Showing posts with label TEXT-CBSE-VI BIOLOGY. Show all posts
Showing posts with label TEXT-CBSE-VI BIOLOGY. Show all posts

Saturday, January 9, 2021


I n our daily life, there are many instances when we notice a substance being separated from a mixture of materials. Tea leaves are separated from the liquid with a strainer, while preparing tea. Grain is separated from stalks, while harvesting. Milk or curd is churned to separate the butter. As we learned in Chapter 3, we gin cotton to separate its seeds from the fibre 

Perhaps you might have eaten salted daliya or poha. If you found that it had chillies in it, you may have carefully taken them out before eating. Suppose you are given a basket containing mangoes and guavas and asked to separate them. What would you do? Pick out one kind and place them in a separate container, right? Seems easy, but what if the materials than mango or guava? Imagine you are given a glass of sand with salt mixed in it. Impossible, even to think of separating salt from this mixture by picking out grains of sand by hand! 

The process with its purpose and the way separated components are used? We see that, before we use a substance, we need to separate harmful or non-useful substances that may be mixed with it. Sometimes, we separate even useful components if we need to use them separately. The substances to be separated may be particles of different sizes or materials. These may be in any three states of matter i.e., solid, liquid or gas. So, how do we separate substances mixed together if they have so many different properties? 

METHODS OF SEPARATION: We will discuss some simple methods of separating substances that are mixed together. You may come across some of these methods being used in day to day activities. 
Homogeneous mixtures :Mixture in which the particles of the substance present cannot be seen are called homogeneous mixtures. For example, solution of sugar and water, air, cold drinks.

Heterogeneous mixtures: Mixture in which particles of the substances present can be seen easily are called heterogeneous mixtures. For example, water in oil, dust in air.

Solution: When a soluble substance is dissolved completely in a liquid (say sugar in water). A homogeneous mixture is formed. It is known as solution.

Saturated solution: A solution in which no more soluble substance can be dissolved at room temperature is called saturated solution.

Need for separation: We carry out the separation of the components of a mixture or an impure substance with the following purposes :
(i) To remove the unuseful or harmful component.
(ii) To obtain the useful component.
(iii) To remove impurities for getting a pure sample.

Principle of separation
1. The substances present in a mixture retain their original properties like particle size, density, melting point, boiling point, volatility, etc.
2. We use the difference in anyone of these properties in the components of a mixture to separate them. 

Methods of separation: Hand picking, winnowing, sieving, magnetic separation, sedimentation, decantation, loading, filtration, evaporation, sublimation, distillation, churning, etc. are some common methods of separation. 
Handpicking: This method is used for separating small particles of dirt, stone, husk etc. from the grains of wheat, rice, pulses, etc. 

Sieving: You might have seen your mother use a sieve to separate impurities and bran from flour before using it. The separation techniques of sieving are mainly used in a flour mill to separate impurities from wheat before grinding it. Sieving removes impurities like stones, stalk, and husk that still remain after threshing and winnowing. The sieve only removes particles of impurities that are larger than the pores in the sieve. Therefore, we can design the sieve according to our need. (i) Sieving is used when two component of a mixture have different particle size. (ii) Sieving allows the fine particles to pass through the holes of the sieve, while the bigger particles remain on the sieve. For examples, sieving of wheat flour, sieving of sand at construction sites. 

Winnowing: Winnowing can be used to separate lighter and heavier components of a mixture. For example : to separate husk from grain with the help of air. Winnowing is used to separate lighter components of the mixture from heavier components by the wind. These separation techniques are commonly used by farmers to separate lighter husk particles from the heavier seeds.The lighter particles are carried away by the wind. The heavier seeds form a heap near the platform of winnowing. We can use either natural wind or blow air while winnowing. 

Threshing: The process that is used to separate grain from stalks is threshing. 

Decantation: It is the transfer of clean liquid from one vessel to other vessel without disturbing the settled (sedimented) particles. 

Loading: It is the process of faster sedimentation by suspending alum to a liquid. 

Filtration: Filtration is used to separate solid particles from liquid by passing the mixture through a filter paper. Filtration is the process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of some substance, called a filter. The liquid which has passed through the filter is called filtrate. The filter may be paper, cloth, cotton-wool, asbestos, slag or glass wool, unglazed earthenware, sand, or any other porous material. 

Evaporation: It is the process of removing water (or moisture) from a mixture either by heating on flame or direct sunlight. For example : salt from sea water is obtained by this method. 

Condensation: The process of conversion of water vapour into its liquid form is called condensation.The process of pouring out a clear liquid from a vessel (after sedimentation) without disturbing the sediments (heavy insoluble settled particles) is called decantation.
The above method has two disadvantages.
(a) It cannot be used for the miscible liquids that dissolve in one another. For example, petrol mixed in kerosene oil or salt or sugar solution in water.
(b) During the process of decantation, a small quantity still remains unseparated thus it gets wasted.  

Churning (or centrifugation): It is the process of separation of the lighter particles of a suspended solid from a liquid. For example : to obtain butter from the curd or milk. 

Crystallisation: The process of crystallization is used for obtaining pure crystallive substance from impure sample. 

Sedimentation: It is the process of settling of heavy solid particles in a mixture at the bottom of the vessel. This process is based on the densities of different components of a mixture. The process of setting down of heavy insoluble particles in a mixture of water and insoluble substances is called sedimentation. 

Coagulation or Loading
Coagulation is the process of improving the settling property of solids by addition of specific chemicals. When solid particles present in a mixture are not heavy enough to settle easily, some chemicals can be added to the mixture to enable the solids to settle. For example, when alum is added to dirty water, it attaches itself to the dirt particles and makes several dirt particles stick to each other. This makes them heavier and helps them to settle down. Alum is said to be a coagulating agent.

Distillation is a process of separating the component of substances from a liquid mixture by selecting evaporation and condensation. 

Saturated Solutions: A solution in which no more substance can be dissolved at a given temperature is called a saturated solution. Characteristics of a Solution:
• A solution is a homogeneous mixture of two or more substances.
• The particles of solute in a solution cannot be seen by naked eye.
• A solution is stable.
• The solute from a solution cannot be separated by filtration (or mechanically).
Solute: A substance dissolved in another substance, water (or any other solvent) is called solute.                    


Wednesday, January 6, 2021


Paheli and Boojho went on vacation to many places of interest. One such trip took them to the river Ganga in Rishikesh. They climbed the mountains of the Himalayas, where it was very cold. They saw many kinds of trees on these mountains — oaks, pines and deodars, very different from the ones near their home on the plains! In yet another trip, they travelled to Rajasthan and moved on camels through the hot desert. They collected different kinds of cactus plants from this trip. Finally, they went on a trip to Puri and visited the sea beach, dotted with casuarina trees. While recollecting all the fun that they had on these trips, a thought struck them. All these places were so different from one another, some were cold, some very hot and dry, and some places so humid. And yet all of them had many organisms (living creatures) of various kinds. 

Different regions in the world have various types of living creatures called organisms. An organism is simply defined as any living thing, ranging from microscopic bacteria to large elephants and everything in between. Different types of plants and animals are found in different areas. E.g. deserts have camel and cacti as plants. Beaches show coconut trees and crabs. Fishes and other marine animals inhabit the sea. 

We see many things around us, which can be grouped into two groups based on their characteristics- living things and non-living things. for example men, dogs, goats, cats, ants, plants, trees, etc. are some of the living things. Car, plastic goods, stones, doors, etc. are some of the non-living things. 

Adaptation: In all this variety of organisms, we will find that they have certain features that help them live in the surroundings in which they are normally found. The presence of specific features or certain habits, which enable an organism to live naturally in a place is called adaptation. Adaptation of organisms differ depending on their place of dwelling. That is why a fish cannot live out of water and a camel cannot live in sea.

Habitat: The surrounding in which a living being lives is called its habitat. For example; the pond is the habitat for a frog. Our home is our habitat. A tree is the habitat for a squirrel. The place where organisms live is called habitat. Habitat means a dwelling place (a home). The habitat provides food, water, air, shelter and other needs to organisms. Several kinds of plants and animals live in the same habitat. The plants and animals that live on land are said to live in terrestrial habitats. Some examples of terrestrial habitats are forests, grasslands, deserts, coastal and mountain regions. On the other hand, the habitats of plants and animals that live in water are called aquatic habitats. Lakes, rivers and oceans are some examples of aquatic habitats. There are large variations among terrestrial habitats like forests, grasslands, deserts, coastal and mountain regions located in different parts of the world. 
Types of Habitat: There are two main types of habitat, viz. terrestrial habitat and aquatic habitat. 
Terrestrial Habitat: The habitat on land is called as terrestrial habitat. The terrestrial habitat can be further categorized as forests, grasslands, coastal, mountain and desert habitats. 

Aquatic Habitat: The habitat in water is called aquatic habitat. The aquatic habitat can be further categorized as ocean, rivers, lakes, ponds and swamps. 

Components of Habitat 
There are two main components of a habitat, viz. biotic and abiotic. 
Biotic Component: The living beings make the biotic component of a habitat. Plants and animals are examples of biotic components. 
Abiotic Component: The non-living things make the abiotic component of a habitat. Soil, air, water, temperature are the abiotic components. Abiotic components provide necessary raw materials and conditions for the living beings to survive. For example; most of the plants need soil for anchorage. Moreover, soil also provides them with water and necessary minerals. Most of the terrestrial animals live on soil. Similarly, water and air are necessary for living beings to survive. 

Some Terrestrial Habitats Deserts We discussed the abiotic factors of a desert and the adaptations in camels. What about other animals and plants that are found in deserts? Do they have the same kind of adaptations? 

Terrestrial Habitats: It refers to land where all plants and animals survive. Animals and plants which live on land are called as Terrestrial animals and Terrestrial plants. 
Terrestrial habitat further classified into: Forests, Grasslands, Deserts, Mountain & Polar region 

Grasslands: Many animals live in the grasslands and in forests. The climate is warm and food is available in good amount. But because of heavy population, the competition for food and other resources is tough in the grasslands and forests. Let us take the example of some animals to understand adaptation for grasslands. 

A lion lives in a forest or a grassland and is a strong animal that can hunt and kill animals like deer. It is light brown in colour. How are the eyes placed in the face for these two animals? Are they in the front or on the side of the face? Lions have long claws in their front legs that can be withdrawn inside the toes. Do the features of a lion help it in any way to survive? 
Lion: A lion is a ferocious hunter. It is strong because of muscular body. The sharp claws of lions help them in killing a prey. These claws retract inside when they are running and thus a lion can walk without making a noise. The colour of lion is pale yellow which mixes with the colour of dry grasses and rocks. Thus the body colour of lion helps it in hiding from its prey. It’s light brown colour helps it to hide in dry grasslands when it hunts for prey (animals to eat). The eyes in front of the face allow it to have a correct idea about the location of its prey. 

A deer is another animal that lives in forests and grasslands. It has strong teeth for chewing hard plant stems of the forest. A deer needs to know about the presence of predators ( animals like lion that make it their prey ) in order to run away from them and not become their prey. It has long ears to hear movements of predators. The eyes on the side of its head allow it to look in all directions for danger. The speed of the deer helps them to run away from the predators. There are many other features of a lion, a deer or other animals and plants that help them to survive in their habitat. Deer is a fast runner. It can sprint very fast to save its life from a predator. A deer has very good hearing ability which helps it in hearing the steps of an approaching predator. 

In the sea, plants and animals are surrounded by saline (salty) water. Most of them use the air dissolved in water. There is very little water available in the desert. It is very hot in the day time and very cold at night in the desert. The animals and plants of the desert live on the desert soil and breathe air from the surroundings. The sea and the desert are very different surroundings and we find very different kind of plants and animals in these two regions, isn’t it? Let us look at two very different kind of organisms from the desert and the sea – a camel and a fish. 

Desert Habitat 
Some examples of adaptation of living beings in the desert are as follows: 
Adaptations in Camel: Camels are synonymous with hot deserts. A camel shows many adaptations which help it to live in the hot desert. The body structure of a camel helps it to survive in desert conditions. Camels have long legs which help to keep their bodies away from the heat of the sand (Fig. 9.2). They excrete small amount of urine, their dung is dry and they do not sweat. Since camels lose very little water from their bodies, they can live for many days without water. 

The padded feet of camels help it in easily walking on the sand. A camel has long eyelashes which prevent the sand from getting into its eyes. A camel can drink lots of water at one go and can go on for many days without drinking water. 

Small creatures; living in deserts; have hard scales on their body which help in preventing the loss of water due to heat. Desert animals like rats and snakes, which do not have long legs that a camel has. To stay away from the intense heat during the day, they stay in burrows deep in the sand (Fig 9.4). These animals come out only during the night, when it is cooler. 

Adaptations in Desert Plants: 
Desert plants lose very little water through transpiration. The leaves in desert plants are either absent, very small, or they are in the form of spines. This helps in reducing loss of water from the leaves through transpiration. The leaf-like structure you see in a cactus is, in fact, its stem (Fig. 9.5). Photosynthesis in these plants is usually carried out by the stems. The stem is also covered with a thick waxy layer, which helps to retain water in the tissues of cacti. Most desert plants have roots that go very deep into the soil for absorbing water. 

Desert plants have very deep roots so that they can access water from great depths. Leaves of some desert plants are modified into spine-like structures. This helps in preventing water loss by way of transpiration. Stems of some desert plants are modified into leaf-like structures. Such stems are spongy and have a coating of wax over them. The wax coating prevents evaporation and spongy inside helps in storing lot of water. 

Forest habitat: Forests and woodlands are places where there are mostly trees. There are many different kinds of forests in different climates, but trees are the one thing they have in common! Forests provide everything that the creatures who live there need – food, water and shelter. Forests can be hot or cold, with different kinds of trees in different climates around the world. There are deciduous forests, coniferous forests, and rainforests 

Raccoons live in forests, among other places. Raccoons often make their dens in trees. They sleep during the day and move around at night. They eat almost anything, including plants, bugs, and small animals. Babies are born in the spring. After a few months, they begin going out at night with their mothers. She teaches them how to feed themselves and stay safe. They remain with her for many months. Raccoons are an important part of the forest habitat! 

Mountain Regions: These habitats are normally very cold and windy. In some areas, snowfall may take place in winters. There is a large variety of plants and animals living in the mountain regions. Have you seen the kind of trees. If you live in a mountain region or have visited one, you may have seen a large number of such trees. But, have you ever noticed such trees naturally growing in other regions? How are these trees adapted to the conditions prevailing in their habitat? 

These trees are normally cone shaped and have sloping branches. The leaves of some of these trees are needle-like. This helps the rainwater and snow to slide off easily. There could be trees with shapes very different from these that are also present on mountains. 

Animals living in the mountain regions are also adapted to the conditions there. They have thick skin or fur to protect them from cold. For example, yaks have long hair to keep them warm. Snow leopard has thick fur on its body including feet and toes. 

This protects its feet from the cold when it walks on the snow. The mountain goat has strong hooves for running up the rocky slopes of the mountains. As we go up in the mountainous regions, the surroundings change and we see different kinds of adaptations at different heights. 

Polar Habitat: Polar habitats are located at the very top and very bottom of the Earth. They are cold, windy and have a lot of snow and ice. It’s too cold for trees to grow, but there are some plants such as moss and lichen in tundra areas. 

Most are carnivores due to the lack of plants and they tend to live in snow caves or holes for shelter. The animals are mostly carnivores and have thick fur to survive in cold. Some blend in ice and some may hibernate in the coldest months. Examples of animals are polar bears, reindeers, penguins etc. 

Rainforest: This habitat receives a lot of rain and hence it’s rich in animal life. Mammals, Amphibians, Reptiles all sorts of animals are found here. The climate is hot and humid and animals have to learn to adapt to survive. 
Aquatic Habitats 
An aquatic habitat is a habitat with water. It includes areas that are permanently covered by water and surrounding areas that are occasionally covered by water. Estuaries, rivers, and marshes are examples of aquatic habitats. 

Marine Habitat: Marine Habitat comprises of oceans and seas, and both have saltwater. They are home to a wide variety of creatures like the most part of fish population is found here. 

Marine Mammals like whales migrate to long distances in order to cope up with the temperature changes. Other types are fish, including bony fish such as groupers an cartilaginous fish such as sharks and rays. 

Oceans Habitat: Many other sea animals have streamlined bodies to help them move easily in water. There are some sea animals like squids and octopus, which do not have this streamlined shape. They stay deeper in the ocean, near the seabed and catch any prey that moves towards them. However, when they move in water they make their body shapes streamlined. These animals have gills to help them use oxygen dissolved in water. In this habitat, plants and animals are surrounded by saline (salty) water. Most of them use the air dissolved in water. 

All fish have a streamlined shape. This helps them move inside water. They have slippery scales on their bodies which protect them and help in easy movement through water. They have flat fins and tails that help them to change directions and keep their body balanced in water. Gills present in the fish help them to use oxygen dissolved in water. 

Squids and octopus do not have a streamlined shape. They stay deeper near the seabed and catch any prey that moves towards them. However, when they move in water they make their body shapes streamlined. 

Dolphins and whales do not have gills. They breathe in air through nostrils or blowholes located on the upper parts of their heads. This allows them to breathe in air when they swim near the surface of water. They can stay inside the water for a long time without breathing. 

Freshwater Habitat: Rivers, lakes, ponds etc comprise the freshwater habitats. Three percent of world’s water is accounted as freshwater but still a wide variety of species are found here. Snails, worms, mollusks etc are found in this habitat. Ponds and lakes Have you seen plants growing in ponds, lakes, rivers and even some drains? Go on a field trip to a nearby pond, if possible, and try to observe the kinds of plants that are seen there. Observe the leaves, stems and roots of these plants. Some of these plants have their roots fixed in the soil below the water In terrestrial plants, roots normally play a very important role in the absorption of nutrients and water from the soil. 

However, in aquatic plants, roots are much reduced in size and their main function is to hold the plant in place. The stems of these plants are long, hollow and light. The stems grow up to the surface of water while the leaves and flowers, float on the surface of water. Some aquatic plants are submerged in water. All parts of such plants are under water. Some of these plants have narrow and thin ribbon-like leaves. These can bend in the flowing water. In some submerged plants, leaves are often highly divided, through which the water can easily flow without damaging them. Frogs usually live in ponds. Frogs can stay both inside the water as well as move on land. They have strong back legs that help them in leaping and catching their prey. They have webbed feet which help them swim in water. 

FLOATING PLANTS: Some aquatic plants float on water, some plants have their roots fixed in the soil below the water, while some are completely submerged in water (like Hydrilla). Totally submerged plants have narrow and ribbon like leaves (tape grass). These can bend in flowing water. Some Water plants float on the surface of water. (like Water Lily, Lotus, Water Hyacinth). Roots are much reduced in size, since their main function is to hold the plant in place. 
Leaves of floating plants are large and flat with waxy coating on them. The leaves of such plants are spongy as well; with lot of air inside. This helps the leaves in floating on water. They have waxy on the upper surfaces that make them waterproof. They have stomata on the upper surfaces which are exposed to air. 
Stems of aquatic plants are long, hollow and light so that these can bend in along with water movement (Water Lily). The stems grow up to surface of water, while the leaves and flowers float on surface of water. Stems have air spaces to enable the plant to float. 

Frogs are adapted to live both on land and water, they have strong back and legs and webbed feet which allows them to swim in water. 

Coastal Habitat: This type of habitat is seen in rocky or sandy areas, this habitat provide homes to both land and sea animals. The changing tides are one of the most unique features of the coastal habitat, as the habitat changes from open air to underwater on a regular basis. Some animals that live in the sea will visit land for egg laying. 

Some coastal animals can survive under water or out of water. Many fish, reptiles and invertebrates live their life along the coast. Birds are numerous on the coast because there is a reliable source of food there. Special type of trees called mangroves are found in this habitat. Coastal plants like seaweed attach to the rocks firmly. so that they are not swayed by the waves. 

Acclimatisation: The ability of an organism to make small adjustments or changes in the body in a short period of time to adjust itself to the surrounding atmospheres is called as Acclimatisation.  For e.g: The changes which take place in the body when we travel from plains to mountains. The adjustment which the body makes is called Acclimatisation 

  Characteristics of Living Organisms 
Plants are living things, but they do not appear to move like a dog or a pigeon. On the other hand, a car or a bus can move, yet we consider them as non-living. So there are certain characteristics that differentiate living from nonliving- 
Living beings are made of cells. Living beings obtain and use energy. Living beings grow and develop. Living beings reproduce. Living beings adapt to their environment. Living beings respond to their environment or stimuli.

Let’s explore the important characteristics of living organisms one by one. 
Nutrition: The process by which animals obtain food and utilize it for all the activities is called as nutrition. Every organism requires nutrition for obtaining energy. 

Growth: All living organisms grow and exhibit growth in different ways. Their body cells divide and grow and thus overall growth is attained. 

Respiration: Respiration is necessary for all living organisms. It is through respiration that the body finally obtains energy from the food it takes. Some animals may have different mechanisms for the exchange of gases, which is a part of the respiration process.  E.g. earthworms breathe through their skin and fish have gills for using oxygen dissolved in water.  In humans, we respire by breathing in oxygen breathing out the carbon dioxide. 

Response to Stimulus: Changes in our surroundings that makes us respond to them are called stimuli. All living beings react to changes in their surroundings. E.g. In response to increased temperature in summer, we use fans to cool our homes. 

All living things take food. Not all the food that is eaten is really used, only a part of it is utilised by the body. Unused/remaining food becomes waste and needs to be excreted. Our body also produces some wastes, like urea, in other life processes. Living organisms get rid of all this waste material and the process is known as excretion. 

Reproduction: All living organisms give rise to a new organism of their own kind, by a process called reproduction. The mode of reproduction may be different, in different animals and plants. Some animals produce their young ones through eggs. Some animals give birth to the young ones. Plants produce seeds which germinate into new plants. Some plants also reproduce through parts other than seeds. E.g: a part of a potato with a bud, grows into a new plant