XII BIOLOGY PRACTICAL -4
- Que. 1-………………………………….4 Marks
- Make a temporary potato osmoscope to study osmosis. Sketch & label the diagram showing the change in the water level.
- OR
- Make a temporary slide to study plasmolysis. Sketch & label the diagram.
- OR
- Make a temporary mount of leaf epidermis to study the structure & distribution of stomata. Sketch & label the structure of stomatal apparatus.
- OR
- Find out the adulteration of the given milk sample, for water and starch.
- OR
- Perform the experiment to isolate DNA from given sample. Show your result to the examiner.
Q. 1 Perform the
experiment to isolate DNA from given sample. Show your result to the examiner.
- Procedure of DNA extraction………………….3 marks
- Observation………………1 Mark
- Total ...........................4 Marks
Aim:-To extract and
isolate DNA from a fruit sample.
Requirements: -Fleshy
berry fruits like banana, liquid soap, distilled water, salt, ice cold
isopropyl alcohol, measuring spoons, glass string rod, test tubes, glass
beakers, plastic cups, strainer or coffee filter, funnel, etc.
Principle: -All plants DNA extraction
protocols, comprise of the basic steps of disruption of cell wall, cell
membrane and nuclear membrane to release the DNA into solution followed by
precipitation of DNA and ensuring removal of the contaminating biomolecules.
Procedure:
- (1) Grind a small amount of fruit tissue in a mortar with little amount of distilled water.
- (2) Filter the solution in a beaker and add 1 teaspoon of liquid soap, 1/4 teaspoon of salt and 2 tablespoons of distilled water.
- (3) Stir the mixture with a glass rod until the soap and salt are dissolved.
- (4) After 10-15 minutes, filter the mixture through a strainer.
- (5) Take a test tube with chilled isopropyl alcohol and add the above filterate slowly with the help of a dropper.
- (6) Leave the test tube undisturbed for a few minutes.
- (7) The precipitated DNA is visible as fine white threads that can be removed by spooling using a glass rod.
Observations: DNA
precipitates as fine, white threads.
Q 1. Answer the following questions
- (1) Where is DNA found in the cell?
- Ans: In a typical
eukaryotic cell, DNA is found in the nucleus, mitochondria and chloroplasts.
- (2) Why salt is added to isolate DNA?
- Ans: During
isolation of DNA salt is added to neutralise the DNA charge and make the
molecule less hydrophilic i.e. less soluble in water.
- The salt also removes proteins that are bound to DNA.
- (3) What is the role of detergent in isolation of DNA?
- Ans: During the
extraction of DNA, the detergent removes the lipids of cell membrane and
nuclear membrane so as to release the DNA from the cell.
- (4) Why is chilled condition required during the expreiment?
- Ans: During DNA
isolation, chilling is necessary to increase the rate of precipitation of DNA.
- It also protects the DNA from the activity of cytoplasmic DNAse.
MULTIPLE CHOICE
QUESTIONS
(1) Which of the
function is not performed by DNA?
- (a) Synthesis of protein
- (b) Transmission of hereditary character
- (c) Synthesis of carbohydrates
- (d) Replication
(2) Purines of DNA/RNA
are ___________ .
- (a)Uracil and guanine
- (b) Uracil and cytosine
- (c) Adenine and guanine
- (d) Cytosine and Guanine
(3) Mark the correct
statement:
- (a) Histones are acidic proteins
- (b) Histones stimulate genetic activity
- (c) Histones are basic proteins
- (d) Nucleosomes are formed in E. coli, during packaging
(4) Which of the
following nucleotide sequences has 4 pyrimidine bases?
- (a) GCUAGACAA
- (b) UAGCGGUAA
- (c) GATCAATGC
- (d) GCAAGAUCAA
(5) A nucleoside is ________ .
- (a) A pentose sugar ribose or deoxyribose + a nitrogen base
- (b) A nucleotide + phosphate
- (c) A pentose sugar + a phosphate
- (d) A pentose sugar ribulose + a N2 base
Ans:(1) - (c), (2) - (c),
(3) - (c), (4) - (c), (5) - (a).