Plant Physiology - AGR122 Chapter 4 PDF

CHAPTER 4 PLANT PHYSIOLOGY ✔ TRANSPORTATION IN PLANT ✔ PHOTOSYNTHESIS ✔ CELLULAR RESPIRATION Objectives: Students should be able ⮚ to define and explain the transportation in plant. ⮚ to define and explain the processes of transpiration, photosynthesis, and cellular re...

CHAPTER 4 PLANT PHYSIOLOGY ✔ TRANSPORTATION IN PLANT ✔ PHOTOSYNTHESIS ✔ CELLULAR RESPIRATION Objectives: Students should be able ⮚ to define and explain the transportation in plant. ⮚ to define and explain the processes of transpiration, photosynthesis, and cellular respiration. TRANSPORTATION IN PLANT  Plants have two transportation systems of substances via two different types of transport tissue. 1. Xylem transports water and solutes from the roots to the leaves via transpiration process 2. Phloem transports food (sugar) and amino acids from the leaves to the rest of the plant parts via translocation process. The vascular bundle structure: anatomy and functions in plant transport (primary growth and secondary growth) The vascular bundle Xylem vessels Phloem vessels Are long, hollow, continuous tubes that Are living cells with end tubes with carry water and dissolved minerals pores (sieve plates) from root up to all parts of the plant All cell contents have disappeared Contain a tough substances called except the cytoplasm lignin that lines the walls to provide The phloem cells have companion cell support near them. Transport sucrose and amino acids from where they are used or stored TRANSPIRATION Transpirationis the process by which water evaporates from the leaves, which results in water being drawn up from the roots to upward. OR Is the loss of water vapor out of the leaves through stomata by diffusion. 90% of water absorbed by roots lost through transpiration Types of transpiration 1.Cuticular Transpiration: the loss of water in the form of water vapor through the cuticle Upper epidermis of leaves secretes thin layer of wax (cuticle) which minimizes loss of water Cuticle prevents evaporation of water from the leaf surface Thicker the cuticle, lesser the transpiration. Types of transpiration 2.Lenticular Transpiration: the loss of water in the form of water vapor through the lenticels present in the woody stem and fruits Lenticel is small openings that develop in the older stem, and fruit Water from the cell surface evaporates and transpiration occur. It amounts of 1 – 5% of the total water loss by the plant Types of transpiration 3.Stomatal Transpiration: Stomata are minute pores confined to epidermis of green shoot and leaves Opening and closing of stomata are controlled by guard cells and depends on the turgidity of the guard cells. When the guard cells are turgid, pores open and close when they are flaccid. When the turgidity increases, guard cells bulge outwards widering the stomatal opening Maximum loss (80 – 90 % of the total water loss) of water from plant tissues takes place through the stomatal openings.  Importance of transpiration 1. Gaseous exchange -It helps in the absorption of carbon dioxide (CO2) from the atmosphere during photosynthesis as the openings of stomata in day time facilitate gaseous exchange. 2. Cooling effect -provides a significant cooling effect which keeps the plant from being over heated. 3. Effect on mineral transport -Minerals that are absorbed and accumulated in the xylem duct of the root move up and are distributed in the plant by the transpiration stream. 4. Effect on water movement -water moves from the xylem vessels to the leaf cells and helps in the ascent of sap. 5. Development of mechanical tissues -The plants become healthier and more compact the cell walls become thick and cutinized and the plants are able to resist the attack of fun and bacteria. 6. Maintenance of turgidity -Under favourable conditions plants absorb excess amount of water, which is given off by transpiration to maintain the optimum turgor for better growth. 7. Increase of taste of fruits -The solutes inside the cell Factors affecting on transpiration Transpiration affected by internal and external factors: External factors affecting transpiration 1.Wind and air movement: increased movement of the air around a plant will result in a higher transpiration rate. This is somewhat related to the relative humidity of the air. 2.Soil moisture availability: when moisture is lacking, plants can begin to senesce (premature ageing, which can result in leaf loss) and transpire less water. 3.Type of plant: Plants transpire water at a different rates. Some plants which grow in arid regions, such as cactus and succulents, conserve precious water by transpiring less water than other plants. 4.Temperature: transpiration rate increase as the temperature increase, especially during the growing season, related to open and close of stomata. 5.Relative humidity: as the relative humidity of air surrounding the plant rises, the transpiration rate falls. It is easier for water to evaporate into dyer air than into more saturated air. TRANSLOCATI ON Translocation is the movement of materials from leaves to other tissues throughout the plant OR The movement of food (sucrose and amino acids) from the sources (leaf) to sinks (developing flowers/fruits, storage organs, root) through the phloem vessels. Plants produce carbohydrates (sugars) in their leaves by photosynthesis, but non- photosynthetic parts of the plant also require carbohydrates and other organic and nonorganic materials. The tissue in which nutrients move is the phloem. The phloem is arranged in long, continuous strands called vascular bundles that extend through the roots and stem and reach into the leaves How translocation occurs Inside a sieve tube is phloem sap. This moves driven by mass flow, so a pressure difference needs to be created so that the plant has to use its own energy. This movement of sucrose decreases the water potential in the sap inside the sieve tube, which causes water to move into the sieve element by the process of osmosis. In the leaf (source), water moves into the sieve tube and moves out of it in the root (sink) and a pressure difference is created. This pressure difference causes the liquid inside the tube to flow from the higher pressure area to the lower one. Factors Affecting Phloem Transport: Phloem transport is affected by several important factors which are as follows: 1.Temperature: plays an important role in translocation. Translocation has also been found to be irreversibly inactivated by temperatures above 50°C. too low temperatures affect translocation rate; ⮚ inhibit active phloem transport by preventing the involvement of metabolic energy. ⮚ increases viscosity of the phloem sap which reduces the speed and alters membrane structures which disorganizes the contents and causes plugging of the sieve pores 2. Inhibitors: Certain metabolic inhibitors such as cyanide and dinitrophenol have been shown to inhibit carbohydrate translocation, supporting the use of respiratory energy in helping movement. 3.Potassium and Boron Deficiency: Potassium is abundantly present in phloem sap. Potassium deficiency affects the growth of fruits and storage organs. Potassium circulation around the sieve plate increases translocation of sugar in sieve tubes Boron is also essential for sugar transport. 4. Hormones: PHOTOSYNTHESI S At the end of this session, students should be able to: ✔ Describe the process of photosynthesis ✔ Explain briefly the processes involved: ⮚ Light reaction ⮚ Dark reaction / Calvin Cycle ✔ Explain the factors affecting photosynthesis rate Definition of photosynthesis ❖ Photosynthesis is a process conducted by green plants in which energy from sunlight is used to convert carbon dioxide and water into organic molecules (sugars) needed for growth. ❖ Light energy is absorbed by the green pigment (chlorophyll) found in the chloroplasts. ❖ Light energy allows the production of glucose by the reaction between carbon dioxide and water. ❖ Oxygen is also produced as a waste product/ by product ❖ This reaction can be summarized in the word equation: Sunlight energy Carbon dioxide + water ………….> glucose + oxygen Chloroph yll is in the 6CO2 + 6H2O --------------> chloropla C6H12O6 + 6O2 st ❖ During the process of photosynthesis, carbon dioxide from the air and water from the soil is converted into oxygen and glucose. ❖ Glucose is a sugar that can be used by the plant for respiration Why is Photosynthesis important? ❖ Photosynthesis provides food for all. The process of photosynthesis occurs in green plants which are the primary producers in a food chain. ❖ Photosynthesis is essential for sustaining life. It is the ultimate source of oxygen and energy for all living organisms. ❖ Photosynthesis helps in growth and development of plants. ❖ It converts atmospheric carbon dioxide (given out during respiration and other activities) back to oxygen. ❖ Makes organic molecules (glucose) out of inorganic materials (carbon dioxide and water). Photosynthesis Overview ❖ Photosynthesis takes place in chloroplasts. ❖ Chloroplasts are located mainly in the mesophyll cells. ❖ Each mesophyll can has 20 to 100 chloroplasts. What are Chloroplast? are the sites of photosynthesis in plant contain a green pigment called chlorophyll that absorbs the energy from the sunlight. 2 kinds of green chlorophylls; chlorophylls a & b Chlorophyll a absorbs the red and blue light and it is the primary pigment in plants Chlorophyll b absorb only blue light and transmitted green light thus the leaves look green This energy is used to convert CO2 and H2O into glucose and O2. Chlorophyll is embedded in disk-like structure called thylakoids which are arrange into stacks. thylakoid membrane – internal membrane arranged in flattened sacs grana – stacks of thylakoid membranes stroma – semiliquid substance surrounding thylakoid membranes Photosynthesis Overview The process of photosynthesis is divided into two main parts: 1.light dependent reaction. the energy-fixing reaction This reaction happens when the light energy from sunlight is captured and pushed into a chemical energy called ATP. reduce NADP+ to NADPH 2.light independent reaction/ dark reaction/ Calvin Cycle the carbon-fixing reaction use ATP and NADPH to synthesize organic molecules (glucose) from CO2  Two stages of photosynthesis: Light reaction & Calvin cycle Occurs in thylakoid Light Reactions: ❖ Light is absorbed by chlorophyll ❖ Energy from the light splits H2O ❖ H from water reduces NADP (electron acceptor) to NADPH ❖ Chemiosmosis makes ATP from ADP (photophosphorylation) ❖ Products of light reactions: ⮚ Energy = ATP & NADPH – Calvin cycle ⮚ By-product = O2  Two stages of photosynthesis: Light reaction & Calvin cycle Occurs in Stroma The Calvin Cycle: Also known as dark reaction/ light independent reaction CO2 from atmosphere enters chloroplast and is incorporated into organic molecules = carbon fixation NADPH from light reaction reduces the fixed carbon (by donating H) to carbohydrate ATP from light reaction is required for this step Product of calvin cycle is glucose  Question: Describe the Calvin Cycle The light-independent reactions/ the Calvin cycle can be organized into three basic stages: Carbon fixation, Reduction of 3-PGA into G3P and Regeneration RuBP 1 2 3 In the second The first stage of stage: ATP and In the last stage: Calvin Cycle is NADPH are used RuBP is carbon fixation; to reduce 3-PGA regenerated, CO2 is fixed into G3P; then which enables from an ATP and NADH the system to inorganic to an are converted to prepare for more organic ADP and NADP+, CO2 to be fixed. molecule. respectively.  Dark Reaction/Calvin Cycle/ light-independent reactions LIGHT REACTION VS DARK REACTION Both occur during daytime Both occur in chloroplast Both uses enzymes LIGHT REACTION DARK REACTION/CLVIN CYCLE Uses sunlight/ depend on sunlight Does not need sunlight/ not depend on sunlight Occurs in grana/thylakoid membrane Occurs in stroma Uses water as substrate Carbon dioxide as substrate or fixed Oxygen as by product Glucose as product ATP and NADPH are produced Involves carbon dioxide Involves photolysis process fixation process Factors that influence the rate of photosynthesis Light The most effective light is red and blue More light more photosynthesis Plants have various adaptations to obtain more light Temperature For optimum photosynthesis, the temperature is between 20-35oC High temperature (above 40oC) denatured enzymes Plant in cool region have adaptation for effective photosynthesis below 0 oC. Co2 concentration Photosynthesis rate has direct relationship to CO2 concentration with the present of optimum light and temperature. If the concentration of CO2 in atmosphere is above 0.03% the rate of photosynthesis will increase. Efficiency of CO2 only up to 1.0%. At concentration higher than that, the rate will decrease because stomata closure. O2 concentration At higher O2 concentration the rate of photosynthesis is lower. This is because O2 and CO2 are competing each other to locate the active site of enzymes 🡪 carbon fixation is slow The phenomenon of O2 is higher than CO2 called photorespiration Chlorophyll concentration Chlorophyll level/quantities is reduced when the plants were infected, experienced senescence's or lack in minerals. The leaves turned yellowish and is said as chlorotic thus the rate of photosynthesis will reduce  CELLULAR RESPIRATION ✔Define cellular respiration ✔Aerobic respiration ▪ Glycolysis ▪ Krebs cycle ▪ Electron transport chain ▪ Anaerobic respiration CELLULAR RESPIRATION is a set of metabolic reactions and processes that take place in the cells of living organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products (CO2) that they require for cell division and development. OR, the biochemical pathway by which cells release energy from the chemical bonds of food molecules and provide that energy for the essential processes of life. OR, respiration is the process of releasing energy from the breakdown of glucose. It can be aerobic respiration (presence of oxygen) or anaerobic respiration (without oxygen). Respiration occurs in mitochondria Cellular Respiration Overview Transformation of chemical energy in food into chemical energy (ATP) cells that can be use Overall Reaction: C6H12O6 + 6O2 → 6CO2 + 6H2O The major step in respiration: 1)Glycolysis Aerobic cellular 2)citric acid cycle (Krebs respiration cycle) Breakdown of glucose (glycolysis) begins in the cytoplasm 3)electron transport/oxidative (cytosol) phosphorylation At this point life diverges into two forms and two pathways: ⮚Anaerobic cellular respiration (fermentation) ⮚Aerobic cellular respiration Food 1. Glycolysis – in cytoplasm Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. 1st phase Glucose is split using ATP into 2 - G3P 2nd phase G3P is then converted to 2 pyruvate Formation of ATP and NADH A. Aerobic Cellular Respiration Oxygen required = aerobic 2 more sets of reactions which occur in mitochondria 1.Kreb’s Cycle ⮚ Occur in mitochondrial matrix ⮚ converts pyruvate via acetyl CoA into CO2; ⮚ generates NADH and FADH2 2.Electron Transport Chain ⮚ Occur in mitochondrial membranes = cristae ⮚ The NADH and FADH2 formed in the KREBS CYCLE enter the electron transport chain system. ⮚ electrons was transfers from NADH and FADH2 to reduce O2 to H2O and generate ATP  Each turn of Krebs cycle produces: ⮚ 1 ATP; ⮚ 3 NADH; ⮚ 1 FADH2 For 1 glucose molecule produces: ⮚ 2 ATP ⮚ 6 NADH ⮚ 2 FAD B. Anaerobic Cellular Respiration It is also known as Fermentation In anaerobic respiration, glucose is still broken down to carbon dioxide with the release of energy, but without the involvement of oxygen Equation: C6H12O6 + O2 → 2 CH2O5 + 2 H2O + 2 ATP or Glucose + Oxygen → 2 Ethanol + 2 Water + 2 ATP End products are ethanol and CO2 or lactic acid (muscle cells) Anaerobic respiration is widely used by many micro-organisms such as bacteria and yeasts also takes place in plants in the presence of little or no oxygen. The energy released by anaerobic respiration is considerably less than the energy from aerobic respiration. Fermentation Glucose is not completely breakdown to CO2 and H2O because lack of oxygen. But glucose was breakdown to ethanol (plant, yeast) and CO2 or lactic acid (certain fungi, prokaryotes, animal) 2 types of fermentation: 1. Alcoholic fermentation 2. Lactic acid fermentation Going from pyruvate to ethanol is a two-step process. 1. 2 molecules CO2 is removed from pyruvate and released thus producing 2 molecules acetaldehyde. Alcohol fermentation by yeast produces the ethanol found in alcoholic beverages like beer and wine 2. NADH passes its electrons to acetaldehyde, regenerating NAD+ and forming 2 molecules ethanol. Comparison