Science Grade 9 PDF

1 Applications of Micro-organisms 1.1 Micro-organisms Recall what you have learnt about micro-organisms in grade 8. You have learnt micro-organisms are unicellular or multicellular organisms which cannot be seen clearly with the naked eye. Do assignment 1.1 using the previous kno...

1 Applications of Micro-organisms 1.1 Micro-organisms Recall what you have learnt about micro-organisms in grade 8. You have learnt micro-organisms are unicellular or multicellular organisms which cannot be seen clearly with the naked eye. Do assignment 1.1 using the previous knowledge. Assignment 1.1 ² Prepare a list of the groups of micro-organisms you know and write names of micro-organisms belong to each group. Micro-organisms live in our environment as well as in our body. Most micro-organisms are favourable to humans and other living beings, but some are harmful. Micro-organisms are a wide spread and common species category of living organisms on Earth. They are a group of living organisms with a simple structure. They grow fast and have high rate of reproduction. Micro-organisms have the ability to adapt for different environmental conditions and modes of nutrition. Unicellular and some of the multicellular organisms can be seen in micro-organism category. These micro-organisms can be categorized into groups as bacteria, fungi, algae and protozoa. Viruses which are a group in between the living and non-living are also studied under micro-organisms. Science | Applications of Micro-organisms 1 Algae ² Unicellular or multicellular ² Chlamydomonas ² Filamentous or thallus body ² Spirogyra forms ² Diatoms ² Microscopic alga floating on the water surfaces are called phytoplanktons Chlamydomonas ² Possess chlorophyll and have the ability of photosynthesis ² Algal varieties such as Ulva are visible to the naked eye Spirogyra Diatoms Viruses ² Electron microscopic ² Influenza virus ² Display both living and ² HIV non-living characteristics ² Ebola virus ² Multiply only inside the living cells ² Dengue virus ² No cellular organization ² They do not show the living characteristics such as respiration and growth * Several enlarged diagrams of microbes are given in the above table. Memorization of the scientific names is not needed. 1.2 Environments and substrates of micro-organisms Micro-organisms live within all the eco systems on the Earth where other living organisms survive. Microbial world spreads among soil, water and for about up to 6 km of the atmosphere. These organisms survive even on and within the body of plants and animals. Meat, fish, fruits, vegetables, human skin, mouth, alimentary canal and urinary tract are some specific substrates that micro-organisms grow. Microbes can survive even under extreme environmental conditions. Hot water springs, salt marshes, liquids such as petrol and diesel are some such environments. Science | Applications of Micro-organisms 3 1.3 Effects of micro-organisms Micro-organisms have been used in different industries by human from the past. Micro-organisms are beneficial for the environmental equilibrium. But, they can also be harmful to human because some of them act as pathogens and spoil food. 1.3.1 Beneficial effects of micro-organisms Micro-organisms are used in agriculture, medicine, conservation of environment and in different kinds of industries in seek of economical advantages and for research purposes. Here we will investigate how they are being used in different fields. Applications of micro-organisms in agriculture ² Gene technology In agriculture, crop harvest is enhanced and enriched by producing drought-resistant and pest-resistant crops and crops with high nutrients and taste, with the aid of micro-organisms. Further, biological pesticides and weedicides are developed Golden Rice Normal Rice using micro-organisms. Figure 1.1 Genes of the bacterium Erwinia uredovora is used in developing golden rice enriched with vitamin A (figure 1.1). Genes of the bacterium Bacillus thuringiensis is muted in Zea maize genome to produce toxins to crop pests. ² Nitrogen fixation Even though 78% of Nitrogen exists naturally in the atmosphere, plants have a limited ability to absorb it directly. But Rhizobium, a type of bacteria that lives in the nodules of legumes such as beans and peas has the ability to absorb atmospheric Nitrogen directly. This process is known as Nitrogen fixation. Commercially produced Rhizobium is used in cultivation lands in order to increase the yield of legumes. Figure 1.2 - Nodules of legumes Azotobacter, a free living Nitrogen fixing bacteria, is directly added to the cultivation lands. They are known as bio fertilizers. Bio fertilizers are the substances which make the soil rich with nutrients by using micro-organisms. 4 Science | Applications of Micro-organisms ² Producing compost Compost is prepared by rapid decomposition of organic matter by micro-organisms. Compost adds mineral to the soil systematically and makes favourable conditions for plants to grow. The organic matter in compost are often decomposed by bacteria and fungi. ² Bio-pesticides Figure 1.3 - Producing compost by using organic matter Some of the micro-organisms can be used as bio pesticides to control insect pests that cause damage to the crops. e.g. The fungus Alternaria is used to combat the aquatic weed, salvinia. Applications of micro-organisms in medicine Use of micro-organisms to treat the diseases caused by another micro-organism is very common in medicine. Micro-organisms are used to produce antibiotics, vaccines and anti-toxins. ² Producing antibiotics Chemicals produced in the body of a microbe to destroy or sabotage another micro-organism are known as antibiotics. Fungi and bacteria are used to produce antibiotics. Antibiotics can kill bacteria and fungi but they do not fight against infections Figure 1.4 - Some antibiotics caused by viruses. Although, antibiotics are not much harmful to human they can cause side effects if used without medical advice. Penicillin, Amoxicillin, Tetracycline and Erythromycin are used against bacterial infections while Griseofulvin is used against fungal infections. Science | Applications of Micro-organisms 5  For extra knowledge ² The antibiotic Penicillin was discovered by the Scottish scientist Alexander Fleming. ² It is produced using the fungus Penicillium notatum. Alexander Fleming ² Producing vaccines A vaccine typically contains an agent that resembles a disease causing micro-organism; and is often made from weakened or killed forms of the microbe or from its toxins. ² Vaccines made from weakened microbes e.g. Polio, Tuberculosis, Measles ² Vaccines made from killed microbes e.g. Cholera, Influenza, Typhoid ² Vaccines made from toxins of microbes e.g. Tetanus, Diphtheria ² Vaccines made from body parts of microbes using genetic engineering e.g. Hepatitis B Assignment 1.2 Collect information about the immunization programmes conducted in Sri Lanka. Display the collected information in a wallpaper in the classroom. ² Producing anti toxins Bio-chemical substances produced by pathogenic bacteria which harm the host’s activity are known as toxins. Anti-toxins are synthesized using these toxins by removing its toxic components. e.g. Tetanus vaccine Applications of micro-organisms in industries Various strains of microbes are used for research and economic benefits. Using micro-organisms in industrial activities for economic benefits is known as Industrial Microbiology. 6 Science | Applications of Micro-organisms Micro-organisms are commonly used in following large scale and small scale industries. ² Producing dairy products (yoghurt, curd, cheese, butter) ² Producing biogas ² Metal extraction ² Products based on plant fibres ² Producing alcohol ² Producing vinegar ² Bakery industry For extra knowledge Industry Micro-organisms used Producing alcohol Saccharomyces cerevisiae Producing vinegar Acetobacter aceti Bakery industry Saccharomyces cerevisiae Producing dairy products Lactobacillus bulgaricus (yoghurt, curd, cheese, butter) Streptococcus thermophilus Producing biogas Methanococcus, Methanobacterium Products based of plant fibres Bacillus corchorus, Bacillus comesii Acidithiobacillus ferrooxidans Metal extraction Thiobacillus ferrooxidans ² Producing biogas A mixture containing organic materials such as straw, cow dung and water is used to produce biogas. Anaerobic bacteria such as Methanococcus react on these organic surfaces and produce biogas. Biogas mainly consists of Methane gas. Therefore, it can be used as an energy source. ² Metal extraction Figure 1.5 - Producing biogas The most simple and effective technology used for the metal extraction from low grade ores, by the use of microbes, is known as bio-leaching. Uranium and Copper are such two metals that are extracted by bio-leaching. Science | Applications of Micro-organisms 7 ² Milk based products Let us do activity 1.1 to demonstrate the production of yoghurt. Activity 1.1 You will need :- Pure cows’ milk, yoghurt sample for culture, sugar, gelatin, a pan to boil milk, some plastic cups, a thermometer Method :- ² Heat cows’ milk for 15-30 minutes in a temperature between 88 0 C - 95 0 C. ² Remove the cream. ² Add sugar and gelatin as required. ² Add culture youghurt sample to the milk in small amount in 60 0C temperature and mix well. ² Put the mixture into plastic cups. ² Keep the mixture for 6 - 7 hours in the temperature between 40 0 C - 45 0 C. ² Cover the cups and keep in the refrigerator (under 4 0 C). Step - I Step - II Step - III Gelatin Sugar 88 - 95 0C Cream Milk Milk Cooling Step - VII Heat for 15-30 min Step - IV Step - V &VI 40 - 45 0C 60 0C Extract Milk Incubating for 6-7 hours Refrigeration under 4 0C Figure 1.6 8 Science | Applications of Micro-organisms When boiling, unfavourable bacteria in milk get destroyed. Lactobacillus and Streptococcus are used as culture in producing yoghurt. They turn Lactose into Lactic acid. Since it creates an acidic medium, growth of other micro-organisms get retarded and enhance preservation. Refrigerating further retards bacterial growth. Figure 1.7 - Dairy products (yoghurt, curd, cheese, butter) ² Products based on plant fibres Plant fibres are used for various products and these fibres are separated by using bacteria. Coconut, hemp, palmyrah and agave plants are used to get fibre. The compound pectate which is among the fibres keep them bound together. The Pectinase enzyme which is produced by the relevant bacteria helps to separate these fibres by digesting pectate. Figure 1.8 - Crushing coconut husks Applications of micro-organisms in environmental conservation Micro-organisms are commonly used for environmental conservation. The technology used to remove environmental pollutants using micro-organisms is known as bio-remediation. Following are some instances where bio-remediation is applied. ² Microbes are used to decompose the organic waste matter in polluted water. ² Pseudomonas; a kind of a bacteria which is released on to the ocean water for the decomposition of oil layers on the ocean. An enzyme released by these micro-organisms decomposes the hydrocarbons in oil. ² Heavy metals such as Chromium (Cr), Lead (Pb) and Mercury (Hg) are released to the environment from different industries. This polluted water is sent through a tower which contains bacteria to remove these toxic heavy metals from water. ² In producing bio-degradable plastics (plastics that are decomposed by bacteria) Science | Applications of Micro-organisms 9 We have discussed the favourable impacts of micro-organisms. Based on the following features, micro-organisms are used in economically important large-scale productions. ² Their biological processes occur very rapidly as their growth rate and metabolic rate is high. ² Various strains/varieties of microbes exist that are capable of acting and multiplying on various substances. ² Since micro-organisms possess simple genes, they can be easily used for genetic engineering. Hence, microbes are often used for modern genetic engineering. ² The majority of micro-organisms can be obtained at very low rates or free of charge from the environment to use in industries. ² Though, large amount of energy is required for other industries, a small amount of energy is required for industries using microbes. ² Though, most of the industries cause heavy environmental pollution and serious environmental deterioration, the industries with microbes cause minimal environmental damages. Assignment 1.3 Gather information regarding the applications of micro-organisms in environmental conservation. Prepare an article to present in the wallpaper. 1.3.2 Adverse effects of micro-organisms Causing diseases for man, plants and animals that are economically important for man, food spoilage and economical damage to non-living surfaces are several adverse effects of microbes. Biological weapons are another instance where man uses microbes adversely. Causing diseases Bacteria, viruses, fungi and protozoa are the groups of micro-organisms that cause diseases. A micro-organism that has the potential to cause a disease is called a pathogen. Mosquitoes and flies are vectors which carry the pathogen to the host. Host is an organism, who provides its body inside or outside as the substrate to growth of the pathogen. e.g. Viruses act as the pathogen for Dengue disease, while mosquitoes are the vectors. Symptoms appear on man, who is the host. 10 Science | Applications of Micro-organisms ² Diseases caused by micro-organisms to human Microbial infections spread by air, water, food, contact, vectors etc. Pathogenic micro-organisms cause different infections to human beings through various methods. Information of such infections is given in table 1.2. Table 1.2 - Information of diseases caused by micro-organisms to human Way the pathogen enters Pathogen Disease Method of spread the body Through respiratory Cold Air system Through the skin by Dengue Mosquito vectors Viruses mosquito bites Blood and other fluids of Through sexual contacts AIDS an infected person or blood transfusion Through respiratory Tuberculosis Air system Bacteria Polluted food and Through digestive system Typhoid fever vectors such as housefly with food Through the skin by Malaria Mosquito (vectors) mosquito bite Amoebic Through digestive Protozoa Polluted water and food dysentery system Through open wounds on Leishmaniasis Vectors such as sandfly the skin Pityriasis Contact of an infected person or through clothes Through skin Fungi Rashes of an infected person * The bacterium Bacillus thuringiensis is used as a biological control to destroy the larval stages of dengue mosquitoes. For extra knowledge Leishmaniasis is a disease caused by a protozoan. It is spread by the bite of Sandfly which acts as the vector. The protozoan can enter through skin ulcers. Then, it infects the skin, mouth and nasal path. Skin ulcers, fever, reducing red blood cells and enlarging liver are symptoms of leishmaniasis. Science | Applications of Micro-organisms 11  ² Diseases caused by micro-organisms to plants Some of the diseases caused by micro-organisms to plants are given below. Powdery mildew disease Powdery mildew is a disease caused by a fungus. The leaves, stem, flowers and fruits of the plant are affected by this disease. Appearing of white or gray colour powdery material is the main symptom of infected parts. This disease can damage every part of the tree (figure 1.9). Late blight Potato plant is commonly affected by this disease which is caused by a fungus. Brown spots can be seen on the leaves and later they turn into black. Then, the whole tree gets affected by the disease (figure 1.10). Wilting Fungi or bacteria cause this disease. The xylem of the plants which transports water throughout the tree gets affected from this disease. Later the xylem does not function properly due to damage. Therefore, the whole plant gets withered due to poor supply of water (figure 1.11). Figure 1.9 - Grapes with powdery Figure 1.10 - Potato wx.udr frda.plant hg with Figure 1.11 - Tomato plant mildew disease late blight m;%with úÑ;% frda.hg f.dÿre bacterial wilt fld< fl f.dÿre jQ w¾;dm,a jQ mefmd,a Ydlhla f.dÿre j Ydlhla Food spoilage caused by micro-organisms 1'11 rEmh Micro-organisms multiply on food as food has the necessary factors for the growth of micro-organisms. Micro-organisms convert the components of the food into unfavourable materials or they add toxic materials to food. Due to this reason the nature of the food is changed. The change of physical and chemical nature of food makes the food unfit for consumption. This process is known as food spoilage. (You have learnt about food spoilage such as fermentation of carbohydrates, putrefaction of proteins and rancidity of lipids in grade 8). 12 Science | Applications of Micro-organisms The table 2.1 shows the information about the main parts of the eye. Table 2.1 - Information about the major parts of the human eye Structural Part Information Sclerotic layer Tough, white outer most layer of the eye Light do not penetrate through it. Cornea The sclerotic layer in front of the iris becomes thin, transparent and forms the cornea Choroid Inside the sclerotic layer is the choroid Supplies blood to the eye Retina Inside the Choroid layer is the retina The light sensitive rod cells and cone cells are located in this layer. Aqueous humour A transparent watery liquid. Fills the space between the lens and cornea. Lens Transparent biconvex lens that has the ability to change its curvature Focuses the images on retina. Iris Controls the amount of light entering the eye Pupil The hole in the centre of the iris. It allows light to enter and pass through the lens. Ciliary muscle Supports to hold the lens Helps to change the curvature of the lens, when necessary. Vitreous humour A transparent elly-like substance, which fills the rear cavity of the lens. Helps to maintain the spherical shape of the eye. Fovea/Yellow spot The sensitive part of the retina, where the sharp images formed. Blind spot The area of the retina, where light sensitive cells are not located. Though, light is focused no vision is possible. Optic nerve The nerve that connects the eye and the brain. Convey the visual stimulus from the retina to the brain for the interpretation of the image. 18 Science | Eye and Ear Let us see how the eye perceives visionary senses. Let us inquire the way that our eye functions to give us sight. To see an object clearly, light rays must be entered to the eye from the object. The rays refract through the lens and converge on to the retina, forming an inverted image. Then, the nerve endings on the retina get stimulated and send the message about the image to the brain through optic nerve. Optical area of brain interpret it as an upright image. Eye lens is convex. Let us engage in the activity 2.2 to study the refraction of light through convex and concave lenses. Activity 2.2 You will need :- A convex lens, a concave lens, a parallel beam of light made by using a torch or by reflecting the sunlight using a mirror, a comb Method :- ² Let the parallel beam of light fall on the convex lens and observe the refracted rays. ² Let the parallel beam of light fall on the concave lens and observe the refracted rays. ² Draw the path of the light in both situations in your note book. The path of a parallel beam of light directed towards a convex lens after refracting through the lens is depicted in the figure 2.5. After refraction the light rays get converged to a point. Focus Focal length Figure 2.5 - Refraction of parallel beam of light through convex lens The point that collects light rays in front of a convex lens is called the focal point of the lens. The distance between lens and focus is focal length. Science | Eye and Ear 19 A parallel beam of light falls on a concave lens after refraction through the lens get diverged as in the figure 2.6. Focal length Focus Figure 2.6 - Refraction of parallel beam of light through concave lens After the refraction, the light rays can be observed to be diverged, as shown in figure 2.6. Here the rays after refraction appear to come from a point called focus. An image of an close object forms far from the convex lens, while far object forms an image, close to the lens. Let us engage in activity 2.3 to study this concept. Activity 2.3 You will need :- A convex lens, a candle, a box of matches, lens holder, a screen (you can prepare a screen by covering a lens holder or a small box with a white paper) Method :- ² Fix the convex lens to the lens holder. Using the lens get a clear image of a distant object on the screen. ² Light the candle in front of the lens and get a clear image on the screen. ² Measure the distance between the lens and the image ( image distance) in both cases, and compare. ou can confirm that the image distance is more when the ob ect is located close by than it is located far away. But, considering the eye, the distance from the lens to the retina (image distance) cannot be changed. Then, how can we clearly see the objects close by and far away? The lens of the eye has the ability to increase or decrease its curvature to the required size. Let us do the activity 2.4 to study about the image formation of a distant object and nearby object without changing the image distance. 20 Science | Eye and Ear  Activity 2.4 You will need :- A convex lens with a less curvature, another convex lens with a higher curvature, candle, lens holder, screen Method- ² Fix the convex lens with less curvature to the lens holder and get a clear image of a distant object on to the screen (figure 2.7 a). Figure 2.7 a ² Fix the convex lens with a higher curvature to the lens holder without changing the distance between the lens and the screen. Now get a clear image of the lit candle on to the screen (figure 2.7 b). Figure 2.7 b The focal length is comparatively high in low-convex lenses (lens with a less curvature) while the focal length is relatively low in higher convex lenses (lenses Figure 2.8 a - Convex Figure 2.8 b - Convex lens with a higher curvature). lens with less curvature with high curvature Figure 2.8 According to the activity 2.4 it can be concluded as follows. To get a clear image without changing the image distance, ² The curvature of the eye lens should be reduced for a distant object. ² The curvature of the eye lens should be increased for a close object. Assignment 2.1 Make a water lens using necessary items. By increasing or decreasing the curvature of the lens, get clear images of a lit candle placed in different places, without changing the image distance. Science | Eye and Ear 21  ² Ray diagram for an image formed from a far object on the retina of eye (figure 2. ). The rays that reach from the far object, can be considered as parallel rays. Figure 2.9 The rays that reach the eye from the far object, get refracted through the lens and converged onto the retina making an image on it. ² Ray diagram for an image formed from a close object on the retina of eye (figure 2. 0). The rays that reach from the close object, can be considered as diverged rays. Figure 2.10 The rays that reach the eye from the close object, get refracted through the lens and converged onto the retina making an image on it. 2.2 Defects of vision Two eye defects can be identified in vision, when the eye ball becomes short or long and when eye is unable to adjust the focal length of its lens to the desired level. ² Long sight (hypermetropia) ² Short sight (myopia) 22 Science | Eye and Ear  ong sight (hypermetropia) A person having this defect is able to see far objects clearly, but close objects become unclear. This happens because of the inability to increase the curvature of the eye lens or the eye ball being too short. This defect can be corrected by using a convex lens. Let us look at how the vision of a person suffering from long sight takes place. ² The person can focus the rays coming from a distant object on the retina to form a sharp image. So, that he can see distant objects clearly (figure 2.11). Figure 2.11 ² The light rays from the nearby object cannot be brought to focus on the retina to give a distinct image. In this case the image is formed behind the retina, as the rays get focused behind the retina (figure 2.12). Figure 2.12 Correcting the long sight ² This defect can be corrected by using a convex meniscus lens. The convex meniscus lens receives the light rays and converge them. The eye lens converges the rays again to focus the image at the retina. Figure 2.13 - Long sight and its correction Let us do the activity 2.5 to understand what happens after long sight is corrected. Science | Eye and Ear 23  Activity 2.5 You will need :- Two convex lenses, a candle, a screen Method :- ² Using one convex lens get a clear image of a distant object on the screen. Figure 2.14 a ² Get a clear image of a somewhat far object on the screen. Figure 2.14 b d ² Light the candle in front of the lens without changing the distance between the lens and the screen. Observe the d blurred image. Figure 2.14 c ² Place the other convex lens between the first lens and the screen. Move it until a clear image of the candle is focused on the screen. d Figure 2.14 d rom the activity 2.5 you can understand that, when nearby ob ects cannot be seen clearly, convex lenses can be used to make the image clear. 24 Science | Eye and Ear Short sight (myopia) A person sees nearby objects clearly while distant objects appear blurred. This defect arises because of the inability to reduce the curvature of the eye lens or due to the elongation of the eye ball. This defect can be corrected by using a concave lens. Let us look at how the vision of a person suffering from short sight takes place. ² The rays coming from close objects can be focused on the retina. So, the close objects can be seen clearly (figure 2.15). Figure 2.15 ² The rays coming from distant objects are focused in front of the retina. So, the image of a distant object is formed in front of the retina and cannot be seen clearly (figure 2.16). Figure 2.16 Correcting the short sight ² This defect can be corrected by using concave meniscus lenses. The rays from the object are diverged through the concave meniscus lens and the eye lens converge them to a point on retina to make the image clear. Figure 2.17 - Short sight and its correction Let us do the activity 2.6 to understand what happens after correcting the short sight. Science | Eye and Ear 25  Activity 2.6 You will need :- A convex lens, a concave lens, candle, screen Method :- ² Light the candle in front of the convex lens and get a clear image of it on the screen. Figure 2.18 a d ² When the candle is kept far away without changing the distance between the lens and the screen (distance “d”), we can get a blurred image of a distant object on the screen. Figure 2.18 b d ² Place a concave lens in front of the convex lens and move it till a clear image of the candle is formed on the screen. d Figure 2.18 c rom the activity 2.6 it can be understood that when distant ob ects cannot be seen clearly, concave lenses can be used to get a clear image of a distant object. Binocular vision and stereoscopic vision The eyes of human, monkey, 'Rilava'/'Mandi', chimpanzee, gorilla and loris are located in front position of the skull (figure 2.19). So, there is a greater chance of seeing the same area with both eyes. 26 Science | Eye and Ear  Human Monkey 'Rilava' / 'Mandi' Chimpanzee Gorilla Loris Figure 2.19 Mammals such as cattle, dog, tiger have no ability to look at the same area using both eyes (figure 2.20). But, they have the ability to look more areas separately using the each eye. Cattle Dog Tiger Figure 2.20 The ability to maintain visual focus on an object with both eyes creating a single visual image, is known as binocular vision. The human has a broader range of a binocular vision. The range of binocular vision of man The range of binocular vision of dog Figure 2.21 Science | Eye and Ear 27 Let us do the activity 2.7 to identify your range of binocular vision. Activity 2.7 Method :- ² Keep the face straight and look forward. ² Do the following things without moving the face. ² Stretch your hands and fold your fingers. ² Straighten the thumb right upwards. ² Close your left eye and move your left hand in the horizontal plane to the left until you cannot see the thumb. ² Keep the left hand in the same position and close your right eye. Now move your right hand in the horizontal plane to your right until you can’t see the thumb. ² Now look at both thumbs using the both eyes. Your eyes can see the objects which lie in the range of the stretched hands. It is your binocular range. But, when both eyes are open, the objects seen to the left of the left hand can be seen only by the left eye. Similarly the objects to the right of the right hand can be seen only by the right eye. Due to the binocular vision human has got the stereoscopic vision and the ability to determine the distance of an object. stereoscopic vision means the ability of eye to determine the depth of an object or the height of it. Let us do the activity 2.8 to study this further. Activity 2.8 You will need :- A ball point pen Method :- ² Hold the clip of the pen keeping its hole upwards in a distance when you stretch the hands to your front. ² Close one eye and insert the pen into the clip. ² Insert the pen again into the clip using both eyes. ² Compare the difference of ease, in both situations. It is easier to insert the pen into the clip by seeing through both eyes rather than seeing through one eye. This is because of the stereoscopic vision of the eye. 28 Science | Eye and Ear 2.3 Eye diseases Two common eye diseases identified at present are ² Cataract ² Glaucoma Cataract A cataract is a cloudiness or opacity in normally transparent crystalline lens of the eye. It happens because of the denaturing of proteins in the eye lens. Then, eye lens turns in to milky colour. The lens of a healthy eye is transparent The lens of a diseased eye is not transparent Figure 2.22 Cataract prevents the light rays coming from an object focusing properly on the retina. Then, all the objects are seen blurred. A lens of a healthy eye A lens of a diseased eye Figure 2.23 Science | Eye and Ear 29  A healthy eye sees an object clearly The diseased eye sees the objects blurred Figure 2.24 Generally, cataract may occur with age and genetic factors. It is believed that ultra violet rays reach the Earth through holes of the ozone layer affect towards the occurrence of cataracts in eye. Glaucoma Glaucoma is a disease that gradually reduces the visual range of the eye and leads to blindness due to the damage of the optic nerve. By detecting at the first stage further increase of glaucoma can be controlled. Glaucoma is usually the result of high blood pressure inside the eye. A person with diabetes has an increased risk of developing glaucoma. The damage caused to the eye from this disease cannot be reversed again. The figures A, B, C and shows how a glaucoma patient loses his vision gradually. A B C D A - healthy eye sees the objects clearly B - first stage of glaucoma C - middle stage of glaucoma - final stage of glaucoma (leads to vision loss or blindness) Figure 2.25 30 Science | Eye and Ear Eye infections In addition to above mentioned diseases, eyes can be infected by viruses. Reddening of eye and secretion of tears are the symptoms. The disease spreads through insects ('Konduruwa') and by contact. This condition is known as "sore eyes". It can be cured by medical treatments (figure 2.26). Precautionary measures should be followed to prevent health problems and possible defects of Figure 2.26 the eye. Such precautions are given below. ² Protect your eyes from harmful light rays ² Do not look at the sun directly at a solar eclipse and necessary safety methods should be used to look at the sun in such situations ² Be sure to wear safety glasses when do welding ² Do not use eye drops or any other liquids into the eye without medical advice ² Do not use someone else’s spectacles ² When using sun glasses follow medical advices ² Should care for personal hygiene ² Do not watch television or use computers continuously and follow relevant precautionary measures. 2.4 Structure and function of the human ear Audio sensory organ of the body is the ear. Let us take a look at the structure of the ear. Activity 2.9 You will need :- A model of the human ear in the laboratory or a diagram Method :- ² Observe the model or the diagram well. ² Identify the parts of the human ear. ² Get the help of a named diagram of the human ear. Figure 2.27 - A model of the human ear Science | Eye and Ear 31  A diagram of the human ear is given by figure 2.28. Outer ear Middle ear Inner ear Pinna Ossicles Semi-circular canals Auditory nerve Cochlea External auditory canal Tympanic membrane Eustachian tube Figure 2.28 Information about the major parts of the human ear is given in the table 2.2. Table 2.2 - Information about the major parts of the human ear Area Part of the organ Information Pinna/ear lobe ² A cartilaginous organ ² Directs sound waves towards the auditory canal Outer External auditory canal ² Directs the sound to tympanic membrane ear Tympanic membrane ² Vibrates in response to the sound wave and acquires the auditory senses Ossicles ² Three bones named malleus, incus and stapes ² Transmit sound related vibration to the cochlea Middle Eustachian tube ² An open tube connected to pharynx ear ² Controls the pressure on either sides of the tympanic membrane Cochlea ² The nerve endings of the auditory nerve is connected to cochlea ² Transmit auditory senses to the auditory nerve Inner Auditory nerve ² Take auditory senses to the relevant part of the ear brain ² That sound is interpreted by the relevant part of the brain Semi-circular canals ² Contribute to maintain the balance of body 32 Science | Eye and Ear Necessary precautions should be taken to protect the ear. ² Avoid inserting foreign objects into the ear ² Refrain exposing to loud noises ² Do not put any medicines for the ear without medical advice ² Avoid diving in deep waters without wearing safety equipment (As pressure is very high in deep Figure 2.30 water) ² Avoid slapping on the ear and dragging by the ear lobe Assignment 2.2 y Using suitable materials, make a model of a stethoscope. Figure 2.31 Assignment 2.3 y Prepare ten short questions on eye and ear to conduct a quiz competition. For extra knowledge Jet Engine Sound pressure level dB(A) Threshold of pain Jackhammer Live rock music Heavy truck Street Traffic Business office Conversational speech Living room Bedroom Woodland 34 Science | Eye and Ear 3 Nature and Properties of Matter Recall what you have learnt about the properties of matter in grade 8. You may call back to your mind how matter was classified as pure substances and non-pure substances (mixtures). Based on that knowledge engage in the activity 3.1. Activity 3.1 Classify and tabulate the substances given below as pure substances and mixtures. air, drinking water, aluminium, silver, copper, salt solution, distilled water, carbon, sulphur, zinc, copper sulphate, sodium chloride Matter that contain only one constituent with specific properties are called pure substances. Accordingly, aluminium, silver, copper, distilled water, carbon, sulphur, zinc, copper sulphate and sodium chloride belong to the class of pure substances. Matter that contain two or more constituents are known as mixtures. Hence, air, drinking water and salt solution can be named as mixtures. In grade 8 you have learnt that pure substances can be further classified as elements and compounds. To strengthen that knowledge further, involve in the activity 3.2. Activity 3.2 Classify and tabulate the following pure substances as elements and compounds. sulphur, glucose, chlorine, sodium chloride, silver, copper, copper sulphate, zinc The pure substances with specific properties which, cannot be further divided by either physical or chemical methods into substances with different properties, are called elements. Accordingly iron, sulphur, chlorine, silver, zinc and copper belong to elements. There are about 120 elements have been discovered upto now. 38 Science | Nature and Properties of Matter  Copper Iron Sulphur Mercury Carbon Aluminium Silver Chlorine Figure 3.1- Some common elements The compounds are pure substances with specific properties, formed by the chemical combination of two or more elements in a fixed ratio. Thus, sodium chloride, copper sulphate and glucose belong to the class of compounds. In nature, there are very large number of compounds, which occur from the combination of various elements in various forms. Glucose Copper sulphate Sodium chloride Figure 3.2 - Some common compounds 3.1 Elements 3.1.1 Symbols for elements We know that, in various instances we use various symbols to facilitate communication. Symbols are also used to indicate elements. All countries in the world use these internationally accepted symbols to indicate elements. Very often, English name of the element is used as the base for these symbols. In such case the first letter of the name of the element is used as the symbol. When a single letter is used as the symbol, compulsorily it should be a capital letter. Table 3.1 presents some examples. Science | Nature and Properties of Matter 39  Table 3.1 Element Symbol Carbon C Oxygen O Sulphur S When the names of several elements commence in the same letter, the next letter or another letter in the name is added to the symbol. In that, the second letter is a simple letter. Table 3.2 gives some examples. Table 3.2 Element Symbol Chlorine Cl Calcium Ca Magnesium Mg Aluminium Al In some elements, the symbol originates in its Latin name. Table 3.3 lists some examples for such symbols. Table 3.3 English name Latin Name Symbol Sodium Natrium Na Copper Cuprum Cu Lead Plumbum Pb Gold Aurum Au Mercury Hydrargyrum Hg Iron Ferrum Fe Silver Argentum Ag Table 3.4 illustrates names of several elements and their symbols. Table 3.4 Element Symbol Element Symbol Hydrogen H Magnesium Mg Carbon C Zinc Zn Oxygen O Silicon Si Nitrogen N Phosphorous P Sulphur S Argon Ar Chlorine Cl Calcium Ca Aluminium Al Iodine I 40 Science | Nature and Properties of Matter 3.1.2 Building units of elements You have learnt that, matter is composed of particles. These particles cannot be observed by the naked eye or even by the powerful microscopes. These very small particles are called atoms. John Dalton (1766 - 1844) was the first scientist to use the term atom for the smallest, indivisible particle from which the matter is made. The English name 'atom' for this particle has originated from the Greek word 'atomos' meaning, Figure 3.3 - John Dalton "cannot be divided further." An element is composed of the atoms of the same type. The atoms which, form different elements are different to each other. For example, the element iron is formed from iron atoms. Aluminium is formed from aluminium atoms. The structures of aluminium atoms and iron atoms differ from each other. The units formed by the combination of one or more atoms of the same type or one or more atoms of different types are called molecules. Under normal conditions, the element oxygen exists as oxygen molecules composed of two oxygen atoms. The smallest form in which oxygen can exist independently is a molecule. Some examples for the elements which can exist as molecules are given in table 3.5. Table 3.5 Symbol of the Element molecule Oxygen (O) O2 O O H H Nitrogen (N) N2 Cl2 Figure 3.4 - Figure 3.5 - Chlorine (Cl) A representation A representation Hydrogen (H) H2 of an Oxygen molecule of a Hydrogen molecule Fluorine (F) F2 Since the above molecules are formed by the atoms of the same elements they are known as homo-atomic molecules. Therefore, elements are composed either, from atoms of the same kind or from molecules formed by combining those same kind of atoms. Thus, they cannot be further divided into simple substances chemically. Science | Nature and Properties of Matter 41 Atomic number (Z) The number of protons present in the nucleus of a given atom of an element is called the atomic number. It is generally designated by the symbol Z. The atomic number or the number of protons in the nucleus is a unique property of the element. As an atom is electrically neutral, number of protons and number of electrons are equal. The atomic numbers of some elements are given in table 3.7. Table 3.7 – Atomic number of atoms of some elements Element Number of Protons Number of Electrons Atomic Number Carbon (C) 6 6 6 Nitrogen (N) 7 7 7 Oxygen (O) 8 8 8 Fluorine (F) 9 9 9 Neon (Ne) 10 10 10 Sodium (Na) 11 11 11 Mass number (A) The sum of the protons and neutrons present in the nucleus of a given atom of an element, is called the mass number of the atom of that element. The mass number is represented by the symbol A. Table 3.8 - Mass number of atoms of some elements Element Number of protons Number of Neutrons Mass number (p) (n) (p + n) N 7 7 14 O 8 8 16 F 9 10 19 Na 11 12 23 Cl 17 18 35 There is a standard method of representing atomic number and mass number of an atom. This standard method is, writing atomic number at the left hand side bottom end and mass number at the left hand side top end of the symbol of the atom. The information related to an atom of element sodium (Na) is given below. Sum of protons and neutrons 23 11 Na (Mass number) Number of protons (Atomic number) Science | Nature and Properties of Matter 43 3.2 Compounds Compounds are formed by the chemical combination of two or more elements in a certain ratio. Some of those compounds exist in nature as molecules. Since those molecules contain atoms that are different from one another, they are called hetero-atomic molecules. e.g. A Hydrogen chloride molecule is formed by the combination of one hydrogen atom and one chlorine atom. H Cl H Cl Hydrogen atom Chlorine atom Hydrogen chloride molecule (compound) Figure 3.8 - Illustration of the formation of a hydrogen chloride molecule Thus, a main difference between elements and compounds is that an element is composed of the atoms of the same kind while a compound is formed from atoms belonging O to two or more kinds of elements. e.g. A water molecule is formed by the H H Figure 3.9 - Water molecule combination of an oxygen atom and two hydrogen atoms. This is illustrated by figure 3.9. Assignment 3.1 Using various materials create models for several homo-atomic and hetero-atomic molecules. Display the models you made in the classroom. A carbon dioxide molecule is formed by the combination of a carbon atom and two oxygen atoms. This is shown by figure 3.10. O C O Figure 3.10 - Carbon dioxide molecule H H C A methane molecule is formed by the combination of a carbon atom with four hydrogen atoms. This is H H illustrated by figure 3.11. Figure 3.11 - Methane molecule 44 Science | Nature and Properties of Matter An ammonia molecule is formed by the combination H of a nitrogen atom with three hydrogen atoms. This is illustrated by figure 3.12. N There are specific chemical symbols for compounds also. These symbols are known as chemical formula of H H compounds. You will study them in higher grades. Figure 3.12 - Ammonia molecule Table 3.9 Compound Chemical formula Elements contained of the compound (Building unit of the compound) Water H2O H and O Glucose C6H12O6 C, H and O Methane CH4 C and H Carbon dioxide CO2 C and O Sodium chloride (Common salt) NaCl Na and Cl Copper sulphate CuSO4 Cu, S and O Calcium carbonate CaCO3 Ca, C and O The elements contained in the smallest unit that form a compound, cannot show the properties of that compound. The different compounds formed by even the same set of elements have different chemical properties. e.g. 1: Same compounds formed by the set of elements C, H are given below. y Methane (a component of biogas) - CH4 y Hexane (a solvent) - C6H14 y Benzene (a solvent) - C6H6 y Acetylene (a gas burnt to generate heat essential for welding metals) - C2H2 y Ethene (a gaseous raw material needed to make polythene) - C2H4 e.g. 2 : Given below are some compounds formed by the set of elements C, H, O y lucose (a simple sugar) - C6H12O6 y Acetic acid (contained in vinegar) - CH3COOH y Ethanol (contained in alcoholic beverages) - C2H5OH y imethyl ether (an anaesthetic) - CH3OCH3 y Sucrose (contained in sugar cane) - C12H22O11 Science | Nature and Properties of Matter 45 3.3 Mixtures Next, let us study about the non-pure substances (mixtures). Pay your attention to sea water. Various salts and various gases are dissolved in it. That means, it contains several constituents. Therefore, sea water is a mixture. In natural environment mostly we come across mixtures and not pure substances. Air, soil, river water and rocks around us are all mixtures. Yoghurt, ice cream and fruit salad we eat are also mixtures. The drinks such as tea, coffee and soft drinks too are mixtures. Fruit salad Coffee Ice cream Figure 3.13 - Some mixtures Mixtures are formed when two or more pure substances get mixed. The pure substances in a mixture are called as constituents. Let us identify constituents in some mixtures. Let us study table 3.10. Table 3.10 - Mixtures and their constituents Mixture Constituents Air nitrogen, oxygen, argon, carbon dioxide, water vapour Sea water water, salts, dissolved oxygen, dissolved carbon dioxide Cake mixture sugar, flour, water, colouring, butter, eggs Crude oil diesel, petrol, kerosene, tar The specific feature of a mixture is that, its constituents can be separated by physical methods. When rice is mixed with sand they can be separated by sifting using the sifting bowl. So, sifting is a physical method of separating constituents in a mixture. Let us involve in activity 3.3 to study about the physical methods of separating constituents in a mixture. 46 Science | Nature and Properties of Matter  Activity 3.3 ² You are provided with the following mixtures. Suggest suitable methods for separating the constituents in those mixtures. 1. A mixture of sugar and sand 2. A mixture of salt and water 3. A mixture of iron powder and sulphur powder 4. A mixture of rice and sand 5. A mixture of chaff and stone ² Describe how the constituents of the mixtures are separated. Given below are some physical methods of separating constituents in a mixture and some instances in which they are used. They will be studied in detail in grade 11. Panning - Separating sand from rice, Separating gems from ores Winnowing - Separating chaff from rice Floating on water - Separating sterile seeds from seed paddy Sifting - Separating gravel from sand Evaporation - btaining salt from sea water Fractional distillation - Separating various fuels from crude oil Steam distillation - Separating cinnamon oil from cinnamon leaves Crystallization - Separating sugar from cane sugar syrup Uses of magnets - Separating some minerals from mineral sands Figure 3.14 - Gem mining Figure 3.15 - Winnowing paddy Assignment 3.2 Prepare a chart to show the physical methods used to separate constituents of a mixture and the instance in which those methods are used. Science | Nature and Properties of Matter 47 According to that, mixtures can be described as follows. A matter which consists of two or more constituents which can be separated by physical methods are called mixtures. According to the nature, mixtures can be divided into two categories. 1. Homogeneous mixtures 2. Heterogeneous mixtures Homogeneous mixtures Let us involve in activity 3.4 to study about homogeneous mixtures. Activity 3.4 1. Weigh about 2 g of salt, add it to a beaker containing 500 ml of water, mix well with a glass rod and allow to stand for a few minutes. 2. Observe carefully. You will be able to see that properties like colour and transparency are alike throughout the mixture. The mixtures with a uniform composition right throughout the mixture are called homogeneous mixtures. e.g. Salt solution, sugar solution, sea water Heterogeneous mixtures Dissolve a little clay in water, allows to stand from some time and observe. If you observe carefully you may be able to see that the colour and transparency of the mixture is different from place to place. The mixtures in which the composition is not uniform throughout the mixture are known as heterogeneous mixtures. e.g. Muddy water, mortar mixture, ice cream, fruit salad Assignment 3.3 ² Prepare mixtures by mixing each of the following with small amount of water and observe these mixtures. salt, soap, copper sulphate, limestone, washing blue, chilli powder ² Record the observations ² Classify the mixtures you have prepared as homogeneous and heterogeneous. 48 Science | Nature and Properties of Matter 4 Basic Concepts Associated with Force 4.1 Force Let us consider situations like lifting an object, pushing a table, opening or closing a door or hitting a ball (figure 4.1). Figure 4.1 In such instances what we do is, pulling or pushing the ob ect. Such a pulling or pushing is called a force, simply a force means a pull or a push. When we push a book on the table, it moves. A ball moves faster if we kick it. But, you can not push and move a wall. A single person cannot push and move a bus or a lorry. Thus, it is clear that, sometimes we can move an ob ect by applying a force and sometimes a force cannot result any motion. When you catch a ball that comes towards you, a force is applied to stop it. When you hit a ball with a bat, you apply a force to change the direction and the speed of the ball. ou can press a ball by keeping it on the ground and tread on it. Here, you change the shape of the ball by applying a force. Accordingly, by applying a force ² ob ect at rest can be moved. ² ob ect in motion can be stopped. ² the speed of motion can be changed. ² the direction of motion can be changed. ² the shape of ob ect can be changed. 52 Science | Basic Concepts Associated with Force 5 Pressure Exerted by Solid 5.1 Pressure You may have experienced that, when the strap of your school bag is narrow, it is uncomfortable to the shoulder. When it is broad it is not that uncomfortable. (a) A child bearing a bag with a (b) A child bearing a bag with a narrow strap uncomfortably broad strap easily Figure 5.1 There are two school bags of equal weight. The shoulder strap of one of them is narrow and that of the other one is broad. Though, the strap is narrow or broad, the force exerted by the weight of school bag is the same. But, when the strap of it is narrow, the contact area is less, and when it is broad that area is more. Thus it is clear that, though the force is the same, the pressure against the shoulder differs with the area of contact of the strap. Consider two bags having the straps of the same breadth and different weights of books. The bag with more weight gives more press against the shoulder. (a) A child bearing a light-weight bag (b) A child bearing a heavy bag easily uneasily Figure 5.2 60 Science | Pressure Exerted by Solid ² The heart has four chambers. The upper chambers are called atria and the lower chambers are called ventricles. ³ Left atrium ³ Right atrium ³ Left ventricle ³ Right ventricle ² There are two valves between the atria and ventricles. ³ Bicuspid valve is in between the left atrium and left ventricle. ³ Tricuspid valve is in between the right atrium and right ventricle. ² There are two main arteries connected to the ventricles. ³ Aorta starts from the left ventricle. ³ Pulmonary artery starts from the right ventricle. ² There are semi lunar valves at the starting points of the main arteries. ³ Aortic semi lunar valve is at the starting point of the aorta. ³ Pulmonary semi lunar valve is at the starting point of the pulmonary artery. ² Main veins are connected to the atria. ³ The superior vena cava and inferior vena cava open to the right atrium. ³ Left and right pulmonary veins open to the left artrium. Assignment 6.1 ² Construct a model of the heart to show the structure of the heart. 6.2 Arteries, veins and capillaries The blood vessels that take blood away from the heart are known as arteries while, the vessels that take the blood towards the heart are known as veins. Main arteries starting from the heart divide into branches. ² The pulmonary artery which starts from the heart transport blood to lungs. Aorta supply blood to the other organs. Within an organ an artery further divides into arterioles and then into capillaries. ² The capillaries join together to form venules and venules join together to form veins. ² Pulmonary veins starting from the lungs take the blood to left atrium. ² Veins from the organs above the heart join the superior vena cava and veins from the organs below the heart join the inferior vena cava. Both the superior and inferior vena cava open into the right atrium. Science | The Human Circulatory System 73 6.3 Components of blood and their functions Although you see blood as a red fluid, only 55 of its value is in liquid form. This liquid part is called as the plasma. The other 45 of its volume consists of corpuscles which is in solid form. Blood Corpuscles Plasma Red blood White blood Platelets Things Things Water soluble in insoluble in cells cells water water Figure 6.5 A microscopic observation of a blood sample shows three types of corpuscles. y Red blood cells/ erythrocytes y White blood cells/ leukocytes y Platelets Erythrocytes and leukocytes are cells while the platelets are cell fragments. Functions of blood Red blood cells/ erythrocytes Red blood cells contain a red pigment which is called haemoglobin. Haemoglobin carries oxygen from lungs to the body cells and also gives blood its red colour. White blood cells/ leukocytes White blood cells defend the body by destroying pathogens and producing antibodies. White blood cells are categorized into neutrophils, eosinophils, basophils, lymphocytes and monocytes. Platelets Platelets help in the clotting process of blood at a bleeding site. Some virus infections cause a rapid decline in a platelet percentage. e.g. Dengue, Leptospirosis Plasma The main function of the plasma is transporting substances dissolved in it. Science | The Human Circulatory System 75  Some examples are given below; ² It transports the digestive products, minerals and vitamins to the cells. ² It transports the excretory products during biochemical reactions within the cells to the excretory organs. ² Plasma transports hormones, proteins, enzymes and gases to the relevant parts of the body. 6.4 Blood transfusion The transfer of blood from one individual to another is known as blood transfusion. The person who donates blood is called the donor and the person who receives is called the recipient. However, blood transfusion is not possible between any two individuals. For a transfusion to take place, compatibility of the blood group and the Rhesus factor between the donor and the recipient is compulsory. Compatibility of the blood group There are four blood groups as A, B, AB Figure 6.6 and O depending on the protein components present in blood cells. Compatibility of blood groups in transfusion is represented in the table 6.1. ( represent positive compatibility of blood group while « represent lack of compatibility of blood group) Table 6.1- Compatibility of blood group Recipient D Blood type A B AB O o A √ « √ « n B « √ √ « o AB « « √ « r O √ √ √ √ According to the table, blood group AB can receive blood from all other blood groups. Therefore, blood group AB is called the universal recipient. Blood group O can donate to all the other blood groups. Therefore, blood group O is called the universal donor. 76 Science | The Human Circulatory System Information in the table 6.1 can be illustrated as in figure 6.7. Donor A B AB O Recipient A AB B AB AB A B AB O Figure 6.7 - Compatibility of blood group For a blood transfusion, not only the blood group, but also the Rhesus factor (Rh factor) must be compatible. Compatibility of Rhesus factor If the Rhesus factor is present in one’s blood it is considered as Rh+ and if Rhesus factor is absent, it is considered as Rh-. The recipients who are Rh+ can receive both Rh+ and Rh- blood. However, the Rh- recipients can receive Rh- blood only. The table 6.2 shows the compatibility of blood with Rhesus factor. (√ represent positive compatibility of blood with Rhesus factor while « represent negative compatibility of blood with Rhesus factor Table 6.2 - Compatibility of Rhesus factor Recipient D Rh+ Rh- o n Rh+ √ « o r Rh- √ √ The figure 6.8 represents the same facts in table 6.2. Rh- Rh+ Hence both the blood group and the Rhesus factor have to be matched to donate blood. Both the blood Rh- Rh+ Rh+ group and Rhesus factor are considered when Figure 6.8 - Compatibility of expressing the blood group of an individual. Rhesus factor e.g. A+, A-, B+, B-, AB+, AB-, O+, O - The National Blood Transfer Service (NBTS) has a list of other qualifications a donor must fulfill. A donor has to complete the Blood onor eclaration correctly and hand it over to the NBTS before donating blood. Blood donor declaration and donation record is given in the extra knowledge frame. Science | The Human Circulatory System 77 Some favourable habits to maintain healthy blood circulation system ² Maintain mentally less stressful lifestyle ² Engage in physical exercises daily ² Maintain the correct Body Mass Index (BMI) value according to height and weight, with a healthy diet. ² Reduce salt consumption ² Control conditions like high blood pressure and diabetes ² Add more vegetables and fruits to meals ² Reduce consumption of fatty foods ² Refrain from smoking and liquor ² Have more concern if there is a family history of heart attacks, high blood pressure and diabetes Assignment 6.3 ² Collect newspaper cuttings about the good health habits that should be followed to maintain a healthy blood circulatory system. ² Share that knowledge with your classmates. Summary ² The human heart has four chambers. ² The upper chambers are the right atrium and left atrium and the lower chambers are the right ventricle and left ventricle. ² Aorta is connected to the left ventricle while pulmonary artery is connected to the right ventricle. ² Left and right pulmonary veins are connected to the left atrium while superior vena cava and inferior vena cava are connected to the right atrium. ² Semi lunar valves are at the beginning of main arteries. ² Bicuspid valve is between the left ventricle and left atrium. ² Tricuspid valve is between the right atrium and right ventricle. ² The blood vessels that take the blood away from the heart are arteries and the vessels that take the blood towards the heart are veins. ² An artery ends up with a capillary and a vein starts with a capillary. ² The main functions of blood are transportation and protection. 80 Science | The Human Circulatory System 7 Plant Growth Substances 7.1 Introduction to plant growth substances You know that air, water, light and minerals are essential for plant growth. It has been discovered that some chemical substances also affect towards the plant growth. Have you ever thought how does a stem of a plant grows upwards and its roots grow downwards after the seed germination? bserve the figures 7.1 a and 7.1 b. Figure 7.1 a Figure 7.1 b Have you ever thought how does a stem of a plant grows upwards and its roots grow downwards even the plant pot falls down? Let us do the activity 7.1 to study about it. Activity 7.1 You will need :- Two similar potted plants Method:- y Cut and remove the apex of one plant. Then, measure the heights of both plants. y Supply same environmental conditions for both plants and measure their heights daily for a week. Figure 7.2 You will observe that the plant with the apex grows and its height increases while the height of the plant without the apex does not change. So, we can guess that there is an effect of the apex on plants to increase their height. Let us do the activity 7.2 to find out more about it. Activity 7.2 You will need :- Two similar potted plants, a box covered with a black paper Method:- y Cut and remove the apex of one plant. y Place the two plants inside the box in a way that both plants get light only from one direction. Science | Plant Growth Substances 83 Auxins, produced in the apex diffuse downwards. It speeds up the growth of new cells and the shoot of the plant grows upwards. IAA (Indole Acetic Acid) is a natural growth substance found in plants. Auxin concentrate more in the side of plant where intensity of light fall is low and auxin concentrate less in the other side of the plant. Auxin move to the darker side of the plant, causing the cells there to grow longer than corresponding cells on the other side of the plant. This causes a curving of the plant stem tip towards the light. This is known as positive phototropic movement. Auxin also inhibit the growth of lateral buds (figure 7.5). Pruning of plant apex is practised in horticuture to maintain bushy plants. Figure 7.5 - Growth of lateral buds in Pomegranate plant Gibberellins Gibberellin promotes mainly the elongation of the stem and growth of the fruits. Cytokinins Cytokinin accelerates the cell division. So, the growth of flowers, leaves, fruits and roots get accelerated. They stimulate seed Figure 7.7 - germination and delay plant ageing. Increasing the rate of rooting in plants Figure 7.6 - Growth of using Cytokinin Cabbage plant due to gibberellin For extra knowledge Abscisic acid is a plant growth substance. It is a chemical substance that cause closing of stomata when the plant experiences shortage of water. Thus, it decreases transpiration. Ethene is a simple organic compound which produces in low amounts in plants. It is necessary for ripening of fruits. In ripening, starch stored in plants converted to sugar. If a plant is damaged, ethene released to the wound area and a new tissue forms to recover the wound. Science | Plant Growth Substances 85 What is the reason for falling leaves and fruits when matured? When you observe a stalk of a naturally fallen leaf and a stalk of a broken leaf, it would be clear to you that, the naturally fallen leaf stalk has a clear abscission layer. The reason for making an abscission layer is, the reduction results in the amount of growth substances in fruits and leaves with their maturity. As a result, fruit fall and leaf fall take place in plants. 7.2 Uses of artificial growth substances Artificial growth substances are widely used in horticulture and growing ornamental plants. Some of these are given in the table 7.1. Table 7.1 Artificial growth substances Uses 2,4 DPA (2,4 ichloro Phenoxyacetic Acid) As a broad leaf weedicide for paddy fields 2,4,5 TPA (2,4,5 Trichloro Phenoxyacetic Acid) (IAA) Indole Acetic Acid To induce root formation of stem cuttings, (IBA) Indole Butyric Acid To grow fruits quickly To prevent pre-mature fruit drop, To induce (NAA) Naphthalene Acetic Acid flowering in pine apple in off-seasons Cytocell To get mango fruits in the off-season Assignment 7.1 ² Collect information about the instances that artificial growth substances are used. ² If possible arrange a visit to a plant nursery where artificial growth substances are used. ² Collect information about the use of artificial growth substances and prepare a report. 86 Science | Plant Growth Substances Elastic band A represents the biceps muscle in the elbow joint. When biceps muscle is contracted the hands bends and lifts up. Elastic band B represents the triceps muscle in the elbow joint. When triceps muscle is contracted the hand is stretched. Then, the biceps muscle comes to its original resting position. 8.3 Support and movements of plants Support of plants Just like in animals, tissues are present within plants for the purpose of mechanical support. Figure 8.5 shows the garden Balsam plant. You may have noticed on sunny days these plants get withered and the stem is bent down. This is due to lack of water supply to the plant. To keep non-woody plants erect and alive it is vital to have water inside the plant, where as woody plants can be kept erect in low water percentages due to presence of various chemical substances such as cellulose, lignin deposited in the walls in heartwood of the plant. They give rigidity to the plant (figure 8.6). Figure 8.5 - Non-woody plant (Balsam) Figure 8.6 - Woody plant (Mango) Movements of plants Growth of a part in a plant as a response to a stimulus or change of the location due to a turgor change , is known as a movement of a plant. These responses can be catogorized into two main groups as, ² Tropic movements ² Nastic movements Tropic movements Tropic movements are growth or movements that occur due to a direct influence between the direction of stimulus and direction of response. Tropic movements occur due to the effect of growth substances. Response may be towards or away from the stimulus. Positive tropism occurs towards the stimulus. Negative tropism occurs away from the stimulus. 92 Science | Support and Movements of Organisms Some of tropic movements are described below. y Positive geotropism - roots growing towards the ground y Negative geotropism - stem of the plant growing away from the ground y Positive phototropism - stem growing towards the light y Positive hydrotropism - roots moving towards the water source y Positive chemotropism - growth of the pollen along the tube towards the ovule y Positive thigmotropism - coiling of tendrils in Passion fruit with the support Let us do activity 8.3 to study about tropic movements. Activity 8.3 You will need:- Two pots, s ome green gram seeds Method :- y Plant 5 soaked seeds in each pot. y After seed germination, keep one healthy plant in each pot and uproot all the other plants. y Keep one pot vertical and the other toppled down as in the figure 8.7. Figure 8.7 y Observe the growth pattern of root and shoot after one week. y Identify and study tropic movements. In both pots, roots grow towards ground. That means movement of a plant root is positive geotropic, and movement of a plant shoot is negative geotropic (figure 8.8), as it move. Figure 8.8 Science | Support and Movements of Organisms 93 Nastic movements In nastic movements, response of the direction does not depend on the direction of stimulus (The direction of these movements are specific). Response is always towards a specific direction irrespective of the direction of stimulus. This reaction is not related with growth substances triggered by external stimulus. Most of them are movements due to turgor change. In legume plants, a structure called pulvinus is located as a swelling at the base of the petiole or leaflet. It contains parenchyma cells, which move Figure 8.9 - Shrinking of Mimosa leaves according to the changes in turgor pressure. Some of nastic movements are as follows. ² Nyctinastic movements - sleeping or shrinking of leaves of 'Kathurumurunga' / 'Agaththi', tamarind, Mimosa and 'Nelli' / 'Nellikkai' leaves when dark falls ² Haptonastic movement - sleeping or shrinking of Mimosa leaves, when the stimulus is touched ² Seismonastic movement - exhibiting sleeping movement during a shock ² Photonastic movement - blooming of flowers with the sunrise Let us do the activity 8.4 to study about responses of plant parts Activity 8.4 You will need :- Mimosa plants Method :- y Touch the leaves of a Mimosa plant. y Make a vibration without touching the leaves. y Report your observations. y Report if there are any special features in the plants responsible for these movements. When you touch a Mimosa plant the leaves show the sleep movement. It is a haptonastic movement. When you create a vibration without touching, the leaves of the Mimosa plant show the sleep movement. It is a seismonastic movement. The pulvinus located at each leaflet and petiole base pulvinus help for these movements of the plant. Pvlvini are also present in plants showing sleeping movement at Figure 8.10 - Place where the dust with the decrease of sunlight. pulvini are located e.g. 'Kathurumurunga', Tamarind, 'Nelli' 94 Science | Support and Movements of Organisms  For extra knowledge Tactic movements In addition to tropic movements and nastic movements there is a type of movement known as tactic, which is related with the direction of stimulus. In tactic movement, the whole organism responds to the stimulus. e.g. Small Algal Species like Chlamydomonas In-situ Conservation Although plants show movements they cannot locomote like animals. Animals can avoid external hazards by locomotion. Plants grow in a habitat, where all necessary external factors needed to growth are present. Hence, plants can get destroyed in its habitat due to external hazards. Therefore, it is essential to conserve plants in their own habitat. Conservation of an organism, in its living environment is known as in-situ conservation. Strictly reserved forests which protect indigenous plants like ebony, satinwood, vitex are examples for in-situ conservation. These species of organisms can also be protected by conserving sensitive zones of environment. Figure 8.11 - 'Vilpattu' reserve Science | Support and Movements of Organisms 95 9 The Evolutionary Process Diversity of living organisms in our environment is a result of the evolutionary process. When studying about the evolution it is important to consider about the origin of the universe and origin of the life. In the past, there were many beliefs about the origin of the universe. 9.1 Origin of the Earth It is believed that the origin of the Earth took place about 4.5 billion years ago. Nebular theory is the first scientific explanation of the origin of the solar system. According to this theory, small particles of materials in the universe drew together by the force of gravity, clumped up, and the galaxies, the sun and other planets were formed. Big Bang theory can be considered as the modern theory about the origin of the Earth. According to this theory, universe was an energy source with a great energy. A giant explosion took place in it and large clouds of dust particles were created. These dust particles clumped up together and the galaxies were created. It is said in the big bang theory that, our solar system was created in the galaxy known as the milky way galaxy. Figure 9.1 - Illustration of the Big Bang Initially the Earth had been a very hot object and its volcanic activities were high. The Earth got gradually cooled and less volatile metals with high density formed the core of the Earth. It is believed that, Earth's crust was created later, by light silicon rocks. 98 Science | The Evolutionary Process Various types of elements at the centre of the Earth reacted with each other and different types of gases were formed. At first the atmosphere of the Earth had gases such as Carbon dioxide (C 2), Methane (CH4) and Hydrogen sulphide (H2S). The absence of xygen ( 2) in the early atmosphere is a significant fact. Initially, the extreme heat of the Earth caused evaporation of water on the planet. This evaporated water got condensed and clouds were formed. Water droplets in these clouds joined together and dropped onto the Earth as rain. There had been continuous heavy rains on the Earth for many years. This rain water which was rich with minerals, collected in lower lands and oceans were formed. Figure 9.2 - Illustrations of primitive Earth 9.2 Origin of life on the Earth There are many beliefs and theories on origin of life on the Earth. It is believed that, about 3.5 billion years ago life originated on the Earth. Let us consider some theories about origin of life on the Earth. Theory of special creation According to this theory, all living organisms on Earth were created by a super natural power. Since there is no scientific evidence to prove this theory, scientist do not pay attention to it. Spontaneous generation theory This theory states that life was originated from non-living things in a spontaneous manner. e.g. y Rats who born from pieces of clothes y Maggots who born from rotten meat y Weevils who born from decayed wood The Spontaneous generation theory has been effectively disproved by the experiments conducted by the scientist Louis Pasteur. Science | The Evolutionary Process 99  For extra knowledge Louis Pasteur prepared an experiment to prove that spontaneous generation theory is not an acceptable theory. y Similar amounts of sterilized nutritional media was added to two similar swan neck flasks. No growth of living organisms was Louis Pasteur observed. y After about one year neck of the one flask was broken and taken away. y Microbial growth was visible in the flask without the neck and no life appeared in the other flask. y As the conclusion, it was stated that living organisms do not generate spontaneously. This was accepted as true in 1862. No growth of Heating micro-organisms Neck of the flask was Growth of Heating broken micro-organisms The experiment which proved the non-applicability of the spontaneous generation theory Cosmozoic theory This theory suggests that, the living materials might have got established on Earth from a fallen meteor with living organisms or by space crafts from other planets. This theory has not been proved scientifically. Theory of biochemical evolution This theory confirms that, at the beginning of the Earth, the gases in the atmosphere reacted with each other and the ingredients that make life possible were formed. It is believed that the energy required for this was supplied by electric discharges during lightning, eruption of volcanoes and by the ultra violet radiation of the sun. These materials dissolved in rain water and collected in oceans. This mixture was known as the primordial soup. 100 Science | The Evolutionary Process The first living cell or the pre-cell appeared as a result of a bio chemical reaction in primordial soup. The first organism was unicellular and was considered anaerobic and heterotrophic. Scientists have experimentally shown that the first living cell was created by the primordial soup. For extra knowledge The two scientists Haldane and parin put forwarded the biochemical evolution theory about the origin of life. This theory was scientifically proved by Stanley Miller by conducting scientific investigations in laboratory. Stanley Miller The first form of life on the Earth is considered to be a simple unicellular bacterium. Then, the first photosynthetic organisms, unicellular algae were formed. After that, an atmosphere containing gaseous oxygen was formed. Many changes took place for a long time period within the body of unicellular organisms and multicellular organisms were born. Gradually, tissues, organs and systems were specialized within these multicellular organisms and the world of animals and plants were created. Cnidarians, some annelids and some arthropods are considered as the first multicellular organisms. The fish are considered as the first type of vertebrates, and amphibians originated from fish. Amphibians can be regarded as the first vertebrates that entered into terrestrial environment. Reptiles evolved as a result of gradual evolutionary changes occurred in amphibians. The reptiles are completely adapted to the terrestrial life than amphibians. It is believed that birds and mammals evolved from reptiles during evolution. The evolution of human took place about 12 million years ago. Modern human originated about 5 million (5 000 000) years ago. The world of plants evolved by the gradual changes resulted in photosynthetic algae on the oceans. First, less developed plants originated which, was then followed by non-flowering plants and flowering plants at last. Science | The Evolutionary Process 101 Accordingly, evolution of life has occurred at different times with several changes. In order to understand that process, study the figure 9.3. Figure 9.3 9.3 Evolution Various changes in the natural environment can have an impact on the existence of life. Life’s existence is confirmed by changes that occur gradually in living organisms in relation to continuous changes in the environment. 102 Science | The Evolutionary Process  Figure 9.5 - Mammoth Figure 9.6 - Dinosaur Let us do the activity 9.1 to create a model fossil Activity 9.1 You will need:- Kaolin clay, plaster of Paris, binder glue, 2 yoghurt cups, a spoon, shapes of animals (an oyster shell, fern leaf) a pair of scissors Method:- ² ill half of a one yoghurt cup with clay. Place the shell or the leaf on it and press. When the print of the shell or the leaf is marked on clay, remove the shell or the leaf. ² Put some plaster of paris into the other yoghurt cup. Add some water and prepare a plaster. Carefully pour the prepared plaster or binder glue on to the prints on the clay. Keep for about 2 hours to dry. ² Then, cut the yoghurt cup with the scissors and take out the clay lump out of the plaster or binder glue. ² bserve the model fossils on the surface of the clay lump and plaster made with plaster of paris. Step I Step II Step III Step IV Figure 9.7 - How to create a model fossil 104 Science | The Evolutionary Process 9.4 Importance of evolution in bio-diversity There is a competition among animals for the limited resources in the environment. The creatures who succeed, will be naturally selected and be established in the environment. These selected organisms become pioneers in the environment and their population increases. These creatures have created a large bio-diversity in the natural environment. In the process of evolution, novel species can also be evolved from former species. This is known as speciation and this process broadens the biodiversity further. For extra knowledge Charles Darwin is considered as the father of evolution. He put forwarded the Natural selection theory which is a scientifically accepted theory about Charles Darwin evolution. Assignment 9.2 Prepare a booklet by collecting information on the evidence found in Sri Lanka, about human evolution. Use the evidence found at Batadombalena in Kuruwita , Pahiyangala cave in Bulathsinhala