Energy SourceThere are two main energy sources forliving organisms: 1. Light energy (phototrophic) 2. Chemical energy (chemotrophic)
ObjectiveOverview :•What is photosynthesis•The importance of photosynthesis•The structure of the leaf
What isphotosynthesis? Photosynthesis is the process by which plants, some bacteria, and some protistans use the energy from sunlight to produce sugar .
photosynthesis Product(S)The primary product of photosynthesis is glucose -the source of carbohydrates likecellulose, starches, etc.The process of photosynthesis also leads to theproduction of fats, proteins, and water solublesugars such as maltose and sucrose. The plantsdepend on this glucose for their growth and energy.
Importance of photosynthesis1. The level of carbon-dioxide in the environment largely depends on the process of photosynthesis. Photosynthesis consumes atmospheric CO2 and yields carbohydrates and atmospheric oxygen, vital to respiration – which allows living organisms to breathe. CO2 helps in keeping our planet warm and live-able. However, too much may cause us to over heat and too little may cause us to freeze.
Importance of photosynthesis Photosynthesis replaces CO2 with O2 which allows living organisms to breathe. 2. Photosynthesis supplies food and energy to all living organisms whether direct or indirect.
The structure of the LeafLeaves are the powerhouse External Featuresof plants. In most plantsleaves are the major site offood production for theplant. Structures withinthe leaf convert the energyin sunlight in to chemicalenergy that the plant canuse as food.
The structure of the Leaf The epidermis secretes a waxy substance called the cuticle. These layers protect the leaf from pests. Internal Features Among the epidermal cells are pairs of guard cells. Each pair of guards cells forms a pore called or stoma. Gases enter and exit the leaf through the stomata. Most food production takes place in the cells of the Palisade Mesophyll. Gas exchange occurs in the air spaces between the cells of the spongy mesophyll. Veins support the leaf and are filled with vessels that support food, water, and minerals toe the plant.
TS OF A TYPICAL DICOTYLEDON
ObjectiveOverview :•What are plastids?•Discuss the common types of plastids•Explain the structure/function of chloroplast•What are pigments and their role in photosynthesis•Explain using a graph common photosynthetic pigments and their absorption and action spectra
PlastidsPlastids are organelles that specialize in photosynthesisfunction in storage.Three (3) types common in different parts of the plants are:1. Chromoplast – lacks chlorophylls but have an abundance of carotenoids. They reflect yellow, orange and red colours of many flowers, autumn leaves, ripening fruits, and carrots and other roots.2. Amyloplast - Lacks pigment. They are responsible for the synthesis and storage of starch granules. It also convert starch back to sugar when the plant needs it. Also, found in fruits and underground storage tissues of some plants such as potato tuber
Plastids (con’t)3. Chloroplast – contained only in eukaryotic cells that are photosynthetic. They reflect or transmit green light. These organelles convert sunlight energy into chemical energy of ATP, which is used to make sugars and other organics compounds. Chloroplast are commonly oval or disk shaped. Their semi- fluid interior the stroma is enclosed by two outer membrane layers. In the stroma is a double membrane organelle called the thylakoid membrane.The thylakoid membrane is a folded system ofinterconnecting, disc-shaped compartments. In manychloroplasts, these compartments stack, one atop the other.
The structure of chloroplast
PigmentsA pigment is a material that changes thecolour of reflected or transmitted light as aresult of wavelength-selective absorption.Most pigments absorb only some wavelengthsand transmit the rest.A few, such as melanins in animals, absorb somany wavelengths they appear dark or black.
Types of photosynthetic PigmentsChlorophyll a – grass green pigment that absorbs blue-violet and red wavelengths- as key player in the lightdependent reactionsChlorophyll b – a bluish pigment occurs in plants, greenalgae and a few photoautotrophic bacterias. Absorbs blue, red and orange wavelengths, in chloroplasts, it is one of several accessory pigments, busily harvesting wavelengths that chlorophyll missesCarotenoids - contained in all photoautotrophs bacteria. Theseare accessory pigments absorb blue-violet and blue-greenwavelengths that chlorophylls miss.
Absorption of Spectra
Excitation of ElectronsMany reactions in Chemistry involve the gain and loss ofreactions. These are called oxidation/reduction reactions. Oxidation is LOSS of electrons Reduction is GAIN of electrons You can use the acronym OILRIG to help remember this. Lithium loses an electron to become a positively charged ion
Excitation of Chlorophyll by lightChlorophyll has a light-catching array ofatoms, which often are joined byalternating single and double bonds.When an atoms electrons absorbenergy, they move to a higher energylevel.Chlorophyll molecule, an input ofenergy destabilizes the electron orbits.Within 10 -15 of a second, excitedelectrons return to a lower energylevel, the electron distributionstabilizes, and energy is emitted in theform of light.All destabilized molecules emits light asit reverts to its more stableconfiguration, this is calledfluorescence.
PhotosystemsPigment molecules organized intophotosystems capture sunlight in the `chloroplast.Photosystems (or Reaction Center) are enzyme which uses light toreduce molecules with clusters of light-absorbing pigments
Photosystem [con’t] Each photosystem is comprised of chlorophyll and carotenoids pigments. In the reaction center of the photosystem, the energy of sunlight is converted to chemical energy. The center is sometimes called a light-harvesting antenna. There are two photosystems within the thylakoid membranes, designated photosystem I and photosystem II. The reaction centers of these photosystems are P700 and P680, respectively. The energy captured in these reaction centers drives chemiosmosis, and the energy of chemiosmosis stimulates ATP production in the chloroplasts.Chemiosmosis is the diffusion of ions across a selectively-permeablemembrane. More specifically, it relates to the generation of ATP by themovement of hydrogen ions across a membrane during cellular respiration.
PhotophosphorylationPhotophosphorylation - the process inphotosynthesis that converts light energy intostored energy – ATP, in plants and bacteria.There are two types: cyclic phosphorylation non-cyclic phosphorylation.
Non-Cyclic PhotophosphorylationNon-cyclic photophosphorylation, is a two-stageprocess involving two different chlorophyll photosystems.First, a photon is absorbed by the chlorophyll core ofphotosystem II, exciting four electrons which aretransferred to the primary acceptor protein. The deficitof electrons is made up for by taking electrons from amolecule of water, splitting it into O2 and 4H+.The electrons transfer from the primary acceptor toplastoquinone, then to plastocyanin, producingproton-motive force as with cyclic electron flow anddriving ATP synthase.
Non-Cyclic Photophosphorylation (con’t) The photosystem II complex replaced its lost electrons from an external source, however, these electrons are not returned to photosystem II as they would in the cyclic pathway. Instead, the still- excited electrons are transferred to a photosystem I complex, which boosts their energy level to a higher level using a second solar photon capturing array. The highly excited electrons are transferred to the primary acceptor protein, but this time are passed on to ferredoxin, and then to an enzyme called NADP+ reductase which uses the electrons to drive the reaction NADP+ + H+ + 2e- → NADPH This consumes the H+ ions produced by the splitting of water, leading to a net production of O2, ATP, and NADPH with the consumption of solar photons and water.
Photosystems in action
Cyclic Photophosphorylation In cyclic phosphorylation, an electron originates from a pigment complex called photosystem I, passes from the primary acceptor to ferrodoxin, then to a complex of two cytochromes , and then to plastocyanin before returning to chlorophyll. This transport chain produces a proton-motive force, pumping H+ ions across the membrane; this produces a concentration gradient which can be used to power ATP synthase.
Photosystems in action
Light dependent stage of photosynthesis
Comparing the two PhotosystemSimilarities : Both photosystems consist of a complex of molecules embedded in thylakoid membranes of the chloroplast. Photosystem I and photosystem II are similar in that they both contain chlorophyll molecules, which can convert light energy into chemical energy. In both photosystems, a photon causes an electron to reach a high energy level. In both photosystems, the energized electron must be passed to a chlorophyll molecule in the reaction center before it can leave the photosystem. Both contain carotenoid molecules.
Contrasting the two PhotosystemDifferences The chlorophyll molecules in the reaction center of photosystem II are P680 (sensitive to wavelengths up to about 680 nm), whereas those in photosystem I are P700, which can therefore respond to slighter longer wavelengths. Photosystem II, unlike photosystem I, contains plastoquinone, which passes the energetic electron to cytochromes b6 and f, but photosystem I passes the electron to ferredoxin. In non-cyclic photophosphorylation, photosystem II is associated with the photolysis of water and subsequent synthesis of ATP; photosystem I is associated with the conversion of NADP+ to NADPH. In cyclic photophosphorylation, only photosystem I produces an energized electron on receipt of a photon. Instead of producing NADPH, this electron travels to plastoquinone, and then to cytochromes b6 and f, as in the non-cyclic process.
Adenosine Triphosphate (ATP)ATPs consist ofadenine, sugar(ribose), and threephosphates.An ATP energy isused when one ofthe phosphatebonds are broken,becoming ADPs.
Importance ATP ATP is needed for the heart to beat, it is needed for muscular effort, in fact everything we do requires ATP as energy. The body cannot function without it. That is why ATP is known as the “energy currency” of each cell in your body and your body must be supplied with energy continuously if it is to function. The harder the body works, for example during exercise, or during recovery from illness or injury, the greater then requirement is for additional energy, and potentially additional ATP. At rest, the body is able to produce all the ATP it needs to maintain a healthy existence.
Nicotinamide adenine dinucleotide phosphate (NADP)NADP (Nicotinamide adenine dinucleotide phosphate):a co enzyme which acts as a hydrogen carrier.The role of NADP is to carry the hydrogen atom from the light dependentstage, which comes from the water molecule ( water molecule splits toform 2H+, 2electrons & oxygen, which is a waste gas).NADP carries this hydrogen atom and gets reduced. The reducing powerof reduced NADPH reduces the 3 Carbon acid that has the group ( -COOH ) to a 3 Carbon sugar that has an aldehyde group ( -CHO ) knownas Glyceraldehyde phosphate (GP), which is a triose phosphate (TP). Thisis the first carbohydrate in photosynthesis. The reason for the conversionof GP to TP is because TP contains more chemical energy.
“when a chemical process is affected by more than onefactor, its rate is limited by that factor which is nearest its minimum value: it is the factor which directly affects a process if its quantity is changed.” first establish by Frederick Blackman, 1905
The Variables of Photosynthesis There are many factors limiting photosynthesis. However, the principal factors are: light intensity carbon dioxide concentration temperature.
Light Intensity In low light intensities the rate of photosynthesis increases linearly with increasing light intensity. Except for shaded plants, light is not normally a major limiting factor. Very high light intensities may bleach chlorophyll and slow down photosynthesis, but plants normally exposed to such conditions are usually protected by devices such as thick cuticles and hairy leaves.
Light Intensity A. Represents a linear increase of a limiting factor. Meaning an increase in the input results in a direct proportional increase in the output. B. Levelling off demonstrates that this factor is becoming saturated and further increase yields diminishing returns on output. C. Factor is no longer the limiting factor. Increases have no effect on output. D. Point at which factor is saturated. Factor has reached maximum level of benefit for process. E. Maximum or ideal output for the input when it is no longer a limiting factor.
Carbon Dioxide Concentration Carbon dioxide is needed in the light-independant stages where it is needed to make sugar. Under normal conditions, carbon dioxide is the major limiting factor in photosynthesis. Its concentration in the atmosphere varies between 0.03% and 0.04%, but increases in the photosynthetic rate can be achieved by increasing this percentage.
Temperature The light-independent reactions and, to a certain extent, the light-dependent reactions are enzyme controlled and therefore temperature sensitive. For temperate plants the optimum temperature is usually about 25 °C. The rate of reaction doubles for every 10 °C rise up to about 35 °C, although other factors mean that the plant grows better at 25 °C.
Other Factors LimitingPhotosynthesis Chlorophyll concentration is not normally a limiting factor, but reduction in chlorophyll levels can be induced by several factors: disease (such as mildews, rusts, and virus diseases) mineral deficiency normal ageing processes (senescence). If the leave becomes yellow is is said to be chlorotic, the yellowing process being known as chlorosis.
Specific Inhibitors An obvious way of killing a plant is to inhibit photosynthesis, and various herbicides have been introduced to do this. A notable example is DCMU (dichlorophenyl dimethyl urea) which short circuits non-cyclic electron flow in chloroplasts and thus inhibits the light-independant reactions. DCMU has been useful in research on the light-dependent reactions.
Water Water is a raw material in photosynthesis, but so many cell processes are affected by a lack of water that it is impossible to measure the direct effect of water on photosynthesis. Nevertheless, by studying the yields (amounts of organic matter synthesized) of water deficient plants, it can be shown that periods of temporary wilting can lead to severe yield losses.
Pollution Low levels of certain gases of industrial origin, notably ozone and sulphur dioxide, are very damaging to the leaves of some plants, although the exact reasons are still being investigated. It is estimated, for example, that cereal crop losses as high as 15% may occur in badly polluted areas, particularly during dry summers.