Study of Physical Properties of Soil :

Experiment 2: Study Of Study of Physical Properties of Soil ( Texture, pH, Moisture Content, Water Holding Capacity Of The Salt)  

Theory

Our Objective

Our aim is to collect and study soil for texture, moisture content, pH and water holding capacity.

Theory

Soil is the upper humus, containing a layer of the earth, consisting of rock and mineral particles mixed with decayed organic matter.  Soil sustains plant life and contains numerous living organisms. Soil, along with air and water, is one of the three most important natural resources, which we cannot live without.  A productive soil contains approximately 46% mineral matter, 4% organic matter, 25 % water and 25% air. An approximate composition of soil shown below

Let’s see the physical characteristics of soil.

The physical characteristics of a soil are due to the size of its soil particles.  Soils are classified according to their particle size as follows:

Texture of Soil

Soil texture is an important physical characteristic of soil which is used in both the field and laboratory to determine classes for soils based on their physical texture. The soil texture depends upon the proportion of the constituent solid particles of different sizes. The terms sand, silt, and clay refer to particle size; sand is the largest and clay is the smallest. The size of sand particles is 0.05–2 mm, silt particles are 0.002–0.05 mm, and clay is smaller than 0.002 mm. The term loam refers to a soil with a combination of sand, silt, and clay sized particles.  Each texture corresponds to specific percentages of sand, silt, or clay. The soil texture triangle is a tool used to visualise and understand the meaning of soil texture names.  The below figure shows each of the 12 textural classes based on the percentage of sand, silt, and clay in each. If we know the sand, silt, and clay percentages of a soil, then the textural class can be identified from the textural triangle. Say for an example soil consists of 12% clay, 55% sand and 31% silt, we will see how to determine the textural class of the soil. Here, the sample soil has 12% clay, so draw a line corresponding to percent clay. Similarly draw the lines for percent sand (55%) and percent silt (31%). The lines which intersect indicate the soil type we have. From the above sample, soil consists of 12% clay, 55% sand, and 31% silt; hence the soil type is sandy loam.

pH of Soil

The chemical property of the soil depends upon the presence of different types of nutrients and pH of the soil. The soil pH is an indication of acidity or alkalinity of soils. The soil pH is important in determining the availability of soil minerals.  Different plants have differing optimum soil pH requirements. The majority of plants prefer a pH of around 6 to 7, which is very slightly acidic.

Water Holding Capacity of Soil

One of the main functions of soil is to retain water and make it available for the plant to access.  All of the water in the soil is not available to plants. The amount of water available to plants is therefore determined by the number and size of the soil’s pore spaces. Water holding capacity of the soil is the amount of water held by the capillary spaces of the soil after the percolation of gravitational water into the deeper layers.  Fine sandy loam, silt loam and silty clay loam soil store the largest amount of water, whereas sand, loamy sand and sandy loam have limited water storage capacity.

Learning Outcomes:

• Students understand the physical properties of soil.
• Students understand texture, pH and water holding capacity of soil.
• Students do the experiment better in the real lab having gone through the animation and simulation.

Materials Required

Viva-Voce [Study of Physical 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 measurment 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 different point. Also, the use of pH indicator paper is known to be the destructive process and the solution used for indication cannot be use 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 offish 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 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 runoff water taking different kinds of pollutants to the water bodies. 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 the 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.          

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.