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SATII Review: Evolu0on, Taxonomy and Development •  Start with general topic ques0ons/
concerns •  We’ll move through the topics one at a 0me, by giving quick case study, example or topic ques0ons/quizzes. All slides posted on website in pdf. (teacherweb) •  Ques0ons over the next couple of weeks? [email protected] Evolu0on: Ch 11-­‐13 (start at p. 153!) A recent study from Framingham, MA shows that humans are evolving as the average height has decreased by 5 cm and mass by 3 kg in the last 60 years. Is this evolu0on taking place? If so, what is your evidence? Evolu0on: Ch 11-­‐13 (start at p. 153!) Has this popula0on evolved such that Framingham people are new species (use p. 161 in your logic)? How could you test this hypothesis? How do you test if some bacteria represent a new species? Evidence for evolu0on • 
• 
• 
• 
• 
Homologous v. analogous structures Ves0gial structures Compara0ve biochemistry/molecular bio Compari0ve embryology Biogeography Lamarck v. Darwin •  Rates of an0bio0c resistance has skyrocketed over the last few decades as scien0sts can’t seem to keep up (i.e. MRSA). Is this because bateria mutate to become resistant to an0bio0cs? Is this evidence of evolu0on? •  What would Thomas Malthus think of if he imagined billions of bacteria on a ro\en tomato? Giraffe necks and Moths •  How would Lamarck view the poten0al evolu0on of giraffe necks vs. Darwin? •  How did industrial melanism provide a useful example for evolu0on? •  Could black wing color have been a point muta0on or the result of gene flow? Cell phones and evolu0on •  What type of selec0on (p. 157) would this be? –  Smaller cell phones are becoming more and more convenient and popular, while larger offer nice screens for videos. –  Very small and very large cell phones are more likely to be broken when dropped and less likely repurchased with contract insurance! Kongido tarantulas •  These spiders are famous for the incomplete dominant yellow variety that shows up well in nature, except on bananas. •  If they can leave islands on rabs of banana tree leaves, suggest how volcanic erup0ons might provide perfect examples of bo\leneck or founder effect. How are they different? Red-­‐haired ness •  A recent study suggests that 4% of Americans have red hair (an autosomal recessive trait). According to Hardy-­‐Weinsburg equilibrium, what percentage of the popula0on is heterozygous for this trait? •  According to H-­‐W, if the pop. Is stable the following must be true… Which pa\ern of evolu0on”?” •  Two new species of eel are found in New England…one in a gulf in Maine another in the cape(?). However, there are many eel species found…all though to have descended from one common ancestor(?). There are species of amphibian that move through soil with the same shape(?). Historically, eels have increased in smell detec0on, but crickets also release less pheromones then their ancestors. Early life video Binomial nomenclature •  What is our 2-­‐name name? •  Are there more species of mammals or vertebrates? Are there more primates or eukaryotes? Make a 3-­‐ring Venn! •  Compare bacteria, archaeans and eukaryotes! •  Write a 6-­‐adjec0ve descrip0on of animals Animals Overview •  Animals are mul0cellular, heterotrophic eukaryotes with 0ssues that develop from embryonic layers. Animal Structure and Specializa0on •  Nutri&onal Mode: Animals are heterotrophs that ingest their food. •  Animals are mul&cellular eukaryotes. •  Their cells lack cell walls. •  Their bodies are held together by structural proteins such as collagen. •  Nervous &ssue and muscle &ssue are unique to animals. Reproduc0on and Development •  Most animals reproduce sexually, with the diploid stage usually domina&ng the life cycle. •  A;er fer&liza&on, the zygote undergoes rapid cell division called cleavage. •  Cleavage leads to forma0on of a blastula. •  The blastula undergoes gastrula,on, forming a gastrula with different layers of embryonic &ssues. Animal Early Embryonic Development Blastocoel
Cleavage
Endoderm
Blastula
Ectoderm
Zygote
Eight-cell stage
Gastrulation
Blastocoel
Cross section
of blastula
Archenteron
Gastrula
Blastopore
•  Many animals have at least one larval stage. •  A larva is sexually immature and morphologically dis0nct from the adult; it eventually undergoes metamorphosis. •  All animals, and only animals, have Hox genes that regulate the development of body form. •  Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology. Three lines of evidence that choanoflagellates pro;sts are closely related to animals
Individual
choanoflagellate
Choanoflagellates
OTHER
EUKARYOTES
Sponges
Animals
Collar cell
(choanocyte)
Other animals
•  Sponges are suspension feeders –  Capturing food par0cles suspended in the water that passes through their body 5 Choanocytes. The spongocoel is lined with feeding cells called choanocytes. By bea0ng flagella, the choanocytes create a current that draws water in through the porocytes. Azure vase sponge (Callyspongia plicifera) Spongocoel. Water 4 passing through porocytes enters a cavity called the spongocoel. Porocytes. Water enters 3 the epidermis through channels formed by porocytes, doughnut-­‐shaped cells that span the body wall. 2 Mesohyl. The wall of this simple sponge consists of two layers of cells separated by a gela0nous matrix, the mesohyl (“middle ma\er”). 1 Figure 33.4 Epidermis. The outer layer consists of 0ghtly packed epidermal cells. Flagellum Collar Food par0cles in mucus Choanocyte Osculum Phagocytosis of food par0cles Spicules Water flow Amoebocyte 6 The movement of the choanocyte flagella also draws water through its collar of fingerlike projec0ons. Food par0cles are trapped in the mucus coa0ng the projec0ons, engulfed by phagocytosis, and either digested or transferred to amoebocytes. 7 Amoebocyte. Amoebocytes transport nutrients to other cells of the sponge body and also produce materials for skeletal fibers (spicules). •  Choanocytes, flagellated collar cells –  Generate a water current through the sponge and ingest suspended food •  Most sponges are hermaphrodites –  Meaning that each individual func0ons as both male and female •  Concept 33.2: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes •  All animals except sponges –  Belong to the clade Eumetazoa, the animals with true 0ssues •  Phylum Cnidaria –  Is one of the oldest groups in this clade •  Cnidarians –  Have diversified into a wide range of both sessile and floa0ng forms including jellies, corals, and hydras –  But s0ll exhibit a rela0vely simple diploblas0c, radial body plan •  The basic body plan of a cnidarian –  Is a sac with a central diges0ve compartment, the gastrovascular cavity •  A single opening –  Func0ons as both mouth and anus •  There are two varia0ons on this body plan –  The sessile polyp and the floa0ng medusa Polyp Medusa Mouth/anus Tentacle Gastrovascular cavity Gastrodermis Mesoglea Body stalk Epidermis Tentacle Mouth/anus Figure 33.5 •  Cnidarians are carnivores –  That use tentacles to capture prey •  The tentacles are armed with cnidocytes –  Unique cells that func0on in defense and the capture of prey Prey Tentacle “Trigger” Nematocyst Figure 33.6 Coiled thread Discharge Of thread Cnidocyte Flatworms •  Members of phylum Platyhelminthes –  Live in marine, freshwater, and damp terrestrial habitats –  Are fla\ened dorsoventrally and have a gastrovascular cavity •  Although flatworms undergo triploblas0c development –  They are acoelomates •  The best-­‐known turbellarians, commonly called planarians –  Have light-­‐sensi0ve eyespots and centralized nerve nets Pharynx. The mouth is at the 0p of a muscular pharynx that extends from the animal’s ventral side. Diges0ve juices are spilled onto prey, and the pharynx sucks small pieces of food into the gastrovascular cavity, where diges0on con0nues. Diges0on is completed within the cells lining the gastro-­‐ vascular cavity, which has three branches, each with fine subbranches that pro-­‐ vide an extensive surface area. Undigested wastes are egested through the mouth. Gastrovascular cavity Eyespots Figure 33.10 Ganglia. Located at the anterior end of the worm, near the main sources of sensory input, is a pair of ganglia, dense clusters of nerve cells. Ventral nerve cords. From the ganglia, a pair of ventral nerve cords runs the length of the body. •  Trematodes that parasi0ze humans –  Spend part of their lives in snail hosts 1 Mature flukes live in the blood vessels of the human intes0ne. A female fluke fits into a groove running the length of the larger male’s body, as shown in the light micrograph at right. Male Female 1 mm 5 These larvae penetrate the skin and blood vessels of humans working in irrigated fields contaminated with infected human feces. 2 Blood flukes reproduce sexually in the human host. The fer0lized eggs exit the host in feces. 3 The eggs develop in water into ciliated larvae. These larvae infect snails, the intermediate hosts. Figure 33.11 4 Asexual reproduc0on within a snail results in another type of mo0le larva, which escapes from the snail host. Snail host •  Tapeworms Tapeworm –  Are also parasi0c and lack a diges0ve system Progloods with reproduc0ve structures 200 µm Scolex Figure 33.12 Hooks Sucker •  Concept 33.4: Molluscs have a muscular foot, a visceral mass, and a mantle •  Phylum Mollusca –  Includes snails and slugs, oysters and clams, and octopuses and squids •  Most molluscs are marine –  Though some inhabit fresh water and some are terrestrial •  Molluscs are sob-­‐bodied animals –  But most are protected by a hard shell Heart. Most molluscs have an open circulatory system. The dorsally located heart pumps circulatory fluid called hemolymph through arteries into sinuses (body spaces). The organs of the mollusc are thus con0nually bathed in hemolymph. Nephridium. Excretory organs called nephridia remove metabolic wastes from the hemolymph. The long diges0ve tract is coiled in the visceral mass. Visceral mass Coelom Mantle Mantle cavity Stomach Shell Radula Anus The nervous Gill system consists of a nerve ring around the esophagus, from which nerve cords extend. Figure 33.16 Foot Intes0ne Gonads Nerve cords Esophagus Mouth Mouth Radula. The mouth region in many mollusc species contains a rasp-­‐like feeding organ called a radula. This belt of backward-­‐ curved teeth slides back and forth, scraping and scooping like a backhoe. •  Most molluscs have separate sexes –  With gonads located in the visceral mass •  The life cycle of many molluscs –  Includes a ciliated larval stage called a trochophore Gastropods •  About three-­‐quarters of all living species of molluscs –  Belong to class Gastropoda (a) A land snail Figure 33.18a, b (b) A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolu0on. •  Molluscs of class BBivalves ivalvia –  Include many species of clams, oysters, mussels, and scallops –  Have a shell divided into two halves Figure 33.20 •  The mantle cavity of a bivalve –  Contains gills that are used for feeding as well as gas exchange Mantle Hinge area Gut Coelom Heart Shell Adductor muscle Mouth Anus Excurrent siphon Palp Water flow Foot Figure 33.21 Mantle cavity Gill Incurrent siphon •  Concept 33.5: Annelids are segmented worms •  Annelids –  Have bodies composed of a series of fused rings •  Anatomy of an earthworm Coelom. The coelom of the earthworm is par00oned by septa. Each segment is surrounded by longitudinal muscle, which in turn is surrounded by circular muscle. Earthworms coordinate the contrac0on of these two sets of muscles to move (see Figure 49.25). These muscles work against the noncompressible coelomic fluid, which acts as a hydrosta0c skeleton. Epidermis Septum (par00on between segments) Circular muscle Many of the internal structures are repeated within each segment of the earthworm. Chaetae. Each segment has four pairs of chaetae, bristles that provide trac0on for burrowing. Longitudinal muscle Dorsal vessel Anus Intes0ne Nerve cords Cerebral ganglia. The earthworm nervous system features a brain-­‐like pair of cerebral ganglia above and in front of the pharynx. A ring of nerves around the pharynx connects to a subpharyngeal ganglion, from which a fused pair of nerve cords runs posteriorly. Table 33.23 Cu0cle Metanephridium. Each segment of the worm contains a pair of excretory tubes, called metanephridia, with ciliated funnels, called nephrostomes. The metanephridia remove wastes from the blood and coelomic fluid through exterior pores. Nephrostome Pharynx Tiny blood vessels are abundant in the earthworm’s skin, which func0ons as its respiratory organ. The blood contains oxygen-­‐carrying hemoglobin. Ventral vessel Clitellum Esophagus Metanephridium Crop Giant Australian earthworm Intes0ne Mouth Gizzard Subpharyngeal ganglion The circulatory system, a network of vessels, is closed. The dorsal and ventral vessels are linked by segmental pairs of vessels. The dorsal vessel and five pairs of vessels that circle the esophagus of an earthworm are muscular and pump blood through the circulatory system. Ventral nerve cords with segmental ganglia. The nerve cords penetrate the septa and run the length of the animal, as do the diges0ve tract and longitudinal blood vessels. •  Concept 33.6: Nematodes are nonsegmented pseudocoelomates covered by a tough cu0cle •  Among the most widespread of all animals, nematodes, or roundworms –  Are found in most aqua0c habitats, in the soil, in moist 0ssues of plants, and in the body fluids and 0ssues of animals •  The cylindrical bodies of nematodes (phylum Nematoda) –  Are covered by a tough coat called a cu0cle Figure 33.26 25 µm •  Some species of nematodes –  Are important parasites of plants and animals Encysted juveniles Figure 33.27 Muscle 0ssue 50 µm •  Concept 33.7: Arthropods are segmented coelomates that have an exoskeleton and jointed appendages •  Two out of every three known species of animals are arthropods •  Members of the phylum Arthropoda –  Are found in nearly all habitats of the biosphere General Characteris0cs of Arthropods •  The diversity and success of arthropods –  Are largely related to their segmenta0on, hard exoskeleton, and jointed appendages •  As arthropods evolved –  The segments fused, and the appendages became more specialized •  The appendages of some living arthropods –  Are modified for many different func0ons Cephalothorax Antennae (sensory recep0on) Abdomen Head Thorax Swimming appendages Walking legs Figure 33.29 Pincer (defense) Mouthparts (feeding) •  Arthropods have an open circulatory system –  In which fluid called hemolymph is circulated into the spaces surrounding the 0ssues and organs •  A variety of organs specialized for gas exchange –  Have evolved in arthropods •  Arachnids have an abdomen and a cephalothorax –  Which has six pairs of appendages, the most anterior of which are the chelicerae Diges0ve gland Intes0ne Stomach Heart Brain Eyes Poison gland Ovary Anus Book lung Spinnerets Figure 33.32 Silk gland Gonopore (exit for eggs) Sperm receptacle Chelicera Pedipalp •  The internal anatomy of an insect –  Includes several complex organ systems The insect body has three regions: head, thorax, and abdomen. The segmenta0on of the thorax and abdomen are obvious, but the segments that form the head are fused. Abdomen Thorax Head Compound eye Antennae Figure 33.35 Malpighian tubules. Anus Metabolic wastes are removed from the Vagina hemolymph by excretory organs called Malpighian tubules, which are out-­‐ pocke0ngs of the diges0ve tract. Tracheal tubes. Gas exchange in insects is accomplished by a tracheal system of branched, chi0n-­‐lined tubes that infiltrate the body and carry oxygen directly to cells. The tracheal system opens to the outside of the body through spiracles, pores that can control air flow and water loss by opening or closing. Heart. The insect heart drives hemolymph through an open circulatory system. Ovary Nerve cords. The insect nervous system consists of a pair of ventral nerve cords with several segmental ganglia. Cerebral ganglion. The two nerve cords meet in the head, where the ganglia of several anterior segments are fused into a cerebral ganglion (brain). The antennae, eyes, and other sense organs are concentrated on the head. Dorsal artery Crop Insect mouthparts are formed from several pairs of modified appendages. The mouthparts include mandibles, which grasshoppers use for chewing. In other insects, mouthparts are specialized for lapping, piercing, or sucking. •  COMPLETE Metamorphosis from the larval stage to the adult stage –  Occurs during a pupal stage (a) Larva (caterpillar) Figure 33.6a–e (b) Pupa (c) Pupa (d) Emerging adult (e) Adult •  Concept 33.8: Echinoderms and chordates are deuterostomes •  At first glance, sea stars and other echinoderms, phylum Echinodermata –  May seem to have li\le in common with phylum Chordata, which includes the vertebrates •  Chordates and echinoderms share characteris0cs of deuterostomes –  Radial cleavage –  Development of the coelom from the archenteron –  Forma0on of the mouth at the end of the embryo opposite the blastopore •  Unique to echinoderms is a water vascular system –  A network of hydraulic canals branching into tube feet that func0on in locomo0on, feeding, and gas exchange A short diges0ve tract runs from the mouth on the bo\om of the central disk to the anus on top of the disk. Central disk. The central disk has a nerve ring and nerve cords radia0ng from the ring into the arms. Diges0ve glands secrete diges0ve juices and aid in the absorp0on and storage of nutrients. Figure 33.39 Radial canal. The water vascular system consists of a ring canal in the central disk and five radial canals, each running in a groove down the en0re length of an arm. Stomach Anus Spine Gills Ring canal Gonads Radial nerve The surface of a sea star is covered by spines that help defend against predators, as well as by small gills that provide gas exchange. Madreporite. Water can flow in or out of the water vascular system into the surrounding water through the madreporite. Ampulla Podium Tube feet Branching from each radial canal are hundreds of hollow, muscular tube feet filled with fluid. Each tube foot consists of a bulb-­‐like ampulla and suckered podium (foot por0on). When the ampulla squeezes, it forces water into the podium and makes it expand. The podium then contacts the substrate. When the muscles in the wall of the podium contract, they force water back into the ampulla, making the podium shorten and bend. •  The radial anatomy of many echinoderms –  Evolved secondarily from the bilateral symmetry of ancestors Paleozoic Era (542–251 MYA) •  The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals. •  There are several hypotheses regarding the cause of the Cambrian explosion –  New predator-­‐prey rela&onships –  A rise in atmospheric oxygen –  The evolu0on of the Hox gene complex. A Cambrian seascape
Animal Body Symmetry (a) Radial symmetry
(b) Bilateral symmetry
Body Plan -­‐-­‐ Tissues •  Animal body plans also vary according to the organiza0on of the animal’s 0ssues. •  Tissues are collec0ons of specialized cells isolated from other 0ssues by membranous layers. •  During development, three germ layers give rise to the &ssues and organs of the animal embryo. Coelom
Triploblas;c Animals Body Cavi;es Body covering
(from ectoderm)
Digestive tract
(from endoderm)
(a)
Tissue layer lining coelom
and suspending internal organs
(from mesoderm)
Coelomate - true body cavity
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
(b)
Pseudocoelomate
Body covering
(from ectoderm)
Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
(c)
Acoelomate - lack a body cavity
Protostome
Deuterostome
Development
molluscs, annelids
Development
echinoderm, chordates
Eight-cell stage
(a) Cleavage
Eight-cell stage
Radial and indeterminate
Spiral and determinate
Key
Coelom
Ectoderm
Mesoderm
Endoderm
(b) Coelom formation
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
Anus
Mesoderm
Folds of archenteron
form coelom.
Mouth
(c) Fate of the blastopore
Digestive tube
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
Derived Characters of Chordates •  All chordates share a set of derived characters –  Although some species possess some of these traits only during embryonic development Dorsal, hollow nerve cord Muscle segments Brain Notochord Mouth Anus Figure 34.3 Muscular, post-­‐anal tail Pharyngeal slits or cleFs Derived Characters of Mammals •  Mammary glands, which produce milk –  Are a dis0nc0vely mammalian character •  Hair is another mammalian characteris0c •  Mammals generally have a larger brain –  Than other vertebrates of equivalent size •  Monotremes –  Are a small group of egg-­‐laying mammals consis0ng of echidnas and the platypus Figure 34.33 •  A marsupial is born very early in its development –  And completes its embryonic development while nursing within a maternal pouch called a marsupium (a) A young brushtail possum. The young of
marsupials are born very early in their
development. They finish their growth
while nursing from a nipple (in their
mother’s pouch in most species).
Figure 34.34a Eutherians (Placental Mammals) •  Compared to marsupials –  Eutherians have a longer period of pregnancy •  Young eutherians –  Complete their embryonic development within a uterus, joined to the mother by the placenta Derived Characters of Primates •  Most primates –  Have hands and feet adapted for grasping •  Primates also have –  A large brain and short jaws –  Forward-­‐looking eyes close together on the face, providing depth percep0on –  Well-­‐developed parental care and complex social behavior –  A fully opposable thumb Adapta0ons Enabling the Move to Land •  In green algae charophytes a layer of a durable polymer called sporopollenin prevents dehydra&on of exposed zygotes. •  The movement onto land by charophyte ancestors provided advantages: unfiltered sun, more plen0ful CO2, nutrient-­‐rich soil, and few herbivores or pathogens. •  Land presented challenges: a scarcity of water and lack of structural support. Three Clades are candidates for Plant Kingdom
Red algae
Chlorophytes
Plantae
Embryophytes
Streptophyta
Charophytes
Viridiplantae
ANCESTRAL
ALGA
Derived Traits of Plants •  A cu,cle and secondary compounds evolved in many plant species. Symbio0c associa0ons between fungi and the first land plants may have helped plants without true roots to obtain nutrients. •  Four key derived traits of plants are absent in the green algae charophytes: –  Alterna&on of genera&ons -­‐ with mul0cellular, dependent embryos. –  Walled spores produced in sporangia –  Mul&cellular gametangia –  Apical meristems Land Plants
Life Cycle
Gametophyte
(n)
Mitosis
n
n
Spore
MEIOSIS
Gamete from
another plant
Mitosis
n
n
Gamete
FERTILIZATION
2n
Zygote
Mitosis
Sporophyte
(2n)
Alternation of generations = Derived traits of land plants
Walled Spores Produced in
Sporangia
•  The sporophyte produces spores in organs called sporangia. •  Diploid cells called sporocytes undergo meiosis to generate haploid spores. •  Spore walls contain sporopollenin, which protects against dessica&on making them resistant to harsh environments. Derived Traits of Land Plants: Walled
Spores
Produced in
Sporangia:
Spores
Sporangium
Longitudinal section of
Sphagnum sporangium (LM)
Sporophyte 2n
Gametophyte n
Sporophytes and sporangia of Sphagnum (a moss)
Derived Traits of Land Plants: Multicellular Gametangia - ‘sex organs’
Female gametophyte
Archegonium
with egg
Antheridium
with sperm
Male
gametophyte
Archegonia and Antheridia of Marchantia (a liverwort)
Apical Meristems
•  Apical meristems are growth regions at plant &ps, allowing plants to sustain con&nual growth in their length. •  Cells from the apical meristems differen0ate into various 0ssues. Apical Meristems - Allow for Growth in Length throughout Plant’s Lifetime.
Apical
meristem
of shoot
Shoot
Developing
leaves
100 µm
Apical meristems
Apical meristem
of root
Root
Derived Traits of Land Plants
100 µm
A Vast Diversity of Modern Plants
•  Ancestral species gave rise to land plants which can be informally grouped based on the presence or absence of vascular ,ssue. •  Nonvascular plants are commonly called bryophytes. •  Most plants have vascular 0ssue; these cons0tute the vascular plants: seedless vascular and seed plants. •  Seedless vascular plants can be divided into clades: –  Lycophytes (club mosses and their rela0ves) –  Pterophytes (ferns and their rela0ves). •  Seedless vascular plants are paraphyle0c, and are of the same level of biological organiza0on, or grade. •  A seed is an embryo and nutrients surrounded by a protec&ve coat. •  Seed plants form a clade and can be divided into further clades: –  Gymnosperms, the “naked seed” plants including the conifers / cone = sex organ –  Angiosperms, the flowering plants including monocots and dicots / flower = sex organ Highlights of Plant Evolution
1 Origin of land plants (about 475 mya)
2 Origin of vascular plants (about 420 mya)
3 Origin of extant seed plants (about 305 mya)
Hornworts
1
Mosses
Pterophytes (ferns,
horsetails, whisk ferns)
3
Angiosperms
450
400
350
300
Millions of years ago (mya)
50
0
Seed plants
Gymnosperms
Vascular plants
2
Seedless
vascular
plants
Lycophytes (club mosses,
spike mosses, quillworts)
500
Land plants
ANCESTRAL
GREEN
ALGA
Nonvascular
plants
(bryophytes)
Liverworts
•  A spore germinates into a gametophyte composed of a protonema and gamete-­‐producing gametophore. •  Rhizoids anchor gametophytes to substrate. •  The height of gametophytes is constrained by lack of vascular 0ssues. •  Mature gametophytes produce flagellated sperm in antheridia and an egg in each archegonium. •  Sperm swim through a film of water to reach and fer&lize the egg. Bryophyte Structures
Thallus
Gametophore of
female gametophyte
Sporophyte
Foot
Seta
Marchantia sporophyte (LM)
500 µm
Marchantia polymorpha,
a “thalloid” liverwort
Capsule
(sporangium)
Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall •  Bryophytes and bryophyte-­‐like plants were the vegeta0on during the first 100 million years of plant evolu0on. •  Vascular plants began to diversify during the Devonian and Carboniferous periods. •  Vascular &ssue allowed vascular plants to grow tall. •  Seedless vascular plants have flagellated sperm and are usually restricted to moist environments. Origins and Traits of Vascular Plants •  Fossils of the forerunners of vascular plants date back about 420 million years. •  In contrast with bryophytes, sporophytes of seedless vascular plants are the larger genera0on. The gametophytes are 0ny plants that grow on or below the soil surface. •  Vascular plants are characterized by: •  Life cycles with dominant sporophytes •  Vascular &ssues called xylem and phloem. •  Well-­‐developed / true roots and leaves. Transport in Vascular Tissue: Xylem and Phloem •  Vascular plants have two types of vascular 0ssue: xylem and phloem. •  Xylem conducts most of the water and minerals and includes dead cells called tracheids. •  Phloem consists of living cells and distributes nutrients: sugars, amino acids. •  Water-­‐conduc0ng cells are strengthened by lignin and provide structural support. •  Increased height was an evolu0onary advantage. Evolu&on of Roots and Leaves •  Roots are organs that anchor vascular plants and enable plants to absorb water and nutrients from the soil. •  Roots may have evolved from subterranean stems. •  Leaves are organs that increase the surface area of vascular plants for capturing more solar energy used for photosynthesis. Seedless Vascular Plants
Lycophytes (Phylum Lycophyta)
2.5 cm
Isoetes
gunnii,
a quillwort
Strobili
(clusters of
sporophylls)
1 cm
Selaginella apoda,
a spike moss
Diphasiastrum tristachyum, a club moss
Overview: Transforming the World •  Seeds changed the course of plant evolu0on, enabling their bearers to become the dominant producers in most terrestrial ecosystems. •  A seed consists of an embryo and nutrients surrounded by a protec&ve coat. •  The gametophytes of seed plants develop within the walls of spores that are retained within 0ssues of the parent sporophyte. Seeds and pollen grains are key adapta0ons for life on land •  In addi0on to seeds, the following are common to all seed plants: –  Reduced gametophytes –  Heterospory –  Ovules –  Pollen Gametophyte / sporophyte rela;onships in different plant groups
Mosses and other nonvascular plants Gametophyte Sporophyte Dominant Reduced, dependent on gametophyte for nutri;on PLANT GROUP Ferns and other seedless vascular plants Reduced, independent (photosynthe;c and free-­‐living) Dominant Sporophyte (2n) Seed plants (gymnosperms and angiosperms) Reduced (usually microscopic), dependent on surrounding sporophyte ;ssue for nutri;on Dominant Gymnosperm Microscopic female gametophytes (n) inside ovulate cone Sporophyte (2n) Gametophyte (n) Angiosperm Microscopic female gametophytes (n) inside these parts of flowers Example Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Gametophyte (n) Microscopic male gametophytes (n) inside these parts of flowers Sporophyte (2n) Ovules and Produc0on of Eggs •  An ovule consists of a megasporangium, megaspore, and one or more protec&ve integuments. •  A fer&lized ovule becomes a seed. •  Gymnosperm megaspores have one integument. •  Angiosperm megaspores usually have two integuments. From ovule to seed in a gymnosperm
Integument Spore wall Immature female cone Megasporangium (2n) Megaspore (n) (a) Unfer;lized ovule From ovule to seed in a gymnosperm Female gametophyte (n) Spore wall Egg nucleus (n) Male gametophyte (within a germinated pollen grain) (n) Micropyle (b) Fer;lized ovule Discharged sperm nucleus (n) Pollen grain (n) From ovule to seed in a gymnosperm Seed coat (derived from integument) Food supply (female gametophyte ;ssue) (n) Embryo (2n) (new sporophyte) (c) Gymnosperm seed Gymnosperms bear “naked” seeds, typically on cones •  The gymnosperms have “naked” seeds not enclosed by ovaries and exposed on modified leaves -­‐ cones. There are four phyla: –  Cycadophyta (cycads) –  Gingkophyta (one living species: Ginkgo biloba) –  Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) –  Coniferophyta (conifers, such as pine, fir, and redwood). The reproduc0ve adapta0ons of angiosperms include flowers and fruits •  Angiosperms are seed plants with reproduc&ve structures called flowers and fruits. •  They are the most widespread and diverse of all plants. •  All angiosperms are classified in a single phylum: Anthophyta. •  The name comes from the Greek anthos, flower. Structure of an Idealized Flower S;gma Stamen Anther Carpel Style Filament Ovary Petal Sepal Ovule Fruits •  A fruit typically consists of a mature ovary but can also include other flower parts. •  Fruits protect seeds and aid in seed dispersal. •  Mature fruits can be either fleshy or dry. •  Various fruit adapta&ons help disperse seeds by wind, water, or animals to new loca0ons. The Angiosperm Life Cycle •  The flower of the sporophyte is composed of both male and female structures. •  Male gametophytes are contained within pollen grains produced by the microsporangia of anthers. •  The female gametophyte = embryo sac, develops within an ovule contained within an ovary at the base of a s0gma. •  Most flowers have mechanisms to ensure cross-­‐
pollina;on between flowers from different plants of the same species. •  A pollen grain that has landed on a s0gma germinates and the pollen tube of the male gametophyte grows down to the ovary. •  Sperm enter the ovule through a pore opening called the micropyle. •  Double fer,liza,on occurs when the pollen tube discharges two sperm into the female gametophyte within an ovule. Double Fer,liza,on: Produces Zygote 2n and endosperm (food) 3n •  One sperm fer&lizes the egg forming a zygote. •  The other sperm combines with two nuclei and ini0ates development of food-­‐storing endosperm. •  The endosperm nourishes the developing embryo. •  Within a seed, the embryo consists of a root and two seed leaves called cotyledons. Angiosperm Diversity Ø The two main groups of angiosperms are: monocots -­‐ one cotyledon eudicots (“true” dicots) -­‐ two cotyledons. •  More than one-­‐quarter of angiosperm species are monocots. •  More than two-­‐thirds of angiosperm species are eudicots. Angiosperms: Monocots and Eudicots Monocot Characteris;cs Eudicot Characteris;cs Embryos One cotyledon Two cotyledons Leaf vena;on Veins usually parallel Veins usually netlike Stems Vascular ;ssue usually arranged in ring Vascular ;ssue scaZered Roots Taproot (main root) usually present Root system usually fibrous (no main root) Pollen Pollen grain with one opening Pollen grain with three openings Flowers Floral organs usually in mul;ples of three Floral organs usually in mul;ples of four or five •  For example, the bending of a grass seedling toward light –  Begins with the plant sensing the direc0on, quan0ty, and color of the light Figure 39.1 •  The potato’s response to light –  Is an example of cell-­‐signal processing CYTOPLASM CELL WALL 1 Recep;on 2 Transduc;on Relay molecules Receptor Hormone or environmental s0mulus Plasma membrane Figure 39.3 3 Response Ac0va0on of cellular responses •  An example of signal transduc0on in plants 2 Transduc;on 1 Recep;on 3 Response Transcrip0on factor 1 NUCLEUS CYTOPLASM cGMP Plasma membrane Phytochrome ac0vated by light Cell wall Second messenger produced 2 One pathway uses cGMP as a second messenger that ac0vates a specific protein kinase.The other pathway involves an increase in cytoplasmic Ca2+ that ac0vates another specific protein kinase. Specific protein kinase 1 ac0vated P Transcrip0on factor 2
P Specific protein kinase 2 ac0vated Transcrip0on Light Transla0on 1 The light signal is detected by the phytochrome receptor, which then ac0vates at least two signal transduc0on pathways. Figure 39.4 Ca2+ channel opened Ca2+ 3 Both pathways lead to expression of genes for proteins that func0on in the de-­‐e0ola0on (greening) response. De-­‐e;ola;on (greening) response proteins •  Ul0mately, a signal transduc0on pathway –  Leads to a regula0on of one or more cellular ac0vi0es •  In most cases –  These responses to s0mula0on involve the increased ac0vity of certain enzymes De-­‐E&oloa&on (“Greening”) Proteins •  Many enzymes that func0on in certain signal responses are involved in photosynthesis directly –  While others are involved in supplying the chemical precursors necessary for chlorophyll produc0on •  Concept 39.2: Plant hormones help coordinate growth, development, and responses to s0muli •  Hormones –  Are chemical signals that coordinate the different parts of an organism The Discovery of Plant Hormones •  Any growth response –  That results in curvatures of whole plant organs toward or away from a s0mulus is called a tropism –  Is oben caused by hormones EXPERIMENT In 1880, Charles Darwin and his son Francis designed an experiment to determine what part of the coleop0le senses light. In 1913, Peter Boysen-­‐Jensen conducted an experiment to determine how the signal for phototropism is transmi\ed. RESULTS Control Boysen-­‐Jensen (1913) Darwin and Darwin (1880) Shaded side of coleop0le Light Light Light Illuminated side of coleop0le Tip removed Tip covered by opaque cap Tip covered by trans-­‐ parent cap Base covered by opaque shield Tip separated by gela0n block CONCLUSION In the Darwins’ experiment, a phototropic response occurred only when light could reach the 0p of coleop0le. Therefore, they concluded that only the 0p senses light. Boysen-­‐Jensen observed that a phototropic response occurred if the 0p was separated by a permeable barrier (gela0n) but not if separated by an impermeable solid barrier (a mineral called mica). These results suggested that the signal is a light-­‐ac0vated mobile chemical. Figure 39.5 Tip separated by mica •  In general, hormones control plant growth and development –  By affec0ng the division, elonga0on, and differen0a0on of cells •  Plant hormones are produced in very low concentra0ons –  But a minute amount can have a profound effect on the growth and development of a plant organ •  The term auxin Auxin –  Is used for any chemical substance that promotes cell elonga0on in different target 0ssues Role to oaf mAodel uxin in Ctell longa0on • The According called he aEcid growth hypothesis –  Proton pumps play a major role in the growth response of cells to auxin •  Cell elonga0on in response to auxin Cross-­‐linking cell wall polysaccharides 3 Wedge-­‐shaped expansins, ac0vated by low pH, separate cellulose microfibrils from cross-­‐linking polysaccharides. The exposed cross-­‐linking polysaccharides are now more accessible to cell wall enzymes. Expansin 4 The enzyma0c cleaving of the cross-­‐linking CELL WALL polysaccharides allows the microfibrils to slide. The extensibility of the cell wall is increased. Turgor causes the cell to expand. Cell wall enzymes Microfibril H2O H+ 2 The cell wall becomes more acidic. Figure 39.8 H+ Cell wall H+ H+ H+ 1 Auxin increases the ac0vity of proton pumps. Plasma membrane ATP H+ H+ H+ Cytoplasm Nucleus Vacuole H+ Plasma membrane Cytoplasm 5 With the cellulose loosened, the cell can elongate. Lateral and Adven00ous Root •  Auxin Forma0on –  Is involved in the forma0on and branching of roots Other Effects of Auxin •  Auxin affects secondary growth –  By inducing cell division in the vascular cambium and influencing differen0a0on of secondary xylem Control of Cell Division and •  Cytokinins Differen0a0on –  Are produced in ac0vely growing 0ssues such as roots, embryos, and fruits –  Work together with auxin Control of Apical Dominance •  Cytokinins, auxin, and other factors interact in the control of apical dominance –  The ability of a terminal bud to suppress development of axillary buds Axillary buds Figure 39.9a Gibberellins •  Gibberellins have a variety of effects –  Such as stem elonga0on, leaf and fruit growth, and seed germina0on •  In stems –  Gibberellins s0mulate cell elonga0on and cell division •  Aber water is imbibed, the release of gibberellins from the embryo –  Signals the seeds to break dormancy and germinate 22 The aleurone responds by synthesizing and secre0ng diges0ve enzymes that hydrolyze stored nutrients in the endosperm. One example is α-­‐amylase, which hydrolyzes starch. (A similar enzyme in our saliva helps in diges0ng bread and other starchy foods.) 1 Aber a seed imbibes water, the embryo releases gibberellin (GA) as a signal to the aleurone, the thin outer layer of the endosperm. 3 Sugars and other nutrients absorbed from the endosperm by the scutellum (cotyledon) are consumed during growth of the embryo into a seedling. Aleurone Endosperm α-­‐amylase GA GA Water Radicle Scutellum (cotyledon) Figure 39.11 Sugar Abscisic Acid •  Two of the many effects of abscisic acid (ABA) are –  Seed dormancy –  Drought tolerance Ethylene •  Plants produce ethylene –  In response to stresses such as drought, flooding, mechanical pressure, injury, and infec0on Response to Mechanical Stress •  Ethylene induces the triple response –  Which allows a growing shoot to avoid obstacles EXPERIMENT Germinating pea seedlings were placed in the
dark and exposed to varying ethylene concentrations. Their growth
was compared with a control seedling not treated with ethylene.
RESULTS All the treated seedlings exhibited the triple
response. Response was greater with increased concentration.
0.00 0.10 0.20 0.40 0.80 Ethylene concentra0on (parts per million) Figure 39.13 Ethylene induces the triple response in pea seedlings,
CONCLUSION with increased ethylene concentration causing increased response.
Apoptosis: Programmed Cell Death •  A burst of ethylene –  Is associated with the programmed destruc0on of cells, organs, or whole plants Leaf Abscission •  A change in the balance of auxin and ethylene controls leaf abscission –  The process that occurs in autumn when a leaf falls 0.5 mm Figure 39.16 Protec0ve layer Abscission layer Stem Pe0ole Fruit Ripening •  A burst of ethylene produc0on in the fruit –  Triggers the ripening process •  Many legumes –  Lower their leaves in the evening and raise them in the morning (photoperiodism) Figure 39.21
Noon Midnight A Flowering Hormone? •  The flowering signal, not yet chemically iden0fied –  Is called florigen, and it may be a hormone or a change in rela0ve concentra0ons of mul0ple hormones •  Plants may detect gravity by the se\ling of statoliths (gravitropism) –  Specialized plas0ds containing dense starch grains Statoliths Figure 39.25a, b (a) (b) 20 µm •  Rubbing the stems of young plants a couple of 0mes daily –  Results in plants that are shorter than controls Figure 39.26 •  Growth in response to touch –  Is called thigmotropism –  Occurs in vines and other climbing plants •  Rapid leaf movements in response to mechanical s0mula0on –  Are examples of transmission of electrical impulses called ac0on poten0als (a) Uns;mulated (b) S;mulated Side of pulvinus with flaccid cells Leaflets aber s0mula0on Side of pulvinus with turgid cells Pulvinus (motor organ) Figure 39.27a–c (c) Motor organs Vein 0.5 µm •  During drought Drought –  Plants respond to water deficit by reducing transpira0on –  Deeper roots con0nue to grow •  Concept 39.5: Plants defend themselves against herbivores and pathogens •  Plants counter external threats –  With defense systems that deter herbivory and prevent infec0on or combat pathogens Defenses Against Herbivores •  Herbivory, animals ea0ng plants –  Is a stress that plants face in any ecosystem •  Plants counter excessive herbivory –  With physical defenses such as thorns –  With chemical defenses such as distasteful or toxic compounds •  Some plants even “recruit” predatory animals –  That help defend the plant against specific herbivores 4 Recruitment of parasitoid wasps that lay their eggs within caterpillars 3 Synthesis and release of vola0le a\ractants 1 Wounding 1 Chemical in saliva 2 Signal transduc0on pathway Figure 39.29