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Comparative studies of natural groups of organisms

Exercise 3.13 Cassytha filiformis are parasitic, hence
they rely on other plants. Others grow as
1. Outline the ways in which epiphytes on other plants without causing
coniferophytes are more advanced any harm. Angiosperms are the dominant
than filicinophytes. plants in all habitats, ranging from terrestrial

2. How would you distinguish to aquatic environments, where plants such
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gymnosperms from other plants? as water lilies and sea grasses are abundant.
3. Explain the importance of wind in Based on their life span, flowering plants are
the life cycle of coniferophytes. classified as annual, biannual or perennial.
Annual plants are normally herbs and
grasses. They complete their life cycle in
3.6.4 Division Angiospermophyta the single growth season. Biannual plants
Angiospermophytes are flowering plants complete their life cycle in two growth
which are the most advanced and adapted seasons. They grow vegetatively in the first
to terrestrial life. The word angiosperm season and flowering in the second season.
is a combination of two Greek words; Perennial plants complete their life cycles
Angeion which means ‘vessels’ or ‘carpels’
and sperma which means ‘seeds.’ They in three or more growth seasons. Example
produce seeds enclosed in the ovary, which of perennial plants are trees.
later matures to become a fruit. Thus, their In angiosperms sporophyte generation
fruit is a mature ovary and the seeds in it
are fertilised ovules. Angiosperms resemble is dominant with gametophytes entirely
coniferophyta in many aspects, such as confined in it. The sporophytes consist
the ability to produce seeds. However, the of roots, the stem, branches, leaves and
presence of flowers and seeds enclosed in flowers. The gametophyte generation is
the fruit makes them distinct. Flowers and associated only by flowers in which the
fruits have contributed significantly to the male gametophyte (polen grain) and female
success of angiosperms in their ecosystems. gametophytes (embryosac) are confined. The
Flowers are diverse in colour, aroma and sporophyte have well developed vascular
morphology. These have made it easy to tissues with xylem containing tracheids and
attract different pollinators, instead of vessels, which make the angiosperm wood
relying solely on the wind. The ability to harder than those of coniferophytes. On the
produce seeds enclosed in the fruit is also other hand, the phloem contains companion
an adaptation for seed dispersal by animals, cells and sieve tubes.
which feed on such fruits.
Angiosperms are heterosporous. They
The number of angiosperm species is over
295,000, with individuals that vary in size, produce microspores (male gametophyte)
shape and growth forms, such as grasses, and megaspores (female gametophyte).
herbs, shrubs, vines, liana, suffrutescents Actually, the male gametophyte is the
and trees. Some plant species, such as germinated pollen grain, which is highly

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