3.5 Energy Transfers in and between Organisms Flashcards
Outline the process of photosynthesis
• Light is absorbed by chlorophyll and this is linked to the production of ATP. ATP production occurs when protons diffuse down an electrochemical gradient through molecules of the enzyme ATP synthase, embedded in the membranes of cellular organelles
• Photosynthesis is common to all photoautotrophic organisms and occurs in two stages; the light-dependent reaction and the light-independent reaction
• Energy from ATP and hydrogen from reduced NADP (NADPH) are passed from the light-dependent to the light-independent stage
• The energy and hydrogen are used in the light-independent reactions (the Calvin Cycle) to produce complex organic molecules
Identify where the light-dependent reaction of photosynthesis takes place
Thylakoid membrane and thylakoid spaces in the chloroplast
Outline the structure and function of a chloroplast
• STRUCTURE:
• Vesicular plastid surrounded by a double membrane envelope, each a phospholipid bilayer
• Filled with a fluid-filled matrix called the stroma
• Contains a series of flattened, fluid-filled sacs called thylakoids (containing photosystems with chlorophyll) that stack to form grana that are connected by membranous channels called stroma lamellae
• Contains small (70s) ribosomes, a loop of DNA and starch grains
• Function: Site of photosynthesis to convert solar energy to chemical energy
Identify the function of the stroma in the chloroplast
Contains a separate system of membranes that contains the pigments, enzymes and electron carriers for light dependent reactions
Identify the function of the stroma lamellae in chloroplasts
To ensure the stacks of thylakoids (grana) are connected but distanced
Identify the function of grana in the chloroplast
• Membranes have a large surface area to increase the number of light dependant reactions that can occur
• Contains a large number of pigment molecules arranged in light-harvesting clusters called photosystems that ensures as much light as necessary is absorbed
Identify the function of the loop of DNA in chloroplasts
Codes for some chloroplast ribosomes that aren’t coded for by the plant cell nucleus
Identify the function of the starch grains in the chloroplast
Sugars formed during photosynthesis are stored as starch inside the starch grains
Identify the four processes make up the light-dependent reaction of photosynthesis
• Photoionisation of chlorophyll
• Chemiosmosis
• Photolysis
• Production of ATP and reduced NADP (NADPH)
Describe the process of the light-dependent reaction of photosynthesis
• Chlorophyll absorbs light, leading to photoionisation of chlorophyll. The light excites electrons in the chlorophyll, which becomes positively charged as the electrons are lost
• Electrons are passed down the electron transfer chain (ETC) in a series of redox reactions, gradually releasing energy as they go.
• The production of ATP is explained by the chemiosmotic theory and involves this energy, which is used to actively transport protons (H+ ions) across the thylakoid membrane to the thylakoid lumen through a proton pump
• This creates a proton concentration gradient which causes protons to return to the stroma down this gradient through transmembrane ATP synthase enzymes providing energy for ATP synthesis
• Photolysis is the breakdown of water by light in the lumen, producing protons, electrons and oxygen.
• The electrons produced replace exited electrons on the ETC and combine with the hydrogen ions and are transported out of the thylakoid lumen by ATP synthase. They also combine with carrier molecule NADP to produce NADPH
• ATP and reduced NADP (NADPH) are produced and transferred to the light-independent reactions and oxygens produced as a waste product
Identify the equation for photolysis in the light-dependent reaction of photosynthesis
H20 -> 2H+ + 2e- + 1/2 O2
Identify the equation for the production of reduced NADP in the light-dependent reaction of photosynthesis
2H+ + 2e- + NADP -> NADPH
Identify the equation for photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
Identify where the light-independent reaction of photosynthesis takes place
Stroma of the chloroplast
Identify the function of the light-independent reaction
• Uses reduced NADP from the light-dependent reaction to form a simple sugar.
• Hydrolyses ATP from the light-dependent reaction to provide additional energy
Describe the process of the light-independent reactions (the Calvin Cycle) of photosynthesis
• Carbon dioxide is fixated and reacts with ribulose biphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP). This reactions catalysed by the enzyme rubisco
• ATP and reduced NADP from the light-dependent reaction are used to reduce GP to triose phosphate
• 5/6 of the time, triose phosphate is used to regenerate RuBP in the Calvin cycle
• 1/6 of the time triose phosphate is converted to useful organic substances
(5+1, 2x3, 2x3, 5)
Outline limiting factors in photosynthesis
Photosynthesis can be considered as a number of metabolic pathways. The overall rate depends upon the slowest reaction in the pathway (the limiting factor), this can be:
• Light intensity
• Temperature
• Carbon dioxide concentration
Describe how light intensity limits the rate of photosynthesis
• More light leads to more photoionisation so there’s more H+ ions, through chemiosmotic theory, this produces more ATP and reduced NADP for the Calvin cycle (light-independent reactions) which can then occur at a greater rate
• As light intensity increases, more photosynthesis can occur until another factor becomes limiting
Describe how temperature limits the rate of photosynthesis
• An optimum temperature will increase the rate of light-dependent reactions and therefore the rate of photosynthesis as enzymes are in their optimal working window, deviation from which can cause them to denature
• Increased temperature causes stomata on a leaf to close in order to reduce water loss, therefore carbon dioxide can’t enter the leaves and therefore can be fixated in the Calvin cycle
• Lower temperature means less kinetic energy and therefore less enzyme-substrate complexes are formed.
- Less rubisco means less GP is formed, so less TP
is formed, so less RuBP and organic molecules
are formed
- Less ATP synthase means less ATP is formed
Describe how Carbon dioxide concentration limits the rate of photosynthesis
• The rate of photosynthesis increases as carbon dioxide concentration increases until something else becomes the limiting factor
• It’s required for the light-independent reaction, during carbon fixation so the more carbon dioxide present, the faster this step of the Calvin cycle can occur and the faster overall rate of photosynthesis
What organic molecules are produced from the Calvin cycle
• Hexose phosphates (6C) which can be used to produce starch, sucrose or cellulose
• Lipids for cell membranes
• Amino acids for protein synthesis
Outline the role of starch, sucrose and cellulose in plants
• Starch; storage of sugars
• Sucrose; translocation around the plant
• Cellulose; making cell walls
Define oxidation
The loss of electrons, gain of oxygen or loss of hydrogen in a substance
Define reduction
The gain of electrons, loss of oxygen or gain or hydrogen in a substance
Outline the process of respiration
• Life depends on continuous transfers of energy. Cellular respiration (common to all organisms) produces ATP and is the process by which the energy contained is made available for all of the active processes within a cell
• In respiration, various substances are used as respiratory substrates. The hydrolysis of these respiratory substrates is linked to the production of ATP
• Anaerobic and aerobic respiration both involve glycolysis, however in aerobic respiration there are three more stages:
1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Oxidative phosphorylation/ETC
Describe the process of glycolysis in anaerobic respiration
• Glycolysis is the first stage of aerobic and anaerobic respiration and is an anaerobic process that takes place in the cytoplasm.
• It breaks down two molecules of glucose to pyruvate to produce 2 molecules of ATP and 2 molecules of NADH
• It involves the phosphorylation of glucose to glucose phosphate, using 2 ATP molecules.
• Triose phosphate is produced and then oxidised to pyruvate, which produces 2 molecules of NADH and 4 molecules of ATP, meaning a net gain of 2 ATP molecules.
• If respiration is only anaerobic, oxygen is unavailable so the Kerbs cycle and ETC cannot operate. There’s no way of disposing hydrogen because oxygen isn’t available to act as the final electron acceptor.
• Pyruvate is then converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysis
Describe the process of glycolysis in aerobic respiration
• Glycolysis is the first stage of aerobic and anaerobic respiration and is an anaerobic process that takes place in the cytoplasm.
• It breaks down two molecules of glucose to pyruvate to produce 2 molecules of ATP and 2 molecules of NADH
• It involves the phosphorylation of glucose to glucose phosphate, using 2 ATP molecules.
• Triose phosphate is produced and then oxidised to pyruvate, which produces 2 molecules of NADH and 4 molecules of ATP, meaning a net gain of 2 ATP molecules.
• If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport.
Describe the process of the Link reaction in respiration
• The second stage of aerobic respiration that takes place in the mitochondrial matrix and converts pyruvate into acetyl coenzyme A and carbon dioxide. NADH is also formed.
• If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport. Pyruvate is oxidised to acetate, producing carbon dioxide (via decarboxylation) and NADH in the process.
• Acetate combines with coenzyme A in the link reaction to produce acetylcoenzyme A.
• Coenzyme A reacts with a four-carbon molecule (oxaloacetate). This releases coenzyme A to be recycled back into the link reaction and produces a six-carbon molecule (citrate) that enters the Krebs cycle
Describe the process of the Krebs cycle in respiration
• Coenzyme A reacts with a four-carbon molecule (oxaloacetate). This releases coenzyme A to be recycled back into the link reaction and produces a six-carbon molecule (citrate) that enters the Krebs cycle
• In a series of oxidation-reduction (redox) reactions catalysed by dehydrogenase enzymes in association with coenzymes, NADH and FADH are produced. The Krebs cycle generates reduced coenzymes and ATP by substrate level phosphorylation and carbon dioxide is lost
Explain what dehydrogenase enzymes are
An enzyme that catalyses the removal of hydrogen atoms (oxidation) from substrates. Often work with coenzymes such as NAD/FAD/NADP
Identify and define the different types of phosphorylation
• Phosphorylation is the addition of a phosphate molecule
• Substrate level phosphorylation is the addition of a phosphate molecule using enzymes
• Oxidative phosphorylation is the addition of a phosphate molecule using oxygen
• Photophosphorylation is the addition of a phosphate molecule using light
Define a coenzyme
Molecules that help enzymes carry out their functions e.g. NAD, FAD, NADP
Define decarboxylation
Chemical reaction that removes a carboxyl group and releases a carbon dioxide
Describe the process of oxidative phosphorylation/ETC in respiration
• Takes place in the cristae of the inner membranes of mitochondria and is broken into three stages;
1. The Electron Transfer Chain (ETC)
2. Chemiosmosis
3. Oxidative Phosphorylation
• Involves the synthesis of ATP by oxidative phosphorylation associated with the transfer of electrons down the ETC and passage of protons across inner mitochondrial membranes (chemiosmotic theory).
• ATP production occurs when protons diffuse down an electrochemical gradient through molecules of the enzyme ATP synthase, embedded in the membranes of cellular organelles.
• Oxygen acts as the final electron acceptor in the ETC by joining with electrons and protons to produce water. If it didn’t collect electrons, no more could travel down the ETC
State the equation for respiration
6O2 + C6H12O6 -> 6Co2 + 6H2O + energy
Explain why ATP is a useful energy currency molecules
• Immediate (only have to hydrolyse one bond)
• Small manageable amounts of energy
• Recycled/regenerated quickly
• Cannot leave a cell
