What Characteristic Define an AnimalWhat Characteristic Define an Animal?

• EukaryotEukaryotic cellsic cells

• MulticellularMulticellular

• Ingestive HeterotrophIngestive Heterotroph

How did the animal kingdom evolve?How did the animal kingdom evolve?

Oldest fossils are 700 million years oldOldest fossils are 700 million years old

Animals probably evolved from an ancestor Animals probably evolved from an ancestor of a colonial choanoflagellateof a colonial choanoflagellateprotistprotist

One hypothesis for the origin of animalsOne hypothesis for the origin of animals

Major Trends in Animal Evolution:Major Trends in Animal Evolution:• Development of Tissue LayersDevelopment of Tissue Layers

• Patterns of Body SymmetryPatterns of Body Symmetry

• Development of a Body CavityDevelopment of a Body Cavity

• Body SegmentationBody Segmentation

• SpecializationSpecialization

Development of Tissue LayersDevelopment of Tissue Layers

Most animals have tissues that arise Most animals have tissues that arise from three embryologic tissues layers:from three embryologic tissues layers:

• EctodermEctoderm – produce skin and – produce skin and nervous systemnervous system

• EndodermEndoderm – produces GI tract – produces GI tract

• MesodermMesoderm – produces muscle, – produces muscle, skeleton and most organsskeleton and most organs

Patterns of Body SymmetryPatterns of Body Symmetry

• AsymmetricalAsymmetrical

• Bilateral symmetryBilateral symmetry

• Radial symmetryRadial symmetry

Development of a Development of a Body Cavity:Body Cavity:

• Allows independent movement of body wallAllows independent movement of body wall

• Cushions internal organs Cushions internal organs

• Provides a hydrostatic skeletonProvides a hydrostatic skeleton

• Increases flexibility and mobility Increases flexibility and mobility

ProtostomesProtostomes: : mesoderm mesoderm forms from forms from mass of cells mass of cells between between endoderm and endoderm and ectodermectoderm

DeuterostomesDeuterostomes: : mesoderm forms as mesoderm forms as outpocketing of outpocketing of gastrulation cavitygastrulation cavity

Visualizing Protostome & Deuterostome Development

Body SegmentationBody Segmentation• Most animals have Most animals have

segmented bodiessegmented bodies

• Segmentation increases Segmentation increases body flexibility and mobilitybody flexibility and mobility

Evolution of Systems for Exchange with the

Environment

The maintenance of constant conditions in the internal environment is called homeostasis. Homeostasis is an essential

feature of complex animals.Animals have evolved variable adaptations to maintain

homeostasis, that depend on their environment and level of sophistication…

Evolution of Systems• Every organism must exchange materials &

energy with environment, which ultimately occurs at the cellular level.

•Most animals have organ systems specialized for exchanging materials, and many have an internal transport system that conveys fluid (blood/interstitial fluid) throughout the body.

Evolution of the Circulatory System

• The bulk transport of fluids throughout the body connects aqueous environment of body cells to organs that exchange gases, absorb nutrients, and dispose of wastes.

• For animals with many cell layers, gastrovascular cavities are insufficient, due to the amount of transports.

Open Circulatory System

• There is no distinction between blood and interstitial fluid, collectively called hemolymph.

• One or more hearts pump the hemolymph into interconnected sinuses surrounding the organs, allowing exchange between hemolymph and body cells.

Closed Circulatory System

•Blood is confined to vessels and is distinct from the interstitial fluid.

•One or more hearts pump blood into large vessels that branch into smaller ones cursing through organs.

•Materials are exchanged by diffusion between the blood and the interstitial fluid bathing the cells.

Arteries carry Away

Veins Veturn

Blood Arrives at AtriaBlood Vacates

Ventricles

Left = oxygenatedRight = deoxygenated

Fig. 42.4

Evolution of the Nervous System

3 evolutionary trends in nervous system development:

1-bilateral

2-cephalization

3-increased numbers of neurons

Evolution of Nervous Systems

• The nervous system monitors and controls almost every organ system through a series of positive and negative feedback loops.

Evolution of Respiratory Systems

• Large animals cannot maintain gas exchange by diffusion across their outer surface. They developed a variety of respiratory surfaces that all increase the surface area for exchange, thus allowing for larger bodies.

• A respiratory surface is covered with thin, moist epithelial cells that allow oxygen and carbon dioxide to exchange. Those gases can only cross cell membranes when they are dissolved in water or an aqueous solution, thus respiratory surfaces must be moist.

Evolution of Respiratory Surfaces

• Single-celled organisms exchange gases directly across cell membrane. However, the slow diffusion rate of oxygen/carbon dioxide limits size. Simple animals lack specialized exchange surfaces have flattened, tubular, or thin shaped body plans

• Earthworms have a series of thin-walled blood vessels known as capillaries. Gas exchange occurs at capillaries located throughout the body as well as those in the respiratory surface.

• Many terrestrial animals have their respiratory surfaces inside the body and connected to the outside by a series of tubes.

• Tracheae = tubes carry air directly to cells for exchange. Spiracles = openings at surface that lead to tracheae that branch into smaller tubes. Body movements or contractions speed up the rate of diffusion. Does not function well in animals whose body > 5 cm.

• Amphibians use skin as a respiratory surface. Frogs eliminate carbon dioxide 2.5 times as fast through their skin as they do through their lungs. Eels (a fish) obtain 60% of their O2 through their skin. Humans exchange only 1% of CO2 through skin. Constraints of water loss dictate that terrestrial animals must develop more efficient gas exchange.

Gills• Gills greatly increase the surface

area for gas exchange. • Gills typically are convoluted

outgrowths containing blood vessels covered by a thin epithelial layer.

• Gills are very efficient at removing oxygen from water: there is only 1/20 the amount of oxygen present in water as in the same volume of air. Water flows over gills in one direction while blood flows in the opposite direction through gill capillaries. This countercurrent flow maximizes oxygen transfer.

Lungs• Lungs are ingrowths of the body wall and connect to

the outside by as series of tubes and small openings. Lung breathing probably evolved about 400 million years ago. Lungs are not entirely the sole property of vertebrates, some terrestrial snails have a gas exchange structures similar to those in frogs.

Evolution of Excretory System• Osmoregulation balances the

uptake and loss of water and solutes.

• An animal's nitrogenous wastes reflect its phylogeny and habitat.

• Diverse excretory systems are variations on tubular theme

• The nephron is organized for stepwise processing of blood filtrate.

• Hormonal circuits link kidney function, water balance, and blood pressure.

Evolution of Digestive System

• Diffusioningestiongastrovascular cavity1 way digestive system.

Evolution of Digestive System• Diffusioningestiongastrovascular cavity1

opening digestive system.

Evolution of Digestive System

Resources

• External Environment I