Life Processes Note

 INTRODUCTION

Can visible movement be considered as the defining characteristic of life? If no,then why? Because besides running, chewing, shouting there are movements that are not visible like : ingestion, digestion, respiration, circulation, excretion and the movements of molecules; these movements are invisible to our naked eyes but are important for the life of living creatures as living creatures keep repairing and maintaining their structures.

So what are living creatures? Those organisms who can breathe, grow , acquire nutrition, produce offsprings and give response to stimuli are living creatures ;these are animals , plants and microorganism(except viruses; as viruses are not living until they infect other other cell).

Life processes

The processes that together maintains the functions of living organisms are known as life processes . For example; Nutrition , respiration , circulation , excretion ,etc.

In unicellular organisms ,single cells carry out these processes but in multicellular organisms, a well-developed organ system carry out these processes.

Nutrition

There are two main modes of nutrition.

1. Autotrophic mode of Nutrition: 

The utilisation of complex substances and broke down them to the simpler ones by the help of bio-catalysts called enzymes.

Example: Green Plants and some Bacteria

• Heterotrophic mode of Nutrition:

Obtainment of the energy from the plants and animals directly or indirectly by using them as food.

Example: Bacteria, Fungi and Animals .

These are of various types : Saprophytic,  Parasitic and Holozoic.

Autotrophic nutrition

The autotrophs performs the process called photosynthesis to acquire nutrition.

There are two types of autotrophs :

1. Photoautotrophs
2. Chemoautotrophs

The photoautotrophs uses the light energy to make their own food by the process called photosynthesis . eg; green plants and the chemoautotrophs uses the chemical energy to make their own food by the process called chemosynthesis. Eg; few bacteria .

Photosynthesis

The process by which autotrophs take in substances(carbon dioxide and water) from outside and convert them into stored forms of energy(carbohydrates) in the presence of sunlight and chlorophyll.

Plants need three elements:

1. Carbon dioxide
2. Water
3. Sunlight

Carbon dioxide is absorbed through small pores or holes called stomata in the leaves and water is absorbed by the roots and goes upto the stem towards the leaves

• These steps need not need not take place one after the other immediately . For e.g. desert plants take up carbon dioxide at night and prepare an immediate which is acted upon by the energy absorbed by the chlorophyll during the day

What is chlorophyll? where it is present? Chlorophyll is the pigment which is present in the green plants inside the cell organelles called chloroplasts ,in which photosynthesis occurs. They traps sunlight energy and convert it into chemical energy.

 

The leaves of green plants have parts like:

• leaf blade or lamina
• midrib and veins
• tissues like xylem(for water transport) and phloem(for food transport)
• epidermal tissue which contains: epidermal cells , stomata and the epidermal appendages.
• Ground tissue which contains chloroplast containing cells and is called mesophyll.

Stomata

Stomata are the structures present in the epidermis of leaves i.e; the surface of leaves. It regulates the process of transpiration and gaseous exchange. Each stoma is composed of two bean-shaped cells known as guard cells which encloses stomatal pore.

Exchange of carbon dioxide and oxygen occurs through the stomata . But it is also important to note that exchange of gases is also occurs in the stems and roots.

Guard Cells

Guard cells are shaped structures that posses chloroplasts and regulate the opening and closing of stomata. The outer walls of guard cells are thin and inner walls are highly thickened and elastic. The immediate cause of opening and closing of the stomata is a change in the turgidity of the guard cells. When water flows through them, turgidity increases within the two guard cells, thin outer walls bulge out causing the stomatal pore to open (a) . Reverse of this happens when water goes out of them due to shrinkage of the guard cells and the stomatal pore closes (b).

The food that is prepared in the photosynthesis is stored in the form of starch in the leaves .

(a)  this is the variegated leaf showing the starch areas, (b)  this is the leaf that has been tested by the iodine identifying (a)

Water used in photosynthesis is taken up from the soil by the roots in terrestrial plants.

Other materials like nitrogen phosphorus, iron, magnesium are taken up from the soil.

Nitrogen is an essential element used in the synthesis of proteins and other compounds. This is taken up in the form of inorganic nitrates or nitrites or as organic compound which have prepared by bacteria from atmospheric nitrogen , this process is known as Nitrogen Fixation.

Heterotrophic Nutrition

There are various types of heterotrophic nutrition such as :

1. Saprophytic:The organisms feed on dead and decaying matter,they digest the food externally before the nutrients absorbed.e.g; bacteria and fungi.
2. Parasitic:The organisms obtains nutrients from living organisms by living on or in the body of the host.e.g; fleas, lice and tapeworm.
3. Holozoic:HolozoicThe organisms feed by ingesting solid organic matter which is then digested and absorbed into their bodies.e.g; human, animals and insectivorous plants
4. Symbiotic:A mutually beneficial relationship between two different organisms for nutrition.

Note:

• Bread moulds , yeast and mushrooms are esaprophytes.
• Cuscutta(amerbel), orchids ,ticks , leeches and tapeworm are examples of parasites.
• Lichen is an example of symbiotic nutrition, as it is the relationship between the algae and the fungi.

 

Nutrition in amoeba

Amoeba is an unicellular organisms and exhibits holozoic type of nutrition, which takes in food using the finger like projections of the cell called pseudopodia which fuse over the food vacuole and the food is broken down inside the food vacuole and diffuse into cytoplasm.

Nutrition in paramecium

Like amoeba , paramecium is also an unicellular organisms and it also exhibits holozoic mode of nutrition, they have celia that helps them to engulf the food through a specific spot.

Nutrition in Human Beings

Nutrition in humans starts from the alimentary canal which is basically a long tube extending from the mouth to the anus. This tube has different parts which are specialized to perform various functions.

 

 

Mouth

• Food is crushed by the teeth and with the saliva , food particles becomes the bolus.
• The soft lining of the canal makes food wetted for smooth passage.
• Saliva secreted by our salivary glands when we eat something.
• the saliva is mainly produced by the three pairs of salivary glands; the parotids(cheeks)the submaxillary/submandibular (lower jaw) and the sublinguals (below the tongue)
• The enzymes present in the saliva broken down the complex food into simpler ones. Salivary amylase present in the saliva broke down starch into glucose, which is easily absorbed from the alimentary canal.
• The muscular tongue in the mouth helps in the mixing and movement of the food in the mouth.

Oesophagus

• From the mouth, the bolus is conveyed to the pharynx and then to the oesophagus (food pipe).
• The rhythemic peristaltic movements occur along the gut which helps in pushing the food forward.
• The gastro-oesophageal sphincter.

Stomach

• Stomach is a large organ which expands when food enters.
• The gastric glands that is released from the stomach wall helps in the digestion of the food. E.g ; mucus, HCl and pepsin.
• Mucus is released by the mucous cells. Mucous protects the inner lining of the stomach from the action of acid under normal conditions.
• HCl is hydrochloric acid and is released by parietal or oxyntic cells.
• Pepsin is released by the peptic or chief cells.
• The proenzyme pepsinogen of the peptic cells gets converted into active enzyme protein on exposure to the HCl.
• Rennin is a proteolytic enzyme found in the gastric juice of infants which helps in the digestion of milk proteins.
• The stomach can stores the food for 4-5 hours.
• The exit of the food from the stomach is regulated by a sphincter muscle which releases it in small intestine.

Small intestine

• This is the longest part of the alimentary canal.
• The length of the small intestine differs in various animals depending on the food they eat.
• Herbivores has longer length of small intestine than the carnivores. because meat is easier to digest than cellulose.
• The small intestine is the main site of complete digestion of carbohydrates , proteins and fats with the helps of secretions of liver and pancreas.
• The bile, pancreatic and intestinal juice are the secretions released into the small intestine.
• The bile juice and Pancreatic juice is released through the hepato-pancreatic duct.

Pancreatic juice

• Pancreatic juice contains inactive enzymes- trypsinogen, chymotrypsinogen, procarboxypeptidases, amylases, lipases and nucleases.
• Trypsinogen is activated by an enzyme, enterokinase, secreted by the intestinal mucosa into active trypsin, which in turn activates the other enzymes in the pancreatic juice.

Bile juice

• The bile juice helps in the emulsification of fats i.e; breaking down fats into small micelles.
• Bile also activates lipases.

Intestinal juice

• The intestinal juice is also known as succus entericus .
• This juice contains variety of enzymes like disaccharides, dipeptidases, lipases, nucleosidases, etc.
• The enzymes in the succus entericus act on the end products to the simple absorbable forms in the mucosal epithelial of the intestine.
• Proteins into amino acids.
• Carbohydrates into glucose.
• Fats into fatty acids and glycerol.

     The digested food is taken up by the walls of the intestine. The inner lining of the small intestine has numerous finger-like projections called villi which increases the surface area for absorption. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body where it is utilized for obtaining energy, building up new tissues and the repair of old tissues.

Large intestine

      The unabsorbed food is sent into the large intestine where more villi absorb water from this material. The rest of the material is recovered from the body via the anus. The exit of this waste material is regulated by anal sphincter.

Respiration

Respiration is the movement of oxygen from the outside environment to the cells within the tissues, and the removal of carbon dioxide in the opposite direction that’s to the environment.

There are two types of respiration :

1. Inorganic Respiration:  Breakdown of glucose in the absence of oxygen. It occurs in cytoplasm.
2. Organic Respiration:Breakdown of glucose in the absence of oxygen. It occurs in  mitochondria.

Inorganic respiration

• First step of respiration starts with broke-down of six-carbon molecule(glucose) into three-carbon molecule(pyruvate). This process takes place in the cytoplasm of the cells.
• Further the pyruvate is converted into ethanol and carbon dioxide. This process is takes place in yeast during fermentation.

Organic respiration

• Break down of pyruvate using oxygen takes place in the mitochondria.
• In this process , pyruvate molecule breaks up to give three molecules of carbon dioxide.
• The outer product is water.

The release of energy in this aerobic respiration is a lot greater than in the anaerobic respiration.

When there is a lack of oxygen in our muscle cells present , pyruvate converted into lactic acid which is also a three carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

The energy released during cellular respiration is immediately used to synthesize a molecule called ATP which is used to fuel all other activities in the cell. ATP is known as the energy currency of the cell.

Exchange of oxygen from the atmosphere with carbon dioxide produced by the cells is called breathing commonly known as respiration. Carbon dioxide and oxygen are exchanged by diffusion through stomata. They can go into cells , or away from them and out into the air.

The direction of diffusion depends upon the environment conditions and the requirements of the plants.

At night , when there is no photosynthesis occurring, carbon dioxide elimination is the major exchange activity and during the day , carbon dioxide generated during respiration is used up for photosynthesis, hence there is no carbon dioxide release.

Animals have evolved different organs for the uptake of oxygen from the environment and for getting rid of the carbon dioxide produced.

Respiration in animals:

• Terrestrial animalsUse the oxygen in the atmosphere for respiration. This oxygen is absorbed by different organs in different animals. The exchanged is take place within the body so there is a mechanism for moving the air in and out of this area where the oxygen is absorbed.
• Aquatic animalsAnimals  that live in water need to use oxygen dissolved in water. Since the amount of dissolved oxygen is fairly low compared to oxygen in air, the rate of breathing is faster as in aquatic animals as compared to terrestrial animals. Fishes take in water through their mouth and force past the gills wand oxygen is taken up by the blood.

 

 

 

 

Respiration in human beings

When we breathe air in, our ribs lifts up and diaphragm flattens as a result the chest cavity becomes larger. Because of this the air sucked inside the body and reach towards the alveoli. Reverse of this happens when the air goes out of the body. Ribs , diaphragm and chest cavity brings back to normal condition.

• In human beings, the air is taken into the body through the nostrils
• The air passing through the nostrils is filtered by fine hairs that line the passage.The passage is also lined with mucus which helps in this process.
• From here, the air passages through the throat and into the lungs. Rings of cartilage are present in the throat.these ensure that the passage does not collapse.
• Within the lungs, the passage divides into smaller and smaller tubes which finally terminates in balloon-like structures which are called alveoli.
• The alveoli provide a surface where the exchange of gases can take place. the alveolar walls contain an extensive network of blood vessels.
• The oxygen in the alveolar air is taken up by the blood in the alveolar blood vessels to be transported to all the cells in the body.

Respiratory pigments

The respiratory pigments takes up the oxygen from the air in the lungs and carry it to the tissues which are deficient in oxygen( in tissues,carbon dioxide= 45mmHg and oxygen=40mmHg). In human beings the respiratory pigment is haemoglobin which has very high affinity for oxygen. This pigment is present in the red blood cells . Carbon dioxide is more soluble in water than air that is why it is mostly transported in the dissolved form in the blood.

 

Circulation/Transportation

Transportation in animals

Blood transports food, oxygen and waste materials in our bodies. blood being a fluid connective tissue. Blood consists of a fluid medium called plasma in which the cells are suspended.

Plasma transports food, carbon dioxide and nitrogenous wastes in dissolved form. Oxygen is carried by the red blood corpuscles. Many other substances like salts, are also transported by the blood. We thus need a pumping organ to push blood around the body, a network of tubes(arteries) to reach all the tissues and a system in place to ensure that this network can be repaired if damaged. And that pumping organ is our heart.

The heart of different animals

Fishes : fishes have only two chambers ,an atrium and a ventricle to their hearts, and the blood is pumped to the gills, is oxygenated there, and passes directly to the rest of the body. Thus, blood goes only once through the heart in the fish during one cycle of passage through the body.

Amphibians : amphibians or many reptiles have three-chambered hearts, and tolerate some mixing of the oxygenated and de-oxygenated blood streams. They have two atrium right and left auricle or atrium and one ventricle. Amphibians also gather oxygen through their moist skin.

Reptiles : like amphibians they also have three chambered heart except crocodile , that has four chambered heart. A septum or wall partly divides the deoxygenated from the oxygenated blood. Reptiles also have the unique ability to redirect the blood leaving the heart back through the body circuit .

Birds and mammals : The separation of the right side and the left side of the heart is useful to keep oxygenated and deoxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body. This is useful in animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature. In animals that do not use energy for this purpose, the body temperature depends on the temperature in the environment.

The heart is a muscular organ which is as big as our fist. Because both oxygen and carbon dioxide have to be transported by the blood, the heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide. The carbon dioxide-rich blood has to reach the lungs for the carbon dioxide to be removed, and the oxygenated blood from the lungs has to be brought back to the heart. This oxygen-rich blood is then pumped to the rest of the body.

The process of circulation inside heart occurs step by step as follows :

• Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, the left atrium.
• The left atrium relaxes when it is collecting this blood. It then contracts, while the next chamber, the left ventricle, relaxes, so that the blood is transferred to it.
• When the muscular left ventricle contracts in its turn, the blood is pumped out to the body. De-oxygenated blood comes from the body to the upper chamber on the right, the right atrium, as it relaxes.
• As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates. This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation.
• Since ventricles have to pump blood into various organs, they have thicker muscular walls than the atria do. Valves ensure that blood does not flow backwards when the atria or ventricles contract.

Arteries

Arteries are the vessels which carry blood away from the heart to various organs of the body. Since the blood emerges from the heart under high pressure, the arteries have thick, elastic walls.

Veins

Veins collect the blood from different organs and bring it back to the heart. They do not need thick walls because the blood is no longer under pressure, instead they have valves that ensure that the blood flows only in one direction.

Capillaries

The arteries divides into smaller vessels called capillaries.Exchange of material between the blood and surrounding cells takes place across the this thin wall. The capillaries then join together to form veins that convey the blood away from the organ or tissue.

Lymph and lymphatic system

There is another type of fluid also involved in transportation. This is called lymph or tissue fluid. Through the pores present in the walls of capillaries some amount of plasma, proteins and blood cells escape into intercellular spaces in the tissues to form the tissue fluid or lymph. It is similar to the plasma of blood but colorless and contains less protein. Lymph drains into lymphatic capillaries from the intercellular spaces, which join to form large lymph vessels that finally open into larger veins. Lymph carries digested and absorbed fat from intestine and drains excess fluid from extra cellular space back into the blood.

Platelets

The blood has Platelets cells that maintains the efficiency of the pumping system when an injury occurs that causes leaking. These platelet cells circulates around the body and plug these leaks by helping to clot the blood at these points of injury.

Transportation in plants

Plants do not move, and plant bodies have a large proportion of dead cells in many tissues. As a result, plants have low energy needs, and can use relatively slow transport systems. The distances over which transport systems have to operate, however, can be very large in plants such as very tall trees. Plant transport systems will move energy stores from leaves(food transport) and raw materials from roots(water transport). These two pathways are constructed as independently organized conducting tubes.

Xylem and phloem are the vascular tissues of the plants that perform the transportation in them. the xylem transports water and minerals obtained from the soil. Phloem transports products of photosynthesis from the leaves where they are synthesized to other parts of the plant.

WATER TRANSPORT

• In xylem tissue, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plant.
• At the roots, cells in contact with the soil actively take up ions. This creates a difference in the concentration of these ions between the root and the soil.
• Water, therefore, moves into the root from the soil to eliminate this difference. This means that there is steady movement of water into root xylem, creating a column of water that is steadily pushed upwards.
• However, this pressure by itself is unlikely to be enough to move water over the heights that we commonly see in plants.

Plants use another strategy to move water in the xylem upwards to the highest points of the plant body known as transpiration.

Transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves. It also helps in temperature regulation. The effect of root pressure in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.

FOOD TRANSPORT

• This transport of soluble products of photosynthesis is called translocation and it occurs in the part of the vascular tissue known as phloem.
• Besides the products of photosynthesis, the phloem transports amino acids and other substances.
• These substances are especially delivered to the storage organs of roots, fruits and seeds and to growing organs.
• The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.
• Unlike transport in xylem which can be largely explained by simple physical forces, the translocation in phloem is achieved by utilizing energy.

• Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material according to the plant’s needs. For example, in the spring, sugar stored in root or stem tissue would be transported to the buds which need energy to grow.

Excretion

The metabolic activities of the body generate nitrogenous materials which need to be removed. The biological process involved in the removal of the harmful metabolic wastes from the body is called excretion. Different organisms use varied strategies to do this.

Many unicellular organisms remove these wastes by simple diffusion from the body surface into the surrounding water. As we have seen in other processes, complex multi-cellular organisms use specialized organs to perform the same function.

Human excretory system

• The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
• Kidneys are located in the abdomen, one on either side of the backbone. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.
• The purpose of making urine is to filter out waste products from the blood.
• Just as CO₂ is removed from the blood in the lungs, nitrogenous waste such as urea or uric acid are removed from blood in the kidneys.
• The basic filtration unit in the kidneys like in the lungs, is a cluster of very thin-walled blood capillaries called nephrons. Each capillary cluster in the kidney is associated with the cup-shaped end of a coiled tube called Bowman’s capsule that collects the filtrate.

• Each kidney has large numbers of these filtration units called nephrons packed close together.
• Some substances in the initial filtrate, such as glucose, amino acids, salts and a major amount of water, are selectively re-absorbed as the urine flows along the tube.
• The amount of water re-absorbed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted.
• The urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder.
• Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra. The bladder is muscular, so it is under nervous control as a result we can easily control when there is urge to urinate.

 

Artificial kidney (Hemodialysis)

Kidneys are vital organs for survival. Several factors like infections, injury or restricted blood flow to kidneys reduce the activity of kidneys. This leads to accumulation of poisonous wastes in the body, which can even lead to death. In case of kidney failure, an artificial kidney can be used. An artificial kidney is a device to remove nitrogenous waste products from the blood through dialysis. Artificial kidneys contain a number of tubes with a semi-permeable lining, suspended in a tank filled with dialyzing fluid. This fluid has the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes. The patient’s blood is passed through these tubes. During this passage, the waste products from the blood pass into dialyzing fluid by diffusion. The purified blood is pumped back into the patient. This is similar to the function of the kidney, but it is different since there is no reabsorption involved. Normally, in a healthy adult, the initial filtrate in the kidneys is about 180 L daily. However, the volume actually excreted is only a litre or two a day, because the remaining filtrate is reabsorbed in the kidney tubules.

Excretion in plants

Plants use completely different strategies for excretion than those of animals. Oxygen itself can be thought of as a waste product generated during photosynthesis . They can get rid of excess water by transpiration. For other wastes, plants use the fact that many of their tissues consist of dead cells, and that they can even lose some parts such as leaves. Many plant waste products are stored in cellular vacuoles. Waste products may be stored in leaves that fall off. Other waste products are stored as resins and gums, especially in old xylem. Plants also excrete some waste substances into the soil around them.