Plant Diversity Note 2 - PDF

DEPARTMENT OF BIOLOGY, FACULTY OF NATURAL AND APPLIED SCIENCES, UMARU MUSA YAR’ADUA UNIVERSITY, KATSINA BIO 102 (GENERAL BIOLOGY 11) LECTURE NOTE 4 SURVEY OF THE PLANT KINGDOM II SEED PLANTS (GYMNOSPERM AND ANGIOSPERM) CONTENTS 1.0...

DEPARTMENT OF BIOLOGY, FACULTY OF NATURAL AND APPLIED SCIENCES, UMARU MUSA YAR’ADUA UNIVERSITY, KATSINA BIO 102 (GENERAL BIOLOGY 11) LECTURE NOTE 4 SURVEY OF THE PLANT KINGDOM II SEED PLANTS (GYMNOSPERM AND ANGIOSPERM) CONTENTS 1.0 Introduction 2.0 Objectives 3.0 Main Content 3.1 General Characteristics of Seed Plants 3.2 Gymnosperms 3.2.1 Classification 3.2.2 Conifers 3.2.3 External Morphology of Conifers 3.2.4 Ecological adaptation of Conifer 3.3 Angiosperms 3.3.1 Classification 3.3.2 General features of Angiosperms 3.4 Terrestrial Adaptation of Vascular Plant (Seed Plants) 4.0 Conclusion 5.0 Summary 6.0 References/Further Readings 1.0 INTRODUCTION Seed plants are seed producing vascular plants. They are also called Spermatophyte. They have well developed roots, stems and leaves. The seeds containing the embryo develops from a fertilize egg of a very small gametophyte which is completely dependent on the sporophytes, the plant form we see around us. The efficient seed dispersal of seed plants account for their continued existence and widespread occurrence. The fertilization of the egg is by the male gamete which is brought by pollination, followed by the growth of the pollen tube which carries the male gamete to the egg. Water is not needed in this process, hence the seed plants are true land plants.  In this unit, we shall be looking at the seed plants: Gymnosperm and Angiosperms. 2.0 OBJECTIVES By the end of this unit, you should be able to: list out general characteristics of seed plants  outline the specific characteristics features of gymnosperms and  angiosperms o highlight morphological characteristic of a named gymnosperm and angiosperm o classify gymnosperms and angiosperm o highlight the terrestrial (ecological) of seed plants. 3.0 MAIN CONTENT 3.1 General Characteristics of Seed Plants  They are terrestrially adapted i.e they are land plants.  The gametophytes of seed plants become more reduced and dependent on the sporophytes.  They produce two types of spores (Megaspores and Microspores) ie. they are heterospores.  They undergo pollution which replaces swimming as the mechanism for delivering sperm to egg.  They produce seed. 3.2 Gymnosperms “Gymnos” is a Greek word meaning naked, while “sperma” means seed. These are plants with naked seeds(i.e seeds are not enclosed in fruit). Their seeds develop on scales or leaves which are modified into cones. Characteristics of gymnosperms a) They possess naked seeds. b) They are terrestrial plants that are mostly found in temperate region (i.e cold region). c) They produce naked seeds which are not enclosed, but attached on scales, leaves or cones. d) They possess cones or strobili (Sing. Strobilus) that contain reproductive  structures. The male cone or microstrobilus or pollen cone produce pollen while the female cone or megastrobilus, or seed cone or ovulate cone contains ovules. e) They have well developed root, shoot and vascular systems. f) They have needle – like and evergreen leaves. g) They lack flowers, but possess cones in lieu. h) They do not produce fruits because they have no ovaries. i) Their fertilization is not dependent on water. Examples include, cycads, pinus, conifers, spruces firs, cedrus etc. 3.2.1 Classification Gymnosperms are generally classified into four divisions. These are - Coniferophyta - the conifers - Cycadeophyta - Cycads - Ginkophyta - ginko - Gnetophyta - gnetae. 3.2.2 Conifers Among the gymnospems, the conifers are the most important. They have the following characteristics:  They are cone bearing plants with vascular tissue.  All are woody plants; the great majority been trees with just a few shrubs.  Species can be found growing naturally in almost all parts of the world.  They are frequently dominating plants in their habitats.  They are of immense value, primarily for timber and paper production.  The wood of conifers is known as softwood.Examples are: Cedars, Cypresses, Pines, Redwoods etc. 3.2.3 External Morphology of Conifers  All are wood plants, and most are trees.  Majority has a monopocal growth (ie. a single, straight trunk with side branches) with optical dominance.  Size varies from less than a metre, to over 100 meters. They are the world largest, tallest and oldest living  things. 3.2.4 Ecological Adaptation of Conifer  The have distinctly scented pesin, which is secreted to protect the tree against insect infestation and fungal infection of woods.  They maintain high rates of photosynthesis at relatively low temperature.  Their needles (leaves) have thick warty coatings and sunken stomatas which prevent excessive loss.  The sapwood column is large and acts as a short-term reservoir that supplies water to foliage during drought periods. Fig. 1.5: Diagram of a Conifers 3.3 Angiosperms “Angio” connotes closed. It means “seeds within a vessel” or “enclosed seeds”. These are flowering plants in which fruit formation follows fertilization. They are the most dominant members of the world flora and are found everywhere. They are the largest group of plants and the most advanced interms of complexity. CHARACTERISTICS OF ANGIOSPERMS 1) Possess complex body which is clearly differentiated into root and shoot system with conspicuous leaves and seeds. 2) Their seeds are protected by fruits which enclose them. 3) They produce flowers for sexual reproduction 4) They have distinct and elaborate supporting and conducting tissues for life on terrestrial environment. 5) They exhibit double fertilization. This is a unique feature of theirs. 6) They have simple and compound leaves which vary in shapes and size. 7) Their fertilization is water – independent. 3.3.1 Classification The angiosperm are further dividend into monocotyledons and dicotyledons MONOCOTYLEDON: These are plants with only one seed leaf or cotyledon. The cotyledon serves as food for a developing embryo. Examples include, rice, maize, millet, guinea corn, wheat etc. DICOTYLEDON: These are plants having two seed leaves or cotyledon. E.g beans, soy beans, cashew plant, mango etc 3.3.2 General features of Angiosperms  They could be photoautotroph, Saprobes or parasitic.  Mostly pollinated by insects, birds, and other animals, while some are by wind  They have vessels (xylem and phloem).  The monocots include lilies, grasses, corn, wheat, palms, while the dicots include roses, maples, oaks, peas, and beans.  Angiosperms posses certain external features that remarkably distinguish them from other seed  plants. This feature includes: 1. Flowers  They have modified leaves Has sepals – usually green  Petals –brightly colored and insect pollinated Petals –drab – wind pollinated  Has carpels – female reproductive organ. Has stamen- male reproductive organ. 2. Fruits  It protects documents seeds. They have mature ovary.  Simple fruit has single ovary flower (e.g. Pea pod, apple)  Aggregate fruit – produce from separate flowers (e.g pineapple) Modifications for dispersal includes: attractive food, dispersal by wind, burns.  Figures: Fruits, flowers and whole plant of angiosperms 3.4 Terrestrial Adaptation of Vascular Plant (Seed Plants)  Possession of cuticle  They do not need immediate aquatic habitat. Roots have no cuticle.  They are woody materials made of Cellulose and lignin. Possession of vascular tissues (Xylem and Phloem). SIMILARITIES BETWEEN ANGIOSPERMS AND GYMNOSPERMS a) They are both seed-producing plants. b) Both have well developed vascular systems. c) Both fertilizations is water – independent. d) Both can survive terrestrial mode of life. e) Both have well developed root and shoot systems. 1.0 CONCLUSION Seed Plants are crucial for human existence. The vast majority of the world’s crops are seed plants. 2.0 SUMMARY In this Unit, you have learnt that:  Gymnosperms and angiosperms are seed producing vascular plants.  The efficient seed dispersal of seed plants accounts for their continued existence and widespread occurrence.  The distinguish features of Angiosperm in the possession of flower and fruits.  Gymnosperms are mostly woody plants.  Conifers are of immense economic value primary for timber and paper production.  Seed plants do not need immediate aquatic habitat. 1.0 REFERENCES/FURTHER READINGS Sarojini, T.R. (1993). Modern Biology for Senior Secondary Schools. AFRICANA – FEP Publishers Limited. http://en.wikipedia.org/wikj/conifer