1
Q
closest relatives of plants: characteristics
A
Charophytes (algae): share the following 4 characteristics
- Distinctive circular rings of proteins in the plasma membrane. These rings synthesize the cellulose microfibrils of the cell wall. In contrast, noncharophyte algae have linear sets of proteins that synthesize cellulose.
- Peroxisomes that contain enzymes that help minimize the loss of organic products resulting from photorespiration
- Similar structure of flagellated sperm
- Particular details of cell division occur only in land plants and certain charophytes. For example, a group of microtubules known as the PHRAGMOPLAST forms btwn the daughter nuclei of a dividing cell. A cell plate then develops in the middle of the phragmplast, across the midline of the dividing cell. The cell plate gives rise to a new cross wall that separates the daughter cells.
2
Q
closest relatives of plants: genera
A
Chara and Coleochaete
3
Q
sporopollenin
A
In charophytes, a layer of a durable polymer that prevents exposed zygotes from drying out. A similar chemical adaptation is found in the tough sporopollenin walls that encase the spores of plants; makes their walls tough and resistant to harsh environments –> enables spores to be dispersed thru dry air w/o harm.
4
Q
embrophyte
A
Alternate name for land plants that refers to their shared derived trait of multicellular, dependent embryos. Another name for land plants.
- As part of a life cycle w/ alternation of generations, multicellular plant embryos develop from zygotes that are retained within the tissues of the female parent (a gametophyte).
- The parental tissues provide the developing embryo w/ nutrients, such as sugars and amino acids.
- The embryo has specialized PLACENTAL TRANSFER CELLS, sometimes present in the adjacent maternal tissue as well, which enhance the transfer of nutrients from parent to embryo thru elaborate ingrowths of the wall surface (plasma membrane and cell wall).
5
Q
Derived traits of land plants:
A
- alternation of generations (w/ an associated trait of multicellular, dependent embryos)
- walled spores produced in sporangia
- multicellular gametangia
- apical meristems
6
Q
alternation of generations
A
- The life cycles of all land plants alternate btwn 2 generations of multicellular organisms: gametophytes and sporophytes.
Steps:
1. The gametophyte produces haploid gametes by mitosis.
2. Two gametes unite and form a diploid zygote.
3. The zygote develops into a multicellular diploid sporophyte.
4. Specialized cells of the sporophyte will undergo meiosis and produce haploid spores.
5. The spores will then develop into the multicellular gametophytes. w/o fusing w/ another spore
7
Q
spore
A
- Meiosis in a mature sporophyte produces haploid spores, reproductive cells that can develop into a new haploid organism w/o fusing w/ another cell.
- Mitotic division of the spore cell produces a new multicellular gametophyte, and the cycle begins again.
8
Q
sporangia
A
The sporophyte has multicellular organs called sporangia that produce the spores. The outer tissues of the sporangium protect the developing spores until they are released into the air.
9
Q
sporocytes
A
Within a sporangium, diploid cells called sporocytes, or spore mother cells, undergo meiosis and generate the haploid spores.
10
Q
Charophytes vs land plants: spores
A
- Multicellular sporangia that produce spores w/ sporopollenin-enriched walls are key terrestrial adaptations of land plants.
- Charophytes also produce spores, but they lack multicellular sporangia, and their flagellated, water-dispersed spores lack sporopollenin.
11
Q
gametangium
A
Multicellular plant structure in which gametes are formed.
12
Q
archegonia
A
- Female gametangia.
- Each archegonium is a pear-shaped organ that produces a single nonmotile egg retained within the bulbous part of the organ.
- Each egg is fertilized within an archegonium.
13
Q
antheridia
A
- Male gametangia.
- Produce sperm and release them into the environment. -
- In many groups of present-day plants, the sperm have flagella and swim to the eggs thru water droplets or a film of water.
14
Q
apical meristems
A
- Localized regions of cell division at the tips of roots and shoots; enable the plant to grow in length.
- Cells produced by apical meristems differentiate into the outer epidermis, which protects the body, and various types of internal tissues.
- Shoot apical meristems generate leaves in most plants.
15
Q
cuticle
A
- The epidermis in many plant species has a covering, the cuticle, which consists of wax and other polymers.
- Acts as waterproofing, helping prevent excessive water loss, while also providing some protection from microbial attack.
16
Q
secondary compounds: description
A
- Many land plants produce molecules called secondary compounds, so named b/c they’re products of 2ndary metabolic pathways – side branches off the primary metabolic pathways that produce the lipids, carbs, amino acids, and other compounds common to all organisms.
- Another derived trait that relates to terrestrial life.
17
Q
secondary compounds: examples
A
- so named because they are products of secondary
metabolic pathways—side branches off the primary metabolic
pathways that produce the lipids, carbohydrates, amino acids,
and other compounds common to all organisms. - Alkaloids, terpenes, tannins, flavonoids.
- The first three have a bitter taste, strong odor, or toxic effect that helps defend against herbivores and parasites.
- Flavonoids absorb UV radiation, and some related compounds deter attack by pathogens.
18
Q
vascular tissue
A
Cells joined into tubes that transport water and nutrients throughout the plant body.
19
Q
bryophyte
A
Commonly used informally to refer to nonvascular plants.
20
Q
Vascular vs non-vascular plants
A
- Shared derived traits: multicellular embryos, apical meristems
- Non-vasculars lack roots and true leaves
- Vasculars comprise 93 percent of all extant plant species
- In nonvasculars, the haploid gametophytes are the dominant stage of the life cycle – larger and longer-living than sporophytes
21
Q
grade
A
- A group of organisms that share the same level of organizational complexity or share a key adaptation.
- Don’t necessarily share the same ancestry.
22
Q
seedless vascular plants
A
- Lycophytes and pterophytes, members of a grade
- Pterophytes share a more recent common ancestor w/ seed plants.
23
Q
seed
A
- An embryo packaged w/ a supply of nutrients inside a protective coat.
- Two groups: gymnosperms and angiosperms.
24
Q
gymnosperms
A
- Grouped together as “naked seed” plants b/c their seeds aren’t enclosed in chambers.
- Most familiar: conifers.
25
angiosperms
- All flowering plants.
- Seeds develop inside chambers called ovaries, which originate within flowers and mature into fruits.
- Nearly 90 percent of living plant species are angiosperms.
26
protonema
- When bryophyte spores are dispersed to a favorable habitat, such as moist soil or tree bark, they may germinate and grow into gametophytes.
- Germinating moss spores characteristically produce a mass of green, branched, one-cell-thick filaments known as a protonema.
- A protonema has a large SA that enhances water and mineral absorption.
- Produces one or more "buds" in favorable conditions.
27
gametophore
- Bud-like growths (produced by protonema) has an apical meristem that generates a gamete-producing structure known as a gametophore.
- Protonema + gamteophore = body of a moss gametophyte
28
rhizoids
- Bryophyte gametocytes are anchored by delicate rhizoids -- long, tubular isngle cells (in liverworts and hornworts) or filaments of cells (in mosses).
- Unlike roots, rhizoids aren't composed of tissues.
- Lack specialized conducting cells and don't play a primary role in water and mineral absorption.
29
bryophyte sperm
- Require a film of water to reach the eggs; this is why many bryoophyte species are found in moist habitats.
- Sexual reproduction is likely to be more successful when individuals are located close to one another b/c sperm swim thru water to reach the egg.
30
bryophyte sporophytes: description
- Usually green and photosynthetic when young; cannot live independently -- remain attached to parental gametophytes, from which they absorb sugars, amino acids, minerals, and water.
- Bryophytes have the smallest sporophytes of all extant plant groups, consistent w/ the hypothesis that larger sporophytes evolved only later, in the vasculars.
31
bryophyte sporophytes: parts
- 3: foot, seta, sporangium
- Foot: embedded in archegonium; absorbs nutrients from the gametophyte
- Seta: aka stalk; conducts these nutrients to the sporangium, also called a CAPSULE, which uses them to produce spores by meiosis
32
capsule
The sporangium of a bryophyte.
33
peristome
- In most mosses, the seta becomes elongated, enhancing spore dispersal by elevating the capsule.
- Typically, the upper part of the capsule features a ring of interlocking, tooth-like structures known as the peristome. These "teeth" open under dry conditions and close again when it's moist. This allows spores to be discharged gradually, via periodic gusts of wind that can carry them long distances.
34
stomata
- Moss and hornwort sporophytes are often larger and more complex than those of liverworts. Both moss and hornwort sporophytes also have specialized pores called stomata, which are also found in all vascular plants.
- These pores support photosynthesis by allowing the exchange of CO2 and O2 btwn the outside air and the sporophyte interior.
- Stomata are also the main avenues by which water evaporates from the sporophyte. In hot, dry conditions, the stomata close, minimizing water loss.
35
peat
- - one wetland moss genus, Sphagnum, or peat moss, is often a major component of deposits of partially decayed organic material known as peat.
- - sphagnum doesn't decay readily, in part bc of phenolic compounds embedded in its cell walls. The low temperature, pH, and oxygen level of peatlands also inhibit decay of moss and other organisms in these boggy wetlands.
36
xylem
- One of 2 types of vascular tissue.
- Conducts most of the water and minerals.
- Includes tracheids, tube-shaped cells that carry water and minerals up from roots.
- The water-conducting cells in vascular plants are lignified -- their cell walls are strengthened by the polymer lignin.
37
phloem
- One of 2 types of vascular tissue.
| - Has cells arranged into tubes that distribute sugars, amino acids, and other organic products.
38
microphylls
- All of the lycophytes (the oldest lineage of present-day vascular plants) -- and only the lycophytes -- have microphylls, small, usually spine-shaped leaves supported by a single strand of vascular tissue.
- may have originated
from sporangia supported by single, unbranched strands of
vascular tissue
39
megaphylls
- Almost all other vascular plants (no lycophytes) have megaphylls leaves w/ a highly branched vascular system.
- may have
evolved by the fusion of branched stems
40
evolution of leaves
- Microphylls originated from sporangia located on the side of the stem.
- Megaphylls may have evolved from a series of branches lying close together on a stem. As one of these branches came to grow above, or overtop, the others, the lower branches became flattened and developed webbing that joined them to one another. These joined branches thus became a leaf attached to the branch that overtopped them.
41
pterophyta
ferns
42
sphenophyta
horsetails
43
psilophyta
whisk ferns and a related genus
44
pterophytes vs lycophytes
- Pterophytes and seed plants share traits that aren't found in lycophytes, including overtopping growth, megaphyll leaves, and roots that can branch at various points along the length of an existing root.
- Lycophytes: roots branch only at the growing tip of the root, forming a Y-shaped structure.
45
equisetum
- The pterophytes called horsetails were very diverse during the Carboniferous period.
- Today, only 15 species survive as a single, widely distributed genus, Equisetum, found in marshy places and along streams.
46
Psilotum
- genus: whisk ferns
- Closely related to the genus Tmesipteris; these 2 genera form a clade consisting mainly of tropical epiphytes.
- Plants in these 2 genera, the only vascular plants lacking true roots, are called 'living fossils' b/c of their resemblance to fossils of ancient relatives of living vascular plants. They absorb through rhizoids.
- DNA sequences and sperm structure indicate that these two genera are closely related to ferns.
47
sporophylls
a milestone in the evolution of plants was the emergence of sporophylls, modified leaves that bear sporangia. Vary greatly in structure.
48
sori
Fern sporophylls produce clusters of sporangia known as sori, usually on the undersides of the sporophylls.
49
strobili
In many lycophytes and in most gymnosperms, groups of sporophylls form cone-like structures called strobili.
50
homosporous
Most seedless vascular plants are homosporous -- they have one type of sporangium that produced one type of spore, which typically develops into a bisexual gametophyte, as in most ferns.
51
heterosporous
- - Has two types of sporangia and produces two kinds of spores.
- - Megasporangia on megasporophylls produce megaspores, which develop into female gametophytes.
- - Microsporangia on microsporophylls produce the comparatively smaller microspores, which develop into male gametophytes.
- - All seed plants and a few seedless vascular plants are hetrosporous.
52
ferns
- - today are by far the most widespread seedless vascular plants.
- - ferns and other pterophytes are more closely related to seed plants than to lycophytes
53
significance of SEEDLESS vascular plants
- - accelerated photosynthesis, dropping CO2 levels by as much as a factor of five.
- - the seedless vascular plants that formed the first forests eventually became coal. In the stagnant waters of Carboniferous swamps, dead plants didn't completely decay. This organic material turned to thick layers of peat, later covered by the sea. Marine sediments piled on top, and over millions of years, heat and pressure converted the peat to coal.
54
Ancient CO2 levels can be estimated in several ways:
- Counting the number of stomata in fossil leaves (data from living species show that this number increases as CO2 levels drops)
- Measuing carbon isotope levels in fossils of plankton.
55
brood bodies
Many bryophyte species can increase the number
of individuals in a local area through various methods
of asexual reproduction. For example, some
mosses reproduce asexually by forming brood bodies,
small plantlets that detach from the
parent plant and grow into new, genetically identical
copies of their parent.
56
ancestors of vascular plants
- Unlike the nonvascular plants,
these species had branched sporophytes that were not dependent
on gametophytes for nutrition
- their branching made possible more complex
bodies with multiple sporangia. As plant bodies became increasingly
complex, competition for space and sunlight probably
increased.
- already had some derived
traits of today’s vascular plants, but they lacked roots and
some other adaptations that evolved later
57
life cycle of a moss
1. spores develop into threadlike PROTONEMATA
2. the haploid protonemata produce "buds" that divide by mitosis and grow into gametophores
3. sperm swim thru a film of moisture to reach the egg.
4. fertilization occurs w/in the archegonium
5. zygote develops into sporophyte embryo
6. sporophyte embryo grows a long stalk (seta) that emerges from the archegonium
7. attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte
8. meiosis occurs and haploid spores develop in the capsule. when the capsule is mature, its lid pops off, and the spores are released
58
life cycle of a fern
1. sporangia release spores. most fern species produce a single type of spore that develops into a bisexual gametophyte
2. each gametophyte develops sperm-producing antheridia and egg-producing archegonia. fern gametophytes typically produce eggs and sperm at diff times, so an egg from one gametophyte is fertilized by a sperm from another.
3. sperm use flagella to swim to eggs in the archegonia. an attractant secreted by the archegonia helps direct the sperm
4. zygote develops into a new sporophyte. the young plant grows out from an archegonium of its parent, the gametophyte
5. on the underside of the sporophyte's reproductive leaves are spots called sori. each sorus is a cluster of sporangia
