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Characteristics of Animals Nutrition Plants vs. Fungi Plants: are autotrophic eukaryotes that generate organic molecules through photosynthesis Fungi: are heterotrophic but grow next to or on their food, and release enzymes that digest food outside of their bodies Animals Unlike plants, animals cannot construct all of their own organic molecules so in most cases they ingest them- either by eating other living organisms or by eating nonliving organic material. Unlike fungi, most animals use enzymes to digest their food only after they have ingested it So, basically • Animals ingest living or nonliving material • Only secret enzymes after ingestion Also, Some animals are: • Herbivores - eat plants or Carnivores - eats meat, or both. Why? Animals don’t sort food, (ex. Lions and bunnies) • Omnivores - Mix of both • Detritivores- eat things in decay ex. earth worms, important aspect of ecosystems (heterotrophs) that obtain nutrients by consuming detritus, by doing so they contribute to decomposition and the nutrient cycles. Many species of bacteria, fungi and protists, unable to ingest discrete lumps of matter, instead live by absorbing and metabolizing on a molecular scale • Parasites - Not in omnivores, specialized mode of life, it’s very specific to it’s host Cell Structure and Specialization Cell structure Animals are multicellular. They lack support of cell walls. Instead, animal bodies are held together by structural proteins, most abundant being collagen. Animals have 3 unique types of intercellular junctions - tight junctions, desmosomes, and gap junctions that consist of other structural proteins. Specialization Two distinct specialized cells: • Muscle cells- organized into muscle tissue, responsible for movement • Nerve cells- organized into nervous tissue, responsible for impulse conduction Also, - Not all animals have true tissues and organs or sexual reproduction (can be lost) - Definition of Eukaryotic and Multicellular = Not limited to the animals, plants, and fungi Reproduction Most reproduce sexually, many are capable of asexual reproduction. Asexually • Considered for the more primitive phylum • Usually takes place through parthenogenesis (where fertile eggs are produced without mating, or in some cases through fragmentation) The diploid stage usually dominates the life cycle. Only haploid part is sex cell, organisms are haplobiontic diploid Most of the time, the small flagellated sperm fertilizes a larger, nonmotile egg forming a diploid zygote. Early Embryonic development in animals a. The zygote undergoes cleavage -(mitotic cell divisions without cell growth between division cycles). b. Cleavage leads to formation of a multicellular stage called a blastula- (a hollow ball) c. Following a blastula stage is gastrulation- (many layers of embryonic tissue develop into adult body parts) d. The resulting stage is called a gastrula * Note: Gastrulation: a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers, the (ecto + endoderm) * Belzer said: In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form a gastrula with a digestive chamber, and two separate germ layers - an external ectoderm and an internal endoderm. In most cases, a mesoderm also develops between them. These germ layers then differentiate to form tissues and organs. Life cycles in many animals also include at least one larval stage. a Larva is a sexually immature form of an animal that is morphologically distinct from the adult stage, it usually eats different food, and may even have a different habitat than the adult, as in the case of a tadpole (larva) of a frog. Larvae eventually undergo metamorphosis, a resurgence of development that transforms the animals into an adult. Also, In sponges, blastula larvae swim to a new location and develop into a new sponge Clues to the origin of animals Colonial Hypothesis Based on the idea that the ancestral animals were heterotrophic colonial flagellates . In essence, the colonial flagellates were free swimming hollow balls of eukaryotic cells. The colonial flagellate probably resulted in choanoflagellate or collar cells found in the choanocyte cells of modern sponges. How? Starts with a colonial protist, which is an aggregate of identical cells. Then, it increases to a hollow sphere of unspecialized cells, then the beginning of cell specialization then a sort of infolding and finally, left with a gastrula like proto-animal. (outer-layer cells could be used for locomotion, and the inner layer of cells for digestion and reproduction) Important animal characteristics: Biologists consider body symmetry, cephalization, number of germ layers, type of body cavity and embryonic development important in the classification of animals. A group of animal species that share the same level of organizational complexity is known as a grade. Grades not the same as clades. An organism can by polyphyletic. Traits that define a grade are called a body plan, Grade vs. Clade Grade = level of adaptational organisms of similar grade due to similar adaptations due to convergence. Clade = a group descended from one common ancestor, a genetic lineage Body Symmetry Most sponges lack symmetry altogether, so animals can be classified by lack of symmetry. Among the animals that do, symmetry can have different forms: 1. Radial Symmetry- The form of a flowerpot. (Ex. sea anemones) The parts radiate from the center, any slice through the central axis divides the animal into mirror images 2. Bilateral Symmetry- The form of a shovel. (ex. lobster) Has a left and right side. Only one cut divides the animal into mirror image halves. (ex. humans and arthropods) A Bilateral animal has • a dorsal (top) side • ventral (bottom) • left and right side • and an anterior (head) end with a mouth, and a posterior (tail) end **Most bilateral animals have sensory equipment concentrated at the anterior end, along with a central nervous system (“brain”) in the head- an evolutionary trend known as cephalization The symmetry of an animal generally fits its lifestyle. Radial animals are sessile (living attached to a substrate) or planktonic (free swimming). Bilateral animals generally move actively from place to place. Their CNS enables them to coordinate complex movements (crawling, burrowing, flying or swimming) Tissues ( Germ layers ) True tissues are collections of specialized cells isolated from other tissues by membranous layers.Sponges lack true tissues. In all other animals, the embryo becomes layered through gastrulation, as development progresses, these concentric layers called germ layers, form the various tissues and organs of the body. Ectoderm- the germ layer covering the surface of the embryo, gives rise to the outer covering of the animal and, in some phyla, to the central nervous system. Endoderm - the innermost germ layer, lines the developing digestive tube or archenteron, and gives rise to the lining of the digestive tract (or cavity) and organs derived from it (ex. liver, and lungs of vertebrates) Animals that have only 2 germ layers are said to be diploblastic. (jellies, corals, cnidarians, comb jellies) Others with 3 layers (3rd being the mesoderm- between the ecto and endo derm) Are said to be triploblastic. In triploblasts the mesoderm forms the muscles and most other organs between the digestive tract and the outer covering of the animal. Triploblasts include all bilaterally symmetrical animals (flatworms, arthropods and vertebrates) Body Cavities Most triploblastic animals have body cavities - a fluid filled space separating the digestive tract from the outer body wall. This body cavity is also known as a coelom. True coelom forms from tissue derived from mesoderm. The inner and outer layers of tissue that surround the cavity connect dorsally and ventrally and form structures called mesenteries that suspend the internal organs. Animals that posses a true coelom are known as coelomates. Some triploblastic animals have a body cavity formed from the blastocoel, rather from the mesoderm. This is called a pseudocoelom, and animals that have one are pseudocoelomates. Currently, true coeloms and pseudocoelom have been gained or lost multiple times in evolution, so thats why the terms refer to grades, not clades. Basically: • Coelomates- (ex. annelids) have a true coelom, a body cavity completely lined by the mesoderm • Pseudocoelomates- (ex. nematodes) have a body cavity lined only partially by mesoderm • Acoelomates- (ex. flatworms) lack a body cavity Modes of Development Protostome and Deuterostome Both distinguished by many features such as: Cleavage Protostomes have a spiral cleavage- in which the planes of cell division are diagonal to the vertical axis of the embryo. Smaller cells lie in the grooves between the larger, underlying cells. This determinate cleavage of some animals with this pattern rigidly casts (“determines”) the developmental fate of each embryonic cell very early. A cell isolated at the four cell stage from a snail for example, forms an inviable embryo that lacks many parts. Deuterostomes have a radial cleavage. Planes are either parallel or perpendicular to the vertical axis of the egg. The tiers of cells are aligned, one directly above the other. Most animals with deuterostome development are further characterized by indeterminate cleavage- meaning that each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo. (ex. if a sea star embryo is isolated at the four cell stage, each cell will form a larva) IN humans, the indeterminate cleavage of the zygote makes identical twins possible. This characteristic also explains the developmental versatility of the embryonic “stem cells” Coelom formation In gastrulation, the developing digestive tube of an embryo initially forms as a blind pouch, the archenteron. As the archenteron forms in protosome development, initially solid masses of mesoderm split and form the coelomic cavity, this pattenr is called schizocoelous development (Greek Schizein: to split). In Deuterosome development, the formation of the body cavity is described as enterocoelous: the mesoderm buds from the wall of the archenteron and its cavity becomes the coelom Fate of the blastopore Blastopore- the indentation that during gastrulation leads to the formation of the archenteron. After the archenteron develops, a second opening forms at the opposite end of the gastrula. Ultimately, the blastopore and this second opening become the two openings of the digestive tube. (mouth and anus) In protostome development, the mouth generally develops from the first opening. In deuterostome development, the anus generally develops from the first opening, and the mouth second.. Phylogeny - Modern phylogenetic systematics is based on the identification of clades, which are monophyletic sets of taxa as defined by shared derived characters unique to those taxa and their common ancestor. - A clade might be defined by key anatomical and embryological similarities that are homologous. Points of agreement 1. All animals share a common ancestor - tree is monophyletic. 2. Sponges are basal animals.- sponges branch from the base of both animal trees. They exhibit a parazoan (meaning “beside the animals”) grade of organization. Tissues evolved only after sponges diverged from other animals. Recent studies believe sponges are paraphyletic 3. Eumetazoa is a clade of animals with true tissues. Every animal but sponges belong in the clade of eumetazoans “true animals”. Basal members of the eumetazoan clade include Cnidaria and Ctenophora. These guys are diploblastic (2 germ layers) and have radial symmetry 4. Most animal phyla belong to the clade Bilateria.- Bilateral symmetry is a shared derived character that helps to define a clade (and grade) containing the majority of animal phyla called bilaterians. 5. Vertebrates and some other phyla belong to the clade Deuterostomia. The name deuterostome refers not only to an animal development grade but also to a clade that includes vertebrates