Insect Size
The success of insect species is partly the result of their size.Small animals are relatively more powerful than large ones, mainly because their muscle mass is large relative to the body mass they are supporting. Humans are able to carry a load roughly equal to their body weight, whereas the load-carrying ability of an ant is many times its own body weight. A chrysomelid beetle hanging on to a leaf in a strong wind may resist a force ten or more times greater than its mass because the adhesive structures on its feet have a relatively huge surface area compared with the rest of its body.
The world is a much finer-grained environment to small animals and offers a lot more places to live. Insects have evolved to occupy many more ecological niches than larger organisms ever could. An oak tree, during the course of its life, may support very few mammal and bird species but many hundreds of different insect species. When the tree ages and finally dies, its decaying structure will be alive with insects for months or years to come.
That there are no really large insects today does not mean that it would be impossible for them to exist. It is often stated that the upper limits to the size of an insect are determined by the mechanics of moving with an exoskeleton (hard body covering) and the difficulties of getting enough oxygen to all the tissues, but this is not really why insects are not bigger than they are. Rather, the explanation lies in environmental adaptations over time. Fossil evidence from the late Carboniferous and early Permian periods (360 to 250 million years ago) shows that most insects were bigger and some very much bigger than they are today. One species of dragonfly had a wingspan of 75 centimeters, while the biggest member of this order today has a span a quarter of that length. It has been suggested that large size evolved as a defensive strategy of smaller insect prey species against their larger insect predators. The larger insect predators. in turn, became bigger and the process continued until it was halted either because the insects were no longer mechanically viable or, more likely, because of the rise and spread of vertebrate predators.such as reptiles. which ate them. From that time on, insects got smaller and smaller and were thus able to occupy all available habitats.
The lower limit of the insect size range is determined by a number of physical constraints. All animal cells need a supply of oxygen, and organisms that are very minute might be able to get enough oxygen by simple diffusion (movement of oxygen from the air into an organism through openings in the body). This is because a small body has a proportionally greater surface area than volume. The tracheal system of insects is a simple and effective means of gaseous exchange. Spiracles are the openings of the system and airways come in pairs, one spiracle on each side of the body. There is usually one pair per body segment. Spiracles are connected to air sacs and large airways (the tracheae), which then branch and branch getting finer and finer. The finest branches, the tracheoles, are in intimate contact with the tissues and are especially abundant in tissues such as muscles where oxygen demand is high. Interestingly.no matter how big or small the insect. the thinnest tracheoles always have a diameter of 0.2 nanometers. If the tubes were narrower than this, oxygen molecules would simply not diffuse any further along them. Evolution has produced a tube diameter that is just right. A small insect can have a small number of tracheoles, but they cannot be any finer than 0.2 nanometers.
Another reason that insects may have reached their minimum potential size might be due to the fairly constant size of animal cells.For various reasons concerning internal transport and operation dictated by surface area and volume relationships, animal cells tend to be the same size. From this, it follows that larger animals are made up of more cells and smaller ones of fewer cells. There must.however, be a minimum number of cells needed to make a functioning insect.
1
The success of insect species is partly the result of their size.Small animals are relatively more powerful than large ones, mainly because their muscle mass is large relative to the body mass they are supporting. Humans are able to carry a load roughly equal to their body weight, whereas the load-carrying ability of an ant is many times its own body weight. A chrysomelid beetle hanging on to a leaf in a strong wind may resist a force ten or more times greater than its mass because the adhesive structures on its feet have a relatively huge surface area compared with the rest of its body.
Paragraph 1 indicates which of the following about ants?
AThey have more load-carrying ability than other insects of a similar size
BCompared with humans, they have more muscle mass relative to their body mass
CCompared with beetles, they are better at resisting the force of strong winds.
Dhey have more surface area in contact with the around than most other insects do
2
That there are no really large insects today does not mean that it would be impossible for them to exist. It is often stated that the upper limits to the size of an insect are determined by the mechanics of moving with an exoskeleton (hard body covering) and the difficulties of getting enough oxygen to all the tissues, but this is not really why insects are not bigger than they are. Rather, the explanation lies in environmental adaptations over time. Fossil evidence from the late Carboniferous and early Permian periods (360 to 250 million years ago) shows that most insects were bigger and some very much bigger than they are today. One species of dragonfly had a wingspan of 75 centimeters, while the biggest member of this order today has a span a quarter of that length. It has been suggested that large size evolved as a defensive strategy of smaller insect prey species against their larger insect predators. The larger insect predators. in turn, became bigger and the process continued until it was halted either because the insects were no longer mechanically viable or, more likely, because of the rise and spread of vertebrate predators.such as reptiles. which ate them. From that time on, insects got smaller and smaller and were thus able to occupy all available habitats.
The word halted in the passage is closest in meaning to
ASlowed
BCompleted
Cstopped
Dreversed
3
That there are no really large insects today does not mean that it would be impossible for them to exist. It is often stated that the upper limits to the size of an insect are determined by the mechanics of moving with an exoskeleton (hard body covering) and the difficulties of getting enough oxygen to all the tissues, but this is not really why insects are not bigger than they are. Rather, the explanation lies in environmental adaptations over time. Fossil evidence from the late Carboniferous and early Permian periods (360 to 250 million years ago) shows that most insects were bigger and some very much bigger than they are today. One species of dragonfly had a wingspan of 75 centimeters, while the biggest member of this order today has a span a quarter of that length. It has been suggested that large size evolved as a defensive strategy of smaller insect prey species against their larger insect predators. The larger insect predators. in turn, became bigger and the process continued until it was halted either because the insects were no longer mechanically viable or, more likely, because of the rise and spread of vertebrate predators.such as reptiles. which ate them. From that time on, insects got smaller and smaller and were thus able to occupy all available habitats.
According to paragraph 3, which of the following is a possible reason why many insects in the late Carboniferous and early Permian periods grew larger?
AThe ability of these insects to move improved with increased size
BLarger size was an adaptation to habitats that had newly become available
CThese insects needed to adapt to environments that had different amounts of oxygen
DLarger size improved the ability of these insects to either obtain prey or avoid being eaten themselves
4
That there are no really large insects today does not mean that it would be impossible for them to exist. It is often stated that the upper limits to the size of an insect are determined by the mechanics of moving with an exoskeleton (hard body covering) and the difficulties of getting enough oxygen to all the tissues, but this is not really why insects are not bigger than they are. Rather, the explanation lies in environmental adaptations over time. Fossil evidence from the late Carboniferous and early Permian periods (360 to 250 million years ago) shows that most insects were bigger and some very much bigger than they are today. One species of dragonfly had a wingspan of 75 centimeters, while the biggest member of this order today has a span a quarter of that length. It has been suggested that large size evolved as a defensive strategy of smaller insect prey species against their larger insect predators. The larger insect predators. in turn, became bigger and the process continued until it was halted either because the insects were no longer mechanically viable or, more likely, because of the rise and spread of vertebrate predators.such as reptiles. which ate them. From that time on, insects got smaller and smaller and were thus able to occupy all available habitats.
In paragraph 3, why does the author present possible reasons why many insects initially increased and then later decreased in size?
ATo show how the fossil record can be used to understand the evolution of insect size
BTo support the claim that changes in insect size were likely environmental adaptations
CTo provide evidence that insects do not have difficulty getting enough oxygen to all tissues
DTo show that size change is often an inadequate strategy for insect predators
5
That there are no really large insects today does not mean that it would be impossible for them to exist. It is often stated that the upper limits to the size of an insect are determined by the mechanics of moving with an exoskeleton (hard body covering) and the difficulties of getting enough oxygen to all the tissues, but this is not really why insects are not bigger than they are. Rather, the explanation lies in environmental adaptations over time. Fossil evidence from the late Carboniferous and early Permian periods (360 to 250 million years ago) shows that most insects were bigger and some very much bigger than they are today. One species of dragonfly had a wingspan of 75 centimeters, while the biggest member of this order today has a span a quarter of that length. It has been suggested that large size evolved as a defensive strategy of smaller insect prey species against their larger insect predators. The larger insect predators. in turn, became bigger and the process continued until it was halted either because the insects were no longer mechanically viable or, more likely, because of the rise and spread of vertebrate predators.such as reptiles. which ate them. From that time on, insects got smaller and smaller and were thus able to occupy all available habitats.
Paragraph 3 supports which of the following statements about the evolution of size in insects?
AThe presence of an exoskeleton made it difficult for insects to evolve a large body
BToday’s insects are more varied in size than were insects living in the late Carboniferous and early Permian periods.
CEarly developmental increases in size allowed more efficient movement of oxygen to insects’ body tissues
DBy becoming smaller, insects were better able to avoid predation by reptiles.
6
The success of insect species is partly the result of their size.Small animals are relatively more powerful than large ones, mainly because their muscle mass is large relative to the body mass they are supporting. Humans are able to carry a load roughly equal to their body weight, whereas the load-carrying ability of an ant is many times its own body weight. A chrysomelid beetle hanging on to a leaf in a strong wind may resist a force ten or more times greater than its mass because the adhesive structures on its feet have a relatively huge surface area compared with the rest of its body.
The word “constraints” in the passage is closest in meaning to
Arequirements
Bproperties
CRestrictions
DLaws
7
The lower limit of the insect size range is determined by a number of physical constraints. All animal cells need a supply of oxygen, and organisms that are very minute might be able to get enough oxygen by simple diffusion (movement of oxygen from the air into an organism through openings in the body). This is because a small body has a proportionally greater surface area than volume. The tracheal system of insects is a simple and effective means of gaseous exchange. Spiracles are the openings of the system and airways come in pairs, one spiracle on each side of the body. There is usually one pair per body segment. Spiracles are connected to air sacs and large airways (the tracheae), which then branch and branch getting finer and finer. The finest branches, the tracheoles, are in intimate contact with the tissues and are especially abundant in tissues such as muscles where oxygen demand is high. Interestingly.no matter how big or small the insect. the thinnest tracheoles always have a diameter of 0.2 nanometers. If the tubes were narrower than this, oxygen molecules would simply not diffuse any further along them. Evolution has produced a tube diameter that is just right. A small insect can have a small number of tracheoles, but they cannot be any finer than 0.2 nanometers.
According to paragraph 4. all of the following are true of the tracheal system of insects EXCEPT:
APairs of spiracles are present on the sides of the insects’ bodies.
BAir sacs are directly connected to all important organs
CThere are more tracheoles where demands for oxygen are high
DThe thinnest tracheoles are never thinner than 0.2 nanometers
8
Another reason that insects may have reached their minimum potential size might be due to the fairly constant size of animal cells.For various reasons concerning internal transport and operation dictated by surface area and volume relationships, animal cells tend to be the same size. From this, it follows that larger animals are made up of more cells and smaller ones of fewer cells. There must.however, be a minimum number of cells needed to make a functioning insect.
According to paragraph 5, which of the following explains why insects have a minimum lower limit on their size?
AInsect cells must have a surface area that is proportional to body volume.
BInsects have internal body processes that cause them to grow quickly.
CAn insect cannot function unless it has a minimum number of cells.
DInsect cells are larger than those of most other animals.
9
The lower limit of the insect size range is determined by a number of physical constraints. All animal cells need a supply of oxygen, and organisms that are very minute might be able to get enough oxygen by simple diffusion (movement of oxygen from the air into an organism through openings in the body). This is because a small body has a proportionally greater surface area than volume. The tracheal system of insects is a simple and effective means of gaseous exchange. Spiracles are the openings of the system and airways come in pairs, one spiracle on each side of the body. There is usually one pair per body segment. Spiracles are connected to air sacs and large airways (the tracheae), which then branch and branch getting finer and finer. The finest branches, the tracheoles, are in intimate contact with the tissues and are especially abundant in tissues such as muscles where oxygen demand is high. Interestingly.no matter how big or small the insect. the thinnest tracheoles always have a diameter of 0.2 nanometers. [■] If the tubes were narrower than this, oxygen molecules would simply not diffuse any further along them. [■] Evolution has produced a tube diameter that is just right. [■] A small insect can have a small number of tracheoles, but they cannot be any finer than 0.2 nanometers.[■]
Look at the four squaresthat indicate where the following sentence could be added to the passage
There is a good explanation for this consistency in minimum diameter size
Where would the sentence best fit？Click on a square sentence to the passage.
10
The success of insect species is party the result of their size.
AInsects are comparatively more powerful than larger organisms, and because of their small size, they have been able to occupy many kinds of ecological niches.
BMechanical challenges and the difficulty of getting oxygen to all the cells by means of simple diffusion are two disadvantages of large size in insects.
CThe lower limits on insect size are determined by the minimum number of cells needed to perform essential functions and physical requirements such as the minimum size of tracheoles.
DScientists abandoned the view that large insects could not exist when fossils from the Carboniferous and Permian periods proved that some insects were once many times larger than today’s insects.
EThe appearance of a new group of predators that ate insects is the likely reason for the eventual decrease in insect size over time.
FIt remains unclear whether today’s insects are as small as insects can be or whether further body modifications are possible that would allow insects to become even smaller.
