Notice how little the leaves overlap each other. This enables them to trap the maximum amount of sunlight. the importance of this will be explained later in the presentation
Most fungi and bacteria get their food by breaking down organic matter, such as plant and animal remains (detritus). They then absorb the soluble breakdown products. These organisms are called detritivores . The name ‘Photosynthesis’ is derived from ‘photo’ (light) and ‘synthesis’ (building up). Plants synthesize their food with the aid of sunlight. (Slides 9 and 10).
When a plant is photosynthesising, it is taking in carbon dioxide and giving out oxygen. Plants which live in ponds, streams etc. are immersed in the water they need for photosynthesis
This reaction is summarised by the equation 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2
These are called palisade cells and they are present in the upper layers of a leaf where most sunlight is absorbed. The chloroplasts are present in the cytoplasm lining the cell
The water travels from the roots, through the stem and into the leaf in a system of vessels. The carbon dioxide diffuses into the leaf through tiny pores called stomata.
The palisade layer traps most of the sunlight. The vessel carries water from the stem to the leaf. Carbon dioxide enters through the stoma and diffuses through the air spaces between the cells.
Without sunlight, photosynthesis could not take place. Without photosynthesis, plants could not survive. Without plants, most animals would die out because, ultimately, animals depend on plants for their food. e.g. sunlight >>>> plants >>>> herbivores >>>> carnivores
Before it is transported, glucose is converted to sucrose. Two glucose molecules combine to make a molecule of sucrose. 2C 6 H 12 O 6 = C 12 H 22 O 11 + H 2 0 glucose sucrose It is the sucrose which is transported throughout the plant
Carbohydrates may be (a) oxidised to provide energy for chemical reactions. (b) turned into starch and stored in storage organs such as potatoes and parsnips. (c) turned into cellulose which builds the cell walls. (d) Combined with nitrogen (from nitrates) to make amino acids , which are combined to make proteins
Proteins are needed for making the cell structures, e.g. cytoplasm, nucleus, chloroplasts. The plant can grow only by making new cells and cell structures Strictly speaking, it is not nitrates salts that are taken up but nitrate ions. When a salt such as potassium nitrate, is dissolved in water it splits into positively charged potassium ions and negatively charged nitrate ions. KNO 3 becomes K + and NO 3 - The plant may take up either or both of these ions.
Nitrates are needed for making proteins. Phosphates are needed for DNA and for chemical reactions involving energy release. Sulphates are needed for some proteins. Iron is needed for certain enzyme reactions. Magnesium is needed for making chlorophyll.
How Plants Get Their Food
How do plants get their food ?The soil was watered but nothing else was added. After 5 years, thetree had gained 74kg in weight but the soil had lost only 52g.van Helmont concluded that the tree had made 74kg of new growthfrom water alone290.72kg soilIn the 17th Century, A Belgian physician, van Helmont, set up anexperiment in which he planted a willow sapling in a weighedamount of soil.90.20kgsoil
Van Helmont’s experiment was effective inshowing that the plant’s food did not comefrom the soil.But he had overlooked the fact that air wasavailable to the plant as well as water.Could it be that the plant made 74kg ofCould it be that the plant made 74kg ofmaterial from justmaterial from just airair andand waterwater??3
Review QuestionReview Question• Which mode of nutrition do the greenplants carry out?A. Autotrophic nutritionB. Heterotrophic nutrition
Sorry! You’re wrong!Sorry! You’re wrong!• Heterotrophic nutrition is the mode ofnutrition in which organisms have to dependon other organisms or dead organic mattersas their food sources. Green plants, however,can make organic food by themselves usingsimple inorganic substances.
Very Good!Very Good!• Autotrophic nutrition is the mode ofnutrition in which organisms can makeorganic food by themselves using simpleinorganic substances.• The process by which the green plantsobtain nutrients is called :Photosynthesis
FeedingPlants make their own foodThey combine carbon dioxide from the air with waterand dissolved salts from the soilPlants do NOTNOT get their food from the soilThe first stage by which plants make food iscalled PHOTOSYNTHESIS4Animals get their food by eating*plants,*plant products*other animalsCarnivores eat animalsHerbivores eat plants
Photosynthesis6from the air (DIFFUSION)(OSMOSIS)a by-product(DIFFUSION)glucose (C6H12O6)
CHLOROPLASTSOnly plants haveIt stores CHLOROPHYLLIt absorbs photons from thesun and converts them in ATP(Green plastids)Chlorophyll is a greencoloured chemical, present inthe leaves of green plants
Leaf cells with chloroplastscell wallnucleuschloroplastcytoplasm vacuole11
All the reactions to combine CO2 and H2O takeplace in the chloroplastsunlightwatercarbon dioxidein the chloroplast,carbon dioxide andwater combine tomake sugar12palisade cellof leaf
Cell structure of a leafThe palisade cells are in theuppermost layers of the leafepidermispalisade cell ( photosynthesis)vessel (carries water)stoma (admits air)13
CO2StomaAir SpaceSpongy MesophyllCellChloroplastRoute of Carbon Dioxide forPhotosynthesis
CO2ChloroplastPalisade MesophyllCellStomaAir Space
Light energy is trapped by chlorophyll inchloroplast Light energy absorbed by chlorophyll splitswater molecules into hydrogen and oxygen Oxygen is released as a gas through stomato outside Hydrogen is fed into dark reactionLight reactionLight reaction
Oxygen is produce as the by-product of photosynthesis.
Dark reactionDark reaction No light is required; can take place eitherin light or darkness Hydrogen produced in light reactioncombines with CO2 to form carbohydrates Water is formed as a by-product
Dark ReactionWaterOxygen Glucose(C6H12O6)Light ReactionHSummary of PhotosynthesisSummary of Photosynthesis6 CO2 + 6 H20 C6H12O6 + 6 O2Light Carbon Dioxideabsorbed and used by a substance calledchlorophyll
This is what you missed on…9PLANT NUTRITIONPLANT NUTRITION
The leaf is thindecrease diffusiondistance for gases &lightThe leaf is broad &flattenedincrease surface area toabsorb more sunlightAdaptation of leaf toAdaptation of leaf tophotosynthesisphotosynthesis
Cuticle exists inupper epidermis andis transparentAllows most light topass intophotosyntheticmesophyll tissues
Palisade mesophyllcells are closelypacked and containmany chloroplastsTo carry outphotosynthesis moreefficiently
Spongy mesophyll cellsare loosely packed withnumerous large airspacesTo allow rapiddiffusion of gasesthroughout the leaf
Numerous stomataon lower epidermisTo allow rapidgaseous exchangewith the atmosphere
Extensive vein system• Allow sufficientwater to reach thecells in the leaf• To carry food awayto other parts of theplant
What happens to the glucose?The glucose made by the chloroplast is either(a) used to provide energy for the chemicalprocesses in the cell (by respiration)(b) turned into sucrosesucrose and transportedtransported toother parts of the plantor(c) turned into starchstarch and storedstored in the cellas starch grainsIn darkness the starch is changed back intoglucose and transported out of the cell15
Other FoodGlucose and starch are carbohydratescarbohydratesCarbohydrates can be oxidised duringrespiration to produce energyPlants need more than carbohydratesThey need proteinsproteins for making newcytoplasm and cells for growthTo make proteins plants combine glucosewith compounds of nitrogennitrogen (nitrates)17
GLUCOSEstorage e.g. starch in potatostarchfruitsother sugarse.g. seed germinationenergycytoplasmproteincell wallscellulose18
NitratesNitrate ions are present in the soil, dissolved inwaterThe plants take up nitrate ions in the soil waterThe nitrate ions are conducted through theroots to the stem and then to the leavesIn the leaves, the nitrate ions and glucose arecombined to make PROTEINSThis process is called assimilation19
Mineral ionsNitrates are not the only ions that plants needto take in from the soilThey need phosphate DNAsulphate Sulfur (proteins)magnesiummagnesium Chlorophylliron, potassium ionsThis is the reason why farmers and gardenersadd fertiliser to the soil20
• “when a chemical process is affected by more thanone factor, its rate is limited by that factor which isnearest its minimum value: it is the factor whichdirectly affects a process if its quantity is changed(limiting the action of the others)”Limiting Factors ofPhotosynthesis
Limiting FactorsTemperatureCarbon dioxide concentrationAmount of sunlightAmount of water
Limiting Factors• In low light intensities the rate of photosynthesisincreases linearly with increasing light intensity.• Except for shaded plants, light is not normally amajor limiting factor.• Very high light intensities may bleach chlorophylland slow down photosynthesis, but plantsnormally exposed to such conditions are usuallyprotected by devices such as thick cuticles andhairy leaves.Light Intensity
Carbon Dioxide ConcentrationCarbon dioxide is needed in the light-independant stages where it is needed to makesugar. Under normal conditions, carbondioxide is the major limiting factor inphotosynthesis.Its concentration in the atmosphere variesbetween 0.03% and 0.04%, but increases in thephotosynthetic rate can be achieved byincreasing this percentage.
TemperatureThe light-independent reactions and, to acertain extent, the light-dependent reactionsare enzyme controlled and thereforetemperature sensitive.For temperate plants the optimum temperatureis usually about 25 °C. The rate of reactiondoubles for every 10 °C rise up to about 35 °C,although other factors mean that the plantgrows better at 25 °C.
WaterWater is a raw material in photosynthesis, butso many cell processes are affected by alack of water that it is impossible tomeasure the direct effect of water onphotosynthesis. Nevertheless, by studyingthe yields (amounts of organic mattersynthesized) of water deficient plants, it canbe shown that periods of temporary wiltingcan lead to severe yield losses.
Chlorophyll concentration is not normally alimiting factor, but reduction inchlorophyll levels can be induced byseveral factors:– disease (such as mildews, rusts, and virusdiseases)– mineral deficiency– normal ageing processes (senescence).Other Factors LimitingPhotosynthesis
*Plants combine carbon dioxide from the air, and waterfrom the soil to make glucose.* The energy needed for this process comes from sunlight* The sunlight is absorbed by chlorophyll contained in thechloroplasts of the leaf.* The glucose can be used for energy or to make othersubstances.* To make other substances, the glucose must be combinedwith other chemical elements such as nitrogen andpotassium.These chemical elements are present as ions in the soil andare taken up in solution by the roots.23TO SUM UP