essential to synthesize energy complex compounds called carbohydrates.
These include
(1) Chlorophyll :- The chlorophyll or green pigment of the plant are the most active and important pigments of the photosynthesis. These are regarded as key pigments of the photosynthesis because of their remarkable ability of absorbing light energy, which is then converted into chemical energy during the process of photosynthesis. All the green plants contain chloroplasts, which give the coloring material and are accordingly called as photosynthetic- organelles of the plants.
(2) CO2:- All green plants utilize free atmospheric carbon dioxide during the process of photosynthesis to synthesis energy rich complex organic molecules called carbohydrates. These photosynthetic plants fix free atmospheric carbon dioxide during daytime when light energy is available to them. But during the night, the process stops.
(3) Water:- Water is another raw material for the process of photosynthesis. Plants absorb the required amount of water by root hairs and pass it on to the leaves through xylem, where it is utilized during the process of photosynthesis to synthesis energy organic compounds.
(4) Light:- The sunlight is a natural and prime source of energy for photosynthesis. It has been verified by experiments that the rate of photosynthesis remains highest in red light. Ordinary light consists of seven colors (VIBGYOR) and during photosynthesis; chlorophyll does not use all the seven colors. It absorbs mostly red and violet portions only. However, the green color reflects back which gives chlorophyll a greenish appearance.
Activities to demonstrate:-
1) Importance of Chlorophyll:- Take a variegated leaf of a garden plant that has been exposed to sunlight for few hours. Test it for starch with iodine test. Only green parts of the plant leaf will turn blue, showing Take a variegated leaf of a garden plant that has been exposed to sunlight for few hours. Test it for starch with iodine test. Only green parts of the plant leaf will turn blue, showing that chlorophyll is necessary for photosynthesis. that has been exposed to sunlight for few hours. Test it for starch with iodine test. Only green parts of the plant leaf will turn blue, showing that chlorophyll is necessary for photosynthesis.
2) Importance of Light:
Take a destarched potted plant, which has been kept in dark for 3 to 4 days. Cover one of its leaves completely with a carbon paper so that no light falls on it. Keep the plant in light for 4 to 6 hours. Test the covered leaf and uncovered leaf for starch with iodine test. The covered leaf will show negligible amount of starch, Take a destarched potted plant, which has been kept in dark for 3 to 4 days. Cover one of its leaves completely with a carbon paper so that no light falls on it. Keep the plant in light for 4 to 6 hours. Test the covered leaf and uncovered leaf for starch with iodine test. The covered leaf will show negligible amount of starch, while the uncovered leaf will give positive test for starch. The process clearly shows light is necessary for photosynthesis. while the uncovered leaf will give positive test for starch. The process while the uncovered leaf will give positive test for starch. The process clearly shows light is necessary for photosynthesis.
3) Necessity of Carbon dioxide:- Take two de starched potted plants and starched potted plants and cover them with transparent polythene bags, so that no fresh air enters cover them with transparent polythene bags, so that no fresh air enters into them. Keep NaoH (Soda lime) that would absorb Co and NaHCo (Sodium Bicover them with transparent polythene bags, so that no fresh air enters into them. Keep NaoH (Soda lime) that would absorb Co and NaHCo (Sodium Bi Co2 into them. Keep NaoH (Soda lime) that would absorb Co2 in one pot Carbonate) solution that would produce more both the pots in the sunlight for 4 to 6 hours in the other pot. Keep Carbonate) solution that would produce more in the other pot. Keep both the pots in the sunlight for 4 to 6 hours and test one leaf from each for starch. The leaf from the first Pot will and test one leaf from each for starch. The leaf from the first Pot will and test one leaf from each for starch. The leaf from the first Pot will show no starch due to the absence of Co2, while the leaf from the second pot will give positive test for the starch, thereby showing that Co2 is necessary for photosynthesis.
4) Evolution of oxygen:- Take a beaker filled with water . Add a pinch of baking soda (NaHC03) to it and put a Hydrilla plant (Aquatic plant) in it. Cover the plant with a funnel. Invert a test tube containing water over the stem of the funnel. Keep this apparatus in the bright sunlight. After some time bubbles start emerging out from the plant, which gets collected in the upper part of the test tube. Remove the test tube and test the gas with a lighted splinter, it keeps on glowing showing that the gas is a supporter of combustion. Thus, the experiment clearly shows that O2 is evolved during photosynthesis.
RESPIRATION
Respiration is a biochemical process of stepwise oxidative breakdown of organic compounds inside living cells releasing small packets of energy at various steps. Respiration is an essential physiological activity of all living organisms by which they obtains energy for carrying out various vital metabolic activities of the body. However, it is a chemical activity taking place within the protoplasm of a cell, which results in the liberation of energy. Energy liberated during oxidative breakdown of respiratory substrate is partly stored in ATP. The rest is dissipated as heat. The process of respiration involves the following steps.
1) External Respiration or Breathing:- It refers to those mechanism by which air is brought into the body from the atmosphere and expulsion of Co2 from the body into the atmosphere. The exchange of the gases takes place at the respiratory surface such as gills, tracheae or lungs.
2) Transport of Respiratory gases:- This phase involves transport of oxygen from respiratory surface to the body tissue_Co2 from the tissues to the respiratory surface. In higher animals it takes place mainly through blood.
3) Internal or Tissue Respiration:- This phase of respiration involves consumption of oxygen by the body cells and production of Co2 as a result of oxidative processes resulting in the liberation of energy necessary for the biological work of the body. The distinct phases of respiration are represented in the diagram.
Aerobic and Anaerobic Respiration:-
Sachs (1890) discovered that respiration can occur with or without oxygen. Therefore, there are two types of respiration, aerobic and anaerobic.
Aerobic Respiration (Gk. Aer-air, bios-life) It is a multistep complete oxidative breakdown of respiratory substrate into carbon dioxide and water with the help of oxygen acting as a terminal oxidant. Aerobic respiration is the usual mode of respiration in all higher organisms and most of the lower organisms. The reason is that it yields maximum amount of energy.
The energy is stored in some 38 molecules of ATP. Aerobic respiration occurs in two steps, glycolysis and Krebs cycle.
Glycolysis (Gk. Glykys- sugar, lysis-breakdown):- Glycolysis or EMP (Embden, Meyerhof and parnas) pathway is the first step of respiration which is common to both aerobic and anaerobic modes of respiration. It occurs in cytoplasm. Respiratory substrate is double phosphorylated before it undergoes lysis to produce 3-carbon compounds glyceraldehydes phosphate. NADH2 and ATP are produced when glyceraldehyde is changed to pyruvate. The net reaction of glycolysis is:
Krebs Cycle (Krebs, 1940):-
It is also known as citric acid cycle or tricarboxlic acid cycle (TCA cycle). Pyruvic acid or pyrovate enters mitochondria. It undergoes oxidative decarboxylation to produce acetyl CoA, carbon dioxide and NADH2. Acetyl CoA enters Krebs cycle. Here two decarboxylation, four dehydrogenations and one phosphorylation or ATP synthesis occur.
NADH2 and FADH2 liberate electrons and hydrogen ions. They are use in building up ATP molecules and activating oxygen molecules to combine with hydrogen for forming water. Water formed in respiration is called metabolic water. As oxygen is used at the end of Krebs cycle for combining with hydrogen, the process is called terminal oxidation. The overall equation of aerobic respiration using glucose as substrate is
Anaerobic Respiration (Gk. An-without, Aer-Air, BOIS- Life):- It is a multi step breakdown of respiratory substrate in which atleast one end product is organic and which does not employ oxygen as an oxidant. Anaerobic respiration occurs in many lower organisms, e.g. certain bacteria, yeast. In human body it occurs regularly in red blood cells and during heavy exercise in muscles (striated muscles). Anaerobic respiration occurs entirely in the cytoplasm. It has two steps. The first step is glycolysis. Here, respiratory substrate glucose breakdown into two molecules of pyruvate, ATP and NADH2. Pyruvate is converted into ethyl alchol (C2H50H) in yeast and certain bacteria. It is changed to lactic acid (CH3CHOH.COOH). In muscle cells when oxygen utilization is faster than its availability as during vigorous exercise. It creates an oxygen debt in the body. No such change occurs in blood corpuscels.
Mechanism of Respiration:-
There are different mechanisms for process of respiration in different form of organism. The mechanisms of respiration in some of organisms may be described as under:-
1. Respiration in simple organisms:- In the simplest forms of life like Amoeba, Euglena, Paramecium, Algae and Spirogyra, the respiratory gases may diffused in and out of the body through general body surface.
2. Respiration in Insects: - In insects, respiration of gases takes place through a system of internally air filled tubules called trachea. These opens into the exterior environment by paired apertures called as spiracles these tissues carry air directly into the tissues of the body and bring out carbon dioxide out from them.
3. Respiration in aquatic animals: - In majority of higher aquatic animals like prawns and fish, the process of respiration or gaseous exchange takes place by a special respiratory organ called as gills. The gills are made up of a large number of gill plates, which increase surface area of the gills. Each gill is provided with a large number of membranous gill lamellae the bold of gills absorb dissolved oxygen from water when it mover over them and carbon dioxide from blood goes out into the water i,e from the higher concentration of oxygen and carbon dioxide towards their lower concentration.
4. Respiration in plants: - In plants the gaseous exchange or respiration takes place through the stomata of the leaves, lenticels of woody stems and surface of the roots. The diffused air passes through the stomatal opening into the mesophyll cells of the leaves. Similarly air is diffused inn through the small microscopic openings in stem and roots of a plant and carbon dioxide is diffused out into the outer atmosphere or soil.
Mechanism of breathing in man: -
Human beings like other land animals breathe through their noses with the help of pair of lungs located in an airtight thoracic cavity. The lungs are spongy, air filled sac's, which do not have any muscle tissue and thus cannot expand or contract at their own. The process of breathing is accomplished through changes in volume and air pressure of the thoracic cavity. The lungs respond passively to the pressure changes within a chest cavity due to contraction and relaxation of muscles of ribs and movements of diaphragm during inspiration and expiration.
In normal breathing, air enters into the nasal chamber through nose, where it is cleaned and warmed by the ciliated epithelium. The warmed and cleaned air then passes into the windpipe or tracheae through larynx and epiglottis. The tracheae at its lower portion bifurcates into two bronchi, each entering into a lung lobe, where a bronchus divides extensively by giving out various small branches called bronchioles. Finally the air is deposited in microscopic air sacs called alveoli.
These are lined by a layer of epithelial cells and surrounded by a network of blood capillaries. The air in the lungs diffuses through the walls of these blood capillaries into the main blood stream and carbon dioxide in turn diffuses out into the lungs, where from it is expelled out into the external environment. This gaseous exchange is completed within a few seconds, while the blood is passed through the alveoli.
