Causes and Effects of Ozone depletion - Ozone Hole

• Ozone is present mainly in the stratosphere extending 16 kms -50 kms.
• Also known as ozone umbrella, or protective layer.
• The presence of ozone layer in the stratosphere is of vital importance for all living organisms, because the harmful solar radiation, such as ultraviolet rays(UV-B), which are lethal to life on the earth are absorbed by it.
• The ozone umbrella does not allow these harmful UV rays to enter the earth’s atmosphere.

Ozone hole

• The thickness of ozone layer is measured in Dobson unit (DU),where 

                                 1 DU =0.01mm

• The average thickness of the stratosphere ozone layer is estimated to be 32 Du
• A fall in thickness or concentration of spring time ozone layer is termed as ozone hole.
• It was discovered by Farman et al 1985, who coined  the term ozone hole.

Causes of Ozone depletion

• The main cause of ozone layer depletion is the build-up of CFCs (chlorofluorocarbons) in the atmosphere.

• When the CFCs reach the upper atmosphere, high UV radiation reacts with CFCs and releases chlorine atoms. These free chlorine atoms react with ozone thereby leading to the depletion of the ozone layer.

CFCl₃-> CFCl₂+Cl

CFCI₂ ->CFCI+CI

CI+O₃->CIO+O₂

CIO+O₃->CI+2O₂

•  An individual chlorine atom can on average destroy nearly a thousand ozone molecules before it is converted into a form harmless to ozone this is why CFCs are extremely damaging to the ozone layer.
•  The build-up of CFCs is caused by many applications like the production of refrigerants, anesthetics, aerosol sprays.

Social issues and the environment :Climate change, Global warming and Acid rain, Green house effect, ozone layer depletion from Biology Exams 4 U

Ozone Depleting Substances (ODS)

• The green house gases like CFC, Methane and nitrous oxide in the stratosphere destruct ozone layer.
• Substances that cause the depletion of the ozone layer are called Ozone Depleting Substances (ODS).

The different ODS are

• CFCs (14% of total depletion)
• Nitrogen oxides(3.5% depletion)
• Halons (Used in fire extinguishers)
• Methyl Chloroform
• Carbon Tetrachloride
• Hydrofluorocarbons (HCFCs)

Effects of Ozone Depletion

• Due to depletion of ozone layer the dangerous UV B radiation passes through this layer and reaches the earth.
• Cornea absorbs UV b radiations and becomes inflamed. The disorder is called ‘snow blindness’ cataract
• The incidence of UV B radiation damage skin cells cause ageing of skin and skin cancer.
• Decreased photosynthetic activity will increase CO2 concentration of the atmosphere resulting in global warming.

September 16: International  Ozone Day

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Green House Gases, Global Warming and its Effects

Industrial and domestic coal burning release high amount of carbon dioxide,carbon monoxide, chloroflurocarbons, methane, nitrous oxide etc from various sources.They are acting as greenhouse gases.

Green House Gases

The various green house gases are 

• Carbon Dioxide, CO2(warming effect 60%),
• Methane, CH4 (effect 20%)
• Chloroflurocarbons or CFCs(14%),
• Nitrous Oxide, N2O  (6%)
• Others of minor significance are water vapours and ozone.

Social issues and the environment :Climate change, Global warming and Acid rain, Green house effect, ozone layer depletion from Biology Exams 4 U

Global warming

• The excessive increase in the amount of green house gases in the atmosphere raises the temperature by retaining more infrared radiations.
• This excessive green house effect is referred to as global warming.
• CO2 is the most important green house gas that plays   a major role in increasing global warming.
• 60% of the global warming is caused by carbon dioxide. Chloroflourocarbon (CFC), nitrous oxide and methane constitute the remaining 40%of the global warming.

Effects of global warming

• Drought is one of the most serious problems arising from major climate change resulting from global warming. 
• Decrease in precipitation.
• Increased evaporation reduces water available for agricultural , and other uses. It may affect the food production.
• Sea level rise: the melting of glaciers
• Rising of sea level produces negative impacts on human existence, freshwater resources, agricultural and dry lands, animals and bird existence etc.
• Effect on range of species distribution.

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Acid rain: Definition, Causes and Effects - Acid Rain Formula

•The term acid rain was first used by Robert Angus Smith (1872).
•It is described as ‘man’s chemical warfare on nature”.

•Also known as Acid precipitation

What is Acid Rain:

•Acid rain refers to the presence of excessive acid content in the atmosphere and also in the precipitation water(rain, snow, mist, fog etc).

•It is the rain fall and other forms of precipitation with a pH of less than 5 of normal rain is 5.6-6.5.

•Two forms: Wet and Dry

•Wet deposition: Rain, snow and fog

•Dry deposition: it is settle down of wind blown acidic gases and particles over trees, various articles and soil. about 50 of acidity is passed to earth as dry deposition.

Causes of Acid Rain: 

      1. Sulphuric acid and nitric acid are the major agents of acid rain.

a) Formation of Sulphuric acid:

2SO₂+O₂->2SO₃

SO₃+H₂O->H₂SO₄   (Sulphuric acid)

b) Formation of nitric acid

2NO+3[O]->N₂O₅

N₂O₅+H₂O->2HNO₃ (Nitric acid
2. Hydrochloric acid, nitrous acid and carbonic acid also contribute to acid rains.

a) Formation of carbonic acid

             CO₂+H₂O-> H₂CO₃ (Carbonic acid)

             b)Formation of nitrous acid

NO+O₃->NO₂+O₂

NO+NO₂->N₂O₃

                           N₂O₃+H₂O-2HNO₂ (Nitrous acid)
Oxides of nitrogen come from combustion of fuels in automobiles as well as in power plants.
Oxides of sulphur are released from smokestacks of coal fired power plants, smelters and other industries (oil furnaces).

Social issues and the environment :Climate change, Global warming and Acid rain, Green house effect, ozone layer depletion from Biology Exams 4 U

Effects of Acid Rain (Acid precipitation):

Acid rain is very harmful to agriculture, plants, and animals. It washes away all nutrients which are required for the growth and survival of plants. Acid rain affects agriculture by the way how it alters the composition of the soil.

Effect on nitrogen cycle: Nitrogen cycle is highly sensitive to the acidification of soil.  Acidity suppresses denitrification, high  pH increases the volatilization of ammonia, Alkalinity affects the survival of nitrogen fixing bacteria.

Effect on fresh water ecosystems: due to acid rain many lakes in Germany and other European countries have a pH of less than 5, an acidity level considered lethal for many species of fish. Acidic water can carry dissolved aluminum to lakes and streams which clogs the gills of fish and deprives them of oxygen.

Effects on soil: It causes leaching of essential minerals of soil

Effects  on terrestrial ecosystems: It causes extensive damage to forest trees and all vegetation.

Effects on buildings, stone structures (stone leprosy) etc: Acid rain corrodes metals, marble, painted surfaces, slate, stone etc. This phenomenon is called Stone leprosy. In Greece and Italy, valuable stone statues have been partially dissolved and Taj Mahal in India is affected by the acid rain.

. Acid rain has the following reaction with the marble (calcium carbonate):

                                 CaCO3 +  H2SO4 -> CaSO4  + H2O + CO2  

Acid rain damages plants  direct effect on foliage and growing point; necrosis, dieback, chlorosis, defoliation. It causes reduced rates of photosynthesis and growth, increased sensitivity to drought and disease.

Effects on human health: Acidification of soil may leads to the aluminum toxicity of drinking water, which may cause kidney failure, bone softening, Alzheimer’s disease  etc.

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Causes and Effect of Climate Change

Climate: the weather conditions prevailing in an area in general or over a long period.

•A number of factors affect and alter the climate.

•It may be natural and anthropogenic(man made)

Image credit

Causes of climate change:

•The quantum of solar energy reaching the earth.

•Increasing concentration of green house gases in the atmosphere.

•Snow, ice and glaciers which reflect solar radiation back to the atmosphere.

•Ocean currents which play a significant role in heating the earth.

• Volcanic eruptions which can directly influence the  temperature and climate of the earth

Effects of climate change:

        1.Increasing heat stress

2.Abnormal changes in the pattern of rainfall which may result in drought.

3.Depletion of freshwater

4.Melting of polar ice caps and mountain glaciers

5.Rise in  sea level, submergence of coastal lands and islands.

6.Loss of natural habitats and biodiversity.

7. The climate changes which result in tsunamies, El Ninos, cyclones and storms have become increasingly higher.

Social issues and the environment :Climate change, Global warming and Acid rain, Green house effect, ozone layer depletion from Biology Exams 4 U

Pollution:

•  Undesirable change in physical, chemical and  biological characteristics of air, water and soil which may cause any harm to man and other living organisms of the environment is known as pollution.

• Various types of pollution occur on earth which includes water, air, soil, noise and radioactive pollution. These pollutants lead to global environmental changes like green house effect, global warming, acid rain, ozone layer depletion etc.

(El-Nino: It is warm water current in the pacific that periodically flows southwards along the coasts of Eduador. It causes a chin of climatic changes and often induces great storms. )

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Antigen Presenting Cells (APC)-Definition,Mechanism of action and Examples

Definition of APC: Any cell that can process and present antigenic peptides in association with class II MHC molecules and deliver a co-stimulatory signal necessary for T cell activation.

These cells possess class II MHC molecules on the surface.

APCs include macrophages (monocytes as blood macrophages and histiocytes as tissue macrophages), B cells and dendritic cells.

Mechanism of APC (Antigen Presenting Cells)

B cell as Antigen presenting cell

Step 1: B cell activation=Antigen binding to Naïve B cell receptor followed by Antigen degradation inside B cell

Step 2: B cell acts as antigen presenting cells (APCs). Degrades antigenic peptides are displayed on MHC Class II recetor.

-T cell receptor (TCR) of Th cell binds to MHC class II bound antigenic peptide

-TCR activates B cells by secreting chemokines such as interleukins.

Step 3: Clonal selection and Differentiation: That activated B cell  divide continuously forming clone of B cells with that specificity.

Late these B cells differentiate into Plasma cells and memory B cells.

Step 4: Plasma cells produce antibodies and are released into the blood stream that binds to the antigen and neutralize it. Thus preventing further infection

-Memory B cells produced are responsible for immunologic memory. (when the same antigen attacks the body for the second time, memory B cells recognizes it quickly and trigger an enhanced immune response, thus preventing further infection).

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B cells as Antigen Presenting Cells or APCs-Mechanism

Definition of APC: Any cell that can process and present antigenic peptides in association with class II MHC molecules and deliver a co-stimulatory signal necessary for T cell activation. This interaction enhances immune response.

B cell as Antigen presenting cell 

Step 1: B cell activation=Antigen binding to Naïve B cell receptor followed by Antigen degradation inside B cell

Step 2: B cell acts as antigen presenting cells (APCs). Degrades antigenic peptides are displayed on MHC Class II recetor.

-T cell receptor (TCR) of Th cell binds to MHC class II bound antigenic peptide

-TCR activates B cells by secreting chemokines such as interleukins

Step 3: Clonal selection and Differentiation: That activated B cell  divide continuously forming clone of B cells with that specificity

Late these B cells differentiate into Plasma cells and memory B cells
Watch this video for better concept clarity

Step 4: Plasma cells produce antibodies and are released into the blood stream that binds to the antigen and neutralize it. Thus preventing further infection

-Memory B cells produced are responsible for immunologic memory. (when the same antigen attacks the body for the second time, memory B cells recognizes it quickly and trigger an enhanced immune response, thus preventing further infection).

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CSIR UGC NET JRF Life Sciences Notification 2018 June

CSIR will hold   the Joint CSIR-UGC Test on 17th June, 2017 for determining the eligibility of the Indian National  candidates for the award of Junior Research Fellowships (JRF) and for determining eligibility for appointment of  Lecturers (NET) in certain subject areas falling under the faculty of Science & Technology. The award of Junior Research  Fellowship (JRF) to the successful eligible candidates will depend on their finding admission/placement in a university/  national laboratory/ institution of higher learning and research, as applicable.

Apply Online

Exam Date: CSIR-UGC JRF NET :17th June, 2018.

# Official Notification  # challan # Books to Refer # Must learn topics

Age Limit & Relaxation:

• For Junior Research Fellowships  (JRF):Maximum 28 years as on 01-07-2017 (upper age limit may be relaxed up to 5 years in case of candidates belonging to SC/ST/OBC, Physically handicapped/Visually handicapped and female applicants).
• For LS (NET): No upper age limit.

Important Dates:

 Exam Opportunities after Post Graduation in Life Sciences

Educational Qualification:

• BS-4 years program/BE/BTech/BPharma/MBBS/Integrated BS-MS/MSc or equivalent degree with at least 55% marks for general and OBC (50% for SC/ST candidates, physically and Visually Handicapped candidates).
• Candidates enrolled for M.Sc or having completed 10+2+3 years of the above qualifying examination are also eligible to apply in the above subject under the Result Awaited (RA) category on the condition that they complete the qualifying degree with requisite percentage of marks within the validity period of two years to
  avail the fellowship from the effective date of award.
  Such candidates will have to submit the attestation format (Given at the reverse of the application form) duly certified by the Head of the Department/Institute from where the candidate is appearing or has appeared.
• BSc (Hons) or equivalent degree holders or students enrolled in Integrated MS-PhD program with at least 55% marks for general and OBC candidates; 50% marks for SC/ST candidates, physically and visually handicapped candidates are also eligible to apply.Candidates with bachelor’s degree, whether Science, engineering or any other discipline, will be eligible for fellowship only after getting registered/enrolled for PhD/Integrated PhD program within the validity period of two years.
• The eligibility for lectureship of NET qualified candidates will be subject to fulfilling the criteria laid down by UGC. PhD degree holders who have passed Master’s degree prior to 19th September 1991, with at least 50% marks are eligible to apply for Lectureship only.

Tips for CSIR UGC NET JRF exam

Syllabus

The question paper shall be divided into three parts, (A, B & C) as per syllabus & Scheme of Exam.

Part 'A' shall be common to all subjects including Engineering Sciences. This part shall contain questions pertaining to General Aptitude with emphasis on logical reasoning, graphical analysis, analytical and numerical ability, quantitative comparison, series formation, puzzles etc.

Part 'B' shall contain subject-related conventional Multiple Choice questions (MCQs), generally covering the topics given in the syllabus.

Part 'C' shall contain higher value questions that may test the candidate's knowledge of scientific concepts and/or application of the scientific concepts. The questions shall be of analytical nature where a candidate is expected to apply the scientific knowledge to arrive at the solution to the given scientific problem.

Negative marking for wrong answers, wherever required, shall be applicable as per subject wise scheme of Exam.

Books to Refer - CSIR UGC NET JRF exam

Examination fee:

How to prepare for CSIR UGC NET JRF Life Science Exam ?

Examination Centres: Bangalore, Bhavnagar, Bhopal, Bhubaneshwar, Chandigarh, Chennai, Cochin, Delhi, Guntur, Guwahati, Hyderabad, Imphal, Jammu, Jamshedpur, Karaikudi, Kolkata, Lucknow, Nagpur, Pilani, Pune, Raipur, Roorkee, Srinagar, Thiruvananthapuram, Udaipur and Varanasi.

CSIR UGC NET JRF Life Science Exam Previous Question Papers

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How do some cells become brain cells and others become skin cells, when the DNA in all cells is exactly the same?

How is cell specialization achieved?

The genetic makeup or DNA of all cells in an adult body is the same. How do some cells become brain cells and others become skin cells, when the DNA in all cells is exactly the same? How this happens?

The reason is differential expression of genes in cells.
Watch this video for more or see the post

            During the process of cell specialization, in each cell types; only specific genes are “turned on” and transcribed to RNA and translated to proteins. Rest of the genes remain inactive. That is, genes active in the neurons may not be active in skin cells.

For instance, genes for actin and myosin filaments are present in all animal cells, but these genes are primarily active in muscle cells. Cell specialization involves the preferential or selective activation of specific genes leading to the synthesis of some specific proteins like antibodies in plasma cells or Hb in erythrocytes.

House keeping genes vs Luxury genes

Remember, there are some genes that are expressed in all types of cells or genes essential for survival  of all cell types like genes making membranes or genes of major metabolic pathways like glycolysis.. These genes are called ‘house keeping’ genes.

But genes that are expressed in only certain types of cells or expressed differentially are called ‘luxury genes’ or smart genes’. Eg: IgG genes in plasma cells; opsin genes for vision (in eyes). This differential expression leads to cell specialization.

After fertilization, the first cell the zygote has nucleus of both the gametes where the cytoplasm is entirely provided by egg. Thus the zygote has only maternal effect genes contributed by egg cytoplasm only. This is conducive for the zygote development. On first division, zygotic gene are expressed that will trigger further development and differentiation.

In short: Zygote-> determination ->differentiation (to specialized cells and tissues).

Characteristics of Cell Differentiation:

• Cell differentiation is a stable phenomenon. Take the example of neurons, once differentiated persist throughout lifetime.
• Differentiation is induced by specific stimuli.
• But once differentiated or established, these cells are stimulus independent.
• Differentiation is accomplished by morphological difference of that fated or determined cell. Look at the figure different shapes or morphology of various types of cells in our body.
• Ultimately differentiation is controlled by genetic factors.

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