PHOTOSYNTHESIS and RESPIRATION

SECTION 1 Photosynthesis

Energy and Living Things Photosynthesis is the process in which light energy is converted into chemical energy. Autotrophs (plants and some bacteria) use the sun’s energy to carry out photosynthesis, and are therefore the foundation of all living systems.

Breaking Down Food For Energy Autotrophs are organisms that use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds. Heterotrophs are organisms that must consume other organisms as food to get their energy.

Photosynthesis Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to produce carbohydrates and oxygen. Photosynthesis has 3 stages: Stage 1: absorption of light energy Stage 2: conversion of light energy into chemical energy, temporarily stored in ATP and NADPH Stage 3: storage of chemical energy in ATP and NADPH powers the formation of organic molecules

Photosynthesis Pigments are light-absorbing substances that absorb only certain wavelengths of light and reflect all others. Chlorophyll is the primary pigment involved in photosynthesis. Chlorophyll absorbs mostly blue and red light and reflects green and yellow light. This reflection of green and yellow light makes many plants, especially their leaves, look green.

Photosynthesis occurs in the chloroplasts and uses the pigment chlorophyll.

Photosynthesis REACTANTS: water, carbon dioxide, light energy The following chemical equation summarizes photosynthesis: 6H2O + 6CO2 + light  C6H12O6 + 6O2 REACTANTS: water, carbon dioxide, light energy PRODUCTS: glucose, oxygen

Photosynthesis: Where Does it Occur? Thylakoid membrane

Photosynthesis: Thylakoids Thylakoids are disk-shaped structures found in the chloroplasts of leaf cells that contain clusters of embedded pigments. These pigment molecules in the thylakoids of chloroplasts absorb light energy. Electrons in the pigments are “excited” by light, and jump from the chlorophyll molecules to other nearby molecules in the thylakoid membrane. The series of molecules along the thylakoid membrane that excited electrons pass through as they jump along the chlorophyll molecules is called the electron transport chain.

Three Factors That Affect Photosynthesis 1.) amount of light – The rate of photosynthesis increases as light intensity increases until all the pigments are being used. At this saturation point, the reactions of the Calvin cycle cannot proceed any faster. 2.) concentration of carbon dioxide – Once a certain concentration of carbon dioxide is present, photosynthesis cannot proceed any faster. 3.) range of temperature – Like all metabolic processes, photosynthesis involves many enzyme-assisted chemical reactions. Unfavorable temperatures may inactivate certain enzymes.

SECTION 2 Cellular Respiration

Cellular Respiration Before energy from food can be utilized, it must be transferred to ATP in a process called cellular respiration. Cellular respiration is the set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. To put it simply, cellular respiration is the process where cells produce energy from carbohydrates.

Cellular Respiration Cellular respiration is the opposite of photosynthesis. The reactants of photosynthesis – carbon dioxide and water – are the products of cellular respiration. The products of photosynthesis – glucose and oxygen – are the reactants of cellular respiration. Cellular respiration releases much of the energy in food to make ATP. ATP provides cells with energy they need to carry out the activities of life.

Cells Transfer Energy From Food To ATP When cells break down food molecules, some of the energy is released into the atmosphere as heat, while the rest is stored temporarily in molecules of ATP. Adenosine triphosphate (ATP) is a nucleotide with two extra energy-storing phosphate groups. ATP molecules are often called the “energy currency” of a cell.

Adenosine Triphosphate RED = ribose (a 5-carbon sugar) BLUE = adenine (a nitrogenous base) GREEN = phosphate groups

ATP Stores and Releases Energy The energy from ATP is released when the bonds that hold the phosphate groups together are broken. The removal of a phosphate group from ATP (3 phosphates) produces ADP (adenosine diphosphate -- 2 phosphates), which releases energy in a way that enables cells to use the energy. Cells use energy released by this reaction to power metabolism.

ATP FYI: The human body uses about 1 million molecules of ATP per second per cell. There are more than 100 trillion cells in the human body. That is about 1 X 1020, or 100,000,000,000,000,000,000 ATP molecules used in the body each second.

Cellular respiration can be aerobic respiration (with oxygen) or anaerobic respiration (without oxygen). Cellular respiration begins in the cytoplasm, and ends in the mitochondria.

Aerobic Respiration Respiration that requires oxygen to form energy. Cardio exercises, which involve maintaining a steady heart rate at 60-80% of one’s maximum, use aerobic respiration because there is enough oxygen to sustain muscle power. Sports activities that use aerobic metabolism include distance running, swimming, biking, and jogging.

Anaerobic Respiration Respiration that does not require oxygen to produce energy. Intense workouts and sports activities that use much energy within short bursts of activity usually require anaerobic respiration, which provides an immediate source of power. This process is needed especially in activities that increase the heart rate beyond 80% of its maximum. Examples of anaerobic sports include football, sprinting and wrestling

Cellular Respiration REACTANTS: glucose, oxygen, ADP, extra phosphate The chemical formula for cellular respiration is: C6H12O6 + 6O2 + ADP + P  6CO2 + 6H2O + ATP REACTANTS: glucose, oxygen, ADP, extra phosphate PRODUCTS: carbon dioxide, water, ATP The process summarized by the equation begins in the cytoplasm of a cell and ends in the mitochondria.

Cellular Respiration: Stage 1 Glycolysis Stage 1 of cellular respiration is called glycolysis. Glycolysis is the stage of cellular respiration where glucose is broken down in the cytoplasm, converted to pyruvate, and produces a small amount of ATP and NADPH. Glycolysis – uses 2 ATP, but produces 4 ATP – net gain = 2 ATP

Cellular Respiration: Stage 2 The Krebs Cycle Stage 2 of cellular respiration is known as the Krebs cycle and is also called aerobic respiration. Cellular respiration is called an aerobic process because it requires oxygen. C6H12O6 + 6O2 + ADP + P  6CO2 + 6H2O + ATP A two-carbon molecule combines with a four-carbon molecule during the Krebs cycle.

Fermentation: Occurs in the Absence of Oxygen If oxygen (O2) is not present in sufficient amounts, the mitochondrial membrane cannot function. Energy molecules (ATP and NADH) cannot be created in abundance. So, what does the cell do to continue to break down organic compounds and release energy if not enough oxygen is present? FERMENTATION

Production of ATP The total amount of ATP a cell is able to harvest from each glucose molecule that enters glycolysis depends on the presence or absence of oxygen. When oxygen is present, aerobic respiration occurs. When oxygen is not present, anaerobic respiration, or fermentation, occurs instead. Fermentation is the anaerobic process that continues the breakdown of carbohydrates when there is not enough oxygen for aerobic respiration.