Chapter 27: Evolution

Chapter 27: Evolution

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Evolution of Small Organic Molecules

• Experiments by Stanley Miller in 1953 tested the hypothesis that small organic molecules were formed at the ocean’s surface.

• The first atmospheric gases (methane, ammonia, and hydrogen) were placed into a closed system, heated, and circulated past an electric spark to simulate lightning.

• A variety of amino acids and organic acids formed.

Miller’s experiment

Macromolecules• There are three hypotheses concerning

how small organic molecules could give rise to macromolecules:

• The RNA-first hypothesis.• The Protein –first hypothosis.• The Clay theory RNA and Protein arose

together

The Protocell• Before the first true cell, there would have

been a protocell that had a lipid-protein membrane and used energy metabolism.

• Fox has shown that if lipids are available to microspheres, the two form a lipid-protein membrane.

• Other work by Alexandr Oparin has shown that concentrated mixtures of macromolecules form coacervate droplets that a semipermeable boundary may form around.

The True Cell• A true cell is a membrane-bounded

structure that can carry on protein synthesis to produce the enzymes that allow DNA to replicate.

• It is possible that the sequence of DNA to RNA to protein developed in stages.

• Once the protocells acquired genes that could replicate, they became cells capable of reproducing, and evolution began.

Microevolution

Five Agents of Evolutionary Change• Mutations provide new alleles and therefore underlie

all other mechanisms that produce variation.• Genetic Drift changes in gene pool by chance due to

fouder effect or bottleneck effect• Gene Flow is the movement of alleles between

populations (via migration)• Nonrandom Mating, when individuals pair up, not by

chance, but by genotype or phenotype.• Natural Selection, where populations become adapted

to their environment (specialized)

Natural Selection• Natural selection is the process by which populations

become adapted to their environment.• Evolution by natural selection requires:

• Variation• Inheritance of the genetic difference

• Differential adaptedness• Differential reproduction.

• Three types of natural selection are known:• Stabilizing selection – an intermediate

phenotype is favored.• Directional selection – one extreme phenotype

is favored.• Disruptive selection – both extreme phenotypes

are favored over an intermediate phenotype.

Chapter 30: Animals: Part I

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Evolution and Classification of Animals

• Animals are multicellular heterotrophs that ingest their food.

• Animals belong to the Eukarya and kingdom Animalia.

• In general, animals have some form of locomotion and have tissues and organs.

• The adult is typically diploid and practices sexual reproduction.

• An embryonic stage undergoes development.

Evolution of Animals• It is difficult to trace the complete

evolutionary tree of animals because soft-bodied animals are poorly preserved as fossils.

• All animals probably evolved from a protistan ancestor.

• All the major animal phyla include some invertebrates, animals without backbones.

• The phylum Chordata is mainly composed of vertebrates.

Animal diversity

Criteria for Classification• The classification of animals is based on

the level of organization or number of germ layers, symmetry, type of coelom, body plan, and presence or absence of segmentation.

• An evolutionary tree based on these features depicts a possible evolutionary relationship between the animals.

Evolutionary tree

Evolutionary tree

Invertebrates

Characterizing Animals• Level of Organization• Type of Body Plan• Type of Symmetry• Type of Coelom

Level of Organization• Animals can have the cellular level, the

tissue level, or the organ level of organization.

• One of the main events during animal development is the establishment of germ layers.

• If two germ layers (ectoderm and endoderm) are present, then the animal has the tissue level of organization; if all three germ layers are present, the organ level of organization is attained.

LOOK! TheseAre “germ layers” that are the basisOf STEM-CELLS!

Type of Body Plan• Two body plans are present in the animal

kingdom: the sac plan and tube-within-a-tube plan.

• Animals with a sac plan have an incomplete digestive system with only one opening.

• Animals with the tube-within-a-tube plan have a complete digestive system.

• Two openings allows for specialization along the length of the tube.

Type of Symmetry• Animals can be asymmetrical, radially

symmetrical, or bilaterally symmetrical.• Asymmetrical animals have no particular

symmetry.• Radial symmetry means the animal is

organized similar to a wheel.• Bilateral symmetry means the animal has

definite right and left halves.• Bilateral symmetry leads to cephalization.

• Type of Coelom• A true coelom (in coelomates) is an internal

body cavity completely lined with mesoderm, where internal organs are found.

• Coelomates are either protostomes or deuterostomes.

• Acoelomates have mesoderm but no body cavity.

• Animals that have a pseudocoelom have a body cavity incompletely lined with mesoderm.

Introducing the Invertebrates• Sponges are asymmetrical. • Cnidarians have radial symmetry. • All other phyla contain bilaterally symmetrical

animals. • Flatworms have three germ layers but no coelom. • Roundworms have a pseudocoelom and a tube-

within-a-tube body plan.

Kingdom Animalia

Sub-Kingdom Parazoa Sub-Kingdom Metazoa

Phyllum Porifera(sponges)

Phyllum Cnidera(jellyfish, hydra, sea anenomae) Phyllum Platyhelminths

(flukes, tapeworm, planeria)

Phyllum Mollusca(snail, clams, octopi)

Phyllum Arthopods(insects, lobsters, spiders)

Phyllum Echinodermata(starfish, sea urchins)

Phyllum Chordata(early and late vertebrates)

Phyllum Aschelminths(rotifers and nemotes: ascaris)

Phyllum Annelida(segmented worms)

Sponges: Phyllus Porifera• Sponges are mainly marine animals at the

cellular level of organization. • The sponge body wall has an outer layer

of epidermal cells; a middle layer consisting of semi-fluid matrix where amoeboid cells transport nutrients, produce spicules, and form sex cells; and an inner layer of collar cells with flagella that wave water through pores and out an osculum.

Sponge

Kingdom Animalia











Phyllum: Cnidara• Cnidarians are mostly coastal marine

animals with a tissue level of organization and radial symmetry.

• They may be a polyp or a medusa or may alternate between the two forms.

• They have cnidocytes that discharge stinging nematocysts, long threads that may have spines and contain a poison.

• Cnidarians are diverse and include sea anemones, coral, and jellyfishes.

Hydra• A hydra polyp has an outer layer of

epidermis derived from ectoderm and an inner layer called gastrodermis derived from endoderm.

• Mesoglea lies between the two layers and contains a nerve net that communicates with muscle fibers so that the animal is able to move.

• Digestion begins in a gastrovascular cavity and finishes in gastrodermal cells.

• Nutrients and gases are distributed from layer to layer by diffusion.

Anatomy of Hydra

Kingdom Animalia











Flatworms• Flatworms are characterized by the tissue

level of organization and a sac body plan. • These acoelomates have three germ

layers, and have all organs except respiratory and circulatory organs.

• The flat body facilitates diffusion of oxygen and other molecules from cell to cell.

Planarian

Schistosomiasis

Kingdom Animalia











Roundworms• Roundworms have the tube-within-a-tube plan;

they are prevalent in soil and some parasitize animals and plants.

• The pseudocoelom is a body cavity incompletely lined with mesoderm.

• The fluid-filled interior forms a hydrostatic skeleton.

• Most species of roundworms have separate males and females.

Coelom structure and function

Roundworm anatomy

Kingdom Animalia











Molluscs

• Molluscs, along with annelids and arthropods, are protostomes because the first embryonic opening becomes the mouth.

• Because the true coelom form by the splitting of the mesoderm, protostomes are also schizocoelomates.

• Many protostomes also have trochophore (top-shaped) larvae.

Molluscan diversity

Kingdom Animalia











Annelids

• Annelids are segmented both externally, and internally by partitions called septa.

• Annelids have a hydrostatic skeleton, and partitioning of the coelom permits each body segment to move independently.

• The tube-within-a-tube body plan allows the digestive tract to have specialized organs.

Polychaete diversity

Earthworm, Lumbricus

Leeches

• Most leeches are fluid feeders that attach themselves to open wounds using suckers.

• Bloodsuckers, such as the medicinal leech, can cut through tissue.

• An anticoagulant (hirudin) in their saliva keeps blood from clotting.

Kingdom Animalia











Arthropods• Arthropods are the most varied and

numerous of animals. • The success of arthropods is largely

attributable to a flexible exoskeleton, jointed appendages, and specialization of body regions.

• Three body regions – head, thorax, and abdomen – with specialized appendages in each region, and a well-developed nervous system characterize this group.

Arthropod diversity

Insect diversity

Arachnid diversity

Chapter 31: Animals: Part II

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Kingdom Animalia











Echinoderms• Echinoderms and chordates are deuterostomes. • In deuterostomes, the second embryonic opening

becomes the mouth and a coelom forms by outpocketing of the primitive gut making these animals enterocoelomates.

• A dipleurula larva is found among some.

Protostomes versus deuterostomes

Evolutionary tree

Invertebrates

Characteristics of Echinoderms

• Echinoderms are a diverse group of marine animals; there are no terrestrial echinoderms.

• They have an endoskeleton consisting of spine-bearing, calcium-rich plates.

• Echinoderms are often radially symmetrical, although the larva is a free-swimming filter feeder with bilateral symmetry.

• Echinoderm Diversity• Echinoderms include:

• Sea lilies (class Crinoidea)• Sea cucumbers (class Holothuroidea)

• Brittle stars (class Ophiuroidea)• Sea urchins and sand dollars (class

Echinoidea)• Sea stars (class Asteroidea)

Echinoderm diversity

Sea star anatomy and behavior

Kingdom Animalia











Chordates

• Chordates (tunicates, lancelets, and vertebrates) have:

• a supporting notochord, • a dorsal hollow nerve cord, • pharyngeal pouches, and a

• post-anal tail at one time during their development.

Chordate characteristics

Evolution of Chordates• The lancelets and tunicates are

invertebrate chordates.• Vertebrates include the fishes, amphibians,

reptiles, birds, and mammals.• Cartilaginous fishes were the first to have

jaws; amphibians evolved legs and invaded land.

• Reptiles, birds, and mammals have means of reproduction suitable to land.

Evolutionary tree of chordates

No way! Invertebrate Chordates• Lancelets and tunicates are the invertebrate

chordates. • Lancelets are small animals found in shallow

water along the coasts; they filter feed on microscopic organisms.

• Tunicates (sea squirts) live on the ocean floor and filter water entering the animal through an incurrent siphon.

• Adult tunicates lack chordate characteristics except gill slits, but adult lancelets retain the four chordate characteristics.

Habitat and anatomy of a lancelet, Brachiostoma

Anatomy of a tunicate, Halocynthia

True Vertebrates• At some time during their lives, all vertebrates

have the four chordate characteristics. • The notochord is replaced by the vertebral

column; this endoskeleton demonstrates segmentation.

• The internal organs are well developed and cephalization places complex sense organs at the head.

• Vertebrates are distinguished in particular by these features:

• Living endoskeleton• Closed circulatory system

• Paired appendages• Efficient respiration and excretion

• High degree of cephalization• The evolution of jaws allowed some

vertebrates to take up the predatory way of life.

Milestones in vertebrate evolution

We made it on land!

We got bones!

We laid land-eggs!

The first vertibrate animals to arrive: Fishes!

• Today there are three living classes of fishes: jawless fishes, cartilaginous fishes, and bony fishes – the last two groups have jaws.

• Jawless Fishes• The first vertebrates were jawless fishes, today

represented by hagfishes and lampreys with no scales or paired fins. (these fish suck the blood of other fishes…like underwater vampires)

• Water moves in and out through gill openings.

The most primitive jawed fishes: Cartilaginous Fishes

• The cartilaginous fishes include the sharks, rays and skates which have skeletons made of cartilage (like our ears and nose…strong, but still soft and flexible).

• Skates and rays are flat fishes that live partly buried in the sand and feed on mussels and clams –”everybody do the stingray shuffle!”

• Sharks and rays have a sense of electric currents in water, a lateral line system, and a keen sense of smell; these attributes help detect prey – they can feel you even when they can’t see you! So don’t thrash!!!!

• Bony Fishes• Bony fishes have jaws and two pairs of fins and

are the most diverse and numerous of all vertebrates (think: tuna, salmon, koi, etc...)

• Bony fishes include those that are ray-finned (most abundant) and a few that are lobe-finned; some of the lobed-finned fishes have lungs and likely gave rise to amphibians.

• A swim bladder may provide buoyancy in ray-finned fishes.

Jawed fishes

Please don’t step on me!

Amphibians• Amphibians evolved from the lobe-finned

fishes and are tetrapods with two pairs of limbs. • They are represented today by frogs, newts,

toads, and salamanders. • Amphibians usually return to the water to

reproduce and require moist habitats. • Frog tadpoles metamorphose into terrestrial

adults with lungs.

Frog metamorphosis

• These features distinguish amphibians:• Usually tetrapods

• Mostly metamorphosis• Three-chambered heart (2 atria, one

ventricle)• Usually lungs in adults

• Smooth, moist skin

Reptiles• Reptiles include the extinct dinosaurs and

today’s snakes, lizards, turtles, alligators, and crocodiles.

• Reptiles have well-developed lungs within a rib cage; they are covered with scales that protect them from desiccation and predators.

• Reptiles have internal fertilization and also lay a shelled egg, which contains extraembryonic membranes, including an amnion that allows the embryo to develop on land.

The tongue as a sense organ

The reptilian egg allows reproduction on land

• Features that distinguish reptiles include:• Usually tetrapods

• Lungs with expandable rib cages• Shelled, leathery egg

• Dry, scaly skin• Fishes, amphibians, and reptiles are “ectothermic”-

also known as….. COLD-BLOODED!• Therefore…reptiles try to regulate their body

temperature by moving to a warmer or cooler location as needed.

• The opposite of this is WARM-BLOODED, or “endothermic” b/c we regulate body temp. from our insides!

Look up! Beautiful Birds• Birds are characterized by the presence of

feathers, which are modified reptilian scales.• Birds lay hard-shelled eggs rather than the

leathery eggs of reptiles.• Birds are likely closely related to bipedal

dinosaurs, although this is still under study.

Bird anatomy

• Anatomy and Physiology of Birds• Features of birds are related to the ability to

fly.• Bird forelimbs are modified as wings.• Bones are hollow (yes way!) and laced with

air cavities; the sternum has a keel to which flight muscles attach. (weigh a bird, VERY light!)

• A horny beak replaces teeth.• Respiration is efficient due to air sacs.• Birds have a four-chambered heart, and birds

are homeothermic.

Bird beaks

Bird circulatory system

• Classification of Birds• The classification of birds is based on beak

and foot types and to some extent on habitat and behavior.

• These features distinguish birds:• Feathers

• Hard-shelled egg• Four-chambered heart• Usually wings for flying

• Air sacs• Homeothermic

Mammals• Mammals evolved from reptiles and

flourished after the demise of dinosaurs. • Mammals have hair that helps them

maintain a constant body temperature.• Like birds, mammals have a four-

chambered heart.• Internal development in the uterus shelters

the young.• Mammary glands allow mammals to

nourish their young.

Lab Ex: 16 histologyDr. L [email protected] Spring 2005: Fundamentals of Biology

Section 1107 Biology 10 4-Units

mailto:[email protected]

Loose fibrous connective tissue

Adipose tissue

Hyaline cartilage

Compact bone

Skeletal muscle

Smooth muscle

Cardiac muscle

Nail anatomy

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Chapter 27: Evolution