26: Seed Plants Flashcards
Evolution of Seed Plants, Gymnosperms, Angiosperms, the Role of Seed Plants (164 cards)
1
Q
What is a flower?
A
Branches specialized for reproduction found in some seed-bearing plants, containing either specialized male or female organs or both male and female organs.
2
Q
What is fruit?
A
Thickened tissue derived from ovary wall that protects the embryo after fertilization and facilitates seed dispersal.
3
Q
What is an ovule?
A
A female gametophyte.
4
Q
What is a pollen grain?
A
A structure containing the male gametophyte of the plant.
5
Q
What is a pollen tube?
A
An extension from the pollen grain that delivers sperm to the egg cell.
6
Q
What is a progymnosperm?
A
A transitional group of plants that resembled conifers because they produced wood, yet still reproduced like ferns.
7
Q
What is a seed?
A
A structure containing the embryo, storage tissue and protective coat.
8
Q
What is a spermatophyte?
A
A seed plant; from the Greek sperm (seed) and phyte (plant).
9
Q
What are some examples of the uses of seed plants?
A
For millennia, human societies have depended on seed plants for nutrition and medicinal compounds: and more recently, for industrial by-products, such as timber and paper, dyes, and textiles. Palms provide materials including rattans, oils, and dates. Wheat is grown to feed both human and animal populations. The fruit of the cotton boll flower is harvested as a boll, with its fibers transformed into clothing or pulp for paper. The opium poppy is valued both as an ornamental flower and as a source of potent opiate compounds.
10
Q
What are the sizes of the sporophytes and gametophytes in seed plants?
A
In seed plants, the evolutionary trend led to a dominant sporophyte generation, and at the same time, a systematic reduction in the size of the gametophyte: from a conspicuous structure to a microscopic cluster of cells enclosed in the tissues of the sporophyte.
11
Q
Are seed plants homosporous or heterosporous?
A
Whereas lower vascular plants, such as club mosses and ferns, are mostly homosporous, all spermatophytes are heterosporous.
12
Q
What are the two types of spores produced by seed plants?
A
Spermatophytes produce two types of spores: megaspores (female) and microspores (male). Megaspores develop into female gametophytes that produce eggs, and microspores mature into male gametophytes that generate sperm.
13
Q
Are the gametophytes of seed plants free-living?
A
Because the gametophytes mature within the spores, they are not free-living, as are the gametophytes of seedless vascular plants.
14
Q
What are the evolutionary forerunners of seed plants?
A
Heterosporous seedless plants are seen as the evolutionary forerunners of seed plants.
15
Q
Which adaptations distinguish seed plants from other vascular plants?
A
Seeds and pollen - two critical adaptations to drought, and to reproduction that doesn’t require water - distinguish seed plants from seedless vascular plants. Both adaptations were required for the colonization of land begun by the bryophytes and their ancestors.
16
Q
When did gymnosperms evolve?
A
The first reliable record of gymnosperms dates their appearance to the Pennsylvanian period, about 319 million years ago.
17
Q
What was the evolutionary success of gymnosperms versus angiosperms?
A
Gymnosperms dominated the landscape in the early (Triassic) and middle (Jurassic) Mesozoic era. Angiosperms surpassed gymnosperms by the middle of the Cretaceous (about 100 million years ago) in the late Mesozoic era, and today are the most abundant plant group in most terrestrial biomes.
18
Q
What are the names of the eons and when did they occur?
A
- Phanerozoic, from 541 million years ago to present
- Proterozoic, from 2.5 billion years ago to 541 million years ago
- Archean, from 3.8 to 2.5 billion years ago
- Pre-Archean, from the formation of the Earth to 3.8 billion years ago
19
Q
What are the names of the eras of the Phanerozoic eon and when did they occur?
A
- Cenozoic, from 66 million years ago to present
- Mesozoic, from 252 million years ago to 66 million years ago
- Paleozoic, from 541 million years ago to 252 million years ago
20
Q
What are the names of the periods of the Cenozoic era and when did they occur?
A
- Quaternary, from 2.6 million years ago to present
- Tertiary, from 66 million years ago to 2.6 million years ago
21
Q
What are the names of the periods of the Mesozoic era and when did they occur?
A
- Cretaceous, from 145 mya to 66 mya
- Jurassic, from 201 mya to 145 mya
- Triassic, from 252 mya to 201 mya
22
Q
What are the names of the periods of the Paleozoic era and when did they occur?
A
- Permian, from 298 to 252 mya
- Pennsylvanian, from 323 to 298 mya
- Mississippian, from 358 to 323 mya
- Devonian, from 419 to 358 mya
- Silurian, from 443 to 419 mya
- Ordovician, from 485 to 443 mya
- Cambrian, from 542 to 485 mya
23
Q
How do seeds facilitate reproduction in seed plants?
A
The small haploid cells are encased in a protective coat that prevent desiccation and mechanical damage. Pollen grains can travel far from their original sporophyte, spreading the plant’s genes. The seed offers the embryo protection, nourishment, and a mechanism to maintain dormancy for tens or even thousands of years, ensuring germination can occur when growth conditions are optimal. Seeds therefore allow plants to disperse the next generation through both space and time.
24
Q
What is the earliest seed plant discovered?
A
The fossil plant Elkinsia polymorpha, a “seed fern” from the Devonian period - about 400 million years ago - is considered the earliest seed plant known to date.
25
What are some characteristics of the first true seed plants and when did they appear?
Seed ferns produced their seeds along their branches without specialized structures. What makes them the first true seed plants is that they developed structures called cupules to enclose and protect the ovule - the female gametophyte and associated tissues - which develops into a seed upon fertilization. Seed plants resembling modern tree ferns became more numerous and diverse in the coal swamps of the Carboniferous period.
26
When did progymnosperms appear?
Fossil records indicate that the first gymnosperms (progymnosperms) most likely originated in the Paleozoic era, during the middle Devonian period, about 380-390 million years ago.
27
Why were seed plants successful during the Permian period?
Following the wet Mississippian and Pennsylvanian periods, which were dominated by giant fern trees, the Permian period was dry. This gave a reproductive edge to seed plants, which are better adapted to survive dry spells.
28
What were the first gymnosperms to appear during the lower Jurassic?
The Ginkgoales, a group of gymnosperms with only one surviving species – the *Ginkgo biloba*.
29
When did gymnosperms reach their evolutionary peak?
Gymnosperms expanded in the Mesozoic era (about 240 million years ago), supplanting ferns in the landscape, and reaching their greatest diversity during this time. The Jurassic period was as much the age of the cycads (palm-tree-like gymnosperms) as the age of the dinosaur. Ginkgoales and conifers also dotted the landscape.
30
What ecosystems do gymnosperms dominate nowadays?
Although angiosperms are the major form of plant life in most biomes, gymnosperms still dominate some ecosystems, such as the taiga (boreal forests) and the alpine forests at higher mountain elevations because of their adaptation to cold and dry growth conditions.
31
How are seeds an evolutionary adaptation to dry land?
Unlike bryophyte and fern spores (which are haploid cells dependent on moisture for rapid development of gametophytes), seeds contain a diploid embryo that will germinate into a sporophyte. Storage tissue to sustain growth and a protective coat give seeds their superior evolutionary advantage. Several layers of hardened tissue prevent desiccation, and free reproduction from the need for a constant supply of water. Furthermore, seeds remain in a state of dormancy - induced by desiccation and the hormone abscisic acid - until conditions for growth become favorable. Whether blown by the wind, floating on water, or carried away by animals, seeds are scattered in an expanding geographic range, thus avoiding competition with the parent plant.
32
How do pollen grains facilitate sexual reproduction?
Pollen grains are male gametophytes and are carried by wind, water, or a pollinator. The whole structure is protected from desiccation and can reach the female organs without dependence on water. Male gametes reach the female gametophyte and the egg cell gamete through a pollen tube: an extension of a cell within the pollen grain.
33
Do the male gametes of gymnosperms have flagella?
The sperm of most modern gymnosperms lack flagella, but in cycads and the *Ginkgo*, the sperm still possess flagella that allow them to swim down the pollen tube to the female gamete; however, they are enclosed in a pollen grain.
34
When did angiosperms appear?
Undisputed fossil records place the massive appearance and diversification of angiosperms in the middle to late Mesozoic era. Fossil evidence indicates that flowering plants first appeared in the Lower Cretaceous, about 125 million years ago, and were rapidly diversifying by the Middle Cretaceous, about 100 million years ago. Earlier traces of angiosperms are scarce. Fossilized pollen recovered from Jurassic geological material has been attributed to angiosperms. A few early Cretaceous rocks show clear imprints of leaves resembling angiosperm leaves. By the mid-Cretaceous, a staggering number of diverse flowering plants crowd the fossil record. The same geological period is also marked by the appearance of many modern groups of insects, including pollinating insects that played a key role in ecology and the evolution of flowering plants.
35
How did angiosperms evolve?
Although several hypotheses have been offered to explain the sudden profusion and variety of flowering plants, none have garnered the consensus of paleobotanists. New data in comparative genomics and paleobotany have, however, shed some light on the evolution of angiosperms. Rather than being derived from gymnosperms, angiosperms form a sister clade that developed in parallel with the gymnosperms. The two innovative structures of flowers and fruit represent an improved reproductive strategy that served to protect the embryo, which increased genetic variability and range. Paleobotanists debate whether angiosperms evolved from small woody bushes, or were basal angiosperms related to tropical grasses. Both views draw support from cladistics studies, and the so-called woody magnoliid hypothesis - which proposes that the early ancestors of angiosperms were shrubs - also offers molecular biological evidence.
36
What is the most primitive living angiosperm?
The most primitive living angiosperm is considered to be *Amborella trichopoda*, a small plant native to the rainforest of New Caledonia, an island in the South Pacific. Analysis of the genome of *A. trichopoda* has shown that it is related to all existing flowering plants and belongs to the oldest confirmed branch of the angiosperm family tree.
37
Why are basal angiosperms considered primitive?
A few angiosperm groups called basal angiosperms are viewed as primitive because they branched off early from the phylogenetic tree. Most modern angiosperms are classified as either monocots or eudicots, based on the structure of their leaves and embryos. Basal angiosperms, such as water lilies, are considered more primitive because they share morphological traits with both monocots and eudicots.
38
Where does fertilization and embryo development occur in angiosperms?
Angiosperms produce their gametes in separate organs, which are usually housed in a flower. Both fertilization and embryo development take place inside an anatomical structure that provides a stable system of sexual reproduction largely sheltered from environmental fluctuations.
39
How diverse are flowering plants?
Flowering plants are the most diverse phylum on Earth after insects; flowers come in a vast array of sizes, shapes, colors, smells, and arrangements.
40
What is the relationship between flowers and pollinators?
Most flowers have a mutualistic pollinator, with the distinctive features of flowers reflecting the nature of the pollination agent. The relationship between pollinator and flower characteristics is a primary example of coevolution.
41
How do seeds and fruits develop?
Following fertilization of the egg, the ovule grows into a seed. The surrounding tissues of the ovary thicken, developing into a fruit that will protect the seed and often ensure its dispersal over a wide geographic range. Not all fruits develop from an ovary, however; such structures are “false fruits”.
42
How do fruits serve as agents of dispersal?
Some may be carried away by the wind. Many attract animals that will eat the fruit and pass the seeds through their digestive systems, then deposit the seeds in another location. Cockleburs are covered with stiff, hooked spines that can hook into fur (or clothing) and hitch a ride on an animal for long distances.
43
What invention did cockleburs inspire?
The cockleburs that clung to the velvet trousers of a Swiss hiker, George de Mestral, inspired his invention of the loop and hook fastener he named Velcro.
44
Which genes are frequently chosen for DNA alignment analysis?
The genes encoding the ribosomal RNA from the small 18S subunit and plastid genes are frequently chosen for DNA alignment analysis.
45
What are conifers?
The dominant phylum of gymnosperms with the most variety of trees.
46
What is a cycad?
A gymnosperm that grows in tropical climates and resembles a palm tree; member of the phylum Cycadophyta.
47
What does it mean to be dioecious?
Describes a species in which the male and female reproductive organs are carried on separate specimens. Literally, “two homes” or unisexual.
48
What is a ginkgophyte?
A gymnosperm with one extant species, the *Ginkgo biloba*: a tree with fan-shaped leaves.
49
What is a gnetophyte?
A gymnosperm shrub with varied morphological features that produces vessel elements in its woody tissues; the phylum includes the genera *Ephedra*, *Gnetum* and *Welwitschia*.
50
What is a gymnosperm?
A seed plant with naked seeds (seeds exposed on modified leaves or in cones).
51
What is an integument?
A layer of sporophyte tissue that surrounds the megasporangium, and later, the embryo.
52
What is a megasporocyte?
A megaspore mother cell; larger spore that germinates into a female gametophyte in a heterosporous plant.
53
What is a microsporocyte?
A smaller spore that produces a male gametophyte in a heterosporous plant.
54
What does it mean to be monoecious?
Describes a species in which the male and female reproductive organs are on the same plant. Literally, “one home” or bisexual.
55
What is an ovulate cone?
A cone containing two ovules per scale.
56
What is a strobilus?
A plant structure with a tight arrangement of sporophylls around a central stalk, as seen in cones or flowers; the male strobilus produces pollen, and the female strobilus produces eggs.
57
What are some characteristics of gymnosperms?
Gymnosperms are paraphyletic, and their characteristics include naked seeds, separate female and male gametes, pollination by wind, and tracheids (which transport water and solutes in the vascular system).
58
In what ways are gymnosperm seeds “naked”?
Gymnosperm seeds are not enclosed in an ovary; rather, they are exposed on cones or modified leaves.
59
In which types of environments do gymnosperms predominate?
They are adapted to live where fresh water is scarce during part of the year, or in the nitrogen-poor soil of a bog. They are still the prominent phylum in the coniferous biome or taiga, where the evergreen conifers have a selective advantage in cold and dry weather. Evergreen conifers continue low levels of photosynthesis during the cold months, and are ready to take advantage of the first sunny days of spring.
60
What is a disadvantage that conifers face?
One disadvantage is that conifers are more susceptible than deciduous trees to infestations because conifers do not lose their leaves all at once. They cannot, therefore, shed parasites and restart with a fresh supply of leaves in spring.
61
What are some reproductive characteristics of gymnosperms?
The life cycle of a gymnosperm involves alternation of generations, with a dominant sporophyte in which the female gametophyte resides, and reduced gametophytes. All gymnosperms are heterosporous. The male and female reproductive organs can form in cones or strobili. Male and female sporangia are produced either on the same plant (monoecious), or on separate plants (dioecious).
62
What are some reproductive characteristics of pine trees?
Pine trees are conifers and carry both male and female sporophylls on the same mature sporophyte. Therefore, they are monoecious plants. Like all gymnosperms, pines are heterosporous and generate two different types of spores: male microspores and female megaspores.
63
How does pollination and fertilization occur in conifers?
In the male cones, or staminate cones, the microsporocytes give rise to pollen grains by meiosis. In the spring, large amounts of yellow pollen are released and carried by the wind. Some gametophytes will land on a female cone. Pollination is defined as the initiation of pollen tube growth. The pollen tube develops slowly, and the generative cell in the pollen grain divides into two haploid sperm cells by mitosis. At fertilization, one of the sperm cells will finally unite its haploid nucleus with the haploid nucleus of the egg cell.
64
How does a female gametophyte develop in conifers?
Female cones, or ovulate cones, contain two ovules per scale. One megaspore mother cell, or megasporocyte, undergoes meiosis in each ovule. Three of the four cells break down; only a single surviving cell will develop into a female multicellular gametophyte, which encloses archegonia.
65
How do pine tree seeds develop after fertilization?
Upon fertilization, the diploid egg in the archegonium will give rise to the embryo, which is enclosed in a seed coat of tissue from the parent plant. Fertilization and seed development is a long process in pine trees: it may take up to two years after pollination. The seed that is formed contains three generations of tissues: the seed coat that originates from the sporophyte tissue, the gametophyte that will provide nutrients, and the embryo itself.
66
What is the life cycle of a conifer?
First, there is a mature diploid sporophyte. Male cones grow in the lower branches, and female cones grow in the upper branches where they may be fertilized by pollen blown on the wind from the male cones. The pollen grains attach to scales on the female cones, and a pollen tube forms, allowing the pollen to migrate toward the female gametophyte (ovule). It may take more than a year between pollination and fertilization while the pollen tube grows towards the megasporocyte, which undergoes meiosis into megaspores. The megaspores will mature into eggs. Upon fertilization, a diploid zygote forms. Seeds are dispersed and grow into mature trees.
67
What are the gymnosperm phyla and some of their characteristics?
Modern gymnosperms are classified into four phyla. Coniferophyta, Cycadophyta, and Ginkgophyta are similar in their production of secondary cambium (cells that generate the vascular system of the trunk or stem and are partially specialized for water transportation) and their pattern of seed development. However, the three phyla are not closely related phylogenetically to each other. Gnetophyta are considered the closest group to angiosperms because they produce true xylem tissue.
68
What is the dominant phylum of gymnosperms?
Conifers are the dominant phylum of gymnosperms, with the most variety of species.
69
What are some adaptations of conifers and where are they found?
Most conifers are typically tall trees that usually bear scale-like or needle-like leaves. Water evaporation from leaves is reduced by their thin shape and the thick cuticle. Snow slides easily off needle-shaped leaves, keeping the load light and decreasing breaking of branches. Adaptations to cold and dry weather explain the predominance of conifers at high altitudes and in cold climates.
70
What are some examples of conifers?
Conifers include familiar evergreen trees such as pines, spruces, firs, cedars, sequoias, and yews. A few species are deciduous and lose their leaves in fall. The European larch and the tamarack are examples of deciduous conifers.
71
What are some uses and characteristics of conifer wood?
Many coniferous trees are harvested for paper pulp and timber. The wood of conifers is more primitive than the wood of angiosperms; it contains tracheids, but no vessel elements, and is therefore referred to as “soft wood”.
72
What are some characteristics of cycads?
Cycads thrive in mild climates, and are often mistaken for palms because of the shape of their large, compound leaves. Cycads bear large cones, and may be pollinated by beetles rather than wind: unusual for a gymnosperm.
73
How prevalent are cycads?
Cycads dominated the landscape during the age of dinosaurs in the Mesozoic, but only a hundred or so species persisted to modern times. They face possible extinction, and several species are protected through international conventions.
74
What is a usage of cycads?
Because of their attractive shape, they are often used as ornamental plants in gardens in the tropics and subtropics.
75
What are some characteristics of ginkgophytes?
The single surviving species of the ginkgophytes group is the *Ginkgo biloba*. Its fan-shaped leaves - unique among seed plants because they feature a dichotomous venation pattern - turn yellow in autumn and fall from the tree.
76
Where is *G. biloba* planted?
For centuries, *G. biloba* was cultivated by Chinese Buddhist monks in monasteries, which ensured its preservation. It is planted in public spaces because it is unusually resistant to pollution. Male and female organs are produced on separate plants. Typically, gardeners plant only male trees because the seeds produced by the female plant have an off-putting smell of rancid butter.
77
What are some characteristics of gnetophytes?
Gnetophytes are the closest relative to modern angiosperms, and include three dissimilar genera of plants: *Ephedra*, *Gnetum*, and *Welwitschia*. Like angiosperms, they have broad leaves. In tropical and subtropical zones, gnetophytes are vines or small shrubs. Like angiosperms, but unlike other gymnosperms, all gnetophytes possess vessel elements in their xylem.
78
What are some characteristics of *Ephedra*?
*Ephedra* occurs in dry areas of the West Coast of the United States and Mexico. *Ephedra*'s small, scale-like leaves are the source of the compound ephedrine, which is used in medicine as a potent decongestant. Because ephedrine is similar to amphetamines, both in chemical structure and neurological effects, its use is restricted to prescription drugs.
79
What are some examples of gnetophytes and where are they found?
*Ephedra viridis*, known by the common name Mormon tea, grows on the West Coast of the United States and Mexico. *Gnetum gnemon* grows in Malaysia. The large *Welwitschia mirabilis* can be found in the Namibian desert.
80
What is an anther?
The sac-like structure at the tip of the stamen in which pollen grains are produced.
81
What is Anthophyta?
The phylum to which angiosperms belong.
82
What are basal angiosperms?
A group of plants that probably branched off before the separation of monocots and eudicots.
83
What is a calyx?
A whorl of sepals.
84
What is a carpel?
A single unit of the pistil.
85
What is a corolla?
A collection of petals.
86
What is a cotyledon?
A primitive leaf that develops in the zygote; monocots have one cotyledon, and dicots have two cotyledons.
87
What is a dicot?
A related group of angiosperms whose embryos possess two cotyledons. AKA eudicot.
88
What is a filament?
A thin stalk that links the anther to the base of the flower.
89
What is a gynoecium?
A structure that constitutes the female reproductive organ. AKA carpel.
90
What does it mean to be herbaceous?
Grass-like plant noticeable by the absence of woody tissue.
91
What is a monocot?
A related group of angiosperms that produce embryos with one cotyledon and pollen with a single ridge.
92
What is an ovary?
A chamber that contains and protects the ovule or female megasporangium.
93
What is the perianth?
The part of the plant consisting of the calyx (sepals) and corolla (petals).
94
What is a petal?
A modified leaf interior to the sepals; colorful petals attract animal pollinators.
95
What is a pistil?
A fused group of carpels.
96
What is a sepal?
A modified leaf that encloses the bud; outermost structure of a flower.
97
What is a stamen?
A structure that contains the male reproductive organs.
98
What is a stigma?
The uppermost structure of the carpel where pollen is deposited.
99
What is a style?
A long, thin structure that links the stigma to the ovary.
100
How many species of angiosperms are there?
With more than 250,000 species, the angiosperm phylum Anthophyta is second only to insects in terms of diversification.
101
What are the functions of flowers and fruit in angiosperms?
The function of the flower is to ensure pollination. Flowers also provide protection for the ovule and developing embryo inside a receptacle. The function of the fruit is seed dispersal. They also protect the developing seed. Different fruit structures or tissues on fruit - such as sweet flesh, wings, parachutes, or spines that grab - reflect the dispersal strategies that help spread seeds.
102
What are the parts of a flower?
Flowers are sporophylls organized around a central stalk. Although they vary greatly in appearance, all flowers contain the same structures: sepals, petals, carpels, and stamens. The peduncle attaches the flower to the plant. A whorl of sepals (collectively called the calyx) is located at the base of the peduncle and encloses the unopened floral bud. Sepals are usually photosynthetic organs, although there are some exceptions. For example, the corolla in lilies and tulips consists of three sepals and three petals that look virtually identical. Petals, collectively the corolla, are located inside the whorl of sepals and often display vivid colors to attract pollinators. Flowers pollinated by wind are usually small, feathery, and visually inconspicuous. Sepals and petals together form the perianth. The sexual organs (carpels and stamens) are located at the center of the flower.
103
What are the parts of the gynoecium?
Styles, stigmas, and ovules constitute the female organ: the gynoecium or carpel. Flower structure is very diverse, and carpels may be singular, multiple, or fused. Multiple fused carpels comprise a pistil. The megaspores and the female gametophytes are produced and protected by the thick tissues of the carpel. A long, thin structure called a style leads from the sticky stigma, where pollen is deposited, to the ovary, enclosed in the carpel. The ovary houses one or more ovules, each of which will develop into a seed upon fertilization.
104
What are the parts of the androecium?
The male reproductive organs, the stamens (collectively called the androecium), surround the central carpel. Stamens are composed of a thin stalk called a filament and a sac-like structure called the anther. The filament supports the anther, where the microspores are produced by meiosis and develop into pollen grains.
105
How do fruits develop?
As the seed develops, the walls of the ovary thicken and form the fruit. The seed forms in an ovary, which also enlarges as the seeds grow. In botany, a fertilized and fully grown, ripened ovary is a fruit.
106
What are some unconventional examples of fruit?
Many foods commonly called vegetables are actually fruit. Eggplants, zucchini, string beans, and bell peppers are all technically fruit because they contain seeds and are derived from the thick ovary tissue. Acorns are nuts, and winged maple whirligigs (whose botanical name is samara) are also fruit. Botanists classify fruit into more than two dozen different categories, only a few of which are actually fleshy and sweet.
107
What are some examples of fleshy fruit?
Fleshy fruit include the familiar berries, peaches, apples, grapes, and tomatoes.
108
What are some examples of dry fruit?
Rice, wheat, and nuts are examples of dry fruit.
109
What are some examples of fruits that are not derived from the ovary?
Strawberries are derived from the receptacle and apples from the pericarp, or hypanthium. Some fruits are derived from separate ovaries in a single flower, such as the raspberry. Other fruits, such as the pineapple, form from clusters of flowers. Additionally, some fruits, like watermelon and orange, have rinds.
110
What are some different modes of dispersal in fruits?
Wind carries the light dry fruit of trees and dandelions. Water transports floating coconuts. Some fruits attract herbivores with color or perfume, or as food. Once eaten, tough, undigested seeds are dispersed through the herbivore's feces. Other fruits have burs and hooks to cling to fur and hitch rides on animals.
111
What are some reproductive characteristics of angiosperms?
The sporophyte phase is the main phase of an angiosperm's life cycle. Like gymnosperms, angiosperms are heterosporous, and generate both microspores, which will generate pollen grains as the male gametophytes, and megaspores, which will form an ovule that contains female gametophytes.
112
How are pollen grains created?
Inside the anthers' microsporangia, male gametophytes divide by meiosis to generate haploid microspores, which, in turn, undergo mitosis and give rise to pollen grains. Each pollen grain contains two cells: one generative cell that will divide into two sperm and a second cell that will become the pollen tube cell.
113
How does the megagametophyte develop?
The ovule, sheltered within the ovary of the carpel, contains the megasporangium protected by two layers of integuments and the ovary wall. Within each megasporangium, a megasporocyte undergoes meiosis, generating four megaspores - three small and one large. Only the large megaspore survives; it produces the female gametophyte, referred to as the embryo sac. The megaspore divides three times to form an eight-cell stage. Four of these cells migrate to each pole of the embryo sac; two come to the equator, and will eventually fuse to form a 2*n* polar nucleus; the three cells away from the egg form antipodals, and the two cells closest to the egg become the synergids.
114
What are the parts of a megagametophyte?
The mature embryo sac contains one egg cell, two synergids or “helper cells”, three antipodal cells, and two polar nuclei in a central cell.
115
How does the sperm from a pollen grain reach the egg in an ovule?
When a pollen grain reaches the stigma, a pollen tube extends from the grain, grows down the style, and enters through the micropyle: an opening in the integument of the ovule. The two sperm cells are deposited in the embryo sac.
116
How does an angiosperm seed develop?
A double fertilization event occurs when the sperm reaches the egg. One sperm and the egg combine, forming a diploid zygote - the future embryo. The other sperm fuses with the 2*n* polar nuclei, forming a triploid cell that will develop into the endosperm, which is tissue that serves as a food reserve. The zygote develops into an embryo with a radicle, or small root, and one (monocot) or two (dicot) leaf-like organs called cotyledons. This difference in the number of embryonic leaves is the basis for the two major groups of angiosperms: the monocots and the eudicots. Seed food reserves are stored outside the embryo, in the form of complex carbohydrates, lipids, or proteins. The cotyledons serve as conduits to transmit the broken-down food reserves from their storage site inside the seed to the developing embryo. The seed consists of a toughened layer of integuments forming the coat, the endosperm with food reserves, and at the center, the well-protected embryo.
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Do flowers generally self-pollinate or cross-pollinate?
Most flowers are monoecious or bisexual, which means that they carry both stamens and carpels; only a few species self-pollinate. Monoecious flowers are also known as “perfect” flowers because they contain both types of sex organs. Both anatomical and environmental barriers promote cross-pollination mediated by a physical agent (wind or water), or an animal, such as an insect or bird. Cross-pollination increases genetic diversity in a species.
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How are angiosperms classified?
Angiosperms are classified in a single phylum: the Anthophyta. Modern angiosperms appear to be a monophyletic group. Flowering plants are divided into two major groups, according to the structure of the cotyledons, pollen grains, and other structures. Monocots include grasses and lilies, and eudicots or dicots form a polyphyletic group. Basal angiosperms are a group of plants that are believed to have branched off before the separation into monocots and eudicots because they exhibit traits from both groups. They are categorized separately in many classification schemes. The *Magnoliidae* (magnolia trees, laurels, and water lilies) and the *Piperaceae* (peppers) belong to the basal angiosperm group.
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What are the groups of basal angiosperms?
*Magnoliidae, Laurales, Nymphaeales, Piperales.*
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What are some characteristics and examples of *Magnoliidae*?
The *Magnoliidae* are represented by the magnolias: tall trees bearing large, fragrant flowers that have many parts and are considered archaic.
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What are some characteristics and examples of *Laurales*?
Laurel trees produce fragrant leaves and small, inconspicuous flowers. The *Laurales* grow mostly in warmer climates and are small trees and shrubs. Familiar plants in this group include the bay laurel, cinnamon, spice bush, and avocado tree.
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What are some characteristics and examples of *Nymphaeales*?
The *Nymphaeales* are comprised of the water lilies, lotus, and similar plants; all species thrive in freshwater biomes, and have leaves that float on the water surface or grow underwater. Water lilies are particularly prized by gardeners, and have graced ponds and pools for thousands of years.
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What are some characteristics and examples of *Piperales*?
The *Piperales* are a group of herbs, shrubs, and small trees that grow in the tropical climates. They have small flowers without petals that are tightly arranged in long spikes. Many species are the source of prized fragrance or spices, for example the berries of *Piper nigrum* are the familiar black peppercorns that are used to flavor many dishes.
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What are some characteristics of monocots?
Plants in the monocot group are primarily identified as such by the presence of a single cotyledon in the seedling. Other anatomical features shared by monocots include veins that run parallel to the length of the leaves, and flower parts that are arranged in a three- or six-fold symmetry. True woody tissue is rarely found in monocots. In palm trees, vascular and parenchyma tissues produced by the primary and secondary thickening meristems form the trunk. The pollen from the first angiosperms was monosulcate, containing a single furrow or pore through the outer layer. This feature is still seen in the modern monocots. Vascular tissue of the stem is not arranged in any particular pattern. The root system is mostly adventitious and unusually positioned, with no major tap root.
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What are some examples of monocots?
The monocots include familiar plants such as the true lilies (which are at the origin of their alternate name of Liliopsida), orchids, grasses, and palms. Many important crops are monocots, such as rice and other cereals, corn, sugar cane, and tropical fruits like bananas and pineapples.
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What are some characteristics of eudicots?
Eudicots, or true dicots, are characterized by the presence of two cotyledons in the developing shoot. Veins form a network in leaves, and flower parts come in four, five, or many whorls. Vascular tissue forms a ring in the stem; in monocots, vascular tissue is scattered in the stem. Eudicots can be herbaceous (like grasses), or produce woody tissues. Most eudicots produce pollen that is trisulcate or triporate, with three furrows or pores. The root system is usually anchored by one main root developed from the embryonic radicle. Eudicots comprise two-thirds of all flowering plants.
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Why is the classification of a plant as a monocot or eudicot not always clearly evident?
Many species exhibit characteristics that belong to either group.
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How do the number of cotyledons differ between monocots and eudicots?
Monocots have one cotyledon, and eudicots have two.
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How do the veins differ between monocots and eudicots?
Monocots have parallel veins, and eudicots have network (branched) veins.
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How does the stem vascular tissue differ between monocots and eudicots?
Monocots have scattered stem vascular tissue, and that of eudicots is arranged in a ring pattern.
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How do the roots differ between monocots and eudicots?
Monocots have a network of adventitious roots, while eudicots have a tap root with many lateral roots.
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How does the pollen differ between monocots and eudicots?
Monocots have monosulcate pollen, while eudicots have trisulcate pollen.
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How do the number of flower parts differ between monocots and eudicots?
Monocots have three or a multiple of three flower parts, while eudicots have four or five or a multiple of four or five, and whorls.
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What is barcoding?
A molecular biology technique in which one or more short gene sequences taken from a well-characterized portion of the genome is used to identify a species.
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What is a crop?
A cultivated plant.
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What is an heirloom seed?
A seed from a plant that was grown historically, but has not been used in modern agriculture on a large scale.
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What is herbivory?
Consumption of plants by insects and other animals.
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What is nectar?
A liquid rich in sugars produced by flowers to attract animal pollinators.
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What is pollination?
The transfer of pollen from the anther to the stigma.
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In what ways are seed plants important?
Plants play a key role in the maintenance of terrestrial ecosystems through stabilization of soils, cycling of carbon, and climate moderation. Large tropical forests release oxygen and act as carbon dioxide sinks. Seed plants provide shelter to many life forms, as well as food for herbivores, thereby indirectly feeding carnivores. Plant secondary metabolites are used for medicinal purposes and industrial production.
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What are the hypothesized contributors to plant and insect diversity?
Coevolution of flowering plants and insects is a hypothesis that has received much attention and support, because both angiosperms and insects diversified at about the same time in the middle Mesozoic. Many authors have attributed the diversity of plants and insects to pollination and herbivory, which is believed to have been as much a driving force as pollination.
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What are some defense mechanisms developed by plants to deter herbivory?
Some plant seeds, such as acorn and unripened persimmon, are high in alkaloids and unsavory to some animals. Other plants are protected by bark, although some animals developed specialized mouth pieces to tear and chew vegetal material. Spines and thorns deter most animals, except for mammals with thick fur, and some birds have specialized beaks to get past such defenses.
143
What mutualistic relationship exists between acacia trees and ants?
The trees support the insects with shelter and food. In return, ants discourage herbivores, both invertebrates and vertebrates, by stinging and attacking leaf-eating insects.
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What are some examples of flowering plants that are wind pollinated?
Grasses are a successful group of flowering plants that are wind pollinated. They produce large amounts of powdery pollen carried over large distances by the wind. The flowers are small and wisp-like. Large trees such as oaks, maples, and birches are also wind pollinated.
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What percent of angiosperms depend on animals for pollination?
80 percent.
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What types of pollen are produced by many bird- or insect-pollinated flowers?
The flowers can produce both fertile pollen, for reproduction, and sterile pollen rich in nutrients for birds and insects.
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What are some examples of adaptation of flowers for attracting specific pollinators?
Butterflies and bees can detect ultraviolet light. Flowers that attract these pollinators usually display a pattern of low ultraviolet reflectance that helps them quickly locate the flower's center and collect nectar while being dusted with pollen. Large, red flowers with little smell and a long funnel shape are preferred by hummingbirds, who have good color perception, a poor sense of smell, and need a strong perch. White flowers opened at night attract moths. Other animals - such as bats, lemurs, and lizards - can also act as pollinating agents.
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How do some plants attract carrion flies for pollination?
Visitation of flowers by pollinating flies is a function mostly of smell. Flies are attracted by rotting flesh and carrions. The putrid odor seems to be the major attractant. The polyamines putrescine and cadaverine, which are the products of protein breakdown after animal death, are the source of the pungent smell of decaying meat. Some plants strategically attract flies by synthesizing polyamines similar to those generated by decaying flesh and thereby attract carrion flies.
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Why are flies attracted to dead animals?
Flies seek out dead animals because they normally lay their eggs on them and their maggots feed on the decaying flesh.
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How can time of death be determined by forensic entomologists?
Time of death can be determined by a forensic entomologist based on the stages and type of maggots recovered from cadavers.
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Which three crops dominate global agriculture?
Rice, wheat, and potatoes.
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How are the main three biological macromolecules supplied by seed plants?
Cereals, rich in carbohydrates, provide the staple of many human diets. Beans and nuts supply proteins. Fats are derived from crushed seeds, as is the case for peanut and rapeseed (canola) oils, or fruits such as olives.
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Which plants are used to produce sugar?
Sugar is produced from the monocot sugarcane and the eudicot sugar beet.
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What are some examples of plants that can be used to make drinks?
Drinks can be made from infusions of tea leaves, chamomile flowers, crushed coffee beans, and powdered cocoa beans.
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What are some examples of spices derived from plants?
Spices come from many different plant parts: saffron and cloves are stamens and buds, black pepper and vanilla are seeds, the bark of a bush in the *Laurales* family supplies cinnamon, and the herbs that flavor many dishes come from dried leaves and fruit, such as red chili pepper.
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What are some industrial uses of seed plants?
Providing wood as a source of timber for construction, fuel, and the material to build furniture. Most paper is derived from the pulp of coniferous trees. Fibers of seed plants such as cotton, flax, and hemp are woven into cloth. Textile dyes, such as indigo, were mostly of plant origin until the advent of synthetic chemical dyes.
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What are some of the first historical references to uses of plants for medicinal purposes?
There are references to the use of plants' curative properties in Egyptian, Babylonian, and Chinese writings from 5000 years ago.
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What does ethnobotany study?
The interaction between a particular culture and the plants native to the region.
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What are the requirements and responsibilities of ethnobotanists?
To become an ethnobotanist, a person must acquire a broad knowledge of plant biology, ecology, and sociology. Not only are the plant specimens studied and collected, but also the stories, recipes, and traditions that are linked to them.
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How is ethnobotany multidisciplinary?
It is a convergence of molecular biology, anthropology, and ecology.
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What does pharmacognosy study?
Pharmacognosy is the branch of pharmacology that focuses on medicines derived from natural sources.
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What are some threats to plant diversity?
The explosion of the human population, especially in tropical countries where birth rates are highest and economic development is in full swing, is leading to human encroachment into forested areas. To feed the larger population, humans need to obtain arable land, so there is massive clearing of trees. The need for more energy to power larger cities and economic growth leads to the construction of dams, the consequent flooding of ecosystems, and increased emissions of pollutants. Other threats to tropical forests come from poachers, who log trees for their precious wood.
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What are some examples of trees on the endangered species list?
Ebony and Brazilian rosewood are examples of tree species driven almost to extinction by indiscriminate logging.
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What is the impact of extinction of plant species and what are some efforts to preserve biodiversity?
The number of plant species becoming extinct is increasing at an alarming rate. Because ecosystems are in a delicate balance, and seed plants maintain close symbiotic relationships with animals - whether predators or pollinators - the disappearance of a single plant can lead to the extinction of connected animal species. A real and pressing issue is that many plant species have not yet been catalogued, and so their place in the ecosystem is unknown. These unknown species are threatened by logging, habitat destruction, and loss of pollinators. They may become extinct before we have the chance to begin to understand the possible impacts from their disappearance. Efforts to preserve biodiversity take several lines of action, from preserving heirloom seeds to barcoding species.
