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All living organisms are dependent on water for living. Water is essential for carrying out metabolic reactions in the body of living organisms. Water is important for other activities also such as agriculture, animal rearing, production and manufacturing activities, etc. 75% of the earth surface has been completely covered by water.
The qualities of water which can be determined by touch, smell, sight and taste are known as the physical properties of water. It includes temperature, colour, taste, odour, etc. We can taste water, we can observe the colour of water just by sight, the odour can be determined by smell and even temperature can be determined by just touching it. Water contains a number of living organisms that can be microscopic or visible to the eyes. It also contains many plants and algae suspended in water. Aquatic organisms possess unique survival abilities. The pH level of water, its turbidity and living organisms present in water are certain features that determine the quality of water. We will study two samples of water collected from two different water bodies for determining the pH, clarity and presence of living organisms through an experiment.
| Table of Content |
Key Terms: Water, Living Organisms, Temperature, pH Level, Aquatic Organisms, Turbidity, Photosynthesis, Algae, Water Bodies
Aim of the Experiment
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To collect water from two different water bodies and study pH level, clarity and presence of any living organism in respective samples.
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Apparatus and Material Required
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Pins, Tape, Dropper, Universal indicator solution, Secchi’s disk, Needles, Compound microscope, filter paper, glass slides, coverslips, tile, pH paper, beaker, test tube.
Also Read: Importance of Water
Procedure
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(I) To Study the pH Level of the Samples of Two Water Bodies
- Take two test tubes which should be clean and dry.
- Pour water from both sources in both the test tubes and label them as A and B for convenience.
- Dip the strip of pH paper in both the test tubes.
- Place those pH papers on tile and let them dry completely.
- pH of the solution can also be found by using a Universal indicator solution. This is an alternate method for determining the pH of a solution.
- Add 5-5 drops of this indicator in both the test tubes and let them change their colour.
Observation:
Observe the change in colour. Try to associate it with broad range indicator paper to know the pH of both the test tubes.
- If pH is less than 7, it indicates that the water sample is acidic in nature.
- If pH is equal to 7, it means that the water is neutral.
- If pH is greater than 7, water is basic in nature.
Precautions:
- Test tubes should be clean and dry before getting filled with water samples of both water bodies.
- Separate droppers should be used for each test tube.
- Dry the pH paper completely before comparing it with the colour scale.
- For determining the correct pH, compare the pH paper with the colour scale carefully.
pH Level of Water
Also Read: Scarcity of Water
(II) To Study the Turbidity of Water in Both Samples
Turbidity refers to the cloudiness in water due to the presence of particles in water.
- Using a small boat, reach the centre of the pond.
- Holding the rope tightly, immerse the Secchi disc slowly into the water. Keep on immersing it till the black and white segment of the disc gets completely disappeared.
- The disc will get invisible at a certain height.
- Mark the length of the rope with the help of a pin when the disc gets disappear. ( say X cm)
- Now, pull up the disc slowly. Do this till the black and white segment reappears.
- When the segment just reappears, mark the length of the rope with a pin. ( say Y cm)
- Find the length between X and Y with the help of a metre of tape.
- With the help of the following method, calculate the mean of the length between X and Y, P=( X+Y/2 )
- Repeat the above procedure in other water bodies to determine the turbidity of water.
Observation:
Photic zone is represented by the value of P. It is the depth till which the sunlight penetrates and photosynthesis takes place in water.
Precautions:
Ensure proper safety measures while going to the centre of the pond.
Turbidity of Water
(III) To Study the Presence of Living Organisms in Both Samples
- Take a test tube which should be clean and dry.
- Pour the collected water sample into the test tube.
- Let the sediments get settle down at the bottom of the test tube. Leave the test tube undisturbed.
- With the help of a dropper, transfer a drop of sample from the test tube on a glass slide.
- Using a needle, place the coverslip gently.
- Under a compound microscope, observe the entire slide.
- Repeat the above steps with another sample also.
Observation:
A large number of microscopic organisms will be observed under the microscope.
Precautions:
- Don’t disturb the test tube till the sediments get settled down at the bottom.
- Place the coverslip gently on the glass slide to avoid the formation of air bubbles.
Aquatic Life
Things to Remember
- Physical properties of water can be determined by touch, smell, sight and taste.
- The quality of water is determined by the pH level of water, its turbidity and organisms present in water.
- If the pH of water is less than 7, it is acidic. If pH is more than 7, it is basic and if the pH is equal to 7, water is neutral.
- Turbidity refers to the cloudiness or haziness in water due to the presence of certain particles in water.
- The survival of aquatic organisms highly depends on the pH of water. Less pH of water can cause the death of the organisms.
- Photic zone refers to the depth upto which sunlight can penetrate in water and photosynthesis takes place.
- Proper safety measures should be taken while reaching the centre of the pond.
- Dry and clean test tubes should be used for determining the pH level and presence of living organisms to get accurate results.
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Sample Questions
Ques. What is the importance of pH in water? (3 Marks)
Ans. pH is an important factor in determining the quality of water in the following ways-
- Water can become harmful for living organisms if its pH is too high or too low.
- The young fishes and aquatic damp can die if the pH is less than 5. Their reproductive process also gets affected at such pH.
- If pH is less than 6.5, it can inhibit the normal growth of aquatic organisms.
- If pH is more than 9, ammonium ions get converted into ammonia which can make the water toxic.
- Water with a pH more than 11 can kill the fish.
Ques. What are the factors which affect the pH of water? (4 Marks)
Ans. The pH of water is affected by the following factors-
- Carbon dioxide concentration- Dissolved CO2 in water can cause an increase in the hydrogen ion concentration which decreases the pH of the water and makes the water acidic. This CO2 comes from the atmosphere. When plants respire at night, they release CO2 which makes it acidic at night.
- Temperature- It affects the solubility of carbon dioxide in water. When the temperature rises, the solubility of Carbon dioxide is reduced and pH gets increased which makes the water alkaline. When the temperature decreases, the solubility of carbon dioxide increases and it leads to a decrease in pH level and water becomes acidic.
- Carbonate and Bicarbonate concentration- The nature of Carbonate and bicarbonate ions is basic. When their concentration increases, pH gets increased and water becomes basic.
- Organic material decomposition process– When decaying of organic matter takes place, Carbon dioxide is released which gets dissolved in water. Dissolved carbon dioxide can change the pH of the water body.
Ques. What are the factors which affect the quality of water? (4 Marks)
Ans. The following factors affect the quality of water-
- Temperature- Fishes and other aquatic organisms can survive in water at a particular temperature. The level of oxygen in water is also affected by the temperature.
- Acidity- It refers to the hydrogen ion concentration present in water. We can know if the water is acidic, basic or neutral if we know the pH of water.
- Dissolved Oxygen- Dissolved oxygen is very important for the survival of fishes and other aquatic organisms. About ten molecules of oxygen are dissolved per million molecules of water.
- Turbidity – It refers to the number of particles present in water. It makes the water cloudy.
- Hardness – This is determined by the amount of dissolved magnesium and calcium in the water.
- Specific conductance- The measure to conduct electricity by water is known as the specific conductance of water. Dissolved solids, salts, etc determine the specific conductance.
Ques. What is the importance of turbidity in determining the quality of water? (4 Marks)
Ans. Determining turbidity is very important due to the following reasons-
- The number of suspended particles are measured by knowing the Turbidity.
- The suspended particles block the path of light to aquatic plants and affect photosynthesis.
- Turbidity also affects the taste and odour of water.
- Turbidity harbours bacteria and viruses. It also acts as a shield to pathogens and particles that cause turbidity.
- It also carries contaminants such as lead and mercury which makes the water unsafe for drinking.
Ques. What are the factors which affect the survival of aquatic organisms? (4 Marks)
Ans. The following factors affect the survival of aquatic organisms in water:
- pH – Aquatic organisms can survive in a narrow range of pH. If the pH of water is less or more than the narrow range, it inhibits the growth of the organisms.
- Light- Photosynthesis can only occur if plants get enough light down the water column.
- Oxygen- Aquatic organisms need oxygen to survive in water. Oxygen gets dissolved in water as a result of photosynthesis by aquatic organisms.
- Movement of water- Water usually moves in the form of waves or currents. It maintains the flow of food and nutrient in the water.
- Temperature- Living organisms in water can survive in a narrow range of temperatures. If the temperature rises or gets decreased, it can lead to the death of organisms.
Ques. What do you mean by normal pH? (3 Marks)
Ans. pH refers to the concentration of hydrogen ion concentration of the aqueous solution.
- If pH is less than 7, water is acidic and if the pH is more than 7, water is basic.
- The pH of pure water 7 at 25°C implies the neutral nature of pure water.
- Plants do their best in the 5 to 7 pH range but some plants such as water hyacinth need a pH range of 6.5 to 7.5.
- The pH range of 6.5 to 9 is best for fishes. Aquariums are often supplied with carbonate and bicarbonate ions to prevent pH changes.
Ques. What do you mean by the physical properties of water? (4 Marks)
Ans. The properties of water which can be determined without the requirement and chemical apparatus is known as the physical properties of water. Such properties can be determined by simple physical activities such as touch, smell, etc. The common physical properties of water are as follows-
- Colour– We can have a general idea about the quality of water just by looking at its colour. If water is not pure, it shows a dull or slightly muddy appearance.
- Temperature- It can be determined by touching the water. It feels slightly warm if the temperature is more.
- Turbidity- The amount of particles present in water is the measure of its turbidity. It makes the water cloudy or muddy.
- Taste- Water quality can also be detected just by tasting it. If water is impure, it will taste different.
- Odour- Pure water is odourless. If water has some odour, it can be determined by smell which can ultimately lead to the determination of water quality.
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