Plant Diversity 2 Lecture Notes PDF

Plant Diversity 2 Concepts 30.1-30.3 Campbell. Biology. 3rd ed Outline • 1. Adaptations of Seed Plants • 2. The Gymnosperms • 3. The Angiosperms http://jessicalovespla nts.blogspot.com/20 12/06/comparison-b etween-mosses-ferns .html 1. Adaptations of seed plants • Seeds enhance reproductive su...

Plant Diversity 2 Concepts 30.1-30.3 Campbell. Biology. 3rd ed Outline • 1. Adaptations of Seed Plants • 2. The Gymnosperms • 3. The Angiosperms http://jessicalovespla nts.blogspot.com/20 12/06/comparison-b etween-mosses-ferns .html 1. Adaptations of seed plants • Seeds enhance reproductive success of embryo • Enclosed in the protective seed • Food source • Prevent drying out • Dormancy • Photo: Silene stenophylla grown from 32,000 year old seeds found in a fossilized squirrel burrow in the Siberian permafrost. The oldest seeds ever to germinate Key adaptations of land plants • Reduced Gametophytes • Heterospory • Ovules and Pollen • Seeds • No Water Required for Fertilization • Advanced Root and Shoot systems Figure 30.2 Gametophyte-sporophyte relationships in different plant groups Reduced Gametophytes • In the Vascular Seed Plants: Sporophyte is the dominant phase of the life cycle. • Gametophyte is microscopic and dependent on the sporophyte tissues for nutrition • Gametophyte is retained inside the parental tissue during development (ie, compare to independent and free living in bryophytes and seedless vascular plants/ferns and their relatives) • Inside the cones/strobili in Gymnosperms and the flowers in Angiosperms • Protects gametophyte • Allows gametophyte to obtain nutrition Heterospory • Seed plants are heterosporous = producing two kinds of spores (male and female) • Megasporangia, located on modified leaves called megasporophylls, produce megaspores which give rise to the female gametophyte • Microsporangia, located on modified leaves called macrosporophylls , produce microspores which give rise to the male gametophyte • Megaspores are larger than microspores • Each megasporangium produces one megaspore, whereas each microsporangium produces many microspores Heterospory in Gymnosperms (eg. Pine Cone) FEMALE CONE megasporangium https://biologyboom.com/type-2-pinus/ Heterospory in Angiosperms FEMALE FLOWER MALE FLOWER https://www.sciencedirect.com/topics/agricultural-andbiological-sciences/microsporangia http://www2.estrellamountain.edu/faculty/farabee/biobk/biobookflowers.html Ovules and Production of Eggs • Megasporangium (structure that produces the megaspore) is held within maternal sporophyte tissues surrounded by a specialized layer called the integument • Integument protects the megasporangium • Seed coat is derived from integument • OVULE = Megasporangium + megaspore + integument • Inside the ovule, the female gametophyte develops from the megaspore and produces one or more eggs • SEED develops from the OVULE following POLLINATION and FERTILIZATION carpel https://www.treeguideuk.co.uk/ovules-and-placentas/ Pollen and Production of Sperm • Microspores (produced in microsporangium) develop into pollen grains • Pollen grain consists of a male gametophyte enclosed with the pollen wall • Pollen wall contain sporopollenin which protect the pollen grain from harsh environmental conditions and assist in transport (ie. Hitching on the bodies of animals) • Adaptation of pollen is transfer by wind and animal pollinator • Pollen grain lands on the female part of the flower and germinates • Once germinated, a pollen tube grows down into the female gametophyte within the ovule and discharge the sperm. • Transfer of pollen to carpel = pollination • Union of sperm and egg = fertilization https://www.nikonsmallworld.com/galleries/2021-photomicrograph y-competition/anther-and-pollen-grains-of-a-bird-of-paradise-shrub https://www.sciencefacts.net/anther.html Ovule to Seed in Gymnosperm SEEDS • Seeds provide a significant adaptation for plants on land. • Protective seed coat • Supply of food for embryo • Capable of dormancy in unfavorable environmental conditions Other Advantages of Seed Plants • True root systems • Advanced root systems • Vascular tissue is present • Xylem = water and mineral transport • Phloem = sugars and amino acids, organic compounds transport 2. Seed Plants – The Gymnosperms • Gymnosperm refers to the exposed (naked/ out in the open) nature of the seeds. • Seeds found on sporophylls of the cone • Four living phyla • Phylum Coniferophyta / The Conifers • Phylum Gingkophyta • Phylum Cycadophyta • Phylum Gnetophyta Coniferophyta Pine, fir, spruce, cedar Cycadophyta Leaves superficially palmlike Ginkgophyta Gnetophyta Tree with fan shaped leaves Three genera. The Life Cycle of the Pine (Coniferophyta) • Pine tree is the sporophyte • Heterosporous = two types of spores (male and female) produced in separate cones • Pollen cones are smaller than ovulate contes • In pines, each tree has both types of cones (monoecious = one house) • Pollen cones • Scales are modified leaves (microsporophyll) that bear microsporangia • Within microsporangium, microsporocytes (cells) undergo meiosis to produce haploid microspores • Each microspore develops into a pollen grain or male gametophyte • Ovulate cones • Scales are modified leaves (megasporophyll) that bear megasporangia (spelling) and also contain stem tissue • Within megasporangium, megasporocytes (cells) undergo meiosis to produce haploid megaspores inside the ovule • Surviving megaspores develop into female gametophyte •Figure 30.5 THE LIFE CYCLE OF A PINE • 1) Coniferophyta - Pines, firs, spruces, cedars, sequoia, redwood • The largest gymnosperm phyla • 600 species of conifers • Woody cones and fleshy cones Gymnosperm Phyla • Needlelike leaves in pines; scalelike leaves in redwoods • Some species dominate northern hemispheres, and some dominate southern hemispheres • Majority are evergreens https://i0.wp.com/arnoldzwicky.s3.amazonaws.com/LeafTypes.jpg • Pines (Pinus) • Dominant trees in coniferous forests of Northern Hemisphere • Include world’s oldest known living organisms - Bristlecone pines • Reach ages of 4600 years • Oldest Bristlecone pine's location is hidden by scientists to protect it Bristlecone pine • Pines - Structure and form: • Have modifications that enable them to survive harsh conditions • Hypodermis located below the epidermis. • One to two layers of thick-walled cells • Thick cuticle/Recessed (attached) or sunken stomata http://generalhorticulture.tamu.edu/lectsupl/anatomy/anatomy.html • Pines - Structure and form: • Resin canals develop in the mesophyll (inner tissue of leaf) • Resin (secretion) is antiseptic and aromatic, prevents development of fungi, and deters insects. • Mycorrhizal fungi associated with roots of most conifers. http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT410/Secretion/PPineNedlWhol400Lab.jpg • 2) Ginkgophyta - Has single living representative, Ginkgo biloba • Strobili = a conelike structure • Tree with fan-shaped leaves; veins branch dichotomously • Known as the maidenhair tree because leaves turn golden in the fall • Seeds enclosed in fleshy covering • Life cycle similar to pines • Dioecious - Male and female structures on separate trees. • Deciduous https://www.britannica.com/plant/cycad • 3) Cycadophyta • Strobili = conelike structure/sporangia bearing structure • Leaves superficially palmlike • Mostly found in tropical and subtropical locations • Life cycle similar to pines • Pollination sometimes by beetles • Dioecious (separate male and female plants) Male cycad Female cycad • 4) Gnetophyta - Three genera - Gnetum, Ephedra, Welwitschia • Morphologically very dissimilar • Unique among the Gymnosperms in having vessels in the xylem. • Note that vessel elements are typically found in flowering plants (Angiosperms) 5. The Angiosperms Angiosperms = flowering plants • Flowers are unique structures in Angiosperms for sexual reproduction • Insect or other animal pollinators are common in angiosperms • Gymnosperms predominantly wind pollinated • Some angiosperms are also wind pollinated • Carpel megasporophyll) • resembles a leaf that has folded over and fused at the margins. Parts of the carpel are the stigma, style and ovary • Ovaries are within carpels • Ovules are contained in an ovary. • As in gymnosperms, each ovule contains a female gametophyte (embryo sac) • If fertilized, the ovule develops into the seed • Seed develops from ovule. • Ovary becomes a fruit. Parts of a Flower • Four organs: Sepals, petals, stamens, carpels (pistils) • Sepals – at the base of the flower • Green, leaflike structures that enclose the flower before it opens • Petals – brightly colored to attract pollinators • Wind pollinated angiosperms (grasses) lack showy floral parts and bright petals • Stamens – male part of the flower • Consists of a filament (stalk) and an anther (where pollen is produced) • Production of pollen grains • Carpel (Pistil) – female part of the flower • Consists of stigma (sticky tip), style (long tube that leads to ovary) and ovary (contains one or more ovules) • OVULES BECOME SEEDS; OVARIES BECOME FRUIT Figure 30.8 The structure of an idealized flower http://boards.cannabis.com/indoor-growing/56721-botany-definitions.html REPRODUCTIVE PARTS OF THE FLOWER Figure 4–13 Pollination occurs with the transfer of pollen from the stamens to the stigma of the pistil. The pollen grain germinates and the pollen tube grows down the style. Eventually, the pollen tube enters the ovule through the micropyle and deposits two male sperm cells. Fertilization involves the fusion of the male and female cells in the embryo sac. Hartmann and Kester’s Plant Propagation Principles and Practices 8e Hudson Hartman, Dale Kester, Fred Davies and Robert Geneve Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Figure 30.9 Some variations in flower structure Fruits – Only found in Angiosperms • Pollination - Transfer of pollen grains from anther to stigma • Self-pollination - Pollen grains germinate on stigma of same flower. • Cross pollination – Pollen grains of one plant germinate of stigma of another plant • Fertilization - Union of sperm and egg • After fertilization, seeds develop from ovules and the ovary wall thickens and the ovary matures into a fruit • Fruits protect the seeds and aid in dispersal • Mature fruits can be fleshy or dry, dehiscent (split at maturity) or non-dehiscent (do not split) • Fruit Regions – Exocarp - Skin – Endocarp - Inner boundary around seed(s) – Mesocarp - Tissue between exocarp and endocarp Peach fruit – Three regions collectively called pericarp. Figure 30.10 Some variation in fruit structure Figure 30.11 Fruit adaptations that enhance seed dispersal The Angiosperm Life Cycle •The flower of the sporophyte produces microspores that form male gametophytes and megaspores that form female gametophytes • Male gametophyte = the pollen grains • Each pollen grain has two haploid cells • One cell is the tube cell that produces a pollen tube • One cell is the generative cell that divides to form two sperm cells • Female gametophyte = embryo sac (found within each ovule) • The embryo sac consists of several specialized cells, one is the egg cell 1. Pollen is released from the anther and carried to the stigma 2. Pollen grain lands on stigma and germinate 3. The tube cell of the pollen grain produces a pollen tube which grows down the style until it reaches the ovary 4. Pollen tube enters into the ovule through the micropyle and discharges sperm • The pollen tube enters the ovule through a pore called the micropyle and releases the two sperm cells into embryo sac • One sperm fertilizes the egg, the other sperm fuses with other cells in the embryo sac and produces a triploid cell. • Double fertilization = zygote + triploid cell = unique to angiosperms • Double fertilization: • One sperm unites with egg, forming zygote (2N), then embryo. • Other sperm unites with central cell nuclei, producing triploid (3N) endosperm nucleus that develops into endosperm tissue. https://www.quora.com/How-can-you-describe-the-process-of-double-fertilization-in-plants • After fertilization, the ovule mature into the seed • Zygote develops into a mature sporophyte embryo with a radicle (embryonic root) and one or two seed leaves called cotyledons • Triploid central cell becomes the endosperm • Nutritive tissue rich in starch and other food reserves for the developing embryo FIgure 30.12 The life cycle of an angiosperm Angiosperm Diversity • Angiosperm are grouped based on number of cotyledons (seed leaves) in the embryo • Monocot = one cotyledon • Dicot = two cotyledons • Eudicots (true dicots) = DNA evidence indicate dicots are paraphyletic and now majority of dicots form the larger clade of Eudicots (true dicots) • Remaining dicots are grouped into four smaller lineages • Basal angiosperms = Amborella, water lilies, star anise, magnoliids Figure 30.17 Characteristics of monocots and eudicots The End THANK YOU QUESTIONS? 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