The 11th unit of first-year Biology delves into the captivating realm of bioenergetics, a fundamental concept that unravels the mysteries of energy flow within living organisms. Bioenergetics serves as a cornerstone in understanding how life sustains and propels itself, illuminating the processes by which cells harness, store, and utilize energy to carry out essential functions.
From the mesmerizing intricacies of cellular respiration to the dazzling elegance of photosynthesis, this unit embarks on a journey through the remarkable mechanisms that power life, offering profound insights into the very essence of existence itself. Through a fusion of biochemical principles and cellular dynamics, these notes will unveil the captivating dance of molecules and reactions that underlie the tapestry of life’s vitality.
Unit 11 Biology of 1st Year Short Answers Questions
What is bioenergetics?
Answer: Bioenergetics is the quantitative study of energy relationships and conversions in biological systems.
What laws do biological energy transformations obey?
Answer: Biological energy transformations obey the laws of thermodynamics.
What powers all life on Earth directly or indirectly?
Answer: All life on Earth is powered, directly or indirectly, by solar energy.
- 1st Year Biology Unit No.1 Introduction Notes
- 1st Year Biology Unit No. 2 Biological Molecules Notes
- 1st Year Biology Unit No. 3 Enzymes Notes
- 1st Year Biology Unit No. 4 The Cell Notes
- 1st Year Biology Unit No. 5 Variety of Life Notes
How do plants capture and convert light energy?
Answer: Chloroplasts in plants capture light energy and convert it into chemical energy stored in sugars and organic molecules.
What role did the emergence of photosynthesis play in the atmosphere?
Answer: Photosynthesis led to the accumulation of molecular oxygen in the atmosphere, enabling the evolution of respiration.
How does respiration release energy?
Answer: Respiration releases a significant amount of energy and couples some of it to the formation of ATP molecules.
What is the role of ATP in energy metabolism?
Answer: ATP serves as a chemical link between catabolism and anabolism in energy metabolism.
What is the primary process by which solar energy is converted into chemical energy?
Answer: Photosynthesis is the process by which solar energy is converted into chemical energy stored in carbohydrates.
What are the reactants and products of photosynthesis?
Answer: The reactants of photosynthesis are carbon dioxide, water, and light, while the products are glucose and oxygen.
How does the timing of photosynthesis and respiration differ?
Answer: Photosynthesis occurs only during the day, while respiration takes place both day and night.
What is the compensation point in relation to photosynthesis and respiration?
Answer: The compensation point is when the rates of photosynthesis and respiration are equal, resulting in no net gas exchange.
How do light intensity changes affect gas exchange in plants?
Answer: As light intensity increases, photosynthesis rate and the need for carbon dioxide increase, leading to net release of oxygen and uptake of carbon dioxide.
Where does the oxygen released during photosynthesis come from?
The oxygen released during photosynthesis comes from water.
Who hypothesized that plants split water as a source of hydrogen during photosynthesis?
Van Niel hypothesized that plants split water as a source of hydrogen, releasing oxygen as a by-product.
How was Van Niel’s hypothesis about the source of oxygen in photosynthesis confirmed?
Scientists confirmed Van Niel’s hypothesis using isotopic tracers (O18) and observed that plants supplied with O18-containing water produced O18-labeled oxygen.
What is the role of NADPH in photosynthesis?
NADPH, formed by the splitting of water, serves as the “reducing power” along with ATP to convert CO2 into sugar during the dark reactions of photosynthesis.
Where are chloroplasts mainly located in plants?
Chloroplasts are mainly located in the cells of mesophyll tissue within the leaves of plants.
What is the function of thylakoid membranes in chloroplasts?
Thylakoid membranes contain chlorophyll and other pigments that absorb light energy, which is then converted into ATP and NADPH during the light reactions of photosynthesis.
How are chlorophyll and other pigments involved in photosynthesis?
Chlorophyll and other pigments absorb light energy, which is converted into chemical energy in the form of ATP and NADPH, used to synthesize sugar in the stroma of chloroplasts.
What is the role of pigments in photosynthesis?
Pigments absorb visible light, allowing it to work in chloroplasts for photosynthesis. They absorb different wavelengths, causing those absorbed wavelengths to disappear.
What instrument is used to measure the abilities of different pigments to absorb light?
A Spectrophotometer is used to measure the relative abilities of pigments to absorb various wavelengths of light.
What is an absorption spectrum in relation to pigments?
An absorption spectrum is a graph showing the absorption of light at different wavelengths by a pigment.
What are the main photosynthetic pigments found in thylakoid membranes?
Chlorophylls are the main photosynthetic pigments found in thylakoid membranes.
Besides chlorophylls, what other accessory pigments are present in chloroplasts?
Yellow and red to orange carotenoids, including carotenes and xanthophylls, are accessory pigments present in chloroplasts.
Why do plants appear green in color?
Chlorophylls absorb mainly violet-blue and orange-red wavelengths, while green wavelengths are least absorbed, leading to green coloration.
How is a chlorophyll molecule structured?
A chlorophyll molecule consists of a light-absorbing hydrophilic head (porphyrin ring with a magnesium atom) and a hydrophobic hydrocarbon tail (phytol).
What causes the yellowing of plants due to magnesium deficiency?
Magnesium deficiency leads to yellowing in plants because magnesium is a central atom in the porphyrin ring of chlorophyll.
What distinguishes chlorophyll a from chlorophyll b?
Chlorophyll a and chlorophyll b differ in one functional group: chlorophyll a has a methyl group (-CH3), while chlorophyll b has a terminal carbonyl group (-CHO).
How do the molecular formulas of chlorophyll a and b differ?
Chlorophyll a: C55 H72 05 N4 Mg
Chlorophyll b: C55 H70 06 N4 Mg
What is the significance of the structural differences between chlorophyll a and b?
The structural differences lead to slightly different absorption spectra and colors, increasing the range of absorbed wavelengths. Chlorophyll a is blue-green, while chlorophyll b is yellow-green.
Which chlorophyll is the most abundant and important in photosynthesis?
Chlorophyll a is the most abundant and important chlorophyll in photosynthesis, as it directly participates in light-dependent reactions.
In what organisms is chlorophyll b found?
Chlorophyll b is found in green plants (embryophytes) and green algae, along with chlorophyll a.
How do chlorophylls interact with solvents?
Chlorophylls are insoluble in water but soluble in organic solvents like carbon tetrachloride and alcohol.
What are carotenoids?
Carotenoids are yellow and red to orange pigments that absorb blue-violet light and broaden the spectrum of light used for photosynthesis.
Why are carotenoids considered accessory pigments?
Carotenoids, along with chlorophyll b, are called accessory pigments because they absorb light and transfer energy to chlorophyll a during photosynthesis.
How do carotenoids protect chlorophyll from intense light?
Some carotenoids protect chlorophyll by dissipating excessive light energy, preventing damage from intense light.
What is the role of chlorophyll in photosynthesis?
Chlorophyll absorbs sunlight energy, converts it into chemical energy, and drives the photosynthetic process.
What is the action spectrum of photosynthesis?
The action spectrum of photosynthesis shows the relative effectiveness of different wavelengths (colors) of light in driving the photosynthetic process.
How is the action spectrum of photosynthesis related to the absorption spectrum of chlorophyll?
The action spectrum of photosynthesis corresponds to the absorption spectrum of chlorophyll, indicating that chlorophyll is the primary photosynthetic pigment.
How does the entry of CO2 occur in leaves?
CO2 enters leaves through stomata, adjustable pores that open during the day when CO2 is needed for photosynthesis and close at night.
What is the significance of carotenoids in photosynthesis?
Carotenoids absorb light in the green range and pass on some of the absorbed energy to chlorophyll, enhancing photosynthesis in those wavelengths.
What is the simplified summary equation for photosynthesis?
Answer: The simplified summary equation for photosynthesis is a ‘redox process’ that can be represented as: CO2 + H2O + light energy → C6H12O6 + O2.
Why do stomata continue their daily rhythm of opening and closing even in the dark?
Answer: The daily rhythmic opening and closing of stomata are controlled by an internal clock located in guard cells, allowing this rhythm to persist even in the absence of light.
What are the two main parts of photosynthesis reactions?
Answer: The reactions of photosynthesis consist of two parts: the light-dependent reactions (light reactions) and the light-independent reactions (dark reactions).
What happens during the light-dependent reactions of photosynthesis?
Answer: In the light-dependent reactions, light energy is absorbed by chlorophyll and other pigments, converting it into chemical energy. This energy is used to form NADPH and ATP, which carry energy to the light-independent reactions.
How does NADPH and ATP contribute to sugar synthesis in photosynthesis?
Answer: NADPH provides energized electrons and hydrogen ions, while ATP provides chemical energy. These molecules are used to reduce CO2 and synthesize sugars during the light-independent reactions.
Why are the light-independent reactions also called dark reactions?
Answer: The light-independent reactions are called dark reactions because they don’t directly use light. They can occur in both light and darkness as long as the NADPH and ATP generated by the light-dependent reactions are available.
What is the function of photosystems in the light-dependent reactions?
Answer: Photosystems are clusters of photosynthetic pigments that absorb light energy and transfer it to reaction centers. These reaction centers are involved in converting light energy into chemical energy.
What is the primary role of chlorophyll a in photosynthesis?
Answer: Chlorophyll a is a key pigment that plays a central role in capturing light energy. It is present in both photosystem I (P700) and photosystem II (P680) and is involved in energy transfer.
How are ATP and NADPH generated in the light-dependent reactions?
Answer: ATP and NADPH are formed through chemiosmosis, where the energy from high-energy electrons moving through an electron transport system is used to pump protons across a membrane, creating a proton gradient that drives ATP synthesis.
What are the two types of electron flow in the light-dependent reactions?
Answer: The two types of electron flow are non-cyclic electron flow, where electrons pass through both photosystems, and cyclic electron flow, which involves only photosystem I.
What happens when photosystem II absorbs light?
When photosystem II absorbs light, an electron in the reaction center chlorophyll P680 gets excited and is captured by the primary electron acceptor of PS II. The oxidized chlorophyll becomes a strong oxidizing agent and needs to be filled with an electron.
How is the electron hole in chlorophyll P680 filled?
The electron hole in chlorophyll P680 is filled by electrons extracted from water through a process known as photolysis. Water is split into two hydrogen ions and an oxygen atom. The released oxygen atoms combine to form O2, which is released as a byproduct.
How are electrons transferred from photosystem II to photosystem I?
Electrons move from the primary electron acceptor of photosystem II to photosystem I via an electron transport chain involving plastoquinone, cytochromes, and plastocyanin.
What is non-cyclic photophosphorylation?
Non-cyclic photophosphorylation is the process in photosynthesis where electrons flow from water through photosystems I and II, generating ATP through a chain of reactions driven by light energy. The produced ATP powers the synthesis of sugar during the Calvin cycle.
What happens when an electron reaches photosystem I?
When an electron reaches photosystem I, it fills an electron hole in P700, the reaction center chlorophyll a molecule. This hole is created when light energy drives an electron from P700 to the primary acceptor of photosystem I.
How is NADPH produced in non-cyclic photophosphorylation?
The photoexcited electrons from the primary electron acceptor of photosystem I are passed to ferredoxin (Fd) through a second electron transport chain. An enzyme called NADP reductase transfers the electrons from Fd to NADP, resulting in the production of NADPH, a molecule that stores high-energy electrons for the synthesis of sugar.
What is chemiosmosis?
Chemiosmosis is the process that uses membranes to couple redox reactions to ATP production. It involves the movement of protons (H+) across a membrane and their subsequent diffusion through ATP synthase to generate ATP.
How does the electron transport chain contribute to chemiosmosis in photosynthesis?
The electron transport chain pumps protons (H+) across the thylakoid membrane during photosynthesis. The energy from electron movement powers this proton pumping, creating a proton gradient across the membrane, which is used for ATP synthesis through chemiosmosis.
What is the role of ATP synthase in chemiosmosis?
ATP synthase is a complex embedded in the thylakoid membrane. It allows protons (H+) to pass through and couples their movement to the synthesis of ATP from ADP and inorganic phosphate. This process occurs during the diffusion of protons down their gradient, using the potential energy stored in the proton gradient.
What are the key phases of the Calvin cycle?
The Calvin cycle consists of three phases: Carbon Fixation, Reduction, and Regeneration of CO2 acceptor (RuBP). Carbon Fixation involves the incorporation of CO2 into an organic molecule. Reduction converts 1,3-bisphosphoglycerate into glyceraldehyde 3-phosphate (G3P) using ATP and NADPH. Regeneration of RuBP rearranges G3P molecules to regenerate the CO2 acceptor RuBP.
How does the Calvin cycle contribute to carbohydrate production?
The Calvin cycle uses the energy and reducing power from ATP and NADPH produced during light-dependent reactions to convert CO2 into glyceraldehyde 3-phosphate (G3P). G3P is a three-carbon sugar that can be used to synthesize glucose, sucrose, starch, and other carbohydrates in plants.
What is respiration?
Respiration is the universal process by which organisms break down complex carbon-containing compounds to harvest usable energy within cells.
How is the term “respiration” used in biology?
The term “respiration” is used in two ways in biology. It can refer to the exchange of respiratory gases (CO2 and O2) between an organism and its environment (external respiration), or to the process by which energy is generated within cells through the breakdown of carbon-chain molecules (cellular respiration).
What is glycolysis?
Glycolysis is the initial step in cellular respiration where glucose is split into two molecules of pyruvic acid. This reaction occurs in the cytosol and is a common pathway in all cells.
What are the two main types of respiration?
The two main types of respiration are aerobic respiration and anaerobic respiration. Aerobic respiration occurs in the presence of oxygen and leads to the complete breakdown of glucose into CO2, water, and energy. Anaerobic respiration includes reactions like alcoholic fermentation and lactic acid fermentation, occurring without oxygen.
What are mitochondria’s role in respiration?
Mitochondria are organelles responsible for cellular respiration. They transfer energy from organic molecules to ATP through a series of enzymatic reactions, making them crucial “powerhouses” for generating energy needed for cellular functions.
What is ATP and its significance?
ATP (adenosine triphosphate) is a vital compound found in cells, serving as a key source of energy for various biological processes. It contains “high energy” phosphate bonds that, when broken through hydrolysis, release substantial energy for cellular activities like synthesis, transport, muscle contractions, and nerve conduction.
What is the ultimate source of free energy for living systems?
The ultimate source of free energy for living systems is derived from various oxidation reduction reactions.
What is the role of photosynthesis and some bacterial chemosynthesis in energy supply?
Photosynthesis and some bacterial chemosynthesis are oxidation reduction reactions that provide free energy directly.
What do most cells depend on for their supply of free energy?
Most cells depend on oxidation reactions in respiratory processes for their supply of free energy.
What is the primary catalyst for the removal of hydrogen during biological oxidation?
Dehydrogenases linked to specific coenzymes catalyze the removal of hydrogen during biological oxidation.
What is cellular respiration, and what are its sub-divisions?
Cellular respiration is an oxidation process. It consists of four stages: Glycolysis, Pyruvic acid oxidation, Krebs cycle, and Respiratory chain.
Where does glycolysis occur and is oxygen essential for it?
Glycolysis occurs in the cytosol and can take place both in the absence (anaerobic) and presence (aerobic) of oxygen.
What is the main end product of glucose breakdown in glycolysis?
The main end product of glucose breakdown in glycolysis is pyruvic acid.
What are the two phases of glycolysis, and what happens in each?
Glycolysis consists of a preparatory phase (glucose breakdown) and an oxidative phase (formation of high-energy phosphate bonds).
What is the key event in the oxidative phase of glycolysis?
In the oxidative phase of glycolysis, two electrons or hydrogen atoms are removed from 3-phosphoglyceraldehyde (PGAL) and transferred to NAD, resulting in oxidation.
How is ATP produced in glycolysis?
ATP is produced in glycolysis through the transfer of high-energy phosphate groups to adenosine diphosphate (ADP) during various reactions.
What is the end product of glycolysis?
The end product of glycolysis is pyruvate (pyruvic acid), equivalent to half a glucose molecule oxidized.
Where do the other three stages of cellular respiration occur, and why is oxygen essential for them?
The other three stages of cellular respiration (Pyruvic acid oxidation, Krebs cycle, and Respiratory chain) occur within mitochondria and require oxygen for their completion.
What is the initial product of glycolysis?
Answer: The initial product of glycolysis is pyruvic acid (pyruvate).
How does pyruvic acid enter the Krebs cycle?
Answer: Pyruvic acid is first converted into a 2-carbon acetic acid molecule, which then forms acetyl CoA upon entering the mitochondrion.
What is the purpose of the Krebs cycle?
Answer: The Krebs cycle, also known as the citric acid cycle, completes the oxidation of acetyl CoA and generates energy-rich molecules.
What is the role of NAD in the Krebs cycle?
Answer: NAD (nicotinamide adenine dinucleotide) mediates oxidation reactions by accepting hydrogen atoms during the cycle.
How does the Krebs cycle begin?
Answer: The Krebs cycle starts with the union of acetyl CoA and oxaloacetate, forming citrate.
What happens during the conversion of isocitrate to α-ketoglutarate?
Answer: Isocitrate undergoes NAD-mediated oxidation and loses a CO2 molecule, resulting in the formation of α-ketoglutarate.
What is the product of the oxidation of α-ketoglutarate?
Answer: The product of α-ketoglutarate oxidation is succinate.
What coenzyme is involved in the oxidation of succinate to fumarate?
Answer: The coenzyme FAD (flavin adenine dinucleotide) is involved in the oxidation of succinate to fumarate.
How is malate formed in the Krebs cycle?
Answer: Fumarate is converted to malate with the addition of a water molecule.
What completes the Krebs cycle?
Answer: The cycle is completed when malate undergoes NAD-mediated oxidation to produce oxaloacetate, the original 4-carbon molecule.
Can the Krebs cycle be repeated?
Answer: Yes, the oxaloacetate produced at the end of the cycle can combine with another molecule of acetyl CoA to initiate the cycle again.
What is the function of NADH in the respiratory chain?
NADH transfers hydrogen atoms to the respiratory chain for electron transport.
What are the oxidation-reduction substances involved in the respiratory chain?
The substances include coenzyme Q, cytochrome enzymes (b, c, a, a3), and molecular oxygen (O2).
What role do cytochromes play in the electron transport chain?
Cytochromes are electron transport intermediates containing iron-based prosthetic groups that undergo valency changes, facilitating electron transfer.
How is ATP synthesized in the respiratory chain?
NADH is oxidized by coenzyme Q, which generates energy for ATP synthesis. Cytochrome b and c also contribute to ATP synthesis through oxidation-reduction steps.
What is the final acceptor of electrons in the respiratory chain?
Molecular oxygen (O2) is the most electronegative substance and serves as the final acceptor of electrons, forming water in the process.
What is oxidative phosphorylation?
Oxidative phosphorylation is the synthesis of ATP in the presence of oxygen, coupled with the respiratory chain. It involves the utilization of energy generated from electron transport.
Where does oxidative phosphorylation take place?
Oxidative phosphorylation occurs in the inner membrane of mitochondria, specifically in the cristae, where the electron transport chain is coupled with ATP synthesis through chemiosmosis.
What is the molecular equation for the synthesis of ATP through oxidative phosphorylation?
2 NADH + H+ + 3 ADP + 3 Pi + 1/2 O2 → NAD+ + H2O + 3 ATP
Exercise Short Questions
(i) List four features of a leaf which show that it is able to carry out photosynthesis effectively.
Answer: Chlorophyll content, presence of stomata, well-developed mesophyll tissue, and a network of veins for water and nutrient transport.
(ii) Summarise the role of water in photosynthesis.
Answer: Water is essential for photosynthesis as it serves as a source of electrons in the light-dependent reactions. It is split during photolysis to release oxygen, electrons, and protons, which contribute to the formation of ATP and NADPH.
(iii) What are T.W. Engelman and Melvin Calvin famous for?
Answer: T.W. Engelman is known for discovering the action spectrum of photosynthesis, which revealed the efficiency of different wavelengths of light for photosynthesis. Melvin Calvin is famous for discovering the Calvin cycle, outlining the biochemical pathway of carbon fixation in photosynthesis.
(iv) What is the difference between an action spectrum and an absorption spectrum?
Answer: An action spectrum shows the effectiveness of different wavelengths of light in driving a specific process, such as photosynthesis. An absorption spectrum illustrates the wavelengths of light absorbed by pigments, like chlorophyll, indicating their absorption capacity at various wavelengths.
(V) What is the role of accessory pigments in light absorption?
Accessory pigments broaden the absorption spectrum of photosynthetic organisms, capturing light energy that chlorophyll a cannot absorb effectively.
(vi) When and why is there not net exchange of CO2 and O2 between the leaves and the atmosphere?
There’s no net exchange during the night due to the absence of light for photosynthesis and the continued respiration of both the plant and its surroundings.
(vii) What is the net production of ATP during glycolysis?
2 ATP molecules are produced during glycolysis.
(viii) What is the main difference between photophosphorylation and oxidative phosphorylation?
Photophosphorylation occurs in photosynthesis and uses light energy to generate ATP, while oxidative phosphorylation occurs in cellular respiration and uses electron transport to create ATP.
(ix) What is the location of ETC and chemiosmosis in photosynthesis and cellular respiration?
In photosynthesis, the ETC and chemiosmosis occur in the thylakoid membranes of chloroplasts. In cellular respiration, they take place in the inner mitochondrial membrane.
(x) How did the evolution of photosynthesis affect the metabolic pathway?
The evolution of photosynthesis introduced a new energy source (light) and led to the development of aerobic respiration, which greatly increased energy production efficiency.
(xi) How does the absorption spectrum of chlorophyll a differ from that of chlorophyll b?
Chlorophyll a absorbs light most efficiently in the blue-violet and red-orange regions, while chlorophyll b’s absorption is highest in the blue and red regions of the spectrum.
(xii) Why are carotenoids usually not obvious in the leaves? They can be seen in the leaves before leaf fall. Why?
Carotenoids are masked by chlorophyll’s green color during the growing season. They become visible before leaf fall when chlorophyll degrades, revealing the yellow and orange carotenoid pigments.
(xiii) How is the formation of vitamin A linked with eating carrots?
Carrots contain beta-carotene, a precursor of vitamin A. When consumed, beta-carotene is converted into vitamin A in the body, contributing to vision and overall health.
Unit 11 Biology of 1st Year Long Answer Questions
Question: (i) Explain the roles of the following in aerobic respiration: (a) NAD+ and FAD (b) oxygen.
Roles of NAD+ and FAD, and the role of oxygen in aerobic respiration
(a) NAD+ and FAD:
NAD+ (Nicotinamide adenine dinucleotide) and FAD (Flavin adenine dinucleotide) are coenzymes involved in electron carrier reactions during aerobic respiration. They play a crucial role in facilitating the transfer of electrons in various stages of cellular respiration.
During glycolysis, NAD+ is reduced to NADH as it accepts electrons from glucose breakdown. In the citric acid cycle, both NAD+ and FAD are reduced as they accept electrons from acetyl CoA and other intermediates. These reduced forms, NADH and FADH2, carry the electrons to the electron transport chain.
(b) Oxygen:
Oxygen is the final electron acceptor in the electron transport chain, which is a crucial step in aerobic respiration. As electrons move through the chain from NADH and FADH2, they lose energy. This energy is used to pump protons (H+) across the inner mitochondrial membrane, creating an electrochemical gradient. Oxygen’s role is to accept the electrons and protons at the end of the chain, forming water and thus maintaining the flow of electrons. This step generates a proton gradient that drives the synthesis of ATP through chemiosmosis.
Question: (ii) Sum up how much energy (as ATP) is made available to the cell from a single glucose molecule by the operation of glycolysis, the formation of acetyl CoA, the citric acid cycle, and the electron transport chain.
(ii) Energy yield from glucose in aerobic respiration:
The total energy yield from one glucose molecule through aerobic respiration involves several stages: glycolysis, the formation of acetyl CoA, the citric acid cycle, and the electron transport chain.
Glycolysis: Glycolysis yields a net of 2 ATP and 2 NADH molecules from one glucose molecule.
Formation of Acetyl CoA: Before entering the citric acid cycle, each glucose molecule is split into two molecules of pyruvate, generating 2 NADH molecules. This step does not yield direct ATP.
Citric Acid Cycle: Each acetyl CoA (from two pyruvate molecules) entering the cycle produces 3 NADH, 1 FADH2, and 1 ATP equivalent (GTP). Since two acetyl CoA molecules are generated from one glucose molecule, the total yield is 6 NADH, 2 FADH2, and 2 ATP equivalents.
Electron Transport Chain (ETC): The NADH and FADH2 molecules generated in previous steps donate electrons to the ETC. The precise ATP yield varies, but around 2.5 to 3 ATP are generated per NADH and around 1.5 to 2 ATP per FADH2.
Adding up the totals from each step:
- Glycolysis: 2 ATP
- Formation of Acetyl CoA: 0 ATP
- Citric Acid Cycle: 2 ATP (equivalent)
- ETC: Approximately 28-34 ATP (considering NADH and FADH2 contributions)
Overall, the estimated net ATP yield from one glucose molecule through aerobic respiration is around 32 to 38 ATP, depending on the specific shuttle mechanisms and efficiency of the ETC.
Question: (iii) Trace the fate of hydrogen atoms removed from glucose during glycolysis when oxygen is present in muscle cells; compare this to the fate of hydrogen atoms removed from glucose when the amount of the available oxygen is insuicient to support aerobic respiration.
Trace the fate of hydrogen atoms from glucose during glycolysis with oxygen present in muscle cells; compare it to when oxygen availability is insufficient for aerobic respiration.
When oxygen is present in muscle cells, the fate of hydrogen atoms from glucose is as follows:
Glycolysis: During glycolysis, glucose is broken down to pyruvate, producing NADH in the process. NADH transfers its hydrogen atoms to the electron transport chain (respiratory chain) in the mitochondria.
Pyruvate Decarboxylation: Pyruvate enters the mitochondria, where it undergoes oxidative decarboxylation to form acetyl-CoA. This process generates more NADH.
Krebs Cycle (Citric Acid Cycle): Acetyl-CoA enters the Krebs cycle, leading to a series of reactions that release high-energy electrons and produce more NADH and FADH2.
Electron Transport Chain (Respiratory Chain): NADH and FADH2 donate their electrons to the electron transport chain, where a series of oxidation-reduction reactions occur, leading to the generation of a proton gradient across the inner mitochondrial membrane. This gradient is used to produce ATP through oxidative phosphorylation, utilizing oxygen as the final electron acceptor to form water.
When there is insufficient oxygen for aerobic respiration (anaerobic conditions), the fate of hydrogen atoms from glucose is different:
Glycolysis: Glycolysis still occurs, producing pyruvate and NADH, but the electron transport chain cannot operate effectively without oxygen.
Fermentation: In the absence of sufficient oxygen, pyruvate is converted to lactic acid (in muscles) or ethanol (in yeast) through fermentation. This process regenerates NAD+ from NADH, allowing glycolysis to continue. However, no additional ATP is generated through this pathway.
Question: (iv) Sketch Kreb’s cycle and discuss its energy yielding steps.
Sketch of Krebs Cycle and discussion of its energy-yielding steps:
The Krebs cycle, also known as the citric acid cycle, is a series of biochemical reactions that occur in the mitochondria. It plays a crucial role in generating energy from carbohydrates, fats, and proteins. Here’s an overview of the energy-yielding steps in the Krebs cycle:
Acetyl-CoA Formation: Acetyl-CoA, derived from pyruvate, enters the cycle by combining with oxaloacetate to form citrate.
Isomerization: Citrate is isomerized through aconitase to form isocitrate.
Energy Release Step 1: Isocitrate undergoes oxidative decarboxylation by isocitrate dehydrogenase, producing α-ketoglutarate and NADH.
Energy Release Step 2: α-Ketoglutarate is further oxidized by α-ketoglutarate dehydrogenase, yielding succinyl-CoA, CO2, and another molecule of NADH.
Succinyl-CoA Conversion: Succinyl-CoA reacts with GDP to form succinate and GTP (which can be converted to ATP).
Dehydrogenation: Succinate is oxidized to fumarate by succinate dehydrogenase, producing FADH2.
Hydration: Fumarate is hydrated to form malate.
Energy Release Step 3: Malate is oxidized by malate dehydrogenase, generating NADH and regenerating oxaloacetate, which can then enter the cycle again.
Overall, the Krebs cycle yields high-energy molecules in the form of NADH, FADH2, and GTP (ATP precursor). These molecules carry the energy extracted from glucose through various oxidative reactions. The NADH and FADH2 molecules generated in the cycle subsequently donate their electrons to the electron transport chain, leading to the synthesis of ATP through oxidative phosphorylation.
Question: (v) Describe various steps involved in oxidative break down of glucose to pyruvate.
Steps involved in oxidative breakdown of glucose to pyruvate
The oxidative breakdown of glucose to pyruvate occurs through a series of steps in a process known as glycolysis. Here’s an overview of the key steps involved:
Glucose Activation: Glucose, a 6-carbon sugar, is phosphorylated twice, using two molecules of ATP. This forms fructose-1,6-bisphosphate.
Cleavage: Fructose-1,6-bisphosphate is split into two 3-carbon molecules, dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P).
Energy Harvesting: G3P is converted to pyruvate through a series of reactions that generate NADH and ATP. NAD+ is reduced to NADH as G3P is oxidized to 1,3-bisphosphoglycerate. In the process, 2 molecules of NADH and 4 molecules of ATP (through substrate-level phosphorylation) are produced.
Pyruvate Formation: Dihydroxyacetone phosphate (DHAP) is isomerized to G3P, and both molecules are converted to pyruvate. In the process, 2 more molecules of ATP are generated.
At the end of glycolysis, one molecule of glucose is converted into two molecules of pyruvate while generating a net of 2 molecules of NADH and 4 molecules of ATP (2 ATP molecules are initially used, but 4 ATP molecules are produced, leading to a net gain of 2 ATP molecules).
Question: (vi) Sketch respiratory electron transport chain. Discuss the signiicance of ETC.
Sketch respiratory electron transport chain. Discuss the significance of ETC
The respiratory electron transport chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane. It plays a crucial role in aerobic respiration, where electrons derived from molecules like NADH and FADH2 are passed through the chain, leading to the generation of a proton gradient across the inner mitochondrial membrane. This gradient is used to synthesize ATP through chemiosmotic coupling.
Here’s a simplified sketch of the respiratory electron transport chain:
NADH/FADH2
↓
Complex I (NADH dehydrogenase)
↓
Ubiquinone (Coenzyme Q)
↓
Complex III (Cytochrome bc1 complex)
↓
Cytochrome c
↓
Complex IV (Cytochrome c oxidase)
↓
Oxygen (O2)
The significance of the ETC includes
ATP Production: The main purpose of the ETC is to generate a proton gradient (proton motive force) across the inner mitochondrial membrane. This gradient is then used by ATP synthase to synthesize ATP from ADP and inorganic phosphate in a process known as oxidative phosphorylation.
Efficient Energy Conversion: The ETC maximizes the energy yield from glucose oxidation. NADH and FADH2, generated in previous metabolic reactions (such as glycolysis and the citric acid cycle), donate their high-energy electrons to the chain. These electrons are then sequentially passed along the chain, releasing energy with each transfer.
Oxygen Utilization: Oxygen serves as the final electron acceptor in the ETC, ultimately combining with electrons and protons to form water. This prevents the accumulation of excess electrons and ensures the continuation of the electron transport process.
Regulation of Cellular Respiration: The ETC is regulated to maintain the balance between ATP demand and production. If the demand for ATP increases, the rate of electron transport and oxygen consumption will also increase.
Overall, the respiratory electron transport chain is a vital component of aerobic metabolism, allowing cells to efficiently produce ATP, the primary energy currency of the cell, while utilizing the energy released during the controlled transfer of electrons.
Question: (vii) Compare photosynthesis with respiration in plants.
Compare photosynthesis with respiration in plants
Photosynthesis and respiration are two interconnected processes in plants, but they have distinct differences. Photosynthesis is an anabolic process occurring in chloroplasts, where light energy is used to synthesize glucose and oxygen from carbon dioxide and water. Respiration, on the other hand, is a catabolic process that takes place in mitochondria, breaking down glucose to produce ATP and carbon dioxide. While photosynthesis stores energy in glucose, respiration releases energy from glucose.
Additionally, photosynthesis releases oxygen, while respiration consumes oxygen. Overall, these processes are complementary, as the oxygen and glucose produced during photosynthesis are used in respiration, and the carbon dioxide and ATP generated in respiration are utilized in photosynthesis.
Question: (viii) Explain the diference between the cyclic and non-cyclic photophosphorylation with the help of Z scheme.
Difference between cyclic and non-cyclic photophosphorylation with the help of the Z scheme
Cyclic and non-cyclic photophosphorylation are two pathways of the light-dependent reactions in photosynthesis. The Z scheme illustrates the flow of electrons in these pathways. In non-cyclic photophosphorylation, electrons from water are excited by light energy and transferred to photosystem II, then to photosystem I, and finally used to reduce NADP+ to NADPH. Protons are pumped across the thylakoid membrane, creating a proton gradient for ATP synthesis through ATP synthase. In cyclic photophosphorylation, electrons cycle back from photosystem I to the electron transport chain, generating ATP but not NADPH. This pathway primarily serves to produce ATP and balance the energy demands of the cell.
Question: (ix) Give an account of light-independent reactions of photosynthesis.
Light-independent reactions of photosynthesis
The light-independent reactions of photosynthesis, also known as the Calvin cycle or the dark reactions, take place in the stroma of the chloroplasts. These reactions do not directly require light energy and primarily aim to convert carbon dioxide (CO2) into glucose.
The Calvin cycle can be divided into three main stages: carbon fixation, reduction, and regeneration of ribulose-1,5-bisphosphate (RuBP).
Carbon Fixation: In this stage, an enzyme called ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) captures carbon dioxide from the atmosphere and incorporates it into a five-carbon sugar molecule called ribulose-1,5-bisphosphate (RuBP). This forms an unstable six-carbon compound, which quickly splits into two molecules of 3-phosphoglycerate (3-PGA).
Reduction: During this phase, ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) produced in the light-dependent reactions are used to convert the 3-PGA molecules into a higher-energy three-carbon compound called glyceraldehyde-3-phosphate (G3P). Some G3P molecules are then used to regenerate RuBP, while others proceed to the next stage.
Regeneration of RuBP: A series of reactions involving ATP help regenerate RuBP from G3P molecules. This is important to keep the Calvin cycle running and allow for continuous carbon fixation.
Ultimately, for every three molecules of carbon dioxide that enter the Calvin cycle, one molecule of G3P is produced. However, only one out of every six G3P molecules is directly used to form glucose, while the rest are recycled back into the cycle to regenerate RuBP.
The light-independent reactions are crucial for the synthesis of glucose and other carbohydrates, which serve as energy storage molecules for plants. These reactions also indirectly depend on the products of the light-dependent reactions, such as ATP and NADPH, which provide the necessary energy and reducing power to drive the conversion of carbon dioxide into glucose.
Overall, the light-independent reactions of photosynthesis play a vital role in maintaining the energy balance of plants and the ecosystems they support.