Chapter 1: Life Processes

Introduction

All living organisms around us show certain fundamental features of life. The living things consist of plants, animals and microorganisms. When the animals breathe, we know that they are alive. Similarly, living plants show certain types of movements. These movements are either growth related or not.

However, some animals can breathe without visible movement. Similarly, the plant that is not visibly growing is still alive. So visible movement may not be the characteristic of life. The invisible movement of molecules of cells are another feature of life. But viruses do not show any types of molecular movement.

Living organisms have a well organized structure:

Smaller components → Cells → Tissue → Organ → Organ systems → Organism

Smaller components are the cell organelles. They are made up of different types of molecules. Due to some environmental factors, this organised and ordered nature of living things may change. These changes affect the survival of organisms. This necessitates a repairing and maintaining mechanism.

Characteristics of Living Things

• Living things have the ability of movement and locomotion.
• They carry out and control numerous chemical processes.
• They respond to changes in environment.
• They grow and reproduce.
• They use food as a source of energy and material for growth.

What are Life Processes?

The processes which together perform the maintenance of body activities are called as life processes. It includes nutrition, respiration, circulation, excretion etc. Such processes are simple in case of unicellular animals but as we move to complex body forms, the processes too become complex. In higher forms, the functions are more specialized.

Nutrition

The maintenance of life processes requires energy to prevent the damage and breakdown. The organisms obtain energy from the external environment in the form of food. The process by which organisms obtain their food from the environment and utilize it for their life processes is called as nutrition. Life on earth depends on organic molecules or food.

Carbon containing molecules are called as organic molecules. Organic molecules in food are carbohydrates, proteins, fats, vitamins and nucleic acids.

Respiration

The source of energy from the external environment can be converted into a uniform source of energy inside the living thing. This energy is used for various molecular movements. These molecular movements are necessary for maintaining life activities. Inside the body, the food undergoes oxidation and reduction reactions and release energy. Oxygen is necessary for these oxidizing reducing reactions in many organisms. The process of acquiring oxygen from outside the body, and to use it in the process of breakdown of food sources for cellular needs is called as respiration.

Circulation

In single celled organisms, the body is in direct contact with water. So nutrients, respiratory gases, wastes etc., are exchanged between body and water by diffusion. But in the case of multicellular organisms, all the cells may not be in direct contact with the surrounding environment. Thus simple diffusion will not meet the requirement of all the cells. But the body requires rapid supply of oxygen and nutrients and elimination of carbon dioxide and wastes. This situation creates a need for a transportation system. This transportation system is called circulatory system.

Excretion

The metabolic reactions of the body generate various harmful by-products. These waste by-products are needed to be eliminated from the body. The process of elimination of toxic waste materials from the body is called as excretion. The circulatory system transports waste away from cells to the excretory organs.

Organs concerned with excretion are called as excretory organs. E.g., Malpighian tubules in insects, kidneys in man.

Nutrition

We need materials from outside in order to grow, develop, synthesise proteins and other substances needed in body. We also derive energy from the food we take.

Some organisms use simple food materials obtained from inorganic sources in the form of carbon dioxide and water. Such organisms are known as autotrophs. E.g., green plants and some bacteria. Some organisms are unable to synthesise their own food. They depend directly or indirectly on autotrophs. Such organisms are called as heterotrophic organisms. E.g., Animals and Fungi.

Autotrophic Nutrition

Autotrophic organisms prepare their food by a process called photosynthesis. It is the process of conversion of carbon dioxide and water into carbohydrates in the presence of sunlight and chlorophyll. Carbohydrates are utilized for providing energy to the plant. The excess of it is stored in the form of starch. The excess energy derived from food is stored by animals in the form of glycogen.

The process of photosynthesis involves the following chemical reaction:

The reaction can be further explained as follows:

1. Chlorophyll absorbs light energy.
2. The light energy gets converted into chemical energy. The reaction is accompanied by splitting of water molecules to form hydrogen and oxygen.
3. Carbon dioxide is reduced to carbohydrates.

However, it is seen that in certain plants such as desert plants, this chemical reaction might not follow the same order. In case of desert plants, carbon dioxide is taken up at night and the plant prepares an intermediate substance. In the presence of sunlight i.e., during the day, this intermediate undergoes a change in the presence of solar energy absorbed by the chlorophyll.

Stomata

The plants obtain carbon dioxide through stomata. Stomata are tiny pores present on the surface of the leaves. In leaves gaseous exchange takes place through stomata. It is an important process for photosynthesis. Since large amounts of water can be lost through stomata, plant closes stomata when it does not need carbon dioxide for photosynthesis. The opening and closing of stomata are controlled by the guard cells.

The guard cells swell when water flows into them. This causes the opening of stomata. The shrinking of guard cells closes stomatal opening.

Nitrogen Fixation: The process of conversion of free atmospheric nitrogen into nitrogen compounds such as nitrates or nitrites is called as nitrogen fixation. Nitrogen fixation carried out with the help of microorganisms is known as biological nitrogen fixation. E.g: Rhizobium living in the root nodules of pea plant; Clostridium living freely in the soil.

Heterotrophic Nutrition

The mode of heterotrophic nutrition depends upon the type and availability of food material and the method by which it is obtained by the organism.

• Saprozoic Nutrition: Some organisms break down the food material outside the body and then absorb it. E.g., Fungi like bread moulds, yeast and mushrooms.
• Holozoic Nutrition: Some animals take in whole material and break it down inside the body. E.g., Paramecium, man etc.
• Parasitic Nutrition: Organisms derive nutrition from plants or animals without killing them. E.g., Cuscuta (amar-bel), orchids, ticks, lice, leeches and tape worms.

The parasites live on the body surface are called as ectoparasites. E.g., Leech, Cuscuta. The parasites live inside the body are called as endoparasites. E.g., Tapeworm, Ascaris etc.

Nutrition in Amoeba

Amoeba takes in food using temporary finger-like extensions of the cell surface. These finger-like projections are known as pseudopodia. The pseudopodia fuse over the food particle forming a food vacuole. Inside the food vacuole, complex food substances are broken down into simpler ones. They then diffuse into the cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out.

In Paramecium, the food is taken in at a specific spot. This is called as cytopharynx. Food is moved to this spot by the movement of cilia, which cover the whole body surface.

Nutrition in Human Beings

In man, the alimentary canal is a long and highly coiled tube extending from the mouth to the anus. The different parts of alimentary canal are mouth, buccal cavity or oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine and anus.

Digestion Process

Mouth: The oral cavity contains different types of teeth. They help in the crushing of food. The food is also wetted to make its passage smooth by the secretion of the salivary glands i.e., saliva. An enzyme salivary amylase which is present in the saliva breaks down starch into sugar.

Oesophagus: From the mouth, food is moved through oesophagus and enters the stomach. The lining of alimentary canal has muscles that contract rhythmically. This creates a wave like movement along the wall of alimentary canal. This movement is known as peristalsis.

Stomach: The stomach is a large muscular organ which expands when food enters it. The gastric juice is secreted by gastric glands. The gastric juice contains hydrochloric acid, pepsin and mucus.

• Hydrochloric acid: Provides an acidic medium for the action of pepsin.
• Pepsin: Digests proteins.
• Mucus: Protects the inner lining of the stomach from the action of acid under normal conditions.

The movement of food from the stomach to the small intestine is controlled by sphincter muscle.

Small Intestine: The small intestine is the longest part of the alimentary canal. It is the site of carbohydrate, protein and fat digestion.

• Liver: Secretes bile. Bile salts help in the emulsification of fats (breaking down large fat globules into smaller ones). This enhances the efficiency of enzyme action. Bile also makes the acidic food alkaline.
• Pancreas: Secretes pancreatic juice containing trypsin (for digesting proteins) and lipase (for emulsified fats).
• Intestinal Glands: Secrete intestinal juice. Enzymes finally convert proteins into amino acids, carbohydrates into glucose and fats into fatty acids and glycerol.

Absorption: The inner lining of small intestine has many finger like projections called villi. Villi increase the absorptive surface area. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body.

Large Intestine: The unabsorbed food is sent to the large intestine. Villi of large intestine absorb water from this food. The undigested and unabsorbed food is removed from the body through anus. The ejection process is regulated by anal sphincter.

Respiration

The food materials taken in during nutritive processes are used for the release of energy. Some organisms use oxygen to break-down glucose completely into carbon dioxide and water. Some others do not use oxygen. In these two cases, the first step is the break-down of glucose into pyruvate. Glucose is a six carbon molecule. Pyruvate is a three carbon molecule. This process takes place in the cytoplasm.

• In Yeast (Absence of Oxygen): Pyruvate is converted into ethanol and carbon dioxide. This process is called fermentation.
• In Mitochondria (Presence of Oxygen): Pyruvate is broken down using oxygen to give three molecules of carbon dioxide and water. This releases a lot of energy.
• In Muscle Cells (Lack of Oxygen): Pyruvate is converted into lactic acid (a three carbon molecule). The accumulation of lactic acid during sudden activity causes cramps.

Respiration in Animals

Terrestrial animals use oxygen in the atmosphere. Aquatic animals use \( O_2 \) dissolved in water. Since the amount of dissolved \( O_2 \) is fairly low compared to the amount of \( O_2 \) in air, the rate of breathing in aquatic organisms is much faster than that in terrestrial organisms.

Human Respiratory System: Atmospheric air is taken into the body through the nostrils. The air is filtered by minute hair and mucus. From the nasal passage, air passes through pharynx, trachea and reaches the lungs. Trachea is lined by tracheal rings of cartilages to prevent collapse.

Pharynx acts as a common pathway for both food and air. The opening of pharynx to trachea is called glottis. It is regulated by a cartilaginous flap called epiglottis.

Within the lungs, the bronchi divide into smaller tubes which finally terminate in balloon-like structures called alveoli. Gaseous exchange between air and blood takes place in the alveoli. The walls of alveoli are richly supplied with blood vessels.

Mechanism of Respiration:

• Inspiration: We lift our ribs and flatten our diaphragm. The chest cavity becomes larger, pressure decreases, and air is sucked into the lungs, filling the alveoli.
• Expiration: Ribs and diaphragm move to their original position. Air is pushed out.

The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body.

Respiratory Pigment: In man, the respiratory pigment is haemoglobin. It is present in red blood corpuscles. It has a high affinity for oxygen. \( CO_2 \) is more soluble in water than oxygen and is mostly transported in the dissolved form in our blood.

Transportation

Transportation in Human Beings

Blood transports food, oxygen and waste materials. Blood has a fluid medium called plasma. The \( O_2 \) is carried by red blood cells.

Our Pump—The Heart

The heart is a conical shaped muscular organ. It has different chambers to prevent the mixing of oxygenated and deoxygenated blood.

• Left Side: The left atrium receives oxygenated blood from the lungs. It relaxes while collecting blood, then contracts, pushing blood to the left ventricle. The left ventricle then contracts, pumping blood out to the body.
• Right Side: Deoxygenated blood from the body enters the right atrium. It contracts, pushing blood to the right ventricle, which pumps it to the lungs for oxygenation.

Valves prevent backward flow of blood.

Double Circulation: Blood goes through the heart twice during each cycle (once through the right side to lungs, and once through the left side to the body). This is known as double circulation. It is useful in animals with high energy needs (birds and mammals) to maintain body temperature.

Amphibians and reptiles have 3 chambered hearts (mixing of blood occurs). Fishes have 2 chambered hearts (single circulation).

Blood Vessels

Capillaries: Arteries divide into very small vessels called capillaries (one cell thick) to exchange material between blood and surrounding cells.

Blood Pressure: The pressure exerted by blood on the walls of blood vessels. Normal systolic pressure (contraction) is about 120 mm of Hg. Normal diastolic pressure (relaxation) is about 80 mm of Hg. Measured using a sphygmomanometer.

Lymph: A tissue fluid involved in transportation. It drains excess fluid from extracellular space back into the blood and carries digested fat from the intestine.

Transportation in Plants

Plants have two pathways for transportation:

• Xylem: Moves water and minerals from the soil.
• Phloem: Transports products of photosynthesis from leaves to other parts.

Transport of Water

Root cells in contact with soil actively take up ions, creating a concentration difference. Water moves into the root to eliminate this difference. This creates a steady movement of water into root xylem.

Transpiration: The loss of water in the form of vapour from the aerial parts of the plant. This evaporation creates a suction force (transpiration pull) which pulls water from xylem cells of roots. Transpiration helps in absorption and upward movement of water and minerals, and temperature regulation.

Transport of Food (Translocation)

The transport of soluble products of photosynthesis is called translocation. It occurs in phloem. Unlike water transport, translocation utilises energy. Sucrose is transferred into phloem tissue using energy from ATP. This increases osmotic pressure causing water to move into the tissue, pushing the material to tissues with less pressure.

Excretion

Metabolic activities generate toxic nitrogenous wastes which need to be eliminated.

Excretion in Human Beings

The excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.

Nephron: The structural and functional unit of the kidney. It consists of a cup-shaped end called Bowman’s capsule containing a cluster of capillaries called Glomerulus.

Urine Formation:

1. Filtration: Blood is filtered in the glomerulus.
2. Reabsorption: Useful substances like glucose, amino acids, salts and major amount of water are selectively reabsorbed as the urine flows along the tube.
3. Secretion: Substances like \( K^+ \), \( H^+ \) are secreted into the urine.

The urine formed enters the ureter and is stored in the urinary bladder until micturition.

Haemodialysis (Artificial Kidney): A device used to remove nitrogenous waste from the blood in case of kidney failure. It involves passing blood through cellophane tubes suspended in a dialysing fluid (which lacks nitrogenous wastes), allowing wastes to diffuse out.

Excretion in Plants

• Oxygen is released as a waste product of photosynthesis.
• Excess water is lost via transpiration.
• Waste products are stored in vacuoles or in leaves that fall off.
• Resins and gums are stored in old xylem.
• Plants excrete some waste substances into the soil around them.

Points to Remember

• Movement implies life; visible or invisible (molecular).
• Life processes include nutrition, respiration, circulation, and excretion.
• Autotrophic nutrition: Synthesis of food from \( CO_2 \) and \( H_2O \) using sunlight and chlorophyll.
• Heterotrophic nutrition: Dependence on other organisms (Saprozoic, Holozoic, Parasitic).
• Respiration: Breakdown of glucose to release energy (ATP). Aerobic (with \( O_2 \)) or Anaerobic (without \( O_2 \)).
• Transportation in Humans: Done by the circulatory system consisting of the heart, blood, and blood vessels.
• Transportation in Plants: Xylem transports water/minerals; Phloem transports food.
• Excretion: Removal of nitrogenous waste via nephrons in kidneys.