Chapter 5 Flashcards
Photosynthesis and Cellular Respiration
Why is life on Earth possible?
Because the Sun provides a constant input of energy in the form of light.
What do living organisms use energy for?
To trap, store, and use energy to maintain and sustain cells.
What do all organisms need to survive?
Some form of energy.
What are autotrophs?
Organisms like green plants that photosynthesize using chloroplasts to trap the Sun’s energy.
What are heterotrophs?
Organisms that cannot photosynthesize and must consume autotrophs or other heterotrophs to obtain energy.
What organelle allows autotrophs to carry out photosynthesis?
The chloroplast.
What is the main function of photosynthesis?
To convert solar energy into chemical energy and store it in sugars and other carbohydrates.
What are the by-products of photosynthesis?
Oxygen, ATP molecules, and some heat.
How is energy stored in autotrophs after photosynthesis?
Some is used immediately, and some is stored as starch or converted to fat for future use.
Where is the chemical energy of glucose stored?
In the chemical bonds of the glucose molecule.
How do organisms release the energy from glucose?
By breaking down its chemical bonds.
What is cellular respiration?
A process in which mitochondria break down carbohydrates and other energy-rich compounds to produce ATP.
What is the full name of ATP?
Adenosine triphosphate.
Why is ATP called the “energy currency” of the cell?
Because cells “spend” ATP to power nearly all cellular activities.
What are some cellular activities powered by ATP?
Active transport, chromosome movement, cilia/flagella motion, muscle contraction, and synthesis of biomolecules.
How is energy released from ATP?
By breaking the bond to the third phosphate group.
What is produced when ATP releases energy?
ADP (adenosine diphosphate) and a free phosphate group.
How is ATP regenerated?
By adding a free phosphate group to ADP, which requires an input of energy.
How often is ATP recycled in a cell?
Thousands of times each day.
Why are parts of plants green?
Because they contain chlorophyll, a pigment that traps solar energy.
Where is chlorophyll found?
In the thylakoid membranes inside chloroplasts.
What is the function of chloroplasts?
To trap solar energy and convert it into chemical energy through photosynthesis.
How many chloroplasts can a photosynthetic cell have?
Between 40 and 200.
How many chloroplasts can be in one mm² of a typical leaf?
Around 500,000.
What are thylakoids?
Flattened sacs within the chloroplasts where chlorophyll is located.
What are grana?
Stacks of thylakoids within the chloroplasts.
What is the stroma?
The fluid-filled space inside chloroplasts that contains materials needed for carbohydrate synthesis.
What is the function of mitochondria?
To efficiently extract energy from food and produce ATP.
What is the matrix in mitochondria?
The fluid-filled space inside the inner membrane containing materials for breaking down carbohydrates.
What are cristae in mitochondria?
Folded structures in the inner membrane that increase surface area for ATP production.
How do chloroplasts and mitochondria compare in size?
Chloroplasts are larger (4–6 µm wide), while mitochondria are smaller (0.5–1.0 µm wide).
Which organisms have mitochondria?
Eukaryotic organisms: plants, animals, fungi, and protists.
What is the balanced chemical equation for photosynthesis?
6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂
What is the balanced chemical equation for cellular respiration?
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
How are photosynthesis and cellular respiration related?
The products of one are the reactants of the other.
Are photosynthesis and cellular respiration exact opposites?
Their overall reactions appear opposite, but each involves many intermediate steps.
Why don’t cells use combustion to release energy from glucose?
Combustion requires high temperatures that would destroy living cells.
What are metabolic pathways?
Series of step-by-step chemical reactions where the product of one reaction becomes the reactant for the next.
What does metabolism refer to?
All the chemical reactions in a cell that support life functions.
What are anabolic pathways?
Metabolic pathways that build larger molecules from smaller ones and require energy.
What are catabolic pathways?
Metabolic pathways that break down larger molecules into smaller ones and release energy.
Why can’t living cells use heat to activate reactions?
Heat would destroy the cells.
What do enzymes do in metabolic pathways?
They act as biological catalysts, lowering the activation energy needed for reactions.
Can each metabolic reaction occur without an enzyme?
No, each reaction requires a specific enzyme to proceed efficiently.
What is oxidation?
The loss of electrons by an atom or molecule.
What is reduction?
The gain of electrons by an atom or molecule.
What is a redox reaction?
A chemical reaction involving both oxidation and reduction.
Why must oxidation and reduction happen together?
Because electrons lost in oxidation must be gained by another compound (reduction).
Do reduced compounds have more or less energy than oxidized ones?
More energy.
What does “reducing power” mean?
The ability of a reduced molecule to donate electrons and provide energy.
What is the function of chloroplasts in cells?
To carry out photosynthesis and trap solar energy.
Where is chlorophyll located in the chloroplast?
In the thylakoid membranes.
What are grana?
Stacks of thylakoids within the chloroplast.
What is the stroma?
The fluid-filled space in chloroplasts containing enzymes for carbohydrate synthesis.
What gives plants their green color?
Chlorophyll.
What is the main function of mitochondria?
To break down high-energy compounds and generate ATP.
What is the matrix in mitochondria?
The fluid-filled inner space containing chemicals for cellular respiration.
What are cristae in mitochondria?
Folds in the inner membrane that increase surface area for ATP production.
What are metabolic pathways?
Series of step-by-step chemical reactions in processes like photosynthesis and cellular respiration.
What role do enzymes play in metabolic pathways?
Enzymes act as biological catalysts that reduce the energy needed to start reactions.
Why are enzymes necessary for metabolic reactions in living organisms?
Without enzymes, the reactions couldn’t occur at temperatures suitable for life.
What happens to a compound when it is oxidized?
It loses electrons.
What happens to a compound when it is reduced?
It gains electrons.
Do reduced or oxidized compounds have more chemical energy?
Reduced compounds have more chemical energy than oxidized ones.
What does photosynthesis transform?
Sunlight energy into the chemical energy of glucose.
How much glucose do photosynthetic organisms produce annually?
About 1.4 × 10¹⁵ kg.
What are some uses of glucose in plants?
Converted to cellulose, other sugars, starch, and amino acids.
What percentage of a plant’s dry weight is from photosynthesis products?
Nearly 95%.
What is the summary equation of photosynthesis?
6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + O₂
What does the arrow in the photosynthesis equation represent?
Over 100 individual chemical reactions.
What are the two main sets of photosynthesis reactions?
Light-dependent and light-independent reactions.
What is produced in the light-dependent reactions?
ATP and NADPH.
What happens in the light-independent reactions?
ATP and NADPH reduce CO₂ to form glucose.
Where are pigments located in chloroplasts?
In the thylakoid membranes.
What is a pigment?
A compound that absorbs certain wavelengths of light and reflects others.
Why are plants green?
Chlorophyll absorbs red and blue light but reflects green light.
What does an absorbance spectrum show?
How much light of different colors a compound absorbs.
What are carotenoids and what do they do?
Pigments that absorb blue and green light; they appear yellow, orange, or red.
What can beta-carotene be converted into?
Vitamin A, then retinal (used in vision).
Why do plants have multiple pigments?
To absorb a broader range of sunlight.
What does an action spectrum show?
The effectiveness of different wavelengths of light in photosynthesis.
What are photosystems?
Clusters of pigments in thylakoid membranes that capture light energy.
What are the two types of photosystems?
Photosystem I (PSI) and Photosystem II (PSII).
What is the role of the reaction centre in a photosystem?
It receives energy from pigments and excites an electron.
What happens to an excited electron in PSII?
It is passed to an electron-acceptor, and a water molecule replaces the lost electron.
What is the electron transport system?
A series of molecules that transfer electrons and release energy.
What is the energy from the electron transport used for?
To move hydrogen ions into the thylakoid space, creating a concentration gradient.
How is the hydrogen ion gradient like a dam?
It stores potential energy that is used to generate ATP.
What happens in PSI after light is absorbed?
An electron is excited and passed to an electron-acceptor.
How is the lost electron in PSI replaced?
By an electron from PSII that has moved through the transport system.
What happens to the excited electron from PSI?
It reduces NADP⁺ to form NADPH.
What is NADPH used for?
Providing reducing power in the light-independent reactions.
Why can’t hydrogen ions diffuse freely across the thylakoid membrane?
The membrane is impermeable to charged particles.
What provides a pathway for hydrogen ions to move through the thylakoid membrane?
ATP synthase.
What is chemiosmosis?
The linking of hydrogen ion movement to ATP production.
How is ATP generated during chemiosmosis?
Hydrogen ions flow through ATP synthase, which bonds a phosphate group to ADP.
Why are scientists interested in how plants trap solar energy?
To design technology that mimics this process for clean energy.
Why isn’t solar energy enough to meet society’s energy needs?
Solar cells at Earth’s surface don’t produce enough energy.
What is a clean alternative fuel being researched?
Hydrogen.
Why isn’t hydrogen used more widely as a fuel?
It’s not found freely in nature and requires energy to extract.
How do plants use water in photosystem II?
They split it using light energy, releasing oxygen and using hydrogen ions.
What is the goal of creating an artificial photosystem II?
To split water and collect hydrogen gas as clean fuel.
When can ATP and NADPH be used to synthesize glucose?
When they are present in sufficient amounts in the stroma.
What is the Calvin-Benson cycle?
A series of reactions that synthesize carbohydrates in the stroma.
Who discovered the Calvin-Benson cycle?
Melvin Calvin and Andrew Benson.
What technique was used to discover the Calvin-Benson cycle?
Radioactive carbon isotope tracing.
What is the first step of the Calvin-Benson cycle?
Fixation of carbon dioxide with RuBP.
What is RuBP?
Ribulose bisphosphate, a five-carbon compound.
What does carbon fixation produce initially?
An unstable six-carbon compound that breaks into two three-carbon compounds.
What type of plants form three-carbon compounds during carbon fixation?
C3 plants.
What is the second step of the Calvin-Benson cycle?
Reduction of three-carbon compounds into PGAL.
What provides the energy and reducing power for this reduction?
ATP and NADPH.
What is PGAL?
Glyceraldehyde-3-phosphate, a high-energy three-carbon sugar.
What happens to PGAL in the cycle?
Some forms glucose, the rest regenerates RuBP.
How many turns of the cycle are needed to make one glucose?
Six.
How many PGAL molecules are made in six cycles?
12 PGAL molecules.
How many PGAL molecules are used to regenerate RuBP?
10
How many PGAL molecules are used to make glucose?
2
What are the two major phases of photosynthesis?
Light-dependent and light-independent reactions.
What pigments absorb light for photosynthesis?
Chlorophylls a and b, and carotenoids.
What happens when pigments absorb light?
Electrons are excited (energized).
What happens to an excited electron from PSII?
It enters the electron transport system.
What is the energy from electron transport used for?
To pump hydrogen ions and create a concentration gradient.
What generates ATP from this gradient?
Chemiosmosis via ATP synthase.
What replaces the lost electron in PSII?
An electron from water.
What happens to oxygen from split water?
It’s released as molecular oxygen.
What happens to an excited electron in PSI?
It reduces NADP⁺ to NADPH.
Where does the Calvin-Benson cycle occur?
In the stroma of the chloroplast.
What catalyzes the carbon fixation reaction in the Calvin-Benson cycle?
Rubisco (ribulose bisphosphate carboxylase).
What is the most abundant protein on Earth?
Rubisco.
How much rubisco is synthesized per second by photosynthetic organisms?
About 1000 kg per second.
What is cellular respiration?
Cellular respiration is the process by which cells release energy from glucose and oxygen to produce ATP, carbon dioxide, and water.
What is the equation for cellular respiration?
C6H12O6(s) + O2(g) → 6CO2(g) + 6H2O(l) + energy (ATP)
What is the difference between aerobic and anaerobic respiration?
Aerobic respiration requires oxygen to produce ATP, while anaerobic respiration occurs without oxygen.
What is fermentation?
Fermentation is an anaerobic process where glucose is broken down to produce ATP, but it does not involve an electron transport system.
Where does glycolysis occur?
Glycolysis occurs in the cytoplasm of all cells.
What is the role of glycolysis in cellular respiration?
Glycolysis splits glucose into two molecules of pyruvate and produces a small amount of ATP.
What happens to pyruvate when oxygen is available?
When oxygen is available, pyruvate is transported to the mitochondria, where it is prepared for the Krebs cycle.
What is the main function of the Krebs cycle?
The main function of the Krebs cycle is to transform the energy of glucose into reducing power (NADH and FADH2) and produce ATP.
What is chemiosmosis?
Chemiosmosis is the process in which a hydrogen ion concentration gradient is used to generate ATP in the electron transport system.
Why is oxygen important in aerobic cellular respiration?
Oxygen acts as the final electron acceptor in the electron transport system, allowing the process to continue and produce ATP.
What is the main product of anaerobic cellular respiration?
The main product of anaerobic cellular respiration is ATP, but it is less efficient compared to aerobic respiration.
What is the difference between lactate fermentation and ethanol fermentation?
Lactate fermentation converts pyruvate into lactate, while ethanol fermentation converts pyruvate into ethanol and carbon dioxide.
What is oxygen debt in muscle cells?
Oxygen debt occurs when muscles function anaerobically, producing lactate and causing muscle fatigue until oxygen is available to clear the lactate.
How does fermentation occur in yeast?
Yeast performs ethanol fermentation, converting pyruvate into ethanol and carbon dioxide under anaerobic conditions.
What are some industrial uses of fermentation?
Fermentation is used to produce alcohol, baked goods, and biofuels like ethanol.
What are the by-products of anaerobic cellular respiration in some bacteria?
By-products of anaerobic respiration in bacteria can include sulfur, nitrite, nitrogen, or methane, depending on the electron acceptor used.
How is ethanol produced for fuel in Canada?
In Canada, ethanol is produced by fermenting grains like corn and wheat, with yeast converting glucose into ethanol and carbon dioxide.
What is the environmental impact of burning ethanol as a fuel?
Burning ethanol produces CO2, but it is considered less harmful than gasoline because ethanol is made from renewable resources.
What is the main equation for cellular respiration?
C₆H₁₂O₆(s) + O₂(g) → 6CO₂(g) + 6H₂O(l) + energy (ATP)
What does aerobic cellular respiration require?
Aerobic cellular respiration requires oxygen to produce ATP.
What is the role of oxygen in aerobic cellular respiration?
Oxygen is the final electron acceptor in the electron transport system, which is necessary for the process to proceed.
What organisms perform anaerobic cellular respiration?
Some bacteria, archaea, and organisms in anoxic environments perform anaerobic cellular respiration.
What is fermentation?
Fermentation is an anaerobic process that does not use an electron transport system to produce ATP, but instead occurs in the cytoplasm.
What is the main difference between anaerobic cellular respiration and fermentation?
Anaerobic respiration involves an electron transport system and produces more ATP, whereas fermentation does not involve an electron transport system and produces less ATP.
What is produced in lactate fermentation?
In lactate fermentation, pyruvate is converted to lactate (lactic acid), and NADH is oxidized to NAD+.
What is the role of NAD+ in glycolysis?
NAD+ is reduced to NADH during glycolysis, which helps carry high-energy electrons for later stages of cellular respiration.
What happens during the Krebs cycle?
During the Krebs cycle, acetyl-CoA is oxidized, releasing CO₂, and producing NADH, FADH₂, and ATP.
What is chemiosmosis in cellular respiration?
Chemiosmosis is the process where the energy from a hydrogen ion concentration gradient is used to produce ATP via ATP synthase.
How does the electron transport chain contribute to ATP production?
The electron transport chain pumps hydrogen ions across the mitochondrial membrane, creating a gradient that drives ATP synthesis via chemiosmosis.
What are the waste products of aerobic cellular respiration?
The waste products of aerobic cellular respiration are carbon dioxide (CO₂) and water (H₂O).
How do muscle cells generate energy during strenuous activity?
Muscle cells use glycolysis to produce ATP, and when oxygen is insufficient, lactate fermentation occurs to sustain energy production.
Why does oxygen debt occur in muscles?
Oxygen debt occurs when muscle cells use more energy than can be supplied aerobically, leading to the accumulation of pyruvate, which is converted to lactate.
What is the end product of ethanol fermentation?
The end products of ethanol fermentation are ethanol and carbon dioxide.
How does fermentation differ in yeast compared to muscle cells?
In yeast, fermentation produces ethanol and CO₂, while in muscle cells, fermentation produces lactate.
What is the role of the electron transport system in aerobic respiration?
The electron transport system transfers high-energy electrons from NADH and FADH₂ to oxygen, which helps produce the majority of ATP in aerobic respiration.
What is the importance of the Krebs cycle in cellular respiration?
The Krebs cycle transforms energy from glucose into reducing power (NADH and FADH₂) and ATP, essential for energy production in cells.
Why is anaerobic respiration less efficient than aerobic respiration?
Anaerobic respiration is less efficient because it produces fewer ATP molecules than aerobic respiration.
What happens if oxygen is not available during cellular respiration?
If oxygen is not available, pyruvate from glycolysis undergoes fermentation instead of entering the Krebs cycle and electron transport.
How do organisms that perform anaerobic respiration produce ATP without oxygen?
These organisms use alternative electron acceptors like sulfate, nitrate, or carbon dioxide, and an electron transport system to produce ATP.
