मकड़ियाँ कैसे सहायक होती हैं?

बहुत से लोग मकड़ियों से घृणित करते हैं या उनसे डरते हैं क्योंकि वे इन आठ पैरों वाले जीवों के बारे में ज्यादा नहीं जानते। हालाँकि, मकड़ियों की कुछ प्रजातियाँ जो मनुष्यों के लिए हानिकारक हैं। लोकप्रिय धारणा के विपरीत, मकड़ियाँ स्वयं कीट नहीं होतीं, बल्कि कीड़ों को खाती हैं। वे जाले बुनते हैं, जिसमें उनके शिकार जैसे मक्खियां, मच्छर और अन्य कीड़े फंस जाते हैं। 

मकड़िया  अक्सर हमें परेशान करने वाले कीड़ों को खाकर मदद करते हैं। मकड़ियों के बिना, हमारे आसपास बहुत अधिक कीड़े होगें । जो हमें बहुत ज्यादा परेशान करते हैं। इस तरीके से मकड़िया हमे   सहायता करती हैं।

 पौधे भोजन कैसे प्राप्त करते हैं?

जंतुओं के विपरीत, पौधे अपना भोजन स्वयं बनाते हैं। हरे पौधे पानी, पोषक तत्वों का उपयोग करते हैं। उनके भोजन का उत्पादन करने के लिए उनकी पत्तियों में 'क्लोरोफिल' नामक हरा पदार्थ होता है। सामान्य रूप से पानी और पोषक तत्व जमीन से उनकी जड़ों के माध्यम से अवशोषित होते हैं। 

हालाँकि, कुछ पौधों ने पानी और पोषक तत्त्व प्राप्त करने के तरीके  विकसित किए हैं। कई पेड़-आवास पौधे फ़नल के आकार बनाते हैं। उनके पत्तों के साथ 'कंटेनर' बनाते हैं। नरभक्षी पादप उनके पाचक रसों का उपयोग करते है। उसमें पकड़े गए कीड़ों को पोषक तत्त्व में परिवर्तित करते है।

 How are spiders helpful?

Many people find spiders disgusting or are afraid of them because they not know much about these eight-legged creatures. However, there are very few species of spiders that are harmful to humans. Contrary to popular belief, spiders are not insects themselves, but feed on insects. 

They weave webs, in which their prey like flies, mosquitoes, and other insects get stuck. Spiders help us by eating insects that often annoy us. Without the spiders, there would be a lot more insects around us.

 How do plants get food?

Unlike animals, plants produce their own food and except for a few carnivorous plants, do not eat other organisms. Green plants use water, nutrients, and a green matter in their leaves called 'chlorophyll' to produce their food. Normally water and nutrients are absorbed from the ground through their roots. 

Some plants, however, have developed other methods for obtaining water and nutrients. Many tree-dwelling plants make funnel-shaped 'containers' with their leaves to catch water. Carnivorous plants use their digestive juices to convert the insects, caught in their folding or sticky traps, into nutrients.

What does 'survival of the fittest' mean?

'Survival of the fittest' describes the evolution theory of Charles Darwin. In the struggle to survive, the species that are healthy, strong, and have adapted themselves best to their environment will win. They ensure their survival through healthier genetic material that is passed on to their offspring. 

Thus, a giraffe with a longer neck can reach leaves high on the trees to feed himself. While a giraffe with a shorter neck may stay hungry, since he has access only to the leaves lower on the tree. Eventually,
the hungry giraffe may become so weak that he falls prey to lions.

 Why do environmental conditions change?

There are many reasons for changes in the environment. Environmental change can be sudden because of a meteorite impact or a volcanic eruption or it can be gradual like a
change in the climate. In the history of the Earth, there have been many sudden changes. Dust clouds and pollution darken and poison the
world and cause catastrophes. 

Slow changes in the environment such as changes in the sea level, ice ages, or torrential rains can be due to different reasons. For instance, parts of the earth are lifted as a result of the displacement of tectonic plates and therefore sea coasts shift. Today,  he environmental changes are mainly due to irresponsible human actions such as draining of marsh areas, cutting of trees, and air pollution.

 What is an 'ecological niche'?

The ecological niche describes a way of living that provides a species with adequate nutrition, an optimum environment, and as few enemies as possible. For instance, several different species of water birds can live together peacefully on the sea because each species prefers a different food or hunts for its food at different depths in the water. 

The birds do not prey on each other's food, and hence are not natural enemies. We can also say that this particular animal species has become specialized.

 Why did dinosaurs become extinct?

Dinosaurs existed on Earth 65 million years ago. Today, the scientists believe that their mass extinction was triggered by a huge meteorite hit to the east of Mexico. The meteorite impact caused blasts and flood waves. Huge quantities of poisonous gases filled the Earth's atmosphere. Then there was acid rain that polluted the seas and the plants died. Huge dust clouds blocked the heat from the sun and it became cold. The cold-blooded dinosaurs became sluggish and starved. Young ones did not hatch from their eggs. Only the small animals, which adapted themselves quickly and did not need a lot of food, survived.

 What is threatening the grey whales?

The grey whale lived around 300 years ago in the Atlantic and Pacific Oceans. The giant animals were hunted extensively for their meat and oil. They became extinct in the Atlantic by the end of the 17th century, but can still be found in the Pacific Ocean. Around 20,000 animals migrate every year in October from Alaska in the north to the coast of Mexico, where they give birth to their young ones in winter.

In west pacific, there are at most 200 grey whales at present and they are listed as critically  endangered These animals are sensed to noise and are being displaced from their habitat because of the construction of drilling rigs for the crude oil industry.

 Why are elephants hunted?

Elephants are hunted for their tusks. These are made of ivory and were used to make jewellery sold at high prices. Many elephants were shot for their tusks, and even today they have to be protected from poachers in wildlife parks. Other animals are also hunted for their body parts. 

The Asian black bear is hunted for its gal bladder, rhinos for their horns, seals and big cats for their skin. A few wild species of crocodiles are killed because their skin is used for making bags and shoes. Hunting is also done for the thrill of the chase and a greed for the trophy, such as a bear or tiger skin.