Cellular Respiration & Photosynthesis

• Cellular respiration and photosynthesis are fundamental biological processes
• These processes involve energy conversion and are essential for life on Earth
• Cellular respiration is the process by which cells break down organic molecules to produce ATP
• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy
• ATP (adenosine triphosphate) is the primary energy currency of cells
• ATP is used to power various cellular processes

Cellular Respiration

• Cellular respiration is a catabolic process
• Organic molecules are broken down to release energy
• The released energy is then used to generate ATP
• Cellular respiration occurs in most organisms, including plants, animals, and microorganisms
• The overall equation for cellular respiration is: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
• Glucose (C6H12O6) is oxidized in the presence of oxygen (O2) to produce carbon dioxide (CO2), water (H2O), and ATP

Glycolysis

• Glycolysis is the first stage of cellular respiration
• It occurs in the cytoplasm of the cell
• Glycolysis involves the breakdown of glucose into two molecules of pyruvate
• This process also yields a small amount of ATP and NADH
• Glycolysis does not require oxygen
• It can occur under both aerobic and anaerobic conditions
• The net ATP production in glycolysis is 2 ATP molecules per glucose molecule
• Glycolysis consists of several steps, each catalyzed by a specific enzyme
• The end product, pyruvate, can then enter the Krebs cycle under aerobic conditions

Krebs Cycle

• The Krebs cycle (also known as the citric acid cycle) is the second stage of cellular respiration
• This occurs in the mitochondrial matrix in eukaryotes
• Pyruvate is converted into acetyl-CoA, which enters the Krebs cycle
• In the Krebs cycle, acetyl-CoA is oxidized to produce CO2, ATP, NADH, and FADH2
• The Krebs cycle is a cyclical pathway
• The starting molecule is regenerated in the final step
• For each molecule of glucose, the Krebs cycle produces 2 ATP, 6 NADH, and 2 FADH2
• These electron carriers (NADH and FADH2) are crucial for the next stage, electron transport chain

Electron Transport Chain (ETC)

• The electron transport chain is the final stage of cellular respiration
• It occurs in the inner mitochondrial membrane in eukaryotes
• NADH and FADH2 donate electrons to the ETC
• Electrons are passed down a series of protein complexes
• Energy is released during electron transfer
• This energy is used to pump protons (H+) across the inner mitochondrial membrane
• This creates an electrochemical gradient
• Protons then flow back down the gradient through ATP synthase
• ATP synthase uses the energy to generate ATP from ADP and inorganic phosphate
• This process is called oxidative phosphorylation
• Oxygen is the final electron acceptor in the ETC, forming water
• The ETC generates the majority of ATP produced during cellular respiration

ATP Production

• ATP is produced through substrate-level phosphorylation and oxidative phosphorylation
• Substrate-level phosphorylation occurs during glycolysis and the Krebs cycle
• This involves the direct transfer of a phosphate group from a substrate molecule to ADP
• Oxidative phosphorylation occurs during the electron transport chain
• It involves the use of energy from the electron transport chain to generate ATP
• Cellular respiration generates a significant amount of ATP
• Approximately 36-38 ATP molecules can be produced from one glucose molecule under ideal conditions
• ATP is used to power various cellular processes such as muscle contraction, nerve impulse transmission, and protein synthesis

Photosynthesis

• Photosynthesis is an anabolic process
• Light energy is converted into chemical energy
• Photosynthesis occurs in plants, algae, and some bacteria
• The overall equation for photosynthesis is: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2
• Carbon dioxide (CO2) and water (H2O) are used to produce glucose (C6H12O6) and oxygen (O2) using light energy

Light-Dependent Reactions

• The light-dependent reactions occur in the thylakoid membranes of chloroplasts
• Light energy is absorbed by chlorophyll and other pigments
• This energy is used to split water molecules into protons, electrons, and oxygen
• This process is called photolysis
• Electrons are passed along an electron transport chain
• ATP and NADPH are produced
• ATP and NADPH are used in the next stage, the light-independent reactions (Calvin cycle)
• Oxygen produced during the light-dependent reactions is released as a byproduct

Calvin Cycle (Light-Independent Reactions)

• The Calvin cycle occurs in the stroma of chloroplasts
• Carbon dioxide is captured from the atmosphere and converted into glucose
• Carbon fixation is the initial step, where CO2 is incorporated into an organic molecule
• ATP and NADPH from the light-dependent reactions are used to power the Calvin cycle
• The Calvin cycle involves a series of enzymatic reactions
• The starting molecule is regenerated in the final step
• Glucose produced during the Calvin cycle can be used for energy or stored as starch

Chlorophyll and Other Pigments

• Chlorophyll is the primary pigment involved in photosynthesis
• Chlorophyll absorbs light energy, particularly in the blue and red regions of the electromagnetic spectrum
• Other pigments, such as carotenoids, also contribute to photosynthesis
• These pigments absorb light energy in different regions of the spectrum
• They transfer the energy to chlorophyll
• Different types of chlorophyll exist, such as chlorophyll a and chlorophyll b
• Chlorophyll a is the main photosynthetic pigment in plants

Factors Affecting Photosynthesis

• Several factors can affect the rate of photosynthesis
• Light intensity, carbon dioxide concentration, and temperature are crucial factors
• Increasing light intensity can increase the rate of photosynthesis up to a certain point
• Increasing carbon dioxide concentration can also increase the rate of photosynthesis up to a certain point
• Temperature affects the rate of enzymatic reactions involved in photosynthesis
• Extreme temperatures can denature enzymes and reduce the rate of photosynthesis
• Water availability is also important
• Water stress can reduce the rate of photosynthesis

Energy Conversion

• Photosynthesis converts light energy into chemical energy
• Cellular respiration converts chemical energy (glucose) into ATP
• These processes are interconnected
• Photosynthesis produces the glucose and oxygen that are used in cellular respiration
• Cellular respiration produces the carbon dioxide and water that are used in photosynthesis
• Energy flows through ecosystems
• Photosynthesis captures energy from the sun
• Cellular respiration releases energy from organic molecules
• ATP is the primary energy currency that links these processes