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A limiting factor is a factor that controls a process. Light intensity , temperature and, CO2 concentration and availability of H2O are all factors which can control the rate of photosynthesis. Usually, only one of these factors will be the limiting factor in a plant at a certain time. This is the factor which is the furthest from its optimum level at a particular point in time. If we change the limiting factor the rate of photosynthesis will change but changes to the other factors will have no effect on the rate. If the levels of the limiting factor increase so that this factor is no longer the furthest from its optimum level, the limiting factor will change to the factor which is at that point in time, the furthest from its optimum level. For example, at night the limiting factor is likely to be the light intensity as this will be the furthest from its optimum level. During the day, the limiting factor is likely to switch to the temperature or the carbon dioxide concentration as

The light-independent reactions take place in the stroma of the chloroplast, where the enzyme ribulose bisphosphate carboxylase , usually known as rubisco , is found. 1. Carbon fixation CO2 diffuses into the stroma from the air spaces within the leaf. It enters the active site of rubisco , which combines it with a 5-carbon compound called ribulose bisphosphate , RuBP . The reaction is called  carbon   fixation. The products of this reaction are two 3-carbon molecules, glycerate 3-phosphate, GP . 2. Reduction  Energy from ATP and hydrogen from reduced NADP are then used to convert the GP into triose phosphate, TP . Triose phosphate is the first carbohydrate produced in photosynthesis. 3. RuBP regeneration Most of the triose phosphate is used to produce ribulose bisphosphate ( RuBP ), so that more carbon dioxide can be fixed. The rest is used to make glucose or whatever other organic substances the plant cell requires. These include: polysaccharides such as starch for energy storag

Chromatography is a method of separation that relies on the different solubilities of different solutes in a solvent. A mixture of chlorophyll pigments is dissolved in a solvent, and then a small spot is placed onto chromatography paper . The solvent gradually moves up the paper, carrying the solutes with it. The more soluble the solvent, the further up the paper it is carried. Paper chromatography is a useful technique in the separation and identification of different plant pigments. In this technique, the mixture containing the pigments to be separated is first applied as a spot or a line to the paper about 1.5 cm from the bottom edge of the paper.  The paper is then placed in a container with the tip of the paper touching the solvent. Solvent is absorbed by the paper and moves up the paper by capillary action. As the solvent crosses the area containing plant pigment extract, the pigments dissolve in and move with the solvent.  The solvent carries the dissolved pigments as it moves

Chlorophyll molecules in photosystern I (PSI) and photosystern II (PSII) absorb light energy. The energy excites electrons, raising their energy level so that they leave the chlorophyll. The chlorophyll is said to be photo-activated. PSII contains an enzyme that splits water when activated by light. This reaction is called photolysis ('splitting by light'). The water molecules are split into oxygen and hydrogen atoms. Each hydrogen atom then loses its electron, to become a positively charged hydrogen ion (proton), H+. The electrons are picked up by the chlorophyll in PSII, to replace the electrons they lost. The oxygen atoms join together to form oxygen molecules, which diffuse out of the chloroplast and into the air around the leaf. The light- dependent reactions. Credit: Pears education.  The electrons emitted from PSII are picked up by electron carriers in the membranes of the thylakoids. They are passed along a chain of these carriers, losing energy as they go. The energy

Photosynthetic pigments are pigments presented in chloroplasts or photosynthetic bacteria. They capture light energy necessary for photosynthesis and convert it to chemical energy .  Pigments A pigment is any substance that absorbs light. The color of the pigment comes from the wavelengths of light that are reflected (not absorbed).  If pigments absorb all wavelengths they will appear black. If pigments reflect most of the wavelengths they will appear white. The light absorption pattern of a pigment is called the absorption spectrum. When pigments absorb light, electrons are temporarily boosted to a higher energy level. Energized electrons move further from the nucleus of the atom. When the e- returns to a lower energy level the energy may be: dissipated as heat re-emitted as a longer wavelength of light - fluorescence captured in a chemical bond (carbon gain!) Photosynthetic pigments in chloroplast Choloroplats contain several different pigments, which absorb different wavelengths of

Photosynthesis takes place inside  chloroplasts . These are organelles surrounded by 2 membranes, called an  envelope . Chloroplasts are found in mesophyll cells in leaves: -  Palisade mesophyll  cells contain most chloroplasts. -  Spongy mesophyll   cells and  Guard  cells also contain chloroplasts. Lamellae and light-dependent reactions  The membranes inside a chloroplast are called  lamellae , and it is here that the  light-dependent reactions take place. The membranes contain chlorophyl molecules, arranged in groups called  photosystems . There are two kinds of photosysterns, PSI and PSII, each of which contains slightly different kinds of chlorophyll. There are enclosed spaces between pairs of membranes, forming fluid-filled sacs called  thylakoids.  These are involved in photophosphorylation - the formation of ATP using energy from light. Thylakoids are often arranged in stacks called  grana  (singular: granum), Stroma and light-independent reactions  The 'background material

Photosynthesis is a series of reactions in which energy transferred as light is transformed to chemical energy. Energy from light is trapped by chlorophyll, and this energy is then used to • split apart the strong bonds in water molecules to release hydrogen • produce ATP • reduce a substance called NADP. NADP stands for nicotinamide adenine dinucleotide phosphate, which - like NAD - is a coenzyme. The ATP and reduced NADP are then used to add hydrogen to carbon dioxide , to produce carbohydrate molecules such as glucose . These complex organic molecules contain some of the energy that was originally in the light. The oxygen from the split water molecules is a waste product, and is released into the air. There are three basic steps in photosynthesis: 1.   Light- dependent reactions   - energy capture     chemiosmosis generation of ATP (adenosine triphosphate) from harvested sunlight 2. Light-independent reactions  - fixation of carbon     enzyme catalyzed reactions using the energy

13.1   Photosynthesis as an energy transfer process 13.2  Investigation of limiting factors 13.3  Adaptations for photosynthesis Photosynthesis is the energy transfer process that  is the basis  of much  of life on Earth. It provides the basis  of most food chains  providing energy directly or indirectly for all other  organisms. In eukaryotes, the process occurs within chloroplasts. Candidates use  their knowledge of plant cells and leaf structure from the section on Cell structure while studying photosynthesis. Various environmental factors influence the rate  at which photosynthesis occurs. Candidates will be expected to use  the knowledge gained  in this section to solve problems in familiar and unfamiliar contexts. Learning outcomes Candidates should  be able to: 13.1  Photosynthesis as an energy transfer process Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce comple