Biology Chapter 11: Bioenergetics
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Questions and Answers

What carbon sources do aquatic photosynthetic organisms use?

Dissolved CO2, bicarbonates, and soluble carbonates

What is the atmospheric concentration of CO2?

0.03 - 0.04 percent

Stomata are responsible for the entry of CO2 into the leaves during photosynthesis.

True

What regulates the opening and closing of stomata?

<p>Guard cells</p> Signup and view all the answers

Which processes are part of photosynthesis?

<p>Chemiosmosis</p> Signup and view all the answers

What molecules are produced during light-dependent reactions?

<p>ATP and NADPH</p> Signup and view all the answers

Which type of molecule serves as the main energy carrier in cells?

<p>ATP</p> Signup and view all the answers

What is the primary function of the Calvin cycle in photosynthesis?

<p>Synthesis of sugar from CO2</p> Signup and view all the answers

Which of the following enzymes is involved in the Calvin cycle?

<p>Rubisco</p> Signup and view all the answers

The dark reactions of photosynthesis can only occur in the presence of light.

<p>False</p> Signup and view all the answers

Match the following photosynthetic pigments with their associated functions:

<p>Chlorophyll a = Primary pigment in photosystems Chlorophyll b = Accessory pigment Carotenoids = Protective pigments</p> Signup and view all the answers

The process of energy synthesis in both cyclic and non-cyclic photophosphorylation is called ______.

<p>Chemiosmosis</p> Signup and view all the answers

What are the two main types of respiration in living organisms?

<p>Aerobic and anaerobic respiration</p> Signup and view all the answers

What is the end product of glycolysis?

<p>Pyruvic acid</p> Signup and view all the answers

What is bioenergetics?

<p>The quantitative study of energy relationships and energy conversions in biological systems.</p> Signup and view all the answers

Which of the following is a product of photosynthesis?

<p>Oxygen</p> Signup and view all the answers

Photosynthesis occurs both day and night.

<p>False</p> Signup and view all the answers

What is the function of chlorophyll in photosynthesis?

<p>To absorb light energy</p> Signup and view all the answers

What is the overall equation for photosynthesis?

<p>6CO2 + 6H2O + light energy → C6H12O6 + 6O2</p> Signup and view all the answers

Plants release oxygen during ______.

<p>photosynthesis</p> Signup and view all the answers

What is the source of oxygen released during photosynthesis?

<p>Water</p> Signup and view all the answers

What is the role of NADPH in photosynthesis?

<p>It acts as a reducing power to help convert carbon dioxide into sugar.</p> Signup and view all the answers

What are accessory pigments in chloroplasts used for?

<p>To broaden light absorption</p> Signup and view all the answers

Chlorophyll a is the only pigment involved in the light-dependent reactions.

<p>False</p> Signup and view all the answers

Who proposed that water is the source of oxygen during photosynthesis?

<p>Van Niel</p> Signup and view all the answers

What does the absorption spectrum indicate?

<p>It shows the relative abilities of different pigments to absorb various wavelengths of light.</p> Signup and view all the answers

Photosynthesis contributes to the carbon dioxide concentration in the atmosphere.

<p>False</p> Signup and view all the answers

Chlorophyll is mainly located in the ______ of plant cells.

<p>chloroplasts</p> Signup and view all the answers

Which of the following chlorophylls absorbs mainly in the blue-green range?

<p>Chlorophyll a</p> Signup and view all the answers

Hydroponics are the plants grown in water culture.

<p>True</p> Signup and view all the answers

Calcium is an essential element for chlorophyll formation.

<p>True</p> Signup and view all the answers

Chlorosis means yellowing of leaves due to deficiency of certain essential elements of plant nutrition.

<p>True</p> Signup and view all the answers

List four features of a leaf which show that it is able to carry out photosynthesis effectively.

<p>Thin structure, large surface area, presence of chlorophyll, and stomata for gas exchange.</p> Signup and view all the answers

Summarise the role of water in photosynthesis.

<p>Water provides electrons and protons, and is a reactant in the light-dependent reactions.</p> Signup and view all the answers

What are T.W. Engelman and Melvin Calvin famous for?

<p>T.W. Engelman is known for his work on photosynthesis and Melvin Calvin is famous for the Calvin cycle.</p> Signup and view all the answers

What is the difference between an action spectrum and an absorption spectrum?

<p>An action spectrum shows the rate of photosynthesis at different wavelengths, while an absorption spectrum shows which wavelengths are absorbed by pigments.</p> Signup and view all the answers

What is the role of accessory pigments in light absorption?

<p>Accessory pigments assist in capturing light energy and transferring it to chlorophyll.</p> Signup and view all the answers

When and why is there not a net exchange of CO2 and O2 between the leaves and the atmosphere?

<p>There is no net exchange during the night when photosynthesis halts but respiration continues.</p> Signup and view all the answers

What is the net production of ATP during glycolysis?

<p>The net production of ATP during glycolysis is 2 ATP molecules.</p> Signup and view all the answers

What is the main difference between photophosphorylation and oxidative phosphorylation?

<p>Photophosphorylation uses light energy to add a phosphate group to ADP, while oxidative phosphorylation uses the energy released by the electron transport chain.</p> Signup and view all the answers

What is the location of the electron transport chain (ETC) and chemiosmosis in photosynthesis and cellular respiration?

<p>In photosynthesis, it occurs in the thylakoid membrane; in cellular respiration, it occurs across the inner mitochondrial membrane.</p> Signup and view all the answers

How did the evolution of photosynthesis affect the metabolic pathway?

<p>It introduced the ability to convert light energy to chemical energy, altering energy dynamics on Earth.</p> Signup and view all the answers

How does the absorption spectrum of chlorophyll a differ from that of chlorophyll b?

<p>Chlorophyll a absorbs light primarily in the blue-violet and red parts of the spectrum, while chlorophyll b absorbs light in the blue and orange-red wavelengths.</p> Signup and view all the answers

Why are the carotenoids usually not obvious in the leaves?

<p>Carotenoids are masked by chlorophyll, which dominates in green leaves.</p> Signup and view all the answers

How is the formation of vitamin A linked with the eating of carrots?

<p>Carrots contain beta-carotene, which the body converts into vitamin A.</p> Signup and view all the answers

Explain the roles of NAD+ and FAD in aerobic respiration.

<p>NAD+ and FAD act as electron carriers, transporting electrons to the electron transport chain.</p> Signup and view all the answers

Summarise how much energy (as ATP) is made available to the cell from a single glucose molecule by glycolysis, the formation of acetyl CoA, the citric acid cycle, and the electron transport chain.

<p>Approximately 36 to 38 ATP molecules are produced from one glucose molecule through these processes.</p> Signup and view all the answers

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 oxygen is insufficient to support aerobic respiration.

<p>When oxygen is present, hydrogen atoms are used in the electron transport chain; when insufficient oxygen is available, they are converted to lactic acid.</p> Signup and view all the answers

Sketch Krebs cycle and discuss its energy yielding steps.

<p>The Krebs cycle involves several steps where acetyl CoA is oxidized, resulting in ATP, NADH, and FADH2 production.</p> Signup and view all the answers

Describe various steps involved in oxidative breakdown of glucose to pyruvate.

<p>The steps include glycolysis, oxidation of pyruvate to acetyl CoA, and entry into the Krebs cycle.</p> Signup and view all the answers

Sketch respiratory electron transport chain. Discuss the significance of ETC.

<p>The ETC is a series of proteins where electrons are transferred, leading to ATP synthesis via chemiosmosis.</p> Signup and view all the answers

Compare photosynthesis with respiration in plants.

<p>Photosynthesis converts light energy into chemical energy, while respiration breaks down glucose to release energy.</p> Signup and view all the answers

Explain the difference between cyclic and non-cyclic photophosphorylation with the help of the Z scheme.

<p>Cyclic photophosphorylation produces ATP only, while non-cyclic produces ATP and NADPH.</p> Signup and view all the answers

Give an account of light-independent reactions of photosynthesis.

<p>Light-independent reactions (Calvin cycle) use ATP and NADPH to convert CO2 into glucose.</p> Signup and view all the answers

Study Notes

Bioenergetics Overview

  • Bioenergetics studies energy relationships and conversions in biological systems, adhering to thermodynamics.
  • All living organisms require free energy for survival, sourced primarily from solar energy.
  • While organisms can't use sunlight directly, they utilize chemical energy from food, like sugars.

Photosynthesis

  • Photosynthesis converts low-energy inorganic carbon (CO2) and hydrogen (water) into high-energy carbohydrates (glucose) using light energy, primarily through chlorophyll.
  • Overall photosynthesis equation:
    6CO2 + 12H2O + light → C6H12O6 + 6O2 + 6H2O
  • Photosynthesis produces glucose and oxygen, while respiration uses products of photosynthesis.
  • Photosynthesis occurs only during daylight, contra respiration which happens day and night.

Compensation Point

  • At twilight, the rates of photosynthesis and respiration may equal, resulting in no net gas exchange; termed the compensation point.
  • Increased light intensity boosts photosynthesis, leading to higher CO2 demand, and oxygen release surpasses cellular respiration needs.

Source of Atmospheric Oxygen

  • Oxygen produced during photosynthesis derives from the splitting of water, confirmed through isotopic tracer experiments involving heavy oxygen (O18).

Chloroplasts

  • Chloroplasts, located in the mesophyll cells of leaves, are the primary sites for photosynthesis.
  • Each chloroplast contains thylakoids where light reactions occur and stroma for the dark reactions.
  • Chlorophylls embedded in thylakoid membranes absorb sunlight, generating ATP and NADPH.

Photosynthetic Pigments

  • Pigments absorb specific visible light wavelengths (380-750 nm); chlorophylls are the main pigments.
  • Accessory pigments, like carotenoids, broaden light absorption spectrum, protecting chlorophyll from excess light.
  • Absorption spectrum for chlorophyll peaks at blue (~430 nm) and red (~670 nm) wavelengths.

Light as Energy Source

  • Light is electromagnetic energy crucial for photosynthesis, but only about 1% is absorbed by leaves.
  • Action spectrum studies show that photosynthesis is most effective where chlorophyll absorbs light, though carotenoids enhance energy transfer.

Role of Carbon Dioxide

  • CO2 is essential for photosynthesis; terrestrial plants utilize atmospheric CO2, while aquatic organisms use dissolved forms.
  • Stomata regulate CO2 intake, opening during the day and closing at night, influenced by guard cells' structure and rhythm.

Reactions of Photosynthesis

  • Photosynthesis is a redox process composed of light-dependent (light) and light-independent (dark) reactions.
  • Light-dependent reactions harness sunlight directly, while dark reactions utilize products of the light phase (ATP and NADPH) to convert CO2 into sugars.### Photosynthesis Overview
  • Photosynthesis consists of light-dependent reactions (energy conversion) and light-independent reactions (energy conservation) that convert light energy into chemical energy stored in glucose.
  • Light-dependent reactions convert solar energy into ATP and NADPH, which provide power for the synthesis of sugars in the Calvin cycle.

Light-Dependent Reactions

  • Occur in thylakoid membranes, where photosynthetic pigments absorb sunlight, organized into photosystems (PS I and PS II).
  • PS II absorbs light at 680 nm (P680), while PS I absorbs at 700 nm (P700).
  • Light energy excites electrons in chlorophyll at the reaction centers, initiating electron transport.
  • The primary electron acceptor captures excited electrons from chlorophyll, leading to ATP production via chemiosmosis.
  • Non-cyclic electron flow involves both photosystems, producing ATP and NADPH and releasing oxygen from photolysis of water.
  • Cyclic electron flow involves only PS I and generates ATP but no oxygen or NADPH.

Photophosphorylation

  • ATP synthesis occurs during the light-dependent reactions driven by light energy.
  • Non-cyclic photophosphorylation produces ATP through a series of redox reactions involving electron transport chains and protons (H+) gradients in thylakoid membranes.

Light-Independent Reactions (Calvin Cycle)

  • Occur in the stroma of chloroplasts, using ATP and NADPH from light reactions to convert carbon dioxide into sugars.
  • The process consists of three stages: Carbon Fixation, Reduction, and Regeneration of RuBP.
  • Carbon fixation incorporates CO2 into ribulose bisphosphate (RuBP) via Rubisco, forming a 6-carbon intermediate that splits into two 3-carbon molecules (3-PGA).
  • Reduction converts PGA into glyceraldehyde 3-phosphate (G3P) using ATP and NADPH, yielding one net G3P for every six produced.
  • Regeneration of RuBP occurs with the rearrangement of G3P molecules, allowing the cycle to continue.

Respiration

  • Respiration is the metabolic process that provides energy to cells by breaking down carbon compounds.
  • Involves both external respiration (gas exchange) and cellular respiration (energy production).
  • Cellular respiration can be aerobic (with oxygen) or anaerobic (without oxygen).
  • Glycolysis splits glucose into pyruvate in the cytosol; oxygen availability determines the next steps.

Anaerobic Respiration

  • Alcoholic fermentation converts pyruvic acid into alcohol and CO2 in yeast.
  • Lactic acid fermentation converts pyruvic acid into lactic acid in anaerobic conditions, such as intense muscle activity.
  • Both fermentation pathways yield small energy amounts from glucose compared to aerobic respiration.

Role of Mitochondria

  • Mitochondria serve as cellular powerhouses, responsible for ATP production through respiration processes.
  • They have an outer membrane and an inner membrane organized into cristae, creating compartments that facilitate energy transfer via enzymes.

Adenosine Triphosphate (ATP)

  • ATP is a key energy carrier in cells, composed of adenine, ribose, and three phosphate groups.
  • The terminal phosphate bond releases energy (approximately 7.3 Kcal) upon hydrolysis, essential for various cellular processes like muscle contraction and active transport.

Biological Oxidation & Cellular Respiration

  • Biological oxidation involves energy-releasing reactions, primarily through oxidation-reduction processes.
  • Cellular respiration stages include glycolysis (anaerobic), pyruvic acid oxidation, Krebs cycle, and the respiratory chain (aerobic).
  • Glycolysis occurs in the cytosol, while subsequent stages occur in mitochondria, requiring oxygen for efficiency.### Glycolysis
  • Glycolysis breaks down glucose into pyruvic acid in both aerobic and anaerobic conditions.
  • It occurs in the cytosol and involves a series of enzyme-catalyzed steps.
  • ATP and NAD (nicotinamide adenine dinucleotide) are essential for glycolysis.
  • Divided into two phases: preparatory phase and oxidative phase.

Preparatory Phase

  • The first step involves transferring a phosphate from ATP to glucose creating glucose-6-phosphate.
  • Glucose-6-phosphate is converted into fructose-6-phosphate.
  • Another ATP adds a second phosphate, forming fructose 1,6-bisphosphate.
  • Fructose 1,6-bisphosphate splits into two three-carbon molecules: G3P and dihydroxyacetone phosphate (DHAP).

Oxidative Phase

  • PGAL (3-phosphoglyceraldehyde) is oxidized, transferring electrons to NAD, forming NADH.
  • Inorganic phosphate adds to PGAL, producing 1,3-bisphosphoglycerate (BPG).
  • A phosphate from BPG transfers to ADP, forming ATP and producing 3-phosphoglycerate (3-PG).
  • 3-PG is further processed into 2-phosphoglycerate (2-PG), which transforms into phosphoenolpyruvate (PEP).
  • PEP donates its phosphate to ADP, yielding ATP and resulting in pyruvate.

Pyruvic Acid Oxidation

  • Pyruvate is converted into acetic acid (2-carbon) through decarboxylation, releasing CO2.
  • Acetic acid binds with coenzyme-A to form acetyl CoA.
  • Hydrogen atoms are transferred to NAD during this conversion.

Krebs Cycle (Citric Acid Cycle)

  • Acetyl CoA enters the Krebs cycle, combining with oxaloacetate to produce citrate (6-carbon).
  • The cycle involves a series of reactions, including the production of isocitrate and further oxidations.
  • Decarboxylation occurs, yielding a-ketoglutarate.
  • ATP is synthesized from the energy changes during the conversion of a-ketoglutarate to succinate.
  • Succinate is oxidized to fumarate, with FAD reducing to FADH2.

Completion of the Krebs Cycle

  • Fumarate converts to malate through hydration.
  • Malate undergoes another oxidation to regenerate oxaloacetate, completing the cycle.

Respiratory Chain and Oxidative Phosphorylation

  • NADH and H+ produced in the Krebs cycle transfer electrons to the respiratory chain.
  • Coenzyme Q and cytochromes aid in electron transport and oxidation-reduction reactions.
  • Electrons ultimately reduce oxygen, forming water and enabling ATP synthesis via oxidative phosphorylation.

Oxidative Phosphorylation Mechanism

  • Occurs within the inner mitochondrial membrane through chemiosmosis.
  • Proton movement across the membrane drives ATP synthesis.
  • Each pair of H atoms entering the chain yields three ATP molecules.

Other Key Points

  • Hydroponics refers to plants grown in nutrient-rich water solutions.
  • Calcium is critical for chlorophyll formation and overall plant health.
  • Chlorosis is a condition of yellowing leaves due to nutrient deficiency.

Energy Yield Summary

  • Glycolysis, formation of acetyl CoA, Krebs cycle, and electron transport chain release total ATP from a single glucose molecule.
  • Comparison of conditions with sufficient and insufficient oxygen availability influences hydrogen atom fate during respiration.

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