[Y2] Energy Transfers In and Between Organisms Flashcards
What adaptations do leaves have to maximise photosynthesis?
- a large SA to absorb as much sunlight as possible.
- an arrangement of leaves on the plant that minimises overlapping and so avoids the shadowing of one leaf by another.
- thin, as most light is absorbed in the first few micrometres of the leaf and the diffusion distance for gases is kept short.
- a transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells beneath.
- long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight.
- numerous stomata for gaseous exchange so that all mesophyll cells are only a short diffusion patheay from one.
- stomata that open and closer in responce to chanegs in light intensity.
- many air spaces in the lower mesophyll layer to allow rapid diffusion in the gas phase of carbon dioxide and oxygen.
- a network of xylem that brings water to the leaf cell, and phloem theat carries away sugars produced during photosythesis.
What is the overall equation of photosythesis?
6CO₂ + 6H₂O →(light)→ C₆H₁₂O₆ + 6O₂
What are the three main stages of photosynthesis?
- The capturing of light energy: by chloroplast pigments such as chlorophyll.
- The light-dependent reaction: light energy absorbed is conserved in chemical bonds. During the process, an electron flow is created causing the photolysis of water into protons (NADP), electrons (ATP), and oxygen.
- The light-independent reaction: where protons are used to produce sugars and other organic molecules.
Describe the structure of chloroplasts.
- Typically disc shaped, 2-10um long, and 1um in diameter.
- They are surrounded by a double membrane.
- Inside the membrane are two distinct regions:
- The grana: stacks of up to 100 disc-like structures called thylakoids.
- Within the thylakoids is the photosynthetic pigment, chlorophyll.
- Some thylakoids join up with thylakoid in adjacent grana, these are called intergranal lamellae.
- The storma: a fluid-filled matrix where the light dependant stage of photosynthesis takes place.
- Within the stroma are a number of other structures such as starch grains.
What is the light energy used for in the light-dependant reaction?
- To add an inorganic phosphate (Pᵢ) molecule to ADP, making ATP.
- Photolysis of water into H⁺ ions (protons) and OH⁻ ions.
Define oxidation and reduction.
What are their energy changes?
Oxidation: oxygen added OR hydrogen lost OR electrons lost. (Exothermic)
Reduction: oxygen lost OR hydrogen gained OR electrons gained. (Endothermic)
What happens during photoionisation in the light dependant reaction?`
- When a chlorophyll molecule absorbs light energy, a pair of electrons are excited, rasing them to a higher energy level.
- Electrons become so energetic that they leave the chlorophyll molecule altogether.
- As a result the chlorophyll molecule becomes ionised.
What happened to electrons after photoionisation?
- The elections that leave the chlorophyll are taken up by a molecule called an electron carrier.
(Chlorophyll oxidised, Electron carrier reduced.)
- Electrons are passed along a number of carriers in a series of redox reactions. These are located in the membrane of the thylakoids.
- Each new carrier has a slightly lower energy level than the previous one in the chain, so the electrons lose energy at each stage.
- Some of this energy is used to combine an inorganic phosphate with ADP to make ATP.
What is the chemiosmotic theory?
- Each thylakoid is an enclosed chamber into which protons (H⁺) are pumped from the stroma using protein carriers in the thylakoid membrane called proton pumps.
- Energy to drive this process comes from electrons released by the photolysis of water.
- The photolysis of water also produces protons which further increases their concentration inside the thylakoid space.
- Overall this creates and maintains a concentration gradient of protons across the thylakoid membrane with a high concentration inside the thylakoid space and a low concentration in the stroma.
- Protons can only cross the thylakoid membrane through ATP synthase channel proteins (the rest of the membrane is impermeable to protons). These channels are also known as stalked granules.
- As protons pass through the ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP.
How do chlorophyll molecules regain electrons lost as a result of photoionisation? Give the equation associated with it.
Gain electrons from the photolysis of water.
2H₂O –> 4H⁺ + 4e⁻ + O₂
What happens to the products of the photolysis of water during the light-dependant reaction?
2H₂O –> 4H⁺ + 4e⁻ + O₂
- Protons: pass out of thylakoid space through ATP synthase and are taken up by an electron carrier (NADP).
- As a result this NADP becomes reduced.
- This reduced NADP is the main product of the light-dependant reaction, carrying with it electrons from the chlorophyll molecules, into the light-independent reaction.
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- Electrons: allows chlorophyll to replace its lost electrons, to allow them to continue to absorb light energy.
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- Oxygen (by-product of photolysis of water): either used in respiration or diffuses out of the leaf as a waste product of photosynthesis.
How are chloroplasts structurally adapted to their function of capturing sunlight and carrying out the light-dependent reaction of photosynthesis?
- The thylakoid membranes provide alarge SA for the attachment of chlorophyll, electron carriers, and enzymes (that carry out the light-dependent reaction).
- A network of proteins in the grand hold the chlorophyll in a very precise manner that allows maximum absorption of light.
- The granal membranes have ATP sythase channels within them, which catalyse the production of ATP. They are also selectively permeable, allowing for a proton gradient.
- Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light-dependent reaction.
What are the requirements of the light-independant reaction of photosythesis?
The products of the light-dependent reation of photosynthesis:
- ATP.
- NADP.
And CO₂
Where does the light-independednt reaction take place?
The stroma of the chloroplast.
Who worked out the details of the light-independent reaction?
Melvin Calvin (and his co-workers). Hence the name Calvin Cycle.
Describe the Calvin cycle.
- CO₂ from the atmosphere diffuses into the leaf through stomata and dissolves in water around the walls of the mesophyll cells.
- It then diffuses through the cell-surface membrane, cytoplasm, and chloroplast membranes into the stroma of the chloroplast.
- In the stroma, the CO₂ reacts with the 5-carbon compound ribulose bisphosphate (RuBP) a reaction catalysed by an enzyme called ribulose bisphosphate carboxylase (rubisco).
- The reaction between carbon dioxide and RuBP produces two molecules of the 3-carbon compound glycerate 3-phosphate (GP).
- Reduced NADP from the light-dependent reaction is used to reduce glycerate 3-phosphate to trios phosphate (TP) using energy supplied by ATP (from the light-dependent reaction).
- The NADP is re-formed and goes back to the light-dependent reaction to be reduced again by accepting more protons.
- Some triose phosphate molecules are converted to organic substrates that the plant requires such as starch, cellulose, lipids, glucose, amino acids, and nucleotides.
- Most triose phosphate molecules are used to regerate ribulose bisphophate using ATP from the light- dependent reaction.
How is the chloroplast adapted to carry out the light-independent reaction of photosynthesis?
- The fluid of the storma contains all the enzymes needed to carry out the light-independent reaction. Stromal fluid is membrane-bound in the chloroplast which means a chemical environment which has a high concentration of enzymes and substrates can be maintained within it - as distinct from the environment of the cytoplasm.
- The stroma fluid surrounds the grana and so the products of the light-dependent reaction in the grana can readily diffuse into the stroma.
- It contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins involved in the light-indepenent reaction.
What are the two different forms of cellular respiration?
- Aerobic respiration: requires oxygen and produces carbon dioxide, water, and much ATP.
- Anerobic respiration: takes place in the absence of oxygen and produces lactate (in animals) or ethanol and carbon dioxide (in plants and fungi) but only a little ATP in both cases.
What are the stages of aerobic respiration?
- Glycolysis: the splitting of the 6-carbon glucose molecule into 3-carbon pyruvate molecules.
- Link reaction: the 3-carbon pyruvate molecules enter into a series od reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule.
- Krebs cycle: the introduction of acetlycoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD.
- Oxidative phosphorylation: the use of the electrons, associated with reduced NAD and FAD, released from the Krebs cycle to synthesise ATP with water produced as a by-product.
Which stage of aerobic respiration is also part of anerobic respiration?
Glycolysis.
Where does aerobi respiration start?
Cytoplasm (as that is where glycolysis takes place).
What are the stages of glycolysis?
- Phosphorylation of glucose to glucose phosphate: before being split into two glucose must be made more reactive, through phosphorylation. The phosphate molecules come from the hydrolysis of two ATP molecules into ADP. This provides the energy to activate glucose and lower the activation energy for the enzyme-controlled reactions that follow.
- Splitting of phosphorylated glucose: each glucose molecule is split into two 3-carbon molecules known as triose phosphate.
- Oxidation of triose phosphate: hydrogen is removed from each of the two triose phosphate molecules and transferred to a hydrogen-carrier molecule known as NAD to form reduced NAD.
- The production of ATP: Enzyme-controlled reactions convert each trios phosphate into another 3-carbon molecule called pyruvate. In the process, two molecules of ATP are regerated from ADP.
What is the overall yeild of one glucose molecule undergoing glycolysis?
- 2 molecules of ATP (four molecules are produce, but two were used up in the initial phosprylation of glucose and so the net increase is two).
- 2 molecules of reduced NAD (these have the potential to provide energy to produce ATP later on).
- 2 molecules of pyruvate.
How does Glycolysis indirect evidece for evolution?
It is a unversal feature of every living organism.
Why must pyruvate be broken down further?
In order to releas the remainder of potential energy stored in the molecules of pyruvate.
Why doesn’t glycolysis require any organelle or membrane for it to take place?
The enzymes for the glycolytic pathways are found in the cytoplasm of cells.
(It can also take place weather or not oxygen is present - does not require oxygen.)
How can pyruvate be broken down further? What must happen first?
Through the Krebs cycle.
It must be oxidised first (in a process known as the link reaction).
Where do the link reaction and Krebs cycle take place?
(In eukaryotic cells) exculsivley inside mitochonria.
How does pyruvate get to where it needs to be inorder for the next stage of aerobic respiration to take place?
It is activly transported into the matrix of mirtochoria from the cytoplasm of the cell (in eukaryotes).
Describe the link reaction.
- The pyruvate is oxidised to acetate. In this reaction the 3-carbon pyruvate loses a carbon dioxide molecule and two hydrogens. These hyrogens are accepted by NAD to form reduced NAD (which is late used to produce ATP).
- The 2-carbon acetate combines with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A.
Give the chemical equation summarising the link reaction.
pyruvate + NAD + CoA → acetyl CoA + reduced NAD + CO₂
Who worked out the Krebs cycle’s sequence?
British Biochemist, Hans Krebs.
Where does the Krebs cycle take place?
The matrix of the mitochondria.
Describe the Krebs cycle.
- The 2-carbon acetylcoenzyme A from the link reaction combines with a 4-carbon molecule to produce a 6-carbon molecule.
- In a series of reactions this 6-carbon molecules loses carbon dioxide and hydrogen to give 4 carbon molecules and singe molecules of ATP produced as a result of substrate-level phosphorylation.
- The 4-carbon molecule can now combine with a new molecule of acetylcoenzyme A to begin the cycle again.
What is the overall yeild of one pyruvate molecule undergoing the link reaction and Krebs cycle?
- Reduced coenzymes such as NAD adn FAD: these have the potential to provide energy to produce ATP molecules by oxidative phosphorylation and thus the important product of Krebs cycle.
- One molecule of ATP.
- Three molecules of carbon dioxide.
(the yield of a single glucose is double this as two pyruate molecules are produced for each original glucose)
What are coenzymes?
NOT ENZYMES.
They are molecules that some enzymes require in order to function.
Give examples of important coenzymes.
- NAD: important throughout respiration.
(it works with dehydrogenase enzymes that catalyse the removal of hydrogenatoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.) - FAD: imporant in the Krebs cycle.
- NADP: important in photosynthesis.
What is the significance of the Krebs cycle on the cells of organisms?
- It breaks down macromolecules into smaller ones - pyruvate is broken down into carbon dioxide.
- It produces hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. This leads to the production of ATP that provides metabolic energy for the cell.
- It regenerates the 4-carbon molecule that combines with acetylcoenzyme A, which would otherwise accumulate.
- It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll.
What is oxadative phophorylation?
The mechanism by which some of the energy of the electrons within hydrogen atoms is conserved in the formation of ATP.
Where does oxadative phosphorylation take place?
In the mitochondria, within inner folded membrane (cristar) where enzymes and other proteins are found.
What adaptation might individual mitochonria have in more metabolically active cells?
More densely packed crisae which provide a greater surface area of membrane incorporating enzymes and other proteins involved in oxidative phosphorylation.
What is the electron transfer chain?
A series of electron carrier molecules that can transfer electrons to eachother.
Describe the chemiosmotic theory of oxidative phosphorylation.
- Hydrogen produced during glycosis and the krebs cycle combine with the coenzyme NAD and FAD.
- The reduced NAD and FAD donate the electrons of hydrogen atoms they are carrying to the first molecule in the ETC.
- The electrons pass along a chan of electron transfer carrier molecules in a series of oxidation-reduction reactions. As the electrons flow along the chain, the energy they release causes the active transport of protons accross the inner mitochonrial membrane and into inter-membranal space.
- The protons accumulate in the inter-membranal space before they diffuse back into the mitochonrial matrix through ATP sythase channels embedded in the inner mitochonrial membrane.
- At the end of the chain the electrons combine with these protons and oxygen to form water. Oxygen is therefore the final acceptor of elections in the electron transfer chain.
