Metabolism in Cells Chapter 4.1 PDF

Metabolism in cells Rice (Oryza sativa) is a staple food for half the world’s population, especially in humid tropics and subtropics of Asia, Africa, and Latin America. It is a cereal crop, like wheat and corn, and is a type of grass cultivated for its hard, dry seeds (which are technica...

Metabolism in cells Rice (Oryza sativa) is a staple food for half the world’s population, especially in humid tropics and subtropics of Asia, Africa, and Latin America. It is a cereal crop, like wheat and corn, and is a type of grass cultivated for its hard, dry seeds (which are technically fruits). Rice is unique because it is usually grown submerged in 10-15 cm of water, a condition in which most crops would die due to lack of oxygen, but rice roots thrive. Rice contains about 10% protein, so diets reliant on rice need to be supplemented with meat, fish, or protein-rich plants like beans. Modern milling processes, which convert brown rice into white rice by removing the bran and germ, reduce its nutritional value, making white rice less nutritious than brown rice. Photosynthesis is the chemical process by which rice and other plants capture energy to produce carbohydrates. Cellular respiration releases energy from these Metabolism Metabolism refers to all chemical processes in a cell, consisting of anabolic and catabolic reactions. Anabolic reactions (anabolism) involve storing energy by synthesizing large, complex molecules from simpler ones (e.g., photosynthesis synthesizes glucose from CO₂ and water). Catabolic reactions (catabolism) involve releasing energy by breaking down large molecules into simpler ones (e.g., cellular 2 respiration breaks down glucose into CO₂ and water). Metabolism Oxidation-reduction (redox) reactions are critical in metabolism, involving the transfer of electrons between molecules. Oxidation is the loss of electrons, while reduction is the gain of electrons. Oxidation and reduction always occur together; as one molecule loses electrons (oxidized), another gains them (reduced), along with the associated energy. 2 Metabolism In cells, oxidation often involves the removal of a hydrogen atom, while reduction involves the gain of hydrogen. The electron transport chain is the sequential transfer of electrons between molecules, crucial for 2 energy flow in photosynthesis and cellular respiration.  Photosynthesis Photosynthesis is a process through which plants, algae, and certain prokaryotes convert solar energy into chemical energy. This transformation produces carbohydrates (formed from carbon dioxide and water) and releases oxygen (O₂) as a byproduct. The significance of photosynthesis cannot be overstated, as it forms the foundation of the energy cycle in the biosphere. Without photosynthetic organisms, there would be no source of energy or oxygen for animals and other non-photosynthetic organisms, including humans. Light exhibits properties of both waves and particles Light as Part of the Electromagnetic Spectrum: Light is a small segment of the electromagnetic spectrum, which includes various forms of radiation, from gamma rays (with very short wavelengths) to radio waves (with very long wavelengths). The visible spectrum, which ranges from 380 to 760 nanometers (nm), is the part of this spectrum that human eyes can detect. Wave and Photon Properties: Light behaves both as a wave (characterized by wavelength) and as a particle, made up of discrete energy packets called photons. The energy of a photon is inversely proportional to its wavelength; shorter wavelengths (e.g., violet light) carry more energy than longer wavelengths (e.g., red light). Role of Visible Light in Photosynthesis: Photosynthesis relies on the visible light portion of the spectrum because photons in this range have just the right amount of energy to excite electrons in biological molecules, particularly in chlorophyll. This excitation leads to the transfer of electrons, a key step in converting light Light exhibits properties of both waves and particles Energy of Photons: Shorter wavelengths (e.g., ultraviolet) have too much energy and can damage biological molecules by breaking chemical bonds. Conversely, longer wavelengths (e.g., radio waves) do not carry enough energy to excite the electrons necessary for photosynthesis. Photon Interaction with Atoms: The lowest energy state an electron possesses is called the ground state, but energy can be added to an electron to boost it to a higher energy level. When an electron is raised to a higher energy level than its ground state, the electron is said to be energized. When a photon is absorbed by an atom, it excites an electron, raising it to a higher energy level. The electron can either return to its ground state, releasing energy as heat or light, or it may leave the atom and be accepted by another molecule, which is what happens in photosynthesis. In plants and algae, photosynthesis takes place in chloroplasts Chloroplasts and Mesophyll Cells: Chlorophyll, the green pigment responsible for capturing light energy, is confined to chloroplasts, which are primarily located in the mesophyll cells of leaves. These cells contain 20 to 100 chloroplasts each and are surrounded by air spaces filled with water vapor, facilitating gas exchange through microscopic pores called stomata. Chloroplast Structure: Chloroplasts are enclosed by two membranes (outer and inner). Inside the chloroplast, the inner membrane surrounds a fluid-filled area called the stroma, which contains enzymes necessary for producing carbohydrates. Suspended within the stroma are interconnected stacks of disc-like sacs called thylakoids. Thylakoids form stacks known as grana, and their membranes house the pigments essential for photosynthesis. In plants and algae, photosynthesis takes place in chloroplasts. Pigments in Photosynthesis: Chlorophyll, the main pigment, absorbs light primarily in the blue and red regions of the visible spectrum. Green light is mostly reflected, giving plants their characteristic green appearance. Chlorophyll a is the principal pigment that initiates the process of photosynthesis, while chlorophyll b acts as an accessory pigment, absorbing different wavelengths of light. Role of Accessory Pigments: Carotenoids, which are yellow and orange pigments, extend the range of light that can be utilized in photosynthesis by absorbing wavelengths not captured by chlorophyll. They also protect the chlorophyll and other components of the thylakoid membrane from damage due to excess light energy. Chlorophyll is the main photosynthetic pigment Spectrophotometry: The absorption spectrum of a pigment measures how well it absorbs different wavelengths of light. A spectrophotometer is used to generate this spectrum, and chlorophyll a and b absorb light differently, as shown in absorption spectra. Action Spectrum: The action spectrum measures the effectiveness of different wavelengths of light in driving photosynthesis. It correlates with the absorption spectrum of chlorophyll but not exactly, due  Chlorophyll is the main photosynthetic pigment Engelmann’s Experiment (1883): Engelmann demonstrated the action spectrum of photosynthesis using the alga Spirogyra. He exposed the algae to different wavelengths of light and measured photosynthesis by tracking the movement of oxygen-loving bacteria toward regions where photosynthesis produced the most oxygen—primarily in the blue and red areas. This confirmed that chlorophyll is the main pigment responsible for photosynthesis. Accessory Pigments: While chlorophyll absorbs most of the light energy, accessory pigments like carotenoids transfer excitation energy to chlorophyll. This explains why the action spectrum of photosynthesis doesn't match chlorophyll’s absorption spectrum exactly. Accessory pigments also become visible in autumn when chlorophyll breaks down, leaving orange and yellow pigments in leaves.  In photosynthesis, plants convert light energy to chemical energy stored in carbohydrate molecules Raw Materials: The main raw materials for photosynthesis are carbon dioxide (CO₂) and water (H₂O). These are converted into glucose (C₆H₁₂O₆), a carbohydrate, using light energy. Photosynthesis can be summarized by the chemical equation: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O. This shows that carbon dioxide and water are converted into water, glucose and oxygen , using light energy and chlorophyll as catalysts. Energy Conversion: The light energy absorbed by chlorophyll is used to split water molecules, releasing oxygen, electrons, and protons. These hydrogen ions (protons and electrons) eventually contribute to the formation of carbohydrates like glucose.  In photosynthesis, plants convert light energy to chemical energy stored in carbohydrate molecules Two Stages of Photosynthesis: Light-dependent reactions: Occur in the thylakoid membranes of chloroplasts, where light energy is used to generate ATP and NADPH, and water is split to release oxygen. Carbon fixation reactions (Calvin Cycle): Occur in the stroma of the chloroplast. These reactions use ATP and NADPH from the light- dependent stage to fix carbon dioxide into organic molecules like glucose. Division of Labor: The two stages are spatially separated, with light-dependent reactions occurring in the thylakoids and carbon fixation in the stroma of the chloroplast. Thank you, ocean! Produces oxygen About half of Earth’s oxygen comes from the The ocean does more for us than ocean. That’s basically every other breath you take, thanks to microscopic organisms and most people realise. marine algae, called phytoplankton, that take up carbon dioxide and use energy from the sun to produce oxygen.