Biology Test - 8

Isogamy is a form of sexual reproduction that involves gametes of similar morphology. The gametes differ in their allele expression. As they look alike they cannot be classified as male and female gametes.

Hence option B is the correct answer.

Sewage is wastewater having food residue, animal and human excreta and waste material from industrial establishments. The domestic sewage in large cities is processed by aerobic and then anaerobic bacteria in the secondary treatment in sewage treatment plant (STP).

Treament of water:-

1. Primary treatment - The treatment utilizes settling tanks of upward, horizontal tanks. The water flow is induced to allow 15-45 min retention time during which 70% of suspended solids either settle to bottom or flow as scum on the top.

2. Secondary treatment - Digestion of organic matter dissolved in wastewater by aerobic/anaerobic processes.

3. Tertiary structure - The aim of this step is to remove suspended matter and to reduced BOD still further. The process is used are either physical or chemical.

4. Sludge treatment - Sludge is the settled solid component of water recovered during the treatment processes. It is treated mainly anaerobically to make it safe before disposal.

So correct answer is A.

Stabilizing selection in a population acts against extremes and favors intermediate phenotypes. This refers often to heterozygous advantage, in which natural selection favors the heterozygote because it possesses benefits that homozygotes lack. In other words, a heterozygous advantage describes the heterozygote genotype which has a higher relative fitness than the homozygote dominant or homozygote recessive genotype. For example, people with homozygous recessive for sickle cell anemia, meaning they have the disease, are also immune to malaria, a disease common in Africa, where sickle cell originated. Those heterozygous for the trait show no symptoms of sickle cell, but they are immune to malaria, greatly benefitting the heterozygote.

Hence option B is the correct answer.

A sustentacular cell is a type of cell that provides structural support. They are of two types. One type of cell is found in the Sertoli cell, in the testicle of mammals. It is present in the walls of the seminiferous tubules and supplies nutrients to sperm as the sertoli cell is nurse cell and another type of cells are found in the olfactory epithelium.

Hence option A is the correct answer.

Emasculation involves the removal of stamens from bisexual flowers of the female parents in order to avoid self-pollination in these flowers. It is done before the anthers are mature. If in a condition the female parent bears bisexual flowers, then elimination of anthers from the flower bud before the anther dehisces by means of a pair of forceps (a large instrument with broad blades) is necessary. And this step is known as emasculation.

Thus, the correct answer is option A.

In a solution with higher salt concentrations or with alcohol added, the DNA structure may change to an A form, which is right-handed helix, but every 2.3 nm makes a turn and there are 11 base pairs per turn. B-DNA is also right handed helix having 10 base pairs per turn.  Z DNA is left-handed. One turn spans 4.6 nm, comprising 12 base pairs.

Hence, option B is correct.

Acrosomes contain digestive enzymes like hyaluronidase and lysins, which helps in breaking down the outer membrane of the ovum called as the zona pellucida, allowing the haploid nucleus in the sperm cell to join the haploid nucleus in the ovum, thus enabling fertilization.

Hence, the correct answer is option C.

Bioremediation or phytoremediation is the cleaning of environment of toxic wastes with the help of microbes, plant and animal species. The organisms involved in bioremediation are of two types: hyperaccumulators and detoxifying species. Hyperaccumulators are used in bioprospecting and removal of minerals from wastes. The detoxifying agents metabolise the harmful chemicals through various biochemical reactions.

Hence option C is the correct answer.

A gynandromorph is an organism that contains both male and female characteristics. It may result from the loss of X chromosome.'

Hence option C is the correct answer.

The genetically identical plants obtained through tissues culture or micropropagation are called as somaclones because it is produced by the culture of somatic cells. Whereas monoclone is the group of cells produced by single cell asexually, the somatic hybrid is the genetic modification of plants by the fusion of somatic cells of two different species and cross hybrid is produced by the crossing between two true breeding organism.

Thus, the correct answer is option (A).

Cultigens are the plants which are cultivated for the commercial value. These are the plants which include crops, ornamentals, fruit trees, etc. These plants require human care and protection because they are cultivated by the breeding techniques and artificial selection method. There are many varieties of cultigens which are produced by genetic modification.

Thus, the correct answer is option A.

DNA polymorphism can be defined as a condition where more than one different normal nucleotide sequences can exist at the same locus in DNA. These two different alleles are the product of single base pair mutation, deletions, insertions etc. The polymorphic DNA contains a variable sequence which may lead to the expression of a various random gene which brings a remarkable change in the gene pool.

Thus, the correct answer is option A.

After ovulation, a structure corpus luteum is formed from the wall of the follicle that ovulated. This structure then begins to secrete estradiol and progesterone. Progesterone prevents ovulation and maintainance of corpus luteum.

Therefore, the correct answer is option A.

A set of genes will be in a complete linkage when they are present in close proximity on a chromosome and are inherited together during meiosis always. Complete linkage means no crossing over or recombination, i.e. the progeny phenotypes will be totally parental. i.e.,P = 100%, R = 0%

Hence option D is the correct answer.

a) Mutation theory was proposed by Hugo de Vries. He proposed that the new species arise not by the accumulation of minor and continuous variations by natural selection but by suddenly appearing saltatory variations for which he coined the term mutation. Mutation is any heritable change in the genetic makeup of an individual.

b) Lamarck explained the mechanism of evolution on the basis of use and disuse of organs. His theory is also known as the theory of inheritance of acquired characters according to which the characters which are acquired during the lifetime of an organism are transferred to the offsprings. This is known as Lamarckism.

c) Darwin proposed the theory of natural selection according to which the organisms with favourable variations would survive because they are fittest to face their surroundings while the organisms which are unfit for surrounding variations are destroyed naturally. This is known as Darwinism.

d) The theory of evolution as proposed by Darwin has been modified in the light of modern evidence from genetics, molecular biology, palantaeology, ecology and is known as Neo-Darwinism. It may be defined as the theory of organic evolution by the natural selection of inherited characteristics.

Hence option A is the correct answer.