LIFE PROCESS - NUTRITION
What is life process?
All the living organisms including human beings perform a number of activities such as nutrition, respiration, excretion, growth and reproduction. These activities are characteristics of living organisms, and through such activities they maintain their lives.
These maintenance functions of living organisms are known as life processes.
Chemical reactions which take place within cells or organisms during various vital activities are called biochemical reactions.Fig: Life processesMetabolism is a word used to describe the sum total of all the chemical and physical changes that are constantly taking place in living matter and are necessary for life. The word metabolite refers to a substance which undergoes various changes during metabolism. For example, carbon dioxide and water are metabolites used in the process of photosynthesis.
The metabolic pathways are of two types:
(i) Anabolic pathways or biosynthetic pathways in which biosynthesis of organic compounds occurs, or in other words, complex substances are synthesized from simpler ones ; for example photosynthesis.
(ii) Catabolic pathways in which the breakdown of complex organic substances into simpler ones occurs (as in respiration).
In anabolic pathways or processes of anabolism energy is used (endothermic reactions), while in catabolic pathways or catabolism, energy is released (exothermic reactions).
Criteria to define something is alive:-
1. Nutrition: The processes by which organisms obtain and utilise the nutrients (food).
2. Respiration: The process that involves breakdown of respiratory substrates through oxidation and release of usable energy.
3. Transport: The process in which the substances absorbed or synthesized in one part of the body is carried to other parts of the body.
4. Excretion: The process involved in removal of the excess or toxic wastes from the body.
5. Control and coordination: The process which helps the living organisms to receive information from the surroundings and behave accordingly in order to survive in the changing environment around them.
6. Growth and development: Permanent increase in the size of the organisms is called growth. The whole series of changes which an organism goes through during its life cycle, is called development.
7. Movement and Locomotion:
Movement is the temporary or permanent displacement of a body or its parts from its original position. Living beings and parts thereof move in response to stimulus from outside or from within the body.
Locomotion, on the other hand, is the displacement of the entire body from one place to another.
Nutrients are inorganic as well as organic substances which the organisms obtain from their surroundings in order to synthesize their body constituents and use them as a source of energy. The process of intake of nutrients and its utilization by an organism in various biological activities.
A process to transfer a source of energy from outside the body of the organism (food), to the inside is called nutrition. There are various types of nutrients on the basis of function they perform:-
e.g. Energy foods: Carbohydrates and fats.
Body building foods: Proteins and mineral salts.
Regulating foods: Vitamins and minerals.
Modes of nutrition: Method of obtaining food by the organism is called mode of nutrition. Fig: Modes of nutrition(A) Autotrophic (Holophytic) nutrition: The mode of nutrition in which the organisms prepare (or synthesize) their own organic food by using inorganic raw material (CO2 & H2O). They are also called autotrophs.
e.g. Plants, Photosynthetic and chemosynthetic bacteria and cyanobacteria etc.
(B) Heterotrophic nutrition: The mode of nutrition in which the organisms derive their nutrition from other organisms. They take ready made organic food from other dead or living plants or animals. The living organisms showing heterotrophic nutrition, are called heterotrophs.
e.g. All animals, fungi, many bacteria and some non-green plants (insectivorous plants) and man.
Types of heterotrophic nutrition:
Depending upon the mode of obtaining food, heterotrophic nutrition is of following types:
(i) Holozoic nutrition (Holo-Complete + Zoon-animal)
The mode of nutrition in which all animals take in complex solid food material is called holozoic nutrition.
It contains the following steps:
- Ingestion: Taking in complex organic food through mouth opening.
- Digestion: Change of complex food into simple diffusible form by the action of enzymes.
- Absorption: Passing of simple, soluble nutrients into blood or lymph.
- Assimilation: Utilization of absorbed food for various metabolic processes.
- Egestion: Expelling out the undigested food.
e.g. All animals including vertebrates and Invertebrates.
Depending upon the type of food habit, animals are divided into three categories:-
(a) Herbivores: Animals that depend upon green plants are known as herbivores.
e.g. Goat, Cow, Deer, Rabbit.
(b) Carnivores: Animals which eat flesh of other animals as food are called carnivores.
e.g. Lion, Tiger.
(c) Omnivores: Animals which eat both plants and animals as food are known as omnivores. e.g. Rat, Pigs, Crows, Cockroaches and Humans.
(ii) Saprotrophic (Sapro - Rotten; Trophos - Feeder) Nutrition: In this type of nutrition the organisms obtain their food from decaying organic substances. Organisms are also called saprotrophs. e.g. Bacteria, Fungi.
(iii) Parasitic nutrition (para-other):
The mode of nutrition in which one organism (called parasite) derives its food from other living organisms (Host) is called parasitic nutrition. e.g. Tapeworm, Ascaris, Plasmodium, Liver flukes, Cuscuta etc.
Differences between Autotrophic & Heterotrophic nutrition:
|Characters||Autotrophic Nutrition||Heterotrophic nutrition|
|(1) Source of Energy||Sunlight or chemical energy||Readymade food|
|(2) Mode of Nutrition||Photosynthesis or Chemosynthesis or animals||Feeding upon dead or living plants|
|(3)Occurrence||Found in green plants, Blue-green algae, certain Bacteria|
Found in Animals, fungi, Most of the bacteria
Differences between holozoic and saprotrophic nutrition:
|Feature||Holozoic nutrition||Saprotrophic nutrition|
|1. Nature of food||Solid food (Whole plant or animal or their parts) is ingested||Liquid food (Dead and decaying organic matter) is ingested|
|2. Site of digestion||Inside the body||Outside the body as enzymes are|
released on the food material, it converts solid food into simple soluble
|Examples||Most of the Animals||Fungi – Yeast, Slime molds, Bacteria.|
Animals which depend upon the blood of other animals known as sanguines. e.g. Bedbug, Mosquito, Leech etc.
Some organisms take in predigested food through their body wall by the process of diffusion. This process of nutrition is known as osmotrophic nutrition. e.g. Tapeworm, Trypanosoma.
(iv) Mutualistic nutrition: The mutualistic nutrition can be defined as the interdependent nutrition in which each organism is dependent mutually on the other.
e.g. The lichens share mutualistic nutrition between a fungus and an Algae.
Food- Amoeba is a holozoic and omnivorous animal. It feeds upon microscopic organisms like bacteria, Paramecium, Diatoms, Algae and dead organic matter.
Mechanisms: Nutrition in Amoeba involves the following steps:
(i) Ingestion: Amoeba has no mouth, so ingestion may occur at any point of body surface but generally it occurs at the advancing end of the body. Ingestion occurs with the help of pseudopodia. The opening of food cup gradually becomes narrower and narrower, and finally closes. So the food is finally enveloped and taken inside a food-vacuole (called phagosome) along with a drop of water.
(ii) Digestion: Amoeba shows intracellular and vacuolar digestion. In the cytoplasm, food vacuole fuses with lysosomes containing digestive enzymes. In this, the complex and non-diffusible nutrients are changed into simple and diffusible nutrients. Medium inside the food vacuole is first acidic but later becomes alkaline, (as in the alimentary canal of man).
(iii) Absorption and assimilation: In absorption, the diffusible nutrients pass through vacuolar membrane into the cytoplasm by diffusion and are then distributed to all the body parts by streaming movements of cytoplasm called cyclosis. Due to this, the size of food vacuole gradually decreases.
In the cytoplasm, a part of the absorbed food is oxidised to produce energy, most of simple nutrients are combined to synthesize complex compounds.
(iv) Egestion: Amoeba has no anus, so egestion may occur at any point on the body surface.
Nutrition in amoeba
1. Food: The substance which is palatable, delicious enough and energy provider is called food.
Chemically food consists of six essential components:-
(i) Carbohydrates (ii) Fats (iii) Proteins (iv) Minerals (v) Vitamins (vi) Water
2. Digestion: Digestion is a catabolic process, in which the complex, non-diffusable and larger components of the food are broken down into their respective simpler, diffusible and smaller form with the help of various hydrolytic enzymes in the alimentary canal of living organisms.
3. Intracellular and Extracellular Digestion:
Intracellular Digestion: This type of digestion occur inside the cell cytoplasm. The food inside the cell occurs as food vacuole. The digestive enzyme in this case is secreted inside the cell. They digest the contents of the food vacuole. So the entire process of digestion occurs inside the cell. e.g. Protozoans [Amoeba], Sponges.
Extracellular Digestion: It takes place outside the cell [i.e. in the intercellular space or a cavity formed by many cells or tissue]. In all animals this cavity is found as a large canal, called Alimentary canal.
4. Hydrolysis: It is a kind of catabolic reaction in which a compound is broken [lysis means break] down into smaller compounds, with the help [addition] of water [hydro = water].
5. Carbohydrates: These are the hydrates of carbon in which the ratio among carbon, hydrogen & oxygen is 1: 2: 1. Carbohydrates are the quickest source of energy.
On the basis of their composition, carbohydrates are of following types:
(a) Monosaccharides: The simplest sugars are called monosaccharides. These sugars cannot be further degraded to produce more sugars. e.g. Glucose, Fructose, Galactose, Ribose and Deoxyribose.
(b) Oligosaccharides: These are complex sugars, formed by the polymerisation of a few [1 to 10] units of monosaccharides.
Sucrose - Glucose + Fructose
Maltose - Glucose + Glucose
Lactose - Glucose + Galactose
(c) Polysaccharides: These are most complex carbohydrates, which are the polymers of thousand of units of monosaccharides. e.g. Starch Stored food in plants, Glycogen Stored food material in Animals.
Cellulose- Constituent of cell wall.
6. Fats: These are energy rich compounds. These are the esters of higher fatty acids. [Esters are formed by the addition of alcohol with acids] Glycerol is a type of alcohol.
7. Proteins: Proteins are the polymers of amino acids. Amino acids are held together by means of peptide bond to form polypeptide chains.
8. On the basis of gross size of food, the mechanism in different animals may be of two main types:-
(a) Microphagy- Feeding on microscopic organisms. e.g. Amoeba, Paramecium.
(b) Macrophagy- Feeding on larger forms of organisms. e.g. Majority of non-chordates and some chordates.
9. In Paramecium, ingestion is aided by beating of cilia. It has definite food passage, mouth (cytostome) and anus (cytopyge).
10. Food vacuole is commonly called temporary stomach or gastritis as it is the site of storage of food.
11. Most common mode of ingestion in Amoeba is circumvallation. In this, pseudopodia extend and form a cup-like structure, called food cup, around the prey.