Bryophytes, Seedless Vasculars, Gymnosperms and Angiosperms

Question 1

What are the five basic steps in the alternation of generation life cycle?

Answer 1

1. Gametophyte produces haploid gametes by mitosis (n)
2. Two gametes unite (fertilisation) and form a diploid zygote (2n)
3. The zygote develops into a multicellular diploid sporophyte (2n)
4. The sporophyte produces unicellular haploid spores by meiosis (2n –> n)
5. The spores develop into multicellular haploid gametophytes (n)

Question 2

What are the three main groups of bryophytes? And what are the bryophytes defining features?

Answer 2

1. Liverworts
2. Hornworts
3. Mosses
   - Usually first colonisers
   - Very small (lack vascular tissue to stabilise and grow high)
   - Gametophyte is free-living and larger than sporophyte
   - Sporophyte is attached and dependent on gametophyte

Question 3

How do bryophytes reproduce asexually? What is required for sexual reproduction to occur? And what structures are involved in sexual reproduction?

Answer 3

• Asexually reproduces via fragmentation
• Sexual reproduction requires water for the sperm to swim to the egg
• Gametangia are antheridia (sperm) and archegonia

Question 4

Within the phylum Bryophyta (Mosses), what are three key classes?

Answer 4

1. Bryopsida (true mosses)
2. Sphagnopsida (peat mosses)
3. Polytrichopsida (hairy-cap mosses)

Question 5

What are some of the defining features of the class Bryopsida (true mosses), such as the male and female sexual structures, and the sporophyte structure?

Answer 5

• Archegonium on female gametophyte
• Antheridia in splash cups (modified enations + gametangia) - water drop is caught to disperse sperm
• Sporophyte composed of seta (stalk) and capsule (sporangium) with a toothed peristome (the very tip of the capsule), which when the capsule dries aids in flicking out the spores

Question 6

Given the structure of male and female gametophytes in Bryophytes, where does the sporophyte arise?

Answer 6

From the female gametophyte, as the sperm are dispersed from the male splash cup, and develop into the zygote within the archegonium, from which the diploid sporophyte sprouts

Question 7

What are some of the defining features of the class Polytrichopsida (hair-cap mosses)?

Answer 7

• Hood over hairy capsules (calyptra)
• Stiff, erect, unbranched stems
• Dark green or reddish leaves with point at the apex

Question 8

What are some defining features of Phylum Marchantiophyta (Liverworts), such as sexual structures in both male and female gametophytes, asexual structures, and sporophyte structures/adaptations?

Answer 8

• Archegonia underneath palm tree-like structure (archegoniophores), while male antheridia in more flat structures (antheridiophores)
• Asexual reproduction via gemma cups - contain gemmae (vegetative cells) which are dispersed by water splashes (similar to splash cups)
• Sporophyte comprised of seta and capsule, which contains spores and elaters (cells that twist when dry to facilitate spore dispersal)

Question 9

What are some of the defining features of the class Marchantiopsida (Thallose Liverworts)?

Answer 9

• Flat body

Question 10

What are some of the defining features of the Class Jungermanniospida (Leafy Liverworts)?

Answer 10

• Enations 1 cell thick, and arranged in a flat plane with a set of smaller underleaves
• Leaves can be lobed
• No midrib
• Stem unspecialised tissue
• Archegonia in perianth (becomes sporophyte) and antheridia borne on side branch (androecium)

Question 11

What are the main differences and similarities between Liverworts and Mosses?

Answer 11

Differences: Liverworts lack a midrib and clear separation between stem and leaves, whereas mosses do. Leaves in liverworts are lobed or dissected, whereas mosses are entire but can have teeth. Capsule stem rigid and persistent in Liverworts whereas mosses capsule stem is fleshy and short-lived.
Similarities: Both 1 cell thick.

Question 12

How are certain mosses such as Dawsonia Superba, which can grow up to 50cm tall, able to reach these heights without vascular tissue?

Answer 12

This is because the gametophyte and sporophyte have water-conducting cells known as hydroids, surrounded by food-conducting cells known as leptoids. These act similarly to vascular tissue, allowing them to transport water and nutrients across their body more efficiently. Although, the cell walls lack lignin so this restricts them from growing too tall.

Question 13

What are the two key groups of Seedless Vascular Plants?

Answer 13

1. Lycophyta (Club Mosses)
2. Monilophyta (Ferns and Horsetails)