MSBSHSE Class 7 General Science Textbook PDF

 The Coordination Committee formed by GR No. Abhyas - 2116/(Pra.Kra.43/16) SD - 4 Dated 25.4.2016 has given approval to prescribe this textbook in its meeting held on 3.3.2017 GENERAL SCIENCE STANDARD SEVEN...

 The Coordination Committee formed by GR No. Abhyas - 2116/(Pra.Kra.43/16) SD - 4 Dated 25.4.2016 has given approval to prescribe this textbook in its meeting held on 3.3.2017 GENERAL SCIENCE STANDARD SEVEN Maharashtra State Bureau of Textbook Production and Curriculum Research, Pune - 411 004. The digital textbook can be obtained through DIKSHA APP on a smartphone by using the Q. R. Code given on title page of the textbook and useful audio-visual teaching-learning material of the relevant lesson will be available through the Q. R. Code given in each lesson of this textbook. A First Edition : 2017 © Maharashtra State Bureau of Textbook Production and Fifth Reprint : 2022 Curriculum Research, Pune - 411 004. The Maharashtra State Bureau of Textbook Production and Curriculum Research reserves all rights relating to the book. No part of this book should be reproduced without the written permission of the Director, Maharashtra State Bureau of Textbook Production and Curriculum Research, ‘Balbharati’, Senapati Bapat Marg, Pune 411004. Science Subject Committee : Coordination : Dr Chandrashekhar Murumkar, Chairman Rajiv Arun Patole Dr Dilip Sadashiv Jog, Member Dr Abhay Jere, Member Special Officer for Science Dr Sulabha Nitin Vidhate, Member Smt. Mrinalini Desai, Member Shri. Gajanan Suryawanshi, Member Translation : Shri. Sudhir Yadavrao Kamble, Member Smt. Mrinalini Desai Smt. Dipali Dhananjay Bhale, Member Dr Sushma Jog Shri. Rajiv Arun Patole, Member-Secretary Scrutiny : Dr Dilip Jog Science Study Group : Smt. Pushpa Khare Dr Prabhakar Nagnath Kshirsagar Dr Shaikh Mohammed Waquioddin H. Dr Vishnu Vaze Coordination : Dr Ajay Digambar Mahajan Dhanavanti Hardikar Dr Gayatri Gorakhnath Choukade Academic Secretary for Languages Shri. Sukumar Shrenik Navale Shri. Prashant Panditrao Kolse Santosh Pawar Shri. Dayashankar Vishnu Vaidya Assistant Special Officer, English Smt. Kanchan Rajendra Sorate Smt. Anjali Khadke Paper : Smt. Shweta Thakur 70 GSM Creamwove Smt. Jyoti Medpilwar Smt. Pushpalata Gawande Print Order : Shri. Rajesh Vamanrao Roman Shri. Shankar Bhikan Rajput Printer : Smt. Manisha Rajendra Dahivelkar Shri. Hemant Achyut Lagvankar Shri. Nagesh Bhimsevak Telgote Shri. Manoj Rahangdale Production : Shri. Mohammed Atique Abdul Shaikh Sachchitanand Aphale Smt. Dipti Chandansingh Bisht Chief Production Officer Shri. Vishwas Bhave Rajendra Vispute Smt. Jyoti Damodar Karane Production Officer Cover and illustrations : Publisher : Shri. Vivekanand Shivshankar Patil Vivek Uttam Gosavi Ashana Advani Shri. Suresh Gopichand Isave Controller Maharashtra State Textbook Bureau, Typesetting : Prabhadevi, Mumbai - 400 025. DTP Section, Textbook Bureau, Pune B C D  Preface Dear students, Welcome to Std VII. We have great pleasure in offering to you this General Science textbook, based on the new syllabus. In Stds III to V you have acquired some knowledge of Science from your Environment Science textbooks. Last year, however, you began to study Science from a separate General Science textbook. The basic purpose of this textbook can be said to be ‘Understand and explain to others’. You will learn Science through many activities such as Observe and Discuss, Use your brain power ! Find Out, Think about it, etc. Do take part in all these activities. Use the activities Can you recall? and Can you tell? to revise the science you have already learnt. The textbook also includes many activities and experiments under the titles Try this and Let's try this. You must yourself carefully carry out these activities, experiments and observations. Wherever necessary you may, of course, take the help of your teachers, parents or classmates. On some occasions you may have to look for some information. You must use the library or technology like the Internet for that purpose. A number of activities that explain the science behind everyday events, have been given. You too must make your own efforts to use science in everyday life. What you learn from the lessons in this textbook will not only help you with the studies of higher classes, but will also enable you to do many new things and equip you with many new skills. Take all precautions while doing the activities and experiments given in the textbook and encourage others to take the same precautions. Understand Science and learn to use it. Lastly, a gentle reminder to you that, while carrying out activities related to plants and animals, all care must be taken to avoid doing them any harm or causing them injury. Do tell us about the parts that you like as well as about the difficulties you face as you read and understand and study this textbook. We are especially eager to know about the questions that come to your mind as you study science. Do write to us about them. Our best wishes for your academic progress. Pune Date : 28 March 2017 (Dr Sunil Magar) Gudi Padwa Director Indian Solar Year : Maharashtra State Bureau of Textbook Chaitra 7, 1939 Production and Curriculum Research, Pune. E  For Teachers We learn many new facts while studying science. So, young children with a lot of curiosity find the subject enjoyable. However, the real objective of learning science is to learn to think about the world and all the events that take place in it, in an objective and rational manner so as to lead a happy confident life. Through the study of science we also expect children to develop social consciousness, awareness about conservation of the environment and adeptness in handling technology. We need to have adequate factual information and understanding about our world. However, in a rapidly changing world, the knowledge gained today may not suffice tomorrow. Hence, the skills required for obtaining knowledge must be learnt. These are the very skills that are learnt in the process of studying science. Many topics in science are more easily learnt by direct observation than by reading about them. Some abstract phenomena become visible through the effects they have. Hence, we do experiments related to them. They help to learn the skills of inference and verification. While learning science, these skills are learnt and internalized. This is an important objective of learning science. That we should be able to articulate what we have learnt, explain it to others, use it for further studies and finally bring about the proper changes in our behaviour is also an expectation from the learning of science. That is why, it is important to ensure that along with the content of the subject, these skills are also developed. Can you recall? is a section for reviewing the related topics already learnt, while the purpose of Can you tell? is to introduce a topic by bringing together what the children might already know about a topic through their own reading or experience. Try this is meant to give some specific experience while Let’s try this are the parts that teachers must demonstrate to the class. Use your brain power! makes children apply the knowledge gained. Always remember- gives some important instructions or values. The sections Find out, Do you know? and Science watch are to create an awareness of the vast information that cannot be included in the textbook and to inculcate the habit of doing reference work independently. Teachers can see for themselves that this textbook is not meant for reading and explaining but for guiding students to gain knowledge by carrying out the given activities. Reading the textbook after the children have carried out the activities and discussed them in the class will make it easy and will also help to bring together and reinforce what they have already learnt. The attractive pictures will support their efforts to learn. Teachers should prepare well for discussions under Can you tell?, Use your brain power! etc. and for the various activities and experiments. They should maintain an informal atmosphere during such discussions and activities, encourage everyone to participate and make efforts to organize Science Days, presentations in the class, etc. Front Cover : Experiments and activities included in the textbook. F Back Cover : Flamingos and other birds visiting Bhigwan in Pune District.  English General Science - Standard VII - Learning Outcomes Suggested Pedagogical Processes Learning Outcomes The learner is to be provided with The learner — opportunities in pairs/groups/ 07.72.01 Identifies materials and organisms, (such as individually in an inclusive setup and animal fibres; types of teeth; mirrors and lenses) encouraged to - on the basis of observable features, for example, appearance, texture, functions, etc. Explore surroundings, natural 07.72.02 Differentiates materials and organisms such as processes, phenomena using senses viz. digestion in different organisms; unisexual and watching, touching, tasting, smelling, bisexual flowers; conductors and insulators hearing. of heat; acidic, basic and neutral substances, Pose questions and find answers through images formed by mirrors and lenses, etc. on the reflection, discussion, designing and basis of their properties, structure and function. performing appropriate activities, role 07.72.03 Classifies materials and organisms based on plays, debates, use of ICT etc. properties/characteristics, for example, plant and animal fibres, physical and chemical changes. Record the observations during the 07.72.04 Conduct simple investigations to seek answers to activity, experiments, surveys, field queries, for example, extract of coloured flowers trips/field visits, etc. and their uses. Do leaves other than green also Analyse recorded data, interpret carry out photosynthesis? Is white light composed results and draw inference/make of many colours? generalisations and share findings with 07.72.05 Relates processes and phenomenon with causes, peers and adults. for example, wind speed with air pressure, crops grown with types of soil, depletion of water table Exhibit creativity presenting novel ideas, with human activities etc. new designs/patterns, improvisation 07.72.06 Explains processes and phenomenon, for example, etc. processing of animal fibres, modes of transfer of Internalise, acquire and appreciate, heat; organs and systems in human and plants, values such as cooperation, heating and magnetic effects of electric current, collaboration, honest reporting, etc. judicious use of resources, etc. 07.72.07 Write word equation for chemical reactions, for example, acid-base reaction, corrosion, Plan for sky watching/observation photosynthesis, respiration, etc. and record the observation of different 07.72.08 Measures of calculates, for example, temperature, constallations and nakshatras. pulse rate, speed of moving objects, time period of Be aware of and act on the various a simple pendulum, etc. crises and disasters happening in the 07.72.09 To understand scientific concepts by using the surroundings. instruments like microscope, thermosflask, centrifuge. 07.72.10 Awaken (dietary) about the diet and identify food adulteration. 07.72.11 To explain the correlation between the measures of various physical quantities. 07.72.12 Draws labelled diagrams/flow charts, for example, organ systems in human and plants; electric circuits; experimental set ups; life cycle of silk moth, etc. 07.72.13 Plots and interprets graphs, for example, distance time graph, sound frequency-high and low pitch of sound. 07.72.14 Constructs models using materials from surroundings and explains their working, for example, stethoscope, anemometer, electromagnets, Newton’s colour disc, bakery food, magnetic needle, etc.. 07.72.15 Discusses and understands the importance of stories of scientific discoveries. 07.72.16 Applies learning of scientific concepts in day-to- day life, for example, dealing with acidity; testing and treating soil; taking measures to prevent corrosion; cultivation by vegetative propagation; connecting two or more electric cells in proper order in devices; taking measures during and after disasters; suggesting methods for treatment of polluted water for reuse; uses of magnet, preparation of soap and their uses; separating components from mixture, etc. G  07.72.17 Explains the uses of natural resources by classifying them. 07.72.18 Makes efforts to protect environment, for example, following good practices for sanitation at public places; minimising generation of pollutants; planting trees; sensitising others with the consequences of excessive consumption of natural resources, etc. 07.72.19 Exhibits creativity in designing, planning, making use of available resources, etc. 07.72.20 Exhibits values of honesty, objectivity, cooperation, freedom from fear and prejudices. 07.72.21 Remains awaken about famine, flood, cloudburst, lightning strikes, storms, etc. in the circumjacent to prevent them, uses the circumventions in day-to-day life. 07.72.22 Understands the different scientific concepts, process by using different ICT equipments and techniques. 07.72.23 Makes efforts to remove misconceptions related to zodiac signs and Nakshatra by observing the sky. CONTENTS No. Chapters Page No. 1. The Living World : Adaptations and Classification.........................................1 2. Plants : Structure and Function........................................................................10 3. Properties of Natural Resources......................................................................16 4. Nutrition in Living Organisms.........................................................................26 5. Food Safety......................................................................................................34 6. Measurement of Physical Quantities...............................................................41 7. Motion, Force and Work..................................................................................46 8. Static Electricity...............................................................................................51 9. Heat..................................................................................................................58 10. Disaster Management......................................................................................64 11. Cell Structure and Micro-organisms...............................................................71 12. The Muscular System and Digestive System in Human Beings.....................81 13. Changes – Physical and Chemical...................................................................88 14. Elements, Compounds and Mixtures...............................................................92 15. Materials we Use..........................................................................................100 16. Natural Resources..........................................................................................104 17. Effects of Light...............................................................................................113 18. Sound : Production of Sound.........................................................................118 19. Properties of a Magnetic Field.......................................................................126 20. In the World of Stars......................................................................................131 H  1. The Living World : Adaptations and Classification Let’s recall. In what different ways is the diversity in living things seen ? A great variety of plants is found on the earth. Some plants have colourful flowers. Some plants grow in water whereas some are to be found in deserts which have a scarcity of water. Some plants are found only in snowy regions. Some plants cannot be seen without a microscope whereas some are huge in size. Like plants, animals too show diversity. Some are unicellular, others, multicellular. Some are vertebrates whereas others are invertebrates. This world is full of a variety of animals  -   aquatic, terrestrial, amphibian, reptilian, aerial, etc. These observations give rise to the question  - How did this great diversity come into being ? Are the plants and animals from Kashmir and Rajasthan Can you tell ? of the same type ? Can you elaborate on any differences between the two ? Coniferous trees like pine and deodar flourish in snowy regions like Kashmir. However, in the deserts of Rajasthan, plants like cactus and acacia (babhul) are to be found. The camel, a desert animal, is not found in Kashmir. What is the reason for these differences ? Adaptation Gradual changes occur in the body parts and also in the behaviour of organisms which help them to adjust to their surroundings. Such changes are called adaptations. They take place over a long period of time. 1.1 Desert Adaptation in plants Observe and complete the chart. (Include other plants from your own region too.) Plant Habitat Type of Characteristics of leaves Characteristics of root stem Lotus Aquatic Fibrous Large and round with waxy layer Hollow and flexible Cactus Banyan Adaptation in aquatic plants Visit various water bodies such as a river, brook, pond, lake, in your surroundings. What differences do you observe between Try this. terrestrial and aquatic plants ? 1  Some of the aquatic plants are firmly rooted in the soil at the bottom of the water bodies. Their stems are submerged, while leaves and flowers float on the surface. However, some plants are entirely afloat. Their roots are not anchored in the soil. The surfaces of leaves and stems of many aquatic plants are covered with a waxy layer. Leaves of some aquatic plants are thin and slender like a ribbon. This shape helps them to withstand fast currents of water. Air spaces in stems and petioles of aquatic plants are useful for floating in water. 1.2 Aquatic plants Use your brain power ! 1. Why does water trickle off lotus leaves ? 2. Why don’t the leaves of these plants rot in water ? 3. Why are their roots short and fibrous ? 1.3 Lotus stalk Adaptation in desert plants Take two potted plants - one, a cactus and the other, a leafy plant. Tie plastic bags loosely around the leaves of these plants Try this. and keep them in sunlight from early in the morning. In the afternoon, bring those pots into the classroom and observe them. Has the same quantity of water collected in both bags ? Desert plants are either leafless or their leaves are like small needles or have been modified into thorns. As a result, they lose very little water by evaporation. The stem stores water and food and is therefore fleshy. The stems are green as they perform photosynthesis in the absence of leaves. Their roots penetrate deep into the soil and some roots spread away into the soil in search of water. There is a thick layer of a waxy 1.4 Cactus substance on the stems of these plants, too. 2 Adaptation in plants of snowy regions In what way are sloping branches useful to plants Can you tell ? in a snowy region ? Plants of snowy regions mainly include conifers like deodar and pine. These trees are conical in shape due to their sloping branches. In the heavy snowfall and extreme cold in these regions, their conical shape prevents the snow from accumulating on the tree and the thick bark helps the tree to withstand the cold. 1.5 Deodar tree Adaptation in plants of forest regions A variety of plants - trees, shrubs and herbs - are found in forests. These plants compete amongst themselves for sunlight. Hence, trees grow tall to get sunlight and climbers and vines grow to a great height with the support of trees. Spring-like tendrils on the stems of some climbers is an example of adaptation. 1.6 Forest Adaptation in grassland plants Diverse types of bushes and grasses are found in the grasslands. Fibrous roots of grasses prevent soil erosion. Forests in the equatorial region are dense. Animals like tiger, elephants and deer can remain hidden in these grasses. However, grasses in cold regions are very short. Animals like the rabbit are found in such grasses. Vast meadows are found in hilly areas as well as plains. Observe and discuss. Observe and note down the adaptations in the parts of plants like potato, groundnut, yam, water hyacinth, aloe, acacia, carrot, onion, beet, bitter-gourd, grape vine, etc. and other plants in your surroundings. 1.7 Yam and potato 3 Adaptation for ingestion of food in plants Most of the plants are anchored in the ground and are autotrophic. However, plants like dodder (cuscuta) are parasitic. The plant body of dodder consists of yellow wire-like stems. It is leafless and cannot perform photosynthesis. However, it has haustorial (sucking) roots for absorbing nutrients from the host plant. These roots penetrate upto the conducting vessels of the host plant to absorb water and food. 1.8 Cuscuta Fungi do not have chlorophyll and cannot perform photosynthesis. They obtain food from starchy foodstuffs like bhakri and bread. They have root-like fibers for absorption of food. Plants need nitrogen, phosphorus and potassium for growth. Plants that grow in soil which is deficient in nitrogen, like drosera (sundew), Venus flytrap, pitcher plant, etc. fulfill their need for nitrogen by consuming insects. Adaptations are seen in these plants which serve to attract insects and hold them captive. My friend, the internet ! 1.9 Venus flytrap Collect information about plant adaptations from websites like – www.mbgnet.net Adaptation in animals Make a list of animals in your surroundings. Compare the diversity of animals listed by your friends, with your list. Discuss the habitats, food-habits, charactersistics of body structures like vertebral column, wings, gills, tails, etc. and prepare a chart. What differences do you see between terrestrial and aquatic animals ? As compared to terrestrial animals, the skin and body shape of aquatic animals appear to have undergone changes. Fishes have scales on the skin and fins on the body. Their body tapers towards both its ends, like a spindle. Fish breathe with gills instead of a nose. Their eyes have transparent eyelids. They have air bladders within the body to help them to float. Observe the bodies of the frog, duck and tortoise. Fins (1) Of what use are their legs to these animals ? (2) What helps frogs to breathe underwater  ? (3) Of what use are the long hind legs of a frog ? Scales (4) Why doesn’t a duck get wet in Gills water ? 1.10 Fish 4  As the frog and duck have webbed toes, they can use their legs like oars. Water flows off the waxy feathers of birds like duck and waterhen. Webbed toes, slippery, smooth skin and a triangular head help Webbed toes frogs to swim easily through water. They can live on land as well as in water due to their ability to breathe through the skin in water and using the nose and lungs on land. The typical colours of a frog’s back help it to hide among grasses. Make a list of the names of some other amphibians you know and study their adaptations. Adaptation in forest and grassland animals 1.11 Duck Carnivorous animals like the wild dog, fox, tiger and lion have strong legs to run fast and capture their prey. They have claws and their canine teeth are sharp and pointed. What is the function of such teeth ? Tigers have padded paws. This enables them to silently stalk their prey and capture it easily. The eyes of predatory carnivores are located in the front of their 1.12 Lion head. It helps them to spot their prey from a long distance. The eyes of herbivores are below the forehead, on either side of the head. This gives them wide-angle vision which helps to protect them from predators. Their legs are long and tapering with strong hooves, which enables them to run fast taking long leaps. Their long and freely moving ears can receive sounds from long distances and different directions. Deer and blackbucks have colours that merge with their surroundings. Their teeth are strong for chewing tough plant material. 1.13 Blackbuck Adaptation in desert animals Deserts are characterized by severe scarcity of water. Hence, desert animals have a thick skin to prevent loss of water from the body. Their legs are long with flat and cushioned soles. The nostrils are protected by folds of skin. The eyelashes are long and thick. Rats, snakes, spiders, lizards in deserts live in deep burrows during daytime and are active at night. 1.14 Desert animals 5 Adaptation in animals of snowy regions From the internet, download images of animals like yak, polar bear, white fox, silver fox, mountain goat, Siberian husky dog and snow leopard. Compare these images with those of similar animals from tropical forests. A white or silver body colour, long, thick hair on the skin are typical characteristics of animals of snowy region. How are these useful to them ? Adaptation in aerial animals Can you tell ? 1.15 Animals of snowy regions What is the main difference between vehicles Wings on the road and aeroplanes ? The spindle-shaped body of birds also minimises the resistance of air while flying. With hollow bones, a body covering of feathers and modification of forelegs into wings, their body is light in weight and adapted for flying. The body of insects also is light in weight and tapers at both ends. They can fly with two pairs Tapering slender body of wings and also walk with six stick-like legs. Bats can fly with the help of the patagium, a thin fold of skin between their forelegs and hind legs. Observe the various birds and insects in your Claws area. 1.16 Adaptations in birds Adaptation in reptiles Observe, from a distance, how snakes and earthworms creep. Which organs do they use for creeping ? Are there any special changes for that purpose ? Note any such changes. Animals like house lizard, garden lizard, crocodile use their muscles for creeping. Similarly, they show adaptations in skin, soles of feet, body colour, etc. For example, the house lizard and monitor lizards have clawed toes and thin soles, whereas snakes have a scaly skin. 1.17 Reptiles 6 Adaptation for food in animals We can categorize animals as herbivores and carnivores. Special adaptations are seen in each category to make the process of feeding easy. We will discuss this in greater detail in the chapter on Nutrition. Watch the programmes on channels like National Geographic Wild, Discovery, etc. to learn about the feeding habits of animals like frogs, snakes, birds, mosquitoes, butterflies, etc. 1.18 Adaptation for food in animals Complete the following chart from your own observations. Adaptation Animal Use of adaptation Sharp teeth Lion, tiger To tear the flesh Long and pointed beak Short beak Long and sticky tongue Long neck Adaptation for blending with the surroundings We cannot easily spot colourful butterflies, lizards and grasshoppers. They get camouflaged amidst grasses, parts of plants like stem, leaves, flowers, etc. That is because their colours blend with those of their surroundings. Changes that take place in the various organs and life-processes of organisms, that enable them to live, feed, reproduce to perpetuate themselves and protect themselves from their enemies in specific surroundings, depending upon the habitat and its geographical conditions, are called adaptations. Always remember - Adaptation is not a sudden process. It is gradual and continuous. Differences in the structure and appearance of present-day animals and animals of thousands of years ago are the adaptations that occured according to prevailing conditions. It is our duty to conserve this diversity. 7  Darwin’s theory of evolution Great Scientists Charles Darwin, a biologist, studied numerous types of plants and animals and suggested that only those organisms are likely to survive which can best adapt themselves to a changing environment. This is called the theory of survival of the fittest. This is Darwin’s first principle. If an organism is born with a new beneficial characteristic and is able to survive, this change is preserved in the next generation. This is Darwin’s second principle and is called the theory of ‘natural selection’. Classification of living organisms Why are living things classified ? Let’s recall. Which are the criteria used for classification of plants and animals ? It is difficult to study and Hierarchy Mango Human remember all the organisms in Kingdom Plantae Animalia this diverse living world at the Phylum Anthophyla Chordata same time. Classification helps in Class Dicotyledonae Mammalia this respect. Order Sapindales Primates Different scientists have used Family Anacardiaceae Hominidae different criteria and Genus Mangifera Homo independently classified plants Species indica sapiens and animals. A hierarchy is formed in the classification that starts with Kingdom Animalia or Kingdom Plantae; further groups and sub-groups are formed depending upon basic similarities and differences. This is called the ‘hierarchy of classification’. Binomial nomenclature by Carl Linnaeus Imagine that there are four students with a name ‘Kabir’ or ‘Kiran’ in a classroom. If you are talking about any one of them, how would you ensure that others know which one of them you are talking about, without any confusion? We would tell the full name i.e., the first name and the last name. This is similar to binomial nomenclature. Binomial nomenclature is used to identify each organism. Accordingly, a scientific name has been assigned to each organism. It consists of two parts – the first part is ‘genus’ and second, ‘species’. All identified organisms have been assigned a binomial name as per the guidelines of the International Code of Nomenclature. All the organisms of a species are so similar that irrespective of differences in colour, height, habitats and habits, they can reproduce among themselves and form new individuals like themselves. For example, all domestic cats in the world belong to the same species. The same is true in the case of animals like hen, cow, dog, etc. and plants like mango, wheat, maize, etc. 8  Following are some examples of organisms from Kingdom Plantae and Animalia classified by the binomial method of nomenclature : Living Things Scientific Name Dog Canis lupus familiaris Cow Bos taurus 29th April is observed as ‘World Frog Protection Hibiscus Hibiscus rosa-sinensis Day’. Jowar Sorghum bicolor Killing or harming frogs is prohibited by the Find out the scientific names of other animals and Wild Life Protection Act. plants in your surroundings and discuss in class. Exercise 1. Find my match ! 3. Who is lying ? ‘A’ Group ‘B’ Group (a) Cockroach – I have five legs. (1) Lotus (a) flower and leaves (b) Hen – My toes are webbed. attract insects (c) Cactus – My fleshy, green part is a (2) Aloe (b) Haustorial roots for leaf. absorption of food 4. Read each of the following statements. (3) Cuscuta (c) Adapted to live in Write a paragraph about adaptation deserts with reference to each statement. (4) Venus flytrap (d) Adapted to live in (a) There is extreme heat in deserts. water. (b) Grasslands are lush green. 2. Read the paragraph and answer the (c) Insects are found in large numbers. following questions. (d) We hide. I am a penguin. I live in polar region (e) We have long ears. covered by snow. My abdomen is 5. Answer the following. white. My skin is thick with a layer of (a) Why is the camel called the ‘Ship fat underneath. My body is spindle- of the desert’ ? shaped. My wings are small. My toes (b) How can the plants like cactus and are webbed. We live in flocks. acacia live in deserts with scarce (a) Why is my skin white and thick water ? and why is there a thick layer of (c) What is the inter-relationship fat underneath ? between adaptations of organisms (b) Why do we live in flocks sticking and their surroundings ? close to each other ? (d) How are organisms classified ? (c) Which geographical region do I inhabit? Why? Activity : Find out how the gradual (d) Which adaptations should you have adaptation from primitive man to enable you to live permanently to modern man must have taken in the polar region ? Why ? place. ttt 9  2. Plants : Structure and Function 1. What helps us to easily identify the plants around us? Let’s recall. 2. Which are the various parts of plants? The root, stem, leaves, flowers, fruits, etc. of different plants are different. We can identify plants with the help of these different charactersistics. Let us now acquaint ourselves with these plant organs in greater detail. Root 1. Keep a moistened ball of crumpled paper in a conical flask. Place some soaked moth beans/gram seeds in the flask between the paper and the glass wall. Observe and note the changes in the seeds Try this. in two or three days. Plumule The part that grows from inside the seed towards the soil is called the radicle and the part that grows above the soil is called the plumule. The root that forms from the radicle, grows into the ground. The root is thick near the ground and gradually tapers to a pointed end. This part of the Radicle plant growing below the soil for support is called 2.1 Formation of root ‘root’. Roots of some plants produce secondary roots; that Secondary grow obliquely and spread far and wide in the soil. root Roots support the plant. This type of root is called a tap root. Primary Roots bear hair-like processes near the root tips. root These are root hairs. The root tip is delicate. This is the region of the growth of the root. The tip is covered Root hair by cap-like structure called the root cap. The root-cap Root tip protects the root-tip from injuries. Root cap (2) Take a glass jar and fill three-quarters of it with water. Place an onion on the mouth of the jar 2.2 Tap root in such a way that its roots are towards the water. Observe the growth of the roots for eight days. Thread-like or fibre-like roots arising from the stem are called fibrous roots. Thus, there are two main types of roots : tap roots and fibrous roots. Dicotyledonous plants have tap roots while monocotyledonous plants have fibrous roots. (3) Sow the seeds of plants like mustard, sorghum (jowar), maize (corn), pea, coriander, etc. in an earthern pot. Cultivate the plant for eight days. Once 2.3 Fibrous roots the plants grow 15 to 20 cm high, uproot them 10 carefully while the soil is moist and put them gently in a large conical flask containing water. The soil will get washed off without any harm to the roots. Observe the roots carefully to see which plants have tap roots and which ones have fibrous roots. Plants like maize, sugarcane, sorghum have two types of roots. Some roots are underground whereas some grow from the stem just above the soil. The latter are called adventitious roots. Besides the normal functions like absorption of water and minerals, anchoring and supporting 2.4 Maize stalk the plant, roots perform some other functions too. Roots show some modifications to perform these additional functions. Some examples of such modified roots are aerial roots, stilt- roots, runners, breathing roots (pneumatophores), etc. (4) Take some water in a small glass jar. Put a plantlet in it in such a way that its roots are dipped in the water. Mark the water-level on the jar and add 5ml of oil to the water. Record the water-level on the next day. Discuss your observations in the class. 2.5 Water level Use your brain power ! (1) What would have happened if plants like tamarind, banyan and mango had fibrous roots ? (2) What will happen if the root-tip is injured ? (3) Which types of roots do the fenugreek, spinach and onion plants have ? Do you know ? Roots emerging from the trunk and branches of a banyan tree grow towards the soil. These roots are called prop roots. What could be the use of these prop roots ? In the beginning, the banyan tree has very few prop roots. But later on, their number increases so much that it appears like a small forest. In Kolkata, a 250 years old banyan tree in the Indian Botanical Garden covers a very large area. It is supported by thousands of prop-roots. Is there any such tree in your neighbourhood ? Why are the underground parts of plants like radish, carrot, beet and sweet potato thick, fleshy and swollen ? Find out. Which part of the plant are they ? Collect images of different types of roots and send them Techno-support to your friends via e-mail. 11 Stem Growing end The stem grows above the soil from Bud the plumule of the sprouting seed. As the sprout grows the length of stem gradually Bud increases, too. There are nodes on the stem. Leaves come out at the nodes. The part of the stem between two nodes is Nodes called an internode. The tip or the apical end of the stem is called a bud. Observe a branch of any plant and identify its Leaf Internode different parts as per the diagram. 2.6 Parts of a stem Complete the chart. (Collect information about other local plants, too.) Name of Plant Thickness (circumference) of node (mm) Length of internode (mm) 1. Sugarcane 2.Fenugreek 3.......... Leaf Leaf apex Leaves grow from the nodes on a stem. Leaves are generally thin, flat and Leaf margin green in colour. The broad, spread-out part of the leaf is called the leaf-blade or Vein lamina and its edge is called the leaf- margin. Leaf margins may be entire, Mid vein dentate or lobed. Leaf blade Petiole Stipule Entire Dentate Lobed Leaf base 2.7 Parts of a leaf The tip of the leaf is called the leaf apex. It may be tapering, pointed or rounded. Leaves of some plants have a stalk called a petiole. Leaves of some plants do not have a petiole. The portion of the leaf attached to the stem is called the leaf-base. Small leaf-like structures may be present near the leaf-base. These are called stipules. Do you see stipules in all plants ? Leaves of some plants have a single undivided leaf blade and a single mid-rib. Such leaves are called simple leaves. However, the leaf-blade of leaves in some plants is divided into many small parts called leaflets. Such leaves are called compound leaves. Simple leaf and compound leaf are the two main types of leaves. 12  Observe a branch of plants like rose, neem, Observe and discuss. coriander, hibiscus, etc. In different plants the arrangement of leaves on the stem is different. It may be alternate, opposite, whorled, spiral, etc. According to shape, leaves are rounded (obovate), palmate, lanceolate, linear, etc. Alternate Decussate Opposite Whorled In the box, draw a special leaf you may have found. 2.8 Different types of leaves Take a peepal leaf and a maize Try this. leaf and observe them carefully. The peepal leaf is divided into two equal parts by a single mid-vein which lies along the mid-line of the leaf blade. Secondary veins arise from the mid-vein. They are branched and form a network or reticulum. On the other hand, in leaves of maize, all the veins are parallel, running from the leaf-base to the leaf apex. Thus, the peepal leaf-blade has reticulate venation and the maize leaf-blade has parallel venation. Observe the leaves of some other plants in your surroundings and identify the type of venation. 2.9 Leaves A little fun ! Take a fallen peepal leaf and soak it in water for 15-20 days. Dry it and make a greeting card of the lace-like leaf you get. Complete the following chart by observing the plants around you. S. Name Type of Shape Venation Shape Shape of Petiole Stipule Arrange- No. of plant leaf of of leaf leaf apex Yes/no Yes/no ment on leaf- margin stem blade 1. Maize 2. Canna 3. Peepal 4. 13  1. Carefully observe a fully opened hibiscus flower. Try this. Flowers may have a long or a short stalk Flower called pedicel. One end of the pedicel is attached to the stem. The other end of the Stigma pedicel is expanded and swollen. It is called Anther the receptacle. Petals and other parts of the flower are supported on the receptacle. Calyx, corolla, androecium, gynoecium are different parts of a flower. Calyx : In the bud condition the petals are covered by leaf-like parts called sepals which Petal are green in colour. They form the calyx. Pedicel Corolla : This is made up of colourful parts called petals. Observe the shape, colour and smell of the corolla of various flowers like the rose, chrysanthemum, hibiscus, mogara, kanher, tagar, etc. Androecium : This is the male reproductive part of the flower. It consists of stamens. Each Style stamen is made up of anther and filament. Stigma Anther Gynoecium : This is the female reproductive Corolla Filament part of the flower. This is made up of carpels. A carpel consists of stigma, style and ovary. 2. Take a vertical section of a hibiscus flower with the help of a sharp blade, by cutting the flower vertically from stigma to pedicel. Both sections of the flower will be Calyx Ovary seen to have the same structure. After maturity, anthers burst and the pollen grains which are released fall on the Pedicel stigma. This process is called pollination. Due to pollination, ovules (egg cells) in the ovary 2.10 Vertical section of a hibiscus flower get fertilized. Fertilized ovules form the seeds and the ovary develops into a fruit. Of what use to a plant are the insects flitting about Use your brain power ! around its flowers ? Observe the various flowers and complete following chart. Name of Number Sepals – Number of Petals Form of androecium flower of Sepals free/united petals free/united and gynaecium 14 Fruit We eat many different types of fruits. Each type of fruit has its own characteristics. There are variations in their shape, colour, taste, etc. Mango contains only one seed where as jackfruit consists of many small fruitlets, each with its own seed. Observe the fruits of ber (ziziphus), mango, chikoo, apple, etc. What do you observe ? Each fruit has a different skin or shell, fleshy part and seed. In case of fruits like cashew, its seed is outside the fruit. Soak the seeds of, pea, wheat, rice, jowar, groundnut in water for 3-4 hrs. Press the seeds with your fingers and observe them. Which seeds get divided into two equal parts? Seeds which get divided into two equal parts are called dicotyledonous 2.11 Various fruits and seeds. Seeds which do not divide into two equal seeds parts are called monocotyledonous seeds. Exercise 1. Give examples of 3 plants that have : 5. Describe the functions of various parts (a) spiny fruits of a plant. (b) spiny stem 6. Certain properties are mentioned be- (c) red flowers low. Find a leaf corresponding to each (d) yellow flowers property and describe those plants. (e) leaves which close at night leaves with smooth surface, leaves with (f) single-seeded fruits rough surface, fleshy leaf, spines on leaf. (g) many-seeded fruits 7. Find the plant parts. 2. Observe any one flower and its various parts and describe it in your own r b u d x s r f words. o w p y e t a l 3. What are the similarities and differences o l l d n e d o between ? t a o i l m i w (a) jowar and moong c n e t a l c e (b) onion and coriander (c) leaves of banana and mango a v o v u m l r (d) coconut tree and jowar stalk plant p e t a l s e o r o o t h a i r 4. Explain the following images in your own words. Activity : Sketch various types of leaves in Paintbrush on the computer and save the sketches in a folder of your own name. A. B. ttt 15  3. Properties of Natural Resources 1. Which are the gases present in air  ? Why is air called a Let’s recall. homogeneous mixture ? 2. What are the uses of the various gases in air ? Properties of air Air is all around us. We cannot see it, yet we feel the presence of air. When we inhale, air is taken in through the nose. If we blow on our hand through our lips, we can feel the air. 1. Take a stick from a broom or a paper or plastic straw. Tie a thread at its centre and hang it so that it Try this. remains horizontal. Tie two rubber balloons of the same size at the two ends of the stick. See to it that the stick remains horizontal. Now remove one balloon, inflate it and tie it again at its original position. Does the stick remain horizontal ? The stick goes down on the side of the inflated balloon. This means that air has weight. Air is a mixture of gases. Therefore, like all other matter, it has mass and weight. 2. Take an injection syringe without the needle. Pull its piston and observe it as you do so. The piston can be pulled out easily. The piston then 3.1 Balloons remains in that position even if you let it go. Now, close Hole the inlet hole of the syringe tightly with your thumb, pull the piston and let it go. Is the force required to pull out the piston more or less than before ? Does the piston remain as it is after you let it go. The molecules of the gases in the air are in constant motion. When these molecules strike a body, they create pressure on that body. This is the pressure of air that Piston we call ‘atmospheric pressure’. On pulling the piston with the inlet hole of the syringe closed, more space becomes available to the air in the syringe, and it becomes rarified. As a result, the pressure of the air in the syringe is lowered. Comparatively the pressure of the outside air is very high. That is why, when the pulled out piston is released, it is immediately pushed in. If this experiment is repeated, holding the syringe in different positions like vertical, horizontal or inclined, the piston is found to go in to the same extent in all the cases. From this, we can infer that atmospheric pressure is the 3.2 Air pressure same in all the directions. 16  Find out. Is there any atmospheric pressure on the moon? Do you know ? A Little Fun ! Under ordinary conditions, Place a piece of cardboard on the atmospheric pressure at sea level is mouth of a glass filled completely with about 1,01,400 Newtons per square water. Holding the cardboard firmly in metre. It can be measured with the help place with one hand, invert the glass of a barometer. As we go higher above quickly. Take your hand away from sea level atmospheric pressure decreases. the card board. What do you see ? Great Scientists Download a In 1726, the Swedish scientist Daniel Bernoulli put forth photograph of the important principle that the pressure of air decreases Daniel Bernoulli when its velocity increases while the pressure of air increases from the internet, print and paste it when its velocity decreases. If a body is moving through air, here. What the air pressure decreases perpendicular to the direction of commands did you the motion and then the air in its surroundings flows rapidly give the computer to do this ? from higher pressure to the lower pressure. Observe and discuss. Take some water in a plastic cup and hold a straw Fountain of water upright in it. Hold a small piece of another straw near the upper end of the first straw and perpendicular to that straw. Blow hard through the small piece of straw. You will see a fountain of water. Why did this happen ? Straw On blowing through the straw, the air at its open end is pushed away and hence the pressure of the air at the opening goes down. As the pressure of the air near the upper end of the erect straw becomes less than atmospheric pressure, the water in the cup is pushed from where the pressure is higher to where it is lower, that Water is, in the upward direction, and the water comes out in the form of a fountain. The more forcefully you blow the higher will be the fountain. This straw fountain works on Bernoulli’s principle. 3.3 Effect of air pressure What is the effect of increased temperature Use your brain power ! on the pressure of air ? 17  When there exists a difference in the air pressure at two different places, the air starts flowing from the place of higher pressure to the place of lower pressure. At such times, we feel a breeze or a wind blowing. Thus, winds are an effect of the difference in air pressure. You will learn more about this in the lesson called ‘Winds’, in Geography. Take ice-cubes in a glass upto three-fourths of its Try this. height. Now observe what happens. How did the water droplets appear on the outside of the glass ? Due to the ice cubes in the glass, the air surrounding the glass cools down. As the water vapour in this air cools down, it condenses and gets transformed into water. It is this water that collects on the outer surface of the glass. The level of humidity is different in different places. Similarly, the humidity levels also change from time to time during the period of a single day. The level of humidity of the air is determined by its capacity to hold water vapour. During the night or at dawn, 3.4 Water droplets collected when the temperature of air is low, its capacity to hold the outside the glass vapour is less. At such times, the excess vapour is transformed into water droplets. This is what we call dew. In the afternoon, when the temperature of the air is high, the capacity of the air to hold the moisture also increases. Then, compared to its full capacity to hold water, the proportion of moisture in the air is less and we feel that the air is dry. The proportion of water vapour in the air is high during the monsoons and in coastal areas. As a result, we feel the dampness or humidity. In summer, wet clothes dry quickly, but in the rains, they do not. Why is this so ? 1. Dip an uncorked inverted empty bottle in a Use your brain power ! slanting position into the water in a wide container. What do you observe ? Try this. 2. What change takes place in a balloon on filling air in it ? We come to know from the activities above, that air has properties like occupying space, having a certain volume, having mass and weight. Air is a mixture of very fine particles of some gases, dust, smoke and moisture. When rays of light fall on these minute particles, the particles spread the light in all the directions. This natural phenomenon is called scattering of light. 3.5 Properties of air 18 Temperature regulation The earth receives energy from the sun. This energy is reflected by the earth in the form of Use your brain power ! heat. The constituents of air surrounding the 1. What would happen if all the earth, such as water vapour, carbon dioxide, air surrounding us is removed  ? absorb a part of this heat and give it to the other 2. Will sound be heard in space ? constituents of air. As a result, the earth’s surface remains warm and thereby becomes suitable for the living world on the earth. If there were no air on the earth, the average temperature of the earth’s surface would have been very low. Transmission of sound All the sounds that we hear reach us through the surrounding air. The density of air also changes due to change in its temperature. In winter, the density of the air increases. We can hear the whistle of a distant train clearly early in the morning in winter. Air is useful as a medium for the transmission of sound. Properties of water 1. What are the states in which Let’s recall. water is found ? What inference will you draw from the pictures alongside ? Water occurs in liquid state under ordinary conditions. Water is a fluid substance. Water does not have its own shape, but has a volume. It can pass through small holes or seep through very small gaps or cracks. On pouring water in an oil-cladded dish, water does not spread but forms small round drops. Why does this happen ? 3.6 Properties of water Try this. 1. Take a plastic bottle, more than half full of water. Mark the water level on the bottle. Keep this bottle upright in the freezer for making ice. Open the freezer after a couple of hours and observe. You will see that the water has changed into ice. Note the level of the ice. You will find that the ice-level is higher than the water-level before freezing. What can you infer from this ? As water freezes to form ice, it expands and its volume increases. On freezing, how much was the increase in the volume of the water ? In what proportion did it increase ? 19  2. Take a bucket of water. Drop many different kinds of articles in it. Make separate lists of the articles which sink in the water and those that float on it. 3. Take some water in a pot and add a few pieces of ice to it. Observe what happens. Why do we see the ice float on water ? Ice is lighter than water. When water freezes to form ice, it becomes lighter than the original liquid. When water freezes, that is, when it transforms into the solid state, its volume increases. Therefore, the density of ice is less than that of water. That is why the ice floats on water. Density of water The inter-relation between the volume and mass of a substance : the space occupied by a substance is its volume. The store of matter in a substance is its mass. mass Density = volume Mass is measured in grams and volume in cubic centimetres. Hence, gm density = cc Hence, g/cc is the unit of density. If the mass of 1 3.7 Density of water litre of water is 1 kilogram, then what is the density of water ? Think : Will the mass of water change when its state changes during the transformation of liquid water into ice? Anomalous behaviour of water Usually, when the temperature of a substance is lowered, its density 00 C increases as the volume decreases; but Ice 10 C water is an exception to this rule. -10 C 4. Keep a glass full of water in the 20 C freezer for five to ten minutes. Then 3 C 0 40 C take it out and observe it carefully. From which part in the glass does 3.8 Anomalous behaviour the water first start freezing ? The density of water is peculiar. When water at normal temperature starts cooling, its density increases like that of most liquids. However, if its temperature falls below 40 C its density starts decreasing. This means that the density of water is maximum at 40 C. If the temperature of water is lowered below 40 C, its density decreases and volume increases. It means that water expands when the temperature falls below 40 C. This is called the anomalous behaviour of water. 20  In cold countries, how do aquatic animals remain Use your brain power ! alive even after the rivers or lakes freeze in winter ? Take two big glasses of water. Add 4-5 spoonfuls of salt to the water in one glass and dissolve it completely. Try this. Now place a potato in the water in the second glass. The potato will sink. Take out the potato from that glass and put it in the salt water and observe. The density of water in that glass Water is greater due to the dissolved salt. The potato floats in that water because of the increased density. Why is it easier to swim in the sea than in a well or a lake ? A In the above activity the salt dissolves in the water in the glass, that is, it disappears. What happens when it disappears like this ? When the salt dissolves in water, its particles spread in Salt solution water. Slowly they become smaller and smaller. Ultimately they become so small that they cannot be seen, that is, they mix completely with water. This is what is called dissolving. B Solute : the substance that dissolves - Salt 3.9 Effect of density Solvent : the substance in which the solute dissolves - Water Solution : what we get when the solute dissolves in the solvent. Uses of water according to its properties 1. Water is useful for water transport due to its fluidity. Water falling down from a height is used to generate electricity with the help of a generator. 2. Water is a good coolant and is used in motor vehicles to control the temperature of the engine. 3. Many substances are soluble in water. Water is a universal solvent. Water is used as a solvent in factories, laboratories, foodstuffs and in various types of biological processes occurring in the body such as digestion, excretion, etc. 4. Water is useful for cleaning purposes such as for bathing, washing clothes. Soil 1. What is meant by soil ? How is soil formed ? Let’s recall. 2. What are the ingredients of soil ? 21 Properties of soil Colour is an important property of soil. The soil gets its colour as a result of several processes. The colour of soil near land surface is darker than the colour of the lower layers. Soil may be of different colours, such as black, red, copper, yellow, gray. The colours of soil are useful for its classification. Besides, they are indirectly useful in indicating several properties of the land. In this way, the properties of the soil such as its fertility, drainage of water, capacity to hold water become clear from its colour. The colour of the soil depends upon its texture and its organic ingredients as well as on chemical ingredients like iron, lime. Apparatus : Three measuring cylinders, Try this. three glass funnels, filter paper, water, fine sand, coarse sand, soil from an earthen pot used for growing plants, etc. Procedure : Fit cones of the filter paper in the three glass funnels. Fill the cones with equal quantities of (a) sand (b), sandy soil and (c) clay respectively. Place the funnels on the measuring cylinders. Pour one test tube of water into each of the funnels and observe how much water is collected in each measuring cylinder. a b c What inference will you draw from this ? 3.11 Collected water Soil texture Soil contains particles of different sizes. The texture of the soil is determined by the proportion of particles of the various sizes in it. Following are the types of soil on the basis of its texture. Sandy soil : The proportion of sand, i.e., large particles is high in sandy soil. Water drains rapidly through sandy Sandy soil soil. It is easy to plough this soil. But it is less fertile. This is because the particles of sandy soil are made of the mineral called silicon dioxide (quartz). These particles do not dissolve in water and, therefore, the soil has very little capacity to supply nutrients. Silt soil Silt soil : The particles of silt soil are of medium size. Silt soil is not as ploughable as sandy soil. However, it is much more ploughable than clay soil. This soil contains a large proportion of organic materials. Its capacity to supply nutrients is much greater. Silt soil is also called Clay sedimentary soil. soil Clay soil : In this soil, the proportion of small particles is maximum. The particles of clay soil feel smooth to touch. Clay soil has a high water holding capacity. 3.12 Types of soil 22  Use your brain power ! 1. Why is it difficult to plough clay soil  ? 2. Why is it easy to plough sandy soil ? 3. What is the water holding capacity of silt soil ? 4. Which soil is suitable for cultivation ? Why ? Soil structure The structure of soil depends upon the different shapes of the particles in it. Soil occurs in the form of columnar, laminar, granular as well as block-shaped structures. Importance of soil structure The fertility of soil depends upon soil structure. The advantages of good soil structure are as follows : 1. Roots get a sufficient supply of oxygen. 2. Water drainage is good. Therefore, the roots of plants grow well. Uses of soil 1. Plant conservation : To help plants grow. 3.13 Soil structure 2. Water conservation : Soil holds water. As a result, by means of bunds and lakes, we can get water for use throughout the year. 3. Plasticity : Soil can be given any required shape. This property of soil is called plasticity. Because of its plasticity, we can use it to make articles of a variety of shapes. These articles can be baked to make them hard. Water storage earthen pots, earthen lamps, idols, bricks, etc. are articles made from soil. Some useful types of soil 1. China clay : (Kaolin) It is white in colour. It is used to make crockery, bathroom tiles, tanks, laboratory apparatus, masks, jars, etc. 2. Shadu soil : It is whitish in colour. It is used for making statues and idols. 3. Terracotta soil : This soil is red in colour. Decorative articles and pots used for growing plants are made from this soil. 3.14 Uses of soil 4. Multani soil : This soil is used in cosmetics. 23  Do you know ? China clay is an industrial mineral of the type ‘Kaolinite’. It is found in China and hence called China clay. Upon heating, this soil acquires a glaze and hardness and, therefore, is used for making crockery. Soil testing The proportions of the various ingredients of soil can be determined by Great Scientists ‘soil testing’. During soil testing, the soil The Danish Scientist Sorensen put is examined for colour, texture and the forth the concept of pH, based on proportion of organic matter in it. Soil the concentration of hydrogen ions. is tested to find out if there is a To determine the pH of soil, a deficiency of any ingredients and to mixture of water and soil in the decide what measures should be taken proportion 1:2 is taken and tested to remove the deficiency. using several indicators. Accordingly, soil may be found to The soil sample collected for testing be one of the following three types. is dried in an open space in the shade for eight to ten days. It is then sifted 1. Acidic soil - pH less than 6.5 through a sieve. 2. Neutral soil - pH 6.5-7.5 Two tests, namely, the pH and the 3. Alkaline soil - pH higher electrical conductivity tests, are particularly useful in finding out the than 7.5 characteristics of soil. You can determine the fertility of the soil in your fields with the help of different tests. Always remember - Causes of diminished soil fertility : 1. Soil pH less than 6 or higher than 8. Soil texture is disturbed if 2. Low proportion of organic matter. chemical fertilizers are used 3. No proper drainage of water. excessively and that land becomes unsuitable for sowing. Crops should 4. Repeated cultivation of the same crop. be rotated in order to maintain the 5. Continuous use of saline water. fertility of the land. 6. Excessive use of chemical fertilizers For example, the fertility of and pesticides. land decreases after a harvesting of wheat. Hence, leguminous crops like peanut, moong, moth bean, World Soil Day : 5th December pea, lentil, Bengal gram, soyabean To make efforts for should be cultivated to restore the conservation of soil fertility of the soil. 24  Exercise 1. Fill in the blanks with the appropriate 6. Explain the picture in your own term. words. (Temperature, volume, mass, density, humidity, acidic, weight, neutral, shape.) (a) The capacity of air to hold moisture depends upon the......... of the air. (b) Water does not have a............. Water but has definite.......... and........... Ice (c) While freezing, the.................... of water is lowered. (d)................. soil has pH 7. 2. Why is it said that - (a) Air is a homogeneous mixture of various gases. a b (b) Water is a universal solvent. 7. Write answers to the following (c) There is no alternative to water for questions in your own words. cleaning purposes. (a) How is light scatterred by the air ? (b) Explain the various properties of 3. What will happen if..... water. (a) The amount of water vapour in the (c) Why is the density of seawater air increases. more than that of rain water ? (b) Only one crop is grown repeatedly (d) What is the importance of good soil in the soil. structure ? 4. With whom should I pair up ? (e) What are the various uses of soil ? Group ‘A’ Group ‘B’ (f) What is the need and importance (1) Air (a) Excretion of soil testing from the point of (2) Water (b) Scattering of light. view of farmers ? (3) Soil (c) Plasticity (g) What is the importance of air in 5. State whether the following statements transmission of sound ? are true or false. (h) Why should a glass bottle completely (a) Sandy soil has low capacity for filled with water never be kept in holding water. a freezer ? (b) The substance in which a solute Project : dissolves is called a solvent. Visit a soil testing laboratory. (c) The pressure exerted by air is called Learn the process of soil testing atmospheric pressure. and share it with others. ttt 25  4. Nutrition in Living Organisms 1. What is malnutrition ? Let’s recall. 2. Which are the ways to prevent malnutrition ? Nutrition The process of taking in and Some life-processes go on using food, which takes place in continuously in living organisms. living organisms is called nutrition. Substances which are digested and Need for nutrition assimilated for obtaining energy and 1. To supply the energy required for for the growth and health of our doing work. body are called foodstuffs. 2. Growth and development of the We get several types of nutrients body. from foodstuffs. Nutrients can be 3. To replace the damaged cells and classified into two types, namely, repair tissues. macro-nutrients and micro- 4. To fight diseases. nutrients. Autotrophic nutrition Nutrients like carbohydrates, proteins and fats are required in large Some organisms can produce their quantity. These are macro-nutrients. own food and thus nourish themselves. Minerals and vitamins are required This is called autotrophic nutrition. in very small quantity. They are Heterotrophic nutrition called micro-nutrients. Some organisms depend on other organisms, plants or animals, for Autotrophic plants their food. This is called heterotrophic nutrition. Can you tell ? How do plants produce their own Oxygen Sunlight food ? Plants also need food for their Carbon dioxide growth. They can produce their own food. With the help of sunlight and chlorophyll, plants make their food in Chlorophyll in their leaves, using water and nutrients the leaves from the soil and carbon dioxide from the air. This process is called as photosynthesis. Water, minerals, salts Carbon dioxide + water Sunlight food (glucose) + oxygen 4.1 Photosynthesis 6 CO2 + 6H2O Chlorophyll C6 H12 O6 + 6O2 26  Plants convert light energy into chemical energy and store it in the form of food. Water, minerals and salts are absorbed by roots from the soil. The stem transports them up to the leaves. The leaves have microscopic openings called stomata through which they take Chloroplast in the CO2 from the air. The chloroplasts present in the leaves contain chlorophyll, 4.2 Chloroplasts in a leaf which absorbs sunlight, helping to convert carbon dioxide and water into food. Oxygen is given out in this process. Find out. Besides leaves, photosynthesis takes place in some other parts like green How does photosynthesis occur in stems, too, as they contain chlorophyll. dark red or purple coloured leaves ? Transport system in plants Take a pumpkin stem having 2-3 ßß ß leaves. Cut it under water with a sharp blade. Take some water in a conical flask and add 7-8 drops of ink to it. Put Section of a leaf ß the pumpkin stem vertically in that flask. ß ß Observe the changes that take place in ß ß it and discuss them in the classroom. ß ß ß ß The transport system of plants ßß Section of a stem consists of the xylem and the phloem. The xylem transports minerals and water ß from the root to all aerial parts of the ß plant. The phloem transports the food ß (glucose, etc.) from the leaves to other ß parts of the plant where it is either Section of a root consumed or stored. Though the plants Xylem have a transport system, they do not Phloem have a separate digestive or excretory system. 4.3 Transport system in plants What is chemosynthesis ? Which plants produce their Find out. food by chemosynthesis ? Let’s recall. Which are the different substances excreted by plants? Why? 27  Plants produce carbohydrates by the process of photosynthesis. Carbohydrates are made from carbon, hydrogen and oxygen. Proteins are made from carbon, hydrogen, oxygen and nitrogen. How do plants obtain the nitrogen necessary for the synthesis of proteins ? Air contains gaseous nitrogen. However, plants cannot utilize gaseous nitrogen. It needs to be fixed i.e. converted into compounds. Fixation of nitrogen occurs by biological and atmospheric methods. Biological fixation of nitrogen Two different types of micro-organisms can bring about biological nitrogen fixation. Root-nodules of leguminous plants contain the rhizobium micro- organisms. These micro-organisms absorb atmospheric nitrogen and convert it into its nitrate, a compound. Micro-organisms like azotobacter are present in soil. They also convert atomspheric nitrogen into nitrates. 4.4 Roots of a leguminous plant Do you know ? Atmospheric fixation of nitrogen : Lightning (thunderbolts) occur in the rainy season. This causes atmospheric nitrogen and oxygen to react with each other to form nitric oxide (NO) which is again oxidized to form nitrogen dioxide (NO2). The nitrogen dioxide dissolves in rainwater and is converted into nitric acid (HNO3) which gets added to the soil along with the rain-water. This acid reacts with different minerals in the soil and convert into salts. Plants use this nitrogen salts for their growth. Symbiotic nutrition In some cases, two or more than two different types