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Zoology, lecture 3
Invertebrates: From acellular to multicellular organisms
| Question | Answer |
|---|---|
| Porifera | םיגופס Phylum of sponges--simple multicellular organisms with some cellular differentiation. |
| What are all acellular organisms so small? | Volume-surface ration increases with size, protoplasm can only be so big before it can't hold up, diffusion distance becomes less efficient, the nucleus can no longer control the cell function. |
| Diploblastic organisms | Organisms made of 2 layers of cells. |
| Triploblastic organisms | Organisms made of 3 layers of cells. |
| Solutions to size restrictions | Building a more complex body with cells of differentiated functions including a circulatory mechanism |
| How did multicellular organisms develop? | Three theories: from multinucleus unicellular organisms, from colonial unicellular organisms, from multicellular plants. |
| Syncitial Theory | Theory of multiple nuclei, all they need is a division to have 2 cells--example: Opalina a commensial symbiont in the gastric system of amphibians. |
| Plant to Animal theory | Acellular phytoflagellates became multicellular and lost their chloroplasts becoming heterotrophic. ex. Bryophytes בחט |
| Bryophytes | Non-vascular land plants with tissues and an enclosed reproductive system. |
| What's the difference between a colony of acellular organisms and a multicellular organism? | In a colony each cell is a separately functioning organism that happens to be connected physically but not functionally. |
| Choanoflagellata | A colony of acellular independent organisms on a common branch structure. |
| Volvox | A colony of acellular organisms within a joint bubble. |
| How do multicellular organisms differ from colonies of unicellular organisms? | Multicellular organisms have differentiation of jobs of different cells. Differentiation is during embryonic development. Cells with similar jobs make up a tissue. Tissues build organs. |
| Why is the most accepted theory that multicellular organisms developed from unicellular organisms from colonial acellular organisms the most accepted theory? | The simplest multicellular organisms, porifera, have many similar qualities to choanoflagellata, unicellular colonial organisms. |
| Support for the acellular colonial to multicellular theory | Many flagellata are colonial, there's a lot of variation in their composition, there are many similarities between flagellate cells and multicelled organism cells, development is like embryonic development. |
| Convergence | We can't say that multicellular organisms didn't develop from different evolutionary origins. |
| Mesozoa | Ciliated organisms similar to worms . All of them are parasitic in marine invertebrates. Most have two layers that are similar to diploblastia in multicellular organisms. |
| Parazoa | Multicellular organisms whose cells are not organized into tissues. |
| Metazoa (Eumetazoa) | Multicellular organisms whose bodies are composed of true tissues. |
| Basic characteristics of multicellular organisms | Embryonic development starts with the development of germ layers and continues with differentiation and specialization of cells. |
| Gametes | Sex cells (each with half a genome) produced through meiosis. |
| Zygote | Fertilized egg that possesses full set of chromosomes. |
| Embryo | When the zygote starts to divide, differentiate and specialize. |
| Larva | Stage in the development of some organisms followed by morphogenesis producing the adult. |
| Ectoderm | External germ layer present in both diploblasts and triploblasts. |
| Endoderm | Also called the gastroderm. It's the internal germ layer present in both diploblasts and triploblasts. It surround the gastric/digestive system. |
| Mesoglea | Layer of material (not cells) between the two germ layers in diploblasts. |
| Mesoderm | Germ layer between the endo/ectoderm in triploblasts. There are two layers of it and it surrounds the coelom. |
| Coelom | Fluid filled cavity present in triploblasts surrounded by mesoderm. |
| Diploblastic Metazoans | Multicellular, two layered organisms: All of the cell originate from one of the two original cell layers: ectoderm/endoderm. |
| Blastula | Ball of cells that are produced from the splitting of the embryonic cells with no specialization to the stage of 128 cells. If its hollow the inside is called the blastocoel |
| Blastocoel | The inside of the blastocoel where the cells are arranged in a ball around it. It's either filled with liquid or cells. |
| Vegetal pole of the blastula | The cells are designated to become endoderm. |
| Animal pole | Pole of the developing embryo where most of the body cells are located. |
| Vegetal pole | Pole where the yolk is found. |
| Epithelial | A tissue that is composed of cells that line cavities and surfaces of structures throughout the body. |
| Gastrula | Stage in embryonic development where the embryo is diploblastic. |
| Archenteron | Primitive gut in diploblasts and triploblasts. It is the space left over when the endoderm folds into the blastocoel forming two germ layers. |
| Blastopore | Embryonic "mouth"--hole in the embryo that results from gastrulation. |
| Is the archenteron the body cavity? | No. The archenteron produces the gastric cavity and the body cavity develops from the coelom. |
| Where does embryonic germ layer production stop in diploblasts? | At gastrulation. |
| Diploblastic digestive system | Bidirectional--food goes in through the same hole that waste goes out. |
| How is the gastrula formed? | Through invagination of the vegetal pole of the blastula to form two layers or migration of cells inwards towards the center. |
| From what stage are the cells designated for differentiation? | Already from the blastula stage. |
| Types of cells produced by differentiation | Epithelial, digestive, nerve, sensory and intermediate. Cellular differentiation can alter size, shape and function of cells. |
| Intermediate cells | Cells that have not yet differentiated and therefore can become different kinds of cells. |
| Porifera | Phylum of sponges--they do not possess true tissues because though they have differentiated cells the cells don't work together. |
| Parazoa | Multicellular organisms with no true tissues (porifera) |
| Sponges | They come in a variety of sizes (mm-m's), colors and shapes. They can be asymmetrical or radially symmetrical. They can be branched, skinny, upright, chunky, page-like or covering. |
| Porifera characteristics | Sessile animals, water flows through pores in their bodies bringing in oxygen and nutrients and taking out waste (no digestive system) No tissues or organs, cells--though differentiated--are relatively independent. hard/soft skeleton. |
| Porifera sensory/nervous systems | They have no nervous system or sensory mechanisms. Their cellular cytoplasm has sensory capabilities. |
| Osculum | Large holes in the porifera through which water leaves the organism carrying waste out with it. |
| Ostium | Small pores through which water comes into the porifera carrying nutrients and oxygen. |
| Types of cells in porifera | Archaeocyte, Pinacocyte, Collencyte, Chanocyte, Spicules, Mosohyl |
| Mesohyl | Connective tissue of porifera within which all of the other cell types are arranged. |
| Spicules | Structural needles that give the sponge its form/toughness. |
| Pinacocytes | Flat epithelial cells that cover the sponge's surface. |
| Choanocytes | Flagellated collar cells that produce a current of water into the cell's ostium. They also absorb nutrients and oxygen. |
| Different Porifera structures | Porifera can be divided according to their level of complexity: Asconid, Synconid, Leuconid |
| םייבובנ | Coelenterata--an obsolete term referred to Ctenophora (comb jellies) and Cnidaria referring to their common hollow body cavity. |
| Cnidaria | Phylum of purely aquatic diploblastic animals whose distinguishing characteristic is cnidoctyes (stinging cells). |
| Cnidocyte | A type of venomous cell unique to cnidaria that stings and catches prey. (also called cnydoblast) |
| Cnidocyst | An organelle in the cnidocyte that is bulb shaped and contains a hollow thread like structure. |
| Cnidocil | The hair-like trigger at the edge of the cnidocyst. |
| Nematocyst | Capsule containing toxins that are injected into the target organism when fired. |
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