Page 171 - Biology_F5

Biology for Advanced Level Secondary Schools
Adaptation of Angiospermophytes to
live on land
Angiosperms are the most recently
evolved plants and are relatively the most
adapted plants to terrestrial environment.
Several factors have contributed to their
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survival, and success on land as follows:
(a) Flowers have contributed to the
diversification of angiosperms.
The adaptation exhibited by any
given flower depends on the type of
pollinators the flower is designed to
attract, and have evolved features to
enable pollinators to recognise and
locate them quickly. For instance,
bees can only see yellow, blue, and
ultraviolet (UV) colours; therefore,
bee pollinated flowers are yellow, blue
or UV, and not red. Butterflies detect
red; hence, they usually pollinate red
flowers. Moths, which are nocturnal,
pollinate brightly white coloured
flowers, which can standout against
darkness. (f) Their male gametes are transferred
(b) Most plants have ability to make
and supply some food in the form of
nectar and advertise their presence to
the pollinators by producing fragrant
scent. They also have a way of putting
pollen on the pollinators for easy of
transfer to the flower of the next plant. (g) Fruits produced by angiospermophytes
(c) To ensure pollination, angiosper-
mophyte flowers have evolved ways of
preventing non beneficial pollinators
from visiting their flowers, while
embracing the beneficial pollinators.
For instance, some flowers can
be pollinated by insects with long
proboscis or birds with long narrow
beaks, only as they secrete nectar at
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the base of a narrow floral tube which
is the right length of their proboscis or
beak of the corresponding pollinators.
(d) Stamens have also become modified
through time to prevent self-
fertilisation in order to increase
genetic diversity that will eventually
enable them to inhabit a wider range
of habitats. Additionally, closed carpel
allows adaptations under specialised
pollination conditions and controls
self-fertilisation.
(e) The male gametophyte in angiosperms
is highly reduced into three nuclei (a
tube nucleus and two sperm nuclei).
This evolved in order to shorten the
duration of time between pollination
and fertilisation. Thus, unlike
Coniferophytes, which take about a
year for fertilisation to take place after
pollination, in angiospermophytes
fertilisation begins soon after
pollination.
through a special tube (pollen tube)
to the female gametes for fertilisation.
The ability to reproduce sexually
without necessity of water availability
is an important feature in terrestrial
environment, where water is limited.
are adapted for dispersal by various
agents, such as wind, water, animals,
and explosive dehiscence of fruits
(bursting). Animal dispersed fruits
have fleshy mesocarp which is
edible or produces edible seeds or
have various kinds of hooks. Wind
dispersed fruits have structures for
buoyancy, such as wings. These have
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