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GASEOUS EXCHANGE IN ANIMAL Norfarahin Norwen | [email protected] Aquila Watercolour Illustrator Finch Fight Illustrator...

GASEOUS EXCHANGE IN ANIMAL Norfarahin Norwen | [email protected] Aquila Watercolour Illustrator Finch Fight Illustrator Mother Daughter Illustrator LEARNING OBJECTIVES To explain the gaseous exchange in human To explain the gaseous exchange in invertebrate and vertebrate  Human respiratory structure  Breathing mechanism of human Exhalation Inhalation External intercostals External intercostals muscles relax, internal muscles contract, intercostals muscle internal intercostals contract. –rib cage muscle relax. –rib moved lowered and cage moved up move inwards toward the front Diaphragm muscles Diaphragm muscles relaxes and curves up contract and flatten Volume of the Volume of the thoracic cavity thoracic cavity decreases increases Higher pressure in Higher atmospheric thoracic cavity pushes pressure pushes air air out of the lungs into the lungs Human respiratory structure Main organ; lung Trachea branches into two main bronchus/bronchi. Further into smaller tubes; bronchioles. Each ends in a cluster of microscopic air sacs; alveolus/alveoli respiratory structure where the gas exchange between the blood and air occurs by simple diffusion Alveolus: Site for Gaseous Exchange Structural adaptations: Small size and high number present –for larger surface area Moist wall –allows respiratory gases to dissolve easily Thin wall –for quick and easy diffusion of gases Rich supplied with blood capillaries –to increase the rate of diffusion and the rate of the transportation of gases  Exchange of O₂ and CO₂ -alveoli and blood capillary During inhalation, partial pressure of O₂ is higher in alveoli than blood capillary. O₂ diffuses into blood capillary PCO₂ is higher in blood capillary than alveoli. So, CO₂ moves into alveoli in opposite direction and gets exhaled out  Exchange of O₂ and CO₂ -blood capillary and tissues Partial pressure of O₂ is higher in blood capillary than tissues. O₂ gets release into tissues PCO₂ is higher in tissue than in blood capillary. So, CO₂ diffused in opposite direction into blood  Transport of Oxygen in Human 98% O2 in blood transported by haemoglobin (Hb) in the form of oxyhaemoglobin (HBO₂) Another 2% dissolved in plasma, transported by it Transport of Carbon dioxide in Human 7% of the CO₂ dissolved in the plasma 23% of the CO₂ combines with haemoglobin (Hb) forming carbaminohaemoglobin (HbCO₂). It then breaks down, releasing CO₂ into the alveoli 70% of excess CO₂ diffuses into red blood cells reacting with water (H₂O) becoming carbonic acid (H₂CO₃). It then moving into the plasma while dissolved CO₂ diffuses into the alveolar air space The Respiratory Control System Respiratory controls centers: Medulla Oblongata –controls respiration to cause breathing to occur by sending signals to the muscles of respiratory structure Also controls the reflexes for nonrespiratory air movements Pons –controls the rate or speed of breathing Regulation of Breathing is a form of negative feedback. The goal is to keep pH blood within normal range. Chemoreceptor detect changes in chemical composition of blood and send information to the brain. An increase of CO2 concentration leads to a decrease in the blood pH, due to the production of H+ ions from carbonic acid. In response, the respiratory center in the medulla sends nervous impulses → external intercostal muscles and the diaphragm, to allow respiratory muscles contract and relax faster. Breathing and ventilation rate increase causing more O2 to be inhaled and the O2 concentrations returns to normal. As excess CO2 is eliminated from the body, the CO2 concentration and blood pH return to normal level. Respiratory Problems 1. Pneumonia lung(s) infection from bacteria / viruses / fungi, causes alveoli fill up with fluid or pus Symptom: mild to serious cough with/without mucus fever, shaking chills Trouble/rapid in breathing, rapid pulse Treatment: can be prevented by vaccines. Can be treat by antibiotic, viral, or fungal medicines, If get worse? Antibiotics given through intravenous line and oxygen therapy Respiratory Problems 2. COPD: Emphysema long-term exposure to airbone irritants damaging air sacs, inner walls become weaken and rupture. It then affect amount of O₂ → bloodstream Symptom: long-termed coughing shortness of breath coughing with mucus wheezing, ongoing fatigue, trouble sleeping chest tightness Treatment: stop smoking, avoid secondhand smoke and air pollutant, wear protection from chemical fumes, varnish, paint or dust Respiratory Problems 3. COPD: Chronic Bronchitis exposure to cigarette smoking, air pollution of dust or toxic gases inflamed the lung airways, destroy cilia; bronchi cause sticky mucus to build up in it Symptom: shortness of breath Coughs for at least 3 months wheezing chest pain tiredness Treatment: lifestyle changes and medication such bronchodilators to relax air passages, steroids to lessen the swelling. Oxygen therapy, specialized rehab programme, lung transplant Respiratory Problems 4. Asthma Major noncommunicable disease (NCD) that makes airways narrow, swell, and blocked due to producing of extra mucus Symptom: breathing difficulty shortness of breath coughing whistling, wheezing trouble sleeping Treatment: inhaled medication, avoid asthma triggers such airborne substances, air- conditions cold and dry Respiratory Problems 5. Tuberculosis contagious infection of Mycobacterium tuberculosis that attacks lungs, can also spread to other part of human body. Start with Primary, Latent, Active to Active outside lungs Symptom: breathing difficulty, chest pain fever, chills cough last more than 3 weeks coughing up blood Night sweats Loss appetite, weigh loss Treatment: most cured by antibiotics, medications for at least 6 to 9 months  Invertebrate Circulatory System Roundworm Phylum Porifera Phylum Cnidaria Phylum Nematoda  The blood flows This system has freely through vessels that cavities since there conduct blood are NO vessels to throughout the conduct the blood body *annelids & *mollucs & arthropods vertebrates Gaseous Exchange in INVERTEBRATE respiration Skin-breathing Movement of O2 and CO2 across moist respiratory surfaces takes place entirely by diffusion Survive for extended periods only in damp or aquatic habitat  Tracheal systems Air enters the spiracles; small holes located at the thorax and abdomen Air is distributed through the body of the organisms via trachea and tracheoles that come into close contact with the organisms' cells  Vertebrate Circulatory System All vertebrates have a closed cardiovascular system Vertebrate heart Two different circulatory pathways in vertebrates; Atrial chamber(s) of heart receive Single-loop blood from general circulation heart only pumps blood to gills Ventricle chamber(s) of heart pump Two-circuits blood out through blood vessels Pulmonary circuit - heart pumps blood to the lungs Vertebrate vessels Arteries carry blood away from heart Systemic circuit - heart pumps blood to all parts Arterioles lead to capillaries of the body except for the lungs Capillaries exchange materials with tissue fluid Venules lead to veins Veins return blood to heart Fishes single loop Amphibians, Reptiles double loop Heart with single atrium and Two atria and single ventricle pumps a single ventricle blood in the pulmonary circuit to the lungs enriched blood with oxygen when it leaves gills Also pumps blood in the systemic circuit to the rest of the body O2 -rich and O2 -poor blood enter the single ventricle, it is kept separated O2-poor blood is pumped firstly out of the ventricle into the lungs before O2- rich blood enters and is pumped into the systemic circuit Birds and Mammals Two atria and two ventricles in the heart and there’s complete separation of the pulmonary and systemic circuits Right ventricle pumps blood under pressure to the lungs, and the larger left ventricle pumps blood under pressure to the rest of the body Gaseous Exchange in VERTEBRATE respiration A fish simply open its mouth and let water flow past its gills Each gill arch has two rows of gills filaments, composed of flattened plates called lamellae Blood flowing through capillaries within the lamellae, picks up oxygen from the water Counter current exchanges mechanisms; water flow over the gills in one direction while blood flows in opposite direction through capillaries Mouth By vascular bucco-pharyngeal. Occur while the frog is not submerged in water Skin Thin, permeable to water and kept moist as it covered by mucous lining. Entirely dependent on respiration through the skin when they are underwater. Lungs Consist of a pair of thin-walled sacs connected to the mouth through an opening called glottis. The membranes of the lungs are thin, moist and covered by a network of capillaries. Use their throats, nostrils and mouths together to bring in and expel gases. Bird’s respiratory system consists of paired lungs with connected to two air sacs. Passage of air through the entire system requires two cycles of inhalation and exhalation cycle, before it is fully used and exhaled out of the body. 1st inhalation: Fresh air travels through trachea, which splits into left and right primary bronchi. Some air enters the lungs where gas exchange occurs while the remaining air fills the posterior air sacs 1st exhalation: Posterior air sacs contract, pushing air into lungs and undergoes gas exchange. *The spent air in the lungs is displaced by the incoming air and flows out the body through the trachea 2nd inhalation: *Fresh air again enters both the posterior sacs and the lungs. Spent air in the lungs is again displaced by incoming air but it cannot exit through trachea because fresh air is flowing inward. Instead, spent air passes through lungs and fills anterior air sacs 2nd exhalation: Anterior air sacs contract, air in the lungs flows out through the trachea, and fresh air in the posterior sacs enters the lungs for gas exchange TRANSPORT IN ANIMALS (Circulatory System) Norfarahin Norwen | [email protected]  LEARNING OBJECTIVES 1. Briefly describe: ▪ The circulatory system in invertebrates and vertebrates 2. Briefly explain: ▪ Human heart and its circulatory system ▪ Human cardiac cycle ▪ Human cardiac conduction system: sinoatrial node (SA) and atrioventricular node (AV) ▪ The lymphatic system in human 3. State: ▪ The common cardiovascular disorders and diseases Circulatory System Responsible for transporting oxygen, nutrients to the cells It picks up wastes, which are later excreted from the body by the lungs or kidneys Heart Anatomy  Human Heart Cardiovascular system; a closed circulatory system, involving heart and blood vessels – Septum divides the heart into right; pumps O2-poor blood → lungs and left sides; pumps O2-rich blood → tissues – Chambers upper, thin-walled of atria receive blood and lower, thick-walled of ventricles pump blood away from the heart  Heart Valves Valves open and close to control blood flow through heart Atrioventricular valves between the atria and ventricles Tricuspid valve right atrium → right ventricle Bicuspid (Mitral) valve left atrium → left ventricle Semilunar valves between the ventricles and their attached vessels Pulmonary valve right ventricle → pulmonary artery Aortic valve left ventricle → aorta  Circulatory Fluid Two main parts: Plasma composed mostly of water (90–92%) and proteins (7–8%). Also contains smaller quantities of many types of molecules including nutrients, wastes, salts Formed elements; red blood cells (erythrocytes), white blood cells (leukocytes), and platelets Red blood cells, assist transportation of oxygen using haemoglobin White blood cells, for protection against illness and diseases – Lymphocytes help fight infections T cells regulate function of other immune cells and directly attack various infected cells and tumors. B cells produce antibodies, specially target bacteria, viruses, and othe foreign materials – Granulocytes help destroy bacteria, viruses by phagocytosis – Neutrophils “immediate response” cell Platelets, for coagulation Formation of fibrin clot, which covers wound and prevents blood leaking  ABO Blood Grouping ABO System Presence or absence of type A and type B antigens on red blood cells determines a person’s blood type Four types of blood: Human Circulatory System 1.The Pulmonary Circuit Heart and lungs deoxygenated blood from body → right atrium → right ventricle → pulmonary trunk → right and left pulmonary arteries → lungs Blood passes through pulmonary capillaries CO2 is given off , O2 is picked up O2-rich blood returns to heart through pulmonary veins 2.The Systemic Circuit Heart and the rest of body oxygenated blood to organs, start with the left atrium → left ventricle → aorta, branches into major arteries to the upper body. Then through the diaphragm further into the iliac, renal, and suprarenal arteries for lower body parts Hepatic portal system Venous system, transports blood from the gastrointestinal tract and spleen → liver Why is it needed to pass through the liver before returns back to the heart? To regulate substances in the blood by ensuring it first processed by liver before reaching the systemic circulation  Blood Vessels Arteries Thick wall, elastic tissue Smaller branch into arterioles carry blood away from the heart → capillaries Capillaries Thin walls (1 cell thick) Extremely narrow (8–10 µm wide) exchange of material with tissues Veins Thin layer of muscle Venules drain blood from the capillaries; join to form a vein return blood from the capillaries → heart Often have valves to allow blood flow → heart and to prevent the backward  Blood Circulation to Coronary Circulation System Blood in the heart chambers is not supplied to the myocardium (cardiac muscle) 2. Coronary Veins Coronary Sinus (largest) Branches feed into sinus of the heart 1. Coronary Arteries Right and Left Coronary Arteries Deoxygenated blood is emptied from myocardium → the right Branches along heart from atrium of heart the ascending aorta Carries oxygenated blood → heart muscle for cellular respiration  Cardiac Cycle 3 phases of each heartbeat; atria contract, ventricles contract, all chambers at rest Diastole = relaxation | Systole = contraction Heart beats produced “lub-dub ” sound as the valves of the heart close  Blood Pressure The beat of the heart supplies pressure that keeps blood moving in the arteries Systolic Pressure pressure in arteries when heart beating Diastolic Pressure pressure in arteries when heart rests between beats Respiratory movements Presence of valves in veins Heart pumps blood through the arteries, puts pressure on the artery walls Flow of blood from the heart → the capillaries Blood pressure falls or low in veins from limbs, resulting blood cannot flow back to the heart Skeletal muscle contraction Blood Pressure Reading Range is variable; Normal systolic 139 – 120 mmHg diastolic 89 – 80 mmHg Hypotension low systolic, below 120 mmHg often associated with illness Hypertension high systolic, above 140 mmHg can be dangerous if it is chronic  Sinoatrial Node and Atrioventricular Node Rhythmic contraction of heart is due to cardiac conduction system Cardiac contraction AV node delays cardiac triggered by SA node, impulses (signals) from SA node send signals to both left to allow atria contract and and right atria to contract, empty their contents, before pump blood to ventricles the ventricles contract electrical signals leaves AV node for ventricles to contract and pump blood to lungs and the rest part of human’s body Heartbeat is produced for every 0.85s and is called as cardiac pacemaker Electrical changes during cardiac cycle in heart is recorded by electrocardiogram  Diseases and Disorders Heart Attack myocardial infarction occurrence of atherosclerosis; cholesterol- containing deposits (plaque) also buildup of fat block the blood stream. It disrupts blood flow in arteries causes tissues in the heart muscle to die Symptoms; Chest pain, pressure, tightness, pain, squeezing, aching pain or discomfort on shoulder, arm, back, neck, jaw, teeth, upper belly Cold sweat, nausea Heartburn, indigestion Fatigue, light-headedness, sudden dizziness Treatments; limit work, limit travel. Lifestyle changes, join cardiac rehabilitation programme  Diseases and Disorders Stroke brain attack occur due to interruption of blood supply to part of the brain; Ischemic stroke also may be cause by blood vessel in the brain ruptures or bursts; Hemorrhagic stroke Symptoms; Trouble speaking and understanding, problem seeing in one or both eyes Face, arm or leg paralysis or numbness, headache, trouble walking Treatments; emergency care, call 999 Diseases and Disorders Hypertension ‘silent killer’ that usually don’t have any serious symptoms. Occur when forces of blood pushing against artery walls consistently too high due to (mostly) unhealthy lifestyle Symptoms; Shortness of breath/Chest pain Headache Blurring vision Vomiting Abdominal pain Treatments; lifestyle changes and medications Lymphatic System A group of; Drainage lymph vessels; Lymphoid tissues (Peyers’ patches) Lymphoid organs that provides protection to human from any infection and balance human body fluids in healthy state Flow accomplished by; Function; skeletal muscle pump, respiratory pump, Collect, drain fluid, and solutes and valves prevent backflow from interstitial tissues (lymph fluid) Transport fats absorbed from small intestine back → circulatory system Body immune system  Components; 1. Lymph fluid Similar in composition to blood plasma except; no erythrocytes and large protein molecules It contains; water, lymphocytes, granulocytes, respiratory gases, nutrients, ion, urea, hormones 90% is returned to blood capillaries 10% that does not return becomes part of the interstitial fluid Function; Intermediary between capillaries and tissue Carries nutrients and hormones to cells Removes carbon dioxide, and waste from cells 2. Lymph nodes Oval structures located along lymphatics, enclosed by a fibrous capsule 3. Lymph organs Tonsils, multiple groups of large lymphatic nodules, located at mucous membrane of the oral and pharyngeal cavities Pharyngeal tonsil - Posterior wall of nasopharynx Palatine tonsils - Posterior-lateral walls of oropharynx Lingual tonsils - Base of tongue Spleen, similar to node capsule present without afferent vessels or sinuses, located between the stomach and diaphragm Function; To filters and stores blood Thymus, capsule divides it into two lobes, located behind the sternum in the mediastinum Function; For differentiation and maturation of T cells Organization flow of Lymph Fluid Lymphatic capillaries Contain capillaries except cartilage, Central Nervous System, eyeball, spleen Epithelial cells overlap and attached loosely to allows fluid to come in but not let it out Lymphatic vessels Accompany and parallel veins in most of body excluding nails and hair Types; Lymphatic capillaries, collecting vessels, trunks, and ducts  Ultimately deliver lymph fluid into two main channels; union of lymphatic trunks the lymphatic ducts 1. Right lymphatic duct drains right side of head, thorax, and right arm (enter right subclavian vein) 2. Thoracic duct drains left side of head, thorax, left arm, and lower ½ of body (enter left subclavian vein)  Oedema Lymphadenopathy / Lymphadenitis  Circulatory versus Lymphatic Circulatory system Lymphatic system is responsible for collecting and is responsible for collecting and removing distributing oxygen, nutrients and hormones waste products left behind in the tissues to the tissues of entire body flows in a closed continuous loop flows in an open circuit from the tissues throughout the body via the arteries, into lymphatic vessels. Once within these capillaries, and veins. vessels, lymph flows in only one direction. Blood is pumped. The heart pumps blood Lymph is not pumped. It passively flows into the arteries that carry it to all of the from the tissues into the lymph capillaries. body. Veins return blood from all parts of Flow within the lymphatic vessels is aided the body to the heart. by other body movements such as deep breathing and the action of nearby muscles and blood vessels.  Circulatory system Lymphatic system Blood consists of the liquid plasma that Lymph that has been filtered and is ready transports the red and white blood cells to return to the cardiovascular system is a and platelets. clear or milky white fluid. Blood is visible and damage to blood Lymph is invisible and damage to the vessels causes obvious signs such as lymphatic system is difficult to detect until bleeding or bruising. swelling occurs. Blood is filtered by the kidneys. All blood Lymph is filtered by lymph nodes located flows through the kidneys where waste throughout the body. These nodes remove products and excess fluids are removed. some fluid and debris. They also kill Necessary fluids are returned to the pathogens and some cancer cells. cardiovascular circulation. LU2: BIOCHEMISTRY, CELL STRUCTURE & FUNCTION: TRANSPORT SYSTEM & GASEOUS EXCHANGE in Plant Mohamad Fhaizal bin Mohamad Bukhori [email protected] 012-3942055 Pejabat Akademik 2  LEARNING OBJECTIVES 1. XYLEM and transpiration. ▪ Describe the basic principle of water and minerals uptake by roots. ▪ Describe the basic concept of root pressure and theory of capillarity: adhesion-cohesion tension. ▪ Explain the basic mechanism of transport based on water potential. 2. PHLOEM and translocation. ▪ Describe the basic concept of mass flow and pressure flow hypothesis. ▪ Explain the basic mechanism of active transport and pressure flow model.  PLANT TRANSPORT SYSTEM Occurs in 3 LEVELS 1. The uptake and loss of water and solutes from cell. 2. Transport of water and substances from cell to cell. 3. Long distance transport with sap in xylem and phloem along the whole plant.  Xylem Transports sap (water) from roots to Transports sap (water and leaves. sugar) from source to sink. Complex principal water conducting tissue in vascular plants. It is also involved in conducting dissolved minerals, in food storage, and in supporting the plant body. Source ▪ Location/region of where photosynthesis occurs and organic solutes are synthesized. ▪ E.g., Green leaves of plants. Organic solutes - sucrose and amino acids loaded into sieve tubes of phloem. Sink ▪ Growing shoot, root regions, developing flowers, fruits, storage organs such as tubers, bulbs etc. ▪ E.g., Sucrose is unloaded from sieve tube. 1. XYLEM AND TRANSPIRATION ▪ Plants imbibe and transpire water more than animals do, as they have no re-circulation system. About 99% of all water entering the roots, leave the leaves via the stomates (transpiration) without ever taking part in metabolism. ▪ A single plant can transpire ±60 L of water in one growing season. ▪ Water movement is due to differences in potential between soil, root, stem, leaf and atmosphere. ▪ Under normal condition, the water potential in soil is higher than in root cell cytosol, resulting in water flowing to follow the potential gradient. This is known as bulk flow, and it is the primary force driving water through xylem. 1. XYLEM AND TRANSPIRATION ▪ The aqueous solution of dissolved minerals in the xylem is known as xylem sap. ▪ Bulk flow is much faster than diffusion or osmosis, reaching the rate of 15-45 moles/hour, depending on environmental conditions and the size of the xylem lumen. ▪ Xylem raises water up to 350’ above the ground in some of the largest trees on earth. ▪ But, is the water being pushed or pulled along the xylem for transpiration?  Absorption and Transport of Water and Minerals in Plants ▪ Mineral's ions are needed for the plant’s metabolism. ▪ Solutes tend to diffuse down concentration gradients. ▪ Root hairs increase the surface area for absorption. ▪ Surface cell membranes and tonoplast of root cells have transmembrane proteins. ▪ Transmembrane proteins functioned as channels, carriers or pumps to move solutes into cells and from cell to cell. Passive Transport ▪ Osmosis: Diffusion across a membrane. ▪ Generally slow, unless solutes travel through transport proteins (or selective channels: gated-environmental stimuli open or close) in the membrane. Active Transport ▪ Require energy to move solutes up to concentration or charge gradient. ▪ E.g., Proton pump create membrane potentials; potential energy can be used to perform cellular work. The membrane potential provides the energy to uptake some minerals, e.g., K+ ions The membrane potential provides the energy for co-transport of ions up their concentration gradients, as H+ ions move down theirs. The membrane potential provides the energy for co-transport of some neutral molecules (e.g., sugar) up their concentration gradients, as H+ ions move down theirs.  Root Pressure : Pushing Xylem Sap ▪ Water enters the root because the water potential of the root tissues is almost always lower than of the soil, with its high dissolved mineral content. ▪ Water entering the stele may travel via one of the 3 routes defined: Apoplast pathway (passive diffusion: important route) ▪ Water moves across spaces between cellulose fibres in the cell wall. Symplast pathway (active transport) ▪ Water moves through cytoplasm of the cells. ▪ Cytoplasmic strands in the plasmodesmata allow water to move between cytoplasm from one cell to adjacent cell down a water potential gradient. Vacuolar/Transmembrane pathway ▪ Water moves through vacuoles, cytoplasm & cell wall. At night; ▪ stomates are usually closed. ▪ endodermis prevents leakage of ions out of the stele into other tissues. ▪ resulting decrease in water potential in the stele (due to the accumulation of ions). ▪ resulting flow of water from the cortex into the stele (root pressure: xylem sap being pushed up the xylem because of incoming water from the root). ▪ root pressure, exerted from below, is positive pressure potential, since potential increases as one moves up the stem. ▪ root pressure is sufficient to lift water no more than a few feet above the ground.  Guttation ▪ In a small plant, root pressure could result in potentially harmful water pressure buildup at night, when stomates are closed. ▪ Many herbaceous plants have special openings on the leaf margins called hydathodes. ▪ These allow root pressure water to escape (forming lovely little beads of dew overnight) and preventing cell rupture due to too much water pressure. ▪ This process is known as guttation, and its results are generally observable only in the early morning, when humidity is relatively high.  Water Transport in Plant Roots ▪ The characteristics of root hairs: i. Thin cell walls. ii. Large surface area over volume ratio for absorption of water and minerals. ▪ Water [high water potential in Soil > Root hair] → Root hair → Cortical cell → Cell to cell. ▪ Water is drawn by osmosis process; i. Root cells actively pump ions (use ATP) into cells. ii. High concentration of ions creates a greater osmotic pressure in plant than surrounding soil water; water moves into cells by osmosis. ▪ 3 main routes for movement of water across root: i. Apoplast pathway ii. Symplast pathway iii. Vacuolar pathway  Shoot Tension : Pulling Xylem Sap 1. Water movement in plants not only from below, via +ve pressure, but also by pulling from above via -ve pressure potential: potential decreases as one (water) moves up the stem. 2. This occurs via transpiration. 3. The air spaces inside spongy mesophyll are quite humid, as they are constantly in contact with moist cell walls and vascular tissue filled with xylem sap. 4. On typical, non-rainy days, the water potential of the atmosphere is far lower (more -ve) than that of the spaces inside the mesophyll. 5. This means that water will want to travel out of the stomates to the area of relatively low water potential. 6. As one moves down the plant, water potential increases. Here's a hypothetical array of water potentials in a soil and plant system:  Theory of Transpiration Water evaporate from cell walls of palisade and spongy mesophyll cells into sub-stomatal cavity; ▪ Lower the water cavity. ▪ Drawn water from neighboring mesophyll cells that has high water potential. ▪ Until water is drawn from xylem vessels in the leaf (via apoplast / symplast / vacuolar) Cohesion: Water molecules form continuous water column in the xylem vessels ≈ by hydrogen bond that formed between the water molecules. Adhesion: Attractive forces between water molecules and the hydrophilic xylem walls ≈ prevent water column from moving down.  Lower Ψ at the top is the tension that pulls water up from the bottom Transpiration creates a water pressure gradient 4. Endodermal cells actively secrete mineral into xylem 3. Water potential decrease 2. Water from root cells drawn into xylem and produce root pressure 1. Root pressure – a +ve hydrostatic pressure to push the water up the stem i. Evaporation at the surface of the leaf keeps the water column moving. ii. This is the strongest force involved in transpiration. Cohesion and adhesion cause water to crawl up narrow tubes. The narrower the tube the higher the same mass of water can climb. i. Cohesion between water molecules creates a water chain effect. ii. As molecules removed from the column by evaporation in the leaf, more are drawn up. i. Pressure differences created by transpiration draws water out of the roots and up the stems. ii. This creates lower water pressure in the roots, which draws in more water.  Transpiration ▪ Loss of water as water vapour from plant to atmosphere (99%). ▪ More water is loss through stomata, little by cuticle layer, lenticels (woody stems). ▪ 1% photosynthesis or other metabolic process, to maintain turgidity. ▪ Rate regulated by two guard cells surrounding each stoma (or stomate). ▪ Guard cells open when water moves into cells by osmosis (i.e., cells are turgid). Turgor results from active uptake of Potassium (K+) ions, stimulated by light; and subsequent influx of water by osmosis.  Factors Effecting Rates of Transpiration Importance of Transpiration ▪ Maintain water potential gradient that moves water and dissolved minerals from roots to aerial part of plants. ▪ Evaporation of water from leaves absorbs latent heat of vaporization, cooling leaves during hot and dry weather.  External Internal 1. Temperature 1. Leaf Surface ▪ Increase kinetic energy, increase movement water ▪ Increase leaf surface, increase transpiration. molecules, thus, diffuse through stomata faster. ▪ Less stomata, thin needle-shaped and rolled leaves, reduce ▪ High temperature, low humidity, increase rate of diffusion of surface area exposed to air ≈ decrease evaporation of water vapour from leaf. water from leaves. 2. Light 2. Location of Stomata ▪ Day: High light intensity, stimulates opening of stomata ≈ ▪ Dicotyledonous plants have stomata on the lower leaf increase transpiration. surface ≈ reduce transpiration. ▪ Night: Low light intensity, stimulates stomata to close ≈ reduce transpiration. 3. Humidity 3. Density of Stomata Pores per unit of leaf and size of stomatal pore. ▪ Low humidity (High vapour pressure). ▪ Increase gradient of water vapour saturation between substomatal cavity and atmosphere ≈ Increase transpiration. 4. Air Movement ▪ Carries away water vapour outside stomata. ▪ Thus, creates steep concentration gradient and water vapour from substomatal cavity diffuses rapidly to outside. ▪ High dry, windy condition, increase transpiration. ▪ Low air movement, water vapours accumulate around stomata, reduce concentration gradient, reduces water loss. 5. Water Supply ▪ Rate of transpiration higher than rate water absorption from soil ≈ stomata close and reduce water loss by transport. 4. Water from top of xylem vessel reduces 3. Reduce hydrostatic pressure 2. Water column under tension and is pulled from roots to leaves 1. Movement of water up the xylem vessel is by mass flow. Thus, what are the characteristic of xylem vessel in facilitating water transport in plants?  Characteristic of Xylem Vessel 1. Hollow, tubular cells. 2. Composed of 5 cell types: tracheids, vessels, parenchyma, sclereids (short sclerenchyma cells), and fibers. ▪ The tracheids (small diameter) and vessel (large diameter) elements form the bulk of the tissue. They are heavily strengthened and are the conducting cells of the xylem. ▪ Parenchyma cells are involved in storage, while fibers, and sclereids provide support. 3. Dead at maturity: no protoplasm, forming a hard skeleton that serves only to support the plant. 4. Lignified cell walls: to give strength (withstand the tension and prevent from collapsing) and makes xylem waterproof; vessels does not collapse under tension and water does not steep out. * Pits: present in the lignified walls, for water to move out laterally to neighbouring cells. 5. Long continuous tube. 6. Narrow and cappilarity: increases adhesion between water molecules and walls of xylem vessels. 2. PHLOEM AND TRANSLOCATION ▪ Movement of organic solutes, e.g., Sucrose, amino acids, organic acids, K, Cl, PO, Mg from leaves (source, site produced or stored) to sieve tubes to be carried to other parts of plant (sink, site used). ▪ Unlike movement of xylem sap, movement of phloem sap requires energy expenditure on the part of the plant. How solutes moved around the phloem? Pressure Flow Model EXPLANATION 1 ▪ Explained by consideration of osmosis, applied to solutions of two sugar solutions across a semi-permeable membrane. i. Carbohydrates actively transported into phloem at source. ii. High concentration of carbohydrates causes greater osmotic pressure in phloem; water moves in from adjacent xylem by osmosis. iii. Water influx creates (turgor) pressure inside phloem; pushing water and dissolved carbohydrates through phloem. iv. At sink, carbohydrates actively removed from phloem; reducing osmotic pressure in phloem. v. water leaves phloem and reenters xylem, maintaining an osmotic pressure gradient between sources and sinks.  Characteristic of Phloem Vessel 1. Sieve Tubes ▪ Long cylindrical structure consisting narrow living, elongated sieve elements joined. ▪ End walls meet to form sieve plate and plasmodesmata enlarge to form sieve tube. When mature, ▪ Nucleus, Golgi apparatus and ribosome degenerates. ▪ A thin layer of cytoplasm and some small mitochondrion found lining inside of the thin cellulose cell wall. This presents less barrier to flow of sap through sieve element. Sieve tubes ruptured, ▪ Protein strands form plugs to block the pores. ▪ Callose deposits are then formed across the sieve plates to prevent loss of phloem sap. 2. Companion Cells ▪ Associated with sieve tubes. ▪ Smaller, shorter. ▪ Contains large nucleus, dense cytoplasm with numerous mitochondrial ribosomes and endoplasmic reticulum. ▪ Cells metabolically very active, connected to sieve tube elements by plasmodesmata.