Chapter 17- The Need For Energy And Photosynthesis Flashcards
Examples of energy requiring metabolic processes?
Active transport
Anabolic Reactions; building of polymers like polysaccharides and nucleus acids.
Movement brought about by cilia, flagella or filaments in muscle cells
What process forms ATP?
Chemiosmosis
Explain chemiosmosis?
Diffusion of protons from an area of high concentration to an area of low concentration through a partially permeable membrane. The movement of protons as they flow down their conc gradient release energy that used in attachment of inorganic phosphate (Pi) to ADP forming ATP
What is chemiosmosis dependent on?
The creation of a proton concentration gradient. The energy to do this comes from excited electronic
What 2 ways can electrons become excited;
Electrons present in pigment molecules are excited by absorbing light from the sun.
High energy electrons are released when chemical bonds are broken in respiratory substrate molecules.
Where so excited electrons go?
Into an electron transport chain and are used to generate a proton gradient.
Describe an electron proton chain?
Made up of a series of electron carriers, each with progressively lower energy levels. As electrons move along the chain, energy is released. This energy is used to pump protons across a membrane creating a proton gradient which is maintained by membrane being impermeable to H+ ions. Protons then diffuse through proton channels linked to enzyme synthase. ATP is synthesised.
What is the basic photosynthesis equation?
6CO2 + 6H2O —> C6H12O6 + 6O2
What are thylakoids?
Flattened discs that have a small internal volume to maximise hydrogen gradient upon proton accumulation.
What are grana / granum?
Thylakoids organised into stacks to maximise SA:Vol ratio of the thylakoid membrane.
What are photo systems?
Pigments organised i to photo systems in thylakoid membrane to maximise light absorption.
What is stroma?
Central cavity that contains appropriate enzymes and a suitable for pH for the Calvin Cycle to occur
What are lamallae?
Connects and separates grana, maximising photosynthetic efficiency.
Why do photosystems need different pigments?
Different pigments absorb different wavelengths of light, having a variety of wavelengths means that they can absorb the most amount of light.
What colours of light does chlorophyll absorb predominantly? Reflects what color?
Red and blue light and reflects green light.
What is the primary pigment?
Chlorophyll A.
What are some secondary pigments?
Chlorophyll B
Xanthophyll
Carotenoids
Where would you find secondary pigments?
Embedded in the thylakoid membrane of the chloroplast.
What is the role of the light harvesting system?
Absorb or harvest light energy of different wavelengths and transfer this energy quickly and efficiently to the reaction centre.
Where is chlorophyll A located?
In the reaction centre , where the reaction involved in photosynthesis take place.
How would you investigate photosynthetic pigments?
Thin Layer Chromatography
How to calculate the Rf value?
Distance travelled by component / distance travelled by solvent
Summarise the light dependent stage of photosynthesis?
Energy from sunlight absorbed and used to form ATP. Hydrogen from water used to reduce coenzyme NADP to NAPDH
Summarise the light independent stage of photosynthesis?
Hydrogen from NAPDH and carbon dioxide is used to build organic molecules, such as glucose. ATP supplies the required energy.
Explain non-cyclic phosphorylation.
Light energy excited electron at reaction centres PS1 and PS2.
Excited electrons passed to electron acceptors then to ETC.
ATP produced by chemiosmosis.
Electrons lost from PS1 replaced from electrons from PS2.
Electrons lost from PS2 replaced by electrons from water.
Electrons leaving PS1 are accepted via ferrodoxin along with H+ by coenzyme NADP forming NADPH.
This provides hydrogen (reducing power) for production of organic molecule such as glucose in light independent phase.
How is reduced NADP produced?
Hydrogen ions return to the stroma.
Combine with electrons from PS1 and coenzyme NADP to form NAPDH for use in light independent stage.
NADPH is a reducing agent.
Explain cyclic phosphorylation?
Electrons leaving PS1 can be returned to PS1 (cyclic)
This is instead of forming NADPH.
PS1 can still lead to ATP production without electrons supplied from PS2.
NADPH is not produced.
What is photolysis?
Water molecules are split into hydrogen ions, electrons and oxygen molecules using light energy from the sun.
Why is photolysis useful?
The electrons released replace the electrons lost from the reaction centre of PS2 - hence why water is a raw material of photosynthesis.
What does photolysis have to do with a proton gradient?
Oxygen releases as by product. Protons released into the lumen of thylakoids increasing proton conc. across the membrane. As they move back through the membrane down a conc. gradient and electrochemical gradient, more ATP is formed. Hydrogen ions return to stroma, they combine with NADP and electron from PS1 to form NADPH. Which is used in light independent photosynthesis.
This process removed hydrogen ions from stroma so it helps to maintain proton gradient across thylakoid membrane.
What are the 3 stages of the Calvin cycle?
Carbon Fixation
Reduction of GP
Regeneration of RuBP
Explain the Calvin cycle.
Carbon enters spaces within spongy mesophyll through the stomata. It diffuses into cells and into the stroma of chloroplasts where it’s combined with 5C RuBP, this is carbon fixation.
Rubisco catalyses the reaction and an unstable 6c compound produced.
The unstable 6C compound formed immediately breaks down forming two 3C GP molecules.
Each GP is converted into another 3C molecule, TP using hydrogen from reduced NADP and light energy supplied by ATP.
TP is recycled to regenerate RuBP and the cycle continues.
Why is Rubisco inefficient?
Because it is competitively inhibited by oxygen so a lot of it is required to carry out photosynthesis successfully. Allows photorespiration to occur
What is photorespiration?
A process by which in the presence of light a plant consumes O2 and releases CO2 during photosynthesis which means that there is reduced photosynthetic output.
How does photorespiration occur?
When the enzyme rubisco is competitively inhibited by oxygen and therefore acts on oxygen rather than carbon dioxide.
When does photorespiration occur?
When the concentration of CO2 is low and the concentration of O2 is high. Tends to occur when stomata are closed (at night) and in high temperatures, drought exacerbates photorespiration.
Why does photorespiration affect carbon fixation?
Because rubisco can no longer catalyse the reaction of carbon fixation due to being inhibited by oxygen.
What toxic 2C molecule is formed in photorespiration?
Phosphoglycolate.
Why is photorespiration bad for commercial farmers?
It may take plant longer to grow due to the inefficiencies of photorespiration.
What is a C3 plant?
A plant with no adaptations to reduce photorespiration. Only use the standard mechanisms.
What is a C4 plant?
A plant that minimises photorespiration by separating initial CO2 fixation and the carbon cycle, performing these steps in different cell types. Light dependent takes place in mesophyll cells and Calvin cycle takes place in bundle sheath cells.
Examples of c3 plant?
Rice
Wheat
Soya bean
Examples of C4 plants?
Crabgrass
Corn
Sugarcane.
Where are C4 plants common?
In hot habitats
What are the 3 limiting factors of photosynthesis?
Carbon dioxide
Light intensity
Temperature.
How does light intensity impact photosynthesis?
High light intensity = increase photosynthesis
Why does a higher light intensity increase photosynthesis?
Light required for photolysis which is necessary to get electrons abs hydrogen. Light is needed to excite the electrons in LDP.
More LD reaction
More ATP and NADPH
More GP and more TP
More regeneration of RuBP
How does CO2 affect photosynthesis?
Increased CO2 increases rate of photosynthesis.
Why does more CO2 impact photosynthesis?
More carbon = more fixation = more GP and TP.
High GP and TP means that higher rate of reaction and more glucose produced.
How do temperatures affect photosynthesis?
Low temp = less photosynthesis
Why do low temperatures impact photosynthesis?
Low temps = less enzyme activity. Particles less kinetic energy= less successful collisions and reduced rate of reaction. Reduced GP and TP output and less RuBP production.
