LIFE PROCESSES

NUTRITION

5.1 WHAT ARE LIFE PROCESSES

• Life processes are basic processes that living organisms perform to maintain their existence.
• Examples include nutrition, respiration, circulation, excretion, locomotion, growth, reproduction, and response to stimuli.

5.2 NUTRITION

• Nutrition is the process by which living organisms obtain energy and essential nutrients for the growth, maintenance, and repair of body tissues.
• Nutrition can be classified into two types: autotrophic and heterotrophic.

5.2.1 Autotrophic Nutrition

• Autotrophic nutrition is the mode of nutrition in which organisms produce their food from inorganic substances such as carbon dioxide and water, using energy from sunlight.
• Photosynthesis is the process by which autotrophs carry out this type of nutrition.
• Autotrophs use photosynthesis to fulfill their carbon and energy requirements by converting carbon dioxide and water into carbohydrates in the presence of sunlight and chlorophyll.
• Carbohydrates not used immediately are stored as starch for later use.
• Chlorophyll, found in chloroplasts in plant cells, is essential for photosynthesis.
• Carbon dioxide is taken in through the stomata on the leaves, which open and close based on the function of guard cells.
• Autotrophs also require other raw materials for building their body, including water, nitrogen, phosphorus, iron, and magnesium.
• Nitrogen, used in protein synthesis and other compounds, is taken up from the soil in the form of inorganic nitrates or nitrites, or as organic compounds prepared by bacteria from atmospheric nitrogen

5.2.2 Heterotrophic Nutrition

• Heterotrophic nutrition is the mode of nutrition in which organisms obtain their food by consuming other living organisms or their products.
• This mode of nutrition is found in animals, fungi, and non-photosynthetic bacteria.
• Organisms are adapted to their environment and have different forms of nutrition depending on the type and availability of food.
• Strategies for obtaining and using food vary, such as breaking down food material outside the body and absorbing it, or taking in whole material and breaking it down inside the body.
• The ability to take in and break down food depends on the body design and functioning of the organism.
• Parasitic nutrition is a strategy used by many organisms, such as cuscuta, ticks, lice, leeches, and tape-worms, which derive nutrition from plants or animals without killing them.

5.2.3 How do Organisms obtain their Nutrition?

• All organisms require energy and materials.
• Different organisms fulfill these requirements in different ways.
• Autotrophs use simple food material from inorganic sources like carbon dioxide and water.
• Autotrophs include green plants and some bacteria.
• Heterotrophs utilize complex substances for their survival.
• Heterotrophs require bio-catalysts called enzymes to break down complex substances into simpler ones.
• The survival of heterotrophs depends directly or indirectly on autotrophs.
• Heterotrophic organisms include animals and fungi.
• The digestive system varies depending on the organism and the way food is obtained.
• In single-celled organisms, food may be taken in by the entire surface.
• Amoeba uses temporary finger-like extensions of the cell surface to take in food, which forms a food vacuole where complex substances are broken down into simpler ones.
• Undigested material is moved to the surface of the cell and thrown out.
• In Paramoecium, which is also a unicellular organism, food is taken in at a specific spot and moved there by the movement of cilia that cover the entire surface of the cell.

5.2.4 Nutrition in Human Beings

• The alimentary canal is a long tube extending from the mouth to the anus, consisting of different parts specialized to perform different functions.
• Food is processed to generate small particles of the same texture by crushing the food with our teeth, mixing it with saliva secreted by salivary glands, and moving it around the mouth by the muscular tongue.
• Enzymes in saliva, such as salivary amylase, break down complex molecules like starch into simple sugars.
• Peristaltic movements along the digestive tube push the food forward in a regulated manner.
• The stomach is a large organ that expands when food enters it and mixes the food with digestive juices released by gastric glands, such as hydrochloric acid, pepsin, and mucus.
• The acidic medium created by hydrochloric acid facilitates the action of the enzyme pepsin, while mucus protects the inner lining of the stomach from the acid.
• A sphincter muscle regulates the exit of food from the stomach into the small intestine, where it is digested by the secretions of the liver and pancreas.
• Bile juice from the liver makes the acidic food alkaline and breaks down fats into smaller globules, increasing the efficiency of enzyme action.
• Pancreatic juice contains enzymes like trypsin and lipase for digesting proteins and breaking down emulsified fats, respectively.
• The walls of the small intestine contain glands that secrete intestinal juice that finally converts proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol.
• Digested food is absorbed by the walls of the small intestine, which has numerous finger-like projections called villi that increase the surface area for absorption.
• The villi are richly supplied with blood vessels that take the absorbed food to each and every cell of the body, where it is utilized for obtaining energy, building up new tissues, and repairing old tissues.
• Unabsorbed food is sent into the large intestine, where its wall absorbs more water from this material.
• The rest of the material is removed from the body via the anus, and the exit of this waste material is regulated by the anal sphincter.

NOTE: Dental caries

• Dental caries is a common dental problem caused by the breakdown of teeth due to the action of bacteria.
• The bacteria produce acid, which breaks down the tooth enamel and dentin, leading to the formation of cavities.
• Dental caries can be prevented by maintaining good oral hygiene, avoiding sugary and acidic foods and drinks, and regular dental check-ups and cleanings.
• Treatment of dental caries involves the removal of the decayed part of the tooth and filling the cavity with a suitable filling material.

EXERCISE QUESTION

1. Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?

ANS: Diffusion is insufficient to meet the oxygen requirements of multicellular organisms like humans because they have a large volume and a low surface area to volume ratio, which limits the amount of oxygen that can diffuse into cells. Therefore, they require specialized respiratory organs and a circulatory system to transport oxygen to cells.

2.. What criteria do we use to decide whether something is alive?

ANS: The criteria we use to decide whether something is alive include the ability to grow and develop, reproduce, respond to stimuli, adapt to the environment, maintain homeostasis, and have a metabolism.

3.. What are outside raw materials used for by an organism?

ANS: Outside raw materials are used by an organism for various purposes such as energy production, growth, repair, and maintenance of cells and tissues, and for other biological processes such as respiration, photosynthesis, and digestion.

4. What processes would you consider essential for maintaining life?

ANS: The essential processes for maintaining life include obtaining and using energy, exchanging gases, excreting waste products, maintaining a stable internal environment (homeostasis), responding to the environment, reproducing, and growing and developing.

1. What are the differences between autotrophic nutrition and heterotrophic nutrition?

ANS:

1. 2. Where do plants get each of the raw materials required for photosynthesis?

ANS Plants get each of the raw materials required for photosynthesis from their surrounding environment. Carbon dioxide is obtained from the air through tiny pores called stomata on the leaves. Water is absorbed by the roots from the soil. Sunlight is captured by the chlorophyll pigment present in the leaves.

1. 3. What is the role of the acid in our stomach?

ANS The acid in our stomach serves several important functions. One of the most important roles is to create an acidic environment that helps in the digestion of proteins. The acid also helps to kill bacteria and other microorganisms that might be present in the food we eat. Additionally, the acid helps to break down some of the complex carbohydrates present in the food.

1. 4. What is the function of digestive enzymes?

ANS Digestive enzymes play a crucial role in breaking down complex molecules present in the food into smaller, more simple molecules that can be absorbed and utilized by the body. For example, amylase enzymes help in breaking down carbohydrates, while lipase enzymes help in breaking down fats.

1. 5. How is the small intestine designed to absorb digested food?

ANS The small intestine is designed to absorb digested food in several ways. First, the inner lining of the small intestine has numerous finger-like projections called villi which increase the surface area for absorption. The villi are richly supplied with blood vessels that take the absorbed food to each and every cell of the body. Additionally, the walls of the small intestine contain glands that secrete intestinal juice. The enzymes present in the intestinal juice finally convert the proteins to amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol, which can be absorbed by the body.

1. How are fats digested in our bodies? Where does this process take place?

ANS: Fats are digested in our bodies through the process of emulsification, which breaks down large fat globules into smaller droplets, increasing the surface area for enzyme action. This process is primarily carried out by bile salts produced by the liver and stored in the gallbladder. Enzymes called lipases, produced by the pancreas, then break down the smaller fat droplets into fatty acids and glycerol. This process primarily takes place in the small intestine.

1. What is the role of saliva in the digestion of food?

ANS: The role of saliva in the digestion of food is to start the process of breaking down carbohydrates. Saliva contains an enzyme called amylase, which begins the process of breaking down complex carbohydrates into simpler sugars. Saliva also helps to moisten and lubricate food, making it easier to swallow and move through the digestive system

1. . What are the necessary conditions for autotrophic nutrition and what are its by-products?

ANS: The necessary conditions for autotrophic nutrition include access to light, carbon dioxide, and water. Autotrophic organisms, such as plants, use light energy from the sun to convert carbon dioxide and water into glucose through the process of photosynthesis. The by-products of photosynthesis include oxygen and water.

RESPIRATION

• Nutrition in organisms involves using food to provide energy for life processes.
• Different organisms use different methods to break down glucose, including aerobic and anaerobic respiration.
• The first step in glucose breakdown is converting it into pyruvate, a three-carbon molecule.
• Pyruvate can be converted into ethanol and carbon dioxide through anaerobic respiration in yeast.
• Aerobic respiration, which takes place in the presence of oxygen, breaks down pyruvate into carbon dioxide and water.
• Cellular respiration releases energy which is used to synthesize ATP, a molecule used to fuel other activities in the cell.
• Lack of oxygen in muscle cells can cause the breakdown of pyruvate into lactic acid, leading to cramps.
• ATP is broken down to release energy which drives endothermic reactions in the cell.

• Aerobic organisms require a sufficient intake of oxygen for aerobic respiration.
• Plants exchange gases through stomata and inter-cellular spaces, allowing for the diffusion of carbon dioxide and oxygen.
• The direction of diffusion depends on environmental conditions and plant requirements.
• At night, CO2 elimination is the major exchange activity, while during the day, oxygen release is the major event.
• Animals have different organs for uptake of oxygen and removal of carbon dioxide.
• Terrestrial animals breathe oxygen in the atmosphere, while aquatic animals use dissolved oxygen in water.
• Aquatic organisms take in dissolved oxygen from water through their gills at a much faster rate than terrestrial organisms take in atmospheric oxygen.
• Terrestrial organisms have specialized organs, such as lungs in humans, to take in atmospheric oxygen for respiration.
• The fine and delicate surface where gas exchange takes place is protected within the body and has passages to allow air to reach it.
• In humans, air is taken in through the nostrils, filtered by fine hairs and mucus, and passes through the throat and into the lungs.
• The lungs contain alveoli, balloon-like structures where the exchange of gases takes place.
• When we breathe in, the chest cavity expands, air is sucked into the lungs and fills the alveoli, and oxygen is absorbed into the blood while carbon dioxide is released.
• Respiratory pigments, such as hemoglobin in humans, are used to transport oxygen to tissues that need it and release it there. Carbon dioxide is transported mostly in its dissolved form in the blood.

1. ATP is an essential molecule that provides energy for a wide range of cellular processes, and the energy released during respiration is used to produce ATP from ADP and inorganic phosphate. The breaking of the terminal phosphate linkage in ATP releases energy, which is used to power endothermic processes in the cell. ATP can be used for many different functions, including muscle contraction, protein synthesis, and nerve impulse conduction.
2. Smoking is harmful to health and a leading cause of lung cancer. The upper respiratory tract has cilia that help remove germs, dust, and harmful particles from inhaled air. Smoking destroys these cilia, allowing harmful particles like smoke, dust, and chemicals to enter the lungs, leading to infection, cough, and even lung cancer.
3. The surface area of an adult human body is estimated to be around 1.5 to 2 square meters. This includes the surface area of the skin, as well as the surface area of the lungs and other internal organs involved in gas exchange such as the alveoli.
4. The large surface area of the alveoli allows for the efficient exchange of gases to occur, as it provides a large interface between the air and blood. This allows for a rapid exchange of oxygen and carbon dioxide, ensuring that the body's cells receive the oxygen they need and are able to get rid of waste carbon dioxide efficiently.
5. If diffusion were the only means of transporting oxygen in our body, it would take an unacceptably long time for oxygen to reach all parts of the body. This is why the respiratory pigment hemoglobin is necessary, as it allows for the efficient transport of oxygen from the lungs to the tissues that require it.

EXERCISE QUESTION

1. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

ANS: Terrestrial organisms have an advantage over aquatic organisms in obtaining oxygen for respiration because the air contains a higher concentration of oxygen than water. Also, terrestrial organisms have evolved various respiratory structures like lungs, tracheae, or gills, which allow them to extract oxygen from the air more efficiently than aquatic organisms.

1. What are the different ways in which glucose is oxidized to provide energy in various organisms?

ANS: Glucose can be oxidized in different ways to provide energy in various organisms. The three common ways are:

• Aerobic respiration: In this process, glucose is completely oxidized in the presence of oxygen to produce carbon dioxide, water, and energy in the form of ATP.
• Anaerobic respiration: In the absence of oxygen, some organisms can still produce energy by anaerobic respiration. Glucose is partially oxidized to produce lactic acid or alcohol and a small amount of ATP.
• Fermentation: This process occurs in some microorganisms and involves the partial oxidation of glucose to produce ATP and organic compounds like lactic acid or ethanol.

1. How are oxygen and carbon dioxide transported in human beings?

ANS: In human beings, oxygen and carbon dioxide are transported by the blood. Oxygen is carried by the red blood cells, which contain a protein called hemoglobin that binds to oxygen in the lungs and releases it in the tissues. Carbon dioxide is transported in the form of bicarbonate ions, which are formed by the reaction of carbon dioxide with water in the red blood cells. Carbon dioxide can also be carried by the hemoglobin in the blood.

1. How are the lungs designed in human beings to maximize the area for the exchange of gases?

ANS: The lungs in human beings are designed to maximize the area for the exchange of gases. They are made up of millions of small air sacs called alveoli, which have thin walls and a large surface area. The walls of the alveoli are surrounded by a network of blood vessels called capillaries. When we inhale, oxygen diffuses from the air in the alveoli into the blood vessels, while carbon dioxide diffuses from the blood vessels into the alveoli, and then we exhale. The large surface area of the alveoli and the thin walls allow for efficient diffusion of gases between the lungs and the blood.

1. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

ANS: Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen. During aerobic respiration, glucose is completely oxidized into carbon dioxide and water, and a large amount of energy is released in the form of ATP. In contrast, during anaerobic respiration, glucose is only partially oxidized, and the end products vary depending on the organism. Some common end products of anaerobic respiration include lactic acid, ethanol, and carbon dioxide. Some organisms that use anaerobic respiration include certain bacteria, yeast, and some muscle cells in animals.

2. How are the alveoli designed to maximize the exchange of gases?

ANS: The alveoli are small air sacs in the lungs where gas exchange occurs. They are designed to maximize the surface area for gas exchange. The alveoli are surrounded by capillaries, which allow for the diffusion of gases between the air in the alveoli and the blood in the capillaries. The walls of the alveoli are very thin, allowing for efficient diffusion of gases. Additionally, the alveoli are highly branched, providing a large surface area for gas exchange. The alveoli are also coated with a surfactant, which reduces surface tension and prevents them from collapsing during exhalation.

TRANSPORTATION

5.4.1 Transportation in Human Beings

• Blood is a fluid connective tissue that transports food, oxygen, waste materials, and other substances in our bodies.
• Plasma is the fluid medium in which the blood cells are suspended and it transports food, carbon dioxide, and nitrogenous wastes in dissolved form.
• Oxygen is carried by the red blood corpuscles.

Our pump — the heart

• The heart is a muscular organ with different chambers to prevent oxygen-rich blood from mixing with carbon dioxide-rich blood.
• Oxygen-rich blood from the lungs enters the thin-walled left atrium.
• The left atrium relaxes to collect the blood, then contracts to transfer it to the left ventricle.
• The left ventricle contracts to pump the oxygen-rich blood to the body.
• De-oxygenated blood from the body enters the right atrium as it relaxes.
• The right atrium contracts to transfer the blood to the right ventricle, which dilates.
• The right ventricle pumps the blood to the lungs for oxygenation.
• Ventricles have thicker muscular walls than atria.
• Valves prevent blood from flowing backward when the atria or ventricles contract.

Oxygen enters the blood in the lungs

• The separation of the right and left sides of the heart prevents mixing of oxygenated and de-oxygenated blood.
• This separation allows for efficient supply of oxygen to the body, which is especially useful for high-energy animals like birds and mammals.
• Animals that do not use energy to maintain their body temperature (like amphibians or many reptiles) have three-chambered hearts and can tolerate some mixing of blood streams.
• Fish have only two chambers in their hearts, and blood is pumped to the gills for oxygenation before passing directly to the rest of the body.
• Double circulation, where the blood goes through the heart twice during each cycle in other vertebrates, is necessary for efficient oxygenation of the body.

The tubes – blood vessels

• Arteries carry blood away from the heart to various organs of the body.
• Arteries have thick, elastic walls due to the high pressure of blood coming from the heart.
• Veins collect blood from different organs and bring it back to the heart.
• Veins have valves that ensure blood flows only in one direction.
• Arteries divide into smaller vessels to bring blood in contact with individual cells of an organ or tissue.
• The smallest vessels are capillaries, which have walls one cell thick.
• The exchange of materials between the blood and surrounding cells occurs across the thin capillary walls.
• Capillaries join together to form veins that convey blood away from the organ or tissue.

Maintenance by platelets

• A leak in the system of blood vessels can occur due to injury or trauma.
• Blood loss from the system has to be minimized to prevent complications.
• Leakage can also lead to a loss of pressure, reducing the efficiency of the pumping system.
• Platelet cells are present in the blood and circulate throughout the body.
• Platelets help to clot the blood at the site of injury and plug the leaks in the system.
• This process is known as hemostasis and is essential to prevent excessive blood loss and maintain blood pressure.

Lymph

• Lymph or tissue fluid is another type of fluid involved in transportation
• It is formed when plasma, proteins, and blood cells escape through pores in the walls of capillaries into intercellular spaces in the tissues
• Tissue fluid or lymph is similar to blood plasma but is colorless and contains less protein
• Lymph drains into lymphatic capillaries from intercellular spaces and joins to form large lymph vessels that open into larger veins
• Lymph carries digested and absorbed fat from the intestine and drains excess fluid from the extracellular space back into the blood

Blood pressure

• Blood pressure is the force exerted by blood against the wall of a vessel.
• Blood pressure is greater in arteries than in veins.
• Systolic pressure is the pressure of blood inside the artery during ventricular systole (contraction).
• Diastolic pressure is the pressure in the artery during ventricular diastole (relaxation).
• Normal blood pressure is 120/80 mmHg (systolic pressure/diastolic pressure).
• Blood pressure is measured using a sphygmomanometer.
• High blood pressure is also known as hypertension.
• Hypertension is caused by the constriction of arterioles, which results in increased resistance to blood flow.
• Hypertension can lead to the rupture of an artery and internal bleeding.

5.4.2 Transportation in Plants

• Plants absorb raw materials such as nitrogen, phosphorus, and minerals from the soil through their roots.
• Energy stored in chlorophyll-containing organs, such as leaves, is also transported separately.
• If distances between soil-contacting organs and chlorophyll-containing organs are large, a proper system of transportation is necessary.
• Plant bodies have low energy needs and can use relatively slow transport systems.
• Plant transport systems consist of independently organized conducting tubes for water and minerals (xylem) and products of photosynthesis (phloem).
• Xylem moves water and minerals obtained from the soil, while the phloem transports products of photosynthesis from the leaves to other parts of the plant.

Transport of water

• Xylem tissue transports water and minerals from roots to all parts of the plant
• At the roots, cells actively take up ions, creating a concentration gradient that causes water to move into the root from the soil
• This creates a steady movement of water into root xylem, creating a column of water that is steadily pushed upwards
• However, this pressure alone is unlikely to be enough to move water to the highest points of the plant body
• Transpiration helps in the upward movement of water from roots to leaves and also in temperature regulation
• Evaporation of water molecules from leaf cells creates a suction that pulls water from the xylem cells of roots
• Root pressure is more important at night, while transpiration pull is the major driving force during the day when stomata are open

Transport of food and other substances

• The transport of soluble products of photosynthesis is called translocation and it occurs in the phloem.
• Phloem transports not only the products of photosynthesis but also amino acids and other substances to storage organs, fruits, seeds, and growing organs.
• Translocation in phloem requires energy, and 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, and this pressure moves the material in the phloem to tissues with less pressure.
• The phloem moves material according to the plant’s needs. For example, sugar stored in the root or stem tissue in the spring would be transported to the buds which need the energy to grow.

EXERCISE QUESTIONS

1. What are the components of the transport system in human beings? What are the functions of these components?

ANS: The components of the transport system in human beings include:

• Heart: a muscular organ that pumps blood throughout the body
• Blood vessels: a network of tubes that transport blood throughout the body
• Arteries: thick-walled vessels that carry oxygenated blood away from the heart to the rest of the body
• Veins: thinner-walled vessels that carry deoxygenated blood back to the heart
• Capillaries: small, thin-walled vessels that allow for exchange of nutrients, gases, and waste products between the blood and body tissues

The functions of these components are to circulate blood, nutrients, oxygen, and waste products throughout the body, and to regulate body temperature, pH, and fluid balance.

1. . Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

ANS: It is necessary to separate oxygenated and deoxygenated blood in mammals and birds because these animals have a four-chambered heart, which allows for complete separation of the two types of blood. Oxygenated blood is pumped out of the left side of the heart and sent to the body, while deoxygenated blood is pumped out of the right side of the heart and sent to the lungs to pick up oxygen.

1. What are the components of the transport system in highly organized plants?

ANS: The components of the transport system in highly organized plants include:

• Xylem: a tissue that transports water and minerals from roots to leaves
• Phloem: a tissue that transports sugars, amino acids, and other nutrients from leaves to other parts of the plant
• Root hairs: small, finger-like projections on the surface of roots that increase surface area for absorption of water and minerals
• Stomata: small openings on the surface of leaves that allow for the exchange of gases and water vapor

The functions of these components are to transport water, minerals, and nutrients throughout the plant, and to facilitate gas exchange and transpiration.

1. . How are water and minerals transported in plants?

ANS: Water and minerals are transported in plants through the xylem tissue. Water is absorbed by root hairs and then transported through the xylem tissue up to the leaves by a combination of root pressure and transpiration pull. Minerals are absorbed by the roots and transported through the xylem tissue along with water.

1. How is food transported in plants?

ANS: Food is transported in plants through the phloem tissue. Sugars, amino acids, and other nutrients are produced in the leaves through photosynthesis and then transported through the phloem tissue to other parts of the plant, including roots, fruits, and seeds. The movement of material through the phloem is achieved by utilizing energy to increase the osmotic pressure of the tissue, causing water to move into it and create pressure that moves the material in the phloem to tissues with lower pressure.

1. What would be the consequences of a deficiency of hemoglobin in our bodies?

ANS: Haemoglobin is an important protein present in red blood cells that helps to transport oxygen from the lungs to various tissues in the body. A deficiency of haemoglobin can lead to a condition called anemia, which is characterized by symptoms like fatigue, weakness, shortness of breath, and pale skin. In severe cases, it can also lead to organ damage and heart failure.

1. . Describe the double circulation of blood in human beings. Why is it necessary?

ANS: Double circulation of blood is a process in which blood flows through two separate circuits in the body. The first circuit is pulmonary circulation, which carries deoxygenated blood from the heart to the lungs, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then returns to the heart, which pumps it out to the rest of the body in the systemic circulation. This allows for more efficient transport of oxygen and nutrients to the body's tissues and organs and helps to maintain a high metabolic rate

1. What are the differences between the transport of materials in the xylem and phloem?

ANS: The transport of materials in xylem and phloem is different in several ways. Xylem transports water and minerals from the roots to the leaves, while the phloem transports the products of photosynthesis and other organic molecules from the leaves to other parts of the plant. Xylem uses a passive transport mechanism driven by transpiration and root pressure, while phloem uses active transport mechanisms driven by the pressure gradient created by the movement of sugars and other solutes. Xylem is made up of dead cells that form a hollow tube, while phloem is made up of living cells that are arranged end to end to form a continuous tube.

OR

EXCRETION

• Excretion is the biological process involved in the removal of harmful metabolic wastes from the body.
• Different organisms use varied strategies to remove these wastes.
• Many unicellular organisms remove these wastes by simple diffusion from the body surface into the surrounding water.
• Complex multi-cellular organisms use specialized organs to perform the same function.
• These specialized organs include the kidneys in vertebrates, the Malpighian tubules in insects, and the nephridia in annelids.
• These organs filter out the waste materials from the body fluids and eliminate them from the body through excretory structures such as the urethra or anus.
• In addition to nitrogenous materials, other metabolic wastes that need to be excreted include excess salts, excess water, and toxic substances such as urea, uric acid, and creatinine.
• Excretion is a crucial process that helps to maintain homeostasis in the body by removing harmful wastes and regulating the body's fluid and electrolyte balance.

5.5.1 Excretion in Human Beings

• 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.
• Urine is produced by filtering waste products from the blood in the kidneys.
• The basic filtration unit in the kidneys is a cluster of very thin-walled blood capillaries associated with the cup-shaped end of a coiled tube called Bowman's capsule.
• 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 reabsorbed as the urine flows along the tube.
• The amount of water reabsorbed depends on how much excess water there is in the body, and on how much 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, and we can usually control the urge to urinate.

Artificial kidney (Hemodialysis)

• Kidneys are vital organs that remove waste products from the body.
• Factors like infections, injury or restricted blood flow to kidneys can reduce their activity, leading to accumulation of poisonous wastes in the body.
• Artificial kidneys can be used in case of kidney failure to remove nitrogenous waste products from the blood through dialysis.
• Artificial kidneys contain tubes with a semi-permeable lining, suspended in a tank filled with dialysing fluid.
• The patient's blood is passed through these tubes, and the waste products from the blood pass into dialysing fluid by diffusion.
• The purified blood is then pumped back into the patient, similar to the function of the kidney.
• 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 re-absorbed in the kidney tubules.

Organ donation

• Organ donation is the act of donating an organ to a person who suffers from non-function of organ(s).
• Donation can be done with the consent of the donor and his/her family.
• Anyone regardless of age or gender can become an organ and tissue donor.
• Organ transplants can save or transform the life of a person.
• Transplantation is required because the recipient’s organ has been damaged or has failed by disease or injury.
• Common transplantations include corneas, kidneys, heart, liver, pancreas, lungs, intestines, and bone marrow.
• Most organ and tissue donations occur just after the donor has died or when the doctor declares a person's brain dead.
• Some organs such as kidneys, part of the liver, lungs, etc., and tissues can be donated while the donor is alive.

5.5.2 Excretion in Plants

• Plants have different strategies for excretion compared to animals.
• Oxygen can be considered a waste product in photosynthesis.
• Plants can eliminate excess water through transpiration.
• Many plant tissues consist of dead cells which can store waste products.
• Plant waste products are stored in cellular vacuoles, leaves that fall off, and resins and gums in old xylem.
• Some plant waste products are excreted into the soil surrounding them.

EXERCISE QUESTION

1. Describe the structure and functioning of nephrons.

ANS: Nephrons are the functional units of the kidney responsible for filtering blood and producing urine. Each nephron consists of a glomerulus, a network of capillaries surrounded by Bowman's capsule, and a renal tubule. Blood from the renal artery enters the glomerulus, where it is filtered through the thin walls of the capillaries into Bowman's capsule, forming a fluid called the filtrate. The filtrate then travels through the renal tubule, which consists of several parts, including the proximal convoluted tubule, loop of Henle, and distal convoluted tubule. Along the way, the tubule selectively reabsorbs necessary substances, such as glucose and ions, and returns them to the bloodstream. The remaining fluid, now known as urine, leaves the nephron and travels through the collecting ducts, eventually reaching the ureter and bladder for excretion

2. What are the methods used by plants to get rid of excretory products?

ANS: Plants use various strategies to eliminate excretory products. They can release excess water through transpiration, and they store many waste products in vacuoles within cells. Other waste products can be stored in leaves that eventually fall off or in resins and gums found in old xylem. Some plants also excrete waste substances into the soil around them.

3. How is the amount of urine produced regulated?

ANS: The amount of urine produced is regulated by a complex feedback mechanism involving several hormones, including antidiuretic hormone (ADH), aldosterone, and atrial natriuretic peptide (ANP). ADH is released in response to high blood osmolality (concentration of solutes) and causes the kidneys to reabsorb more water, resulting in less urine production. Aldosterone, released by the adrenal gland, increases the reabsorption of sodium and water in the kidneys, also resulting in less urine production. ANP, released by the heart in response to high blood pressure, decreases sodium reabsorption in the kidneys and increases urine production. Additionally, the amount of urine produced is influenced by the amount of fluids and electrolytes consumed and the level of physical activity.

4. What are the differences between the transport of materials in the xylem and phloem?

ANS: Xylem and phloem are two types of specialized plant tissues responsible for transporting materials throughout the plant. Xylem transports water and minerals from roots to leaves, while phloem transports organic nutrients like sugars from leaves to other parts of the plant. The main differences between xylem and phloem are as follows:

• Structure: Xylem consists of dead cells that are elongated and lignified to form a long tube, whereas phloem consists of living cells that are arranged in a tube-like structure.
• Direction of transport: Xylem transports materials in one direction only, from roots to leaves, while phloem can transport materials in both directions.
• Transported materials: Xylem transports water and minerals, while phloem transports organic nutrients like sugars.
• Pressure: Xylem transport is driven by negative pressure or tension, while phloem transport is driven by positive pressure or flow.

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5. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

ANS: Alveoli in the lungs and nephrons in the kidneys are both specialized structures responsible for filtering and exchanging materials. The main similarities and differences between them are as follows:

• Structure: Both alveoli and nephrons have a complex, folded structure that provides a large surface area for exchange. Alveoli are tiny, air-filled sacs located in the lungs, while nephrons are tubular structures located in the kidneys.
• Functioning: Alveoli are responsible for gas exchange, allowing oxygen to enter the bloodstream and carbon dioxide to exit. Nephrons are responsible for filtering waste products from the blood and producing urine.
• Blood supply: Alveoli are surrounded by capillaries, while nephrons are supplied by a complex network of blood vessels called the renal vasculature.
• Exchange mechanism: In alveoli, gas exchange occurs through diffusion across a thin membrane. In nephrons, filtration occurs through a semi-permeable membrane, and then selective reabsorption and secretion occur in different segments of the nephron.
• Efficiency: Both alveoli and nephrons are highly efficient at their respective functions, with alveoli able to exchange gases rapidly and nephrons able to filter large volumes of blood and produce concentrated urine.

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