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Plant Biology - Seed Plants

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    Study Guide Plant Biology – Seed Plants 1. The Gymnosperm Phyla Gymnosperms are seed - producing plants that do not form flowers or fruits . The word gymnosperm means “naked seed.” This refers to the fact that their ovules and seeds are exposed , usually on cone scales, rather than being enclosed inside a fruit. Unlike angiosperms (flowering plants), which all belong to one single evolutionary lineage , gymnosperms are divided into four different phyla , each representing a separate evolutionary line . 1.1 Phylum Coniferophyta (The Conifers) Conifers are the largest and most familiar group of gymnosperms . They are mostly woody, evergreen trees with needle - shaped or flattened leaves . Habitat and Distribution Conifers are especially well adapted to cooler and drier environments . Today, they dominate many forests of the Northern Hemisphere , but they are also found in parts of the Southern Hemisphere . Common examples include: • Pines • Firs • Spruces • Hemlocks • Yews • Junipers • Araucaria (Southern Hemisphere) Some conifers are record holders: • Sequoias are among the tallest trees on Earth • Bristlecone pines are among the oldest living plants

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    Study Guide 1.2 Pines (Genus Pinus ) Pines are one of the most studied conifers, with more than 90 species . Leaves (Needles) • In young seedlings, needles grow singly along the stem • In mature trees, needles grow in bundles called fascicles • Each fascicle is a short branch with limited growth , which is important evolutionarily 1.3 Adaptations of Pine Needles (Xeric Adaptations) Pine needles are adapted to xeric conditions , where water is scarce or frozen. Key features include: • Thick cuticle to reduce water loss • Epidermis and hypodermis with thick - walled cells • Sunken stomata (helps reduce transpiration) • Resin canals for protection • Vascular bundles surrounded by transfer tissue Needles are not shed all at once. Instead: • Each needle lives 2 – 4 years (or more) • Because some needles remain, the tree stays evergreen 1.4 Wood Structure in Conifers Conifer wood is commonly called softwood . Important features: • Made mainly of tracheids (no vessels) • Tracheids have circular bordered pits • Very little parenchyma tissue • Vascular cambium is bifacial , producing: o Secondary xylem (wood) inward o Secondary phloem outward

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    Study Guide 1.5 Life Cycle of Pine (Very Important Exam Topic) 1.6 A Two - Year Life Cycle The life cycle of pine takes about two years to complete. Year 1: Pollination (Spring) • Pollination occurs in spring • Wind carries pollen to the ovulate cone • The pollen grain germinates and forms a pollen tube • At this stage: o No egg cells are present yet

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    Study Guide o No archegonia exist o The megagametophyte has not formed This lack of synchronization is not a problem because: • The pollen tube takes over one year to grow through the nucellus • During this time: o The megaspore mother cell divides o The megagametophyte develops o Archegonia with eggs are formed o The generative cell divides to form two sperm cells Year 2: Fertilization and Seed Formation In the spring of the following year : • Fertilization occurs • Eggs in 2 – 3 archegonia may be fertilized ( polyembryony ) • Usually, only one embryo survives 1.7 Structure of the Pine Seed A pine seed contains tissues from three generations : 1. Seed coat – parent sporophyte (2n) 2. Embryo – new sporophyte (2n) 3. Megagametophyte – nutritive tissue (1n) By late summer , the seed: • Matures • Is released from the cone • Germinates if conditions are favorable • Grows into a new pine tree, continuing the cycle

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    Study Guide 1.8 Other Conifers (Beyond Pines) Not all conifers look or behave like pines. Deciduous Conifers Some conifers shed their leaves , such as: • Larch ( Larix ) • Bald cypress ( Taxodium ) • Dawn redwood ( Metasequoia ) Yews • Have flattened leaves • Do not form typical cones • Produce a fleshy red structure called an aril 1.9 Global Distribution and Evolutionary History • Conifers are found in both hemispheres • Many grow in areas unsuitable for angiosperm trees • Some genera exist only in small, isolated populations Examples: • Dawn redwood • Wollemia pine Interestingly: • Botanists discovered some of these species only recently • 17 conifer species grow only along the California coast

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    Study Guide 1.10 Evolutionary Decline Conifers reached their peak during the Mesozoic Era , when they dominated Earth’s forests. Since then, their diversity has slowly declined, a trend that continues today. Summary • Gymnosperms = naked seeds • Conifers are the most important gymnosperms • Pines show strong xeric adaptations • Pine life cycle takes two years • Seeds contain tissues from three generations • Conifers once dominated Earth but are now declining 2. Other Living Gymnosperm Phyla

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    Study Guide Living gymnosperms today are a small but diverse group of plants . Most of them survive in special habitats where flowering plants (angiosperms) struggle to grow. These places may be very hot, very dry, or very cold . Many gymnosperms show ancient features in their structure and life cycles. Some of these features look like early experiments in plant reproduction — ideas that were later refined and successfully used by flowering plants. In this way, gymnosperms give us a window into plant evolution . 2.1 Phylum Cycadophyta Cycads are gymnosperms that look like palm trees , but instead of flowers, they produce cones . They are found mainly in tropical and subtropical regions around the world. Interestingly, two cycad species grow naturally in Florida . Some cycads grow 15 meters or more in height, while others have short trunks and form a rosette shape , with leaves spreading out from the center. The ovulate (female) cones of cycads are very large — some can weigh over 30 kilograms . These cones grow upright and develop among the leafy structures called megasporophylls . Male and female cones are produced on different plants , meaning cycads are dioecious . Even though cycads do not look like pine trees, their life cycle is very similar to that of pines . One important difference is their sperm. The sperm are delivered to the archegonia through a pollen tube, but they are multiflagellate , meaning they have hundreds of flagella that help them move.

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