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Biology Practicals Class XII

Study of Chemical Properties of Different Soils

Study of Chemical Properties of Different Soils :

Experiment 3:  Study of Chemical Properties of Soil (Turbidity, pH and Microbial Presence in Water)

 

 

 

Our Objective

Our aim is to  Study of Chemical Properties of Soil

 

Theory

Our Objective

Our aim is to study different water bodies for pH, clarity and presence of any living organisms.

Theory

Water covers about three-quarters of the earth's surface and it is essential for all known forms of life. Water is a habitat for a variety of plants and animals which have special adaptations to survive in their habitats. Some of the characteristics that control the quality of water are the turbidity of water, pH of water and different types of plants and animals and their density.

Turbidity of Water

Turbidity is the measure of the relative clarity of a liquid. Turbidity of the water body determines the depth to which light can penetrate and thus affects the distribution and photosynthesis of phytoplankton and macrophytes. The more turbid the water body, the less is the thickness of its photic zone (the layer of a body of water that is penetrated by sufficient sunlight for photosynthesis).

Turbidity can be measured using several methods. The easiest and least expensive method is through a Secchi disk. Water turbidity can be measured with a Secchi disk, a circular white or black-and-white disk attached to a tape measure that is lowered through the water to a depth where it disappears from view. In clear lakes, the Secchi depth may be greater than 10 metres, while in eutrophic lakes, with dense growth of algae and other organisms, creating low visibility, the Secchi depth can be less than 1 metre.

pH of Water

The pH is a measure of the relative amount of free hydrogen and hydroxyl ions in an aqueous solution. Solutions with a pH less than 7 are said to be acidic and with a pH greater than 7 are basic. The pH of pure water is 7 at 25°C.

The pH value of a water sample can be determined by indicator dye method and electrometric method using a pH meter. For routine purposes, the indicator dye method, using universal pH indicator solution or paper strips containing the pH indicators, is used.

Living Organisms in Water

The productivity and the trophic state of a water body are determined by quantities of nitrogen, phosphorus, and other biologically useful nutrients. Nitrogen and phosphorus are nutrients that induce plant growth in standing water bodies, so increased concentrations tend to result in increased plant growth.

A productive water body has high nutrient concentrations, and has a very high density of phytoplankton per unit area. These water bodies have high amounts of nutrients and dissolved oxygen and bear large number of organisms at different trophic levels. A water body with a very low density of phytoplankton per unit area is a non-productive water body. The status of health of a water body can be determined by analyzing water samples for the number and type of organisms present in it at a given time.  Such assays also help us to find whether a water body is polluted, as some of the organisms are strong indicators of water pollution. When you look at a water sample with a microscope you will likely see a variety of tiny living things.  Some of them are shown below.

Learning Outcomes

  • Students understand the meaning of turbidity of water, pH of water and about the different living organisms in water bodies.
  • Students understand the term Secchi’s disk.
  • Students do the experiment better in the real lab having gone through the animation and simulation.

 

Theory Of The Experiment
Viva-Voce On Study of Chemical Properties of Different Soils Experiment (Q&A)

Materials Required

  1. Study Turbidity of Water Samples using Secchi’s Disc Method

    Materials Required:

    Procedure:

    • Reach the centre of the pond in a small boat.
    • Slowly immerse the Secchi’s disc into water vertically holding the rope tightly till the black and white segments of the disc disappear.
    • On reaching a particular depth, the disc becomes completely invisible.
    • Using a pin, mark the length of the rope when the disc disappears (say A cm).
    • Slowly pull up the disc till the black and white segments of the disc just reappear.
    • Using a pin, mark the length of the rope where they just reappear. (say B cm).
    • Using a meter tape, find the length of A and B.
    • Find the mean length (Say X cm) of the rope by the following method. X=(A+B)/2

    Observation:

    The value of X represents the depth of the photic zone up to which sunlight penetrates in the water body and photosynthesis takes place.

    Precaution:

    Students are advised to perform this experiment under the strict supervision of a teacher to prevent danger, such as drowning.

    To Study the pH of Water

    Materials Required:

    Procedure

    • Let’s first check the pH of the water sample using pH paper.
    • Take a pH paper strip and dip into the beaker that contains back water.
    • Keep the wet pH paper strip on the tile.
    • Do the same procedure for borewell water and pond water.
    • Wait for some time to dry the pH paper.
    • Note the colour and compare with the colour chart given on the broad range indicator paper and get a rough estimate of pH of the sample solution.
    • We can observe that backwater and bore well water has pH 8 and pond water has pH 5.
    • Let’s check the pH of the water sample using universal indicator solution.
    • Using a dropper take some universal indicator solution.
    • Put 5 drops of indicator solution into the test tube that contains the water sample.
    • Note the colour developed and compare it with the colour chart.
    • We can observe that backwater and bore well water has pH 8 and pond water has pH 5.

    To Analyse Living Organisms in Water Sample

    Material Required:

    Procedure:

    • Take beaker containing pond water and pour into a test tube.
    • Leave the water sample undisturbed till the sediment settles to the bottom of the test tube.
    • Decant the clear water, leaving concentrated sediment at the bottom of the test tube.
    • With the help of a dropper, transfer a drop of water from the test tube to the centre of a glass slide.
    • Take a cover slip and place it gently on the slide with the aid of a needle.
    • Remove the extra water using a filter paper.
    • Place this glass slide on the stage of the compound microscope and view it.

    Observations:

    We can observe a large number of different organisms in the water sample.

    Simulator Procedure (as performed through the Online Labs)

    You can select the experiment from the ‘Select the experiment’ drop-down list (pH of water samples, the turbidity of water samples, living organisms in water samples).

    pH of Water Sample

    • Choose any one of the water samples in the beakers by clicking on it.
    • There are two ways of finding the pH value of the solution:

    Using the pH strip:

    • Click and drag the dropper from the stand and move into the solution in the beaker to collect the water sample in the dropper.
    • Still holding the dropper, move it from the beaker over to the pH strip and release it.
    • To find the pH value of the solution, select the colour from the colour chart by clicking and dragging it to the pH strip and comparing it.
    • The colour that matches with the spot on the pH strip indicates the pH value of the solution.

    Using the Universal Indicator:

    • Click and drag the dropper from the Universal Indicator bottle and move it into the solution in the beaker to drop the Universal Indicator into it.
    • To find the pH value of the solution, select the colour from the colour chart by clicking and dragging it next to the solution in the beaker and comparing it.
    • The colour that matches with the solution in the beaker indicates the pH value of the solution.

    Note:

    • Once the test is done using the Universal Indicator, you cannot do it with the pH strip. To do it with the pH strip, click the ‘Reset’ button and vice versa.
    • The ‘Reset’ button can be used to redo the experiment with other solutions.

    Turbidity of Water Sample

    • You can select the method of checking turbidity of water from the ‘Select the method’ drop-down list (Secchi’s disk method and measuring cylinder method).

    Secchi’s disk method:

    • You can immerse Secchi’s disc into the water by moving the ‘Disc movement’ slider.
    • On reaching a particular depth, the disc becomes completely invisible.
    • The length of the rope when the disc disappears (say A =95 cm).
    • You can pull up the disc until the black and white segments of the disc just appear by moving the ‘Disc movement:’ slider.
    • The length of the rope where they just reappear. (say B =90 cm).
    • We can find the mean length (Say X cm) of the rope by the following method. X= (A+B)/2. The mean length is shown in the left pane.
    • You can redo the experiment by clicking on the ‘Reset’ button.

    Note:

    • The value of X represents the depth of the photic zone up to which sunlight penetrates in the water body and photosynthesis takes place.
    • You can move the Secchi’s disc by using the up and down arrow keyboard keys.

    Measuring Cylinder Method

    • Click on the ‘Start’ button to start the experiment.
    • A timer is shown and you need to wait until the timer stops.
    • Observe the amount of sediment settled at the bottom of each cylinder.
    • Click on the information icon to see the inference.
    • You can redo the experiment by clicking on the ‘Reset’ button.

    Note:

    • Turbidity is a measure of the amount of suspended particles in the water column. Pond water has fewer suspended particles, so it has a low turbidity level. Bore well water and backwater have more suspended particles, so they have a high turbidity level.

    Living Organisms in Water

    • Choose any one of the water samples by clicking on the corresponding icon.
    • Click and drag the dropper from the stand and move into the water sample in the vial to collect into the dropper.
    • Still holding the dropper, move it from the vial over to the glass slide and release it.
    • Click and drag the cover slip and move towards the glass slide to place cover slip on it.
    • Drag and drop the glass slide onto the stage of the compound microscope.
    • Click on the eye piece of the compound microscope to view the living organism.
    • We can observe a large number of different organisms in the water sample.
    • Click on each species to display its name.
    • You can redo the experiment by clicking on the ‘Reset’ button.

Viva-Voce [Study of Chemical Properties of Soil ]

As Per Pattern of CBSE (2018-19)

 Q.1.     What pH range favours the best plant growth?

Ans.    Most plants thrive well in the neutral pH. Slightly acidic pH favours the tree growth and forms forests. Slightly alkaline pH is preferably favoured for grasses.

Q.2.     Leaves and twigs of trees and other vegetable matter is continuously collected on top of the soil. Name the scientific term used for it.

Ans.    It is called litter.

Q.3.     What do you understand by the term 'buffer'?

Ans.    Any solution which can resist change in pH on adding some chemicals (acid/base) is called buffer.

Q.4.     What would be the pH of tap water?

Ans.    The pH of tap water would be nearly 6.5-7 (neutral).

Q.5.     How does water gets polluted?

Ans.    Addition of any undesirable substance which degrades its quality makes water to be polluted. This phenomenon is called water pollution.

Q.6.    'pH measurement with indicator paper is not very accurate'. Comment.

Ans.    It is correct that the measurement with the pH indicator paper is not as much accurate as the pH meter because indication made by the pH paper is subjective and different people see the colour change at the different point. Also, the use of pH indicator paper is known to be the destructive process and the solution used for indication cannot be used afterwards.

Q.7.     'Waterlogged soils are acidic'. Comment.                                                          

Ans.    Water is present in ionic form in soils, Le. it contains H+ and OH" ions. Also, most of the chemicals that come in contact with the water-logged soil also dissociate into their ionic forms. These positively charged or metal ions react with OH" ions of water to form various hydroxides with a simultaneous release of more protons (H+ ions).

Q.8.     Why are soils around mineral minings areas acidic?

Ans.    Soils around mineral mining areas are acidic in nature due to the presence of H+ ion and Al3+ ion containing solutions in the soil. Al3+ is considered to be important in acidic soil because it has the ability to react with water forming Al(OH)2+ thus releasing more H+ ions.

Q.9.     What degrades the quality of water bodies?

Ans.    The presence of organic and inorganic wastes degrades the quality of water bodies.

Q.10.   What promotes the algal growth in water bodies?

Ans.    The run off water from agricultural fields gets accumulated in nearby water bodies. It carries fertilisers which leads to accumulation of various nutrients that in turn promotes algal growth in the water bodies.

Q.11.   Define pollution.

Ans.    Any undesirable change in the physical, chemical or biological characteristics of water, that harms the life form is called pollution.

Q.12.   Define pollutant

Ans.    Any material/substance which has harmful effect on different forms of life is a pollutant.

Q.13.   Name few water pollutants.

Ans.    Water pollutants can either be chemical or biological. The chemical pollutants are nitrates, fluorides, heavy metals, etc. Biological pollutants are disease-causing microbes like viruses, bacteria, Protozoa and helminthes.

Q.14.   Name a disease caused by polluted water.

Ans.    Minamata disease is caused due to the consumption of fish that inhabited a water body containing accumulated mercury.

Q.15.   Name a few sources of water pollution.

Ans.  (i)        Discharge of domestic sewage and factory outlets.

            (ii)        Agriculture run-off water.

            (iii)       Clay and silt from soil erosion.

            (iv)       Oil spills and discharge of thermal wastewater

Q.16.   Is turbid water fit for drinking? Explain.                                                                

Ans.    No, turbid water contains huge amount of water pollutants. So, it is not considered to be fit for drinking. However, it can be used for other purposes after it undergoes extensive treatment.

Q.17.   Why is the penetration of sunlight in any water body important?

Ans.   The penetration of sunlight in any water body is considered to be important for all forms of life'living
in it. First of all, it makes the photic zone, maintains or affects the water temperature. Secondly,
phytoplanktons are the producers and they make first trophic level in the ecosystem. If more light is
there, stronger will be the trophic level on which other forms of life depend.

Q.18.   What is BOD?

Ans.   BOD is known as the Biological Oxygen Demand of any water body.

Q.19.   How are BOD and water turbidity/clarity are related?

Ans.   High BOD indicates the presence of high microbial activity. So, if more microbes are present in
water more turbidity will be there in water and vice-versa.

Q.20.   How is the clarity of water important to any water body?

Ans.    If a water body is clear light will penetrate to its deeper layers that will have effect on the positive
growth of water plants, zooplanktons and phytoplanktons.

Q.21.   Green plants are seen only in the photic zone. Comment.                                  

Ans.   All green plants perform photosynthesis, for this they require light. The photic zone is the zone of
light in the water bodies. That is why green plants are found in the photic zone.

Q.22.   It is a common practice to use alum for clearing turbid waters. Explain

Ans.   Murky, muddy, cloudy or turbid water is caused by microscopic water impurity (less than 1 pm or
even smaller). They remain suspended in water and gravity has little effect on them. When alum is
added, it neutralises electrical charges present on suspended particles and they begin to clump
together and sink to the bottom. This is called flocculation or coagulation.

Q.23.   The turbidity of water varies with season. Comment.                                              

Ans.    Turbidity is the key parameter in assessing the water quality and is linearly related to the backward
scattering of light of organic and inorganic particles in water.

In rainy season, there will be more run off water taking different kinds of pollutants to the
waterbodies. So, it will definitely increase the turbidity of waterbodies. Whereas in non-rainy/windy
season, waterbodies might have settled water/stagnant water. At this time, large pollutants get
settled at the bottom due to gravity, only suspended particles less than 1 pm size remain in water.

Q.24.   Define phytoplanktons.

Ans.   Phytoplanktons are microscopic, photosynthesizing organisms that inhabit the upper sunlight layer of almost all oceans and lakes, e.g. Spirogyra and Anabaena.

Q.25.   What do you understand about prokaryotic organisms?

Ans.   These are unicellular organisms, which lack well developed cellular organisations. They possess primitive membrane-less nucleus called nucleoid.

Q.26.   Name any single-celled algae present in water.

Ans.   Chlamydomonas.

Q.27.   What leads to eutrophication?

Ans.   Addition of excess organic matter and fertilisers that promote growth of algae leading to the depletion of 02 from water bodies and death of aquatic life. This whole process is eutrophication.

Q.28.   How are eukaryotic organisms different from prokaryotic organisms?

Ans.   Eukaryotic organisms containing cells have true nucleus bounded by nuclear membrane and they also contain membrane bound organelles like ER, Golgi apparatus, mitochondria and chloroplast. Prokaryotic organisms are simple, do not have nucleus and other cell organelles.

Q.29.   Why do you find few organisms in polluted water? Explain.                 

Ans.   The polluted water usually has toxic materials, which is not suitable for any form of life. So, organisms are not able to live in such water and their number gets limited to few only because conditions do not favour them to reproduce.

Q.30.   Why is FAA (Formaline Aceto Alcohol) added after collecting the water sample?

Ans.   FAA is a fixative. It is used as a preservative of plant and animal specimens. So, it is added to water samples for the preservation of organisms present in the water samples.

Q.31.   Name at least one phytoplankton and zooplankton commonly found in polluted water.

Ans.                Phytoplankton             -           Chlamydomonas
Zooplankton                -           Paramecium

Q.32.   In the polluted water, the dissolved oxygen content is very less. How is this related to biological oxygen demand?

Ans.   The dissolved oxygen in water is usually the available form of oxygen to the aquatic organisms. Biological oxygen demand is the requirement ofO2 for the microbial activities of living organisms present in water. It is usually less in the unpolluted water because there are few organisms present in this water.

Q.33.   What does high BOD indicate?

Ans.    The high BOD indicates the presence of high amount of organic matter in the water This means there is high microbial activity involved to decompose the organic matter, so oxygen requirement is high. High BOD represents high level of pollution.

Q.34.   Give an example of biodegradable pesticide.

Ans.    Extract of the neem tree is a biodegradable pesticide.

Q.35.   What are pollutants?

Ans.    These are the agents that pollute the environment.

Q.36.   What is PAN?

Ans.    Peroxyacetyl nitrate.

Q.37.   Expand B.O.D.

Ans.    Biological Oxygen Demand. It is the amount of oxygen required for decomposition of organic matter present in water.

Q.38.   At what pH the highest number of organisms survive?

Ans.    pH 6-5 -7-5.

Q.39.   What is the importance of pH?

Ans.        it determines chemical nature and affects diversity and distribution of organisms.

Q.40.      What is pollution?

Ans.   An undesirable change in the physical, chemical or biological characteristics of air, water and land that harmfully affect the human life is called pollution.

Q.41.      What are pollutants?

Ans.    The agents pollute our air, water and land are called pollutants.

Q.42.      Define water pollution.

Ans.    It is the addition of any undesirable substance to water which make it harmful for the organisms.

Q.43.      What is biochemical oxygen demand (BOD) ?

Ans.   The amount of oxygen required by microorganisms for decomposition of organic matter present in water is called biochemical oxygen demand.

Q.44.      What does high BOD indicate ?

Ans.    High BOD indicates the presence of higher amount of organic matter in the water.

 

 

 

 

 

NCERT Practical Manual For The Study of Chemical Properties of Soil Experiment (Download PDF)

Additional Resources For The Biology Practical  Class XII :

Significance & Overview Of Biology Class XII Practicals 

There are altogether twenty-five exercises in the present manual which are based on Biology curriculum for Class XII.

For each practical work, principle, requirements, procedure, precautions, observations, discussion and the questions are given in the book.

The methodology of preparation of any reagent, if required, has been given along with the requirements, for the convenience of students and teachers. The questions are aimed to develop learner’s understanding of the related problems.

Precautions must be well understood by the learners before proceeding with the experiments and projects. In addition to the core experiments enlisted in the syllabus for Class XII emphasis has also been given for pursuing Investigation Project Work.

Appropriate appendices related to the observation and study of organisms are given along with the experiment. International symbols for units, hazards and hazard warnings are given at appropriate places in the book.