5-7: Bryophytes, Ferns, Lycopods and Gymnosperms

Question 1

In the unicellular alga, Chlamydomonas reinhardtii, summarise the reproductive cellular process

Answer 1

Haploid cells combine to form a diploid zygospore (note that sexual reproduction only occurs under stress)

Question 2

Describe the ‘Alternation of Generations’ seen in plants and some other species

Answer 2

Alternation of Generations is a type of life cycle, in which a diploid, multicellular, spore-producing organism (sporophyte) gives rise to a multicellular, haploid, gamete-producing organism (gametophyte). Two gametes then fuse to form the diploid generation again.

Question 3

What is the name of the first group of land plants? (And what are the 3 main types?)

Answer 3

Bryophytes - liverworts, mosses and hornworts

Question 4

What did land plants evolve from?

Answer 4

Unicellular algae, which formed a ‘mat’ on the land surface

Question 5

Describe the nature of the two generations in Liverworts

Answer 5

The gametophyte can be thalloid or leafy; the sporophyte is just a few cells, grows on the surface, and is completely dependent on the gametophyte

Question 6

Describe the nature of the two generations in mosses

Answer 6

The gametophyte is leafy, the sporophyte grows apically, above the gametophyte

Question 7

Describe the nature of the two generations in Hornworts

Answer 7

The gametophyte is thalloid, the sporophyte grows basally, with a degree of independence, and is persistently green

Question 8

Describe the adaptations of Liverworts, Mosses and Hornworts to obtain water and nutrients.

Answer 8

Liverworts have rhizoids which grow down, mosses show ombrotrophy (obtain from rainwater), Hornworts show symbiosis with nitrogen-fixers

Question 9

Which three things does the Rhynie Chert provide some of the earliest evidence of (that are mentioned)?

Answer 9

Vascular bundle, sporophyte beginning to grow on its own, and fungal associations

Question 10

What is significant about the generations of the Lycophytes?

Answer 10

The sporophyte is now dominant and photosynthetic

Question 11

Besides the dominant sporophyte, which 3 other key features are seen in the Lycophytes?

Answer 11

XYLEM, microphylls and secondary growth (lignin)

Question 12

What change ended the dominance of the Lycophytes?

Answer 12

Falling CO2 in the atmosphere due to organic carbon stores -> transpiration-photosynthesis dilemma.

Plants with megaphylls (e.g., ferns) were better adapted to the new climate.

Question 13

What are the two key non-reproductive features of the Gymnosperms?

Answer 13

Wood AND seeds (they were the first to bring them together)

Question 14

What key reproductive feature is an innovation of Gymnosperms?

Answer 14

No free gametophyte generation (replaced by dispersed pollen, and a seed with a protected ovule and a nucellus)

Question 15

5 key features of cycads

Answer 15

• Simple, inflexible growth form
• Dioecious (separate male and female plants)
• Very drought-resistant
• Motile sperm (as opposed to pollen tube)
• Sharp spines and toxins as defences

Question 16

4 key features of Ginkgos

Answer 16

• Seed wall is fleshy, like a fruit
• Dioecious
• Deciduous leaves (novel among Gymnosperms)
• Branched growth structure allows better competition for light

Question 17

3 key features of Conifers

Answer 17

• Very stress-tolerant
• Often monoecious
• Some have evolved features which attract birds to pollinate

Question 18

Which other plant group do Gnetophytes share some features with?

Answer 18

Angiosperms

Question 19

Where are Conifers dominant today and why?

Answer 19

Only in extreme habitats, e.g., Arctic and Alpine.

They cannot out-compete Angiosperms in most environments, but their stress-tolerance gives them an advantage here.