science

1. AMPHIBIANS
characteristics:
 Amphibians have a backbone. ...
 Amphibians are cold-blooded. ...
 Amphibians spend at least part of their lives in water and on land.
 Amphibians do not have scales and their skin is permeable (molecules and gases can
pass through).
HARMFUL EFFECT
Poisonous amphibians are amphibians that produce toxins to defend themselves from predators.
Except certain salamandrid salamanders that can extrude sharp venom-tipped ribs,[1][2]
amphibians
are not known to actively inject venom. Most toxic amphibians are instead known to be poisonous to
touch or eat. Amphibians usually sequester toxins from animals and plants on which they feed,
commonly from poisonous insects or poisonous plants. One example of this is the well-known
poison dart frog. They get a deadly chemical called lipophilic alkaloid from consuming a poisonous
food in the rainforest. They are immune to the poison and they secrete it through their skin as a
defense mechanism against predators. This poison is so efficient, the native people of the South
American Amazon rainforest use the frogs' toxins on their weapons to kill their prey, giving the frogs
their nickname the "poison dart frog". Some people use the bufotoxins of some species of toxic
toads as a drug to get high, but this can become very dangerous. Usually due to the toads' size and
toxicity, the poisons would not be deadly to a fully grown, healthy adult. But if too much of the toxin is
absorbed, or if the person is young or ill, then the poisons can become a serious threat. It also
depends on species: some amphibians do have toxins strong enough to kill even a healthy mature
person within just a few minutes, while other species may not have toxins potent enough to have any
effect. Licking toads is not biologically practical. For these tryptamines to be orally activated, the
human monoamine oxidase system must be inhibited. Therefore, licking a poisonous amphibian will
not guarantee a sufficient dose.
BENEFICIAL EFFECT
Amphibians as indicators of environmental health and their contribution to humanity
Amphibians profoundlyenhance our lives and our world in countless ways.They provide vital biomedicines,including
compounds thatare being refined for analgesics,antibiotics,stimulants for heartattack victims,and treatments for
diverse diseases including depression,stroke,seizures,Alzheimer’s,and cancer.The Australian red-eyed tree-frog
(Litoria chloris) and relatives give us a compound capable ofpreventing HIV infection,the cause of AIDS.
Amphibians’ thin skins help them drink and breathe,butalso make them susceptible to environmental contaminants,
particularlyagricultural,industrial,and pharmaceutical chemicals.For example,atrazine is the mostwidelyused
herbicide in the US with an estimated 61 to 73 million pounds used per year during the 1990s.Scientific studies have
found that atrazine may cause a variety of cancers and act as an endocrine disruptor,mimicking the feminizing
hormone estrogen and harming human and animal reproductive and hormone systems.Atrazine is generallyapplied
in spring and can accumulate in amphibian breeding pools.Laboratorystudies have shown thatatrazine can
chemicallysterilize tadpoles atlevels well below the EPA maximum allowable level for drinking water.Although
lawsuits broughtagainstthe EPA by the Natural Resources Defense Council date back to 1999, the EPA announced
on October 31 2003 that it had negotiated a deal with industrythat would not require any new restrictions on atrazine
use.
Other organochlorine pollutants (e.g.,DDT, PCBs,dioxins) can also actas endocrine disruptors,inducing similar
feminizing effects in amphibians.It has been demonstrated thatthese responses are occurring in nature,but it is yet
unclear whatlong-term effect they will have on wild populations.Amphibians have been likened to canaries in the
coal mine:justas miners used sensitive canaries to warn them of toxic gases in the mines,amphibians mightbe
warning us of unsafe environmental conditions thatcould eventually seriouslyimpactour health. Could we be

2. similarlyaffected by these widespread endocrine disruptors,or are we already? Atrazine, for example, has been
detected in more than 1 million Americans'drinking water atlevels higher than EPA's drinking water standard.Some
human studies suggestthatthe average sperm countof adultmen in certain populations is significantlydecreased,
as much as 50% of what it was two generations ago.Are we also suffering the same feminizing effects of
agrochemicals,industrial waste,and other estrogen-mimics thatwe see affecting amphibians so
drastically?Amphibians are also vital components oftheir ecosystems.In the 1970s,it was discovered thatthe
northern redback salamander (Plethodon cinereus) was possiblythe mostabundantvertebrate in eastern US forests,
exceeding the biomass ofall the bird or mammal species combined.Amphibians feed primarilyon insects and other
invertebrates.It was estimated thata single population of~1,000 cricket frogs (Acris crepitans) could consume almost
five million invertebrates in one year. Clearly they serve as significantpredators ofsmall invertebrates,as abundant
prey for larger predators,and as a vital link in the food web between the two. In areas of the world where amphibians
have declined,there has been an increase in invertebrate pests thatdamage crops and that carry human diseases.
Amphibians have also played a vital role in human culture.While in some cultures frogs and toads have been
despised and regarded as evil,other cultures have embraced them as life-giving keepers ofthe rains or agents of
fertility and good luck. Some simplyuse them for food. Amphibians have been both cherished and persecuted by
different cultures as characters in fantasystories,ingredients in folk medicine,and as spiritual beings.
Ecological Importance
Amphibians play a pivotal role in ecosystem as secondary consumers in many food chains.
Tadpoles have significant impact in nutritional cycling. They are herbivorous to omnivorous
and are the prey items for both invertebrates and vertebrates. Adult amphibians are the
best biological pest controllers. Invertebrates and vertebrates also predate them. Because
of their importance in ecosystem, decline or extinction of their population has significant
impact on other organisms along with them.
From the ecological perspective, amphibians are regarded as good ecological
indicators. Due to high degree of sensitivity, either during tadpole stage or as adults, they
respond to very slight change in the environment. Such responses have been used to
indicate habitat fragmentation, ecosystem stress, impact of pesticides, and various
anthropogenic activities.