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Summary Plant Diversity Notes
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Plant DiversityPLANT CLASSIFICATION:
The plant kingdom is classified into four major groups:
bryophytes, pterophytes, gymnosperms and angiosperms
Plants are classified by the following:
• Vascular tissue (xylem and phloem)
• True leaves and roots
• Dependence on water to reproduce
• Seeds or spores
• Cones or flowers
• Fruit
NON-VASCULAR PLANTS:
1. Bryophyta - mosses and liverworts
• No vascular tissue – can’t transport water and
food around plant and so they absorb water
through their entire surface
• No true roots, stems or leaves – they have
rhizoids that anchor the stem
• No cuticle – no means to prevent water loss
• No strengthening tissues – no xylem so can’t grow tall
• Homosporous – haploid spores are all the same size
• Depend on water for fertilisation – sperm has to swim to female egg
• Life cycle: Life cycle = alternation of generations, gametophyte = dominant
generation (haploid), sporophyte (diploid) In plants the sporophyte (2n)
generation produces the spores which give rise to the gametophyte (n)
generation.
VASCULAR PLANTS:
Adaptions needed for terrestrial life:
• Prevent desiccation – the cuticle and stomata help decrease water loss
• Aid nourishment – roots: absorb water and minerals from soil via xylem and phloem
& anchor plant
vascular tissue: xylem and phloem to conduct water and minerals
supporting tissue: xylem that holds up the leaves to get
maximum sunlight for photosynthesis
• Aid reproduction: the development of spores and seeds provide a means of
reproducing
, - Early land plants: bryophytes and pterophytes are seedless and reproduce with
spores
- Later land plants: gymnosperms and angiosperms produce seeds
Differences between nonvascular and vascular plants:
• Vascular plants possess vascular tissue – xylem and phloem from a central column
(stele) through the plant
• Vascular plants have a longer sporophyte phase and more conspicuous generation of
the life cycle
Classification of vascular plants:
• Seedless plants – reproduce by spores and are seedless e.g. pterophytes
• Seed-bearing plants – reproduce by seeds e.g. gymnosperms and angiosperms
SEEDLESS PLANTS:
(reproduce by seeds, cone-bearing/flowering plants)
2. Pterophytes
• Either terrestrial or epiphytic (growing on other plant)
• Have leaves, stems & roots: leaves = fronds for photosynthesis roots = fibrous,
anchor & absorb H2O
• Have vascular tissue (xylem & phloem)
• Thin cuticle and stomata
• Reproduce by SPORES released from dehiscent sporangia which grow on the
back of sporophylls (leaf) & in clusters = sori (dehiscent = to burst, releasing
spores / sporophylls = spore bearing leaves)
• Produce motile male gametes (sperm) rely on water for fertilization – found in
moist environments
• Dominant, have independent sporophyte
• No flowers, seeds or cones
• New leaves are coiled up and unroll from base to tip as they develop
• Sporangia are found on under surface of leaves they occur in clusters (sori)
• Have proper roots with water conducting tissue, xylem for the absorption and
transportation of water from soil / have waxy cuticle to prevent water loss = can
grow in drier places
Why can ferns grow in drier places than mosses? Ferns have proper roots with water
conducting tissue (xylem) for the absorption and transport of water from soil. They also
have a waxy cuticle which prevents water loss from leaves
Seed-bearing plants:
1. Cone-bearing – gymnosperms
2. Flowering plants – angiosperms
, Similarity to ferns:
• Plant body differentiated into root, stem and leaf
• Presence of vascular tissue
• Dominant and independent sporophyte
generation
Differences to ferns:
• Gametophyte reduced in size &
dependent on sporophyte
• Gametes do not depend on water for
fertilization
• Heterosporous spore (male = microspore,
female = megaspore)
Major Evolutionary advances:
• Body of plant more complex (plants grow taller + receive more sunlight)
• Pollen grains (produced from microspores) – male gametes carried (wind, water,
animals)to female by pollination and pollen tubes (takes over)
• Seeds resistant to drying out [seed includes embryonic plant (sporophyte), food
storage tissue and hardened protective covering (seed coat) Seed = allows a plant
embryo to lie dormant until conditions become suitable for germination, has food for
the embryos needs in early growth and development
3. Gymnosperms
• Has needles / evergreen
• Mostly trees with leaves simple/needle like with single vein or strap-shaped with
multiple veins
• Reproductive structures (sporangia) [ovule = megasporangium in female cone/
pollen sac (microsporangium) in the male cone] carried on open spore-bearing
leaves (sporophylls) arranged into well-defined male and female cones
• Heterosporous: male cones produce microspores that develop into pollen grains
which contain the male gamete, female cones produce megaspores that develop
into an ovule containing a female gamete
• After fertilization, ovule develops into seed that’s exposed on ovuliferous scale
of female cone, the seed = “naked” as it’s not enclosed by protective ovary wall
like pod or a fruit as in flowering plants, gymnosperms do not produce flowers
which have an ovary (ovary wall = sporophyll with fused margins)
• Xylem tissue of gymnosperms is more primitive than flowering plants as it only
contains tracheids with no vessel elements
• Examples: conifers (yellowwoods, cedars, pines, and fir trees), welwitschia,
cycads, ginkgo
• Most gymnosperm seeds are borne in cones and not visible (not the same as
fruits)
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