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The Plant Kingdom
Diagnostic structural features
Members of the kingdom Plantae share the following features:
♥ Form: eukaryotic and multicellular
♥ Evolutionary origin: came from green algal plants
♥ Cell wall: cellulose cell wall with plasmodesmata
♥ Nutrition: autotrophic and photosynthetic, which occurs in chloroplasts which
are surrounded by a double membrane (envelope) and contain pigments
chlorophyll a and b, xantophyll and carotene
...

♥ Development: form embryos protected by tissues of the parent plant –
embryophytes
...
They all possess tracheids – water-conducting
cells of the xylem in all tracheophytes except the angiosperms
...

♥ Non-tracheophytes: lack tracheids and vascular tissue

Group

Phylum

Common name

Non-tracheophytes

bryophyta

Mosses

Polypodiophyta

Ferns

Pinophyta

Conifers (Gymnosperms)

Magnoliophyta

Flowering plants
(angiosperms)

Tracheophyte
s

Non-seed
tracheophytes
Seed plants

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Alternation of generations
♥ Haploid gametophyte generation – produces gametes (produces by mitosis
since the parent plant is already in the haploid state)
...
The diploid sporophyte produces unicellular spores by meiosis,
which in turn will give rise to the haploid gametophyte
...

In the bryophytes the gametophyte generation is dominant
...


Phylum Bryophyta – the mosses
♥ They live in damp, shady environments and retain water to cope with the
dryness of land
...
The organs are described
as ‘root-like’, ‘stem-like’ and ‘leaf-like’
...

♥ Leaf-like structures have no cuticle and no functional stomata
...

♥ Multicellular root-like structures called rhizoids occur along the lower surface
and anchor the plants to the substratum
...
Nutrients are obtained from dust, rainwater and substances
dissolved in water at the soil’s surface since they have no roots to penetrate
the soil
...

Mosses cannot grow large because:
-

They have no supporting tissue to keep their bodies erect

-

Their photosynthetic parts above group and the non-photosynthetic parts
below ground must be close together because there is no vascular tissue for
the transport of nutrients and minerals
...
Numerous sterile hairs called paraphyses are present in
between archegonia and antheridia, these help to retain moisture within the
antheridial and archegonial heads
...


Mosses depend on water for reproduction
...

Biflagellate sperm swim through water to the archegonia on a neighbouring plant
...
A diploid zygote is produced which becomes a new
sporophyte
...
It produces a terminal sporangium
(spore capsule) in which spores are produced
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The lid (operculum) of the capsule is shed after spore development is complete
...
When the atmosphere is wet, the peristome
teeth close tightly but when the atmosphere is dry, they fling out and the spores are
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released
...


Spores give rise to a branched filamentous protonema which is anchored to the
substratum by rhizoids
...

Mosses found in Malta: Tortula muralis and Funaria hygrometrica

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Phylum Polypodiophyta – the ferns
♥ Restricted to damp, shady habitats
♥ Sporophyte is dominant in the alternation of generations
♥ Do not produce seeds
♥ Vascular tissue present in sporophyte:
o Forms a transport system, for food and water over long distance,
allowing it to form large complex bodies
o Provides support since it contains lignified cells of great strength and
rigidity
♥ Sporophyte has true roots, stems and leaves (roots penetrate soil and absorb
water and dissolved nutrients)
♥ Leaves are called fronds which are large and have a cuticle to minimise water
loss and stomata for gas exchange
...
The rhizome curls the leaves in the
winter into fiddleheads
...
The main axis of the
frond is the rachis; it attaches the frond to the rhizome
...


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Ferns found in Malta: Maidenhair Fern
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Life cycle


The diploid sporophyte produces haploid spores by meiosis (single type of spore –
homosporous)
...
Gametes fuse to form diploid zygotes
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Each sorus has a protective covering called an
indusium
...
The
exposed sporangium wall dries out and ruptures and the spores are catapulted from
the sporangia
...

The spores germinate to form gametophyte: a small, simple, heart-shaped
prothallus
...
It is
anchored to the soil by rhizoids
...

The prothallus produces both antheridia and archegonia on its lower surface which is
covered with a thin layer of moisture
...
Antheridia
produce numerous sperm cells (antherozoids) and each archegonium one ovum
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When ripe and wet the antheridium releases its sperm
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The product of fertilisation is a diploid zygote
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The young embryo absorbs nutrients from the
gametophyte until its own roots and leaves can take over the role of nutrition, and
the sporophyte can lead an independent existence
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Seed bearing plants


This includes the conifers and angiosperms (flowering plants)
...
The
sporophyte has complex vascular tissue in roots, stems and leaves
...
These are called heterosporous
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A megaspore is not shed but remains completely enclosed in the megasporangium,
where it gives rise to a female gametophyte (megagametophyte)
...
The female
gametophyte only produces female gametes (egg/ova) and remains within the
megaspore (endosporic) and is never shed from the sporophyte ensuring protection
against the dry terrestrial environment
...
They are shed from the sporophyte and
transferred to the female structures by air currents or animals (pollination)
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Therefore water is not needed for sexual reproduction
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The fertilised ovule becomes a seed
...
When conditions are favourable, the seed germinates and
gives rise to a new saprophyte
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Phylum Magnoliophyta – angiosperms (flowering plants)
They are adapted to life on land:
♥ Complex vascular tissues in roots, stems and leaves their xylem contains of
vessel elements and fibres
...
Their phloem
contains companion cells
...
They are
associated with the evolution of complex mechanisms for pollen transfer and
seed dispersal
...
This protects the ovules and
developing embryo from desiccation
...
They aid for seed dispersal by wind, water and animals
...
Both gametophytes are reduced
and contained within the flower of the sporophyte, therefore it is difficult to
realize that alternation of generations occurs

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