The rate at which pollen settles is dictated principally by the size and
density of the grain. The slower the settlement rate, the greater the
dispersal range. Numerous species reduce the density of their pollen
grains through air cavities in their walls. The grains of many species
quickly dehydrate after release.
There is a limit, however, to the lower range of pollen size. The smaller
a particle becomes, the more difficult its capture, because as airflow
carrying particles sweeps past surfaces, inertia represents a principal
component of the mechanism for capture. Usually considered a
¨Dprimitive¡¬ feature in textbooks, wind-pollination has, in fact, reappeared
independently in many plant groups relatively recently in geological time.
General textbooks still often give the impression that the anemophilous
syndrome is rather uninteresting, often defining it mainly as a
combination of negatives: a lack of nectar, scent, petals, etc. Wind
pollination has traditionally been viewed as a reproductive process
dominated by random events-the vagaries of the wind and weather. This
view seems justified by the potential hazards a pollen grain is subject to
when transported over long distances.
Pollen loss through happenstance is compensated for in wind-pollinated
plants to a large degree by pollen-to-ovule ratios that greatly exceed
those of insect-pollinated species. And unlike the sticky pollen grains of
plants pollinated by insects, the pollen grains of wind-pollinated plants
are smooth and dry, to avoid clumping and precipitating, and the stigma
of the female is huge, sticky, and feathery, the better to catch any
floating pollen grains. Similarly, wind-pollinated plants typically evolved
to grow in stands, such as pine forests, corn fields and grasslands.
Indeed the wind vector is only useful in large, near-monoculture
populations.
However, recent research has shown that several remarkably
sophisticated mechanisms for dispersal and capture are characteristic of
wind-pollinated plants. Pollen release is often tied to the recognition of
unambiguous environmental clues. The devices that operate to prevent
self-pollination are also sometimes extremely intricate. Many species take
advantage of the physics of pollen motion by generating aerodynamic
environments within the immediate vicinity of their reproductive organs.
Two biological features appear to be critical in this process: the density
and size of the pollen grain and the morphology of the ovulate organ.
The shape of the female organ creates patterns of airflow disturbances
through which pollen grains travel. The obstructing organ causes airflow
to separate around windward surfaces and creates turbulence along
leeward surfaces as ambient wind speeds increase. Because the
geometry of female organs is often species-specific, airflow disturbance
patterns that are also species-specific can be generated. The speed and
direction of this pattern combines with the physical properties of a
species' pollen to produce a highly synergistic pattern of pollen collision
on windward surfaces and sedimentation on leeward surfaces of
reproductive organs. The aerodynamic consequences of this synergism
can significantly increase the pollen-capture efficiency of an ovulate
organ.
3. Based on the information set forth in the passage, all the following
mechanisms serve to reduce pollen loss in wind-pollinated plants EXCEPT:
A. retention of pollen within the male organ when weather conditions are
not conducive to dispersal.
B. growth of plants in large populations with few species.
C. creation of species-specific air-flow disturbance patterns by the
morphology of the ovulate organ.
D. development of intricate mechanisms to prevent self-pollination.
E. high pollen-to-ovule ratios
4. Based on passage information, it is reasonable to conclude that windpollinated
plants are LEAST likely to be found:
A. in tropical rain forests of South America.
B. in the taiga and other northern European coniferous forests.
C. in the valleys of California.
D. along river banks in temperate climates
E. on the windy slopes of the Himalayas
can someone please help to answer question 3 and 4? The correct anser is D/A.
I got a/c
density of the grain. The slower the settlement rate, the greater the
dispersal range. Numerous species reduce the density of their pollen
grains through air cavities in their walls. The grains of many species
quickly dehydrate after release.
There is a limit, however, to the lower range of pollen size. The smaller
a particle becomes, the more difficult its capture, because as airflow
carrying particles sweeps past surfaces, inertia represents a principal
component of the mechanism for capture. Usually considered a
¨Dprimitive¡¬ feature in textbooks, wind-pollination has, in fact, reappeared
independently in many plant groups relatively recently in geological time.
General textbooks still often give the impression that the anemophilous
syndrome is rather uninteresting, often defining it mainly as a
combination of negatives: a lack of nectar, scent, petals, etc. Wind
pollination has traditionally been viewed as a reproductive process
dominated by random events-the vagaries of the wind and weather. This
view seems justified by the potential hazards a pollen grain is subject to
when transported over long distances.
Pollen loss through happenstance is compensated for in wind-pollinated
plants to a large degree by pollen-to-ovule ratios that greatly exceed
those of insect-pollinated species. And unlike the sticky pollen grains of
plants pollinated by insects, the pollen grains of wind-pollinated plants
are smooth and dry, to avoid clumping and precipitating, and the stigma
of the female is huge, sticky, and feathery, the better to catch any
floating pollen grains. Similarly, wind-pollinated plants typically evolved
to grow in stands, such as pine forests, corn fields and grasslands.
Indeed the wind vector is only useful in large, near-monoculture
populations.
However, recent research has shown that several remarkably
sophisticated mechanisms for dispersal and capture are characteristic of
wind-pollinated plants. Pollen release is often tied to the recognition of
unambiguous environmental clues. The devices that operate to prevent
self-pollination are also sometimes extremely intricate. Many species take
advantage of the physics of pollen motion by generating aerodynamic
environments within the immediate vicinity of their reproductive organs.
Two biological features appear to be critical in this process: the density
and size of the pollen grain and the morphology of the ovulate organ.
The shape of the female organ creates patterns of airflow disturbances
through which pollen grains travel. The obstructing organ causes airflow
to separate around windward surfaces and creates turbulence along
leeward surfaces as ambient wind speeds increase. Because the
geometry of female organs is often species-specific, airflow disturbance
patterns that are also species-specific can be generated. The speed and
direction of this pattern combines with the physical properties of a
species' pollen to produce a highly synergistic pattern of pollen collision
on windward surfaces and sedimentation on leeward surfaces of
reproductive organs. The aerodynamic consequences of this synergism
can significantly increase the pollen-capture efficiency of an ovulate
organ.
3. Based on the information set forth in the passage, all the following
mechanisms serve to reduce pollen loss in wind-pollinated plants EXCEPT:
A. retention of pollen within the male organ when weather conditions are
not conducive to dispersal.
B. growth of plants in large populations with few species.
C. creation of species-specific air-flow disturbance patterns by the
morphology of the ovulate organ.
D. development of intricate mechanisms to prevent self-pollination.
E. high pollen-to-ovule ratios
4. Based on passage information, it is reasonable to conclude that windpollinated
plants are LEAST likely to be found:
A. in tropical rain forests of South America.
B. in the taiga and other northern European coniferous forests.
C. in the valleys of California.
D. along river banks in temperate climates
E. on the windy slopes of the Himalayas
can someone please help to answer question 3 and 4? The correct anser is D/A.
I got a/c
