BIOL 1407 Ch 24&25 Manual
The Green Machine: Understanding Seed Plants (Gymnosperms)
Overview of Seed Plants
Seed plants comprise the majority of the plants on Earth, with an estimated 300,000 species.
There are two major groups:
Gymnosperms: Non-flowering seed plants including conifers and cycads.
Angiosperms: Flowering plants that constitute the majority of plant diversity.
Key Groups of Gymnosperms
Cycadophyta: Includes cycads and sago palms.
Ginkgophyta: Contains only one living species, Ginkgo biloba.
Gnetophyta: Encompasses three genera: Ephedra, Welwitschia, and Gnetum.
Coniferophyta: Largest group including pines, spruces, cedars, and junipers.
Evolutionary History
Appearance in the fossil record:
First seed plants appeared approximately 360 million years ago.
Elkinsia polymorpha, an ancient seed fern, is one of the oldest known.
Gymnosperms flourished during the Permian period and by the Triassic period, all major phyla were represented.
Angiosperms emerged around 140 million years ago and dominated by the Paleocene epoch (approx. 60 million years ago).
Objectives of the Chapter
Compare and contrast gymnosperms and angiosperms.
Explain basic reproduction and biology of the four gymnosperm phyla.
Trace the natural history and features of specific plants.
Describe conifers: their cones, leaves, and age determination by growth rings.
Identify wood anatomy: springwood vs summerwood, heartwood vs sapwood.
Morphology of Seed Plants
Seed Structure: Contains three parts:
Seed coat: Protects the seed.
Embryo: Develops into the new plant.
Endosperm: Provides nourishment.
Pollination Process: Involves pollen carrying sperm to ovules, resulting in fertilization and seed formation.
Phylum Specifics
Cycadophyta
Morphology: Often mistaken for ferns or palms, cycads have palmlike leaves.
Reproductive Structure: Dioecious with distinct male and female cones.
Notable Example: Cycas revoluta (Sago palm).
Contains carcinogenic compounds; not safe to eat without processing.
Ginkgophyta
Ginkgo biloba is the only surviving member, known for its unique fan-shaped leaves.
Pollination: Male trees produce pollen, which is wind-dispersed; the fleshy seeds of females emit a strong odor when ripe.
Known for longevity, with some trees living over 3,500 years.
Gnetophyta
Genera include: Gnetum, Welwitschia, Ephedra.
Have vessel elements in their wood, unlike other gymnosperms.
Specific uses: Ephedra sinica has medical applications but also has safety concerns with certain supplements.
Coniferophyta
Composed mostly of woody evergreens; major source of timber and paper.
Life Cycle: Involves male (pollen) and female (seed) cones, where fertilization occurs after pollen tube formation.
Notable species: Pinus longaeva (oldest non-clone living organism) and Sequoiadendron giganteum (largest tree by volume).
Unique Features of Gymnosperms
Naked Seeds: Gymnosperm seeds are not enclosed within an ovule, differing from the angiosperms.
Sporophyte Dominance: The life cycle predominantly features the sporophyte phase.
Seed Advantages: Provides nourishment and protection, allowing plants to thrive in diverse environments.
Summary
Gymnosperms play a crucial role in ecosystems and have economic importance through lumber, medicine, and ornamental uses. Understanding their biology aids in conservation efforts and agricultural practices.
Overview of Seed Plants
Seed plants, which include both gymnosperms and angiosperms, are a dominant group on Earth with around 300,000 species.
Major Groups:
Gymnosperms: Non-flowering seed plants such as conifers and cycads.
Angiosperms: Flowering plants that represent the majority of plant diversity.
Key Differences between Gymnosperms and Angiosperms
Reproductive Structures: Gymnosperms have naked seeds while angiosperms have seeds enclosed in fruits.
Pollination Methods: Gymnosperms generally rely on wind for pollination, while angiosperms often utilize insects, birds, and other animals.
Diversity: Angiosperms are more diverse, contributing to complex ecosystems with various adaptations, resulting in a wide range of forms and functions.
Morphology of Angiosperms
Flowers: Serve as reproductive structures, attracting pollinators and facilitating fertilization.
Fruits: Develop from flowers and protect seeds, aiding in their dispersal.
Seed Structure: Consists of seed coat, embryo, and endosperm, with the endosperm often serving as a food source for the developing plant.
Importance of Angiosperms
Angiosperms play a crucial role in ecosystems, providing food, habitat, and contributing to the planet's oxygen supply. They are also significant economically, used in agriculture, horticulture, and pharmaceuticals.
Angiosperms: An Overview
Angiosperms, commonly referred to as flowering plants, represent the largest group of plants on Earth, with an estimated 300,000 species. They are characterized by the presence of flowers and the ability to produce seeds enclosed within fruits, which distinguishes them from gymnosperms.
Key Characteristics
Flowers: The reproductive structures of angiosperms, designed to attract pollinators such as insects, birds, and mammals, facilitating fertilization.
Fruits: Develop from the fertilized ovary of flowers; they protect seeds and aid in their dispersal through various mechanisms (e.g., wind, water, animals).
Seed Structure: Consists of three main parts: seed coat (protection), embryo (development of the new plant), and endosperm (nourishment for the developing plant).
Major Groups of Angiosperms
Angiosperms are divided into two main classes based on their seed structure:
Monocots:
Seeds contain one cotyledon (seed leaf).
Examples include grasses, lilies, and orchids.
Features: parallel leaf veins, fibrous root systems, and floral parts typically in multiples of three.
Dicots:
Seeds contain two cotyledons.
Examples include beans, roses, and sunflowers.
Features: net-like leaf venation, taproot system, and floral parts typically in multiples of four or five.
Importance of Angiosperms
Angiosperms play a crucial ecological role, contributing to food webs as primary producers. They are integral to human agriculture, providing staple crops, fruits, and vegetables. Additionally, they contribute to biodiversity and habitat stability, making them essential for ecosystem health.
Summary of Angiosperms and Gymnosperms
Angiosperms:
Also known as flowering plants, angiosperms are characterized by flowers and seeds enclosed within fruits. They represent the largest group of plants on Earth, with around 300,000 species.
Key features include flowers for attracting pollinators and fruits that protect and aid in the dispersal of seeds. Angiosperms are essential for ecosystems, agriculture, and biodiversity.
They can be divided into two classes: Monocots (one seed leaf) and Dicots (two seed leaves).
Gymnosperms:
Gymnosperms, or non-flowering seed plants, include conifers, cycads, ginkgos, and gnetophytes. They are known for having naked seeds that are not enclosed within fruits.
Key groups include Cycadophyta, Ginkgophyta, Gnetophyta, and Coniferophyta.
Gymnosperms play significant ecological roles and are important sources of timber and other resources.