As with any respirometer investigation if the respiring material used are invertebrates, it is very important to handle these organisms carefully. Students conduct Thin Layer Chromatography TLC individually or in pairs to separate and identify the photosynthetic pigments from plant material within half an hour. This simple method has been designed to produce good separation of photosynthetic pigments using solvents that are suitable for use in a school biology laboratory.
By using grass from a school lawn or playing field, students can see the variety of different molecules that can be separated from a plant that they are all very familiar with. These resources and this practical allow students to develop their understanding of photosynthetic pigments and how chromatography separates molecules.
By taking simple distance measurements from the chromatogram for calculating Rf values, this practical provides a good opportunity to introduce the concept of percentage error. It provides students with the opportunity to develop and demonstrate their skills of taking quantitative measurements as well as their ability to consider variables that need to be controlled. Sign in Register Search. Energy for biological processes - ATP, photosynthesis and respiration All organisms need energy.
Students will also enjoy making their own algal balls. This practical provides the opportunity for skills development in the use of appropriate instrumentation a colorimeter to record quantitative measurements the safe and ethical use of organisms to measure plant responses to changing conditions the use of computer modelling, or a data logger to collect data, or the use of software to process data immobilisation of organic material in this case algae but the technique is often used for enzymes as well the use of a smart phone as a lux meter optional graphical skills including plotting graphs with lines of best fit and reading off intercept points.
It would also be possible to link sensors and data loggers to this investigation. Advanced investigation of the light dependent reaction in photosynthesis This investigation is a good way to test A level biologists understanding of the link between the light-dependent and light-independent reactions in photosynthesis.
This is a straightforward observation activity however students could be asked to alter the protocol to consider one or more of the following: Does the rate of respiration vary during the ripening process?
Does the temperature of storage affect the rate of respiration? Does the skin affect the exchange of gases between a fruit or vegetable and the atmosphere? Does an infected fruit or vegetable have a higher respiratory rate than a healthy one? This is an especially vital source of ATP for plants because ATP is also needed for them to synthesize glucose in the first place.
A transparent-green solution of chlorophyll is made by grinding up spinach or grass leaves in acetone in a mortar and pestle , and then filtering it through cheesecloth and course filter paper. When a bright beam of light is directed at this chlorophyll solution, a deep red glow is emitted from the test tube. This phenomenon is known as fluorescence, and is essentially the same principle as a fluorescent light bulb.
In a fluorescent light bulb, the electrons of neon gas become excited and then release their energy of activation as a white glow inside the glass tube.
In an intact chloroplast with thylakoid membranes, ATP is generated by an electron flow along the cytochrome transport system. Since the electrons are being transported to other "carrier" molecules, their energy is used to generate ATP and no reddish glow is emitted.
Leaves generally appear green because wavelengths of light from the red and blue regions of the visible spectrum are necessary to excite the chloroplast electrons, and unused green light is reflected. Thus, we perceive trees, shrubs and grasses as green. During the fall months when chlorophyll production ceases in deciduous trees and shrubs, the leaves turn golden yellow or red due to the presence of other pigments, such as yellow and orange carotenoids and bright red anthocyanins.
A nother important ingredient for photosynthesis is also produced during the light reactions. During these light-dependent reactions of photosynthesis, a chemical called NADP nicotinamide adenine dinucleotide phosphate picks up two hydrogen atoms from water molecules forming NADPH 2 , a powerful reducing agent that is used to convert carbon dioxide into glucose during the dark reactions of photosynthesis also called the Calvin Cycle.
When the two atoms of hydrogen join with NADP, oxygen is liberated, and this is the source of oxygen gas in our atmosphere. ATP and NADPH 2 from the light reactions are used in the dark reactions of photosynthesis that take place in the stroma region of the chloroplast. N ADP the vital coenzyme required for photosynthesis is derived from nicotinic acid, a B-vitamin also known as niacin.
Niacin prevents pellagra, a disease characterized by severe damage to the tongue, skin and digestive tract. Nicotine is a mild stimulant of the central nervous system. In its pure form, nicotine is highly poisonous and is used as an insecticide. Read About Plant Alkaloids Dark Reactions Of Photosynthesis I n the dark reactions of photosynthesis also known as the Calvin Cycle , carbon dioxide CO 2 is converted into glucose through a series of complicated reactions involving ATP adenosine triphosphate and NADPH 2 nicotinamide adenine dinucleotide phosphate , two essential compounds synthesized during the light reactions of daylight.
Ordinary C-3 plants form a 3-carbon compound called phosphoglyceric acid PGA during the initial steps of the dark reactions. Two PGAL molecules combine to form a 6-carbon glucose molecule.
CAM Crassulacean Acid Metabolism photosynthesis is found in cacti and succulents, including the crassula family Crassulaceae. During the hot daylight hours their stomata are tightly closed; however they still carry on vital photosynthesis as carbon dioxide gas is converted into simple sugars. During the cooler hours of darkness their stomata are open and CO 2 enters the leaf cells where it combines with PEP phosphoenolpyruvate to form 4-carbon organic acids malic and isocitric acids.
The 4-carbon acids are stored in the vacuoles of photosynthetic cells in the leaf. During the daylight hours the 4-carbon acids break down releasing CO 2 for the dark reactions Calvin cycle of photosynthesis inside the stroma of chloroplasts. The CO 2 is converted into glucose through a series of complicated reactions involving ATP adenosine triphosphate and NADPH 2 nicotinamide adenine dinucleotide phosphate , the latter two compounds which were synthesized during the light reactions of daylight in the grana of chloroplasts.
The adaptive advantage of CAM photosynthesis is that plants in arid regions can keep their stomata closed during the daytime, thereby reducing water loss from the leaves through transpiration; however, they can still carry on photosynthesis with a reserve supply of CO 2 that was trapped during the hours of darkness when the stomata were open.
The tropical strangler Clusia rosea also has CAM photosynthesis. The importance of energy balance in improving photosynthetic productivity. How acidic is the lumen? Balancing the central roles of the thylakoid proton gradient. Dynamic flexibility in the light reactions of photosynthesis governed by both electron and proton transfer reactions. Krause, G. The intact chloroplast. Barber, J. Krieger, A.
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FAQs What is photosynthesis? Where do the protons used in the light reactions come from? How do you distinguish between the Calvin cycle and the Krebs cycle? Do photosynthesis and cellular respiration occur at the same time in a plant?
Common Misconceptions A common student misconception is that plants photosynthesize only during daylight and conduct cellular respiration only at night. Some teaching literature even states this. Though it is true the light reactions can only occur when the sun is out, cellular respiration occurs continuously in plants, not just at night.
This is not true. It is preferable to use the term Calvin cycle or light-independent reactions instead of dark reactions.
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