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CELLULAR ENERGY – CH. 8 All cellular activities require energy to live. Nearly all energy for life comes from the Sun. Autotrophs – make their own food Heterotrophs – ingest food to obtain energy. Metabolism – all chemical reactions in a cell. ALL organisms use a 2-step process to get the energy they need: 1. Chemical energy from organic molecules (i.e. glucose) is used to make ATP (this is cellular respiration) 2. ATP provides the energy we need (for muscle contraction, synthesizing molecules, etc.) On average, each ATP molecule in our body is used and resynthesized more than 30 times per minute when we are at rest and more than 500 times per minute during strenuous exercise. ATP (adenosine triphosphate) – most important biological molecule that provides energy. Any time the cell needs energy the bonds of the ATP molecule are broken to release energy. triphosphate = 3 phosphate groups (PO43-) Remember PO43is a charged ion. Since each PO43- ion is negative and like charges repel each other, it takes a lot of energy to put the 3 PO43- groups together. ATP ADP (adenosine diphosphate) when a bond is broken and energy is released ADP can then bond with another phosphate group and form ATP again. This is a renewable cycle so energy is always available for cells to use. 1. PHOTOSYNTHESIS – Energy Storage -anabolic pathway that uses energy to make larger molecules from smaller ones Light energy from the sun is converted into chemical energy. Plants use the sun’s energy to make simple sugars. These simple sugars are converted to complex carbohydrates, like starches, which store energy. 6CO2 + 6H2O + ☼ C6H12O6 + 6O2 NOTE: products are glucose and oxygen! Occurs in chloroplasts TWO PHASES of Photosynthesis: Light Energy Light – Dependent reactions (phase 1) Light – Independent reactions (phase 2) Glucose A. PHASE 1. Light-dependent reactions – convert light energy into chemical energy ATP produced in these reactions is used to fuel lightindependent reactions. Light is captured in the chloroplasts B. PHASE 2. Light-independent reactions (Calvin Cycle) – Does not require light ATP formed in phase 1 is not stable enough to provide all energy needs so phase 2 converts energy into organic molecules such as glucose. Takes the products made in the light-dependent reactions to make sugars. Occurs in the chloroplasts. 2. CELLULAR RESPIRATION – Energy Releasing -catabolic pathway in which energy is released as larger molecules are broken into smaller ones C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP) occurs in both plant and animal cells Purpose make ATP for energy NOTE: products of photosynthesis are reactants of cellular respiration. 3 Parts of cellular respiration: 1. Glycolysis – anaerobic (does not require oxygen) Occurs in cytoplasm Breaks down glucose Fermentation - follows glycolysis when oxygen is not present. o Lactic Acid fermentation – continues glycolysis to continue production of ADP. (muscle fatigue, cheese making) o Alcoholic fermentation – used by some types of bacteria (like yeast) to make CO2 and ethyl alcohol --- used to make bread and alcoholic beverages. 2 - Kreb’s cycle – aerobic (requires oxygen) citric acid cycle Occurs in mitochondria 3 - Electron transport – aerobic Most ATP produced here (~32) Occurs in mitochondria