A2 Biology Past Paper - Photosynthesis - 2021 PDF

A2 BIOLOGY SEM TER THREE 2021 Student N es 12s8 PHOTOSYNTH IS Learning objectives: I. 5.1 understand the overall reaction of photosynthesis as requiring energy from light to split apart the strong bonds in water molecules, storing the hydrogen in a fuel (glucose) by combining it with carbon dioxide and releasing oxygen into the atmosphere II. 5.2 understand how photophosphorylation of ADP requires energy and that hydrolysis of ATP provides an immediate supply of energy for biological processes III. 5.3 understand the light-dependent reactions of photosynthesis, including how light energy is trapped by exciting electrons in chlorophyll and the role of these electrons in generating ATP, reducing NADP in cyclic and non-cyclic photophosphorylation and producing oxygen through photolysis of water IV. 5.4 (i) understand the light-independent reactions as reduction of carbon dioxide using the products of the light-dependent reactions (carbon ﬁxation in the Calvin cycle, the role of GP, GALP, RuBP and RUBISCO) (ii) know that the products are simple sugars that are used by plants, animals and other organisms in respiration and the synthesis of new biological molecules (polysaccharides, amino acids, proteins, lipids and nucleic acids) 1 V. 5.5 understand the structure of chloroplasts in relation to their role in photosynthesis VI. 5.6 understand what is meant by the terms absorption spectrum and action spectrum VII. 5.7 understand that chloroplast pigments can be separated using chromatography and the pigments identiﬁed using Rf values ATP molecule ★ Made up of adenine (nitrogenous base), a ribose sugar and three phosphate groups. ★ Second and third covalent bonds are unstable and can be broken down easily. ★ Break down of ATP release energy - Hydrolysis (exergonic) ★ Synthesis of ATP from ADP and phosphate – Phosphorylation (endergonic) 2 Structure of a chloroplast 3 Structure of a thylakoid 4 Photosystems ★ On the thylakoid membrane photosensitive pigments are organized into complex systems. ★ Primary pigments, accessory pigments and electron carriers are assembled together in this chlorophyll complex. ★ These chlorophyll complexes are called photosystems. ★ There are two photosystems:- PSI and PSII Photosystem I ★ Accessory pigments or antennae pigments (chlorophyll a, carotenoid, chlorophyll b) are arranged around the primary pigment chlorophyll a. ★ PSI is found on the single thylakoids. ★ The absorption peak of this chlorophyll a is 700 nm and it is the reaction centre. ★ Antennae pigments absorb light energy (diﬀerent wavelengths), transfer to the reaction centre. ★ Reaction centre molecule (Chlorophyll) gets oxidized and releases high energy electrons. Photosystem II ★ It is larger than PSI. ★ PSII is found on the thylakoids which are stacked into grana. ★ The reaction centre is chlorophyll a, with an absorption peak of 680 nm. 5 Chlorophyll ★ Chlorophyll is present in the thylakoid membrane. ★ Have a polar porphyrin head and a nonpolar hydrocarbon tail. ★ Tail is lipid soluble. ★ The hydrocarbon tail anchors the pigment molecules into the lipid bilayer. ★ The head absorb light energy Adaptations of leaf for photosynthesis Thin lamina ★ Fast / maximum gas exchange /uptake of carbon dioxide ★ Help in the penetration of light ; ★ Carbon dioxide is used in the Calvin cycle ★ Light is used in light-dependent stage / photolysis / photophosphorylation. Veins / vessels in the midrib ★ Xylem transport water to the leaves ★ Phloem transport sucrose / sugar /carbohydrates away from the leaves ★ Water is the source of hydrogen ions in light-dependent reactions. ★ Transporting sugar to make more room for more carbohydrate synthesis 6 Adaptations of Spongy mesophyll for gas exchange ★ The gas exchange surface is the cell wall and membrane ★ The spongy mesophyll cells are loosely packed and have air spaces between them and large surface area to volume ratio. ★ So the diﬀusion distance is small between air space and cytoplasm ★ Air spaces and loosely packed cells make diﬀusion fast ★ Carbon dioxide can continuously enter the leaf and circulate around the cells ★ This maintains a concentration gradient between air space and cell 7 Chloroplast ★ A double membrane bound organelle found in green plant cells. ★ Two membranes are separated by an intermembrane space. ★ Envelope is semi permeable. ★ The matrix of the chloroplast is called stroma. ★ Stroma contains enzymes (RUBISCO) that catalyzes light independent reactions of photosynthesis. ★ Disc shaped structures in the stroma are called thylakoids ,surrounded by the thylakoid membrane. ★ These are the sites of light dependent reactions of photosynthesis. ★ Thylakoids contain chlorophyll molecules, accessory pigments and electron transport systems. ★ Light absorbing molecules are arranged in photosystems. ★ This is the site of ATP synthesis in chloroplast ★ Stalks of thylakoids are called grana (granum). ★ Grana are connected with each other by lamella. ★ Lamella acts as the skeleton of the chloroplast and maximizes the eﬃciency of the chloroplast. ★ Chloroplast also contains a circular DNA, lipid globules, starch granules and 70s ribosomes. 8 Thylakoid:- t e t o g d e d s e f to n s ★ Thylakoid membrane- ○ provide a space for accumulation of H+ ○ Chlorophyll / carotenoids / photosystems / electron carrier proteins / ATP synthase / NADP reductase are present. ○ compartmentalization from stroma ○ site of light-dependent reaction ★ Photosystem- Contains pigments for trapping light energy ★ Proteins- ○ pump the hydrogen ions into the thylakoid space. ○ Electron carrier proteins- high energy electrons pass along and undergo redox reaction and provide energy for ATP synthesis ★ ATP synthase- ○ Channels allow hydrogen ions to pass through into stroma. ○ Energy released from this movement of hydrogen ions results in the production of ATP ★ Lumen- provide space for the accumulation of H+ which is needed for photophosphorylation. 9 Chloroplast- s uc re d o n on ★ Compartmentalisation (from cytoplasm); ★ Thylakoid membranes are site of light-dependent reaction ★ Chlorophyll / carotenoids / photosystems / electron carrier proteins / ATP synthase / NADP reductase are present within/ on thylakoid membranes ★ Thylakoid membranes provide a space for accumulation of H+ ; ★ Stroma is the site of Calvin cycle ★ Stroma contains RuBP / RUBISCO Mechanism of photosynthesis ➔ A process of energy transduction. ➔ Light energy into electrical energy. ➔ Electrical energy into chemical energy. Three main phases of photosynthesis ★ Light harvesting- light energy is captured by the pigments. ★ Light dependent stage (photolysis)- splitting of water into Hydrogen ion and oxygen. + − 2𝐻 2𝑂 → 4𝐻 + 𝑂 2 + 4𝑒 ★ Light independent stage- the reduction of carbon dioxide and form sugars. 6𝐶𝑂 2 + 12𝐻 2𝑂 → 𝐶 6𝐻 𝑂 12 6 + 6 𝐻 2𝑂 + 6𝑂 2 10 Light Dependent Stage of photosynthesis ★ Occurs in the thylakoid of chloroplast. ★ It involves the splitting of water by light (photolysis) and producing ATP. ★ Accessory pigments absorb light energy and transfer it into the reaction centre. ★ The electron within the molecule gets excited and possesses high energy. ★ These electrons are emitted by the chlorophyll a molecule and are received by the electron carriers. ★ Then passed on to other molecule. ★ The light dependent stage leads to the synthesis of ATP (phosphorylation) and the production of reduced NADP. ★ This stage includes cyclic and non-cyclic photophosphorylation 11 Non-cyclic photophosphorylation ★ Light energy is trapped in PSII and boosts electrons to higher energy levels. ★ The electrons are received by electron acceptor (TM). ★ The electrons are passed along a series of electron carriers to PSI. + ★ 𝐻 ions pump from stroma to the lumen of the thylakoid. + ★ Concentration of 𝐻 increases in the thylakoid which diﬀuse back to stroma by chemiosmosis. ★ The energy from chemiosmosis is used for the synthesis of ATP from ADP and Pi by the enzyme ATP synthase. ★ PSI also absorbs light and emits electrons even to a higher energy level which are received by the electron acceptor. ★ The protons from the water molecule combine with the electron from the electron acceptor and reduces NADP (temporary store of energized electrons) to NADPH ★ This passes to the reactions of the light independent stage. ★ The PSI gains its lost electron from the PSII, and PSII gains its lost electron from the splitting of water (photolysis). ★ Oxygen is produced as a waste gas during the photolysis of water. 12 Diﬀerences between PS I andPS II PS I PS II Found mainly on the lamellae and the Found mainly on the inner surface of outer surface of grana. granal thylakoid. Reaction centre is P700. Reaction centre is P680 Both cyclic and non-cyclic Participate only in non-cyclic photophosphorylation. photophosphorylation. Can undergo cyclic photophosphorylation No independent function. independently. Lost electron is regained from PSII Lost electrons are regained from photolysis of water. 13 Cyclic photophosphorylation ★ Cyclic photophosphorylation involves only photosystem I (PSI). ★ Light hits a chlorophyll molecule in PSI and energizes electrons. ★ Light-excited electrons leave the chlorophyll molecule and are collected by the electron acceptor. ★ These high energy electrons pass down directly along an electron transport chain and the energy released is used to pump hydrogen ions from the stroma into the lumen of the thylakoid. ★ Hydrogen ion concentration increases within the lumen of the thylakoid. ★ So, these hydrogen ions diﬀuse back into the stroma through a protein channel on the thylakoid membrane. ★ Diﬀusion of Hydrogen ions from lumen to stroma (chemiosmosis) activates ATP synthase to phosphorylate ADP to form ATP.This is called photophosphorylation. ★ The electron will be returned to the chlorophyll molecule in PSI. 14 Light Independent Stage of photosynthesis ★ Takes place whether or not light is present. ★ The details of this stage were analyzed by Melvin Calvin. ★ It is the reduction of 𝐶𝑂 2 using the reduced NADP and ATP from the light reaction. ★ The light-independent reactions of photosynthesis take place in the stroma of the chloroplasts, using the reduced NADP and ATP from the light-dependent reactions. ★ NADP acts as a hydrogen carrier. ★ Carbon dioxide is reduced to carbohydrate. ★ This stage consists of a series of reactions known as the Calvin cycle and each stage of the cycle is controlled by enzymes. LIS ★ 𝐶𝑂 2 diﬀuse into the leaf through stomata. ★ 𝐶𝑂 2 combine with a 5C compound- Ribulose bisphosphate (RuBP) and form an unstable 6C compound. (Ribulose bisphosphate carboxylase- RuBISCO) ★ The 6C compound breaks down into two molecules of 3C compound – Glycerate-3-phosphate (GP). ★ GP is converted (reduced) to Glyceraldehyde-3-phosphate (GALP) by using reduced NADP and ATP. ★ From every 12 GALP formed 10 are used to regenerate RuBP and the remaining two into Glucose. ★ The high concentration of RuBP keeps running the Calvin Cycle at a high rate. 15 IN OUT six 𝐶𝑂 2 One glucose 18 ATP 18 ADP 12 NADPH 12 NADP 16 Interdependence between light dependent and Calvin cycle Summary of photosynthesis 17 Fate of glucose Glucose can be converted, using enzymes, into starch, cellulose, fats, amino acids/proteins and nucleic acids. The extra elements needed to make some of these compounds, such as nitrogen and phosphorus, are taken up by the roots of the plant from the soil The calvin cycle is the starting point for making all the organic substances a plant needs. Glyceraldehyde-3-phosphate (GALP) and glycerate-3-phosphate (GP) molecules are used to make essential biological molecules: ★ Carbohydrates:- simple sugars (eg. glucose) are made by joining two GALP molecules together, and polysaccharides (eg. starch and cellulose) are made by joining hexose sugars together in diﬀerent ways. The production of glucose is very important as it's used in respiration, which provides energy needed for biological processes. ★ Lipids:- these are made using glycerol, which is synthesised from GALP, and fatty acids which are synthesised from GP. ★ Amino acids:- some amino acids are made from GP. ★ Nucleic acids:- the sugar in RNA (ribose) is made using GALP. 18 Using the products of photosynthesis ★ Two molecules of GALP join to form glucose (gluconeogenesis). ★ This glucose may be converted into disaccharides such as sucrose for transport round the plant. ★ (Alpha glucose molecule joins with fructose by 1,2-glycosidic bond through condensation reaction and forms sucrose). ★ (starch is a polymer of alpha glucose. Glucose monomers join together by glycosidic bond through condensation reaction. Starch has two polymers- unbranched amylose with only 1,4-glycosidic bond and branched amylopectin with 1,4 and 1,6-glycosidic bond). ★ (cellulose is a polymer of beta glucose. Beta glucose molecules join by I,4-glycosidic bond through condensation reaction. This forms a long unbranched chain of beta glucose molecule-cellulose). ★ The GALP that enters cellular respiration is used to provide energy in the form of ATP for the functions of the cells and for the active uptake of nitrates and phosphates from the soil. ★ The compounds from the respiration pathways are used as the building blocks of amino acid by combining with nitrates from the soil. ★ GALP may continue round the Calvin cycle and combine with phosphates from the soil and form nucleic acids. ★ GALP is converted to glucose which again is converted to deoxyribose. ★ Glucose is used in respiration and provides energy in the form of ATP for DNA synthesis or active transport of substances such as nitrates. ★ GALP is also used in the synthesis of bases such as adenine, thymine, cytosine and guanine. ★ GALP also synthesises amino acids for enzymes involved in the synthesis of DNA. 19 ★ Some of the GALP that enters the cellular respiration pathways is converted into a chemical called acetyl coenzyme A. ★ This compound is then used to synthesise the fatty acids. ★ GALP is converted to glycerol. One molecule of glycerol joins with three molecules of fatty acids by ester bond through condensation reaction and form lipids. GP to Strach ★ Using energy from ATP and hydrogen from NADPH, GP is converted to GALP. ★ Two molecules of GALP joined to form glucose, which is alpha glucose. ★ Starch is a polymer of alpha glucose and consists of two polymers amylose and amylopectin. ★ Glycosidic bonds are formed between glucose molecules by condensation reaction and form two polymers. ★ amylose is straight chained with only 1.4-glycosidic bonds and amylopectin is branched with 1,4 and 1,6-glycosidic bonds. GALP to Cellulose ★ Two molecules of GALP joined to form glucose, which is beta glucose. ★ Cellulose is a polymer of beta glucose. ★ Beta glucose molecules joined by 1,4-glycosidic bonds through condensation reaction and form a long unbranched chain of glucose. 20 GALP to Triglycerides/lipids ★ GALP is used to produce glucose which is a source of energy for lipid/ triglyceride synthesis. ★ GALP is used to make glycerol and GP is used to make fatty acids. ★ Three fatty acids and one glycerol joined by ester bonds through condensation reaction and form triglyceride. ★ GALP is converted to amino acids which are used to synthesise enzymes. ★ These enzymes are involved in lipid synthesis GALP to Protein ★ Two molecules of GALP joined to form glucose. ★ Amino acids are made from glucose and nitrates. ★ Proteins are formed by joining these amino acids by peptide bond through condensation reaction. ★ Glucose is used in respiration to produce ATP for protein synthesis GALP to DNA ★ GALP is converted to Glucose which is converted to deoxyribose. ★ Glucose is used in respiration to produce ATP which provides energy for the active transport of substances such as nitrates and sulphates. ★ GALP is used in the synthesis of nitrogen bases using nitrates. ★ GALP also synthesises amino acids for enzymes involved in the synthesis of DNA. ★ DNA is polynucleotide, where mononucleotide is made up of deoxyribose, nitrogen base and phosphate group. ★ Mononucleotides joined together by phosphodiester bond through condensation reaction and form polynucleotide. 21 Factors Aﬀecting The Rate Of photosynthesis Mainly three factors which aﬀect the rate of photosynthesis: 01.Light intensity 02. 𝐶𝑂 2 concentration 03.Temperature Limiting factor: Among the factors that control the rate of photosynthesis, the factor which is closest to its minimum.The rate is limited by that factor and only a change in that factor changes the rate of photosynthesis. Light intensity and rate of photosynthesis ★ At very low light intensity, the rate of photosynthesis is very low. ★ Further increase in light intensity increases the rate of photosynthesis until light saturation is reached. ★ This is the maximum rate of photosynthesis. ★ Beyond this no change in rate of photosynthesis as high light intensity destroys chloroplast. ★ Light is trapped by chlorophyll and excites high energy electrons. ★ Light splits water molecules to produce protons ★ Electrons and protons are involved in photophosphorylation 22 The eﬀect of reduced light levels on the relative concentrations of GP,TP and RuBP in the Calvin cycle 1. GP cannot be reduced to TP. 2. TP levels fall and GP accumulates. 3. If TP levels fall, RuBP cannot be regenerated. Temperature and rate of photosynthesis ★ Calvin cycle is temperature dependent as enzyme Rubisco is involved in it. ★ The minimum temperature for photosynthesis is 0°C. ★ The optimum temperature is 25°C. ★ The rate doubles for each rise of 10°C up to an optimum temperature. ★ KE of molecules increases so does eﬀective collision between enzyme and substrate ★ Above 25°C bonds in enzymes are broken down ★ Changes the shape of the active site. 23 Concentration of 𝐶𝑂 2 and rate of photosynthesis ★ Major limiting factor to photosynthesis. ★ Increasing concentration increases the rate of photosynthesis till a certain level. ★ Further increase in 𝐶𝑂 2 will add no eﬀect. 1. As the amount of carbon dioxide goes up, so does the rate. The limiting factor is carbon dioxide. 2. Here, increasing the amount of carbon dioxide has no eﬀect on the rate. Light or warmth is now the limiting factor The eﬀect of changing the carbon dioxide concentration on the Calvin cycle If the concentration carbon dioxide falls below 0.01%: 1. RuBP cannot accept it, and accumulates. 2. GP cannot be made. 3. Therefore, TP cannot be made. 24 Absorption and action spectra Absorption spectrum:Graph showing the degree of absorbance of diﬀerent wavelengths of light by a pigment. Action spectrum:Graph showing the eﬀectiveness of diﬀerent wavelengths of light stimulating photosynthesis. 25 Chromatography: Sep in h me s 26 ★ The pigments can be separated by chromatography using paper or silica gel. ★ Draw a pencil line about 25 ㎜ from the bottom edge. ★ Extract the pigments from a plant by grinding up the leaves with 10㎤ propanone and then ﬁlter it. ★ The extract should be as concentrated as possible. ★ Place one small drop of this extract in the centre of the pencil line and allow to dry before adding another drop on top. ★ Build up a pigment spot that is as small as possible but dense enough that it contains suﬃcient pigment. ★ Carefully pour the chromatography solvent into a boiling tube to a depth of no more than 1 ㎝. ★ Suspend the chromatography paper inside the boiling tube by pinning it to the underside of the bung. ★ The bottom of the paper should be dipped into the solvent but the pigment spot must not be immersed in the solvent at any time. ★ The pigments travel up the solid medium at diﬀerent speeds and are separated. ★ The distance travelled by the solvent needs to be marked as soon as you remove the paper or plate from the solvent bath (Several of the pigments fade quickly in light so you may need to draw around the spot in pencil and label it). ★ Once the pigments are separated, determine their Rf values and compare them to the Rf values of known pigments in the same solvent (pigments can have very diﬀerent Rf values with diﬀerent solvents). ★ The Rf value is the ratio of the distance travelled by the pigment to the distance travelled by the solvent alone. ★ The Rf value is always between 0 and 1. 27 QU TIONS *With reference to the structures in a chloroplast, explain how the energy from light is made available in ATP molecules for the synthesis of organic materials. (6) ★ Stack of thylakoids present in grana. ★ Thylakoid membrane contains photosystems. ★ Chlorophyll molecule and accessory pigments in the photosystem absorb light energy and electrons are excited from chlorophyll ★ These high energy electrons passed down through electron carrier and undergo a series of redox reactions ★ While passing through the carriers energy level of electrons falls + ★ The released energy is used by the proton pump to pump 𝐻 ions into the thylakoid lumen from stroma. + ★ Diﬀusion of 𝐻 ions from lumen to stroma activate ATP synthase to phosphorylate ADP to form ATP ★ This is called photophosphorylation ; ★ Electrons from photolysis is used to replace those lost from PSII ; Describe the structures in a chloroplast that are involved in the light-dependent reactions of photosynthesis. ★ Chloroplast contain disc shaped structures called thylakoids ; ★ Thylakoids are made of membranes ; ★ These are arranged as stacks called grana ★ It contain pigment / chlorophyll ★ These pigments are arranged as photosystems 28 Explain the role of light in the photosynthesis ★ Light results in excitation of electrons from chlorophyll / photosystems ★ This results in energy to generate in the form of ATP ; ★ Light is needed for breakdown of water (photolysis) ★ Electrons from photolysis replace electrons lost by chlorophyll / photosystems + ★ Photolysis produce 𝐻 ions / protons + ★ Both ATP and reduced NADP / 𝐻 ions are needed in the light-independent reaction / Calvin cycle to convert GP to GALP ★ ATP / reduced NADP / hydrogen ions used in production of GALP from GP. ★ Study well Structures in a chloroplast that are involved in photophosphorylation ★ Grana present in the chloroplast ★ A granum is a stack of thylakoids and grana are connected by lamellae ; ★ Thylakoids contain electron carriers /chlorophyll / photosystems ; ★ Thylakoid membranes contain ATPase Explain how oxygen is produced during the light-dependent reactions of photosynthesis ★ By the photolysis of water using energy from light Describe and explain how the products of the light dependent reaction are involved in the production of glyceraldehyde-3-phosphate (GALP). (4) ★ In the light independent stage of photosynthesis, GP is reduced to GALP using hydrogen from reduced NADP and energy from ATP. These ATP and reduced NADP are the products of light dependent stage. 29 One of the reactions of photosynthesis can be summarised as shown below. Water → hydrogen ions + oxygen gas + electrons (A) name the reaction shown. ★ Photolysis (of water) ; (b) give one other factor, not shown above, that would be required for this reaction to occur in a chloroplast. ★ Light / enzyme / chlorophyll / Describe the role of the electrons in the light dependent reaction of photosynthesis. (4) ★ Electrons passed to photosystems to replace electrons lost by chlorophyll. ★ Light energy promotes electrons to higher energy level and the electrons emitted ; ★ High energy electrons carried through the electron transport chain. ★ Occurs as a series of redox reactions. ★ Energy released is used in ATP production ; ★ Electron is used in reduction of NADP / production of NADPH Describe the role of the proteins in the thylakoid membrane in the formation of ATP. ★ Electron carriers pump the hydrogen ions into the thylakoid space ★ ATPase channels allow hydrogen ions to pass through into stroma ★ Energy released from this movement of hydrogen ions results in phosphorylation of ADP. 30 GALP does not accumulate in a chloroplast during photosynthesis. Explain how GALP is used following its production. (2) 10 ★ is used for the regeneration of RuBP 12 ★ Rest is used to form glucose and which is for starch / other organic chemical The graph below shows the results of the investigationDescribe and suggest an explanation for the changes in the concentrations of RuBP and GP shown in the graph. ★ Both RuBP and GP levels constant until carbon dioxide lowered ★ RuBP and GP are produced in Calvin cycle ; ★ RuBP: At lower carbon dioxide levels the RuBP increases and drops and then stays constant ; ★ Rises because being regenerated ★ Falls as being used to ﬁx carbon dioxide ; ★ RuBP level remains constant once new equilibrium reached ; ★ GP: At lower carbon dioxide levels the GP drops and then stays constant ★ Drops because less carbon dioxide is available to convert into GP) / less carbon ﬁxation ★ Levels out at a lower level as carbon dioxide still available but at lower level; 31 A2 BIOLOGY SEM TER THREE 2021 Student N es 12s8 Energy Flow Through an Ecosystem LEARNING OBJECTIV : I. Carry out calculations of net primary productivity and explain the relationship between gross primary productivity(GPP), net primary productivity(NPP) and plant respiration(R). II. Calculate the eﬃciency of energy transfers between trophic levels. ★ Study of energy ﬂow through an ecosystem- ecological energetics ★ 1-5% of the radiant energy is captured by the green plants. ★ Energy is ultimately derived from the sun. ★ The captured energy is converted into chemical energy and ﬂow through the ecosystem 1 Trophic level: the level at which an organism feeds in a food chain ★ Energy is lost between trophic levels due to several reasons such as inedible body parts and energy loss to decomposers. ★ There will not be enough energy to sustain many trophic levels. Productivity ★ It is the rate of generation of biomass in an ecosystem. −2 −1 ★ Its unit is 𝐽𝑚 𝑦𝑒𝑎𝑟 (it is the energy per unit area per unit time) ★ Productivity of autotrophs- primary productivity. ★ Productivity of heterotrophs- secondary productivity Gross primary production (GPP) ★ The total amount of energy captured in the organic material by green plants in the process of photosynthesis. −2 −1 ★ Its unit is 𝑘𝐽𝑚 𝑦𝑒𝑎𝑟 Net primary production (NPP) ★ It is the net useful chemical energy. ★ It is the amount of energy trapped in the plant biomass that is available for consumption by heterotrophic organisms. 𝑁𝑃𝑃 = 𝐺𝑃𝑃 − 𝑟𝑒𝑠𝑝𝑖𝑟𝑎𝑡𝑖𝑜𝑛 𝑏𝑦 𝑝𝑙𝑎𝑛𝑡𝑠 2 Mean annual rainfall and NPP ★ Increase in rainfall increases the availability of water. ★ Water is needed for light-dependent reaction and transport of mineral ions. ★ This increases the GPP and there by increases NPP Why an increase in temperature may cause an increase in NPP ★ Increase in temperature increases the kinetic energy of molécules and leads to more successful collisions between enzyme and substrate. ★ So the rate of Photosynthetic reactions increases. 3 Depth of water and NPP ★ As depth increases NPP decreases. ★ Light is reduced by the deeper water ; ★ Carbon dioxide levels might be lower deeper down ; ★ Temperature might be lower deeper down ; ★ Photosynthesis will be reduced ; ★ Less glucose / GALP / GP will be produced to convert into biomass / NPP ★ GPP goes down but respiration stays the same / increases NPP values would be of use to a farmer who wanted to use a particular land for cattle ★ Cattle is primary consumer ★ They gain energy available as NPP ★ Farmer is ensuring that there is enough NPP in the grassland ★ This aﬀects the yield of milk and meat. ★ So if the NPP is not suﬃcient they can move to a more eﬃcient NPP yielding farm. NPP decreases with the age of the forest ★ More growth occurs in young trees / less growth in older trees. ★ The rate of photosynthesis decreases with age ★ This decrease may be due to lower ratio of leaves or ‘trunk is thickening but no more leaves’ produced or trees shade each other ★ The mineral ions in the soil will be depleted 4 ★ As age of the forest increases, R also decreases because some of the trees are not respiring / dead. ★ Due to these reasons GPP also decreases Biomass ★ Biological material derived from living or recently living organisms. ★ It is the mass of living biological organisms in a given area or ecosystem at a given time. (Kg/hectare) Secondary production ★ Formation of heterotrophic biomass through time. ★ It is the energy used to make new animal biomass. 5 Measurement of biomass in a grassland in a year is more useful than on a particular day ★ NPP varies over short periods of time. ★ Whole year gives an average value of NPP. ★ Because biomass includes all inedible organic materials. 6 Transfer of energy from producers to consumers ★ A part of the energy is lost as it passes from one trophic level to the next. ★ Only 10% is stored to make new biomass. ★ That 10% is transferred to the next trophic level. ★ Plants respire using the products of photosynthesis ★ 𝑁𝑃𝑃 = 𝐺𝑃𝑃 − 𝑟𝑒𝑠𝑝𝑖𝑟𝑎𝑡𝑖𝑜𝑛 𝑏𝑦 𝑝𝑙𝑎𝑛𝑡𝑠 ★ All plant materials are not edible. ★ Remaining 90% of the energy is lost during the transfer. The fate of light energy that reaches the green leaf Why the energy transfer from sunlight to the producer is low 7 ★ Light is reﬂected back into space ★ Light energy reﬂected from leaves ★ Light energy is used in evaporating water ★ Light energy is missing chloroplast/passing through the leaf ★ Incorrect wavelength of light Percentage eﬃciency of photosynthesis It can be calculated by dividing GPP by the total amount of energy striking the plant multiplied by 100 Explain why the energy eﬃciency between secondary and tertiary consumer is greater than that between producers and primary consumers ★ In plants some parts are inedible; ★ Cannot digest cellulose or lignin; ★ More material goes to decomposers than consumers; ★ Plant material is less energy rich; Ways in which energy is transferred from primary consumers to decomposers ★ Death/ dead remains, Excretion, Egestion, Moulting of fur 8 9 10 QU TIONS The diagram below shows what happens to 200 J of energy eaten by a caterpillar.Calculate the percentage of this energy available to any bird that eats this caterpillar. Show your working. (energy used ) = 100 + 67 / 167 (J) (energy available) = 200 - 167 / 33 (J) Ans =16.5 (%) Biomass energy (trophic level 1)= 5300 kJ Ingested food by the animal (trophic level 2) = 2800 kJ Energy lost during respiration (trophic level 2)= 1750 kJ Calculate the percentage energy transfer between these two trophic levels ★ Ans (1050/5300)*100 =19.8 Of the 800 000 kJ of energy reaching the producers only 10 000 kJ of energy is converted to growth in the producers.Calculate the percentage of energy reaching the producers that is converted to growth in the producers. Show your working. ★ Ans (10 000/ 800 000)*100 ★ 1.25%/ 1.3%/ 1% 11 Only 10% of the energy in the robins passes to the owls. Describe what happens to the other 90% of the robins’ energy. ★ Some amount of energy is lost to the surroundings as heat; ★ Some will be used for movement / keeping the body warm; ★ Not all parts of the robin are eaten by the owl. Keeping cattle indoors, in barns, leads to higher eﬃciency of energy transfer. Explain why ★ Less energy lost as heat/in maintaining body temperature/in movement tion 12 Q. A farmer’s livelihood depends on the eﬃciency of energy transfers between trophic levels. The farmer will be interested in how eﬃcient grass is at turning solar energy into NPP, and how eﬃcient a bullock is in converting the energy in grass into beef production. Examine Figure 3 showing energy ﬂow through a typical grazing food chain. Calculate the following values: a) Eﬃciency of photosynthesis (percentage of incident solar energy that is converted to GPP). Ans 2.24% b) The energy lost to the environment through plant respiration. Ans 1968 −2 −1 𝑘𝐽𝑚 𝑦𝑒𝑎𝑟 c) The percentage of solar energy falling on the grass that becomes beef (secondary production). Ans 0.012% d) Assuming all the grass in 1m2 were eaten by just the bullocks, how much energy would be incorporated as beef in a year? Ans 876.8 kJ 13 A2 BIOLOGY SEM TER THREE 2021 Student N es 12s8 Distribution and abundance Learning objectives: 5.11 understands what is meant by the terms population, community, habitat and ecosystem. 5.12 understand that the numbers and distribution of organisms in a habitat are controlled by biotic and abiotic factors 5.13 understand how the concept of niche accounts for the distribution and abundance of organisms in a habitat 1 Ecology is the study of the interaction between organisms and their environment. These interrelationships determine the distribution and abundance of organisms within a particular environment. Ecosystem – it is a life supporting environment which includes all of the living organisms, the nutrients that cycle throughout the system and the physical and chemical environment in which the organisms are living. Habitat- the place where an organism lives (examples: rocky shore, rain forest) Many organisms live in a small part of a habitat and such type of habitat is called microhabitat. Population- a small group of organisms of the same species, living and breeding together in a habitat. Community- all the populations of all the diﬀerent species of organisms living in a habitat at any one time. Niche- the role of the organism in the community or its way of life. Abiotic factors- the non- living elements of the habitat of an organism which has an eﬀect on the success of an organism Biotic factors- the living elements of the habitat that aﬀect the ability of a group of organisms to survive. 2 Major biomes- a community of plants and animals that have common characteristics for the environment they exist Abi ic factors affecting the distribution of organisms ★ Climatic factors e.g. temperature, water availability, light, wind ★ Edaphic factors (associated with soil) e.g. pH, texture ★ Aquatic factors e.g. salinity, amount of dissolved oxygen ★ Topographic factors- aspect, inclination, altitude 3 Climatic factors Temperature An organism will survive only within a range of temperature- limits of tolerance. ★ If temperature falls below zero- freezing of protoplasmic water and the cell becomes physiologically damaged. ★ If the temperature is too high- proteins become denatured. Temperature and rate of development At higher temperatures metabolic rate increases. KE of the molecules increases. More eﬀective collision and more enzyme substrate complexes formed. Decrease in temperature leads to inactivation of enzymes. Temperature above optimum results in denaturation of enzymes. This aﬀects diﬀerentiation. Each species need a particular range of temperature Temperature aﬀects metabolism. Enzymes aﬀect metabolism. Temperature aﬀects enzymes. Diﬀerent species have diﬀerent enzymes. 4 Why temperatures below 0 °C or above 40 °C would be unsuitable for most organisms Metabolism stops or become slow Below 0°c enzymes are inactive / cells disrupted Inactivity / cell disruption is because of freezing of protoplasm or lower kinetic energy Above 40 °c More vibrations in the enzyme break bonds Enzyme denatures. This changes the shape of active site Fewer enzyme substrate complexes form 5 Light ★ Light is the source of energy for photosynthesis. ★ This inﬂuences primary productivity. ★ All other organisms depend upon primary productivity directly or indirectly. ★ Some plants reproduce early to avoid the shade caused by larger plants. ★ Other plants are able to photosynthesize and reproduce successfully in low light levels. ★ They may have extra chlorophyll or diﬀerent ratios of photosynthetic pigments that are sensitive to lower light levels. ★ Some will have very large leaves to collect light. ★ Animals are aﬀected by light levels indirectly as a result of the distribution of food plants ★ Seasonal light changes aﬀect the reproductive pattern of many animals. ★ This also changes much of the animal physiology and behaviour 6 Wind and water current ★ Wind increases cooling and water loss from the body. ★ Strong winds (hurricanes) can cause extreme damage to populations. ★ This results in the loss of plant and animal communities. ★ In water when the strength of currents increases suddenly this may damage the entire population. ★ Only strong swimmers or one which is able to attach to a surface can resist the force of water and can survive. ★ Air movements accelerate dissemination of spores and seeds of plants which help them to colonize in favourable habitats. Water availability ★ The availability of water is aﬀected by several factors such as the amount of rain, snow or hail, the rate of evaporation and the rate of loss by drainage through the soil. ★ Availability of water leads to germination of seeds, and growth of plants. This changes the habitat and increases the population size. ★ The population size of organisms which are directly or indirectly dependent on those plants also will increase. 7 Oxygen availability ★ When water is cold or fast ﬂowing, there will be enough oxygen dissolved in it. ★ So, organisms which need oxygen for their survival can exist. ★ With rise in temperature of the water or if the water becomes still and no longer ﬂows, then the oxygen content will drop. ★ Mostly anaerobic organisms survive in those areas. ★ In terrestrial habitat, the spaces between the soil particles contain air, so there is plenty of oxygen for the respiration of plant roots. ★ In waterlogged soil, as the air spaces are ﬁlled with water oxygen availability is very less. So, plants with special adaptation (aerial roots) to obtain oxygen only can survive there. 8 Edaphic factors- factors related to the structure of the soil Soil structure and mineral content aﬀect the survival of various populations. Soil pH ★ Measure of hydrogen ion concentration in aqueous solution. ★ This indicates the level of acidity or alkalinity. Low altitudes have high pH (4.5-8) and support many microbes. ★ Microbes help to break down the litter into humus. Higher altitude have low pH (3-6.5) ★ Fewer microbes survive and fungi help to form humus 9 pH and growth of organisms ★ pH aﬀects enzymes and enzymes aﬀect metabolism ★ Due to change in pH the shape of active site is altered by the ionisation of the R groups ★ This aﬀects the metabolism as substrates cannot ﬁt into the active site. Topographic factors ★ Aspect (slope):- angle of the sun on a south facing slope is greater. So receive more sunlight and are warmer. ★ Inclination (steepness):- water drains more readily from steep slopes. ★ Altitude (height):- at higher altitude the temperature is lower, the wind speed is greater and there is more rainfall. 10 Bi ic factors Involve all those factors that are living. ★ Competitors ★ Predators ★ Decomposers ★ Population Density ★ Disease Competition Organisms compete with each other for various available resources. Animals compete for food, water, shelter, mate and nesting sites. Two types of competition- interspeciﬁc competition and intraspeciﬁc competition 11 Intraspeciﬁc competition Competition between members of the same species within the same niche for a limited source. ★ If the territory is small or relatively little food available ★ Intraspeciﬁc competition occurs. ★ They may not survive and reproduce, and population growth slows down. ★ If large quantities of resources are available, there is little or no competition for the resources ★ and the number of individuals increases 12 Interspeciﬁc competition ★ Competition between members of two diﬀerent species within a community for the same resource. ★ The niches of the species overlap. ★ Competition will reduce the abundance of the competing species. ★ The greater density and faster reproduction rate in a species leads to the extinction of the other competitor 13 Ecological niche It is the status or the role of an organism in its environment. Diﬀerent niches avoid competition The abiotic and biotic factors aﬀecting the number of organisms occupying a particular niche may be density-independent or density-dependent ★ The density-independent factors- regardless of population size. Extremes of temperature will adversely aﬀect all the individuals in the population. This type of factor will limit the distribution of species. 14 The density-dependent factors- depend on the number of organisms in a speciﬁc area. Examples: Disease and parasitism, territory ★ If the number of individuals are more in a speciﬁc area, there will be more chance of transmission of disease and parasites. ★ Breeding success is density dependent. ★ Individuals without territory or reduced territory are less able to breed. ★ Density-dependent factors also will limit the abundance of species. Parasitism and disease- biotic factors ★ Diseased animals will be weakened. ★ They do not reproduce successfully. ★ They cannot hunt well, and they are more likely to be caught by their predators. ★ Some diseases are infectious which will spread very fast without direct contact. ★ Parasites aﬀect their hosts. ★ They usually feed oﬀ the living body of the host and weaken it. ★ This may wipe out the entire population of the host. 15 Mutualism – relationship between two organisms where both partners beneﬁt by their association. Predation ★ Interactions of predators and prey are a factor in regulating the population size. ★ A predator is any organism that feeds on another living organism called the prey. ★ The population is an oscillating population. ★ Predator –prey population was regulated by a negative feedback mechanism. ★ Predation aﬀects the abundance of species. ★ Here the population of prey and predator change between two extremes. ★ As prey population increases, more food is available for the predator and its population increases. ★ The rate at which the prey are being eaten is greater than the rate of reproduction. So the number of prey will fall. ★ This reduces the food supply of the predators. ★ This reduces their reproduction rate and the number will fall. ★ This allows the abundance of prey to increase. 16 Antibiosis ★ Organisms sometimes produce deterrent chemicals to repel other organisms. ★ Many mammals use these chemicals to mark their territories. ★ Example: pheromones produced by ants warn oﬀ other members of the species. ★ Penicillium produces antibiotics to prevent the competition with bacteria for the sources either by inhibiting the growth or killing them. Dispersal of seeds enables plants to colonize new and favourable habitats. This prevents competition with the parent and the oﬀspring for available resources. 17 Pollination Angiosperms utilize insects to transfer their pollen grains from one member of a species to another. Mimicry The resemblance of an animal species to another species object to escape from the predators 18 Anthropogenic factors As hunters, farmers, ﬁshers, developers, polluters etc. Introduction of grazers and removal of predators of grazing animals. 19 20 A2 BIOLOGY SEM TER THREE 2021 Student N es 12s8 Ecological Succession Learning objective: I. Understand the stages of succession from colonization to the formation of a climax community 1 ★ Succession is the process by which an ecosystem changes over time. ★ The biotic conditions (e.g. plant and animal communities) change as the abiotic conditions (e.g. water availability) change. ★ Succession is the gradual replacement of one plant community by another through natural processes over time. ★ There are two types of succession- primary succession and secondary succession. Primary Succession ★ This type of succession starts with an empty inorganic surface such as bare rock. ★ There is no soil or organic material to start with. ★ The ﬁrst stage of this succession is colonization and the ﬁrst organism to appear are pioneer species (e.g. lichen). Why only pioneer species and what is its role? ★ The abiotic conditions are hostile (harsh), e.g. there is no soil to retain water. ★ Only pioneer species grow because they are specially adapted to cope with the harsh conditions. ★ The pioneer species secrete acids which will dissolve the rocks. ★ They can penetrate the rock and help to break the rock into small grains. ★ When they die the microorganisms decompose the organic material to form humus and mix up with small grains of rock and form a shallow layer of soil. 2 Primary succession ★ The pioneer community lichens and mosses started to grow. They are able to grow in little / no soil. ★ This breaks up rock fragments and forms a thin shallow layer of soil. ★ Plants with small roots are able to grow in thin / shallow soil. ★ This changes the soil by holding more water and minerals. As plants die it adds organic material to the soil and increases the soil fertility. ★ Competition occurs between organisms and better adapted ones survive. ★ Changes in soil structure enable trees to grow. ★ Biodiversity increases. ★ Finally reaches a stable stage of community called climax community. Biomass change during primary succession ★ There are few very small plants at the beginning. ★ So, the initial biomass is very low. ★ The biomass increases during succession as the plants in the later stages are larger than the pioneer plants and grasses. 3 Climax Community ★ A stable group of plants and animals that is the end result of the succession process. ★ It has high biodiversity and there will be more interaction between species. ★ There is a balanced equilibrium of species and contains dominant plant or animal species. ★ It is stable if no change to environment / human inﬂuence Diﬀerent ecosystems have diﬀerent climax communities ★ The species which make up the climax community depends upon the climatic condition in that ecosystem. ★ Such a type of climax community is climatic climax. ★ In a temperate climate, the climatic climax will contain large trees because they can grow in these conditions (plenty of water, mild temperatures and not much change between the seasons.) once deep soils have developed. ★ In a polar climate the climatic climax contains only herbs or shrubs, but it is still the climax community (not much available water, temperatures are low and there are massive changes between the seasons). 4 Succession can be Prevented ★ Human activities can prevent succession, stopping a climax community from developing. When succession is stopped artiﬁcially like this the climax community is called a plagioclimax. ★ Such type of succession is deﬂected succession. ★ A plagioclimax is a sub- climax community where succession has been deﬂected by human activity. ★ Example: A regularly mown grassy ﬁeld will not develop shrubs and trees (woody plants), even if the climate of the ecosystem could support them. ★ With more frequent mowing, succession cannot progress, and diversity will be lower — only the grasses can survive being mowed. 5 Trends of succession ★ The kind of plants and animals change continuously. ★ Increasing biomass and decomposing plant and animal material. ★ Species diversity increases. ★ A progressive reduction in net community production. ★ Increase in community respiration. Mixed woodland and biodiversity ★ Diﬀerent food items are available. ★ Provide many niches. ★ Provide many nesting places and shelter. ★ Species diversity increases. 6 Secondary succession ★ This type of succession happens on land that has been cleared of all the plants, but where the soil remains, e.g. after a forest ﬁre or where a forest has been cut down by humans. ★ The sequence of events is similar to that seen in primary succession. ★ The numbers of plants and animals present right from the beginning of this succession is much higher because the soil is already formed and contains seeds, roots, and small organisms. Which type of succession would occur faster? ★ Secondary succession occurs faster. ★ Soil is already present. ★ Seeds or roots of earlier plants might be still existing in the soil. ★ They can grow quickly into new plants when enough water and sunlight is available. 7 Describe the eﬀect of change in the plant community on the number of species of small birds. GIVE REASONS ★ Increased number of species as succession progresses / number of species increases from grassland to woodland (Any suitable manipulation of data) ★ Grassland is open habitat, but trees provide more cover ★ Birds easily spotted by predators in grass / converse for trees and shrubs ★ Trees provide roosting / nesting sites ★ Mixed woodland provides greater variety of food to support more species ★ Trees provide more niches for species (b) the population density of birds drops when shrubs are replaced by pine trees, but then increases with the change to mixed woodland. Suggest reasons for these changes in population density. ★ Pine trees have less food available for birds ★ Reduction in the variety of niches 8 A2 BIOLOGY SEM TER THREE 2021 Student N es 12s8 THE CARBON CYCLE Learning objective Understand how knowledge of the carbon cycle can be applied to methods to reduce atmospheric levels of carbon dioxide CARBON CYCLE The movement of carbon between organisms and the atmosphere is called the carbon cycle 1 CARBON CYCLE ★ Carbon (in the form of CO2 from the atmosphere) is absorbed by plants when they carry out photosynthesis — it becomes carbon compounds in plant tissues. ★ Carbon is passed on to animals when they eat the plants and to decomposers when they eat dead organic matter. ★ Carbon is returned to the atmosphere as all living organisms carry out respiration, which produces CO2 ★ If dead organic matter ends up in places where there aren't any decomposers, e.g. deep oceans or bogs, the carbon compounds can be turned into fossil fuels over millions of years. ★ The carbon in fossil fuels is released as CO2 when they’re burnt — this is called combustion. To reduce atmospheric CO2 concentration Either ★ The amount of CO2 going into the atmosphere (due to respiration and combustion) needs to be decreased Or ★ The amount of CO2 being taken out of the atmosphere (by photosynthesis) needs to be increased. 2 Carbon in oceans ★ Additional carbon is stored in the ocean. ★ Many animals pull carbon from water to use in shells, etc. ★ Animals die and carbon substances are deposited at the bottom of the ocean. ★ Oceans contain earth’s largest store of carbon. Human Impact ★ Fossil fuels release carbon stores very slowly ★ Burning anything releases more carbon into atmosphere — especially fossil fuels ★ Increased carbon dioxide in atmosphere increases global warming ★ Fewer plants mean less CO2 removed from atmosphere What We Need to Do: ★ Burn less, especially fossil fuels ★ Promote plant life, especially trees 3 Carbon sinks ★ The ultimate place where carbon compounds are locked up for a long period of time. ★ These are reservoirs. ★ In the biotic part of the system carbon is removed from the atmosphere by photosynthesis and stored in the bodies of living organisms. ★ In the abiotic system rocks (limestone and chalk) and fossil fuels contain large amounts of inorganic carbon. ★ Limestone- largest Carbon reservoir in Carbon cycle ★ Ocean is also a carbon reservoir. ★ Carbon once trapped in these sinks rarely escapes. ★ CO2 concentration is increased by the destruction of natural sinks (things that keep CO2 out of the atmosphere by storing carbon). ★ E.g. trees are a big CO2 sink — they store the carbon as organic compounds. ★ CO2 is released when trees are burnt, or when decomposers break down the organic compounds and respire them. 4 The concentration of carbon dioxide The accurate measurement of the amount of Carbon dioxide began in the year 1957 The results are: ★ Atmospheric carbon dioxide is low in summer and high in winter. ★ This is due to the diﬀerence in rate of photosynthesis. ★ In winter carbon dioxide concentration is higher than in summer. ★ This is due to reduced photosynthesis. ★ Trees are leaﬂess or temperature is limiting. ★ There is a rising trend in atmospheric carbon dioxide concentration. ★ 1957- 315ppm ★ 1988-350ppm Rise in atmospheric carbon dioxide concentration ★ Combustion of fossil fuels ★ Deforestation Combustion of fossil fuels Fossil fuels are carbon sinks. Burning fossil fuels releases the additional carbon as carbon dioxide in the atmosphere. 5 Deforestation Trees would act as carbon reservoirs. Plants use carbon dioxide for growth. Deforestation creates an increase in atmospheric carbon dioxide. Carbon dioxide released by the respiration process is absorbed by various natural sinks like rivers and lakes Maintaining balance Using biofuels Reforestation 6 Biofuels and Reforestation Decrease the Atmospheric 𝐶𝑂 2 concentration ★ Biofuels are fuels produced from biomass — material that is or was recently living. They’re often made from crops, which can be replanted after harvesting — making biofuels a sustainable resource. ★ Biofuels are burnt to release energy, which produces CO2. ★ There is no net increase in atmospheric CO2 concentration when biofuels are burnt — the amount of CO2 produced is the same as the amount of CO2 taken in when the material was growing (carbon neutral). ★ So using biofuels as an alternative to fossil fuels stops the increase in atmospheric CO2 concentration caused by burning fossil fuels. Biofuel production is not carbon neutral ★ Biofuel production may overall results in more carbon dioxide in the atmosphere ★ Forests are carbon sinks. ★ Deforestation results in net increase in carbon dioxide in atmosphere ★ Less plants means less carbon dioxide is removed by photosynthesis ; ★ Burning of trees would produce carbon dioxide ; ★ Increased decomposition produces carbon dioxide; ★ Using fossil) fuels by vehicles and machinery produces carbon dioxide ; ★ Burning of biofuels produces carbon dioxide ; 7 ADVANTAGES DISADVANTAGES Reduce the use of limited fossil fuels Destruction of carbon sinks release stored carbon Provide renewable energy source and Loss of habitat and reduces reduce C emission biodiversity Waste biomass can be recycled to Food shortage can occur where produce biofuels biofuels are replacing food crops Reforestation ★ Planting young and fast growing trees. ★ Because of rapid growth they absorb more carbon dioxide for photosynthesis. ★ Rate of photosynthesis is greater than respiration. ★ So net carbon dioxide absorption occurs. ★ As the forest matures respiration= photosynthesis. ★ The wood of the tree becomes a carbon store. ★ Continuous reforestation slows down increase in CO2 ★ More carbon dioxide removed from the atmosphere by photosynthesis ; ★ Carbon (dioxide) is used in forming permanent plant biomass ★ Carbon is incorporated in organic molecules Limitations of reforestation ★ Mature forest is carbon neutral as respiration= photosynthesis. ★ So beneﬁts only last while the forest grows. ★ Limited amount of land can be used for reforestation. 8 More carbon in soil (carbon sinks) due to less ploughing / farming ★ Less oxygen can enter the soil ★ Oxygen is needed for aerobic respiration in soil microorganisms like bacteria and fungi. ★ Less breakdown of organic matter / humus / dead plants / dead animals ★ Less carbon dioxide released 9 10 Role of microbes in soil ★ It helps for decomposition of plants / animals ★ Helps to improve the quality / mineral content of the soil ★ Release carbon dioxide back into the atmosphere by respiration. ★ This carbon dioxide is used in photosynthesis ★ Also help to recycle the nitrogen ★ Microbes provide food for other soil organisms ★ Pls study Role of microorganisms in recycling carbon ★ Microorganisms like bacteria and fungi release extracellular enzymes onto organic material. ★ This breaks down complex organic materials like starch and cellulose into simpler soluble monomers such as glucose. ★ It is done by breaking glycosidic bonds by these enzymes. ★ Then glucose is used as a respiratory substrate by the microorganism and releases carbon dioxide into the atmosphere. ★ This carbon dioxide is used by green plants for photosynthesis 11 A2 BIOLOGY SEM TER THREE 2021 Student N es 12s8 GreenHouse Gases And Climate Change Learning objective: understand the diﬀerent types of evidence for climate change and its causes, including records of carbon dioxide levels, temperature records, pollen in peat bogs and dendrochronology, recognizing correlations and causal relationships Understand the causes of anthropogenic climate change, including the role of greenhouse gases in the greenhouse eﬀect. Understand that data can be extrapolated to make predictions and that these are used in models of future climate change Understand that models for climate change have limitations. Understand the eﬀects of climate change (changing rainfall patterns and changes in seasonal cycles) on plants and animals (distribution of species, development and life cycles) Understand the eﬀect of temperature on the rate of enzyme activity and its impact on plants, animals and microorganisms, to include Q10 1 Greenhouse eﬀect ★ Solar energy reaches the earth in the form of short wave radiation. ★ When the radiation strikes a surface much of its energy is converted into heat (long wavelength radiation). ★ Greenhouse gases like Carbon dioxide and water vapour in the atmosphere absorb and retain these long wave radiation and prevent them from escaping into space. ★ Some may reﬂect towards the earth surface. ★ This is a natural process of warming up the earth’s atmosphere. This is greenhouse eﬀect ★ without this greenhouse eﬀect the Earth would be as cold as the moon 2 Global warming ★ Because of human activities like burning of fossil fuels greenhouse gases like Carbon dioxide and methane accumulate in the atmosphere. ★ Solar radiation reaches the earth surface as short wave radiation. ★ Reﬂect back from the earth’s surface as long wave IR radiation ★ These are trapped by greenhouse gases and re-radiate back towards earth’s surface. ★ This increases the earth’s mean surface temperature. ★ This is global warming. 3 Greenhouse gases ★ CO2 - by the combustion of fossil fuel and deforestation. / Naturally by volcanic eruption and respiration ★ CH4 - Produced by the activity of anaerobic bacteria in landﬁll sites, guts of certain insects and ruminants. (anaerobic respiration by microorganisms like bacteria release methane) ★ CFC- from refrigerator and aerosol spray ★ Water vapour - transpiration and evaporation These gases accumulate in the atmosphere and trap infrared radiation resulting in an increase in the temperature of the Earth's atmosphere / surface Climate - the average weather in a relatively large area such as a country over a long period of time. Weather - the conditions in the atmosphere at a particular time. Climate change - a large-scale change in the global or regional weather patterns that happens over a period of many years. Abundance - abundance is the number of a particular organism Distribution - distribution is where the organism is found 4 Evidence for global warming 1) Temperature records 2) Dendrochronology –tree ring analysis 3) Pollen in peat bogs 4) Ice core samples Temperature record ★ A data set of the annual mean surface temperature that was made in central England and Toronto, Canada over 3 centuries to the present time shows a ﬂuctuating trend. ★ The Central England Temperature dataset is the oldest in the world – with 351 years of temperature records drawn from "multiple weather stations located both in urban and rural areas of England. ★ Starting in 1659, the Central England Temperature Record (CET) is the world's longest continuous temperature record, ★ Line of best ﬁt suggests temperature has gradually increased by about 1.8oC between mid C17 and present. ★ Closer analysis of the trend line shows ﬂuctuations between 1700 and 1900 then a gradual rise until the present day. 5 Dendrochronology ★ Tree ring analysis (dating of past events using tree ring growth) ★ Tree ring is growing yearly ★ Tree rings can be dated by counting inwards ★ Thicker / wider tree rings reﬂects amount of growth ★ In warmer conditions the rings are thicker and it shows better growth ★ Scientists can see what the climate is like each year How it provide evidence for climate change Each year a new tree ring is formed. So the number of rings can be used to work out the timescale. The size of the ring reﬂects the growth of the tree that year Size of ring / growth is aﬀected by climatic factors like temperature. Because photosynthesis is aﬀected by these climatic factors. ★ The diagram shows a core taken from a tree in 2000. ★ The most recent rings are the thickest and the rings get steadily thinner the further in the past they were formed. ★ The trend of increasingly thicker rings from 1920 to 2000 suggests that the climate where the tree lived had become warmer over the last century 6 In order to know more about climate over an even longer period of time, in some cases thousands of years, it is possible to look at dead trees of an unknown age that are still well preserved. One can correlate their rings to the rings of a living tree (whose age you know), and see where the rings match up and get a longer record of climate through time. 7 How global warming may aﬀect tree ring growth ★ An increase in temperature increases ring thickness / tree ring growth. ★ So the rate of photosynthesis is faster as enzymes work faster with higher temperature. ★ So more material is laid down in the tree trunks. ★ At higher temperatures (above optimum) enzymes denature. ★ So the rate of enzyme activity and photosynthesis decreases and the tree rings would be thinner. 1) Which two separate years were particularly cold or dry? 900 AD and 1450 AD 2) Which was probably the warmest or the wettest? 1150 AD 8 Problems ★ If conditions vary a lot within one year more than one ring may be produced. ★ Tree growth depends on many factors- amount of sunshine, temperature, carbon dioxide levels and the amount of rainfall. ★ So it is hard to say what led to the large cells being laid down. ★ Was it one of the above factors or was it a combination of several of them? The diagram above shows a core taken from a pine tree in 2009. Analyse the data shown in the diagram to explain how the core provides evidence for climate change. ★ The diagram shows that the thickness of the pine tree rings ﬂuctuated, but there was a trend of increasingly thicker rings from 1909 to 2009. ★ The thickness of each tree ring depends on the climate when the ring was formed. ★ Warmer climates tend to give thicker rings than colder climates as the rate of photosynthesis increases due to increased rate of enzyme action. ★ This suggests that the climate where the pine tree lived became warmer over the last century, which is evidence of climate change 9 Pollen in Peat Bogs ★ Pollen in peat bogs can be used to show how temperature has changed over thousands of years. ★ Pollen is often preserved in peat bogs- partly decomposed plant material (acidic wetland areas). ★ Peat bogs accumulate in layers so the age of the preserved pollen increases with depth. The lowest layers are the oldest ★ Scientists can take cores from peat bogs and extract pollen grains from the diﬀerent aged layers. They then identify the plant species the pollen came from. ★ The samples only show the species that were successful at that time. ★ Scientists know the climates that diﬀerent plant species live in now. When they ﬁnd preserved pollen from similar plants, it indicates that the climate was similar when that pollen was produced. ★ Because plant species vary with climate the preserved pollen will vary as climate changes over time. ★ So a gradual increase in pollen from a plant species that’s more successful in warmer climates would show a rise in temperature (a decrease in pollen from a plant that needs cold conditions would show the same thing). 10 Pollen in peat bogs is preserved for many years ★ The condition in peat is very acidic and anaerobic. ★ Lack of decomposition due to lack of microorganisms like bacteria. ★ Low pH reduces enzyme activity ★ Low oxygen aﬀects respiration of microorganisms ★ Bacteria cannot produce enzymes to breakdown the outer covering of pollen This is a pollen diagram taken from peat cores from Hockham Mere in Norfolk. Describe the changes that have occurred in the species abundance from the distant past to the present ★ Initially almost exclusively birch ★ this was replaced by pine, ★ then elm then oak ★ pine disappeared, ★ lime and alder appeared ★ elm disappeared ★ leaving mainly oak and alder, with some lime, until the present day. Example: oak grows best in warmer conditions than pine, so in warm conditions oak will out-compete pine. So if the amount of oak pollen increases and pine pollen decreases we can infer that the climate was getting warmer 11 Explain how the pollen of present-day species can be used to show what the climate was like in the past. ★ Peat bogs can preserve pollen and are formed in layers ★ Pollen in diﬀerent layers can be used to identify plant species in diﬀerent time periods, with pollen in deeper layers being older. ★ Scientists know the climate that diﬀerent plant species live in now. ★ When they ﬁnd preserved pollen from similar plants, they know that the climate must have been similar when that pollen was produced. Continued draining and clearance of peat lands may contribute towards global warming ★ Combustion of biofuels releases carbon dioxide recently removed from atmosphere ★ There is no net increase in carbon dioxide in atmosphere ★ Carbon dioxide is a greenhouse gas ★ That absorbs infra-red radiation reﬂected from earth’s surface ★ And prevents infra-red from escaping into space ; ★ Therefore mean temperature of earth’s surface increases ; ★ Carbon in peat land was trapped a long time ago ★ Peat land clearance releases the trapped carbon dioxide ; ★ So there is a net gain of carbon dioxide in the atmosphere ★ Removal of plants during clearance reduces photosynthesis and reduces the removal of carbon dioxide from the atmosphere ★ Carbon dioxide is also released from clearance machinery ; 12 Ice core sampling ★ Bubbles in the ice core preserve actual samples of the world’s ancient atmosphere. ★ Seasonal diﬀerences in the snow properties create layers – just like rings in trees. ★ Examining the ice cores gives you a history of what happened in the atmosphere for hundreds and thousands of years. ★ Bubbles in the ice trap prehistoric atmosphere, which can be analyzed. ★ Scientists analyse the air trapped in diﬀerent layers. ★ Measure the carbon dioxide levels in the air trapped in the ice core sample. ★ The oxygen isotopes in the melted ice reﬂect the air temperature at the time the ice layer was formed. 13 Climate Change Can be Caused by Human Activity ★ An increase in human activities (anthropogenic causes) like burning fossil fuels (for industry and in cars), farming and deforestation has increased atmospheric concentrations of CO2 and methane. ★ This has enhanced the greenhouse eﬀect and caused a rise in average global temperature — global warming ★ greenhouse gases absorb outgoing energy, so that less is lost to space. ★ The greenhouse eﬀect is essential to keep the planet warm, but too much greenhouse gas in the atmosphere means the planet warms up. ★ CO2 concentration is increasing as more fossil fuels like coal, oil, natural gas and petrol are burnt, e.g. in power stations or in cars. ★ Burning fossil fuels releases CO2. ★ It is also increased by destroying of natural sinks like forest(deforestation) ★ Methane concentration is increasing because more fossil fuels are being extracted, there’s more decaying waste and there are more cattle which give oﬀ methane as a waste gas. ★ Methane can also be released from natural stores, e.g. frozen ground (permafrost). ★ As temperatures increase it is thought these stores will thaw and release large amounts of methane into the atmosphere. 14 Scientists do not agree that a reduction in the use of fossil fuel will prevent further global warming ★ Carbon dioxide produced by burning fossil fuels. ★ No direct evidence that increased carbon dioxide leads to global warming. ★ Because carbon dioxide is released from other processes like decomposition. ★ Removal of carbon sinks like forests also leads to an increase in carbon dioxide. ★ Other greenhouse gases like CFC, water vapour and methane are released from other source; ★ Methane is from ruminant animals, paddy ﬁelds and CFC from refrigerator aerosol spray ★ Natural phenomena like volcanic eruptions may also be involved in global warming. ★ Evidence from past is being used and is not in indicator of future events 15 Interpret Evidence for the Causes of Climate Change Interpret data on things like atmospheric CO2 concentration and temperature, and recognize correlations and causal relationships ★ The temperature ﬂuctuated between 1950 and 2006, but the general trend was a steady increase from around 13.8 °C to around 14.5 °C. ★ The atmospheric CO2 concentration also showed a trend of increasing from around 310 ppm in 1950 to around 380 ppm in 2006. ★ There’s a positive correlation between the temperature and CO2 concentration. ★ The increasing CO2 concentration could be linked to the increasing temperature. ★ However, there is no causal relationship — other factors may have been involved, e.g. changing solar activity. ★ Other studies would need to be carried out to investigate the eﬀects of other factors 16 Climate Change can be Extrapolated to make Predictions ★ Data that has already been collected on atmospheric greenhouse gas concentrations can be extrapolated — used to make predictions about how it will change in the future. ★ These predictions can then be used to produce models of how the global climate might change in the future ★ If they extrapolate the data by ignoring the annual ﬂuctuation the prediction will not be accurate. ★ Photosynthesis may vary during winter and summer and carbon dioxide production by natural processes also will change. ★ Scientists use computer models to study the interaction of diﬀerent factors. ★ By extrapolating the data, prediction can be made about how it will change in the future ★ Use investigation of correlations Providing evidence for global warming ★ By using graphs showing increase in temperature ★ Using this data along with data from other sources 17 Climate models and limitation There are many limitations even with the best models. This is because: ★ It is impossible to tell the exact impact of carbon dioxide on global warming ★ Impossible to predict the impact of global warming on particular aspects of the world climate. ★ The change in atmospheric greenhouse gas concentrations due to natural causes (without human inﬂuence) is not known ★ Extrapolations from the past data cannot take into account unknown factors in the future (including how current trends in resource usage and technologies may change) ★ Limited data ★ Limited knowledge about how the climate system works ★ Limited computer resources ★ Failure to consider all the factors aﬀecting climate change ★ Change in trends in CO2emission and ice cover. 18 Global warming aﬀects plants and animals An increasing temperature aﬀects the rate of enzyme activity which can aﬀect organisms’ life cycles, development and distribution. ★ The rate of an enzyme-controlled reaction increases when the temperature is increased. ★ This is because more heat means more kinetic energy, so molecules move faster. ★ This makes the enzymes more likely to collide with the substrate molecules. ★ But, if the temperature gets too high, the reaction stops. ★ This is due to the denaturation of the enzyme at higher temperatures. ★ An organism’s metabolic reactions are controlled by enzymes. ★ An increase in temperature will mean that the metabolic reactions in some organisms will speed up, so their rate of growth will increase. ★ This also means they will develop and progress through their life cycle faster. ★ But the temperature will become too high for some organisms. ★ Their metabolic reactions will slow down, so their rate of growth will decrease and they will progress through their life cycle slower. ★ Global warming will also aﬀect the distribution of some species — all species exist where their ideal conditions for survival are, e.g. their ideal temperature. ★ When these conditions change, they will have to move to a new area where the conditions are better. ★ If they can’t move they may die out in that area. ★ Also, the range of some species may expand if the conditions in previously uninhabitable areas 19 Describe and explain how global warming could aﬀect plant species ★ Due to global warming earth’s mean surface temperature is increasing ★ Loss of existing species in places where the temperature is not ideal for them to survive ★ Changes in distribution of plant species. ★ There will be changes in rainfall patterns and growing seasons ★ Temperature may become too hot for some species and this may aﬀect enzyme activity. ★ Increased carbon dioxide results in more photosynthesis / GPP/ NPP / biomass ★ This changes the numbers / size / growth of plants The Eﬀects Of Global Warming On Plant Species Aﬀect Animal Species. ★ If the temperature increases above the optimum temperature some of the plant species may die ★ So, there is a reduction of herbivore because of reduction in food supply ★ Results in a reduction of predator or secondary consumers. ★ A change in distribution of plants could result in a change in distribution of herbivores. ★ Loss of habitat decreasing the numbers of animal species ★ Loss of shelter provides more food for predators so the predator would increase in number 20 Eﬀect of increased temperature for animals from global warming ★ Global warming increases the earth’s mean surface temperature ★ When the temperature increases up to optimum temperature metabolic reactions speed up ★ So, the rate of growth increases and the life cycle becomes faster. ★ Above optimum temperature, metabolic reactions fall ★ So their rate of growth falls and life cycle slows down [***Anytime you see temperature having an eﬀect, consider the activity of enzymes as a reason for the eﬀect] Global warming causes other types of climate change- Global rainfall patterns and the timing of seasonal cycles aﬀect plants and animals Changing Rainfall Patterns Due to Global warming some areas will get more rain, others will get less rain. Changing rainfall patterns will aﬀect the development and life cycles of some organisms Changing rainfall patterns will also aﬀect the distribution of some species, e.g. deserts could increase in area because of decreases in rainfall So, species that are not adapted to live in deserts will have to move to new areas or they will die out. 21 Seasonal Cycles Global warming is thought to be changing the timing of the seasons, e.g. when winter changes to spring. Organisms are adapted to the timing of the seasons and the changes that happen, e.g. changes in temperature, rainfall and the availability of food. Changing seasonal cycles will aﬀect the development and life cycles of some organisms Changing seasonal cycles will also aﬀect the distribution of some species Example:- ★ Some swallows live in South Africa over the winter and ﬂy to diﬀerent parts of Europe to breed at the start of spring (when more food is available). ★ An early British spring will produce ﬂowers and insects earlier than usual, so the swallows that migrate to Britain at the normal time will arrive when there isn’t as much food available (there will be fewer insects because the ﬂowers will have disappeared earlier). ★ This will reduce the number of swallows that are born in Britain, and could eventually mean that the population of swallows that migrate to Britain will die out. ★ The distribution of swallows in Europe will have changed. 22 23 Eﬀect of global warming on distribution ★ Because of global warming temperature may be too high ★ Organisms migrate to places with suitable temperature ★ This results in a change of biodiversity. Biodiversity increases at places with suitable temperature. ★ Increased competition eﬀects ★ Range of organisms increasing as the place is suitable for the organism ★ Plants can move less easily than animals (accept converse) ★ So the animals / plants survive more / less ★ If organisms involved in the spread of disease are aﬀected, patterns of world health could change as well. ★ Global warming could be responsible for a major increase in insect-borne diseases. ★ Because the condition could be ideal for disease-carrying organisms such as mosquitoes in many new areas of the world. 24 Seasonal cycle aﬀect life cycles ★ Global warming aﬀects the beginning of the seasons. ★ This aﬀects both the life cycle and the distribution of species. ★ In warmer temperature plants grow and ﬂower earlier. ★ Insects become active earlier in this warmth and the food they need for their caterpillars is available. ★ Some birds can adapt to these changes and some cannot. Example: Great tits in UK ★ According to the changes in global temperature, their life cycle has also moved forward (The UK tits lay eggs two weeks earlier now). ★ So the winter moth larvae that form the main food for the baby birds are also present on the leaves. Great tit in Netherlands ★ Their breeding time is becoming earlier every year but the caterpillars are emerging even earlier. ★ So the birds are missing the peak population of caterpillars and raising fewer chicks. Changes in temperature could change the male female sex ratio. ★ Example: embryos of some reptiles are sensitive to temperature during development. ★ Male crocodiles develop only if the eggs are incubated at 32-330C. ★ If the eggs are cooler or warmer, females develop. ★ Due to global warming if all the females develop, then it could be the end of that species 25 Global warming and decomposition ★ As temperature of soil increases enzyme activity of decomposers increases ★ So more decomposition of dead organic matter in soil occurs. ★ Products of decomposition are used by the decomposers, like bacteria for respiration which itself increases as a result of the warmer temperatures. ★ So more greenhouse gases like CO2 and methane are released. ★ Climate change already involves changes in temperature. ★ In many parts of the world, this change will be an increase in temperature, but some places will get colder. ★ Temperature has an eﬀect on enzyme activity, which in turn aﬀects the whole organism. ★ A 100℃ increase in temperature will double the rate of an enzyme - controlled reaction. ★ This eﬀect of temperature on the rate of any reaction can be expressed as temperature coeﬃcient (Q10) ★ Q10 for any reaction between 0℃ and 400℃ is 2. ★ This means that a 100℃ rise in temperature produces a doubling of the rate of reaction within the temperature range where most living things live. 26 Potato tuber moths infest potato crops in warm climates, such as southern Europe. a) They complete their life cycle faster at 21 °C than at 16 °C. Explain why this is the case. [4 marks] An increase in temperature causes an increase in enzyme activity which speeds up metabolic reactions. Increasing the rate of metabolic reactions in a potato tuber moth will increase its rate of growth, so it will progress through its life cycle faster b) Describe what may happen to their range in Europe over the next 25 years if global warming continues. [2 marks] The range of the potato tuber moth may expand northwards into the rest of Europe because rising temperatures due to global warming may make the climate in northern Europe more suitable for the moth than it was previously 27 Climate Change And Evolution Learning objectives: Understand how evolution (a change in allele frequency) can come about through gene mutation and natural selection Understand how isolation reduces gene ﬂow between populations, leading to allopatric or sympatric speciation Climate change and selection pressure ★ In many places the climate is becoming warmer. ★ In some places the climate is becoming colder or wetter or drier. ★ These climatic changes are acting as selection pressures. ★ This changes the allele frequency and results in evolution through natural selection. Evolution is when the frequency of an allele in a population changes over time. It occurs by natural selection. Rising temperatures do not cause mutations. Rising temperatures cause environmental variation which results in selection pressure on the organisms. 28 Individuals within a population vary because they have diﬀerent alleles due to gene mutations. This means some individuals are better adapted to their environment than others. Individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes (including the beneﬁcial allele), than individuals with diﬀerent alleles. This means that a greater proportion of the next generation inherit the beneﬁcial allele. They, in turn, are more likely to survive, reproduce and pass on their genes. So the frequency of the beneﬁcial allele increases from generation to generation. Isolation reduces gene ﬂow leading to Speciation ★ Speciation happens when populations of the same species become reproductively isolated, reducing gene ﬂow (transfer of genes) between two populations. ★ This means that natural selection acts on each population separately — so new species can develop. ★ Reproductive isolation may occur because of geographical isolation (allopatric speciation) or because random mutations produce changes in phenotype that prevent populations from mating (sympatric speciation). 29 Allopatric Speciation Requires Geographical isolation ★ Populations that are geographically separated will experience slightly diﬀerent conditions. E.g. there might be a diﬀerent climate on each side of the physical barrier. ★ The populations will experience diﬀerent selection pressures and so diﬀerent changes in allele frequencies could occur ★ The changes in allele frequency will lead to diﬀerences accumulating in the gene pools of the separated populations, causing changes in phenotype frequencies. ★ Eventually, the diﬀerent populations will have become genetically distinct — their DNA will have become signiﬁcantly diﬀerent. ★ Individuals from the diﬀerent populations will have changed so much that they won’t be able to breed with one another to produce fertile oﬀspring ★ They have become reproductively isolated. ★ The two groups will have become separate species 30 Reproductive Isolation Occurs in Many ways Reproductive isolation occurs because the changes in the alleles and phenotypes of the two populations prevent them from successfully breeding together. Prezygotic mechanisms prevent interspecies mating and fertilization. I. Seasonal changes/temporal - individuals from the same population develop diﬀerent ﬂowering or mating seasons, or become sexually active at diﬀerent times of the year. II. Mechanical changes - changes in genitalia prevent successful mating. III. Behavioural changes - a group of individuals develop courtship rituals that aren’t attractive to the main population IV. Ecological changes – species occur in the same area but they occupy diﬀerent habitats and rarely encounter each other. Seasonal isolation Behavioural isolation 31 Post-zygotic mechanisms prevent the hybrid zygote from developing into healthy and fertile adults. There are two likely cases that will occur to ensure that the hybrid does not reproduce: I. Hybrid inviability is when the embryo does develop but the hybrid experiences reduced ﬁtness and often an early death. II. Hybrid sterility occurs when a hybrid develops into a mature adult but is unable to undergo successful meiotic division, and is unable to produce oﬀspring. (seen in donkey-horse hybrids: mules) 32 Sympatric Speciation Doesn’t Require Geographical Isolation Speciation without geographic isolation is called sympatric speciation. A population doesn’t have to become geographically isolated to become reproductively isolated. Random mutations could occur within a population, resulting in changes which prevent members of that population breeding with other members of the species. 33 A2 BIOLOGY SEM TER THREE 2021 Student N es 12s8 CORE PRACTICAL 13 INV TIGATE THE RATE OF GROWTH OF MICROORGANISMS IN A LIQUID CULTURE, TAKING INTO ACCOUNT THE SAFE AND ETHICAL USE OF ORGANISMS Learning objectives: I. To understand how microorganism growth rate in liquid culture can be measured II. To be able to culture microorganisms with due regard for safe practice Independent Variable: Time / hours (since initiation of experiment) Dependent variable: Light absorbance (turbidity) / a.u. (OR) number of yeast cells / cells cm-3 Confounding variables: Volume of culture tested - 3 cm3 Temperature - Using a temperature controlled room (25oC) Concentration of nutrients in culture medium Concentration of cells in culture medium at start 1 Risk assessment RISK HAZARD PRECAUTION Spillage that could cause ★Wipe up any liquid spillages as soon as they Liquids surfaces to be slippery leading occur to an accident ★Put lids on bottles and put them away once used Glassware Cuts from sharp objects ★Take care when handling glass objects ★Keep away from edge of desk ★Wear gloves when handling to avoid skin ★May cause an allergic contact, if it gets on skin rinse thoroughly with reaction. cold water Yeast ★Contamination of yeast with ★Use aseptic techniques throughout other microorganisms could ★Give the culture to the lab technician to destroy occur. after the experiment ★Wear eye protection ★Avoid skin contact by wearing gloves and allow it Disinfectant May cause an allergic reaction. to soak into the work bench (10 mins) before carrying out the experiment ★ The culture of yeast is a possible biological hazard as there is potential for contamination. ★ A single yeast culture ﬂask should be set up for the class. ★ If samples are taken this should be over a period of no more than 12 hours. ★ Wear eye protection. ★ Avoid skin contact with disinfectant or any other stain used 2 ★ Measuring the growth of yeast culture ★ A colorimeter can be used to measure turbidity or absorbance ○ The more yeast cells in the culture, the more turbid the culture is Method 1:- Colorimetry Method 2:- Light Sensor with Datalogger Method 1. Before starting the experiment disinfect the workbench, thi

A2 Biology Past Paper - Photosynthesis - 2021 PDF

Document Details

Tags

Related

Summary

Full Transcript

Upgrade to continue