Chapter 31: Plants and the Conquest of Land (Part 2, Week 6)

Question 1

[Start 31.2 How Land Plants Have Changed the Earth]

A _______ years ago, Earth’s terrestrial surface was comparatively devoid of life. Green or brown crusts of _________ most likely grew in moist places, but there would have been very little soil, no plants, and no animal life.

Answer 1

Billion; cyanobacteria

Question 2

What was key to development of the first substantial soils, the rise to modern levels of atmospheric oxygen, the evolution of modern plant communities, and the colonization of land by animals?

Answer 2

The origin of the first land plants.

Question 3

What are the several types of

decay-resistant materials evolved in early seedless plants? (3)

Answer 3

Such as sporopollenin, cutin, and lignin.

Question 4

What happens when the plants died, and the decay resistant materials were buried in sediments?

Answer 4

They eventurally transformed into rock.

Such fossil carbon can accumulate and remain buried for very long time periods with the consequence of lowering the level of atmospheric CO2.

Question 5

What happened with fossil carbon accumalted over a large period of time?

Answer 5

CO2 is a greenhouse gas that causes global temperaturesto rise.

Therefore, the accumulation of fossil carbon is expected to lower global temperatures.

Question 6

Give an example of how modern bryophytes play important roles by storing CO2 as decay-resistant organic compounds, suggesting that ancient relatives likewise played this role.

Kinda long but you should get it!

Answer 6

1. Modern peat moss contain so much decay-resistant body mass that in many places, dead moss accumulated over long time periods has formed deep peat deposits.
2. By storing very large amounts of organic carbon for a long time, diverse species of Sphagnum moss help to keep Earth’s climate steady.
3. Under cooler than normal conditions, the mosses grow more slowly and thus absorb less CO2, allowing atmospheric CO2 to rise a bit, warming the climate alittle.
4. As the climate warms, the mosses grow faster and take up more CO2, storing it in peat deposits. Such a reduction in atmospheric CO2
   returns the climate to slightly cooler conditions.

Question 7

What do peat mosses also contain which also helps moderate the world’s climate?

Answer 7

Harbor bacteria that consume methane, another powerful greenhouse gas.

Question 8

What has an important factor affecting the evolution of species on Earth?

Answer 8

Atmospheric O2

Eukaryotic species tend to have high demands for O2 because they use it to obtain energy via cellular respiration.

Photosynthetic bacteria were the earliest organisms to produce O2, and later in evolution, algae also contributed to atmospheric O2.

Question 9

Why is the Carboniferous period (354-290 mya) considered the Coal Age?

Answer 9

Extensive forests dominated by tree-sized lycophytes, pteridophytes, and early seed plants occurred in widespread swampy regions.

As dead plants fell into the water, low oxygen levels there inhibited microbes that would have caused the plant matter to decay. The dead plants were then buried in sediments that later formed coal.

Question 10

Why did giant dragonflies exist during the Carboniferous period, but not now?

Answer 10

During the Carboniferous period (Coal Age), atmospheric oxygen levels reached historically high levels, enough to supply the large needs of giant insects, which obtain oxygen by diffusion.

Question 11

What was proposed about the Carboniferous proliferation of vascular plants?

Answer 11

Correlated with a dramatic decrease in atmospheric CO2, which reached the lowest known levels about 290 mya.

Question 12

What favored extensive diversification of the first seed plants, the gymnosperms?

Answer 12

Cooler, drier conditions.

Question 13

Diverse phyla of gymnosperms dominated Earth’s vegetation through what era? Also called the Age of the Dinosaurs.

Answer 13

Mesozoic era (245-65 mya)

In addition, fossils provide evidence that early mammals and flowering plants existed in the Mesozoic. Gymnosperms and early angiosperms were probably sources of food for early mammals as well as for herbivorous dinosaurs.

Question 14

Where was the fateful day, 65 mya, when disaster struck from the sky, causing a dramatic change in the types of plants and animals that dominated terrestrial ecosystems?

Answer 14

That day, at least one large meteorite crashed into the Earth near the present-day Yucatán Peninsula in Mexico.

This collision is known as the Cretaceous-Paleogene event (also sometimes referred to as the K/T event).

Question 15

What are the descedants of dinosaurs?

Answer 15

Birds

Question 16

[Start 31.3 Evolution of Reproductive Features in Land Plants]

What serves as the earliest models that diverged into land plants?

Answer 16

Bryophytes

Question 17

Since Streptophyte algae display a haploid-dominant life cycle, what happens?

Answer 17

The only diploid cell is the zygote, whose meiotic division produces relatively few spores.

Question 18

How does land plant life cycle differ to the point it has an advantage over the Streptophyte algae?

Answer 18

By contrast, land plant zygotes do not undergo meiosis. (well meiosis is delayed, mitotic cell division happens first!)

Land plants undergo mitosis to form a multicellular sporophyte which allows many cells to undergo meiosis and thereby producing a large number of spores!

This life cycle difference allows bryophytes and other land plants to increase the number of spores generated per sexual cycle, an important advantage in terrestrial habitats.

Question 19

What does producing more spores aid in? (2)

Answer 19

Dispersal but also increases the genetic diversity of progeny.

Question 20

What are specialized structures produced by some fungi and many land plants in which developing gametes are protected by a jacket of tissue?

Answer 20

Gametangia (from the Greek, meaning gamete containers).

Question 21

What does the jacket accomplish in gamtangium?

Answer 21

This jacket protects the delicate gametes from drying out and from microbial attack while they develop.

Question 22

What is a flask-shaped gametangia that each enclose a single egg cell in plants?

Answer 22

Archegonia (singular, archegonium)

Question 23

What are spherical or elongate gametangia that produce many sperm in plants?

Answer 23

Antheridia (singular, antheridium)

Question 24

What happens when the sperm of antheridia mature and moist conditions exist?

Answer 24

The antheridia open and release sperm into films of water.

Question 25

How does archegonia gametangium attract sperm from the antheridium gametangium to its single egg cell?

Answer 25

The influence of sex-attractant molecules secreted from archegonia…

The sperm swim toward the eggs, twisting their way down the tubular neck of the archegonium.

The sperm then fertilize egg cells to form diploid zygotes, which grow into embryos.

Question 26

Explain the life cycle of the early-diverging moss genus Sphagnum (bryophyte). Do it 6 Steps!

The lifecycle of this bryophyte illustrates reproductive adaptations that likely helped early plants reproduce on land. Among modern bryophytes, Sphagnum
is the single most abundant and ecologically important genus.

Answer 26

1. Meiosis within a sporophyte sporangium (2n) produces thousands of haploid spores (n) which are released in the wind once the sporangium (2n) pops open.
2. Haploid spores (n) grow into young gametophytes (n). Bryophytes may have separate male and female gametophytes!
3. Gametophytes (n) grow and mature, producing their respective gametes (n) in protective gametangia at their tips (jacket). (many sperm/one egg)
4. If water is present, flagellate sperm (n) are released and swin toward the egg (n). Fertilization occurs.
5. Delicate diploid zygote (2n) is protected and nourished by female gametophyte tissues while it grows into an embryo (2n).
6. Embryo (2n) develops into a mature sporophyte, which remains attached to the female gametophyte (n).

Question 27

What is a key reproductive advantage of the plant life cycle for the embryos and eventual growth into a zygote?

Answer 27

They remain enclosed by gametophyte tissues that provide protection and food.

Question 28

What is the term in plants, is the phenomenon in which zygotes remain enclosed within gametophyte tissues, where they are sheltered and fed.

Answer 28

Matrotrophy (from the Latin,meaning mother, and the Greek, meaning food)

Question 29

Because all groups of land plants possess matrotrophic embryos, what are they known as?

Answer 29

Embryophytes (Em (for embryo) + bryophytes)

Question 30

Why does the formation of spores give land plants more reproductive advantages?

Answer 30

To produce haploid spores, meiosis occurs in cells that are within enclosures known as sporangia (from the Greek, meaning sporecontainers).

Remember: They are structures that produce and disperse the spores of plants, fungi, or protists.

Answer: The cells of such enclosures are surrounded by tough cell walls that protect developing spores from harmful UV radiation and microbial attack. Bryophyte sporangia open in specialized ways that foster dispersal of mature spores into the air, allowing spore transport by wind.

Question 31

What is a reproductive advantage of the spores themselves!?

Answer 31

The cell walls of mature plant spores contain a tough material, known as sporopollenin, that helps to prevent cellular damage during transport in air.

If spores reach habitats favorable for growth, their cell walls crack open, and new gametophytes develop by mitotic divisions.

Question 32

Bryophytes illustrate a number of valuable reproductive features that appeared early in plan evolution and were inherited by their vascular plant descendants. What were these features?

This is review! A total of 6 terms already learned.

Answer 32

Alternation of generations, gametangia, embryos, matrotrophy, sporangia, and sporopollenin-enclosed spores.

Alternation of generations - life cycle alternates between multicellular diploid organisms, called sporophytes, and multicellular haploid organisms, called gametophytes.

Gametangia - Specialized structures produced by some fungi and many land plants in which developing gametes are protected by a jacket of tissue. (archegonia (egg enclosure) & antheridia (sperm enclosure))

Embryos - The embryo develops from the zygote. When a male gamete fuses with the egg cell.

Matrotrophy - In plants, the phenomenon in which zygotes remain enclosed within gametophyte tissues, where they are sheltered and fed. (This led to the name embryophytes)

Sporangia - Structures that produce and disperse the spores of plants, fungi, or protists.

Sporopollenin-enclosed spores - A tough material found in the walls of plant spores that helps to prevent cellular damage during transport in air.

Question 33

How has the size of gametophytes and sporophytes in bryophytes changed because of the evolution of vascular plant descendants?

_____________________________________

With that said, what is the advantage to ferns and seed plants of having larger sporophytes relative to those of bryophytes?

Answer 33

For bryophytes, gametophyte is relatively large and the mature sporophyte is usually small and depends on the gametophyte for its nutrition.

The evolution of vascularity shifted the relative sizes.

The gametophyte generation has become smaller in later-diverging phyla, whereas the sporophyte generation has become larger and more complex.

Larger sporophytes are able to capture more resources for use in producing larger numbers of progeny and therefore increase the fitness of ferns and seed plants.

Question 34

Even though sporophyte embryos of vascular plants are dependent upon supportive gametophytes, how do these embryos eventually become independent, free-living organisms?

Answer 34

Vascular-plant sporophytes canbranch, continue to grow, and produce sporangia on lateral branches, often for many years. (hence trees and bushes!) Their lifspan can range from a few decades to more than 5,000 years!

These features allow vascular plants to produce more progeny than bryophytes, whose sporophytes remain small, never become independent of parental gametophytes, are unable to branch, and have short lifetimes.

Question 35

What is the dominant generation in vascular plants meaning that it is larger, more complex, and longer-lived than the other?

Answer 35

The sporophyte generation.

The evolutionary shift toward sporophyte dominance explains why vascular plants are more prevalent in most modern terrestrial habitats.

Question 36

What seedless vascular plants exhibit a life cycle in which the sporophyte is the larger, more conspicuous organism whereas the gametophyte is smaller?

Answer 36

Lycophytes and pteridophytes

Life cycle of a fern, which is a pteridophyte. The organism that we associate with the name fern is the sporophyte.

Stem branching allows adult plants to produce many leaves, and roots supply stems with large amounts of soil water and minerals.

Lycophytes and pteridophytes use such resources to produce large numbers of sporangia. You might have seen clusters of sporangia as dark brown dots or lines on the undersides of fern leaves.

Question 37

Describe the life cycle of the typical fern!

In eight steps!

Answer 37

1. The diploid sporophyte (2n) is the dominant generation in the life of ferns and other vascular plants.
2. Sporangia (2n) are multicellular structures that develop on the undersides of the mature sporophyte leaves. Sportangia (2n) occur in clusters known as sori (singular, sorus).
3. Meiosis occures in cells within sporangia to produce haploid spores (n), which are dispersed by the wind.
4. Under favorable conditions spores undergo mitosis to produce gametophytes. These are often thumbnail-sized and heart shaped, anchored by cells known as rhizoids.
5. Mature gametophytes produce eggs (n) in female gametangia and sperm (n) in male gametangia.
6. When water is present, the maile gametangia release the flagellate sperm, which swim to the female gametangia and fertilize the eggs.
7. The resulting diploid zygote (2n) is retained on the gametophyte, undergoes mitosis, and grows into a multicellular embryo that recieves essential nutrients from the gametophyte.
8. The embryo matures into a sporophyte (2n). After developing a root and leaf, fern sporophytes become independent of their gametophyte (n) parent, which eventually rots away.

Question 38

Lycophyte and pteridophytesperm are flagellate, where did this feature originate from?

Answer 38

Inherited from algal and bryophyteancestors.

Question 39

[Start 31.4 Evolutionary Importance of the Plant Embryo]

What was on of the first critical innovations acquired by land plants?

Answer 39

The embryo

Recall that plant embryos are young sporophytes that develop from zygotes and are enclosed by maternal tissues that provide nutrients and protection.

Drought, heat, UV light, and microbial attack could kill delicate plant egg cells, zygotes, and embryos if these were not protected and nourished by enclosing maternal tissues.

Question 40

T/F Plant embryos are unicellular and haploid.

Answer 40

False. They are multicellular and diploid.

Plant embryos develop by repeated mitotic divisions from a single-celled zygote

Question 41

What are nutritive tissues in plants that aid in the transfer of nutrients from maternal parent to embryo?

Answer 41

Placental transfer tissues

Question 42

What do placental transfer tissues function in plants function similarily as?

Answer 42

Placental transfer tissues function similarly to the placenta present in most mammals, which fosters nutrient movement from the mother’s bloodstream to the developing fetus.

Question 43

Where does the plancetal transfer tissues typically occur? (2)

Answer 43

Haploid gametophyte tissues that lie closest to the embryo.

Diploid tissues of embryos themselves.

For example, the cells of placental transport tissues display complex arrays of finger-like cell-wall ingrowths.

Because the plant plasma membrane lines the plant cell wall, the ingrowths vastly increase the surface area of the plasma membrane. This increase allows for more abundant membrane transport proteins, which move solutes into and out of cells.

With more transport proteins present, materials can move at a faster rate from one cell to another. (Similar finger-like structures in animal intestines and placenta likewise foster nutrient flow by increasing cellular surface area.)

Question 44

[Start 31.5 The Origin and Evolutionary Importance of Leaves and Seeds]

What are two more critical innovations that increases plant fitness and fosters diversification?

Answer 44

Leaves and seeds (just like embryos)

Unlike the plant embryo, which likely originated just once at the birth of the plant kingdom, leaves and seeds may have independently evolved several times during plant evolutionary history.

Comparative studies of diverse types of leaves and seeds in fossil and living plants suggest how these critical innovations originated.

Question 45

Among the vascular plants, what produces the simplest and most ancient type of leaves?

Answer 45

Lycophytes

Modern lycophytes have tiny leaves, known as
lycophylls (also known as microphylls), which typically have only a single unbranched vein.

Question 46

What is a leaf that is bigger than lycophylls (or microphylls), has more than one branched vein, and is typical of ferns and seed plants (from the Greek, meaning true leaves)?

Answer 46

Euphylls

Question 47

What is a benefit of Euphylls (AKA megaphylls) over Lycophylls?

Answer 47

Branched veins of euphylls are able to supply relatively large areas of photosynthetic tissue with water and minerals. (which, makes them much larger and much bigger than euphylls)

Question 48

In the studying of fern fossils, what is indicated on how Euphylls arose?

Answer 48

From leafless, cylindrical, branched-stem systems.

The Steps!

1. one branch assumed the role of the main axis, while the other was reduced in size and became flattened in one plane.
2. the spaces between the branches of this flattened system became filled with photosynthetic tissue.

Such a process explains why euphylls have branched vascular systems; individual veins apparently originated from the separate branches of an ancestral branched stem.

Question 49

Why could you suggest that seeds offer reproductive advantages?

Answer 49

Because seed plants dominate modern ecosystems!

Seed plants are also the plants with the greatest importance to humans.

Question 50

What do you call the process, in seed plants, where the production of two different types of spores: microspores and megaspores; microspores produce male gametophytes, and megaspores produce female gametophytes?

Answer 50

Heterospory

As mentioned earlier, plants produce spores by meiosis within sporangia, and seed plants are no exception. However, seed plants produce two distinct types of spores in two types of sporangia.

Question 51

What in seed plants and some seedless plants, a relatively small spore that produces a male gametophyte within the spore wall?

Answer 51

A microspore!

Give rise to male gametophytes, which develop into pollen grains.

Question 52

What in seed plants and some seedless plants, a large spore that produces a female gametophyte within the spore wall?

Answer 52

A megaspore!

Give rise to female gametophytes, which develop and produce eggs while enclosed by protective megaspore walls.

Question 53

Since the enclosed female gamteophytes are not photosynthetic, how do they get help in feeding the embryos that develop from fertilized eggs?

Answer 53

Female gametophytes get this help by remaining attached to the previous sporophyte generation, which provides gametophytes with the nutrients needed for embryo development.

Question 54

What reproductive structures are UNIQUE to seed plants which help them produce seeds?

Answer 54

Ovules and pollen.

Question 55

What is in a seed plant which is a megaspore-producing sporangium with enclosing structures known as integuments?

Answer 55

An ovule.

They typically contain only a single spore that develops into a very small egg-producing gametophyte; the entire structure is enclosed by leaflike structures known as INTEGUMENTS!

Integuments are leaflike structure that encloses the sporangium to form an ovule.

Question 56

What is an excellent example of how to explain an ovule using a russian nesting doll? (the dolls that have smaller dolls inside)

Answer 56

You can think of an ovule as being like a nesting doll with four increasingly smaller dolls inside.

The smallest doll corresponds to an egg cell

Intermediate-sized doll represents the gametophyte, spore wall, and mega sporangium

Largest doll represents the integuments.

Question 57

How does the layered ovule convert into seeds?

In seed plants, how does the needed sperm for ____________ supplied?

Answer 57

By fertilization.

fertilization; It is supplied by pollen, which tiny male gametophytes enclosed by protective sporopollenin-containing microspore walls.

Question 58

For the seed plants, where is food stored in developing seeds for gymnosperms (without flowers) and for angiosperms (flowers, fruits)?

Review: These seed plants are called spermatophytes! While all vascular plants, which includes the lycophytes and pteridophytes, are called tracheophytes.

Land plants combined, including the non-vascular Byrophytes such as liverworts, mosses, and hornworts, in the Kingdom Plantae are called embryophytes.

Answer 58

In gymnosperms seeds, the food is stored in female gametophytes.

In angiosperm seeds, the food is stored in the endosperm.

These seeds and their food storages are all within the seed coat.

Question 59

Can you hypothesize why the mature angiosperm seed does not show obvious endosperm tissue?

Answer 59

Although some angiosperm seeds, such as those of corn and coconut, contain abundant endosperm, many angiosperm embryos consume most or all of the nutritive endosperm during their development.

Question 60

What is the process in which pollen grains are transported to an angiosperm flower or a gymnosperm cone primarily by means of wind or animal pollinators?

Answer 60

Pollination

Question 61

For pollination to occur, a male gametophyte extends a slender pollen tube that carries two sperm toward an egg which then the tube enters through an opening in the integument of the megasportangium in which as access to the multicellular female gametophyte? What is the opening called? (For further clarification of what is being asked.

What happens next?

Answer 61

The microphyle in which the sperm is released.

The fertilized egg becomes an embryo, and the ovule’s integument develops into a protective, often hard and tough seed coat.

Seed Coat = A hard, tough covering that develops from the ovule’s integuments and protects a plant embryo.

Question 62

What is the main difference between how gymnosperms and angiosperms store nutrients for their seeds?

Answer 62

Angiosperm seeds also contain this useful food supply, but most angiosperm ovules do not store food materials before fertilization. Instead, angiosperm seeds generally store food only after fertilization occurs, ensuring that the food is not wasted if an embryo does not form.

How is this accomplished?

The answer is a process known as double fertilization.

This process produces both a zygote and a food storage tissue known as endosperm, a feature unique to angiosperms.

One of the two sperm delivered by each pollen tube fuses with the egg, producing a diploid zygote, as you might expect.

The other sperm fuses with different gametophyte nuclei to form an unusual cell that has more than the diploid number of chromosomes; this cell continues to divide and generates the endosperm food tissue.

Question 63

What are some advantages that seeds confer which are important for reproduction?

Answer 63

• Seeds can remain dormant for long periods until favorable conditions allow for germination.
• Seed coats have adapatations that improve dispersal in some habitats. For example, many plants produce winged seeds that are effectively dispersed by wind. Other plants produce seeds with fleshy coverings that attract animals, which consume the seeds, digest the fleshy covering, and eliminate the bare seeds at some distance from the originating plants.
• They can store considerable amounts of food which helps embryos mature enough to compete for light, water, and minerals. Especially important in shady forests.
• Sperm of most seed plants do not need to swim since pollen tubes deliver sperm directly to ovules. Consequently, seed plant fertilization is not typically limited by lack of water, in contrast to fertilization of seedless plants. Consequently, seed plants are better able to reproduce in arid and seasonally dry habitats.

This is why seeds are considered to be a key adaptation to reproduction in a land habitat.

Question 64

Where have ovules and seeds evolved from?

Answer 64

Spore-producing structures by descent with modification!

Seed plants reproduce using both spores and seeds, and seed plants have not replaced spores with seeds.

Recall that this evolutionaryprinciple involves changes in pre-existing structures and processes.

Fossils provide some clues about ovule and seed evolution, and other information can be obtained by comparing reproduction in living lycophytes and pteridophytes.

Question 65

What do most modern lycophytes and pteridophytes release?

Answer 65

One type of spore that develops into one type of gametophyte.

Such plants are considered to be homosporous, and their gametophytes live independently and produce both male and female gametangia.

Question 66

When it comes to spores, what do some lycophytes and pteridophytes produce and release?

Answer 66

Produce and release two distinct kinds of spores: relatively small microspores and larger megaspores, which grow into male and female gametophytes, respectively.

EVEN THOUGH they are typically homosporous, some of early seedless vascular plants are actually herterosporous! Amazing evolution!

Question 67

Describe the steps that homosporous lycophytes and pteridophytes became hetersporous (creating two kinds of spores rather than one). (4)

Answer 67

1. Sporangium containing spores that are similar in size
2. In early evolution, the sporangium containing the spores began to evolve creating two different types.
   2a. Microsporangium containing many small microspores.
   2b. Megasporangium containing fewer, larger megaspores.
3. Eventually the sporangium with the megaspores was reduced to 1 megaspore per megasporangium. THIS led to the enclosure of megasporangium within integuments to form ovule; when fertilized, ovule develops into a seed.

Question 68

What are the advantages of heterospory?

Answer 68

1. It mandates cross-fertilization by allowing different gametophytes (with different DNA) to increase the potential for genetic variation.
2. Genetic variation of cross-fertilization may enhance survival and reproduction of individuals with favorable phenotypes and result in evolution.
3. Heterosporous plants have their gametophytes grow within the confines of micro and megaspore walls which protects them.

Question 69

What is a plant gametophyte that grows within the confines of microspore or megaspore walls?

Answer 69

Endosporic gametophyte