Photosynthesis: Chloroplasts & Light Reactions

• Photosynthesis uses energy in sunlight to produce the chemical energy needed for life.
• Leaf cells are packed with chloroplasts, organelles containing chlorophyll and other pigments.
• Chlorophyll traps light energy to build glucose molecules.
• Photosynthesis transforms light energy into chemical energy during the production of carbon compounds.
• Carbon dioxide is converted into glucose in photosynthesis using hydrogen obtained by splitting water.
• Oxygen is a by-product of photosynthesis in plants, algae, and cyanobacteria.
• Photosynthetic pigments can be separated and identified by chromatography.
• Specific wavelengths of light are absorbed by photosynthetic pigments.

Transformation of Light Energy

• During photosynthesis, light energy is transformed into chemical energy when carbon compounds are produced.
• Carbon dioxide and water are used to produce carbohydrates, releasing oxygen as a waste gas through a metabolic pathway.
• Light energy is transferred to chemical energy and stored in glucose molecules.
• Water is split, and the hydrogen is used to produce glucose, while oxygen is excreted as waste.
• Carbon is 'fixed' from carbon dioxide, and used in order to produce glucose.

CO2 Conversion to Glucose

• Energy consumed during photosynthesis is used in photolysis (splitting of water molecules).
• Photosynthesis generates a chemical energy store as carbohydrates.
• Light-dependent reactions use light energy to produce ATP and split water (photolysis), releasing H⁺ ions.
• Light-independent reactions use ATP and H⁺ ions to 'fix' carbon dioxide, creating glucose.
• Most of the oxygen produced is excreted as waste.

Oxygen as a By-product

• Most of the oxygen is excreted as waste.
• Photolysis increases oxygen concentration inside chloroplasts.
• Oxygen diffuses out of chloroplasts, then out of leaf cells into air spaces, and finally through stomata into the air.

Polysaccharides

• Energy is essential to produce carbohydrates and other carbon compounds from carbon dioxide.
• Starch and cellulose are polysaccharide molecules found in plants.
• Starch serves as a chemical energy store.
• Cellulose is used as a building material.
• Monosaccharides are combined to make carbohydrates through process of dehydration or condensation.

Wavelengths of Light

• Radiation has both a frequency and a wavelength.
• High-frequency radiation contains more energy per unit of time.
• UV, X-rays, and gamma rays can be harmful to living organisms causing cell and DNA damage.
• Only a small part of the electromagnetic spectrum is visible.
• Pigments (like chlorophyll) in photosynthetic organisms absorb beneficial wavelengths of light.
• Photosynthesis has action and absorption spectra that correspond with the electromagnetic spectrum.
• Chlorophyll is the main photosynthetic pigment.
• Chlorophyll absorbs red and blue light most effectively, reflecting green light.
• A photon is a particle or unit of light having discrete quantities of energy.
• Energy of a photon is related to its wavelength, where longer wavelengths have less energy.
• Photons are absorbed by pigment molecules when their energy causes an electron in an atom in the respective pigment molecule to jump to a higher energy level (excitation).
• Specific amounts of energy for this process is supplied only by certain wavelengths of light.

Photosynthesis Spectra

• Action spectrum shows rate of photosynthesis across wavelengths as a percentage of the maximum possible rate.
• Absorption spectrum shows absorbance of light by photosynthetic pigments.
• The action spectrum of photosynthesis and the absorption spectrum of chlorophyll overlap.
• Chlorophyll is the most important pigment in photosynthesis, also the most abundant.
• Artificial light sources can be used though the light is not as strong as the sun.
• More energy is contained in the the blue end of light spectrum than what is in the red.
• UV radition has even higher energy but is unusable and causes damage to the cell and mutations.
• Plants do not all have the same action/absorption spectrum.
• Accessory pigments allow some plants to utilize green wavelengths of light, which offers competitive advantage.
• In autumn, the chlorophyll breaks down, so accessory pigments become more visible.

Photosynthetic Pigments

• Chlorophyll a: yellow-green pigment
• Chlorophyll b: blue-green pigment
• Carotene: orange pigment
• Xanthophyll: yellow pigment

Chromatography

• Thin Layer Chromatography (TLC) can separate photosynthetic pigments to determine what is in a leaf.
• Two SAPS protocols can provide guidance on how to perform TLC.
• Bioknowledgy has a simplified chromatography protocol as well.
• A virtual lab and self-test quiz are also available to use.

Experimental Techniques

• Concentration of CO2, light intensity, and temperature are variables that can affect the rate of photosynthesis.
• For the rate of photosynthesis, at a high light intensity, any increase would have no effect.
• Increased light increases rate of photosynthesis is until another factor is limiting, which happens at low levels.
• Light intensity refers to the amount of light, of a given wavelength available to a plant.
• Alternative factors including temperature, light, and the amount of enzymes can limit photosynthesis

Environmental factors

• In high light intensity and warm temperatures, carbon dioxide concentration limits affect the rate of photosynthesis most.
• Greenhouse experiments have demonstrated that at constant, optimal temperature and light, if carbon dioxide concentration is varied it proves that temperature and light levels are being limited.
• A carbon dioxide concentration above current atmospheric levels of about 400 ppm has been found to increase rates of photosynthesis and plant growth.
• Boilers can burn gas to produce both head and light for greenhouse. More sustainable options include bacteria and fungi from compost-making where the plant wastes break down animal manure.
• FACE(free air carbon dioxide enrichment experiments) can be done while the other factors remain unchanged.
• FACE uses a method and infrastructure to experimentally enrich the atmosphere surrounding the area without using chambers or walls.
• Elevated carbon dioxide levels tested on plots greater than 20m in diameter on plant responses with minimal microclimate modificiations to plant responses.
• The first FACE tests saw plant growth as a result on agricultural crops and tree plantations. Followed by a second sereies focused on Australia and an oak forest England.

Chloroplast functions

• Chloroplast contain chloroplast envelope for inner and outer membranes
• The stroma consists of 70S ribosomes and naked DNA for light independent reactions.
• The thylakoid membranes consist of thylakoid stack (granum) for light dependent reactions.
• The starch grain and oil droplet create a chemical energy store (products of photosynthesis).
• The structure of chloroplast is well adapted to its function.
• Light in and a photon causes a number of reactions, including photolysis of water
• There is carbon fixation and the Calvin cycle in photosynthesis.
• Light indepenedent and dependent reations generate NADP, ATP, carbon dioxide, and glucose.

Light-dependent reactions

• Occur on thylakoids of water photolysis and photophosphorylation.
• Photosytem I has pigment molecules to absorbs longer and shorter wavelengths of light.
• The reaction center is P700 and is found on the outer surface of thylakoids.
• Molecular oxygen is not released
• Photosystem II has pigment molecules to absorbs shorter wavelengths of light.
• The reaction center is P680 on the inner surface of thylakoids.
• molecular oxygen is released.

Photosystem Organization

• Light is scattered.
• Photosystems combine over 100 pigment molecules, increasing the number of photons absorbed per second by two orders of magnitude.
• Range of wavelengths vary between pigments.
• Chlorophyll doesn't green light.
• A photosystem combines pigment types so more energy in the light can be used.
• Energy is transferred only when molecules are closely oriented or else the light is lost to florescence.
• They also funnel absorbed energy to the reaction center.
• Reactions and processes that absorb energy from their surroundings are endothermic.

Light Dependent Reactions

• Light energy is used to split water to then release H+ for ATP synthetase to use.
• NADP+ is reduces to NADPH and H+.
• In light independent reactions the oxygen is the waste product.
• The light dependent reactions happen of the thylakoid membrane.
• The flow of electrons through ATP syththase will couple with ADP and PH to creat ATP.
• The hydrogen ions accumulate in the thylakoid with protons moving through the gradient through chemiosmosis to create ATP.
• Electons will be in photosystem 1 being activated by light.

Chlorophyll

• Photosystem II in light raises the energy level of the electrons.
• It does this throught the use of photoactivation.
• Photoactivation releases carriers along the membrane
• The energy used will then be placed intto the thylakoid membrane.
• Electrons are replaced throught phototlyssi of water.

Comparing and Contrasting Chloroplasts and Mitochondria

• Chloroplasts both compartmentalize the membranes.
• They stack, in their case, thylakoid membranes.
• The inter-membrane spaces are low for rapid production of high H+
• The space is also fluid
• Similarities include how the mitochondria carries out the electron transport chain
• They also generate ATP, along with a matrix to aid in their cyclic reactions.

Calvin's Experiment

• Calvin used algae which was placed in lollipop glass vessels.
• It also contained CO2, light, and hydrogen carbonate with normal carbon.
• At the start of the test carbon is replaced wiht radoiactive versions and tested at different interevals.
• The use of chormatography separated compounds for analyzation. Only 5 seconds was needed to label the glycerate.
• Radioactive materials followed by improved tech made these findings possible.
• The Calvin Cycle turns glycerate into glucose.

Explore the critical role of chlorophyll in photosynthesis within chloroplasts, including water molecule activity during light-dependent reactions. Learn about energy conversion, thylakoid arrangement, and the importance of the stroma for plant metabolic pathways.