Bryophytes

Question 1

description of bryophytes

Answer 1

• non-vascular
• Include Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerophyta (hornworts) - a basal grade, not a clade

Question 2

why did they evolve to land?

Answer 2

• More carbon dioxide in the atmosphere - diffuses 1000x faster through air than in water
• Aquatic algae can be starved of carbon dioxide when it photosynthesises fast - limits photosynthesis
• Carbon dioxide is not a limiting factor on the land

Question 3

how did bryophytes adapt?

Answer 3

1. Cuticle: waxy, waterproof polymer coating cells which protects against desiccation
   Provides a problem: access to carbon dioxide becomes harder requiring pores
2. Pores for gas exchange: multi cell structure that allows carbon dioxide in
3. Gametangia (antheridia - sperm sac and archegonium - egg sacs) with multicellular jacket: sterile jacket protects against desiccation
4. Spores with sporopollenin: useful for dispersal through the dry atmosphere as the coating protects from desiccation

Question 4

describe marchantiophyta

Answer 4

• thallus structure with dichotomous branching
• cells that store water
• rhizoid
• small
• similar to earliest terrestrial plants
• simple pores that are always open

Question 5

marchantiophyta life cycle

Answer 5

1. Haploid thallus
2. Develops gametangia on the surface of the thallus (produced by mitosis)
3. Rain allows sperm to swim to the egg sacs (form a diploid zygote)
4. Zygote undergoes cell divisions in the egg sac, forming an embryo
5. Eventually embryo grows diploid plant on the haploid thallus
6. Diploid plant has a sporangium (like a capsule) which produces spores by meiosis
7. Spores are released and dispersed through the air to grow into haploid thallus

Question 6

bryophyta description. how is the gametophyte different? Are they vascular?

Answer 6

• moss
• Gametophyte: long and green vertical axis with branching leaves (some can be relatively complex)
• Usually small but can be half a metre tall (raises the photosynthetic leaves closer to the sun)
• Vertical axis is favoured by evolution to overcome competition for sunlight
• In the centre of the axis is a conducting strand (made of two cells: hydroids for water and leptoids for dissolved sugar). Why are they not vascular? In vascular plants the vascular system acts as a skeletal system which does not happen in moss

Question 7

bryophyte life cycle

Answer 7

• Haploid gametophytes are either male or female
• Antheridia clustered in splash cups at the tip of leaf axis
• Archegonia is clustered at the tip of the leafy axis
  Rain splashes sperm to female egg sac to form diploid zygote
• Sporophyte: polytrichum emerges from leafy gametophyte where spores can be dispersed

Question 8

Anthocerophyta description

Answer 8

• 100 species
• Closest related group to vascular plants
• Have leafy thalloid gametophytes and erect sporophytes grow out of the thallus
• Sporophytes have pores with guard cells allowing them more control over gas exchange. They are also long-lived and capable of photosynthesis
• Intercalary growth: sporophytes grow from the base and the tip with the spores is the oldest

Question 9

gametophyte definition

Answer 9

haploid plant that produces haploid gametes by mitosis.

Question 10

sporophyte definition

Answer 10

diploid plant that produces haploid spores by meiosis.

Question 11

how did bryophytes change the earth?

Answer 11

• Rapid radiation of bryophytes caused atmospheric carbon dioxide levels to plummet
• Atmospheric carbon dioxide was stored in soil and plants
• Creation of soil increased speed of geochemical cycles (allowed for breakdown of parent material)

Question 12

description of all bryophytes and the limitation of this

Answer 12

• all have a single axis, no branching and one terminal sporangium
• lateral spore sacs allow for more spores to be produced

Question 13

discussion of sphagnum moss

Answer 13

• Wetland ecosystems where accumulation of peat which forms faster than it decomposes due to acidity and lack of oxygen
• Peat can accumulate in 10-20m depths (50m in Siberian peat soils)
• Peat soils contain 20-30% of world’s soil organic carbon
• As climate warms, the peat soil is being decomposed, returning carbon dioxide to the atmosphere