1 About This Course
2 Course Contents at a Glance
3 Learning Outcomes
4 Request Access
5 Pacing
7 Why It Matters: Introduction to Biology
8 Introduction to Characteristics of Life
11 Introduction to The Study of Biology
12 The History of Biology
13 The Diversity of Life
16 Introduction to the Process of Science
20 Putting It Together: Introduction to Biology
25 Evidence of Evolution
26 Misconceptions of Evolution
29 What is a Species?
30 Types of Speciation
31 Reconnection
33 Introduction to the Evolution of Populations
34 Population Genetics
37 Hardy-Weinberg Principle of Equilibrium
40 Taxonomy
42 Cladistics
43 Perspectives on the Phylogenetic Tree
44 Putting It Together: History of Life
45 Why It Matters: Prokaryotes
47 Evolutionary History of Prokaryotes
49 Introduction to the Structure of Prokaryotes
50 The Prokaryotic Cell
53 Introduction to Prokaryotic Metabolism
56 Role of Prokaryotes in Ecosystems
57 Introduction to Bacterial Diseases in Humans
58 Long History of Bacterial Disease
59 Antibiotic Resistance
63 Microbes and the Human Body
64 Putting It Together: Prokaryotes
66 Introduction to the Characteristics of Protists
67 Cell Structure and Motility
68 Metabolism
72 Primary Producers
73 Protists as Decomposers
75 Putting It Together: Protists
78 Fungal Structure and Habitats
80 Reproduction
82 Introduction to the Ecology of Fungi
84 Mutualistic Relationships
85 Introduction to Fungal Parasites and Pathogens
88 Antifungal Therapy
91 Fungi as Antibiotics
93 Putting It Together: Fungi
97 Green Algae: Precursors of Land Plants
98 Bryophytes
101 Evolution of Seed Plants
102 Gymnosperms
103 Angiosperms
106 Why It Matters: Plant Structure and Function
108 Plant Cells
110 Stems
111 Leaves
112 Roots
114 Transport of Water and Solutes in Plants
116 Plant Growth
118 Plant Photorespiration
120 Why It Matters: Plant Reproduction
122 Stages of a Plant’s Life Cycle
124 Sexual Reproduction in Angiosperms
129 Natural and Artificial Asexual Reproduction
133 Introduction to the Evolutionary History of the Animal Kingdom
143 Introduction to Animal Form and Function
146 Introduction to Animal Primary Tissues
148 Epithelial Tissues
152 Processes of Animal Reproduction and Development
153 Embryological Development
157 Thermoregulation
160 Introduction to Phylum Porifera
163 Introduction to Phylum Cnidaria
164 Characteristics of Phylum Cnidaria
165 Classes in the Phylum Cnidaria
170 Phylum Nemertea
172 Phylum Annelida
173 Introduction to Superphylum Ecdysozoa
176 Subphylums of Arthropoda
177 Introduction to Superphylum Deuterostomia
178 Characteristics of Superphylum Deuterostomia
181 Why It Matters: Vertebrates
183 Characteristics of Chordates
185 Craniates
187 Jawless Fishes
188 Jawed Fishes
191 The Life Cycle of Amphibians
194 Amniotic Animals
195 Evolution of Amniotes
196 Introduction to Reptiles
198 Classes of Reptiles
206 Evolution of Humans
208 Why It Matters: Overview of Body Systems
211 Maintaining Homeostasis
212 Blood Calcium and Glucose Levels
215 Endocrine System
217 Sensory Systems
220 Respiratory System
222 Digestive System
224 The Muscular System
226 Integumentary System
230 What Is Ecology?
231 Levels of Ecological Research
232 Branches of Ecology
234 Biogeography and Species Distribution
247 Life Histories and Natural Selection
251 Competition
252 Symbiosis
254 Putting It Together: Ecology of Living Things
262 The Carbon Cycle
265 The Sulfur Cycle
268 Evidence for Global Climate Change
277 Current Biodiversity
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163 Introduction to Phylum Cnidaria
163 Introduction to Phylum Cnidaria
What you’ll learn to do: Identify the common characteristics of phylum Cnidaria
Cnidarians represent a more complex level of organization than Porifera. They possess outer and inner tissue layers that sandwich a noncellular mesoglea. Cnidarians possess a well-formed digestive system and carry out extracellular digestion. The cnidocyte is a specialized cell for delivering toxins to prey as well as warning off predators. Cnidarians have separate sexes and have a lifecycle that involves morphologically distinct forms. These animals also show two distinct morphological forms—medusoid and polypoid—at various stages in their lifecycle.