chapter 2 Flashcards
What are the most dominant group of plants living today?
Seed plants(gymnosperms and angiosperms)
From where did seed plants appear to have evolved from?
spore-bearing plants known as progymnosperms(extinct).
Progymnosperms
seedless plants that have simple reproduction
What features do progymnosperms share with gymnosperms?
having secondary vascular tissues (2ndary xylem and 2ndary phloem which allow the plant to increase in width/girdth)
Gymnosperms and angiosperms features
-Vascular plants (with more efficient food and water conducting systems)
-Sporophyte generation is dominant and independent
-Gametophyte is greatly reduced to a few tissues or cells within the sporophyte.
-Heterosporous
Gymnosperms and angiosperms advanced features
-Have seeds(embryo is protected within sporophyte tissues)
-Most adapted to live on land
-No need of water for fertilization to occur
All seed plants are heterosporous or homosporous?
Heterosporous
What was the precursor for seed development?
Heterospory
Define heterospory. Explain
It is the production of 2 types of spores and it results in the production of 2 types of gametophytes.
A microspore germinates into a male gametophyte which produce antheridia. Each antheridium produces many sperm
In seed plants, what is the male gametophyte?
there are no antheridia; the male gametophyte is called the pollen grain.
How are pollen grains transferred for fertilization?
Pollen grains are dispersed by wind or pollinators →no need of water for fertilization(most adapted to live on land).
In seed plants, what is the female gametophyte?
In seed plants, the female sporangium is called megasporangium/ovule.
During the whole process of fertilization, what happens within the ovule/megasporangium?
-Within the ovule (megasporangium), megasporocytes undergo meiosis to produce (N) megaspores.
-Each megaspore divides by mitosis/germinates into a female (N) gametophyte, which is reduced to a few tissues within the sporophyte.
-The gametophyte forms (N) archegonia; each archegonium produces a single (N) egg/female gamete.
After fertilization, what happens to the ovule?
After fertilization, the diploid egg (zygote) becomes the embryo, which is enclosed withing a seed (the ovule becomes the seed)
List the advantages of seeds. 5
1-A seed is covered by a seed coat (integument is made of 1 or 2 layers of sporophyte tissue that hardens into a seed coat)
2-The seed coat protects the embryo
3-A seed contains nutrients for embryo to give energy during germination.
4-A seed becomes dormant under unfavorable conditions (like spores)
5-The seed is easily dispersed.
stored food
endosperm
seed coat
integument
integument
integument is made of 1 or 2 layers of sporophyte tissue that hardens into a seed coat.
How many divisions and phyla do the seed plants consist of?
Seed plants consist of 2 divisions and 5 phyla
What are the 2 divisions of the seed plants?
Gymnosperms and Angiosperms
What are the 5 phyla of the seed plants?
—For the gymnosperms:
1)Coniferophyta/sometimes called Pinophyta: conifers
2)Cycadophyta: cycads
3)Gnetophyta: gnetophytes
4)Ginkgophyta: ginkgo trees
—For the angiosperms:
5)Anthophyta: flowering plants or angiosperms
Coniferophyta/sometimes called Pinophyta: conifers, pines, spruces, firs, yews, redwoods… 6
-largest phylum of gymnosperms; It includes some of world record trees
-Sperm not motile; accesses the egg by a pollen tube.
-Leaves mostly needle-like.
-con bearing trees or shrubs
-found in cold, temperate and dry regions
-sources of important products:
Timber, paper, resin, and taxol (anti-cancer).
Cycadophyta: cycads
-Sperm flagellated and motile but confined within a pollen tube that grows to the vicinity of the egg.
-Water is NOT needed for fertilization to occur.
-slow-growing
-Found in tropical and subtropical regions
-The tree are dioecious = male or female trees: making either pollen-bearing or ovule-bearing cones (respectively), but not both.
-Female cones are huge.
Male cones produce pollen grains, which are usually carried by wind (or by beetles
-Palm-like plants with pinnate leaves.
-Secondary growth slow compared with that of the conifers.
-Seeds in cones
Gnetophyta: gnetophytes
-Sperm not motile; accesses the egg by a pollen tube.
-The only gymnosperms with vessels in their vasculature.
-Trees, shrubs, vines. Three very diverse genera (Ephedra, Gnetum, Welwitschia).
Ginkgophyta: ginkgo trees
-Sperm flagellated and motile but accesses the egg by a pollen tube.
-Only one living species remains: Ginkgo biloba
-Dioecious = male and female reproductive structures form on different trees.
-Female trees produce seeds on fleshy structures.
-Trees are resistant to pollution and frequently planted as ornamental trees in cities.
-Deciduous tree with fan-shaped leaves.
-Trees are either male or female.
-Seeds resemble a small plum with fleshy, foul-smelling outer covering.
-One genus
Anthophyta: flowering plants or angiosperms
-Sperm not motile; accesses the egg by a pollen tube.
-Seeds enclosed within a fruit.
-Leaves greatly varied in size and form.
-Herbs, vines, shrubs, trees.
-Most significant foods consumed by humans and animals.
-About 14,000 genera
General characteristics of gymnosperms
1-They are plants with “naked seeds”
2-They consist of 4 groups or lineages of seed plants.
3-All have ovule exposed on a scale:
In gymnosperms, the ovule (which becomes a seed) rests exposed on a scale (modified leaf or shoot)→ It is not completely enclosed by sporophyte tissues at the time of pollination.
4-They have no flowers and no fruits
What are pines’ leaves like?
-tough needle-like leaves in clusters.
-thick cuticle and recessed (hidden) stomata to minimize water loss when the soil freezes in winter.
-have canals with resin to deter insect and fungal attacks
What is the function of the thick cuticle and hidden stomata in pines’ leaves?
minimize water loss when the soil freezes in winter
What is the function of having canals with resin in pines’ leaves?
to deter insect and fungal attacks
Is pines’ wood soft or hard? why?
Soft; it lacks some of the more rigid cell types.
Is pines’ bark thick or thin? why?
Thick; an adaptation to survive fire and low temperature.
Pine tree sporophyte/gametophyte
The pine tree is a sporophyte.
It has tiny gametophyte in its cones
Is the pine tree homosporous or heterosporous?
it is heterosporous, it produces micro-and megaspores in separate cones.
What do the male cones look like? and where do they develop?
-The male cones are small and green. It has leaf-like papery scales, arranged in a spiral.
-It develops at the tip of lower branches.
-A pair of microsporangia are found on each scale.
During the pine life cycle, what happens inside the microsporangia?
-There are many microspore mother cells (2N), which undergo meiosis, and give rise to (N) microspores.
-Each microspore develops into a male gametophyte (N), called the pollen grain.
What does the pollen grain consist of? And how is it dispersed?
-The pollen grain; male gametophyte; consists of 4 cells, including 2 air sacs for buoyancy (to make it light).
-Pollen grains are dispersed by air (wind).
What do the female cones look like? and where do they develop?
-larger and woody (brown). woody scales. Two ovules develop at the base of each scale.
-found on upper branches.
How many ovules develop at the base of each scale in the female cone?
2 ovules
What does each ovule in the female cone consist of?
-Each ovule contains a megasporangium called nucellus which is surrounded by a thick layer of cells, the integument, which has a small opening :the micropyle = opening for sperm entry.
-One of the layers of the integument will become the seed coat.
Nucellus
Megasporangium in the female cone’s ovule which is surrounded by the integument.
Integument
Thick layer of cells which has the micropyle.
One of its layers becomes the seed coat.
micropyle
small opening in the integument for sperm entry
small opening in the integument for sperm entry
micropyle
What happens inside the megasporangium?
-Only one megaspore mother cell (2N) undergoes meiosis to produce 4 (N) megaspores.
-3 megapores breakdown
-1 megaspore survives and develops into a female gametophyte: producing 1 (N) egg per archegonium.
How is the pollen carried to the female cone?
Wind brings pollen on female cones. The pollen grain sticks on the micropyle.
When does the female cone become mature?
The female cones take 2 or more seasons to mature.
So, when pollination occurs, the female cone is still immature.
What happens during pollination?
-The pollen grain slowly produces a pollen tube that travels slowly down the nucellus to reach the egg (still developing).
-One of the pollen grain’s 4 cells, the generative cell, divides by mitosis resulting in two (N) cells:
—2 non-mobile (non-flagellated) sperm
-1 sperm degenerates
-1 fuses with the (N) egg to produce a (2N) zygote/the pine embryo.
-The embryo is within the seed, surrounded by a seed coat.