Gymnosperms and Seed Evolution Quiz

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Questions and Answers

What distinguishes the point of germination between pollen grains and Selaginella male gametophyte?

Pollen grains germinate from a point opposite the meiotic scars, while Selaginella male gametophyte germinates at the tetrad scars left by the other daughter microspores.

Name the four extant phyla of gymnosperms.

The four extant gymnosperm phyla are Coniferophyta, Cycadophyta, Gnetophyta, and Ginkgophyta.

What reproductive feature do gymnosperms share that differentiates them from angiosperms?

Gymnosperms have seeds and lack flowers, as their ovules rest on modified leaves.

How do the male gametes differ in the Ginkgo and cycad gymnosperms compared to other gymnosperms?

Ginkgo and cycads have motile, flagellate male gametes, while the male gametes in other gymnosperm phyla are immotile. Signup and view all the answers

Explain the origin of the term 'gymnosperm'.

The term 'gymnosperm' is derived from Greek, meaning 'naked seed', referring to the open nature of their seeds. Signup and view all the answers

What are two disadvantages of non-seed plants compared to seed plants?

Non-seed plants require water for male gametes to swim to female gametes and their new sporophytes are dependent on gametophytes in early stages. Signup and view all the answers

Explain the significance of the ovule in seed evolution.

The ovule allows for the retention of the macrospore and female gametophyte within the macrosporangium, promoting embryo protection. Signup and view all the answers

How has pollen grain evolution contributed to reproduction in seed plants?

Pollen grains transfer the entire male gametophyte to the female gametophyte, allowing fertilization without water. Signup and view all the answers

What role does dormancy play in the seed life cycle?

Dormancy allows the embryo to survive until favorable environmental conditions are present for germination. Signup and view all the answers

In what way did the evolution of seeds influence the ecology of plants?

Seeds provided enhanced protection for embryos and allowed for survival during unfavorable conditions, leading to a broader ecological range. Signup and view all the answers

What differentiates gymnosperms from angiosperms in terms of ovule structure?

In gymnosperms, ovules are exposed to the atmosphere, while in angiosperms, they are enclosed in sporophyte tissue like carpels and ovaries. Signup and view all the answers

What distinguishes conifers in the Phylum Coniferophyta from other gymnosperms?

Conifers are known for their needle-shaped leaves, producing cones, and are typically found in colder habitats. Signup and view all the answers

Describe two preconditions necessary for the evolution of seeds.

Necessary preconditions include a shift from homospory to heterospory and the inclusion of the gametophyte inside the spore wall. Signup and view all the answers

Explain the significance of resin in Pinus species.

Resin protects Pinus species from freezing and guards against insect and fungal damage. Signup and view all the answers

What does the term Spermatophyta refer to?

Spermatophyta refers to all plants that produce seeds, which includes both gymnosperms and angiosperms. Signup and view all the answers

Describe the structure of male cones in Pinus.

Male cones, or microstrobili, are small, typically 1-4 cm long, and borne in groups at the tips of lower branches. Signup and view all the answers

How do integuments contribute to seed structure?

Integuments surround the nucellus and form the seed coat, providing extra protection to the developing embryo. Signup and view all the answers

What happens to microspore mother cells in the male cones?

Microspore mother cells undergo meiosis to produce four microspores. Signup and view all the answers

What is the role of the micropyle in seeds?

The micropyle allows for the entry of water and triggers the germination process for the seed's embryo. Signup and view all the answers

How do female cones differ from male cones in the Pinus life cycle?

Female cones, or macrostrobili, are larger, woody, and contain ovules, while male cones are smaller and produce pollen. Signup and view all the answers

What is the function of the micropyle in the ovule?

The micropyle serves as a small opening that allows pollen grains to enter the ovule. Signup and view all the answers

What evolutionary significance do the fossils of Archaeosperma hold?

Archaeosperma fossils represent some of the oldest plants with fully-developed seed-like structures, indicating early seed evolution. Signup and view all the answers

Describe the development of the female gametophyte in Pinus.

The female gametophyte develops from the surviving macrospore after three others disintegrate, and takes over a year to mature. Signup and view all the answers

How did the male gametophyte evolve in seed plants?

The male gametophyte evolved through progressive reduction and became enclosed within the microspore wall. Signup and view all the answers

Why did the evolution of the seed have massive ecological implications?

The seed provided improved embryo protection, promoting survival during unfavorable conditions and enabling colonization of diverse habitats. Signup and view all the answers

What triggers the pollen grain to move toward the nucellus during fertilization?

The secretion of a sticky pollination droplet in the micropyle draws the pollen grain toward the nucellus. Signup and view all the answers

How is the diploid zygote formed in Pinus fertilization?

The zygote is formed when one sperm cell fuses with the egg cell after the pollen tube reaches the archegonium. Signup and view all the answers

What is the difference between spermatophyte and non-spermatophyte plants in terms of reproduction?

Spermatophyte plants reproduce using seeds that allow for a dormancy phase, whereas non-spermatophyte plants rely on water for their gametes to unite. Signup and view all the answers

What are the components of a seed in Pinus?

A seed consists of the embryo, seed coat, and tissues from the integument and nucellus. Signup and view all the answers

What is the relationship between macrosporangium and nucellus in seed plants?

The nucellus is the macrosporangium of seed plants, where the female gametophyte develops. Signup and view all the answers

What is the importance of heterospory in conifers?

Heterospory allows for the production of distinct male and female gametophytes, enhancing reproductive success. Signup and view all the answers

How do seeds from Pinus germinate after a dormancy period?

Seeds germinate after a dormancy period under favorable environmental conditions, leading to the growth of a new sporophyte. Signup and view all the answers

Why is the development of the macrosporangium significant in the life cycle of Pinus?

The macrosporangium houses the macrospore mother cell, which is crucial for the formation of female gametophytes. Signup and view all the answers

What adaptations do needle-shaped leaves provide for Pinus trees?

Needle-shaped leaves reduce water loss with a thick cuticle and deeply sunken stomata. Signup and view all the answers

Study Notes

Gymnosperms and Seed Evolution - Conifers

Gymnosperms evolved from free-sporing progymnosperms about 425 million years ago.
Seed evolution had significant ecological impacts.
A sporophyte tissue layer protects the developing embryo.
Nucellus is the macrosporangium of the seed plant, surrounded by integuments.
Integuments harden into the seed coat.

Non-Seed Plant Life Cycle Disadvantages

Water is still necessary for male gametes to reach female gametes.
New sporophyte is temporarily dependent on small gametophyte plants (zygote and embryo).
Many sporophytes die.

Advantages of Seed Plants

Embryo utilizes pre-existing sporophyte photosynthetic and absorptive capabilities (leaves and roots).
Female gametophyte (embryo sac) and embryo can remain within the maternal sporophyte, made possible by retention of the macrospore within the macrosporangium.

Transfer of Male Gametophyte

The whole male gametophyte is now transferred to the female gametophyte (not just the male gametes).
Vectors like wind carry mature microspore products (pollen grains) to female gametophytes.
Pollen grain germinates on the maternal sporophyte.
Male gametophyte develops within the microspore wall, becoming the pollen grain wall.
Spermatophyta is the formal name for all plants that produce seeds.

Seed Plant Adaptations

Seeds enclose the embryo in protective seed tissue, allowing for dormancy.
Dormancy ensures the embryo can survive until favorable conditions for germination arise.
This leads to optimal germination and seedling development.

Gymnosperm Classification

Spermatophyta:
- Gymnospermae: ovules are exposed to the atmosphere
- Angiospermae (Anthophyta): ovules are enclosed within the sporophyte tissue.
Although gymnosperm phyla exhibit morphological variation, their life cycles, gametophyte structures, and fertilization processes are relatively similar.

Early Seeds

Early seeds of the late Paleozoic era (400-250 million years ago) typically occurred terminally on the stem axis, exhibiting bilateral or radial symmetry.
Archaeosperma is one of the oldest plants with well-developed seed structures.
Archaeosperma lived in the late Devonian (360 million years ago).
Archaeosperma is interpreted as a group of loosely arranged, radially symmetric seeds.
Every seed has a macrosporangium (nucellus) surrounded by a protective integumentary layer with finger-like outgrowths.
Later Carboniferous fossils show typical seed structures, with progressively more deeply enclosed macrosporangia within integuments.

Pollen - Male Version of a Seed

Pollen is the male version of a seed.
Immature male gametophyte inside the microspore wall.
Evolved through the progressive reduction of the male gametophyte and gradual inclusion within the spore wall.
This evolution happened independently in Selaginella.

Selaginella and Pollen Grains

Selaginella male gametophytes germinate from tetrad scars.
In contrast, true pollen grains emerge from a point opposite meiotic scars.
In seed plants, these scars are absent, likely through evolutionary time.

Extant Gymnosperm Phyla

Four extant gymnosperm phyla: Coniferophyta, Cycadophyta, Gnetophyta, and Ginkgophyta.
Two extinct phyla: Progymnospermatophyta and Pteridospermatophyta
Relationships between gymnosperm phyla remain somewhat contentious but gymnosperms are generally considered to be monophyletic.

Coniferophyta (Conifers)

Most well-known gymnosperms, including pines, cedars, cypresses, and sequoias.
Among the oldest and tallest living things, found in cold, temperate, and arid habitats worldwide.
Commercially valuable resources like wood, paper, resin, turpentine, and taxol.

Pinus (Pine Tree)

More than 100 species, confined to the Northern Hemisphere.
Needle-shaped leaves in groups of 2-5 on short branches.
Leaves adapted to minimize water loss (thick cuticle, sunken stomata).
Contain resin ducts for protection against freezing and insects/fungi.
Commercially important sources of turpentine and resin.

Pinus Life Cycle - Male

Heterosporous, developing spores into two types of gametophytes.
Pollen grains form in microsporangia of male cones (microstrobili).
Male cones borne in groups on lower branches.
Papery bracts (microsporophylls) spirally arranged.
2 microsporangia below the bract.

Pinus Life Cycle - Female

Female cones (macrostrobili) larger than male cones, with bracts that become woody.
2 ovules develop on the top of each macrosporophyll.
Each ovule has a macrosporangium (nucellus).
Nucellus surrounded by integumentary layer.
Tiny opening in integument (micropyle).
Integument hardens into seed coat.

Pinus Life Cycle - Fertilization

Pollen grain carried by wind lands in sticky pollination droplet on micropyle.
Pollen tube germinates and grows to the archegonium.
Zygote develops within the seed, into an embryo.
Seeds released after dormancy.
Seeds germinate to form new sporophyte generation.
One sperm fuses with the egg to form a zygote, creating the embryo.
The other parts of the male gametophyte disintegrate.

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Description

Test your knowledge on the evolution of gymnosperms and seed plants. This quiz covers key concepts including the advantages of seed plants, the life cycle of non-seed plants, and the transfer of male gametophytes. Explore the ecological impacts of these evolutionary advancements!