Transcript Lecture 5
Biology 103 - Main points/Questions 1. How do plants keep growing for their entire lives? 2. How do animal cells differentiate? 3. What are tissues? 4. How do organisms support themselves? Fig. 21.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings All animals start out as a fertilized egg that undergoes mitosis. In deuterostomes (?) cells divide at right angles while in protostomes (?) they divide in a spiral pattern (a) Fertilized egg Animal Development • We will focus on two basic strategies for development seen in two major groups – Protostomes include arthropods and mollusks – Deuterostomes include all the chordates • These groups have several differences in their development we focus on 3 – Cleavage pattern – Timing of cell specialization – Fate of blastopore Protostome development (examples: molluscs, arthropods) Eight-cell stage Spiral and determinate Deuterostome development (example: chordates) Eight-cell stage Radial and indeterminate In mammals these cells can be separated and each will produce a separate identical embryo – deuterostome development (b) Four-cell stage Other organisms (protostomes - like arthropods and mollusks) specialize each cell as it is made. Pull one off and the embryo will not develop. In many animals in both groups the cells divide and produce a hollow ball of cells called a blastula. (c) Early blastula Specific cells on the outside of this ball then “crawl” up inside the hollow space in a process called gastrulation (d) Later blastula • During gastrulation cells further specialize into three embryonic tissues – Endoderm – the innermost cells – Mesoderm – cells in the middle – Ectoderm – cells that remain on the outside • This process also creates an opening into the ball called a blastopore Video: Sea Urchin Embryonic Development Cleavage Zygote Eight-cell stage Cleavage Zygote Cleavage Blastula Eight-cell stage Blastocoel Cross section of blastula Blastocoel Cleavage Endoderm Cleavage Blastula Ectoderm Zygote Eight-cell stage Gastrulation Gastrula Blastopore Cross section of blastula Protostomes and Deuterostomes • We have seen: – Cleavage pattern differences, spiral vs. radial – Timing of cell specialization differences • The last difference we look at is the fate of the blastopore. – As the embryo develops the open space inside the gastrula will be the digestive tract – the blastopore will be one of the openings – either the mouth or the anus. Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Anus Mouth (c) Fate of the blastopore Key Digestive tube Ectoderm Mesoderm Endoderm Anus Mouth Mouth develops from blastopore. Anus develops from blastopore. • As embryos continue to develop tissues continue to specialize • Each of these 3 embryonic tissues will give rise to numerous tissues/organs in the adult Section 36.6 in your book – gastrulation video Hierarchy of Biology: • Tissues are groups of cells with similar structures/functions • In humans there are many different tissues that work together to build organs • Organs working together to perform a task are called organ systems Tissue of the Day • Connective tissue – Made up of cells surrounded by large extracellular matrix (ECM) – Often (but not always) includes collagen – Many types including: – Loose connective – Bone – Cartilage – Blood (liquid ECM) Table 28.3 Cartilage cartilage cells collagen Cartilage chondrocytes collagen matrix Bone bone cells central canal concentric bone matrix Support system terminology: • Internal skeleton • External skeleton • Hydrostatic skeleton • Primary vs. secondary cell wall • Secondary growth in plants Skeletal systems in Animals • Hydrostatic skeleton – Uses pressurized fluids support organisms weight – Lacks strength – Common example: • Earthworm Skeletal systems in Animals • Exoskeleton – external rigid tissue protects and supports – Gives a lot of protection but... – Can be very heavy – Can interfere with growth – Examples • Arthropods: • Mollusks Adult cicada sheds its exoskeleton as it outgrows it, forming a new exoskeleton. Skeletal systems in Animals • Endoskeleton – – Uses internal rigid tissue to support weight – Offers less protection but... – Lighter weight – Growth is simpler – Examples • Vertebrates A cat skeleton is a nearly ideal balance of high strength and low weight. Cats are adept at surviving long falls in part because of this balance. Heavy Organisms Require Large-Diameter Support Structures - in part to support the added weight of the skeleton itself Axial skeleton (blue) skull Appendicular skeleton (beige) mandible clavicle scapula sternum humerus rib pelvis ulna vertebral column radius coccyx (tail bone) carpals metacarpals phalanges femur patella tibia fibula tarsals metatarsals phalanges The skeletal system in humans is divided into two parts the axial (in blue here) and the appendicular (in tan) skeletons Axial skeleton (blue) skull Appendicular skeleton (beige) mandible clavicle scapula sternum humerus rib vertebral column pelvis ulna radius coccyx (tail bone) carpals metacarpals phalanges femur patella tibia fibula tarsals metatarsals phalanges How does the Vertebrate Skeleton develop? • Bone and cartilage develop from mesodermal tissue • Bone replaces cartilage during development bone cartilage In this human fetus much of the skeleton is still cartilage - which will be replaced by bone as the fetus ages. Connecting microscopic view to macroscopic view • Remember what bone tissue looks like where do you find tissue like this in your body? • What do bones look like? (b) osteon compact bone osteocytes (within spaces) capillary central canal Fig. 28.5 • Notice that there is blood flow in living bone! (Its alive!) • This is crucial for bone growth & healing. large blood clot compact bone spongy bone 1 The Vertebrate Skeleton is alive! • Notice several types of tissue are actually present in a living bone – Bone – blood – connective tissue and epithelial tissue building membranes new blood vessels callus of cartilage and bone replaces clot 2 bony callus 3 healed fracture 4 callus of new blood cartilage and bone vessels replaces clot bony callus healed fracture periosteum large blood clot compact bone spongy bone 1 2 3 Bone healing is only one way that your body modifies its skeleton 4