Pollen Gathering by Animals
Pollen contains a seed plant’s male reproductive cells, and in flowering plants it is produced by anthers, part of the male reproductive organs. Pollination in flowering plants is the process whereby pollen is transported from a flower’s anthers to the female reproductive organ (stigma), enabling reproduction. This is sometimes accomplished by wind or water. but pollen is more commonly transported by animals that visit flowers, especially bees, butterflies, moths, and other insects, but also including some birds reptiles, and mammals. It is generally assumed that most pollen is transferred passively (without deliberate effort) onto a visiting animal’s body when physical contact is made. Pollen adheres to the surfaces of visitors because of its naturally sticky properties. Its adhesion is often enhanced by the characteristics of the animal’s surfaces: branched hairs for bees. scaled surfaces for butterflies, and moths, and fur or feathers in vertebrates.
There are some indications that what is termed passive gathering can be augmented by electrostatic attraction between pollen grains and animals’ bodies. Plants are inherently slightly negatively charged in warm. still air, the magnitude of the charge field depending on the plant’s composition and architecture and on weather conditions. The charge is greater at sharp tips and is therefore often higher in flowers than elsewhere. Hence it is possible that pollen grains acquire negative charges within the flower. In contrast, insects, and especially hairy bees, tend to acquire a positive surface charge as they fly. The charge difference might aid the transfer of pollen onto visiting insects. In short, even without direct contact, pollen grains could be attracted onto a closeup bee. Pollen might also be unloaded from bees onto dry stigmas in reverse fashion (the pollen having acquired a positive charge while on the flying insect), especially where stigmas stick out from flowers and thus concentrate charge. Small electrostatic charges could also lead a visiting insect to leave an electrical “footprint” or flowers, detectable to subsequent visitors for at least several minutes and thus potentially allowing avoidance of recently depleted flowers.
Rather few kinds of pollinators eat pollen and so gather it deliberately, but those that do are important and numerically dominant kinds. Syrphids (a type of fly that gathers in high numbers) may eat pollen directly from the anthers. A few bees also gather pollen directly with their mouthparts, eating some immediately and carrying the rest back to the nest in their crop (a part of the foregut that functions like an expandable sack). In such cases, only the pollen that is accidentally scattered during consumption (or that passively adheres to other parts of the insect) is of any use for pollinating. Most bees normally do not eat pollen at the flower but instead collect it-with their legs and mouthparts-by rubbing the underside of their body across a flower, or by using various comblike or rake-like structures. In these cases, the pollen is then packed away on or into specific collecting areas of the insect’s body, often with the addition of some moistening flower nectar, a sugary liquid. Hence there may be substantial interruptions to food gathering while a bee lands, grooms (removes pollen from its hair), and packages its pollen, although more advanced bees require only a brief hover between flower probings to achieve grooming and packaging.
Although active pollen gathering may be highly beneficial to a flower-visiting animal, there are problems from the plant’s point oi view. First. much of the pollen is hidden away in sites on the visitor where it will never contact a stigma. Therefore, plant evolution might act to place as much pollen as possible in sites on the visitor that are hard to groom. With suitable arrangement of floral parts, there is then a good chance that the stigma of another flower of the same species will receive some pollen from the insect. Second, many insect pollinators, especially ants, have special glands that produce small quantities of substances that protect their nests against fungal and bacterial growth but that can also kill pollen. Third, when saliva and nectar are added to the pollen gathered by bees, the pollen may suffer damaging biochemical change, since bees do not “want” the pollen to germinate (develop) once deposited in the nest. For such reasons, usually the longer pollen adheres to a visitor, the more its viability is compromised.
1
Pollen contains a seed plant’s male reproductive cells, and in flowering plants it is produced by anthers, part of the male reproductive organs. Pollination in flowering plants is the process whereby pollen is transported from a flower’s anthers to the female reproductive organ (stigma), enabling reproduction. This is sometimes accomplished by wind or water. but pollen is more commonly transported by animals that visit flowers, especially bees, butterflies, moths, and other insects, but also including some birds reptiles, and mammals. It is generally assumed that most pollen is transferred passively (without deliberate effort) onto a visiting animal’s body when physical contact is made. Pollen adheres to the surfaces of visitors because of its naturally sticky properties. Its adhesion is often enhanced by the characteristics of the animal’s surfaces: branched hairs for bees. scaled surfaces for butterflies, and moths, and fur or feathers in vertebrates.
Paragraph 1 suggests that most of the pollen that results in pollination of flowers by animals
Ais transported less effectively than pollen transported by wind or water
Bis not intentionally transported from the anther to the stigma
Cis carried by insects other than bees, butterflies, and moths
Dis less sticky than pollen that is transferred by wind or water
2
There are some indications that what is termed passive gathering can be augmented by electrostatic attraction between pollen grains and animals’ bodies. Plants are inherently slightly negatively charged in warm. still air, the magnitude of the charge field depending on the plant’s composition and architecture and on weather conditions. The charge is greater at sharp tips and is therefore often higher in flowers than elsewhere. Hence it is possible that pollen grains acquire negative charges within the flower. In contrast, insects, and especially hairy bees, tend to acquire a positive surface charge as they fly. The charge difference might aid the transfer of pollen onto visiting insects. In short, even without direct contact, pollen grains could be attracted onto a closeup bee. Pollen might also be unloaded from bees onto dry stigmas in reverse fashion (the pollen having acquired a positive charge while on the flying insect), especially where stigmas stick out from flowers and thus concentrate charge. Small electrostatic charges could also lead a visiting insect to leave an electrical “footprint” or flowers, detectable to subsequent visitors for at least several minutes and thus potentially allowing avoidance of recently depleted flowers.
The word “augmented” in the passage is closest in meaning to
Amade active
Bincreased
Ccaused
Dexplained
3
There are some indications that what is termed passive gathering can be augmented by electrostatic attraction between pollen grains and animals’ bodies. Plants are inherently slightly negatively charged in warm. still air, the magnitude of the charge field depending on the plant’s composition and architecture and on weather conditions. The charge is greater at sharp tips and is therefore often higher in flowers than elsewhere. Hence it is possible that pollen grains acquire negative charges within the flower. In contrast, insects, and especially hairy bees, tend to acquire a positive surface charge as they fly. The charge difference might aid the transfer of pollen onto visiting insects. In short, even without direct contact, pollen grains could be attracted onto a closeup bee. Pollen might also be unloaded from bees onto dry stigmas in reverse fashion (the pollen having acquired a positive charge while on the flying insect), especially where stigmas stick out from flowers and thus concentrate charge. Small electrostatic charges could also lead a visiting insect to leave an electrical “footprint” or flowers, detectable to subsequent visitors for at least several minutes and thus potentially allowing avoidance of recently depleted flowers.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
AA visiting insect might lead other insects to a flower by leaving electrical “footprints” in the form of small electrostatic charges that can be detected for at least several minutes.
BSome flowers may be detectable to insects because of small electrostatic charges, which are not present on flowers that have been recently depleted
CThe small electrostatic charges left by a visiting insect may be detected by other insects and help them avoid flowers that have recently been depleted
DAn insect visitor that remains on a flower for at least several minutes could leave an electrical “footprint” that is detectable by other insects.
4
There are some indications that what is termed passive gathering can be augmented by electrostatic attraction between pollen grains and animals’ bodies. Plants are inherently slightly negatively charged in warm. still air, the magnitude of the charge field depending on the plant’s composition and architecture and on weather conditions. The charge is greater at sharp tips and is therefore often higher in flowers than elsewhere. Hence it is possible that pollen grains acquire negative charges within the flower. In contrast, insects, and especially hairy bees, tend to acquire a positive surface charge as they fly. The charge difference might aid the transfer of pollen onto visiting insects. In short, even without direct contact, pollen grains could be attracted onto a closeup bee. Pollen might also be unloaded from bees onto dry stigmas in reverse fashion (the pollen having acquired a positive charge while on the flying insect), especially where stigmas stick out from flowers and thus concentrate charge. Small electrostatic charges could also lead a visiting insect to leave an electrical “footprint” or flowers, detectable to subsequent visitors for at least several minutes and thus potentially allowing avoidance of recently depleted flowers.
Which of the following explanations is presented in paragraph 2 as a reason for thinking that pollen grains have an electrical charge?
AThey are produced in an area of a plant where charge is greater.
BThey lose their charge when the air is warm and still.
CThey have sharp tips as part of their architecture.
DThey are affected by weather conditions
5
There are some indications that what is termed passive gathering can be augmented by electrostatic attraction between pollen grains and animals’ bodies. Plants are inherently slightly negatively charged in warm. still air, the magnitude of the charge field depending on the plant’s composition and architecture and on weather conditions. The charge is greater at sharp tips and is therefore often higher in flowers than elsewhere. Hence it is possible that pollen grains acquire negative charges within the flower. In contrast, insects, and especially hairy bees, tend to acquire a positive surface charge as they fly. The charge difference might aid the transfer of pollen onto visiting insects. In short, even without direct contact, pollen grains could be attracted onto a closeup bee. Pollen might also be unloaded from bees onto dry stigmas in reverse fashion (the pollen having acquired a positive charge while on the flying insect), especially where stigmas stick out from flowers and thus concentrate charge. Small electrostatic charges could also lead a visiting insect to leave an electrical “footprint” or flowers, detectable to subsequent visitors for at least several minutes and thus potentially allowing avoidance of recently depleted flowers.
According to paragraph 2, electrostatic attraction can cause pollen grains to be deposited on the stigma of a flower in part because
Athe charge of pollen carried through the air is equal in magnitude to the charge of a flower’s stigma
Belectrostatic attraction has the effect of drying out a flower’s stigma
Cstigmas stick out from flowers when there is a nearby positive charge
Dpollen grains acquire the charge of any insect carrying them through the air
6
Rather few kinds of pollinators eat pollen and so gather it deliberately, but those that do are important and numerically dominant kinds. Syrphids (a type of fly that gathers in high numbers) may eat pollen directly from the anthers. A few bees also gather pollen directly with their mouthparts, eating some immediately and carrying the rest back to the nest in their crop (a part of the foregut that functions like an expandable sack). In such cases, only the pollen that is accidentally scattered during consumption (or that passively adheres to other parts of the insect) is of any use for pollinating. Most bees normally do not eat pollen at the flower but instead collect it-with their legs and mouthparts-by rubbing the underside of their body across a flower, or by using various comblike or rake-like structures. In these cases, the pollen is then packed away on or into specific collecting areas of the insect’s body, often with the addition of some moistening flower nectar, a sugary liquid. Hence there may be substantial interruptions to food gathering while a bee lands, grooms (removes pollen from its hair), and packages its pollen, although more advanced bees require only a brief hover between flower probings to achieve grooming and packaging.
Which of the following is NOT identified in paragraph 3 as a way that bees collect pollen?
AThey use their mouthparts to pick up pollen.
BThey rub against pollen that has been accidentally scattered by other insects.
CThey scrape the downward-facing parts of their bodies across flowers.
DThey scoop up pollen using structures that are similar to rakes or combs
7
Although active pollen gathering may be highly beneficial to a flower-visiting animal, there are problems from the plant’s point oi view. First. much of the pollen is hidden away in sites on the visitor where it will never contact a stigma. Therefore, plant evolution might act to place as much pollen as possible in sites on the visitor that are hard to groom. With suitable arrangement of floral parts, there is then a good chance that the stigma of another flower of the same species will receive some pollen from the insect. Second, many insect pollinators, especially ants, have special glands that produce small quantities of substances that protect their nests against fungal and bacterial growth but that can also kill pollen. Third, when saliva and nectar are added to the pollen gathered by bees, the pollen may suffer damaging biochemical change, since bees do not “want” the pollen to germinate (develop) once deposited in the nest. For such reasons, usually the longer pollen adheres to a visitor, the more its viability is compromised.
Why does the author provide the information that “many insect pollinators, especially ants, have special glands that produce small quantities of substances that protect their nests against fungal and bacterial growth but that can also kill pollen”?
ATo help explain why bees are more effective pollinators than many insects like ants
BTo argue that pollen sometimes brings problems into insect nests, such as fungal and bacterial infestations
CTo provide a second example of how insects, such as ants, have adapted to being pollinators
DTo identify one of the ways in which active pollen gathering can be problematic for plants
8
Although active pollen gathering may be highly beneficial to a flower-visiting animal, there are problems from the plant’s point oi view. First. much of the pollen is hidden away in sites on the visitor where it will never contact a stigma. Therefore, plant evolution might act to place as much pollen as possible in sites on the visitor that are hard to groom. With suitable arrangement of floral parts, there is then a good chance that the stigma of another flower of the same species will receive some pollen from the insect. Second, many insect pollinators, especially ants, have special glands that produce small quantities of substances that protect their nests against fungal and bacterial growth but that can also kill pollen. Third, when saliva and nectar are added to the pollen gathered by bees, the pollen may suffer damaging biochemical change, since bees do not “want” the pollen to germinate (develop) once deposited in the nest. For such reasons, usually the longer pollen adheres to a visitor, the more its viability is compromised.
According to paragraph 4, flowering plants may have evolved which of the following responses to the problem of insects hiding pollen away so it cannot contact a stigma?
AThey produce pollen that falls out of the storage places on insects’ bodies.
BThey arrange their floral parts in such a way that different species of insects visit them.
CThey produce small quantities of substances that make pollen unsuitable for eating.
DTheir flowers are designed to leave pollen on parts of an insect’s body that are difficult for it to reach
9
There are some indications that what is termed passive gathering can be augmented by electrostatic attraction between pollen grains and animals’ bodies. Plants are inherently slightly negatively charged in warm. still air, the magnitude of the charge field depending on the plant’s composition and architecture and on weather conditions. [■]The charge is greater at sharp tips and is therefore often higher in flowers than elsewhere. Hence it is possible that pollen grains acquire negative charges within the flower. In contrast, insects, and especially hairy bees, tend to acquire a positive surface charge as they fly. The charge difference might aid the transfer of pollen onto visiting insects.[■] In short, even without direct contact, pollen grains could be attracted onto a closeup bee. Pollen might also be unloaded from bees onto dry stigmas in reverse fashion (the pollen having acquired a positive charge while on the flying insect), especially where stigmas stick out from flowers and thus concentrate charge. [■]Small electrostatic charges could also lead a visiting insect to leave an electrical “footprint” or flowers, detectable to subsequent visitors for at least several minutes and thus potentially allowing avoidance of recently depleted flowers.[■]
Look at the four squaresthat indicate where the following sentence could be added to the passage
Being extremely light, the pollen grains may even be drawn through the air toward the positive charge.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Bees and other animals can affect the reproduction of flowering plants
AAnimals that visit flowers aid pollination, as pollen is readily transferred to and from animals’ surfaces through physical contact or as a result of electrostatic charges
BPlants and insects, especially hairy bees, have similar charges because they share similar air and weather conditions and because of sharp tips that stick out of flowers and bee hairs.
CSome bees have developed collecting areas in their bodies that are used primarily to spread pollen from one flower to another and thus assist in pollination.
DSome bees have developed collecting areas in their bodies that are used primarily to spread pollen from one flower to another and thus assist in pollination.
ESome insects eat pollen, either at the flower or by storing it on various parts of their bodies to take back to their nests, and so they only help with pollination accidentally.
FDeliberately collected pollen can be a problem for plants because it either never reaches a flower or cannot germinate because of substances added to the pollen by the animal.
