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Animals are: • Eukaryotic (they have membrane-bound organelles) What is an animal? • Heterotrophic (they consume food – they cannot make their own food) Animals… • Do not have cell walls • Usually have specialized cells that form tissues and organs Animals… • Can move around at some point in their life • However, some become permanently attached to a surface – organisms like this are described as ‘sessile’ Animals… • Develop from a fertilized egg cell called a zygote • Most reproduce sexually, with females producing egg cells and males producing sperm cells • Occasionally, animals may be hermaphrodites – having both male and female sexual organs • Rarely, animals can regenerate tissue – sea stars and earthworms can re-grow lost body parts • Fertilization may be internal or external 1 Stages of embryonic development • 1. formation of a blastula – a cell-covered, fluid-filled ball • 2. gastrulation – the inward movement of cells to form two cell layers, endoderm and ectoderm • 3. formation of the mesoderm – the development of a cell layer between the endoderm and ectoderm What happens to embryonic layers? • Ectoderm cells develop into skin and nervous tissue • Endoderm cells develop into the lining of the digestive tract and the digestive organs • Mesoderm cells develop into muscles, circulatory system, excretory system, respiratory system. Stages in development of an animal egg • 1a. Cleavage – the process of cellular division • 1b. Blastula – a single-celled layer of cells that forms a fluid-filled ball • 1c. Gastrula – a structure made up of two layers of cells with an opening at one end • 1d. Ectoderm – outer surface of the gastrula Stages in development of an animal egg • 1e. Endoderm – inner surface of the gastrula • 1f. Protostome – an animal with a mouth that developed from the gastrula • 1g. Deuterostome – an animal in which the mouth develops elsewhere in the gastrula • 1h. Mesoderm – cell layer which forms between the ectoderm and endoderm 2. What are examples of groups of animals that follow these developmental strategies? • a. protostome – earthworms, insects • b. deuterostome – sea urchins, fishes, humans 2 3. Which group of animals does not go through the gastrula stage of development? • Sponges 4. Where do mesoderm cells originate? • Mesoderm cells break away from the endoderm and migrate to the area between the endoderm and ectoderm Bilateral animals have… • An anterior end – usually a head with sensory organs • A posterior end – sometimes with a tail • A dorsal surface – upper or back side • A ventral surface – lower or front side Animal body plans • Radial symmetry – organism has a center axis and can be divided along many planes • Bilateral symmetry – organism can be divided along only one plane • Asymmetry – irregularly shaped body Animal body plans, cont. • Coelom – a fluid-filled space completely surrounded by mesoderm – Specialized organs and organ systems develop inside this body cavity – Cushions and protects the organs – Allows room for the organs to grow and move Evolution of the coelom allowed for the development of greater biodiversity among animals Acoelomate – no coelom Pseudocoelomate – partial coelom coelomate 3 Support and protection • Exoskeleton – hard covering on the outside of the body – Protects soft body parts – Protects against water loss – Protects against predators – Attaches to muscles – Must be shed for growth to occur Support and protection • Endoskeleton – internal skeleton – Provides support – Protects internal organs – Braces muscles Animal body plans, cont. • Vertebrates – animals with backbones and endoskeletons Human Taxonomy • Species – – Homo sapiens • Invertebrates – animals without backbones • All people on Earth – Some have exoskeletons Human Taxonomy • Genus – – Homo – All other species in the genus Homo are extinct 4 Human Taxonomy • Family – Human Taxonomy • Order – – Primate – Hominidae • Eyes that face forward, fingernails, collarbones • Bipedal, upright walking Human Taxonomy • Class – Human Taxonomy • Phylum – – Mammalia • Mammary and sweat glands, hair, breathe air Human Taxonomy • Kingdom – – Animalia • Multicellular heterotrophs – Chordata • Notochord, ‘gill’ slits, tail Human Taxonomy • Domain – – Eukarya • Have membrane-bound organelles and nuclei 5
