Bryophytes Flashcards
1
Q
description of bryophytes
A
- non-vascular
- Include Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerophyta (hornworts) - a basal grade, not a clade
2
Q
why did they evolve to land?
A
- 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
3
Q
how did bryophytes adapt?
A
- Cuticle: waxy, waterproof polymer coating cells which protects against desiccation
Provides a problem: access to carbon dioxide becomes harder requiring pores - Pores for gas exchange: multi cell structure that allows carbon dioxide in
- Gametangia (antheridia - sperm sac and archegonium - egg sacs) with multicellular jacket: sterile jacket protects against desiccation
- Spores with sporopollenin: useful for dispersal through the dry atmosphere as the coating protects from desiccation
4
Q
describe marchantiophyta
A
- thallus structure with dichotomous branching
- cells that store water
- rhizoid
- small
- similar to earliest terrestrial plants
- simple pores that are always open
5
Q
marchantiophyta life cycle
A
- Haploid thallus
- Develops gametangia on the surface of the thallus (produced by mitosis)
- Rain allows sperm to swim to the egg sacs (form a diploid zygote)
- Zygote undergoes cell divisions in the egg sac, forming an embryo
- Eventually embryo grows diploid plant on the haploid thallus
- Diploid plant has a sporangium (like a capsule) which produces spores by meiosis
- Spores are released and dispersed through the air to grow into haploid thallus
6
Q
bryophyta description. how is the gametophyte different? Are they vascular?
A
- 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
7
Q
bryophyte life cycle
A
- 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
8
Q
Anthocerophyta description
A
- 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
9
Q
gametophyte definition
A
haploid plant that produces haploid gametes by mitosis.
10
Q
sporophyte definition
A
diploid plant that produces haploid spores by meiosis.
11
Q
how did bryophytes change the earth?
A
- 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)
12
Q
description of all bryophytes and the limitation of this
A
- all have a single axis, no branching and one terminal sporangium
- lateral spore sacs allow for more spores to be produced
13
Q
discussion of sphagnum moss
A
- 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
