Class 7 Science Chapter 7- Weather, Climate, Adaptations

According to the weather cycle and climate of a particular place, adaptation of body occurs in animals to live in that place.

WEATHER

• The day-to-day condition of the atmosphere at a place with respect to the temperature, humidity, rainfall, wind speed, etc., is called the weather at that place.
• The temperature, humidity, and other factors are called the elements of the weather. The weather of a place changes day after day and week after week.
• The weather is such a complex phenomenon that it can vary over very short periods of time.
• The maximum and minimum temperatures are recorded every day. There are special thermometers for this purpose, called maximum and minimum thermometers.
• The maximum temperature of the day occurs generally in the afternoon while the minimum temperature occurs generally in the early morning.
• Rainfall is measured by an instrument called the rain gauge. It is basically a measuring cylinder with a funnel on top to collect rainwater.
• The weather reports are prepared by the Meteorological Department of the Government. This department collects data on temperature, wind, etc., and makes the weather prediction.
• In winters it becomes dark early. Days are shorter in winter than in summer.

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THE SUN AND THE WEATHER

The sun is the primary source of energy that causes changes in the weather. Energy absorbed and reflected by the earth’s surface, oceans and the atmosphere play important roles in determining the weather at any place.

CLIMATE

• Meteorologists record the weather every day. The records of the weather have been preserved for the past several decades. These help us to determine the weather pattern at a place. The average weather pattern taken over a long time, say 25 years, is called the climate of the place.
• If we find that the temperature at a place is high most of the time, then we say that the climate of that place is hot. If there is also heavy rainfall on most of the days in the same place, then we can say that the climate of that place is hot and wet.
• The mean temperature for a given month is found in two steps. First we find the average of the temperatures recorded during the month. Second, we calculate the average of such average temperatures over many years. That gives the mean temperature.
• In the western region of India, for example Rajasthan, the temperature is high during most part of the year. But during winter, which lasts only for a few months, the temperature is quite low. This region receives very little rainfall. This is the typical desert climate. It is hot and dry.
• The northeastern India receives rain for a major part of the year. Therefore, we can say that the climate of the north-east is wet.

CLIMATE AND ADAPTATION

• Climate has a profound effect on all living organisms.
• Animals are adapted to survive in the conditions in which they live. Animals living in very cold and hot climate must possess special features to protect themselves against the extreme cold or heat.
• Adaptation- Features and habits that help animals to adapt to their surroundings are a result of the process of evolution.

(i) Adaptation in polar regions

• The polar regions present an extreme climate. These regions are covered with snow and it is very cold for most part of the year. For six months the sun does not set at the poles while for the other six months the sun does not rise. In winters, the temperature can be as low as –37°C. Animals living there, like polar bears and penguins, have adapted to these severe conditions.
• Polar bears have white fur so that they are not easily visible in the snowy white background. It protects them from their predators. It also helps them in catching their prey. To protect them from extreme cold, they have two thick layers of fur. They also have a layer of fat under their skin. In fact, they are so well-insulated that they have to move slowly and rest often to avoid getting overheated.
• Physical activities on warm days necessitate cooling. So, the polar bear goes for swimming. Its paws are wide and large, which help it not only to swim well but also walk with ease in the snow. While swimming under water, it can close its nostrils and can remain under water for long durations. It has a strong sense of smell so that it can catch its prey for food.
• Another well-known animal living in the polar regions is the penguin. It is also white and merges well with the white background. It also has a thick skin and a lot of fat to protect it from cold. Penguins are also good swimmers. Their bodies are streamlined and their feet have webs, making them good swimmers.
• Other animals living in the polar regions are many types of fishes, musk oxen, reindeers, foxes, seals, whales, and birds. Fish can remain under cold water for long, but birds must remain warm to survive. They migrate to warmer regions when winter sets in. They come back after the winter is over.
• India is one of the destinations of many of these birds. The Siberian crane that comes from Siberia to places like Bharatpur in Rajasthan and Sultanpur in Haryana, and some wetlands of north east and some other parts of India.

Some migratory birds travel as much as 15000 km to escape the extreme climatic conditions at home. Generally they fly high where the wind flow is helpful and the cold conditions allow them to disperse the heat generated by their flight muscles. But how these birds travel to the same place year after year is still a mystery. It seems that these birds have a built–in sense of direction and know in which direction to travel. Some birds probably use landmarks to guide them. Many birds may be guided by the sun during the day and stars at night. There is some evidence that birds may use the magnetic field of the earth to find direction. And it is not only birds that migrate; mammals, many types of fish and insects are also known to migrate seasonally in search of more hospitable climates.

(ii) Adaptation in the tropical rainforests

• The tropical region has generally a hot climate because of its location around the equator. Even in the coldest month the temperature is generally higher than about 15°C. During hot summers, the temperature may cross 40°C. Days and nights are almost equal in length throughout the year. These regions get plenty of rainfall.
• An important feature of this region is the tropical rainforests. Tropical rainforests are found in Western Ghats and Assam in India, Southeast Asia, Central America and Central Africa.
• Because of continuous warmth and rain, this region supports wide variety of plants and animals. The major types of animals living in the rainforests are monkeys, apes, gorillas, tigers, elephants, leopards, lizards, snakes, birds and insects.
• The climatic conditions in rainforests are highly suitable for supporting an enormous number and a variety of animals.

Rainforests cover about 6% of the earth’s surface, but they have more than half of the animal life and about two-thirds of the flowering plants of the planet. However, much of this life is still unknown to us.

• Since the numbers are large, there is intense competition for food and shelter. Many animals are adapted to living on the trees. Red-eyed frog has developed sticky pads on its feet to help it climb trees on which it lives. To help them live on the trees, monkeys have long tails for grasping branches. Their hands and feet are such that they can easily hold on to the branches.
• As there is competition for food, some animals are adapted to get food not easily reachable. A striking example is that of the bird Toucan, which possesses a long, large beak. This helps a toucan to reach the fruits on branches which are otherwise too weak to support its weight.
• Many tropical animals have sensitive hearing, sharp eyesight, thick skin and a skin colour which helps them to camouflage by blending with the surroundings. This is to protect them from predators. For example, big cats (lions and tigers) have thick skins and sensitive hearing.
• The lion-tailed macaque (also called Beard ape) lives in the rainforests of Western Ghats Its most outstanding feature is the silver-white mane, which surrounds the head from the cheeks down to its chin. It is a good climber and spends a major part of its life on the tree. It feeds mainly on fruits. It also eats seeds, young leaves, stems, flowers and buds. This beard ape also searches for insects under the bark of the trees. Since it is able to get sufficient food on the trees, it rarely comes down on the ground.
• Another well-known animal of Indian tropical rainforest is the elephant. It has adapted to the conditions of rainforests in many remarkable ways. It uses its trunk as a nose because of which it has a strong sense of smell. The trunk is also used by it for picking up food. Moreover, its tusks are modified teeth. These can tear the bark of trees that elephant loves to eat. So, the elephant is able to handle the competition for food rather well. Large ears of the elephant help it to hear even very soft sounds. They also help the elephant to keep cool in the hot and humid climate of the rainforest.Read More…
  

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  [Source : NCERT]