Biology 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?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 21.2

(a) Fertilized egg 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

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

Eight-cell stage Spiral and determinateRadial and indeterminate Protostome development (examples: molluscs, arthropods ) Deuterostome development (example: chordates)

(b) Four-cell stage In mammals these cells can be separated and each will produce a separate identical embryo – deuterostome development Other organisms (protostomes - like arthropods and mollusks) specialize each cell as it is made. Pull one off and the embryo will not develop.

(c) Early blastula In many animals in both groups the cells divide and produce a hollow ball of cells called a blastula.

(d) Later blastula Specific cells on the outside of this ball then “crawl” up inside the hollow space in a process called gastrulation

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 Video: Sea Urchin Embryonic Development

Zygote Cleavage Eight-cell stage

Zygote Cleavage Eight-cell stage Cleavage Blastula Cross section of blastula Blastocoel

Zygote Cleavage Eight-cell stage Cleavage Blastula Cross section of blastula Gastrulation Blastopore Gastrula Ectoderm Endoderm Blastocoel

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.

Anus Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Anus Mouth Digestive tube (c) Fate of the blastopore Key Ectoderm Mesoderm Endoderm 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 videovideo

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 extra- cellular matrix (ECM) –Often (but not always) includes collagen –Many types including: –Loose connective– Bone –Cartilage– Blood (liquid ECM)

Table 28.3

cartilage cells collagen Cartilage

chondrocytes collagen matrix Cartilage

central canal bone cells concentric bone matrix Bone

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

skull Axial skeleton (blue) Appendicular skeleton (beige) mandible sternum rib vertebral column coccyx (tail bone) clavicle scapula humerus pelvis ulna radius 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

skull Axial skeleton (blue) Appendicular skeleton (beige) mandible sternum rib clavicle scapula humerus vertebral column

coccyx (tail bone) pelvis ulna radius 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) compact bone osteon osteocytes (within spaces) capillary central canal

Fig 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

periosteum large blood clot compact bone spongy bone new blood vessels callus of cartilage and bone replaces clot bony callus healed fracture Bone healing is only one way that your body modifies its skeleton