16. Plant Diversity

Question 1

Understand (from phylogenetic tree) that charophytes are closest relatives of land plant (embryophytes)

Answer 1

Question 2

List four key traits of land plants that are absent in green algae charophytes

Answer 2

1. Alternation of generations -
2. Walled spores
3. Multicellular gametangia
4. Apical meristems

Question 3

What does alternations of Generations describe?
5 MAIN STEPS

Answer 3

“Alternation of generations” is a reproductive strategy observed in the life cycles of some organisms, particularly plants and certain algae. It involves two distinct multicellular stages in the life cycle: the haploid (n) gametophyte stage and the diploid (2n) sporophyte stage.

In this pattern, the gametophyte produces haploid gametes (such as eggs and sperm) through mitosis. These gametes fuse during fertilization to form a diploid zygote. The zygote then develops into a multicellular sporophyte through mitosis, which produces haploid spores through meiosis. These spores, in turn, develop into the next generation of gametophytes, completing the cycle.

This alternation between haploid and diploid stages is a key feature of plant life cycles and contributes to their reproductive diversity and adaptability. It allows for genetic diversity, dispersal, and adaptation to different environmental conditions.

Question 4

What are Walled Spores?

Answer 4

Walled spores are reproductive structures produced by certain organisms, particularly fungi, algae, and some plants.

Question 5

What are Multicellular gametangium?

Answer 5

Gametangium = specialized organ or cell in which gametes are found in algae, ferns, and some other plants

Question 6

What are Apical meristems?

Answer 6

Growth regions in plants found within root tips and tips of new shoots and leaves

Question 7

What is a Gametophyte?

Answer 7

The multicellular gametophyte is haploid and produces haploid gametes by mitosis

Question 8

What is a Zygote?

Answer 8

Fusion of the gametes (eggs and sperm) results in fertilization, which gives rise to the diploid zygote

‒ The diploid embryo is retained within the tissue of the female gametophyte

‒ Nutrients are transferred from parent to the embryo through specialized placental transfer cells

Question 9

What is a diploid sporophyte?

Answer 9

The zygote divides by mitosis and develops into a multicellular, diploid sporophyte

The sporophyte produces haploid spores by meiosis

Spores divide by mitosis and develop into the gametophyte

Question 10

• Describe life cycle of non-vascular plants (mosses, liverworts and hornworts)
  7 KEY MOMENTS

Answer 10

1. The multicellular/haploid gametophyte produces haploid gametes by mitosis
2. Gametes fuse giving rise to the diploid zygote
3. The diploid embryo is retained within the tissue of the female gametophyte
4. Nutrients are transferred from parent to the embryo through specialized placental transfer cells
5. The zygote divides by mitosis and develops into a multicellular, diploid sporophyte
6. The sporophyte produces haploid spores by meiosis
7. Spores divide by mitosis and develop into the gametophyte

Question 11

2 Important things to remember about the life cycle of non-vascular plants.

Answer 11

gametophytes are dominant part of life cycle;

male and female gametophytes are separate organism

Question 12

What are the similarities and differences
between zygotes and spores?

Answer 12

• SIMILARITY =
  Zygotes and spores are both single cells that divide by mitosis to form a multicellular individual
• DIFFERENCE =
  Zygotes result from the fusion of two cells, such as sperm and an egg (so they are diploid), but spores are not formed by the fusion of two cells (so they are haploid)
• DIFFERENCE = Zygotes produce sporophytes while spores produce gametophytes

Question 13

What is a Sporangia?

Answer 13

an organ in which the sporophyte produces spores

Question 14

What are Sporocytes?

Answer 14

Diploid cells which undergo meiosis to generate haploid spores

Question 15

What is Sporopollenin?

Answer 15

Spore walls contain sporopollenin, which protects against desiccation (drying up) making them resistant to harsh environments

Question 16

What are Gametangia?

Answer 16

Sex Organs in which Gametes are produced

Question 17

What are Female gametangia?

Answer 17

archegonia, produce eggs and are the site of fertilization

Question 18

What are Male gametangia?

Answer 18

antheridia are the site of sperm
production and release

Question 19

What are Apical meristems?

Answer 19

Apical meristems comprise of embryonic cells and are the growth regions at plant tips (root tips and shoot tips), thereby allowing plants to sustain continual growth in their length

Question 20

What are Bryophytes?

Answer 20

Bryophytes are non-vascular and represented today by:
– Liverworts
– Hornworts
– Mosses

-Gametophytes are dominant part of the life cycle: larger in terms of size and longer-living than sporophytes…also gametophyte produces most of the food required by the individual

– Sporophytes are present only part of the time and are dependent on gametophytes

Question 21

What are Rhizoids?

Answer 21

Rhizoids anchor gametophytes to a substrate

Question 22

The life cycle of moss (non-vascular plant)

Answer 22

• Sperm swim through water to reach and fertilize the egg (fertilization occurs within the archegonium)
• Diploid zygote develops within archegonium, which then becomes an embryo via mitosis
• Embryo will give rise to the diploid sporophyte (this sporophyte will grow out of the archegonium)
• Sporophyte will produce spores which will be contained within the sporangia (sporocytes will go through meiosis to produce haploid spores)

Question 23

What is Vascular Tissue?

Answer 23

Vascular tissue (i.e., xylem and phloem) allowed vascular plants to grow tall compared to the non-vascular plants

Question 24

bryophytes vs. sporophytes

Answer 24

• In contrast with bryophytes, sporophytes of
  seedless vascular plants are a dominant part of the life cycle compared to the gametophyte
• Sporophytes are much larger in size and longer-lived than bryofights
• We will look at the fern life cycle as an example of a seedless vascular plant for this lecture

Question 25

What are sporophylls?

Answer 25

spore-bearing leaves of the sporophyte,
there are sporangia present

Question 26

What is a Sorus?

Answer 26

Group of sporangium
(plural is sori)

Question 27

What is hermaphroditic?

Answer 27

both antheridia and archegonia are found

Question 28

What is common to all seed vascular plants?

Answer 28

– Reduced gametophytes
(instead, sporophytes are a dominant part of the life cycle)
– Heterospory
– Ovules
– Pollen

Question 29

Gametophyte / sporophyte relationships in different plant groups

Answer 29

Question 30

What does it mean to be homosporous?

Answer 30

Non-vascular plants and most seedless vascular plants like ferns are homosporous – they produce one type of spore of the same size

Question 31

What is Heterospory?

Answer 31

Heterospory is the production of spores of two different sizes and sexes by the sporophytes

Seed vascular plants (i.e., gymnosperms and angiosperms) are heterosporous

Question 32

What is Megasporangia?

Answer 32

Megasporangia produce megaspores that give rise to female gametophytes

Question 33

What is Microsporangia?

Answer 33

Microsporangia produce microspores that give rise to male gametophytes

Question 34

What are Ovules?

Answer 34

Unfertilized, immature seed = ovule
(so a fertilized ovule is called a seed)
– Ovules of gymnosperms develop on scales of cones

– Ovules of angiosperms are enclosed in chambers called ovaries (a fruit is a fertilized, fully grown, ripened ovary that contains the seeds)

Question 35

What is a Megasporangium?

Answer 35

Megasporangium = Diploid
inner cell mass of ovule, comprising of diploid sporophytic cells

Question 36

What is a Megasporocyte

Answer 36

Megasporocyte = Diploid
a diploid cell that undergoes meiosis to produce four haploid megaspores – at least one of the spores develops into the haploid female gametophyte (which includes an egg cell)

Question 37

What is a Integument?

Answer 37

Integument =
layer of sporophyte tissue (diploid) that envelops and protects the megasporangium and the megaspore – the integuments develop into the seed coat when the ovule matures after fertilization

Question 38

At Maturity, what does the mature seed contain?

Answer 38

At maturity, the mature seed contains:
– the diploid integument which develops into the seed coat

– the haploid female gametophyte (food supply), and

– the diploid embryo (which will germinate to become a new sporophyte)

Question 39

What is a Microsporangium?

Answer 39

Microsporangium is a pollen sac that contain microsporocytes, which develop into microspores

• diploid

Question 40

What is a Microsporocyte?

Answer 40

Microsporocyte =
a diploid cell that undergoes meiosis to produce four haploid microspores – each microspore will ultimately form a haploid pollen grain (which is the male gametophyte)
§ The pollen grains then produce sperm cells via mitosis

Question 41

What are Microspores?
What are Megaspores?

Answer 41

microspores that give rise to male gametophytes

megaspores that give rise to female gametophytes

HAPLOID

Question 42

What is sporopollenin?

Answer 42

The tough pollen wall, which contains
sporopollenin, which protects the pollen grain as it is transported from the parent plant by wind or by hitchhiking on the body of an animal

Question 43

What is Pollination?

Answer 43

Pollination is the transfer of pollen from the male to the female part containing the ovules

Question 44

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Question 49

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