Science Grade 8 PDF

SCIENCE Part - I Grade 8 Educational Publications Department i  Contents page 01 Importance of Microorganisms 01 1.1 Microor...

SCIENCE Part - I Grade 8 Educational Publications Department i  Contents page 01 Importance of Microorganisms 01 1.1 Microorganisms 01 1.2 Effects of microorganisms on food 03 1.3 Impact of microorganisms on humans and their activities 06 02 Animal Classification 12 2.1 Main invertebrate groups 13 2.2 Main vertebrate groups 17 03 Diversity and Functions of Plant Parts 24 3.1 Diversity and functions of plant leaves 25 3.2 Diversity and functions of plant stems 30 3.3 Diversity and functions of plant roots 33 04 Properties of Matter 39 4.1 Discontinous nature of matter 39 4.2 Utilizing physical properties of matter 45 05 Sound 62 5.1 Musical instruments that produce sound by vibrating membranes 65 5.2 Musical instruments that produce sound by vibrating air columns 67 5.3 Musical instruments that produce sound by vibrating strings/rods 69 ix 06 Magnets 78 6.1 Poles of a magnet 79 6.2 Magnetic field of a magnet 81 6.3 Compass 83 6.4 Geomagnetism 85 6.5 Temporary magnets and permanent magnets 86 07 Measurements Associated with Electricity 95 7.1 Electric current 95 7.2 Potential difference 99 7.3 Resistance of a conductor 103 08 Changes in Matter 107 8.1 Physical changes and chemical changes 107 8.2 Changes of state as physical changes 109 8.3 Chemical changes 110 8.4 Combustion 115 8.5 Tarnishing of metals 119 8.6 Neutralisation 122 x 1 Importance of Microorganisms 1.1 Microorganisms There are living organisms which are visible and also invisible to the naked eye in our environment. Let us do Activity 1.1 to observe the invisible living organisms. Activity 1.1 You will need: - A sample of coconut water, a glass slide, a cover slip, light microscope Method: - ² Put the coconut water into a clean container and keep it for three days. ² Then put a drop of coconut water on to the glass slide and cover it with a cover slip. Figure 1.1 Microorganisms in a ² Observe the prepared slide through the light sample of aged coconut water microscope under low power. (Get the help of your teacher) ² Present your observations through diagrams. It is obvious that the unicellular fungal variety called 'yeast' can be observed mainly in the above sample. This organism cannot be examined to the naked eye in isolation, but can be observed through a microscope. Therefore, yeast is a microorganism. The uni-cellular (single celled) or multi cellular organisms which cannot be observed clearly by naked eye are called microorganisms. These microorganisms can be observed clearly through microscopes. Microorganisms are found in every habitat on the earth. They live and thrive in all environments such as atmosphere, water, soil, in and on living organisms including hostile environments (glaciers, deserts, hot springs, deep sea and saline environments). There is a tremendous biological diversity among microorganisms. They differ in their morphological characters as well as in their physiological mechanisms. Science | Importance of Microorganisms 1  e.g.:- bacteria, some algae, some fungal species, protozoans like Amoeba and Paramecium You can observe some permanent slides of microorganisms in your laboratory. Bacteria Yeast Chlamydomonas (Algae species) Mucor (a fungal variety) Amoeba Paramecium Figure - 1.2 Microscopic appearance of some microorganisms Use Figure 1.2 to identify different species of microorganisms. For extra knowledge Viruses show living features as well as non-living features. Although viruses are discussed under microorganisms, there is no conclusion yet as to whether they are living or non-living. Viruses can be observed through electron microscope. The Dutch scientist Antonie van Leeuwenhoek observed microorganisms for the very first time in 1674, using a simple microscope that he invented. Exploration of microorganisms was possible with further developments in microscopy. Figure 1.3 Antonie van Leeuwenhoek 2 Science | Importance of Microorganisms 1.2 Effects of microorganisms on food The growth of some microorganisms on foods make them not suitable for human consumption. Do Assignment 1.1 and Activity 1.2 to observe the effects of microorganisms on food. Assignment 1.1 ² Get some food samples of bread, vegetables, fruits, milk, meat/fish, rice, butter in fresh condition. ² Observe their nature carefully. ² Again observe the nature of these samples after 24 hours, 48 hours and 72 hours. ² Tabulate your observations. Table 1.1- Effect of microorganisms on food Food item Fresh food After 24 After 48 After 72 hours hours hours colour texture 1. Bread odour appearance 2.................. The microbial activities change the colour, texture, odour and appearance of food. The taste and the nutritional value of food also change. Food become unfavourable for consumption due to the changes of properties. This is known as spoilage of food. The main reason for food spoilage is the growth of microorganisms on food. Activity 1.2 You will need: - A slice of bread, some water, a glass slide, a cover slip, microscope Method: - ² Spray some water on the slice of bread and keep it for three days. ² Take some of the substance grown on the slice of bread and place on the glass slide. Put a drop of water on it. ² Cover the slide with a cover slip. ² Observe the slide through the microscope under the low power. ² Draw what you observed. Science | Importance of Microorganisms 3  Slice of bread with fungi Microscopic view of fungi Figure 1.4 You will observe that there are some fibres and black structures on bread. They are a kind of fungi which spoils bread. So, you can observe that microbial growth causes food spoilage. The main reason for food spoilage is the growth of microorganisms on food and release of their byproducts. Let us do Activity 1.3 to study microbial activity. Activity 1.3 You will need: - Sugar, yeast, a balloon, warm water (40 oC), a bottle (500 ml), a beaker/suitable container Method: - ² Dissolve two teaspoons of sugar in 200 ml of warm water. ² Add one teaspoon of yeast into the above sugar solution. ² Leave it for about 20 minutes and observe (Figure 1.5 a). Sugar (2 teaspoons) Yeast (1 teaspoon) Sugar and yeast mixture Figure 1.5 (a) 4 Science | Importance of Microorganisms ² Next pour a newly prepared solution into the bottle. ² Then fix a balloon to the mouth of the bottle. ² Record your observations after about 20 minutes. (Figure 1.5 b). Before After Figure 1.5 (b) When sugar and yeast are mixed in a solution, it will bubble and become warm (Figure 1.5a/1.5b). You will smell the odour of alcohol. It is because ethyl alcohol is produced due to the activity of yeast in sugar solution. As shown in Figure 1.5 b you will see that the balloon has been inflated. This is because a gas is produced due to the activity of yeast in sugar solution. The gas produced here is carbon dioxide. Yeast is a key ingredient in bakery products. The activity of yeast forms carbon dioxide and makes the dough rise. Ethyl alcohol evaporates during the process of baking. Figure 1.6 Rising of bread due to the activity of yeast When food is exposed to air, microbes act on it very easily. This is because the environment provides suitable moisture and temperature for their growth. Microorganisms start to grow rapidly when a moist food item is exposed to an environment with favourable temperature. But if the food is refrigerated the microbial activity is minimized because the amount of moisture and temperature are controlled in a refrigerator. Science | Importance of Microorganisms 5 Moisture and temperature are the main factors that contribute to microbial activity. Food spoils rapidly at room temperature (25oC - 30oC). This is because room temperature is favourable for microbial growth. The enzymes produced by these microbes change the taste, odour, colour, texture and the nutritional value of the food. Microbial activities depend on the type of food. ² Fermentation :- Microbial activity on food high in sugars leads to fermentation. ² Putrefaction :- Microbial activity on food high in protein leads to putrefaction. ² Rancidity : - Microbial activity on food high in fats leads to rancidity. A substrate, suitable temperatures and pH ranges are the factors for the growth of different microbes. Therefore, microbial activity can be controlled by controlling these factors. 1.3 Impact of microorganisms on humans and their activities Some microorganisms are beneficial to humans while some are harmful. Let us do Assignment 1.2 to understand the importance of microorganisms. Assignment 1.2 ² Collect information about beneficial and harmful effects of microorganisms and present them to the class. Beneficial effects of microorganisms Beneficial effects of microorganisms are of several types. Some of the advantages are, usage of microorganisms in different industries, microbial decomposition of dead plant and animal matter, biological pest control. ² Since ancient times man has been using microorganisms in different industries. Some examples are given in Figure 1.7. 6 Science | Importance of Microorganisms  producing curd producing yoghurt producing cheese bakery products producing antibiotics producing vaccines producing vinegar food (mushrooms) & alcohol making compost producing bio gas coir industry Figure - 1.7 Applications of microorganisms in different industries ² Microorganisms decompose dead plant and animal matter. If not these matter get collected and it affects the balance of environment. Therefore, microorganisms contribute to the well-being of the environment. ² Microorganisms are also used to control pests. This is one of the biological control methods of pests. Next let us consider harmful effects caused by microorganisms. Harmful effects of microorganisms Harmful effects of microorganisms are of several types. Food spoilage, causing infectious diseases for man, animals and crops, cause economical damage to clothes and wooden furniture are some of them. Science | Importance of Microorganisms 7 ² Microbial activity causes food spoilage (This was discussed in section 1.2). growth of growth of growth of microorganisms on microorganisms on microorganisms on vegetables bread fruits Figure - 1.8 ² Microorganisms cause various infectious diseases for man, animals and crops. Infectious diseases caused to man Virus - common cold, dengue, AIDS (Acquired Immuno Deficiency Syndrome) Bacteria - tuberculosis, leprosy, typhoid fever Protozoa - malaria, leishmaniasis, amoebisis Fungi - pityriasis, sore dengue haemorrhogic deformity due to leprosy fungi on skin (Pityriasis) patient Figure - 1.9 8 Science | Importance of Microorganisms Infectious diseases caused to animals Animals get infectious diseases due to microorganisms. Figure 1.10 shows some of the examples for such diseases. a dog suffering from Rabies a bull suffering from a cow suffering from mastitis foot and mouth disease Figure 1.10 Infectious diseases caused to plants Plants get infectious diseases due to microorganisms. Figure 1.11 shows some of the examples for such diseases. a potato plant with papaw leaves with chillie plant with blight mosaic disease leaf curled disease Figure 1.11 ² Damage caused due to the growth of microorganisms, on surfaces of objects. Growth of microorganisms on clothes, walls of buildings and wood has been caused adverse effects on the economy. These effects are mostly caused by fungi. fungi on clothes fungi on walls fungi on wooden surfaces Figure - 1.12 Growth of microorganisms on different surfaces Science | Importance of Microorganisms 9  Summary ² The organisms which cannot be observed by naked eye are called microorganisms. ² Microorganisms cause beneficial effects as well as harmful effects. ² Usage in various industries, decomposition of dead plant and animal matter and pest control are beneficial effects. ² Food spoilage, cause infectious diseases for man, animals and crops and damage to economically important surfaces are harmful influences caused by microorganisms. ² Nutrients, moisture, favourable temperature and favourable pH values are necessary for microbial growth. ² Food can be preserved by implementing necessary methods to control microbial activities. Exercise 1) State whether the following statements are true (√) or false (×) i) Bacteria belong to the category of microorganisms. () ii) A virus causes Tuberculosis. () iii) Refrigerating food helps to control the temperature suitable for microorganisms. () iv) Moisture and warmth are necessary factors for the growth of fungi. () v) The scientist Antonie van Leeuwenhoek observed microorganisms for the first time. () 2) Select the correct answer I. A disease not caused by a virus is 1) AIDS 2) Measles 3) Leprosy 4) Rabies II. The food type that undergoes fermentation in the presence of microorganisms is 1) Food with proteins 3) Food with sugars 2) Food with lipids 4) All three types 10 Science | Importance of Microorganisms III. Environmental conditions, suitable for microbial growth are given below. a)Temperature b) Moisture c) pH which of the above conditions are controlled by refregerating food? 1) a and b 2) a and c 3) b and c 4) a, b and c IV. The microbial activity on lipid food such as ‘dodol’/‘dothal’ and ‘kavum’/ ‘paniyaram’ is known as, 1) Fermentation 2) Putrefaction 3) Rancidity 4) All the above V. A favourable impact for humans by microorganisms, 1) Decomposition of dead plant and animal matter 2) Cause diseases to humans, animals and crops 3) Make food unsuitable for consumption 4) Cause economical impact by growing on non living surfaces 3) Give short answers. I. Write four examples for microorganisms II. Mention two factors required for microbial activity III. Name three products in which microorganisms are used. IV. What factor needed for microbial growth is controlled when food is stored in sugar/honey ? V. Mention two microbial applications in the field of medicine Technical Terms Microorganisms - laIqø Ôùka - ~sn[QPÒ Microscopic - wKaùlaISh - ~qUSUPõmi Food spoilage - wdydr krla ùu - EnÄ £ÊuøhuÀ Microbial degradation - laIqø Ôù ydhkh - ~sn[Q¨ ¤›øP¯õUP® Application of microbes - laIqø Ôù Ndú; - ~sn[QPÎß ¤μ÷¯õP® Infectious diseases - fndajk frda. - öuõØÖ ÷|õ´PÒ Science | Importance of Microorganisms 11 2 Animal Classification There is a vast diversity among animals that live in our environment. It is easy to study about them by classifying organisms, based on different criteria. Grouping of animals in a systematic way by considering their common features is known as animal classification. Animals can be classified on different criteria. In grade 7 you learnt how to classify animals based on presence or absence of a vertebral column (backbone). Let us do Activity 2.1 from the knowledge and facts you learnt in grade 7. Activity 2. 1 Method:- ² Observe given pictures of the animals living in your surroundings. ² Divide and tabulate them into two groups using the feature, presence or absence of a vertebral column. Snail Crab Yellow fin tuna Dog Cock Butterfly Python Spider Lion Figure 2.1 12 Science | Animal Classification Among those animals, yellow fin tuna, dog, cock, python and lion have a backbone. Snail, crab, butterfly and spider do not have a backbone. The animals without a backbone / vertebral column are known as invertebrates while the animals with a backbone / vertebral column are known as vertebrates Therefore, animals can be classified into two groups; ² Invertebrates ² Vertebrates 2.1 Main invertebrate groups Engage in Assignment 2.1 to study about invertebrates. Assignment 2.1 ² Observe given diagrams of the invertebrate animal species. ² Classify them based on different criteria. Leech Bivalve Beetle Sea anemone Dragonfly slug Figure 2.2 You have already classified the animals based on different criteria. Science | Animal Classification 13 Invertebrates are scientifically classified by using their common features. Some of the groups are given below. 1. Cnidaria 2. Annelida 3. Mollusca 4. Arthropoda Let us consider the features of each of the above groups. Cnidaria The animals belong to Cnidaria are predators and they live in water. Hydra, sea anemone, jellyfish are some examples for the group of Cnidaria. Hydra Sea anemone Jellyfish Figure 2.3 Some Cnidarians The features of Cnidaria are given below. ² Cnidarians have radially symmetrical body (If the body of an animal can Tentacles be divided into two equal halves Mouth along several axes we call it a radially symmetrical animal). ² There are two forms as Polyps and Medusa. (Polyps are fixed to the substrate and lead a sedentary life while Medusa are free floating organisms) Figure 2.4 Body form of ² They cripple small creatures with their Cnidarian (Hydra) special tentacles having cnidocytes and use them as food. 14 Science | Animal Classification  For extra knowledge The coral polyps belong to the Cnidaria group build up coral reefs. Annelida Annelids live in both marine and fresh water environments as well as in wet terrestial environments. Earthworm, leech, Nereis are some examples for Annelids. Earthworm Leech Nereis Figure 2.5 Some Annelids Common features of Annelids are given below. ² Body is bilaterally symmetrical (If the body of an Segments animal can be divided into two equal halves along one axis we call it a bilaterally symmetrial animal). Mouth ² They are vermiform (worm-like body shape). Anus Figure 2.6 Body form of ² Body is divided into segments. Therefore, known an Annelid (earthworm) as segmented worms. Mollusca Molluscs live in terrestial, marine and fresh water environment. Snail, bivalve, chiton, slug, cuttle fish, octopus are some examples for Molluscs. Snail Bivalve Octopus Figure 2.7 Some Molluscs Science | Animal Classification 15 The features of Molluscs are given below. ² They are bilaterally symmetrical. Shell Antenna ² Soft bodied animals. Mouth ² Possess a muscular foot. ² Possess a skin moistened with Muscular foot mucus. Figure 2.8 Body form of a molluscs (Snail) ² Some Molluscs bear shells. Figure 2.8 Body form of a molluscs (Snail) Arthropoda Arthropods live in terrestial as well as in aquatic environments. Arthropoda is the group to which the highest number of animals belongs. Insects, spiders, scorpions, millipedes, centipedes, prawns, crabs are some organisms that belong to the group Arthropoda. Butterfly Scorpion Centipede Prawn Figure 2.9 Some Arthropods Features of Arthropods are given below. Eyes ² Arthropods are bilaterally symmetrical. Antenna ² Their body possesses an external skeleton/ exoskeleton. Wings ² Some species possess wings. Jointed ² Arthropods have externally segmented body. appendages ² All Arthropods have jointed appendages. Figure 2.10 Body features of an Arthropoda (Insects) 16 Science | Animal Classification  Assignment 2.2 ² Collect the bodies of dead insects. ² Get a box (wood, metal or card board) and fix a piece of styrofoam to the bottom of the box. ² Fix the bodies on the styrofoam using long pins. ² Paste a name tag for each insect. (Discuss with your teacher how to keep the bodies of insects without Figure 2.11 Insect box decaying) 2.2 Main vertebrate groups Engage in Assignment 2.3 to study about vertebrates. Assignment 2.3 ² Observe the given pictures of different vertebrate animal species. ² Classify them using different criteria. Blue fin tuna Turtle Crocodile Common commorant Toad Hawk Bat Chimpanzee Salamander Figure 2.12 Science | Animal Classification 17 Now you can classify vertebrates based on different criteria. Vertebrates can be scientifically classified depending on their common features. Let us discuss the features of each of these groups. 1. Pisces 2. Amphibia 3. Reptilia 4. Aves 5. Mammalia Pisces Fish, the group of animals well adapted to live in water belong to Pisces. Tilapia, skate, shark, blue fin tuna, sear, gold stripped sardine, sprat are some fish that belong to Pisces. Tilapia Skate Shark Blue fin tuna Figure 2.13 Some Pisces Features of Pisces are given below. ² Body is invariably streamlined. This feature helps them to swim through water. ² The body is covered with scales. ² Has fins to swim through water and to balance while swimming. ² Respiration through gills ² Possess eyes without eye lids. Amphibia Amphibians spend part of their life cycle in water. Frogs, toads, salamanders, Ichthyophis are some animals that belong to the group Amphibians. Frog Toad Salamander Ichthyophis Figure 2.14 Some Amphibians 18 Science | Animal Classification Features of Amphibians are given below. ² Undergo metamorphosis. ² Skin is thin, moist and glandular. No scales in the skin. ² Some species use limbs for locomotion. ² Respiration is carried out by lungs, through wet skin or mouth. Reptilia Reptiles belong to this group. They are well-adapted for the terrestrial environment. Tortoise, turtle, cobra, python, viper, krait, lizard, monitor, iguana, crocodile belong to this group. Tortoise Crocodile Cobra Viper Figure 2.15 Some Reptiles Features of Reptilia are given below. ² Possess a dry skin with scales. No glands are present in the skin. ² Use limbs for locomotion. But some reptiles are limbless. They are adapted for crawling ² Respiration through lungs Aves Birds belong to the group Aves. They are well-adapted for flying. Blue magpie, swan, owl, parrot are some examples for Aves. Swan Owl Parrot Blue magpie Figure 2.16 Some Aves Science | Animal Classification 19 Features of Aves are given below. ² Streamlined body is designed for flying. ² Body is covered with feathers. ² Possess limbs for locomotion. Forelimbs are adapted as wings. ² They do not have teeth but the beak is adapted for feeding. ² Breathe using lungs. For extra knowledge There are some birds that cannot fly. Some examples are given below. Ostrich Cassowary Emu Rhea Penguin Kiwi Mammalia These animals feed on mother's milk. Man, rat, loris, orangutan, gorilla, chimpanzee, bat, whale, dolphin, stag, deer are some examples for mammals. 20 Science | Animal Classification  Gorilla Dolphin Deer Loris Figure 2.17 Some Mammals Features of Mammalia are given below. ² Has mammary glands. ² Skin has sweat glands, sebaceous glands and hair. ² Possess an external ear with ear lobe. ² Mammals have lungs to breathe. Assignment 2.4 ² Collect some pictures of mammals. ² Collect information about them. ² Prepare a booklet allocating one page for each animal. (Consider about the cover page, foreword, contents, acknowledgement etc.) By studying this lesson, you have identified that there is a wide diversity among animals. You can further study about them by visiting zoological gardens and wildlife parks. All animals contribute immensely to maintain the balance of the environment. Science | Animal Classification 21  Summary ² There is a vast diversity among animals in the environment. ² Animals with a backbone / vertebral column are known as Vertebrates and animals without a backbone / vertebral column are known as Invertebrates. ² Considering the common features, invertebrates can be classified into different groups. Cnidaria, Annelida, Mollusca and Arthropoda are some groups of Invertebrates. ² Considering the common features, vertebrates can be classified into different groups as Pisces, Amphibia, Reptilia, Aves and Mammalia. Exercise 1. Select the most suitable answer. i' The group of animals, not belonging to invertebrate is, 1' Annelida 2' Cnidaria 3' Amphibia 4' Arthropoda ii. The group with highest number of animals is, 1' Aves 2' Athropoda 3' Mollusca 4' Mammalia iii. An animal belonging to Reptilia group is, 1' shark 2' salamander 3' whale 4' turtle 2. Fill in the blanks. i' Sea anemone belongs to ''''''''''''''''''''''''' group. ii' Possessing segmented appendages is a feature of ''''''''''''''''''''''''''''''''' group. iii …………………….. breathe using lungs, wet skin and the mouth. 22 Science | Animal Classification 3. Name the invertebrate group that bears each of the features given below. i' Muscular foot - ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ii' Worm-like segmented body - ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' iii' Jointed appendages - ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' iv' Radial symmetry - ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 4. Write down the answers. i' Name two forms of Cnidaria with an example for each form. ii' Name four Arthropods that can fly. iii. Give three basic features of Mammalia. iv. Give three basic features of Aves. Technical Terms Classification - j¾.SlrKh - £õS£õk Radial symmetry - wÍh iuñ;sh - Bøμa \©a^º Bilateral symmetry - oaúmd¾Yaúl iuñ;sh - C¸£UPa \©a^º Morphological features - rEmSh ,laIK - E¸Á¯À C¯À¦PÒ Invertebrates - wmDIaGjxYSka - ÒÍ¢usi¼PÒ Vertebrates - mDIaGjxYSka - ÒÍ¢uskÎPÒ Cnidaria - ksvdßhdjka - {hõ›¯õ / SÈUSh¼PÒ Annelida - wefk,svd - AÚ¼hõ / xsh¨ ¦ÊUPÒ Mollusca - fud¨iald - ö©õ»ìPõ / ö©ßÝh¼PÒ Arthropoda - wdf;%dfmdavd - Bzvμ¨÷£õhõ / ‰mkUPõ¼PÒ Pisces - msiaflaia - ¤ìéì / «ßPÒ Amphibia - weï*sìhd - A®¤¯õ / D¹hPÁõÈPÒ Reptilia - frmaà,shd - öμ¨Ÿ¼¯õ / FºÁÚ Aves - wdfõia - B÷Áì / £ÓøÁPÒ Mammalia - uefï,shd - ©÷©¼¯õ / £õ¿miPÒ Science | Animal Classification 23 3 Diversity and Functions of Plant Parts Plants in our environment show an enormous diversity as animals. Observe the diversity of plants in the forest shown in Figure 3.1. Figure 3.1 A rain forest The major reason for the beauty and the wonder of a forest is the diversity of plants. Plants differ each other in its size and morphological features. The reason for this vast diversity is the adaptations of plants to survive in different environments. You have already learnt the parts of a plant in grade 7. Recall what you have learnt and engage in Activity 3.1 to study further about the parts of a plant. Activity 3.1 You will need : - 'Kuppameniya'/'kuppaimani' or a 'monarakudumbiya'/ 'seethaviyar selugkaluner' plant. Method : - ² Uproot the plant from the soil without damaging the root system, and wash properly. ² Observe the plant and identify its parts. ² Draw a diagram and name the parts. 24 Science | Diversity and Functions of Plant Parts Figure 3.2 shows the main parts of a plant. Flowers Compare your diagram with the given figure. Fruits Shoot Every flowering plant consists system of fruits, leaves, stem and roots. But they do not appear same Leaves in every plant. They have an extensive diversity. Let us have Stem a review about the diversity and Tap root the functions of leaves, stem and roots of a plant. Root system Lateral roots Figure 3.2 Parts of a plant 3.1 Diversity and functions of plant leaves Leaves are considered as the most significant part of a plant. Most of the leaves are green in colour. The main function of a leaf is photosynthesis. Food is produced in plants having chlorophyll by using carbon dioxide, water and light energy. This process is known as photosynthesis. Plant leaves are well adapted for efficient photosynthesis. Let us do Activity 3.2 to study about this. Activity 3.2 You will need : - Some leaves of jak, mango, temple flower and manioc Method : - ² Observe the leaves well. ² Compare the thickness of the leaves. ² Draw the area of the leaves on a square ruled Figure 3.3 sheet and compare them. Science | Diversity and Functions of Plant Parts 25  For the purpose of photosynthesis a leaf is typically flat and thin to expose to light over a broad area and allow light to penetrate fully into the tissues. Thick and fleshy leaves can also be seen as an adaptation to adverse (arid) environmental conditions. e.g:- Aloe, temple flower, yellow oleander (kaneru) Figure 3.4 shows the parts of a leaf. Veins Base Tip Margin Petiole/ leaf stalk Lamina/blade Figure 3.4 Parts of a leaf Does every leaf have the same shape of petiole, margin, base and tip? Do Activity 3.3 to study about it. Activity 3.3 You will need : - Some leaves that can be found in your environment (e.g: mango, papaw, rose, temple tress, 'Bo leaf'/zarasa illaiZ) Method: - ² Obtain leaves from different plants in your environment. ² Observe the leaves and draw pictures having different blades, bases, margins and tips. When you observe the blades of these leaves you will understand that they have different shapes (Figure 3.5). 'Gotukola'/ 'Kottamba' / ʻVallaraiʼ ʻKottankachchiʼ Radish Mango 'Kohila'/ ʻKohilaiʼ Figure 3.5 Diversity of leaf blades 26 Science | Diversity and Functions of Plant Parts You would have observed that there is a wide variation in leaf structure. That is due to their adaptations for the main function as well as various other functions. Study the following diagrams and identify further the diversity of leaves. If you observe the tips of those leaves you will notice that the tips are different as sharp, curved, pointed, divided etc (Figure 3.6). 'Niyangala'/ 'Koboleela'/ jak 'Bo' leaf/'Arasa ilai' Temple trees 'Karthikaipoo' 'Thiruvaththi' Figure 3.6 Diversity among leaf tips The margins can be serrate or smooth. (Figure 3.7) Hibiscus/Shoe 'Akkapana' Rose Flower Temple trees Begonia 'Sadaikaraichan' Figure 3.7 Diversity among leaf margins The bases and the petiole of leaves too have different forms (Figure 3.8). 'Kohila' Lotus 'Bo' leaf Shoe flower Temple trees Figure 3.8 Diversity among leaf base When you observe the environment you will be able to study more about other adaptations of leaves. Science | Diversity and Functions of Plant Parts 27  Leaf arrangement The leaves are fixed to the stem in a way to expose all the leaves to the sun light. The pattern of fixing the leaf to the stem of a plant is known as leaf arrangement. Leaf arrangment supports efficient photosynthesis. Some leaf arrangements are given below. ² Leaves are on alternate sides of the ² Leaf attachments paired at nodes and stem. in opposite directions. Figure 3.9 'Anona' ('Katu Anoda')/ 'Annamunna' Figure 3.10 Guava ² Three or more leaves attach at each ² Leaves are attached in a spiral manner node on the stem in a whirl. around the stem. Figure 3.11 'Rukkaththana'/ 'Earlilaippalai' Figure 3.12 'Kanda'/'Vattakkanni' Assignment 3.1 ² Observe the environment and identify the leaf arrangements as much as possible. ² Complete the given table using your observations. Table 3.1 Leaf arrangement Examples of trees Leaves are on alternate sides of the stem. '''''''''''''''''''''''''''''''''''''' Leaf attachments paired at nodes and leaves in opposite '''''''''''''''''''''''''''''''''''''' directions. Three or more leaves attach at each node on the stem in a '''''''''''''''''''''''''''''''''''''' whirl. Leaves are attached in a spiral manner around the stem. '''''''''''''''''''''''''''''''''''''' 28 Science | Diversity and Functions of Plant Parts Let us now consider the other functions of leaves. ² Transpiration is the process of evaporation of water from plants (Figure 3.13). It mainly takes place through stomata in leaves. Transpiration helps to transport water to the upper parts of the plant. The leaves of plants in arid environments, are adapted to minimize transpiration. Stomata Figure 3.13 Internal structure Some adaptations are given below. of a leaf ² Thick, waxy cuticle e.g. - temple trees, oleander ² Leaves reduced to spines e.g. - cactus ² Thin leaves e.g. - 'kasa' / 'savukku' ² Reduced number of leaves e.g. - 'navahandi' / 'kally', 'heerassa'/'pirattai' Temple trees Cactus 'Kasa' Figure 3.14 Adaptations to minimize transpiration ² Some leaves are adapted to store water. They have become fleshy because they have specialized tissues to conserve water (Figure 3.15). 'Akkapana' Aloe Figure 3.15 Plants with water storage leaves Science | Diversity and Functions of Plant Parts 29  ² Some leaves produce new plants through asexual reproduction. e.g. :- 'Akkapana', 'begonia' Let us do Activity 3.4 to study how some plant leaves produce new plants. Activity 3.4 You will need : - some leaves of plants such as akkapana, begonia, peparomia Method : - ² Make a small cut at the veins of the above mentioned leaves and cover the place with soil. ² Keep them watering for several days. ² After 3-4 days observe the roots near the veins of the leaves. ² Find other ways of getting plants from leaves. 'Akkapana' Begonia Peparomia Figure 3.16 3.2 Diversity and functions of plant stems The basic functions of a stem are supporting and bearing leaves, buds, flowers, fruits, seeds of the plant and keeping the plant upright. Also the stem transports water and minerals throughout the plant. Most stems are found above the ground. Some stems grow underground and are known as underground stems. In addition to the basic functions, stems have adapted to fulfill other functions. Let us study the diversity of stems based on their adaptations. ² Most stems produce new living tissues allowing plants to grow and reproduce. These stems are known as propagative stems. Given below are some examples for propagative stems (Figure 3.17, 3.18). 'Gotukola' 'Undupiyaliya'/ 'Sirupulladi' 'Ambul ambiliya'/ 'Puliyarai' Figure 3.17 Some plants reproduced by runners/ stolon 30 Science | Diversity and Functions of Plant Parts  Banana 'Kalanduru'/ 'Paalargu' Paddy Figure 3.18 Some plant species re-produced by Suckers ² Some plants store food in aerial stems (Figure 3.19). Sugarcane 'Kithul' Figure 3.19 Some plants with storage stems ² Some underground stems serve the functions of storage of food perennation and sexual propagation. During the adverse seasons the aerial parts get destroyed but the underground stem survives. During favourable seasons new sprouts come out from the underground stem using stored food (Figure 3.20). Turmeric Ginger Onion Potato Figure 3.20 Some plants reproduced by underground stem Science | Diversity and Functions of Plant Parts 31  ² Some stems are green and photosynthetic. Such stems are called photosynthetic stems (Figure 3.21). Cactus 'Daluk' / 'Sathurakkalli' Figure 3.21 Some photosynthetic stems ² Some plants fix to a support to climb up and absorb sunlight efficiently. Such stems are called climbing stems (Figure 3.22). 'Venival/ Maramanjal' Beans Figure 3.22 Some plants with climbing stems 32 Science | Diversity and Functions of Plant Parts  Assignment 3.2 ² Complete Table 3.2 using examples for each type of stems which have adapted to carry out the functions given below. Table 3.2 Propagative Aerial stems with Underground Photosynthetic stems food storage stems stems 3.3 Diversity and functions of plant roots The basic function of root is to anchor the plant in the soil, absorb water and minerals. There are some roots adapted to satisfy other functions. Other than the tap root and its branches, there are roots which arise from other parts of the plants. These roots are known as adventitious roots. There are roots that adapted to fulfill many other functions. They are given various names. ² Tuberous roots - The roots that are swollen due to storage of food are known as tuberous roots. Some tuberous roots allow the plant to survive in unfavourable seasons. Food can be stored either in the tap root or in adventitious roots. Storage of food in tap root Carrot Radish Beet Figure 3.23 Some plants that store food in tap root Science | Diversity and Functions of Plant Parts 33  Storage of food in adventitious roots Manioc Sweet potato Dahlia Figure 3.24 Some plants that store food in adventitious roots ² Prop roots - Adventitious roots that arise from branches. They penetrate the soil and helps to support branches. Banyan Tree 'Rath kadol '/ 'Sen kandal' Figure 3.25 Some plants with prop roots ² Stilt roots - Adventitious roots arise from the stem, grow below the ground and support the stem. 'Vetakeyya'/'Thalai' 'Rampa' 'Maha kadol'/'Perung kandal' Figure 3.26 Some plants with stilt roots 34 Science | Diversity and Functions of Plant Parts ² Climbing /Clasping roots - Roots that help the climbing stem/ creepers to fix to a surface/support. Betel Pepper Figure 3.27 Some plants with climbing roots ² Aerial roots - These roots absorb moisture from the atmosphere and supply the plant. These specialized roots can be found mostly in epiphytes. Orchid Vanilla Figure 3.28 Some plant with aerial roots ² Respiratory roots - These roots absorb air from the atmosphere and supply to the plant. They are specialized roots which can be found mostly in mangroves. Sonneratia 'Maha kadol' Figure 3.29 Some plants with respiratory roots Science | Diversity and Functions of Plant Parts 35  ² Propagative roots - These roots produce new plants. Curry leaves Guava 'Beli/Vilvam' Figure 3.30 Some plants with propagative roots Assignment 3.3 Collect some root specimens and study them. Consider the necessary steps that should be taken to conserve these roots. Assignment 3.4 Plan a field visit to observe the nature and the diversity of plants. Study the adaptations of plants and relate them to their functions. Plants play a vital role in the environment. Therefore, it is your duty to explore and collect specimens with minimum damage to the environment. 36 Science | Diversity and Functions of Plant Parts  Summary ² The major parts of a plant are roots, stem, leaves, fruits and flowers. ² There is vast diversity among parts of the plants. Adaptation of plant parts to their functions is the reason for this vast diversity. There are some plant parts that exhibit special adaptations. ² The basic function of a leaf is photosynthesis. Some leaves are adapted to store food and water and also for propagation. ² The basic function of a stem is to hold leaves, flowers, fruits and transport water and minerals throughout the plant. ² Some stems are adapted for photosynthesis, to climb up, propagation and to store food. ² The basic function of roots is to anchor the plant in the soil, absorb water and minerals. ² Tuberous roots, prop roots, stilt roots, climbing roots, aerial roots and respiratory roots are adapted for special functions. ² The reason for vast diversity among plants is their functions and adaptations to survive in different environments. Exercise 1) Write the main function of the given plant parts. a) Plant leaves.................................... b) Stem.......................................... c) Roots.......................................... 2) Write the special adaptations of the following plant roots/stems/leaves. i. Cactus v. Sweet potato ix. 'Niyangala' ii. Carrot vi. Pepper x. Orchid iii. Banyan vii. Begonia xi. Guava iv. Aloe viii. 'Navahandi' xii. 'Rampa' Science | Diversity and Functions of Plant Parts 37  3) Fill in the blanks. i) The pattern in which leaves grow on the stem is known as ……………….. ii) Sugarcane, palmyrah are examples for ………………. stems. iii) The leaves of the cactus tree reduced to spines is an adaptation to minimize …………………. iv) Curry Leaves, beli, bread fruit trees often use the ……………………. for propagation. v) Respiratory roots are specialized roots that can be seen in ………...……… plants. Technical Terms Diversity of leaves -- m;%j, úúO;ajh -- Cø»PÎß £ÀÁøPø© Diversity of stems -- l|kaj, úúO;ajh -- uskPÎß £ÀÁøPø© Diverstiy of roots -- uq,aj, úúO;ajh -- ÷ÁºPÎß £ÀÁøPø© Photosynthetic stems -- m%NdixYaf,aIl l|ka -- Cø»zöuõÈÀ uskPÒ Climbing stems -- wdfrdayl l|ka -- HÖ® uskPÒ Propagative stems -- m%pdrK l|ka -- CÚ®ö£¸US® uskPÒ Underground stems -- N+.; l|ka -- {»URÌz uskPÒ Tuberous stems -- wdlka§ l|ka -- QʸÁõÚ uskPÒ Tuberous roots -- wdlka§ uq,a -- QʸÁõÚ÷ÁºPÒ Prop roots -- lre uq,a -- uõ[S®÷ÁºPÒ Stilt roots -- lhsre uq,a -- ªsi÷ÁºPÒ Aerial roots -- jdhj uq,a -- PõØÔØS›¯ ÷ÁºPÒ Respiratory roots -- Yajik uq,a -- ‰a_÷ÁºPÒ Storage roots -- ixÑ; uq,a -- ÷\ª¨¦ ÷ÁºPÒ Propagation -- m%pdrKh -- CÚ¨ö£¸UP® 38 Science | Diversity and Functions of Plant Parts 4 Properties of Matter 4.1 Discontinous nature of matter The environment around us is composed of matter and energy. Recall the facts you learnt in grade 6 about matter and energy. To validate that knowledge further, do Assignment 4.1. Assignment 4.1 Classify and tabulate following items as matter and energy. Air, water, ball, light, bulb, sound, table, chair, electricity, heat, magnet Table 4.1 Matter Energy air light Of the above, air, water, ball, bulb, table, chair and the magnet require space and have a mass. Such things are known as matter. When considering light, sound, heat and electricity, they do not occupy space and have no mass. They are considered energy. Components of the environment such as soil, water and rocks and the man made structures and various equipments are examples for matter. Evidence for discontinuous nature of matter An acceptable notion about the nature of matter was first put forward by the Greek philosopher Democritus who lived in the era 460-370 B.C. According to him, matter is made of very small particles. Later, the Greek philosopher Aristotle (384-270 B.C.) stated that matter is not composed of particles. It is said that in Athens of Greece, a public debate was held between the proponents of Aristotle and Democritus. The idea that "matter is particulate in nature" became victorious at that debate and later modern scientists confirmed experimentally the fact that matter is made up of particles. The status matter exists as a collection of particles with spaces among them is known as discontinuous nature or particulate nature of matter. Science | Properties of Matter 39 Matter can be classified as solid, liquid and gas according to its physical nature. Various activities can be done to confirm the discontinuous nature of solid, liquid and gaseous matter. Discontinuous nature of solid matter Take a piece of chalk and break it into two pieces. Break one of those pieces again into two pieces. Likewise, break the pieces you get successively till you obtain the smallest possible particle. When the initial piece was broken into two, you would have got two smaller pieces. When the chalk is broken again and again we get more and more smaller pieces. The smallest piece of chalk that we obtain like this without changing the properties of chalk is called a chalk particle. Accordingly, you would be able to imagine that a piece of chalk is formed by the union of a large number of chalk particles. The piece of chalk which is a collection of small particles has a particulate nature. There are spaces among those particles. Let us do Activity 4.1 to investigate the discontinuity of solid matter. Activity 4.1 You will need:- A container of water, a watch glass, blue or red ink, a few crystals of potassium permanganate, a piece of white chalk Method:- ² Add a small amount of blue/red ink or a potassium permanganate solution to a watch glass. Take a piece of chalk and place one end of it on ink or the solution. Record your observations. ink chalk chalk on ink Figure 4.1 When the piece of chalk is placed on the blue/red ink or the potassium permanganate solution in the watch glass, you can see the colour soaking up through the piece of chalk. The ink is able to move up because the piece of chalk is discontinuous. It is because the piece of chalk consists of a large number of very small particles, each with the properties of chalk, and a large number of spaces through which the coloured particles can move. This activity confirms that solid matter is discontinuous. 40 Science | Properties of Matter Have you heard what happens when mercury comes into contact with items made of gold? In such an event, we will be able to observe mercury particles in the item of gold. The reason for this is the movement of mercury particles through the gold particles because gold is discountinuous. Because of this, when gold objects come into contact with mercury they get damaged. Figure 4.2 A gold ring that came into contact with mercury Assignment 4.2 ² Plan and implement simple activities to show that solid matter is particulate in nature. Let us next consider about the discontinuous nature of liquid matter. Discontinuous nature of liquid matter Take a small volume of water and divide into two portions. Divide one of them again into two portions. Likewise, divide one half again and again until you get the smallest possible volume. Even though the small volume of water was divided into two, both volumes contain water. Even at the moment when the volume becomes extremely small after repeated divisions, water is the substance which occupies that volume. In such a way, the smallest volume of water that can be obtained while retaining the properties of water can be called a water particle. Hence, water is formed by the assembling of a large number of water particles with one another. Let us engage ourselves in Activity 4.2 to look into the discontinous nature of liquid matter. Activity 4.2 You will need:- A watch glass, a beaker with water, potassium permanganate/ coloured ink Method:- ² Fill a beaker in half with water and put a crystal of potassium permanganate into it. Record the observations after about five minutes. Then, shake the water in the beaker gently. State the observations. ² Add a drop of coloured ink to a (a) water beaker with (b) water beaker potassium permanganate with coloured ink beaker containing water. Record the Figure 4.3 observations. Science | Properties of Matter 41 It can be observed that the colour of the potassium permanganate crystal placed in the beaker of water gradually spreads in water. It happens because the potassium permanganate particles move into spaces among the water particles. When a drop of ink is added to a beaker of water, the water gradually becomes coloured due to the movement of ink particles among water particles. Hence, it is clear that liquid matter also has a particulate nature. Assignment 4.3 Plan and implement some simple activities to demonstrate that liquid matter is particulate in nature. Discontinuous nature of gaseous matter Let us conduct Activity 4.3 to verify that gases are discontinuous. Activity 4.3 You will need:- Two gas jars, nitrogen dioxide gas, joss stick, a few drops of perfume Method:- ² Fill a gas jar with brown-coloured nitrogen dioxide gas and close it with another gas jar. Record your observation after two minutes. (Do this as a teacher demonstration.) ² Light a joss stick. ² Place some perfume in a watch glass and leave for some time. ² Record observations. When a gas jar is filled with brown nitrogen dioxide gas and an inverted gas jar containing air is placed over it, mixing of the two gases can be observed. The reason for this movement of the nitrogen dioxide particles is the existence of spaces among the air particles. The scent of the lighted joss stick spreads throughout the classroom. While the smell of perfume diffuses across the classroom, you would be able to see that the perfume had got removed from the watch glasses. We get its smell because its particles have moved through air and entered our nose during the spread of particles. Figure 4.4 Spread of nitrogen This leads to the explanation that gaseous matter too dioxide gas in gas jars is particulate in nature. 42 Science | Properties of Matter  Assignment 4.4 Plan and implement with your teacher simple activities to support the fact that gaseous matter has a particulate nature. Based on the above, we can conclude that all matter (solid, liquid or gas) is composed of particles and there are spaces among those particles. Thus, we can conclude that matter is discontinous. 4.1.1 Physical properties of matter in relation to its particulate nature It is the difference in the organisation of particles that leads to the variation of the specific characteristics of the three states in which matter exists. This can be illustrated as follows. Solid ² Particles are orderly arranged. ² Particles are strongly bound to each another. ² Particles do not move relative to one another, but can vibrate in the same positions. Organisation of particles in ² Space among particles is less. a solid Liquid ² Particles are not orderly arranged. ² Though, the particles are close to one another, the binding forces are not as strong as in a solid. ² The particles can move within the liquid. Organisation of particles in ² Space among particles is less, but higher than a liquid that of a solid. Gas ² Particles are not orderly arranged. ² Binding forces among the particles are very weak. ² Particles move freely and randomly. ² Much space is left among the particles. Organisation of particles in a gas Science | Properties of Matter 43 The reason for the variety of physical properties of solid, liquid and gaseous matter is the diversity of their prticular arrangement. Let us have a look at Table 4.2 which presents these differences. Table 4.2 Property Solid Liquid Gas Shape Has a definite No definite shape. No definite shape. shape (Takes the shape of (Takes the shape of the occupied part the occupied part in in the container) the container) Volume Has a fixed Has a fixed No fixed volume. volume volume.(Does not (Spreads throughout spread throughout the entire volume of the entire volume the container) of the container) Compressibility Connot be Cannot be Can be compressed compressed easily. compressed easily. easily. Density Has a high density Has a high density Density is low A solid has a definite shape because the particles forming it are organised in a regular pattern and are strongly bonded. Liquids and gases lack a definite shape because their particles are not arranged orderly. Solids and liquids have a definite volume, but gases do not have a definite volume. This is because the gas particles spread freely and occupy the entire volume of the container as the binding forces among gaseous particles are very weak. Compression means the decrease in volume of matter by increasing pressure. Solid and liquid matter cannot be compressed easily. However, gaseous matter can be compressed easily. In order to compare the compressibility of liquids and gases let us do Activity 4.4. Activity 4.4 You will need:- Two identical syringes, water, nitrogen dioxide gas Method:- ² Draw water into one syringe until half of it is filled with water. ² Take an equal volume of nitrogen dioxide gas to the other syringe. (Do this as a teacher demonstration.) ² In both syringes close the open end and push the piston forward. ² In both cases compare the ability to move the piston forward. 44 Science | Properties of Matter You will note that the piston in the syringe with water cannot be pushed forward whereas the piston in the syringe with air can be pushed forward. This shows that it is difficult to compress water but air can be compressed easily. Let us find out the reason for this. Water is a liquid. As the particles of a liquid are closely packed they cannot be brought closer by applying a force. Therefore, they are relatively difficult to compress. In a gas there are wider spaces among the particles, therefore, by applying a force the particles come closer. That is why the gases can be compressed easily. When comparing the densities of solids, liquids and gases it is seen that solid and liquid matter have a high density but gases have a low density. Density will be studied further in a future lesson. Solids, liquids and gases are used for various purposes depending on their properties. Some examples for the instances in which they are used are given below. ² Solids - parts of machinery, parts of vehicles, building materials, weapons ² Liquids - mercury thermometer, hydraulic jack, as a medium of transport ² Gases - inflating tyres, in pressure cookers, in hydrogen balloons, in liquid petroleum gas (LP gas) cylinders Assignment 4.5 Make models to demonstrate the particulate nature (discontinuity) of the three states of matter. 4.2 Utilizing physical properties of matter 4.2.1 Pure substances and non pure substances Consider a cylinder containing nitrogen gas and a cylinder containing ordinary air. The cylinder of nitrogen gas contains only nitrogen gas. The cylinder of air contains several gases such as nitrogen, oxygen, argon and carbon dioxide. On the otherhand potable water contains gases and various salts dissolved in it. But, pure water contains only water. Let us do Assignment 4.6 to explore this further. Science | Properties of Matter 45  Assignment 4.6 ² Pay your attention to the substances given in Table 4.3. ² Find out about the components in those substances and complete the table. Table 4.3 Substance Components Contains one Contains component more than one only component air hyrogen, oxygen, argon, carbon dioxide pure water water drinking water water, various gases, dissolved in water, salts sugar sugar salt solution salt, water a piece of copper copper tea tea, water, sugar aluminium iron silver Of the substances given in the table, if you focus your attention to sugar, silver, pure water, aluminium, iron and copper, it is clear that they are composed of only one component. You may also be able to identify that the salt solution, tea and potable water contain more than one component. Thus, on the basis of the components contained, matter can be divided into two main categories as follows. ² Pure substances - Matter that contains only one component. ² Non pure substances - Matter that contains two or more components. ² Pure ² substances Pure substances Substances having a constant composition, that is, substances containing only one component with definite properties, are called pure substances. Hence, sugar, copper, pure water, aluminium, silver and iron given in Table 4.3 are pure substances. 46 Science | Properties of Matter Based on the nature of the pure substances, they can be classified into two groups, elements and compounds. Elements Let us consider copper, aluminium, silver and iron classified under pure substances. These cannot be divided further into simpler substances. Pure substances with definite properties which cannot be further divided by physical or chemical methods into substances are known as elements. As at now, scientists have identified nearly 120 elements. Each of these elements has unique properties of its own. Iron, aluminium, sulphur, carbon, oxygen, nitrogen, mercury, copper, gold, silver, lead, hydrogen and chlorine are a few examples for elements. Sulphur A bottle filled with Iron Copper chlorine gas Carbon Mercury Aluminium Zinc Figure 4.5 Some commonly used elements Compounds Let us consider about sugar and pure water you classified under the pure substances above. They are formed by the combination of two or more elements. Compounds are homogeneous, pure substances in which two or more elements are chemically combined in a fixed ratio. The properties of a compound are different from the properties of the elements that contributed to form that compound. Although, there are only 120 elements, there are millions of compounds in existence. The reason for this the possibility of combining elements in a vast multitude of ways with one another. Let us inquire into the formation of compounds by the combination of elements chemically through the following example. Science | Properties of Matter 47  ² Iron powder is a greyish black solid substance. ² Sulphur powder is a yellow coloured solid. ² When these two are mixed and heated till the solid mass melts, a black solid is formed. Iron Sulphur Iron sulphide Figure 4.6 It can be observed that the substance formed finally is different in properties from the substances that were used initially. Now, it may be clear to you that here, the element iron has combined chemically with the element sulphur to form the black coloured compound, iron sulphide. Given below are some compounds used in everyday life. Copper sulphate Sodium chloride A fire extinguisher filled with carbon dioxide Calcium carbonate Sodium hydroxide Glucose Figure 4.7 Oxygen, nitrogen and argon present in ordinary air are elements. Nevertheless, carbon dioxide is a compound. The compound carbon dioxide is formed by the combination of the elements carbon and oxygen chemically. Table 4.4 shows the elements contained in some compounds. Table 4.4 Compond Elements present copper sulphate copper, sulphur, oxygen sodium chloride sodium, chlorine sodium hydroxide sodium, hydrogen, oxygen calcium carbonate calcium, carbon, oxygen carbon dioxide carbon, oxygen water hydrogen, oxygen 48 Science | Properties of Matter You will study about non pure substances/ mixtures in a higher grade. 4.2.2 Various physical properties of matter Different substances have different physical properties. There are a number of physical properties in matter that help to identify and distinguish them. Some of these are presented in Table 4.5 Table 4.5 Physical property Simple introduction to the physical property Lustre Shiny suface due to reflection of light falling on it. Hardness Resistance of the material to wear and tear and scratching Brittleness Being subject to breaking / crushing into pieces when a force is applied Thermal conductivity Ability to conduct heat through the substance Electrical conductivity Ability to conduct electricity through the substance Sonority Emitting a lasting sound when struck with an object Colour The visual quality of the substance Elasticity Ability to stretch upon pulling and returning to the initial state when the force is released Density Mass of a unit volume Malleability Ability to be hammered into sheets without breaking into pieces Ductility Ability to be drawn into a wire without breaking Smell Sensation caused in the nose due to the volatility of the substance Expansivity Increase in volume without an increase in the mass upon increasing temperature Texture The rough or smooth nature felt to the touch Melting point/ temperature The temperature at which a substance turns from the solid state to the liquid state Boiling point/ temperature The temperature at which a substance turns from the liquid state to the gaseous state Some of the physical properties of a substance can be used to examine its purity. e.g.:- Density, melting point, boiling point Science | Properties of Matter 49 Density What can you observe if you put a piece of iron, a cork stopper and a candle to water ? The piece of iron sinks while the cork and the candle float. The reason for this is the fact that the density of iron is greater than that of water wheres the density of cork and candle wax is less than that of water. Density is a property unique for a particular substance. Density is the mass of a unit volume of a given substance. Let us do Activity 4.5 to find out whether the density of water has a constant value. Activity 4.5 You will need:- Density bottle, distilled water, triple beam balance, fresh water, brackish water, hard water Method:- ² Fill the density bottle (specific gravity bottle) with water, blot it and weigh using the triple beam balance. Figure 4.8 ² Remove the water, refill the density bottle with distilled water, blot it and weigh. ² Compare the masses obtained. ² Repeat same experiment using the same density bottle but filling it with samples of water obtained from different environments such as fresh water, brackish water, brine and tank water and compare the masses. Even if the masses are taken by repeating weighing several times, you will be able to see that the mass of an equal volume of distilled water takes a constant value. But the masses of equal volumes of fresh water, brine and brackish water will not be equal. Distilled water is the water free from dissolved solids. Since, the density of pure water always takes the same value, pure water can be identified by measuring the density. Similarly, for other pure substances, the density is a fixed value. Therefore, the purity of solids, liquids and gases can be determined by finding their densities. 50 Science | Properties of Matter Table 4.6 gives densities of some pure substances. Table 4.6 Substance Density/kg m-3 Gold 19300 Mercury 13600 Lead 11300 Copper 8900 Iron 7700 Aluminium 2700 Water 1000 Melting point There is a fixed temperature at which a solid turns into a liquid. This temperature is known as its melting point. Pure substances have a fixed melting point. Let us conduct the following experiment to find out whether the melting point of pure substances has a constant value. Thermometer Activity 4.6 Stirer You will need:- A boiling tube, a beaker, some ice chips, water, a thermometer, a burner, a stand, a stirer Method:- Ice chips ² Fill about one fourth of a boiling tube with ice chips. Water ² Arrange the apperatus as in Figure 4.9. ² Heat till the ice melts. ² Stir the water well, using a stirer. ² Tabulate temperature against time. Heat Figure 4.9 Table 4.7 Time Temperature You would have observed that the temperature remains constant until all the ice melts. Science | Properties of Matter 51 When heat is supplied, matter turns from the solid state to liquid state without changing its temperature. The specific temperature at which this change in state occurs is called the melting point. In the above experiment the temperature remained at 0 oC until all the ice turned into liquid water. So, the melting point of pure water at normal atmospheric pressure is 0 oC. Table 4.8 indicates melting points (at standard atmospheric pressure) of some pure substances. Table 4.8 Substance Melting point/ (oC) Ice 0 Sulphur 132 Lead 317 Aluminium 660 Copper 1083 Iron 1539 The melting point of pure substances is a constant. Therefore, the purity of a substance can be determined by measuring its melting point. Boiling point There is a definite temperature at which a liquid turns into a gaseous state. That temperature is known as its boiling point. Pure substances have a constant boiling point. In order to find out whether there is a constant value for the boiling point of pure substances let us conduct Activity 4.7. Activity 4.7 Thermometer You will need:- A boiling tube, water, a thermometer, a stand, a burner Method:- ² Add water to a boiling tube and fix a thermometer as shown in Figure 4.10. Water ² Heat the water with the burner. ² Tabulate the change in temperature with time. Heat Stand Figure 4.10 52 Science | Properties of Matter  Table 4.9 Time Temperature When water is heated temperature rises gradually. At a certain moment, the rise in temperature stops and water turns into the vapour state from the liquid state. That temperature remains unchanged till all the water is vapourised. That temperature is called the boiling point of water. The boiling point of pure water at standard atmospheric pressure is 100 oC (The boiling point of a liquid depends on the surrouding pressure. If the surrounding pressure falls, the boiling point falls. The boiling point of water on a high mountain is lower than 100 oC). If water is not pure due to the dissolving of foreign substances the boiling point (100 oC) may be elevated or lowered. From this it is clear that the boiling point is also a physical characteristic that can be used to probe the purity of a compound. Table 4.10 shows boiling points of some substances under normal atmospheric pressure. Table 4.10 Substance Boiling point (oC) Ethyl alcohol 77 Water 100 Sulphur 444 Lead 1744 Iron 2900 Now let us see whether we can classify the elements that we identified as pure substances based on their physical properties. Activity 4.8 You will need:- Iron, copper, sulphur, carbon (graphite), magnesium, aluminium, lead, zinc Method:- ² Identify observations or simple activites appropriate to examine the properties such as metallic lustre, sonority, thermal conductivity, electrical conductivity, malleability and brittleness. You can have an understanding about this by reading the paragraph coming after this activity. ² Do the relevant activities and record the observations using a table such as Table 4.11. Place a tick (√) when the element has the relevant property and a cross (×) if it does not' Science | Properties of Matter 53  Table 4.11 Thermal Electrical Substance Lustre Sonority Malleability Brittleness conductivity conductivity Iron √ √ √ √ √ × Copper Sulphur Graphite Magnesium Aluminium Lead Zinc Some methods which you can adopt to examine each physical property are described below. To investigate the physical properties you can use either those methods or other methods after discussing with your teacher. To examine the lustre, you can scratch the surface of the substance with a knife or clean it with a sand paper. The material used to examine sonority should be at least one millimetre thick. It can be done by striking with a metal rod or dropping on the cement floor from a suitable height. To inquire into the thermal conductivity a change that can be observed during the transmission of heat has to be used. For example, drops of candle wax can be placed on rods made of different materials and melting of the wax during conduction of heat can be done. Plate of an insulator Candle wax such as asbestos Bunsen burner Tripod Figure 4.11 Examine thermal conductivity 54 Science | Properties of Matter  In order to examine electrical conductivity a simple circuit should be constructed. It could be constructed on a circuit board or made by connecting the pieces of equipment using crocodile clips. If the substance to be tested placed between A and B, conduct electricity, the bulb will light. If the substance does not Figure 4.12 conduct electricity the bulb will not light. To observe malleability and brittleness a piece of the relevant substance can be struck lightly with a hammer after placing it on a fairly thick surface. If it turns into a sheet on hammering, it shows malleablilty. If it crumbles, it is a brittle substance. Based on the results of the above experiment and other characteristics, elements can be divided into two classes, metals and non metals. The diversity of the physical properties of metals and non metals can be illustrated as follows. Good conductors Poor of heat conductors of Poor conductors of Can be drawn into Good conductors heat electricity (except wires (ductility) of electricity carbon) Metals Non metals Can be hammered lustrous into sheets Breaks into Not (malleability) Sonorous pieces when lustrous struck (brittle) Figure 4.13 Figure 4.14 Assignment 4.7 Classify the substances given in Table 4.11 in Activity 4.8 as metals and non metals. Science | Properties of Matter 55 Based on their physical properties, elements can be classified as metals and non metals. Moreover, based on the physical state of matter they can be classified as solid, liquid and gas. Study Table 4.12 well and get to know the diversity of elements. Table 4.12 Element Metallic/Non metallic Physical state nature (solid, liquid, gas) Sodium Metal Solid Aluminium Metal Solid Calcium Metal Solid Iron Metal Solid Copper Metal Solid Magnesium Metal Solid Zinc Metal Solid Lead Metal Solid Mercury Metal Liquid Carbon Non metal Solid Silicon Non metal Solid Phosphorus Non metal Solid Sulphur Non metal Solid Iodine Non metal Solid Hydrogen Non metal Gas Nitrogen Non metal Gas Oxygen Non metal Gas Chlorine Non metal Gas Argon Non metal Gas Bromine Non metal Liquid 4.2.3 Day-to-day applications of various physical properties of matter The physical properties of matter can be usefully applied in various ways in our everyday life. Table 4.13 presents a few such instances. 56 Science | Properties of Matter  Table 4.13 Physical property of Instances of application Substance matter Metallic lustre making jewellery gold, silver withstanding weight steel rails Hardness cutting glass diamonds stylets Compressibility storing gases in cylinders oxygen, LP gas detecting gas leakages LP gas Odour spreading the scent perfumes, sweet smelling smoke cooking pans aluminium Thermal conductivity soldering lead Electrical conductivity conducting electricity copper, aluminium cables Elasticity Tyres and tubes rubber measuring temperature mercury/ alchol theremometers Expansivity automatic electrostats electrical appliances with a bimetallic strip Brittleness breaking larger pieces chemical compounds, cereals, into smaller pieces granite, egg shells Texture (smooth) applying talcum powder talc (a mineral) chalk Texture (rough) smoothening the surface sand paper of wood, walls etc Assignment 4.8 Explore information relating to the instances where the properties of matter are exploited in real life and present the information in a creative manner. At the end of the chapter, a schematic diagram such as one given below can be constructed. Matter Pure substances Non pure substances (Mixtures) Elements Compounds Metals Non metals Science | Properties of Matter 57  Summary ² The things that have a mass and that occupy space are known as matter. ² The making of matter from particles and the existence of spaces among them is referred to as the discontinous nature of matter. ² All three states, solid, liquid, and gas are discontinuous. ² The reason for the specific features of matter in solid, liquid and gaseous state is the diversity of the arrangement of particles in them. ² The different properties of solids, liquids and gases make them applicable for different purposes. ² Based on composition, matter can be classified as pure substances and non pure substances. ² Pure substances can further be classified into two catergories; elements and compounds. ² Pure substances with definite properties and indivisible by physical or chemical methods into substances with different properties are called elements. ² The pure substances formed by the chemical combination of two or more elements in a constant ratio are known as compounds. ² Sonority, thermal conductivity, electrical conductivity, malleability, ductility, density, melting point, boiling point, hardness, elasticity, expansivity, lustre, etc are physical properties of matter. ² In pure substances the physical properties such as density, boiling point and melting point have a constant value. ² Based on the physical properties, elements can be classified as metals and non metals. ² Various physical properties of substances are used for daily activities in life. Exercise 01) For the following questions, select the correct answer or the most suitable answer from the responses given 01. Which of the following response contains only matter? 1. Air, water and light 2. Water, heat and a brick 3. Electricity, a brick and ink 4. A brick, ink and air 02. A property only common to solids and liquids is, 1. having a definite shape 2. having a definite volume 3. the ability to compress 4. the free movement of particles 58 Science | Properties of Matter 03. When a drop of ink is added to a vessel of water, the colour of ink spreads throughout water. Which of the following response explains this observation best ? 1. Water is discontinuous 2. Ink is discontinuous 3. Water and ink are discontinuous 4. Ink is discontinous and water is continuous 04. Which of the following is a pure substance? 1. Bottled water 2. Fizzy drinks 3. Colourless toothpaste 4. Crystals of sodium hydroxide 05. The property of crumbling upon the application of a small force is called the, 1. Hardness 2. Brittleness 3. Elasticity 4. Ductility 06. Given below are three ideas expressed by three students about the masses of equal volumes of water and kerosene. A) Their masses are equal B) Mass of kerosene is less C) Mass of water is greater The correct response of these is /are 1.only A 2. only B 3. only C 4. only B and C 07. Which of the following substance is an electrical conductor? 1. Iron 2. Wood 3. Sand 4. Wax 08. What is the boiling point of pure water at standard atmospheric pressure?. 1. 0 0C 2. 30 0C 3. 100 0C 4. Between 30 0C - 100 0C 09. What is the liquid metal that conducts electricity? 1. Water 2. Mercury 3. Alcohol 4. Wine spirit 10. Some ideas expressed by students about the boiling point of a liquid are as follows. A) It is the temperature at which a change in state occurs B) It is the temperature at which a solid turns into a liquid without changing temperature upon heating C) It is the temperature at which a liquid turns into a gas without changing temperature on heating. The correct statements of the above are; 1. only A 2. only B 3. only C 4. only A and C Science | Properties of Matter 59  11. Which of the following is correct about the density of a metal? 1. It always takes a high value 2. Mostly it takes a low value 3. It takes a definite value 3. Densities of all the metals are equal 02) Place the mark √ if each of the following statements is correct and mark × if it is wrong. 01. Air does not belong to the category of matter. ( ) 02. All matter has a particulate arrangement. ( ) 03. Gas particles move freely. ( ) 04. Sun contains only energy. ( ) 05. Solids, liquids and gases can be compressed easily. ( ) 06. A liquid has a fixed shape as well as a fixed volume. ( ) 07. Copper is a brittle metal. ( ) 08. Sulphur is an electric conductor and a non metal. ( ) 09. Sonority is a property seen in most of the metals. ( ) 10. All metals have malleable and ductile properties. ( ) Technical Terms Energy - Yla;sh - \Uv Matter - mod¾:h - \h® Discontinous nature - wika;; iajNdjh - öuõhºa]¯ØÓ ußø© Shape - yevh - ÁiÁ® Volume - mßudj - PÚÁÍÄ Compressibility - iïmSvkh - ö|¸UPØÓPÄ Density - >k;ajh - Ahºzv Pure substances - ixY=oaO øjH - y¯ £uõºzu® Elements