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Revision test - 1 (Chemical reactions, life processes, Electricity)

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16^th June, 2013, STRT -1, Full marks – 45, Time – 1 ½ hr

1.     Write balanced equation for the following chemical reactions (a)Hydrogen + Chlorine à Hydrogen chloride (b)Sodium + Water à Sodium hydroxide + Hydrogen (c)Sodium hydroxide solution (in water) reacts hydrochloric acid solution (in water) to produce sodium chloride solution and water.

2.     Differentiate between respiration and photosynthesis, write their equation and balance them, what happens to glucose in aerobic, anaerobic respiration.[5]

3.     In an experiment with iron nail dipped in copper sulphate solution, why does the iron nail become brownish in colour and blue colour of copper sulphate solution disappear. [3]

4.     Give a balanced example each of (a) double displacement (b) exothermic (c) endothermic (d)double displacement reaction[4

5.     What are the benefits of separation of oxygenated blood from deoxygenated blood in mammals and aves. With the help of a diagram show the course of flow of blood in human circulatory system. What are the components of transport system in human beings? [2+2+1]

6.     Describe the structure and functioning of nephrons. What are the necessary conditions for autotrophic nutrition and what are its byproducts. [3+2]

7.     Differentiate between artery and veins.         [5]

8.     How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω? (b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω?[5]

9.     An electric lamp, whose resistance is 20 Ω, and a conductor of 4 Ω resistance are connected to a 6 V battery in series.  Calculate (a) the total resistance of the circuit, (b) the current through the circuit, and (c) the potential difference across the electric lamp and conductor. [5]

10.                        What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series? [3]

11.                        Derive an equation for a system of resistors in series. [2]

Sex linked inheritance in humans

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Mendel’s laws are not applicable on those genes which are exclusively located either on X or Y gene chromosome. It has been observed that the genes only in X chromosomes are represented twice in females and once in male (because male have only one X-chromosomes). The sex linked inheritance can be classified into three types in XY type organisms.

1.      X-linked: here the linked genes are exclusively located on the non-homologous sections of X-chromosome, and do not have any corresponding allele on the Y-chromosome. These are called commonly as X-linked genes.

2.      Y-linked: the Y-Linked genes are localized on the non-homologous sections of Y-chromosome, and have no corresponding allele on the X-chromosome. The Y-linked genes are commonly known as Holandric genes.

3.      XY-linked: the XY linked genes are located on the homologous sections of X and Y chromosomes.

In human beings more than 150 confirmed or highly probable X-linked traits are known; most of these are recessives. Certain well known example of X-linked recessive genes in humares are those for red-green colour blindness and haemophilia.

Inheritance of X-linked genes:

1.      these genes whether dominant or recessive show there effects in male phenotypes.

2.      It shows criss-cross inheritance pattern (X-linked recessive genes are transmitted from P1 male to F1 female and from F1 female to F2 male)

3.      Usually none of the offspring of the affected male will be affected, but all of his daughters will carry the gene in masked heterozygous conditions.

Example: colour blindness, haemophilia.

Inheritance of Y-linked genes: the genes linked to Y-chromosomes are also called holandric genes. They are always transmitted from father to son.

Ex: the gene responsible for icthyosis hystrix gravis hypertrichosis (excessive development of pinnae hair) are transmitted from father to son only, because only the male posses the Y-Chromosomes.

INHERITENCE OF X-Y-LINKED GENES: the genes which occur in homologous sections of X and Y chromosomes have inheritance like an autosomal genes. .

PLEIOTROPISM

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• Pleiotropy refers to the situation in which a single gene influences more than one phenotypic trait.
• Most genes, if not all have their multiple effects and are called pleiotropic genes.
• The phenomenon of multiple effect (multiple phenotypic expressions of a single gene is called pleiotropism)
• Even though a structural gene may have many end effects, it usually has only one primary function, of producing one polypeptide. This polypeptide may give rise to different expressions at the phenotypic level.

Examples of pleiotropism

1.     In Drosophila the recessive gene for vestigial wings causes vestigial wings in homozygous condition and also effects other traits like:

Ø The tiny wing like balancer behind the wing

Ø Certain bristles

Ø The structure of reproductive organs

Ø Egg production is lowered

Ø Longevity is reduced

2.     In Drosophila the gene for white eyes may affect shape of sperm storage organs in females and also some other structures

3.     In human beings the gene for disease phenylketonuria has pleiotropic effect and produce various abnormal phenotypic traits. The affected individuals secrete large amount of an acid phynylalanine in their urine, cerebrospinal fluid and blood. They are short statured, mentally deficient with widely spaced incisors, pigmented patches on skin with excessive sweating and with non-pigmented hairs and eyes.

·      Pleiotropic genes must be more common because indirectly every gene may be involved in the expression of more than one trait. Thus most genes are pleiotropic IN NATURE

Hershey and chase experiment to prove that DNA is genetic material.

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Hershey (Alfred Hershey) and Chase (Martha Chase) performed a series of experiments in 1953 to prove that the DNA is the genetic material. The DNA was known to biologists since 1869, but still some scientists assumed that protein has some role in the inheritance. The key concept of their experiments was that Phage infection proved that DNA is the genetic material of viruses. When the DNA and protein components of bacteriophages were labelled with different radioactive isotopes, only the DNA is transmitted to the progeny phages produced by infecting bacteria.

First they labelled the bacteriophages with ³⁵S, since Sulphur is a component of protein coat of bacteriophage, the ³⁵S is incorporated to the coat of the bacteriophage. This bacteriophage was allowed to infect the bacteria. The bacteriophages infect the bacteria in a manner that their protein coat is left behind out side the bacterial cell and only the DNA of the bacteriophage enters the bacteria and incorporates with the genome of the bacteria. After the infection of the bacteriophage centrifugation is done to separate the capsids and the bacterial cells. It was found that ³⁵S was only found in the protein coat and not in the bacterial cells.

Secondly they labelled the bacteriophages with ³²P. Since Phosphorus is the essential component of the DNA. The ³²P was incorporated in the DNA of the bacteriophages. These labelled bacteriophages were allowed to infect the bacteria. The bacteriophages left their protein coat outside the bacterial cell and they injected their DNA into the bacterial cell which incorporated with the genome of bacteria. Then centrifugation was done to separate the protein coat and the bacteria. On testing ³²P was found in the bacterial cell. And not in the protein coat.

This experiment prominently proved that the DNA is the only genetic material, and the protein has nothing to do with the inheritance and genetic information.

Griffith and Avery’s experiment for the evidence that DNA is the genetic material.

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Genome consists of long sequence of nucleic acids that stores the information needed to construct the organism. The genome is the only thing that defines the hereditary nature of an organism.

The genome can be functionally divided in to genes. Each genes are nucleotide sequences that represent a particular protein. That is the genes code for the protein (Rather the genes code for an RNA which in turn may code for a specific protein.)

Experimental Evidence for DNA’s Role as Genetic material:

Griffith's experiment to show that DNA is genetic material.

The first direct evidence that the DNA transmits genetic information comes from the experiments of Griffith. In the year 1928 Griffith performed a fantastic experiment with mouse and bacteria (Streptococcus pneumoniae). The Streptococcus pneumoniae has two strains. One has smooth appearance due to presence of capsule, and are virulent to cause pneumonia, as the capsule allows the bacteria to escape destruction by the host. The other strain appears rough due to absence of the capsule, and is avirulent, because the host can easily destroy it. Avery first infected a mouse with the rough strain of bacteria, the mouse survived. Then he infected other mouse with the smooth strain, the second mouse died due to pneumonia. To the third mouse he infected it with heat killed smooth strain. The mouse survived. To the fourth mouse he infected with the mixture of heat killed smooth strain and live rough strain bacteria. Here the mouse died. Thus they concluded that the rough strain bacteria somehow transformed[1] itself to smooth strain and killed the mouse. These transformed bacteria were recovered from the dead mouse and then cultured. The result was culture of smooth strain, proofing that the transformation was permanent.

Drawbacks:

·         Griffith cannot explain the role of mouse in transformation of rough strain to smooth strain.

·         He also cannot make it clear, that which part of the smooth strain bacteria(DNA, RNA, protein etc) transformed the rough strain bacteria.

Experiment of Avery:

In 1944 Avery, C. Macleod and M. Mc Carty separated the extract of smooth, virulent bacteria into proteins, DNA, carbohydrate fractions. The incubated the rough strain of bacteria with all of these fractions. And they got the results. The only the bacteria incubated in the DNA fragment of the smooth strain bacteria, transformed to smooth strain. In other fractions there was no transformation. This experiment proved that it is the DNA which acts as genetic material.

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[1] It is a permanent, inheritable change produced in one strain of bacteria by a substance (DNA) isolated from another strain of the same kind of bacteria