In a food chain the initial organism is usually

A food web consists of all the food chains in a single ecosystem. Each living thing in an ecosystem is part of multiplefood chains. Each food chain is one possible path that energy and nutrients may take as they move through the ecosystem. All of the interconnected and overlapping food chains in an ecosystem make up a food web. Trophic Levels Organisms in food webs are grouped into categories called trophic levels. Roughly speaking, these levels are divided into producers (first trophic level), consumers, and decomposers (last trophic level). Producers Producers make up the first trophic level. Producers, also known as autotrophs, make their own food and do not depend on any other organism for nutrition. Most autotrophs use a process called photosynthesis to create food (a nutrient called glucose) from sunlight, carbon dioxide, and water. Plants are the most familiar type of autotroph, but there are many other kinds. Algae, whose larger forms are known as seaweed, are autotrophic. Phytoplankton, tiny organisms that live in the ocean, are also autotrophs. Some types of bacteria are autotrophs. For example, bacteria living in active volcanoes use sulfur, not carbon dioxide, to produce their own food. This process is called chemosynthesis. Consumers The next trophic levels are made up of animals that eat producers. These organisms are called consumers. Consumers can be carnivores (animals that eat other animals) or omnivores (animals that eat both plants and animals). Omnivor...

An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. Because autotrophs produce their own food, they are sometimes called producers. Plants are the most familiar type of autotroph, but there are many different kinds of autotrophicorganisms. Algae, which live in water and whose larger forms are known as seaweed, is autotrophic. Phytoplankton, tiny organisms that live in the ocean, are autotrophs. Some types of bacteria are autotrophs. Most autotrophs use a process called photosynthesis to make their food. In photosynthesis, autotrophs use energy from the sun to convert water from the soil and carbon dioxide from the air into a nutrient called glucose. Glucose is a type of sugar. The glucose gives plantsenergy. Plants also use glucose to make cellulose, a substance they use to grow and build cell walls. All plants with green leaves, from the tiniest mosses to towering fir trees, synthesize, or create, their own food through photosynthesis. Algae, phytoplankton, and some bacteria also perform photosynthesis. Some rare autotrophs produce food through a process called chemosynthesis, rather than through photosynthesis. Autotrophs that perform chemosynthesis do not use energy from the sun to produce food. Instead, they make food using energy from chemical reactions, often combining hydrogen sulfide or methane with oxygen. Organisms that use chemosynthesis live in extreme environments, where the toxic chemicals needed f...

4 Cell Structure • Introduction • 4.1 Studying Cells • 4.2 Prokaryotic Cells • 4.3 Eukaryotic Cells • 4.4 The Endomembrane System and Proteins • 4.5 The Cytoskeleton • 4.6 Connections between Cells and Cellular Activities • Key Terms • Chapter Summary • Visual Connection Questions • Review Questions • Critical Thinking Questions • 6 Metabolism • Introduction • 6.1 Energy and Metabolism • 6.2 Potential, Kinetic, Free, and Activation Energy • 6.3 The Laws of Thermodynamics • 6.4 ATP: Adenosine Triphosphate • 6.5 Enzymes • Key Terms • Chapter Summary • Visual Connection Questions • Review Questions • Critical Thinking Questions • 7 Cellular Respiration • Introduction • 7.1 Energy in Living Systems • 7.2 Glycolysis • 7.3 Oxidation of Pyruvate and the Citric Acid Cycle • 7.4 Oxidative Phosphorylation • 7.5 Metabolism without Oxygen • 7.6 Connections of Carbohydrate, Protein, and Lipid Metabolic Pathways • 7.7 Regulation of Cellular Respiration • Key Terms • Chapter Summary • Visual Connection Questions • Review Questions • Critical Thinking Questions • 14 DNA Structure and Function • Introduction • 14.1 Historical Basis of Modern Understanding • 14.2 DNA Structure and Sequencing • 14.3 Basics of DNA Replication • 14.4 DNA Replication in Prokaryotes • 14.5 DNA Replication in Eukaryotes • 14.6 DNA Repair • Key Terms • Chapter Summary • Visual Connection Questions • Review Questions • Critical Thinking Questions • 15 Genes and Proteins • Introduction • 15.1 The Genetic Code • 15.2...

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