Biological Processes: Homeostasis and Plant Adaptations PDF

# Introduction The internal conditions of an organism are referred to as its internal environment. It includes H₂O quantity, different solutes, temperature, etc. For proper metabolic functions, the body requires all these conditions at a particular level. So homeostasis is a set of metab...

# Introduction The internal conditions of an organism are referred to as its internal environment. It includes H₂O quantity, different solutes, temperature, etc. For proper metabolic functions, the body requires all these conditions at a particular level. So homeostasis is a set of metabolic processes that maintain the internal environment of an organism within suitable limits. Why should the internal environment remain constant? Let’s take the example of temperature. The temperature of the external environment continuously changes during the day, but the enzymes work within a certain range of temperature; therefore, living organisms must keep their internal temperature within this range. Organisms maintain internal conditions by feedback mechanisms. How do organisms maintain homeostasis by feedback mechanisms? ## Feedback Mechanisms - **Condition Decrease/Condition Increase:** detected by feedback - **Receptor:** **-ve Feedback** - **Temp Decrease/Increase/ Glucose** - **Normal or set point:** **Feed Back Check & Balance** - **Condition back to normal by increasing/decreasing:** **Corrective Mechanism** - **Control center** ## Adaptation of Plants for Different Internal Conditions There are three main aspects of homeostasis: ### Osmoregulation: It is the maintenance of internal water and salt conditions by osmosis. ### Thermoregulation: The maintenance of temperature within suitable limits where enzymes can work optimally. ### Excretion: The process where metabolic excess substances from the body i.e. NH₃, urea, or uric acid, gums, latex, etc. are excreted or stored. ### Excretion or Storage of CO₂ At daytime, plants perform photosynthesis in green cells and respiration in all living cells. The CO₂ produced in respiration is utilized in photosynthesis. When the rate of photosynthesis is higher than respiration, the plant gets extra CO₂ from air and releases extra O₂ through stomata. At night, plants only perform respiration only CO₂ produced, which is removed by the process of diffusion through both surfaces. The green parts perform this gaseous exchange through stomata, while non-green parts perform this gaseous exchange through both surfaces. ### Removal of Extra Water The plant stores a large amount of water; this water can be removed from the plant in two ways: * **Transpiration:** The removal of water in the form of vapors from the aerial part of a plant. It occurs only at daytime. * **Guttation:** The removal of water in the form of liquid from the margin of leaves through special pores, hydathodes. It only occurs at night when water pressure is high in leaves and low temperature environment is present. Plants modify their leaves' size, structure, and structure of stomata to control the rate of transpiration. ### Osmetic Adjustment in Plants Plants grow in different conditions of water and salts. On the basis of water and salt quantity, there are four types of plants: * **Hydrophytes (hydro = water; phyta = plants)**: The plant which grows in fresh water; they live completely or partially in fresh water so called totally or partially submerged plants. They adapt themselves for removal of excess water which can enter in this condition. * These plants do not contain roots or have poorly developed roots. * They have broad leaves if partially submerged and have stomata at upper epidermis e.g. water lilly. * They may have thin and spongy tissues in leaves and stem in totally submerged plants e.g. Hydrilla. * **Halophytes (Halos= salt):** They grow in sea marshes or in salty water. In salty conditions water moves outside the cell which is not suitable for plants. To move water from outside to inside the plant develop following characters: * Plants develop salt glands where plants store salts by taking it through active transport. * Plants oppose salt to move outside from vacuole. * Some salt accumulated at the surface of the leaf which attracts water from air * **Mesophytes:** These plants grow in moderate water-containing soil. They will develop the following characters: * They have developed root systems which do not grow very deep. * They have moderate-sized leaves. * **Xerophytes:** Plants grow in soil of low water quantity. They grow in deserts, steep slopes, or at high altitude. To conserve water and absorb a proper amount of H₂O they develop following characters: * They have vertically growing deep root systems to absorb proper amounts of water (H₂O). * They possess thick waxy cuticles over epidermis to conserve water. * They have short-sized leaves or leaves are modified into spines to reduce the loss of water by reducing the number of stomata. * Some xerophytes have special parenchyma cells in the stem where they store water; this makes the stem soft, wet, and juicy called succulent organs e.g. cacti. # Homeostasis In Animals Like plants, animals also live in aquatic and terrestrial habitats. According to their environment, their cells require a more critical balance of water and solutes. Water continuously leaves and enters the cells with solutes to keep the water and solute in a constant quantity, which are required for smooth metabolic functions. ## Osmoregulation in Aquatic Environment The aquatic conditions are classified on the basis of the concentration of salt present in it. (i) **Freshwater:** The water which contains very low amounts of salt is called freshwater. (ii) **Marine Water:** The water which contains high salt is called marine water. Animals osmoregulate differently in both waters. ### Osmoregulation In Freshwater Freshwater animals have hypertonic conditions inside their body or cells. So, they always face the problem of flooding of H₂O and loss of salts. **Unicellular:** * **Pump out excess water by contractile vacuole** e.g. Amoeba, Paramecium, etc. **Multicellular:** * **Pump out excess water by producing dilute urine** * **Loss of salt is compensated by active uptake of salt by gills and skin as well as use of salt containing food.** ### Osmoregulation in Marine Animals Usually, marine animals have hypotonic conditions (low salt) inside the body. However, some marine animals develop hypertonic (high salt) or isotonic (the same salt condition) by metabolism. ## Osmoregulation in Terrestrial Condition Terrestrial conditions are harsh for living organisms because direct contact of heat to the body causes a loss of water which leads to dehydration. This is a major problem for terrestrial life. Only arthropods, molluscs, reptiles, birds, and mammals can survive in this habitat because: * **Their bodies are covered by exoskeleton or thick skin, which prevents the loss of water.** * **They conserve water by reabsorption in kidneys and rectum.** * **Some of them can produce water from fats catabolism with the help of peroxysomes i.e. camel, kangaroos.** * **Continuously drinking water or using liquid food.** ### Excretion During metabolism, living organisms catabolize protein and other nitrogen containing compound which produce toxic nitrogen generally called toxic compounds. If these compounds are retained they may be reaccumulated, and they can damage cells; therefore, they must be removed from the body. The removal of these nitrogenous metabolic waste is called excretion. **Plants** are autotrophs, initially they produce carbohydrates, which are products of carbohydrates are catabolized to produce CO₂ and H₂O. The products are not toxic. Autotrophs synthesize a variety of compounds, so the waste products of one reaction are utilized in other metabolic reactions as reactants and consumed. ### Excretion in Animals Animal cells produce their nitrogenous waste during metabolism and removed them either in tissue fluid or blood. So, the animals develop some organs to filter the tissue fluid or blood; these organs are called excretory organs. | Name of animal | Excretory Organs | Excretory Compound | Source | | ----------- | ----------- | ----------- | ----------- | | Janaria (Platyhelminthes) | Flame cells (Protonephridia) | Dilute urine | Tissue fluid | | Arthworm (Annelids) | Excretory ducts | Dilute urine | Coelomic fluid | | Cockroach (Arthropod) | Malpighian tubules | Uric acid pellets | Haemolymph | | Vertebrate | Kidneys | NH₃, Urea, Uric acid | Blood | ## Homeostasis In Man Humans have well-developed homeostasis systems. The main organs involved in homeostasis are: 1. **Skin:** The skin is considered as the largest organ of the body. It basically functions as a protective organ as the first line of defense. However, it also works efficiently as a homeostatic organ by maintaining temperature, water and salt. 2. **Lungs:** They maintain the levels of O₂ and CO₂ in the blood, body fluids, and the continuous flow of energy. 3. **Kidneys:** Kidneys are called filters of the body fluids since they maintain water by removing excess water. They also maintain urea, uric acid, creatinine, and other waste by excreting them through urine.. ### Structure of Human Skin Human skin consists of three layers called epidermis, dermis, and hypodermis. * **Epidermis:** The outer layer of skin is epidermis, made up of flat cells containing keratin protein. This layer does not contain any blood vessels. It is impermeable to water and prevents water loss from the body as well as acting as a protective layer by preventing the entry of microorganisms * **Dermis:** The layer present between epidermis and hypodermis contains many different structures i.e. nerve endings, receptors to detect temperature change, pain, pressure, etc. The dermis also contains sweat glands which secrete sweat on the surface to maintain temperature and also secrete urea, water, and salt. A network of arterioles are also present in the form of a network, which are involved in temperature regulation. The dermis also contains hair follicles and sebaceous glands which secrete oily sebum. * **Hypodermis:** The innermost layer of skin containing fat which acts as insulation against loss of heat, It also stores energy. ### Role of Skin In Regulating Body Temperature The skin is the organ which helps in regulating body temperature. When the receptor in skin detects change in body temperature from the set point, it sends nerve impulses to the brain. This occurs by feedback mechanisms to correct the temperature. **Body Temperature Start Rise** * **Production of Sweat:** The sweat glands starts to produce and secrete sweat. The sweat accumulates at the surface of the skin which evaporates with heat energy, so the body feels cooling. * **Laying down of hairs:** In hot conditions, muscles attached to the hair relax. This allows the hair to lie flat against the surface of the skin. * **Vasodilation:** Arterioles found in the form of a network in dermis dilate (become wider), which increases the flow of blood as well as bringing the blood vessels near the surface of the skin which allows more heat loss. This process of vessel dilation is called vasodilation. **Cold Condition** When body temperature starts decreasing * **Erection of hairs:** The muscles contract pulling the hairs upright and trapping a layer of insulating air next to skin. This is not very much effective in humans. * **Vasoconstriction:** Narrowing of blood arterioles of the dermis occurs which reduces the blood flow in capillaries of the skin, so less heat is lost. * **Decrease in sweat production:** The sweat glands stop to produce and secrete sweat, so it prevents the loss of energy. **Body Temperature Falls** * **Blood vessels constrict so that heat is conserved.** * **Sweat glands do not secrete fluid.** * **Shivering (involuntary contraction of muscles) generates heat, which warms the body.** **Body Temperature Rises** * **Blood vessels dilate, resulting in heat loss to the environment.** * **Sweat glands secrete fluid; the fluid evaporates, and heat is lost from the body.** ### Role of Lungs to Keep the CO₂ Concentration Low to Certain Levels Tissues/cells produce a large amount of CO₂ during aerobic respiration. As blood passes through tissues via blood capillaries, CO₂ diffuses into the blood where it reacts with water to form carbonic acid. This reaction takes place by an enzyme called carbonic anhydrase, present in R.B.C. The carbonic acid dissociates into H⁺ and bicarbonate (HCO₃^-). The level of H⁺ in blood is continuously monitored by special detectors (receptors), carotid bodies, and aortic bodies. Most of the bicarbonate ions are diffused out from R.B.C to blood plasma. A small amount of bicarbonate ions diffused back into the R.B.C., where it is again converted into carbonic acid, then into CO₂. This CO₂ diffuses out of the blood and into alveoli, where it is expelled out when breathing out. If the CO₂ level increases in blood, the pH of the blood starts increasing, so **the receptor sends a message to the control center**, which ultimately increases the breathing rate to **expel out the CO₂** efficiently. ### Role of Kidneys in Controlling the Blood Composition Blood is the fluid having cells. In plasma, it contains a high amount of H₂O and some solutes like Na⁺, Cl^-, Ca⁺², K⁺, etc. with nitrogenous waste. Liver continuously produces urea and NH₃ by breaking down amino acids. We continuously take different solute ions in our food, like Na⁺ Cl^-, Ca⁺², K⁺, etc. The concentration of H₂O, solutes and nitrogenous waste are maintained by kidney through processes of filtration and reabsorption, which we will study in the next topics. # Urinary System in Man The urinary system of man consists of: * **A pair of kidneys** ### Structure of A Kidney Kidneys are reddish-brown bean-shaped organs, situated at the dorsal side of the abdominal cavity on either side of the vertebral column. The kidneys lie above the waistline. Each kidney has an area in the center of its concave surface which faces the vertebral column. This area is called the **hillus**. The **renal** **artery**, **renal** **vein**, nerves, and **ureter** are connected to each kidney at the **hillus**. * **The ureter** is a narrow tube which connects the kidney to the urinary bladder. Urine passes through the ureter to the urinary bladder. * **The urinary bladder** is a thin-walled muscular bag situated toward the bottom of the abdominal cavity in front of the rectum which stores urine. * **The urethra** is a tube, which comes out from the urinary bladder and runs down and opens outside the body through the urinary opening; It passes urine from the bladder to outside the body. ### Structure of a Kidney * **Kidney** is enclosed in a membrane called **peritoneum**. A fluid is filled in between peritoneum and kidney; this is called **peritoneal fluid**, which reduces friction. A longitudinal section of kidney shows three main parts: the **cortext**, the **medulla**, and the **pelvis**. ## Function of Nephron The renal artery when enters into the kidney, it divides into millions of branches called **afferent arteriole**. Blood enters the kidney by renal artery gets into **afferent arterioles**. * **Each afferent arteriole further divides into numerous blood capillaries in Bowmann's capsule; these are collectively called glomerulus. Bowmann's capsule with glomerulus are collectively called the Malpighian body or renal corpuscle.** * **Blood leaving the glomerulus through the efferent arteriole enters the blood capillaries surrounding the nephron.** * **Blood capillaries surrounding a loop of Henle's unite to form venule, which ultimately joins to form a branch of the renal vein.** ### Role of Kidney in Urine Formation ### Urea Formation Urea is formed within the liver cells. The liver stores surplus glucose from food by converting it into glycogen and other foods but it cannot store proteins. Excess amino acids break down and get the energy from it. So the amino group (NH₂) is removed from amino acids which is very poisonous and can kill the cell when stored in a high concentration. So the liver cells quickly convert NH₃ into a less poisonous substance, urea. This urea is carried by blood to the kidneys and excreted. A small amount of urea is also excreted in sweat. ### Urine Formation Excess mineral salts and nitrogenous waste products i.e. creatinine and uric acid, which are poisonous if accumulated in the body, are removed from the body with water. This mixture is called urine. Urine formation takes place in the kidney. There are two main processes involved in the formation of urine within the nephron: 1. **Filtration:** Filtration is the process of taking out material from the blood: * **Ultrafiltration:** Ultrafiltration occurs at the Malpighian body when the blood from the afferent arteriole enters into glomerulus located in Bowmann's capsule. Most of the blood plasma is forced out of the glomerulus blood capillaries into Bowman's capsule without any selection. The process of non-selective filtration is called ultrafiltration. * **Selective filtration:** Selective filtration occurs at the proximal and distal convoluted tubules when blood flows into the convoluted tubules. Only those substances which are required by the body are filtered out from the blood by active transport. It requires some energy. 2. **Reabsorption:** In a normal adult about 120 cm³ of filtrate is formed in the kidney every minute; if this large amount of filtrate is allowed to pass out from the body as urine, the body will dehydrate, and death may occur. To prevent this huge loss of water and useful salts, as the filtrate passes through the nephron, useful substances and excessive water are reabsorbed into the blood stream by: * **Non-selective reabsorption:** Non-selective reabsorption occurs at distal and proximal convoluted tubules without any selection. * **Selective reabsorption:** Selective reabsorption occurs at the loop of Henle's and collecting duct with the help of hormones i.e. Antidiuretic hormone (ADH), Parathyroid hormone (PTH) and calcitonin. ### Role of Kidneys in Osmoregulation The water potential (the ability to lose water) of blood in the body needs to be kept constant because big and sudden changes in the water potential of blood can lead to serious problems e.g. if plasma becomes too dilute, the water will move out of the cell, and it will swell and possibly burst. On the other hand, if the blood plasma becomes too concentrated, issues will become dehydrated and shrink. This control of water and salt content of the body is known as osmoregulation. * **Sweating:** The loss of H₂O stimulates the water potential of blood to decrease. * **Intake of H₂O by drinking:** The intake of water increases the water potential of blood. The hypothalamus releases ADH hormone, which is carried by the blood stream to the pituitary gland. The pituitary gland releases less ADH hormone for collecting duct of the nephron. * **Collecting duct of nephron absorbs less H₂O into the cells and capillaries:** Results in **concentrated urine**. * **Collecting duct of nephron absorbs more H₂O into the cells and capillaries:** Results in **dilute urine.** # Disorders of Kidneys ### Kidney Stone Kidney stones are solid masses that form from the crystals of calcium oxalate or calcium carbonate. Sometimes uric acid and cysteine are also present in it. These molecules separate out from urine, precipitate in the kidney, and deposit in the form of a stone. However, these stones are sometimes not hard, therefore they break into sand-like crystals which can pass out of the body with urine, without pain. However, larger sized stones damage the kidney tissues; they may stick anywhere in the urinary tract and cause renal failure with pain. ### Kidney Stone Treatment * **Lithotripsy:** If the size of the stone is comparatively small, lithotripsy can be used to break the stone by ultrasonic waves (sound waves). The broken rudiments drain out from the kidney along with urine. * **Renal Surgery:** Larger sized stones cannot be broken by lithotripsy, so they are removed only by the process of renal surgery. * **The large intake of water is the only measure to minimize the chances of formation of stones in the kidney.** ### Kidney Failure Sometimes the nephrons in the kidney stop working; it is called renal failure. This is mainly due to solute imbalance in blood and the kidneys. The failure of kidneys allows urea and other waste materials to accumulate in blood. The amount of H₂O is not regulated also. This imbalance of solutes in the blood results in death, unless the patient is given treatment to filter out the waste by machine: ### Kidney Dialysis A patient with two healthy kidneys may donate one kidney and survive with one kidney. A patient with kidney failure may get a kidney transplant. However, if a donor is not available, the patient can be treated with dialysis. Dialysis helps to clean the patient’s blood from metabolic waste products and toxics. For effective treatment, the patient needs undergoing dialysis 2 - 3 times a week. Each session lasts about 3-5 hours, depending on the patient’s body size and medical condition.