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Zoology - Paper II
For Class XII (Science Group)
Model papers 2020 -2021
Time: 01 hour (14 marks)
SECTION B
NOTE: Attempt any FOUR questions from Reasoning questions and THREE from Non-reasoning questions. All questions carry equal marks.(a) Reasoning Questions:
i. Why hypothalamus is called thermostat of the body.
Ans: Hypothalamus is called thermostat of our body as it is act at 37 °C. Temperature above or below this is detected by thermoreceptors and message is conveyed to the hypothalamus which initiates body response accordingly to decrease or increase body temperature.
OR
i. Why do freshwater fishes excrete dilute urine and marine fishes excrete concentrated urine?
Ans: Fresh water fish retain urea in their blood and urine, in this way they have a hypertonic body fluid than the surrounding water. They do not loose water from their body surface. Thus they remove excess water by passing large quantities of very dilute urine. During the excretion process, they lose some essential ions as well, this is overcome by actively absorbing selected ions from outside, through gills.
On the other hand Marine fishes have hypotonic body fluid than the surrounding water, so they loose water from body surface, to compensate water loss they produce concentrated urine, Thus in order to conserve water they constantly drink water and remove remove excess salts from their gills.
ii. Why moderate form of fever is good for health.
Ans: Fever or pyrexia is defined as body temperature above normal set point, i.e. 98.6 °F or 37 °C. It could be a result of bacterial or viral infection or non viral infection or non infection. The fever in case of infection is a consequence of the activity of macropahge, which release to raise the body temperature to inhibit the growth of pathogenic organism. In this way moderate fevers is good for health because it decrease morbidity and increase survival rate.
OR
ii. Why the cardiac muscles are striated and involuntary in nature.
Ans: Cardiac muscles form the muscular walls of heart only. These muscles contractions pump blood throughout the body and maintain blood pressure. These muscles show unique combination of properties. Like skeletal muscles cardiac muscle is striated so that heart wall can withstand high pressure without any danger of being fatigue or damaged. However the rhythmic contraction and relaxation of cardiac muscles are not consciously controlled by and so they are involuntary in nature like smooth muscles.
iii. What causes abnormal muscle contraction in sportsman?
Ans: A sudden involuntary muscles contraction occur as a cramps or tetany in sportsman, which is type of an abnormal muscle contraction and is commonly called a muscles pull. It occurs due to dehydration, electrolyte imbalance or a low blood sugar level or low calcium level in the blood. Particularly, these abnormal muscles contraction is caused after a heavy exercise, which produced lactic acid due to lack of oxygen.
OR
iii. How hydrostatic skeleton facilitates locomotion in soft bodied animals?
Ans: In soft bodied animals (like earthworm) hydrostatic skeleton facilitates locomotion. This movement is brought about by the contraction of two sets of muscles and the body fluid. Contraction of longitudinal muscles shortens the body and contraction of circular muscles lengthens (elongation) the body. As a result of interaction of muscles contractions and compressed body fluid the soft bodied animals move.
iv. What are the causes of eutrophication?
Ans: Eutrophication is caused due to the formation of algal growth in lakes. Excess phosphorus from sources like fertilizers, sewage or detergents leads to harmful effects and promote the algal growth called algal bloom, which deplete the oxygen and causes death of aquatic animals.
OR
iv. Why nervous coordination is quick as compared to the chemical coordination?
Ans: Nervous co-ordination occurs by neurons which release its neurotransmitters to specific cells and are inter connected and they response to new stimulus within second. While chemical-coordination occurs by hormones, which has to be first released, it moves throughout the bloodstream and then arrives to its target cell to generates its action. This is reason that nervous coordination is quick as compared to the chemical coordination.
v. Why parthenogenesis is considered as semi-sexual in nature.
Ans: This is a type of reproduction which is neither strictly asexual nor sexual. Although like sexual reproduction gametes are produced, but like asexual reproduction it requires one parents. That's why it is considered as semi-sexual in nature. Parthenogenesis is common in some insects like honey-bees, ants and wasps.
OR
v. Why identical twins are similar but fraternal twins are not?
Ans: Twins are the two children which develop and are born together. Twins are of two types i,e. Identical twins and fraternal twins. Identical twins are exactly alike and of the same sex because both of them develop from just one zygote (monozygotic) which somehow divides mitotically into two separate blastomeres, each of which develops into a new individual. As both of these develop from one zygote they share the same genes, and thus are of the same sex and exactly identical in features. Being the product of mitosis, identical twins are often said to have developed asexually. Fraternal twins on the other hand are the children which develop from two independent eggs. As each egg is fertilized by a separate sperm they are dizygotic and thus the genotype of each zygote is different hence they are not identical and are said to be the product of sexual reproduction.
vi. How hermaphroditic condition is advantageous for the parasitic mode of life?
Ans: Among sexually reproducing parasites, hermaphroditism (bisexual or monoecious) is a common strategy, in which individual parasites possess both male and female reproductive organs. This is the case among parasites like liver fluke and tapeworms. Hermaphrodites have the great advantage for the parasitic mode of life, They are capable of reproduction by self-fertilization, even if they cannot find another member of their species in a host.
OR
vi. How DNA fingerprinting helps in solving criminal cases?
Ans: DNA fingerprint is performed to identify criminals and to resolve parental disputes. This technique is used to compare DNA of individuals with the sample of DNA fingerprint to be suspected on the basis of RFLPs (restriction fragments length polymorphism). Since RFLPs of each human are unique analogous to the finger prints, which are used as marks of identity. If it is matched, the criminal is identified.
(b) Non-Reasoning Questions:
SOURCE: Board Of Intermediate Education Karachi
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