Biodiversity Of Plants Flashcards
(43 cards)
3 large main types of bryophytes
Mosses and liverworts
What are angiosperms
Flowering plants that produce seeds within fruits (e.g., roses, sunflowers).
Pteridiophytee
Ferns and related plants reproducing via spores.
Gymnosperms
Gymnosperms: Plants with naked seeds (e.g., conifers like pine trees).
Alternation of generations
Stages of alternation of generations
Haploid stage: Unicellular spores undergo mitosis to form multicellular gametophytes.
Gametophyte stage: The gametophyte produces gametes (sperm and egg) through mitosis.
Diploid stage: The fusion of gametes forms a diploid zygote, which undergoes mitosis to form a sporophyte.
Sporophyte stage: The multicellular sporophyte undergoes meiosis to produce haploid spores.
4 major plant groups:
●Bryophytes
●Pteridophytes
●Gymnosperms
●Angiosperms
multicellular
an organism made up of many cells
eukaryotic
any single or multicellular group of organisms that have a
membrane-bound nucleus containing genetic material
autotrophic
organisms which can synthesize their own food e.g. green
plants, algae and some bacteria.
phylogenetic
diagram/
cladogram
a diagram which shows the evolutionary relationship between
organisms
thallus
a plant body that is not differentiated into stem and leaves and
lacks true roots and a vascular system; thalli are typical of
algae, fungi, lichens, and some liverworts
rhizoids
a filamentous outgrowth or root hair on the underside of the
thallus in some lower plants, especially mosses and liverworts,
serving both to anchor the plant and (in terrestrial forms) to
conduct water
The four plant divisions have these in common
multicellular
eukaryotic (cells have a membrane bound nucleus)
cell walls are made of cellulose
most are autotrophic and have chloroplasts for photosynthesis
a life cycle involving two generations: a diploid, spore producing generation
called a sporophyte and a haploid, gamete producing generation called a
gametophyte – referred to as an alternation of generation
51
The characteristics used to place a plant into one of the four groups depends on:
the presence or absence of true conducting tissues such as xylem and
phloem
the presence or absence of true, roots, stems and leaves
the type of reproduction and reproductive structures formed
the degree of dependence on water for reproduction
Characteristics of Bryophytes
Mosses are generally small (< 20 cm).
They do not have true roots, stems or leaves. For this reason, the plant body
is referred to as a thallus.
52
Water can be absorbed directly through the leaves because there is not a
waxy cuticle covering the leaves.
The leaves are not true leaves and are often referred to as ‘leaflets’.
The size of mosses is limited because they do not have any conducting
tissues i.e. no xylem or phloem (vascular tissue) is present.
Rhizoids at the base of the plant are responsible for anchoring the plant to a
substrate.
Bryophytes can reproduce either asexually or sexually.
The gametophyte generation is the dominant generation and consists of a
green leafy plant, capable of photosynthesis.
No fruits or seeds produced.
Division Pteridophyt
frond
the leaf of a fern usually with many divisions
rhizome
a stem which grows horizontally
adventitious roots
roots which arise at the nodes of stems
sori
a cluster of sporangia found on the underside of fern leaves
Characteristics of Pteridiophytes
Ferns have true leaves, roots and stems.
Fern leaves are covered by a waxy cuticle to prevent excessive loss of water.
The leaves are often divided into smaller leaflets. A leaf which is divided into
smaller leaflets is called a compound leaf. Fern leaves are referred to as a
frond.
The presence of vascular tissues allows ferns to grow taller than mosses.
They have both xylem and phloem which transport water and photosynthetic
products respectively.
The stems of most ferns grow horizontally and are called rhizomes. The
rhizomes are usually protected by brown scale-like leaves.
Adventitious roots grow from the nodes of the horizontal stem. These are
true roots because they have xylem and phloem and absorb water for the
plant. The roots also anchor the plant in the soil.
Ferns reproduce both sexually and asexually. The dominant generation in
ferns is the sporophyte generation. Spores are produced in sporangia
arranged in sori under the leaf (Figure 4).
No fruit or seeds are produce.
Characteristics of Gymnosperms
Gymnosperms have true roots, stems and leaves.
Vascular tissues, namely xylem and phloem are present. Unlike higher plants,
the xylem in pine trees does not have vessel elements. Only xylem tracheids
are present to transport water. This is the reason why the wood of pine trees
is softer than the wood of higher plants.
The leaves of pine trees are needle-like (Figure 6) and have a cuticle to
reduce the loss of water through evaporation.
The natural habitat of a pine tree is very cold in winter. The reduced volume of
the leaves, prevents ice crystals from forming which would damage the leaves
internally. The shape of the tree also stops snow from collecting on the
branches.
Figure 5A: Cycad
Figure 5C: Welwitschia Figure 5D: Pine
Figure 5B: Gingko biloba
55
Figure 6: The needle-like leaves of a pine tree
Pine trees have well developed root systems.
Gymnosperms do not produce flowers. They form both male and female
cones. It is important to note that fertilization is not dependent on water.
Pollen is carried by the wind from a male cone to the female cone.
The seeds of the pine are said to be “naked” because they are not protected
by a fruit. The seeds are carried on the exposed scales of the female cone.
When the seeds are ripe, they fall out of the cone and are carried by wind to
another location. Each seed has a wing to help with wind dispersal .
It is important for the survival of the species that the seed does not fall under
the tree. If it germinates under the mother tree it will be in the shade and in
competition with the mother tree for water and nutrients.
Pine trees are not indigenous to South Africa and are able to make better use
of available water than the natural vegetation because of their extensive root
system.
fibrous/
adventitious
root system
formed by many thin, moderately branching roots growing from the
stem – common in monocotyledons
tap root
system
characterized by a main root or primary root system, growing
vertically downward – common in dicotyledonous plants
Characteristics of Angiosperms
The sporophyte generation is the dominant generation in angiosperms. It
consists of true roots, stems and leaves.
Xylem and phloem are responsible for transporting water and photosynthetic
products, respectively Angiosperms have either fibrous (adventitious) root systems or tap root
systems. The roots are capable of absorbing water and dissolved mineral
salts.
The stems of angiosperms are divided into nodes and internodes. Leaves
form at the nodes on the stem. The leaves are covered in a waxy cuticle to
prevent excessive loss of water by evaporation.
Angiosperms produce seeds protected by fruit.
