Life Processes: Exam Notes

• Overview of Life Processes,

  Life Processes: Exam Notes

  Life Processes Defined: Life processes are the basic and essential functions performed by living organisms to maintain and sustain their life. These are crucial for an organism’s survival, unlike non-essential activities.
  Four Main Life Processes: The chapter focuses on four life processes in detail:
  1. Nutrition
  2. Respiration
  3. Transportation
  4. Excretion
  1. Nutrition
  Definition: Nutrition involves how an organism obtains its food and subsequently absorbs it. Different organisms have different ways of obtaining food, e.g., humans ask for food, lions hunt, and plants perform photosynthesis.
  Types of Nutrition:
  • Autotrophic Nutrition:
      ◦ Definition: Organisms that can make their own food.
      ◦ “Auto” means self.
      ◦ Examples: Green plants and some autotrophic bacteria.
      ◦ Process in Plants: Green plants use sunlight, carbon dioxide (CO2), water, and chlorophyll to perform photosynthesis and produce their food.
  • Heterotrophic Nutrition:
      ◦ Definition: Organisms that cannot make their own food and depend on other organisms for their food.
      ◦ “Hetero” means different.
      ◦ Examples: Human beings, animals (cats, dogs), etc.. They obtain food from plants (vegetables, fruits) or other animals.
  Types of Heterotrophic Nutrition:
  1. Holozoic Nutrition:
      ◦ Definition: Organisms that consume organic food from outside and digest it internally within their body (e.g., in a stomach or inside cells).
      ◦ Examples: Humans, dogs, cats. The board exam specifically asks for Amoeba and Paramecium as examples. These are single-celled (unicellular) organisms.
      ◦ Nutrition in Amoeba:
          ▪ Amoeba is a unicellular organism with no fixed shape.
          ▪ It takes in food using temporary finger-like projections called pseudopodia. Pseudopodia also help in movement.
          ▪ The food particle is enclosed within a food vacuole inside the Amoeba.
          ▪ Enzymes are released into the food vacuole to break down complex food substances into simpler ones.
          ▪ The digested food is then absorbed into the cytoplasm by diffusion.
          ▪ Undigested waste food is moved to the cell surface and thrown out.
      ◦ Nutrition in Paramecium:
          ▪ Paramecium is also a single-celled organism, but it has a fixed slipper-like shape.
          ▪ It uses hair-like structures called cilia to move food to a specific spot where the food vacuole is formed. Cilia also help in movement.
          ▪ Similar to Amoeba, enzymes break down food in the food vacuole, digested food is absorbed, and waste is expelled.
  2. Saprophytic Nutrition:
      ◦ Definition: Organisms that obtain food from dead and decaying matter.
      ◦ Examples: Bread molds, yeast, mushrooms.
      ◦ They secrete digestive enzymes onto the dead matter and then absorb the digested nutrients.
  3. Parasitic Nutrition:
      ◦ Definition: Organisms that obtain food from another living organism (host), either by living on or inside the host’s body, and often harm the host in the process.
      ◦ Examples: Leeches, lice.
      ◦ Cascuta plant (Amarbel): This is an important plant example. Unlike most plants, Cascuta does not make its own food because it lacks chlorophyll. Therefore, it lives as a parasite on other plants.
  Photosynthesis: The Process of Autotrophic Nutrition
  • Definition: The process by which green plants make their own food (glucose) using sunlight, carbon dioxide, water, and chlorophyll.
  • Conditions Necessary for Photosynthesis (frequently asked in exams):
      1. Sunlight
      2. Chlorophyll (a pigment)
      3. Carbon Dioxide (CO2)
      4. Water (H2O)
  • Balanced Chemical Equation: 6CO2 (Carbon Dioxide) + 6H2O (Water) –(Sunlight, Chlorophyll)–> C6H12O6 (Glucose) + 6O2 (Oxygen) (Note: The transcript mentions 12 water molecules on the reactant side and 6 on the product side in an alternative representation, but the simpler one provided above is also correct and commonly taught).
  • Three Steps of Photosynthesis:
      1. Absorption of light energy by chlorophyll.
      2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen. The oxygen is released.
      3. Reduction of carbon dioxide to carbohydrates (glucose) using the hydrogen and chemical energy.
  • Site of Photosynthesis:
      ◦ Organelle: Chloroplast (a cell organelle). Chlorophyll is present inside chloroplasts. Chloroplasts are responsible for the green color of leaves.
      ◦ Organ: Leaves are the primary organs where photosynthesis occurs.
  • Absorption of Carbon Dioxide (CO2):
      ◦ Leaves have tiny pores called stomata on their surface.
      ◦ Stomata facilitate the absorption of CO2 from the atmosphere.
      ◦ The opening and closing of stomata are regulated by guard cells.
      ◦ Mechanism of Stomatal Opening/Closing:
          ▪ Opening: Guard cells absorb water (H2O), swell, and cause the stomata to open, allowing CO2 entry.
          ▪ Closing: Guard cells lose water (H2O), shrink, and cause the stomata to close.
  • Absorption of Water and Minerals:
      ◦ Water is absorbed from the soil by the roots.
      ◦ Along with water, essential minerals like nitrogen, phosphorus, magnesium, and iron are also absorbed.
      ◦ Nitrogen is specifically taken up in the form of nitrates and nitrites.
  • Storage of Food:
      ◦ In plants, the glucose produced during photosynthesis is stored in the form of starch.
      ◦ In animals (including humans), food is stored in the form of glycogen.
  • Photosynthesis in Desert Plants:
      ◦ Desert plants keep their stomata closed during the day to conserve water.
      ◦ They open their stomata at night to absorb CO2.
      ◦ This CO2 is then used during the day (when sunlight is available) to perform photosynthesis.
  Experiments Related to Photosynthesis:
  1. Variegated Leaf Experiment (to prove Chlorophyll is essential):
      ◦ A variegated leaf has green (chlorophyll present) and non-green (chlorophyll absent) parts.
      ◦ After exposing the leaf to sunlight and then dipping it in iodine solution, only the green parts turn blue-black.
      ◦ Iodine turns blue-black in the presence of starch. This proves that starch (food) is formed only where chlorophyll is present, thus chlorophyll is essential for photosynthesis.
      ◦ Note: The leaf is often boiled in water and then in alcohol to remove chlorophyll and make the color change more visible.
  2. Bell Jar/Glass Jar Experiment (to prove CO2 is essential):
      ◦ A plant is placed inside a sealed bell jar.
      ◦ Potassium Hydroxide (KOH) is placed in a small plate inside the jar.
      ◦ Role of KOH: KOH absorbs any carbon dioxide present inside the jar.
      ◦ The setup is kept in sunlight to ensure all other conditions for photosynthesis (sunlight, water, chlorophyll) are met.
      ◦ After some time, if a leaf from this plant is tested with iodine solution, it does not turn blue-black.
      ◦ Conclusion: No starch is formed because CO2 was absent, proving that CO2 is essential for photosynthesis.
  2. Nutrition in Human Beings (Holozoic)
  • Humans are holozoic and process food internally.
  • The entire system from mouth to anus is called the alimentary canal, which is essentially a single long tube.
  • Process of Digestion:
  1. Mouth:
      ◦ Teeth: Crush and cut food into smaller pieces.
      ◦ Tongue: Mixes food with saliva and helps in swallowing.
      ◦ Salivary Glands: Located in the mouth, they secrete saliva.
      ◦ Saliva: Contains an enzyme called salivary amylase.
      ◦ Function of Salivary Amylase: Breaks down complex carbohydrates (starch) into simple sugars. Digestion begins in the mouth.
      ◦ Saliva Experiment: Mixing starch with saliva and testing with iodine shows no blue-black color, proving starch breakdown.
  2. Esophagus (Food Pipe):
      ◦ Connects the mouth to the stomach.
      ◦ Movement of food is regulated by peristaltic movement – rhythmic contractions and expansions of the food pipe walls that push food towards the stomach, preventing it from falling abruptly.
  3. Stomach:
      ◦ A J-shaped muscular organ.
      ◦ Gastric Glands: Present in the stomach walls, they secrete gastric juice.
      ◦ Gastric Juice Contains Three Components:
          ▪ Hydrochloric Acid (HCl):
              • Creates an acidic medium for the enzyme pepsin to act.
              • Kills bacteria and germs present in food.
          ▪ Pepsin: An enzyme that digests proteins.
          ▪ Mucus: Protects the inner lining of the stomach from the corrosive action of HCl.
  4. Small Intestine:
      ◦ A very long, coiled tube and the longest part of the alimentary canal (up to 7 meters).
      ◦ Primary Site: It is the site of complete digestion and maximum absorption of food.
      ◦ Receives secretions from two accessory organs:
          ▪ Liver:
              • Secretes bile juice, which is stored in the gall bladder.
              • Functions of Bile Juice:
                  ◦ Makes the acidic food coming from the stomach alkaline (basic). This is important for pancreatic enzymes to function.
                  ◦ Emulsification of fats: Breaks down large fat globules into smaller ones, increasing the surface area for enzyme action.
          ▪ Pancreas:
              • Secretes pancreatic juice.
              • Pancreatic Juice Contains Two Enzymes:
                  ◦ Trypsin: Digests proteins (similar to pepsin in function).
                  ◦ Lipase: Breaks down emulsified fats.
      ◦ Complete Digestion Products:
          ▪ Proteins are converted into amino acids.
          ▪ Carbohydrates are converted into glucose.
          ▪ Fats are converted into fatty acids and glycerol.
      ◦ Absorption in Small Intestine (Villi):
          ▪ The inner surface of the small intestine has numerous finger-like projections called villi.
          ▪ Function of Villi: They increase the surface area for the absorption of digested food.
          ▪ Villi are richly supplied with blood vessels (capillaries).
          ▪ Digested food (glucose, amino acids, fatty acids, glycerol) diffuses from the villi into the blood capillaries, which then transport it to all the cells of the body.
  5. Large Intestine:
      ◦ Receives unabsorbed food from the small intestine.
      ◦ Main Function: Absorbs more water from the remaining undigested material.
      ◦ The rest of the waste material is then removed from the body.
  6. Anus:
      ◦ The exit of waste material (feces) via the anus is regulated by the anal sphincter. This muscular control allows for controlled defecation.
  Differences in Herbivores and Carnivores Small Intestine Length:
  • Herbivores (e.g., cows) have a longer small intestine. This is because they primarily consume plant matter (cellulose), which is hard to digest and requires more time and effort to break down and absorb.
  • Carnivores (e.g., lions) have a shorter small intestine because meat is comparatively easier to digest than cellulose.
  3. Respiration
  Definition: Respiration is the process of breaking down food (glucose) to release energy in the form of ATP (adenosine triphosphate), which is the energy currency of the cell.
  Difference between Respiration and Breathing:

  Feature	Breathing	Respiration
  Nature	Physical process (inhalation/exhalation)	Chemical (Biochemical) process (food breakdown, energy release)
  Energy	Requires energy (for muscle movement)	Releases energy (as ATP)
  Site	Occurs primarily in the lungs	Occurs in every cell of the body (cytoplasm and mitochondria)
  Purpose	Exchange of gases (O2 in, CO2 out)	Energy production from food

  • Breathing is necessary for respiration because oxygen (O2) acts as the fuel for breaking down food to release energy.
  Pathways of Glucose Breakdown (Respiration):
  The first step of glucose breakdown is common for all types of respiration and occurs in the cytoplasm:
  • Glucose (6-carbon molecule) is broken down into Pyruvate (3-carbon molecule) and some energy is released.
  After pyruvate formation, the pathway diverges based on the presence or absence of oxygen:
  1. Aerobic Respiration (Presence of Oxygen):
      ◦ Occurs in: Mitochondria (powerhouse of the cell).
      ◦ Conditions: Presence of sufficient oxygen (O2).
      ◦ Products: Carbon Dioxide (CO2), Water (H2O), and a large amount of Energy (ATP).
      ◦ This is complete oxidation of pyruvate.
      ◦ Most efficient in terms of energy production.
  2. Anaerobic Respiration (Absence of Oxygen):
      ◦ Occurs in: Yeast and some bacteria.
      ◦ Conditions: Complete absence of oxygen (O2).
      ◦ Products: Ethanol (2-carbon alcohol), Carbon Dioxide (CO2), and less energy compared to aerobic respiration.
      ◦ This is also known as Alcoholic Respiration or Alcoholic Fermentation. It’s an incomplete oxidation.
  3. Anaerobic Respiration (Lack of Oxygen):
      ◦ Occurs in: Muscle cells (especially during vigorous exercise) and some bacteria.
      ◦ Conditions: Insufficient (lack of) oxygen (O2).
      ◦ Products: Lactic Acid (3-carbon molecule) and less energy compared to aerobic respiration.
      ◦ This is known as Lactic Acid Respiration or Lactic Acid Fermentation. It’s an incomplete oxidation.
      ◦ The build-up of lactic acid in muscle cells causes fatigue and cramps during intense physical activity.
  Differences between Aerobic and Anaerobic Respiration:

  Feature	Aerobic Respiration	Anaerobic Respiration
  Oxygen	Required	Not required (or in lack)
  Energy	More energy produced	Less energy produced
  Oxidation	Complete oxidation of glucose	Incomplete oxidation of glucose
  Site	Occurs in cytoplasm and mitochondria	Occurs only in cytoplasm
  End Products	Carbon Dioxide (CO2), Water (H2O), Energy	Ethanol + CO2 (in yeast) or Lactic Acid (in muscles), Energy

  Human Respiratory System (Breathing System):
  The system responsible for taking in oxygen and expelling carbon dioxide.
  1. Nostrils: The two openings in the nose through which air enters.
  2. Nasal Passage:
      ◦ Lined with hair and mucus.
      ◦ Function: Filters the air by trapping dirt and dust particles, preventing them from entering the lungs.
  3. Pharynx:
      ◦ A common passage for both food and air. This is why talking while eating can lead to food getting stuck.
  4. Larynx (Voice Box):
      ◦ Located below the pharynx.
      ◦ Contains vocal cords and is responsible for sound production.
      ◦ Allows air to pass into the trachea.
  5. Trachea (Windpipe):
      ◦ A tube that carries air from the larynx to the lungs.
      ◦ Supported by rings of cartilage.
      ◦ Function of Rings of Cartilage: Prevents the air passage (trachea) from collapsing when there is less air pressure.
  6. Bronchi:
      ◦ The trachea divides into two smaller tubes called bronchi, with one leading to each lung.
  7. Bronchioles:
      ◦ Inside the lungs, each bronchus further divides into a network of smaller, finer tubes called bronchioles.
      ◦ They increase the surface area for air distribution.
  8. Alveoli (Air Sacs):
      ◦ The bronchioles terminate in tiny, balloon-like structures called alveoli.
      ◦ Structure: They have very thin, moist walls and are richly surrounded by a network of blood capillaries.
      ◦ Function: They are the primary sites for gas exchange (oxygen and carbon dioxide) in the lungs. Millions of alveoli provide a large surface area for efficient gas diffusion.
      ◦ Gas Exchange Process: Oxygen from the alveoli diffuses into the blood capillaries, and carbon dioxide from the blood diffuses into the alveoli to be exhaled.
  Mechanism of Breathing (Inhalation and Exhalation):
  • Diaphragm: A dome-shaped muscular structure that separates the chest cavity from the abdomen.
  • Inhalation (Inspiration):
      ◦ The diaphragm contracts and moves downward, becoming flatter.
      ◦ The chest cavity becomes larger.
      ◦ This creates a pressure difference, causing air to be sucked into the lungs.
  • Exhalation (Expiration):
      ◦ The diaphragm relaxes and moves upward, returning to its dome shape.
      ◦ The chest cavity becomes smaller.
      ◦ This pushes air out from the lungs.
  Residual Volume:
  • A certain amount of air always remains in the lungs even after forceful exhalation.
  • Purpose: This residual volume provides sufficient time for the absorption of O2 and the release of CO2 into and from the blood.
  Respiration in Plants:
  • Daytime:
      ◦ Photosynthesis occurs: Plants take in CO2 and release O2.
      ◦ Respiration occurs: Plants take in O2 and release CO2 (to produce energy from stored food).
      ◦ The CO2 released during respiration is largely used up by photosynthesis.
      ◦ Net effect: Plants primarily give out oxygen during the day.
  • Nighttime:
      ◦ No photosynthesis (due to lack of sunlight).
      ◦ Respiration continues: Plants take in O2 and release CO2.
      ◦ Net effect: Plants primarily give out carbon dioxide at night.
  Respiration in Fish (Aquatic Organisms):
  • Fish take in water through their mouth and force it over the gills.
  • Gills: Are specialized respiratory organs that absorb dissolved oxygen from the water.
  • The remaining water is expelled through the gills.
  • High Breathing Rate: Aquatic organisms like fish have a higher rate of breathing compared to terrestrial organisms. This is because the amount of dissolved oxygen in water is much lower than the oxygen available in the atmosphere.
  4. Transportation
  Definition: Transportation involves the movement of various substances (like oxygen, food, waste products, hormones) from one part of the body to another.
  Human Circulatory System:
  This is the primary transport system in humans. It consists of three main components:
  1. Blood
  2. Blood Vessels
  3. Heart
  1. Blood:
  • A red-colored fluid connective tissue that transports various substances.
  • Components of Blood:
      ◦ Plasma: The fluid part of the blood (pale yellow).
          ▪ Function: Primarily transports carbon dioxide (CO2), food, and waste products.
      ◦ Red Blood Cells (RBCs) / Red Blood Corpuscles:
          ▪ Function: Primarily transports oxygen (O2).
          ▪ Contains a special protein called hemoglobin, which binds to oxygen and is responsible for the red color of blood.
      ◦ White Blood Cells (WBCs) / White Blood Corpuscles:
          ▪ Function: Provides immunity, fights infections and diseases.
      ◦ Platelets:
          ▪ Function: Helps in blood clotting (coagulation) to prevent excessive bleeding.
  2. Blood Vessels: A network of tubes that carry blood throughout the body. There are three main types:
  • Arteries:
      ◦ Function: Carry blood away from the heart to different organs and cells of the body.
      ◦ Blood Type: Rich in oxygen (oxygenated blood) (except pulmonary artery).
      ◦ Pressure: Blood flows under high pressure as it’s pumped directly from the heart.
      ◦ Walls: Have thick and elastic walls to withstand high pressure.
      ◦ Valves: No valves are present, as the high pressure prevents backflow.
      ◦ Color in diagrams: Typically shown in red.
  • Veins:
      ◦ Function: Carry blood back to the heart from various organs and cells.
      ◦ Blood Type: Contains deoxygenated blood (rich in CO2, poor in O2) (except pulmonary vein).
      ◦ Pressure: Blood flows under low pressure.
      ◦ Walls: Have thin and less elastic walls.
      ◦ Valves: Valves are present to prevent the backflow of blood, especially against gravity (e.g., in leg veins).
      ◦ Color in diagrams: Typically shown in blue.
  • Capillaries:
      ◦ Function: Tiny, extremely thin-walled blood vessels that connect arteries and veins. They are the site of exchange of gases, nutrients, and waste products between blood and body cells.
      ◦ Blood Type: Transport both oxygenated and deoxygenated blood.
      ◦ Pressure: Moderate pressure.
      ◦ Walls: Very thin (one-cell thick) to facilitate efficient diffusion and exchange.
      ◦ Valves: No valves.
  Exceptions to Blood Vessel Rules:
  • Pulmonary Artery: Carries deoxygenated blood from the heart to the lungs. (Normally arteries carry oxygenated blood).
  • Pulmonary Vein: Carries oxygenated blood from the lungs to the heart. (Normally veins carry deoxygenated blood).
  3. Heart:
  • A muscular organ about the size of a fist.
  • Function: Its sole function is to pump blood to all parts of the body; it does not purify or make blood.
  • Structure:
      ◦ Four Chambers: The human heart is divided into four chambers:
          ▪ Left Atrium (LA)
          ▪ Left Ventricle (LV)
          ▪ Right Atrium (RA)
          ▪ Right Ventricle (RV)
      ◦ Septum: A dividing wall that separates the left and right sides of the heart.
      ◦ Atria (Upper Chambers): Receive blood from veins; have thinner walls; lower pressure.
      ◦ Ventricles (Lower Chambers): Pump blood into arteries; have thicker, muscular walls to generate high pressure.
  Pathway of Blood Flow (Double Circulation in Humans):
  The human heart has a double circulatory system, meaning blood flows twice through the heart for each complete circuit of the body. This ensures complete separation of oxygenated and deoxygenated blood.
  1. Pulmonary Circulation (Heart to Lungs and back):
      ◦ Deoxygenated blood from the body (via Vena Cava) enters the Right Atrium.
      ◦ It passes into the Right Ventricle.
      ◦ The Right Ventricle pumps this blood into the Pulmonary Artery, which carries it to the lungs.
      ◦ In the lungs, blood releases CO2 and picks up O2 (becomes oxygenated).
      ◦ Oxygenated blood returns from the lungs to the Left Atrium via the Pulmonary Vein.
  2. Systemic Circulation (Heart to Body and back):
      ◦ Oxygenated blood from the Left Atrium passes into the Left Ventricle.
      ◦ The Left Ventricle pumps this blood into the Aorta (the largest artery), which distributes it to all parts of the body.
      ◦ Body cells use oxygen and release CO2, making the blood deoxygenated.
      ◦ Deoxygenated blood returns from the body to the Right Atrium via the Vena Cava (main vein from upper and lower body).
  Significance of Four Chambers / Double Circulation:
  • Humans are warm-blooded (homeothermic) creatures. This means we need to constantly maintain a high and stable body temperature.
  • Maintaining body temperature and meeting high energy demands requires a constant, high level of oxygen supply.
  • The four-chambered heart and double circulation prevent the mixing of oxygen-rich and oxygen-poor blood.
  • This ensures that every cell in the body receives the richest possible supply of oxygen, maximizing efficiency for functions like thinking, moving, and digesting.
  Circulation in Other Vertebrates:
  • Birds and Mammals (e.g., humans): Four-chambered heart, complete double circulation, warm-blooded (high energy needs).
  • Amphibians and Reptiles: Three-chambered heart (two atria, one ventricle), partial double circulation, cold-blooded (lower energy needs, can tolerate some mixing of blood).
  • Fish: Two-chambered heart (one atrium, one ventricle), single circulation (blood passes through the heart only once per circuit), cold-blooded.
  Lymphatic System:
  • Lymph: A colorless fluid that is formed when some plasma, proteins, and blood cells (mainly white blood cells/lymphocytes) leak out from the capillaries into the intercellular spaces.
      ◦ It contains less protein than blood and no red blood cells.
  • Lymphatic System: A network of lymphatic capillaries and vessels that collect this leaked fluid (lymph).
      ◦ Lymphatic vessels do not connect directly to the heart but eventually merge into larger veins.
  • Functions of Lymph:
      1. Transports digested and absorbed fat from the intestine.
      2. Drains excess fluid from extracellular spaces back into the blood.
      3. Contains lymphocytes (a type of WBC) that help defend the body against infection.
  5. Transportation in Plants
  • Plants have a slow transport system.
      ◦ Reasons:
          ▪ Plants do not move (unlike animals).
          ▪ They have a large proportion of dead cells in many tissues, leading to low energy needs.
      ◦ Despite being slow, the transport distance can be very large (e.g., tall trees).
  • Two Main Transport Tissues:
  1. Xylem:
      ◦ Function: Transports water and minerals.
      ◦ Direction of Flow: Unidirectional (upward only) – from roots to aerial parts (leaves, stem).
      ◦ Mechanism: Primarily by physical forces; it’s a passive transport (no energy required).
          ▪ Root Pressure: Roots actively take up ions (minerals/salts) from the soil, creating a concentration difference. Water then moves into the roots by osmosis, generating pressure that pushes water upward in the xylem.
          ▪ Transpiration Pull: The loss of water in the form of vapor from the aerial parts (leaves) through stomata (transpiration). This evaporation creates a suction force (pull) that draws water upward from the roots to the leaves.
              • Role of Transpiration:
                  ◦ Creates the transpirational pull for water and mineral absorption and upward movement.
                  ◦ Helps in temperature regulation (cooling) due to evaporation.
              • Day vs. Night: During the day, transpiration pull is the major force; at night, root pressure is the primary force for water transport.
      ◦ Components: Xylem vessels and tracheids.
  2. Phloem:
      ◦ Function: Transports food (soluble products of photosynthesis), amino acids, and other substances.
      ◦ Direction of Flow: Bidirectional (both upward and downward) – from leaves (where food is made) to all other parts of the plant (roots, fruits, seeds, growing organs).
      ◦ Mechanism: This movement of food is called translocation. It is an active transport process that requires energy in the form of ATP.
      ◦ Components: Sieve tubes and companion cells.
  6. Excretion
  Definition: Excretion is the removal of harmful metabolic waste products (mainly nitrogenous waste like urea and uric acid) from the body. This is different from egestion (removal of undigested food).
  Human Excretory System:
  The system responsible for filtering blood and forming urine. It includes:
  1. Kidneys (Pair):
      ◦ Bean-shaped organs located in the abdomen.
      ◦ Main Function: Filter blood to remove nitrogenous waste products (urea, uric acid), excess salts, and water.
      ◦ Nephrons: Each kidney is composed of millions of tiny structural and functional units called nephrons.
  2. Ureters (Pair):
      ◦ Thin tubes that connect the kidneys to the urinary bladder.
      ◦ Function: Transport urine from the kidneys to the bladder.
  3. Urinary Bladder:
      ◦ A muscular, bag-like structure that stores urine until it is passed out.
      ◦ Its function is under nervous control, allowing for voluntary control over urination.
  4. Urethra:
      ◦ A tube that transports urine out of the body from the urinary bladder.
  Urine Formation in Nephrons (Kidneys):
  Blood reaches the kidneys through the renal artery (carrying oxygenated but impure blood with waste). The renal artery branches into capillaries that enter each nephron. The process of urine formation involves three main steps within the nephron:
  1. Glomerular Filtration:
      ◦ Glomerulus: A cluster of blood capillaries located within a cup-shaped structure called Bowman’s Capsule in each nephron.
      ◦ Process: Blood flowing through the glomerulus is filtered under pressure. Nitrogenous wastes (urea, uric acid), glucose, water, amino acids, and excessive salts are filtered out of the blood and collected in the Bowman’s Capsule. This collected fluid is called the filtrate.
  2. Selective Reabsorption:
      ◦ As the filtrate passes through the tubular part of the nephron, essential and useful substances are reabsorbed back into the blood capillaries surrounding the tubules.
      ◦ Substances Reabsorbed: Glucose, amino acids, a major amount of water, and necessary salts.
      ◦ Factors Affecting Water Reabsorption:
          ▪ The amount of excess water present in the body.
          ▪ The amount of dissolved waste to be excreted (more waste requires more water to excrete it).
  3. Tubular Secretion:
      ◦ After reabsorption, remaining waste products (mainly urea, extra water, and some salts) are secreted into the collecting duct.
      ◦ This final urine then flows from the collecting ducts into the ureters and eventually to the urinary bladder.
  Artificial Kidney (Dialysis):
  • When kidneys fail, an artificial kidney can be used to remove nitrogenous waste products from the blood through a process called dialysis.
  • Key Difference from Natural Kidney: An artificial kidney does not involve selective reabsorption of useful substances.
  • The dialyzing fluid used has the same osmotic pressure as blood but without nitrogenous waste.
  Excretion in Plants:
  Plants use various methods to excrete waste products:
  1. Gaseous Wastes (O2, CO2): Exchanged by diffusion through stomata in leaves, lenticels in stems, and the general surface of roots.
  2. Excess Water: Removed through transpiration (loss of water vapor from aerial parts).
  3. Solid/Liquid Wastes:
      ◦ Plants can shed old leaves, bark, or fruits where waste products have been stored.
      ◦ Some waste substances are stored as resins, gums (especially in old xylem).
      ◦ Plants also secrete some waste substances into the soil around them.
  This concludes the detailed notes on “Life Processes” based on the provided transcript.