Bio 102 General Biology 11 PDF

LAGOS STATE UNIVERSITY FACULTY OF SCIENCE DEPARTMENT OF BOTANY COURSE: BIO 102 (GENERAL BIOLOGY11) TOPIC: BRYOPHYTES, PTERIDOPHYTES AND SPERMATOPHYTES BY ASSOCIATE PROF. A. A. ADU AND DR. K.T. OMOLOKUN 1 ...

LAGOS STATE UNIVERSITY FACULTY OF SCIENCE DEPARTMENT OF BOTANY COURSE: BIO 102 (GENERAL BIOLOGY11) TOPIC: BRYOPHYTES, PTERIDOPHYTES AND SPERMATOPHYTES BY ASSOCIATE PROF. A. A. ADU AND DR. K.T. OMOLOKUN 1  BRYOPHYTES INTRODUCTION Bryophytes are the simplest land plants that lack vascular tissues. Hence, they are referred to as non-vascular seedless plants. They are considered to have evolved from algae. Bryophyta is a Greek word ”BRYON” meaning Moss; and “Phyton” meaning Plants. They colonize terrestrial habitat, but they are still dependent on water for completion of their life cycle. 2 The study of bryophytes is known as bryology. They occupy immediate position between the higher algae and lower pteridophytes. They are considered as “Amphibians” of the plant kingdom. ; since they require water for fertilization.  They are widely distributed throughout the world (notably moist forest of Tropics, Subtropics and Antarctic). There are 25,000 species of liverworts and mosses. 3  GENERAL CHARACTERISTICS OF BRYOPHYTES They undergo alternation of generation in which the gametophyte is dominant. ”Alternation of generation is a phenomenon whereby plants exhibit two phases (i.e. gametophyte and sporophyte) in their life cycle”. The phases are two forms of the same plant, which regularly or alternately follow each other and one phase dominant at a time. Gametophyte is a thallus or leafy green plant body.  Gametophyte is the haploid (n) sexual generation that produces gametes by mitosis. Sporophyte is the diploid (2n) asexual generation that produces spores by meiosis; and it is parasitic or dependent on gametophyte. 4 They lack vascular tissues (i.e. no xylem and phloem). They have no true stem, leaf and root. The gametophyte is anchored by filamentous rhizoids. The rhizoids help to absorb water and mineral salt; and also attach the plant (i.e gametophyte) to the substratum. They live mostly in damp shady places. They are cryptogams (i.e. non –seed producing plants).  They are oogamous They are lower in evolutionary line to Pteridophytes. 5 6  CLASSIFICATION OF BRYOPHYTES  The division bryophyta is divided into three classes: Class I:Hepaticopsida OR Hepaticae (commonly referred to as Liverworts) Order 1:Marchantiales e.g genus Riccia and genus Marchantia Order 2: Jungermanniales e.g genus Pellia and genus Porella Class II: Anthoceropsida OR Anthocerotae (commonly referred to as Hornworts] Order I: Anthocerotales (only order) e.g genus Anthoceros Class III:Bryopsida OR Musci (commonly referred to as Mosses) Order1. Sphanales e.g genus Sphagnum Order 2. Andreaeales e.g genus Andreaea Order 3. Bryales (or true mosses) e.g genus Funaria, genus Polytrichum, genus Barbula 7 Classification of Marchantia Kingdom- Plantae Division-Bryophyta Class- Hepaticopsida OR Hepaticae Order- Marchantiales Family- Marchantiaceae Genus-Marchantia 8 Classification of Funaria Kingdom- Plantae Division-Bryophyta Class- Bryopsida OR Musci Order- Funariales Family- Funariaceae Genus-Funaria 9  Characteristics of the Class Hepaticae (Hepaticopsida) Thalloid liverwort with distinct dichotomous branching taking on a rosette form. Thallus have a flattened structure. Leaves of the leafy type in three ranks along the stem.  Thalloid with complex upper air chamber and photosynthetic filament. Upper surface is a longitudinal groove and lower surface has a role of scales at the apex. Ventral scales are common. Unicellular hairy structures known as the rhizoids are present. Elaters aid spore dispersal. 11  Characteristics of the Class Musci (Bryopsida) Gametophyte have well differentiated body consisting of axis leaves and rhizoids The leaves are spirally arranged in three to eight rows on the axis. Each leaf has a mid-rib but no vascular tissue Sporophyte differentiated into foot, seta and capsule The wall of the capsule consist of several layer of chlorophyllous cells and stomata The peristome teeth are present in one or two rows and surround the terminal opening of the capsule; they are absent only in few mosses Gametophyte is filamentous or simple thallus called protonema producing upright branch [gametophytes] which bear the sex organs Rhizoids borne by both protonema and gametophyte are multicellular and with diagonal cross walls Sex organs are unique in having early growth stages initiated by an apical cell with two cutting faces 12 13 Ecological Adaptations of Bryophytes A waxy cuticle that prevents dessication. Gametangia that protect developing gametes. The gametangia are antheridium (male gametangium) and archegonium (female gametangium). The antheridium produces flagellated sperm cells (male gametes); while the archegonium produces egg (female gamete). Presence of rhizoids for absorption of water and mineral salts from the soil; and also attach the plant (i.e gametophyte) to the substratum. 14 Ecological Importance of Bryophytes They aid soil formation. They play important role in soil conservation. They help in ecological succession. They aid peat formation. They play major role in maintaining soil moisture and nutrient recycling. They serve as indicator of acid rain. 15  PTERIDOPHYTES INTRODUCTION Pteridophytes are referred to as vascular seedless plants (i.e. they have vascular tissues (i.e. phloem and xylem), they have no seeds, but have spores. They are lower and intermediate between bryophytes and gymnosperms.colonize terrestrial habitat, but they are still dependent on water for completion of their life cycle. The possession of vascular tissues is a major evolutionary advancement over bryophytes and algae. 16 GENERAL CHARACTERISTICS OF PTERIDOPHYTES They undergo alternation of generation in which the sporophyte is dominant.  The gametophyte is reduces to a small, simple prothallus (i.e male and female gametophytes). They are flowerless. The leaves of ferns are called fronds; specialized for reproduction. Spores are produced in sporangia which are usually in cluster called sori. 17 They have vascular tissues (i.e. xylem and phloem) in sporophyte. They have true stem, leaf and root.. They are mostly terrestrial. They are cryptogams (i.e. non - seed producing plants).  Pteridophytes, in general, are homosporous (i.e. they produce only one type of spore). However, presence of heterosporous (i.e. two types of spores such as microspore and megaspore) are found in some members. E.g. Selaginella, Roots are generally adventitious. They exhibit a great variation in form, size and structure. 18  CLASSIFICATION OF PTERIDOPHYTES  It is divided into four classes: Class I: Psilotopsida Order 1:Psilotales e.g genus Psilotum; genus Tmesipteris Class II: Lycopsida Order I: Lycopodiales; e.g genus Lycopodium Order 2: Selaginellales; e.g. genus Selaginella Order 3: Isoetales; e.g. Isoetes Class III:Sphenopsida Order1. Equisetales; e.g genus Equisetum 19 CLASSIFICATION OF PTERIDOPHYTES CONTD. Class IV:Pteropsida Order 1: Ophioglossales; e.g. genus Ophioglossum, genus Botrychium; genus Helminthostachys Order 2: Osmundales; genus Osmuda Order 3: Marattiales; genus Marattia; genus Angiopteris Order 4: Filicales; genus Dryopteris, genus Nephrolepsis, genus Pteris, genus Polypodium; genus Adiantum Order 5: Marsileales; genus Marsilea Order 6: Salviniales; genus Salvinia, genus Azolla 20 Classification of Dryopteris (fern) Kingdom- Plantae Division-Pteridophyta Class- Pteropsida OR Filicinae Order- Filicales Family- Polypodiaceae Genus-Dryopteris. 21 Classification of Nephrolepsis (fern) Kingdom- Plantae Division-Pteridophyta Class- Pteropsida OR Filicinae Order- Filicales Family- Polypodiaceae Genus-Nephrolepsis 22 Ecological Adaptations of Pteridophytes A waxy cuticle that prevents desiccation. Gametangia that protect developing gametes. The gametangia are antheridium (male gametangium) and archegonium (female gametangium). The antheridium produces flagellated sperm cells (male gametes); while the archegonium produces egg (female gamete). presence of true roots which aid the absorption of water and minerals; as well as for support to the plants. Presence of vascular tissues (i.e. phloem and xylem) which help to conduct water and minerals from the roots to the rest parts of the plant (i.e xylem); and to transport food from the leaves to other parts of the plants (i.e. phloem). 23 Ecological Adaptations of Pteridophytes Contd. The xylem and sclerenchyma tissues in the petiole and rachis support the leaves of pteridophytes. The leaves are rolled in the bud stage to avoid premature destruction. The leaf blade is protected by cutin of the epidermis. Leaf curling and drought avoidance by cshedding of leaves in the dry season 24  SPERMATOPHYTES These are higher vascular plants that produce seed. They form most of the present world vegetation. The seed habit is considered as an advancement over heterospory of lower vascular plants. They include gymnosperms and angiosperms.  Characteristics of Spermatophytes They undergo alternation of generation in which the sporophyte is dominant, while the gametophyte is highly reduced. Reproductive organs are grouped into cones or strobilli as in gymnosperms, and flowers as in angiosperms. Sporophyte produces two types of spores (i.e. heterosporous). The two types are microspore (pollen grain) and megaspore (embryo sac). The embryo sac remains completely enclosed in the ovule Water is not needed for sexual reproduction because the male gametes do not swim, they are transferred via pollen tube to the ovum to effect fertilization. Complex vascular tissues in roots, stems and leaves. They are mainly terrestrial, but some are aquatic representative. There is highest degree of inter tissue differentiation. Seeds are produced. The seeds may be borne naked (gymnosperms) or closed (angiosperms). Classification of Spermatophytes The two major groups are as follows: Gymnosperms: Non-flowering seed plants or naked seed plants Angiosperms: Flowering plants or enclosed seed plants Gymnosperms They are group of plants with naked seeds (i.e. not enclosed in an ovary) Their reproductive organs are grouped into cones or strobilus. Characteristics of Gymnosperms Vascular system is well developed, but xylem lacks vessels, and phloem do not contain companion cells. Plant body is differentiated into distinct root and shoot. They are heterosporous (i.e producing two types of spores such as microspore and megaspore) and flowers are primitive. Spores are borne or grouped into cones/strobili. Agency for pollination is air current or wind. No fruits because there is no ovary. The xylem elements are always tracheids. The phloem tissue contains no companion cells. Pollen grains lodge on the nucellus. Female gametophyte is relatively large with distinct archegonia embedded in it, each with an ovum. Classification of Gymnosperms There are four living groups in gymnosperms; which are as follows: Division Pinophyta or Coniferophyta : These are conifers; i.e. the cone bearing trees and shrubs such as pines (e.g. genus Pinus), cedars, juniper, red wood, spruces, firs and cypresses. Division Cycadophyta : These are cycads (e.g. genus Cycas). Division Ginkophyta : Represented by a single living tree species (e.g. Ginkgo biloba). Division Gnetophyta :These are woody plants represented by three genera such as Gnetum, Welwitschia and Ephedra. There are eight orders in gymnosperms; but only four are still living; while the remaining four orders are represented by fossils (i.e. extinct or non-existing plants). There are 3 well known orders out of the living gymnosperms. The orders are as follows: 1. Cycadofilicales (fossil or extinct) 2. Bennettiales (fossil or extinct) 3. Pentoxylales (fossil or extinct) 4. Cordaitales (fossil or extinct) 5. Cycadales ((living); family Cycadaceae; e.g Cycas sp.  6. Coniferales (living); family Abietaceae or Pinaceae; e.g. Pinus sp. 7. Ginkgoales (living); family Ginkgoaceae; e.g. Ginkgo biloba 8. Gnetales (living); Represented by three families and three genera such as Family Gnetaceae; genus Gnetum Family Welwitschiaceae; genus Welwitschia Family Ephedraceae; genus Ephedra Classification of a Typical Gymnosperm: Cycas Kingdom- Plantae Division-Cycadophyta Class- Cycadopsida Order- Cycadales Family- Cycadaceae Genus-Cycas 31  Angiosperms These are flowering plants in which their seeds are enclosed in an ovary, which develops into a fruit. Their reproductive organs are grouped into flowers. They are exceptionally large and successful group of plants. They live in all sorts of habitats. They dominate most parts of the world where there is vegetation (except in cold regions with poor soils). They also provide most of man’s food and many of its raw materials. They are the most numerous plants in terms of biomass and their success can be attributed to a number of factors; which are as follows: Production of large number of seeds. Variability in structure. Genetic flexibility. Efficient pollination. 32 Characteristics of Angiosperms The plant body is differentiated into distinct shoot and root systems. They produce flowers from which sporangia, spores and seeds are developed. Their seeds are enclosed in an ovary. Their vascular system (i.e. xylem and phloem) is well developed. The xylem is made up of vessels, while the phloem contain companion cells. Pollination is by various agents such as wind, insects and mammals. They have well developed flowers with sepals and petals. The flowers are either unisexual or bisexual. The microspore or pollen grains grow into a pollen tube which carries the male gametes to the position close to the ovules; and the pollen grains are deposited directly on the stigma. 33  The carpel is differentiated into stigma, style and ovary. The ovary encloses the ovule. There is little evidence of the presence of male gametophytes, as it has been reduced to two nuclei, generative and tube nucleus. The megasporangium remain enclosed by the integument which are usually 2 in number; and this gives rise to a more complicated structure (i.e. the ovule). The ovule later develop into seed, and the purpose is for protection of the embryo. The female gametophyte is represented by 8 nucleate embryo sac. Classification of Angiosperms It belongs to the division Magnoliophyta; which is divided into two classes or groups namely: Class Magnoliopsida (Dicotyledoneae) Class Liliopsida (Monocotyledoneae) 34 Classification of a Typical Dicot Plant (e.g.Talinum triangulare) Kingdom- Plantae Division-Magnoliophyta/Angiospermatophyta/Spermatophyta Class- Magnoliopsida /Dicotyledoneae Order- Caryophyllales Family- Portulacaceae Genus-Talinum Species- Talinum triangulare 35 Classification of a Typical Monocot Plant (e.g. Cyperus esculentus) Kingdom- Plantae Division- Magnoliophyta/Angiospermatophyta/Spermatophyta Class- Liliopsida /Monocotyledoneae Order- Cyperales Family- Cyperaceae Genus – Cyperus Species-Cyperus esculentus 36  Differences between Dicotyledons and Monocotyledons S/N Dicotyledons Monocotyledons 1. Embryo has two cotyledons (seed leaves) Embryo has one cotyledon (seed leaf) 2. Net-like pattern of veins (reticulate venation) Veins are parallel (parallel venation) 3. Vascular bundles are arranged in a circle Vascular bundles are scattered in within stem stem 4. Floral parts mainly in ‘fours’ or ‘fives’ Floral parts usually in ‘threes’ 5. Most of them posses tap root system Most of them posses adventitious root system 6. Examples are pea, rose, buttercup, dandelion, Examples are grasses, iris, orchids, Talinum triangulare, e.t.c lilies, Cyperus sp. e.t.c 37  (Tap root) (lateral root) Diagram of Talinum triangulare (Dicot Plant) Source: Science Direct.com 38 Structure of a Typical Dicot Plant SOURCE: Science Direct.com 39  Diagram of a typical Monocot Plant (Cyperus species) Diagram of a typical Monocot Plant (Cyperus species) SOURCE: Science Direct.com 40  Life Cycle of Angiosperms This is the process whereby plants exhibit two phases (that is, sporophyte stage and gametophyte stage) in their life cycle (i.e. Alternation of generation). The main plant body is the sporophyte, and this has reached a high degree of complexity; while the gametophyte has been greatly reduced and has become inconspicuous. The embryo sac with the 8-nuclei is the female gametophyte; while the germinating pollen grain is the male gametophyte.  Life Cycle of Angiosperms Contd. All the stages from the zygote to the microspore mother cell and megaspore mother cell represent the sporophyte generation; while the stages from the microspore and megaspore to the male gamete and female gamete represent the gametophyte generation. The flower bears the stamen (i.e. microsporophyll) and carpel (i.e. megasporophyll). The stamen bears pollen sac (i.e. microsporangium) which produce pollen (i.e. microspore mother cell).  Life Cycle of Angiosperms Contd. The diploid pollen microspore mother cell undergoes reduction-division (i.e. meiosis) to produce haploid pollen grain (i.e. microspore). The carpel produces the nucellus (i.e. megasporangium) within the ovule; and the ovule is enclosed by the ovary, this produces the diploid embryo-sac (i.e. megaspore mother cell); which undergoes meiosis to give rise to haploid megaspore.  Life Cycle of Angiosperms Contd. The pollen grain germinates on the stigma of the carpel, and this gives rise to the male gametophyte (i.e. the germinating pollen grain); while the megaspore gives rise to the female gametophyte (i.e. the embryo-sac with the 8 nuclei). The female gametophyte is completely endosporous and dependent on the sporophyte for protection and nutrient. The male gametophyte bears the 2 male gametes; while the female gametophyte bears the female gametes or egg cell.  Life Cycle of Angiosperms Contd. One of the male gametes of the pollen tube fuses with the egg cell of the female gametophyte to produce zygote or oospore; which is the first fertilization in angiosperm. The other male gamete fuses with the two polar nucleic to form a triploid nucleus (3n) called the primary endosperm nucleus. This process is called double fertilization. The zygote divides mitotically and grows into the embryo. The primary endosperm nucleus develops into the endosperm. The fertilized ovule is transformed into seed; while the fertilized ovary is transformed into fruit. Generalized Life Cycle of Angiosperms Adaptation of Seed-Bearing Plants to Life on Land The gametophyte generation is reduced. It is always protected inside a sporophyte. Fertilization is not dependent on water. The male gametophytes are carried by within the pollen grains by wind or insects. The fertilized ovule (seed) is retained for some time on the parent sporophyte from which it obtains protection and food before dispersal. Many seed plants show secondary growth with production of large amount of wood for support. The plants become trees or shrubs and are able to compete effectively for light and other resources. Possession of extensive root system. They exhibit seed dormancy which help them to survive adverse condition. The various pollinating agents ensures success of fertilization and embryo formation, which is limited. They have thick cuticle, thick bark, sunken stomata and various modifications in stem and leaves which help them to reduce water loss. 47  Differences between Gymnosperms and Angiosperms S/N Gymnosperm Angiosperms 1. Seed do not enclosed in a carpel or bear Seed enclosed in a carpel or enclosed in a fruit naked seed 2. Reproductive organs grouped into Reproductive organs grouped into flowers cones/strobili 3. Leaves are mostly needle-like or thin Leaves are generally large and broad 4. Xylem consists of tracheids only or lack Xylem consists of vessels and tracheids vessels 5. Phloem lacks companion cells Phloem possesses companion cells 6. Do not exhibit double fertilization Show double fertilization 7. Restricted in ecological range Widely distributed 8. Often with xerophytic character Include xerophytic, mesophytic and hydrophytic 9. Seeds mainly dispersed by wind Seeds dispersed by a variety of mechanisms(like water, wind, animals and insects) 10. Gametophyte more prominent Gametophyte reduced 48