Topic 13 Photosynthesis. Flashcards
Describe the process of photosynthesis, including the role of chloroplasts, the conversion of light energy to chemical energy, and the significance of oxygen as a byproduct.
How do chloroplasts facilitate this process through their structure and components?
Photosynthesis is a biochemical process where light energy is transformed into chemical energy in the form of glucose, occurring primarily in chloroplasts.
6H₂O + 6CO₂ → C₆H₁₂O₆ + 6O₂.
Chloroplasts contain thylakoid membranes organized into stacks called grana, which house photosynthetic pigments like chlorophyll.
These pigments absorb light, facilitating the conversion of light energy into chemical energy.
The stroma, the fluid surrounding the grana, contains enzymes necessary for the light-independent reactions.
Oxygen is produced as a waste product and released into the atmosphere.
Define the role of photosynthetic pigments in the process of photosynthesis.
How do different pigments, such as chlorophyll and carotenoids, contribute to light absorption and protection of the photosynthetic apparatus?
Photosynthetic pigments are crucial for capturing light energy necessary for photosynthesis.
Chlorophyll, the primary pigment, absorbs red and blue-violet light while reflecting green, giving it its characteristic color. There are two main types: chlorophyll a with the highest abundance, which absorbs light at specific wavelengths (430nm and 663nm), and chlorophyll b, which absorbs at slightly different wavelengths (453nm and 642nm).
Carotenoids, including beta-carotene which is orange in colour and xanthophyll which is yellow in colour, not only assist in light absorption but also protect chlorophyll from damage.
Explain the differences between an absorption spectrum and an action spectrum in photosynthesis, highlighting how each is used to study pigment light absorption and its impact on photosynthetic efficiency.
An absorption spectrum shows which wavelengths of light a pigment absorbs and how much light is absorbed at each wavelength. This helps identify the pigments in a sample.
In contrast, an action spectrum shows how the rate of photosynthesis varies with different wavelengths, revealing which are most effective.
Explain the process of separating photosynthetic pigments using chromatography, detailing the steps involved from pigment extraction to calculating Rf values, and how these values help identify the pigments present in a leaf.
To separate photosynthetic pigments, one begins by extracting pigments from a leaf and applying them to a pencil line drawn on filter paper.
The paper is then placed in a solvent, which moves up the paper, carrying the pigments with it. Once the solvent reaches near the top, a line is drawn to mark its progress.
The Rf value for each pigment is calculated using the formula:
Rf = distance moved by solute / distance moved by solvent.
The further a pigment travels, the higher its Rf value, allowing for identification of the pigments based on their movement.
Define the term ‘Rf value’ in the context of chromatography for pigment separation, and explain how it is calculated and interpreted to determine the presence of specific pigments in a leaf sample.
The Rf value, or retention factor, is a crucial measurement in chromatography that indicates how far a pigment has traveled relative to the solvent front.
It is calculated using the formula: Rf = distance moved by solute / distance moved by solvent.
A higher Rf value suggests that a pigment is less polar and has moved further up the chromatography paper.
By comparing the Rf values of pigments from a leaf sample to known standards, one can identify the specific pigments present, aiding in the understanding of the leaf’s photosynthetic capabilities.
How do the light-dependent reactions of photosynthesis occur, detailing the role of chlorophyll, electron transport chains, and the process of photolysis of water in generating ATP and oxygen?
The light-dependent reactions of photosynthesis begin when light energy excites electrons in chlorophyll molecules located in the thylakoid membrane.
Excited electrons are transferred to an electron acceptor and travel through an electron transport chain, undergoing redox reactions that produce ATP via chemiosmosis.
Water is split in a process called photolysis, generating protons, electrons, and oxygen.
2H₂O → 4H+ + 4e- + O₂.
The electrons replace those lost from photosystem II, while protons create a chemical gradient that drives ATP synthesis, ultimately producing energy for the plant.
Describe the process of non-cyclic photophosphorylation in photosynthesis, including the roles of photosystems II and I, the generation of reduced NADP, and the production of ATP.
How does this process differ from cyclic photophosphorylation?
Non-cyclic photophosphorylation is a key process in the light-dependent stage of photosynthesis where electrons flow from photosystem II (PSII) to photosystem I (PSI).
During this process, water is photolyzed, releasing electrons that replace those lost by PSII. As electrons move through the electron transport chain, they facilitate the generation of ATP and reduce NADP.
In contrast, cyclic photophosphorylation involves only PSI, where electrons are recycled back to PSI instead of forming reduced NADP, allowing for ATP production without the involvement of PSII.
How does the light-independent reaction, also known as the Calvin cycle, utilize ATP and reduced NADP produced in the light-dependent stage of photosynthesis?
Describe the steps involved in carbon fixation and the subsequent transformations leading to glucose production.
The light-independent reaction, or Calvin cycle, occurs in the stroma and utilizes ATP and reduced NADP generated during the light-dependent reactions to synthesize glucose.
The process begins with carbon fixation, where ribulose bisphosphate (RuBP) combines with carbon dioxide, catalyzed by the enzyme ribulose bisphosphate carboxylase (RUBISCO), forming two molecules of glycerate 3-phosphate (GP).
These GP molecules are then reduced to triose phosphate using ATP and reduced NADP (which becomes oxidized in the process).
Some triose phosphate is converted into glucose every six cycles, while the remaining molecules are used to regenerate RuBP, ensuring the cycle can continue.
Explain the concept of limiting factors in photosynthesis.
What are the primary limiting factors that affect the rate of photosynthesis, and how do changes in these factors influence the overall process?
Limiting factors in photosynthesis refer to environmental conditions that restrict the rate at which photosynthesis occurs.
The primary limiting factors include:
- Carbon dioxide concentration.
- Light intensity.
- Light wavelength.
- Temperature.
As these factors increase, the rate of photosynthesis typically rises, leading to greater production of glucose.
However, if light intensity or temperature becomes excessively high, it can damage plant tissues and denature enzymes, ultimately slowing down the rate of photosynthesis.
Discuss the role of ATP synthase in the light-dependent reactions of photosynthesis.
How does the process of facilitated diffusion of protons contribute to ATP production, and what is the significance of ATP in the overall photosynthetic process?
ATP synthase plays a crucial role in the light-dependent reactions of photosynthesis by synthesizing ATP from ADP and inorganic phosphate.
As protons are pumped into the thylakoid lumen through the electron transport chain, a proton gradient is established.
Protons then return to the stroma through ATP synthase via facilitated diffusion, driving the conversion of ADP to ATP.
This ATP is vital for the light-independent reactions, as it provides the energy necessary for the conversion of carbon dioxide into glucose during the Calvin cycle, thus linking the light-dependent and light-independent stages of photosynthesis.
Define cyclic photophosphorylation and describe its significance in the context of photosynthesis.
How does this process differ from non-cyclic photophosphorylation in terms of electron flow and the products generated?
Cyclic photophosphorylation is a process that occurs in the light-dependent reactions of photosynthesis, specifically involving only photosystem I (PSI).
In this process, electrons that are excited by light energy are transferred through the electron transport chain and ultimately return to PSI, rather than being used to reduce NADP.
This results in the production of ATP without generating reduced NADP.
In contrast, non-cyclic photophosphorylation involves both photosystems II and I, leading to the production of both ATP and reduced NADP.
Cyclic photophosphorylation allows plants to generate additional ATP when reduced NADP levels are sufficient, thus balancing the energy needs of the plant.
Describe the relationship between carbon dioxide concentration and the rate of carbon fixation in the Calvin cycle, including how this affects the production of triose phosphate (TP).
As carbon dioxide concentration increases, the rate of carbon fixation in the Calvin cycle also rises, leading to an increased production of triose phosphate (TP).
This is crucial for plant growth as TP is a key intermediate in the synthesis of glucose and other carbohydrates.
How does temperature influence enzyme activity in plant processes, particularly in relation to the Calvin cycle, and what are the consequences of exceeding optimal temperature ranges?
Temperature plays a significant role in enzyme activity, particularly in enzyme-controlled reactions within the Calvin cycle.
As temperature rises, enzyme activity typically increases, enhancing the rate of photosynthesis and carbon fixation.
However, if temperatures exceed the optimal range, enzymes can denature, losing their functional shape and leading to a decrease in reaction rates.
