Zoology Lecture Notes (Animal Architecture) PDF

ZOOLOGY LECTURE 3: Sept. 17 Animal concept, architecture, Sponges 1 Last week: We used Evolution theory to understand change in zoology...

ZOOLOGY LECTURE 3: Sept. 17 Animal concept, architecture, Sponges 1 Last week: We used Evolution theory to understand change in zoology Today: Animal concept Architecture: from simple to complex Sponges: the simplest animals Animal characteristics? Is there a set of characteristics that define what we call ”animals”…? 2 1  Animal characteristics? Is there a set of characteristics that define what we call ”animals”…? The following are not the best: Animals move (run or swim or fly) Animals eat, hunt or fish Animals respond or are sensitive to stimuli Animals have behavior…. Some animals are not very good at that Some plants are rather good at that 3 Animal’s four distinctive characteristics: 1. Heterotrophic… (*) Not autotrophic 2. Multicellular… (*) Not unicellular 3. Eukariote… Not prokariote 4. Have no cell walls… (*) Are there any issues…? 4 2  Animal’s four distinctive characteristics: ISSUES? 1. Are all animals really heterotrophic…? Some animals live associated with algae… (symbiosis) so they don’t always eat… Others live associated to chemosynthetic bacteria (vent worms)… and don’t need to eat… 5 Animal’s four distinctive characteristics: ISSUES? 2. Are all animals pluricellullar…? Is that true? A zygote (fertilized egg) is a single cell… So virtually all animals are, at some stage, single-cell creatures 6 3  1. Heterotrophic Animal’s four 2. Multicellular distinctive characteristics: 3. Eukariote 4. Have no cell walls We use these characteristics to unify animals. And we use everything else to describe them and classify them … ANIMAL ARCHITECTURE: FROM SIMPLE TO COMPLEX Over the course of evolution, animal architecture is the result of various major “decisions” 7 ANIMAL ARCHITECTURE: FROM SIMPLE TO COMPLEX 4. What type of development? 3. Need a 2ARY cavity? 2. Which symmetry? 1. How complex? Ancestral protozoan 8 4  1 How complex? Our first question identifies an intriguing fact: Multi-cellular animals can become big and complex… while unicellular organisms remain simple and small… Why unicellular organisms cannot be larger? Unicellular metabolism is based on osmosis and therefore, it requires high Surface to Volume ratios (S:V) - absorption, - excretion, - respiration 9 1 How complex? Imagine this is one animal cell S/V ratio =6 =3 As size increases, S:V ratio decreases, limiting metabolism… So, the only way to grow is by becoming complex or multi-cellular 10 5  1 How complex? versus Simple Complex Complexity promotes some generic changes at the cellular level: Generally speaking… - Complexity reduces average cell size - Complexity increases cell specialization - Complexity increases inter-cellular dependency 11 1 How complex? Multi-cellularity creates a problem for the cells located inside the body… They cannot do the usual exchange (absorption, excretion, respiration, etc) because they are not exposed to the surrounding media… There are two solutions for this: 1. Fold or invaginate becoming very flat to increase S:V ratio, just so every cell is nearby the exterior 2. Specialize groups of cells for transport and delivery of O2, nutrients, residuals, etc, etc TISSUE: Group of cells carrying on a similar function (usually involving more than one type of cell) 12 6  1 How complex? Animal architecture requires a specialization in tissues: Four types Epithelial  The coverage or lining of internal and external surfaces, including skin and organs Examples of simple epithelium Simple Stratified 13 1 How complex? Animal architecture requires a specialization in tissues: Four types Connective  A tissue that binds, protects, supports and gives structure to other tissues and organs Ligaments, bones, blood, lymph… 14 7  1 How complex? Animal architecture requires a specialization in tissues: Four types Muscular  Tissue in charge of movement by contraction of cells and fibers. At least three types of muscle… (voluntary) Smooth Cardiac Skeletal 15 1 How complex? Animal architecture requires a specialization in tissues: Four types Neural  (Nervous) tissue in charge of controlling and coordinating other tissues. Reception and conduction of stimuli is done by neurons and glias (support). Neuron 16 8  Having defined that animals need to be complex, we can start our review of animal groups from the simplest ones…. Or MULTICELLULAR True animals 1. How complex? Either UNICELLULAR UNICELLULAR Ancestral protozoan Protozoans = NO animals 17 Let’s start our review of animal diversity PORIFERA Or MULTICELLULAR True animals 1. How complex? Either UNICELLULAR Ancestral protozoan Protozoans = NO animals 18 9  THE DIVERSITY of ANIMALS SPONGES or PORIFERA The simplest animals: Aquatic creatures Simple feeding (filter feeding) and the simplest morphology: DIPLOBLASTIC: 2 germ layers: Endo + Ectoderm They lack a mesoderm. Instead, they have a MESOGLEA or MESOHYL 19 Sponges have three basic body shapes: 1 1 Osculum Stolon 20 10 A closer look into choanocytes: Choanocytes: The main and most typical cell in sponges. Distinguished by their flagellum and collar. The flagellum moves the water, the collar retains food particles Choanocyte video 21 Spicules and cells in the mesohyl: Spicules are not cells, just structures Spongocoel forming the skeleton of sponges Cell that secretes spicules T-shaped “epithelial” external cell Water-flow regulation cell archaeocyte Multi-purpose cell (digestion / reproduction) Choanocyte 22 11 What’s next in sponges? Thursday: Reproduction, diversity and classification, and then, animal symmetry https://www.youtube.com/watch?v=ntFczZew5lQ 1:19-2:36 23 12