Intro to botany Flashcards
Terrestrial plants
All terrestrial life dependent on plants
Plants = primary producers
Provide with – oxygen, food, raw materials and energy, medicine, recreation
Plants + geology = landscape
Plants and global ecology
Global ecosystems are classified into biomes – biome classification is based on plants = plant formations (physiognomy)
Plants are consumers of global co2
Plants provide habitat and food for animals
Forest fires exacerbated by climate change and result in habitat loss (and loss of plants to absorb co2)
Plants
Eukaryotic organisms
Cells with plastids – e.g chloroplasts
Photoautotrophic
Cell wall
Exhibit great diversity of structure on land
Kingdom plantae made up of – bryophytes (non-vascular plants), pteridophytes (seedless vascular plants), seed plants (vascular plants)
Evolution of plants
Associated with the evolution of structures and physiological strategies to obtain water and minimise water loss without compromising the uptake and light dependent assimilation of co2 (photosynthesis)
At the same time support and strengthening systems evolved at the anatomical level
Key adaptations to terrestrial life in higher plants
- Root system – absorption of nutrients and anchorage
- Vascular system – a plumbing system for the transport of water, minerals, sugars and hormones, made up of xylem and phloem
- Waterproof covering – cuticle
- Stomata – pores through which gases enter and leave the plant by diffusion
Support and strength in plants
Some have cell walls composed of cellulose and lignin
Very tough polymer, giving rigidity and support allowing plants to reach great heights (lignified cells are dead)
Strategic anatomical positioning of lignified cells aids support
Earliest plants may have only been able to strand erect by turgor pressure
Xylem is lignified and preforms dual function of water transport and support
Features that distinguish plants
Presence of gamete producing structures (gametangia) called antheridia (m) and archegonia (f) which have a protective sterile jacket of cells
Zygote develops into a multicellular embryo which is retained within the archegonium
Embryo develops into a multicellular diploid sporophyte generation which produces multicellular sporangia
Sporangia produce spores with walls containing sporopollenin – one of the most resistant substances known
In true plants (embryophytes) reproductive structures are complex and multicellular
Only inner cells become reproductive
Outer cells constitute a protective layer and persist after reproductive cells are released
Alteration of generations
All land plants show a heteromorphic alternation of generations
2 generations – gametophyte (n) and sporophyte (2n) = both morphologically and genetically very different
All land plants show a heteromorphic alternation of generations = gametophyte and sporophyte are morphologically and genetically very different
Bryophytes
Liverworts, hornworts, mosses
Small plants which are either leafy (all mosses and most liverworts), or thalloid (some liverworts and all hornworts)
Earliest terrestrial plants similar to bryophytes
Modern bryophytes are transitional between charophytes (green algae) and the vascular plants
Often inconspicuous but grow in many situations
Although usually associated with wet environments they are often found in dry, desiccating environments (rocks, walls, dunes)
Some bryophytes are aquatic but none are marine
Dominate certain ecosystems, e.g wetlands, large areas north of the arctic circle
Home for many specialised animals – e.g tardigrades (water bears)
About 16,000 species known, mostly mosses
UK has ~1,000 species, >70% Europe’s bryophytes
The life cycle exhibits an alternation of the 2 distinct generations
Gametophyte gen haploid = dominant gen
Sporophyte gen diploid = completely dependent on the gametophyte gen
Sperm require water in order to swim from antheridium to archegonium
Can absorb nutrients over their whole surface
Do not have roots, but do produce rhizoids which help to anchor plants and absorb nutrients
Mosses do not have a xylem and phloem (vascular tissue)
Some mosses have a simple conducting system in their stems
Gametophyte generation of bryophytes
Dominant, haploid gen produces gametangia called antheridia and archegonia
If the gametophyte is bisexual, then both are produced on the same individual plant
If the gametophyte is dioecious, an individual will either be male or female
Antheridia produce lots of haploid, motile sperm
Archegonia produces haploid egg
Sporophyte generation of bryophytes
Fertilisation of the egg cell (n) by sperm (n) results in the production of a diploid zygote (2n) which develops into a diploid multicellular embryo within the archegonium (on the gametophyte)
Embryo grows and differentiates to produce the diploid sporophytes
At maturity, the sporophyte consist of an absorptive foot, a seta and a capsule
Inside the capsule, diploid cells undergo meiosis to produce tetrads of haploid spores
Sporophyte capsule is complex - at first it has a calyptra derived from the archegonium, capsule lid (operculum) which breaks off the reveal the peristome teeth which regulate the release of the spores by opening and closing in response to humidity, presence of stomata, full of spores and elaters to aid spore dispersal
