AIPMT 2009 Chemistry Question Paper with Answer and Solution

(A) The pinna (external ear) is supported by yellow elastic cartilage. This type of cartilage is also found in the tip of the nose,epiglottis,the external auditory canal,the eustachian tube,and certain laryngeal components. The presence of abundant elastin fibres in the matrix gives this cartilage its characteristic yellow colour and high degree of elasticity.

(C) Cell junctions are specialized structures that provide both structural and functional links between individual cells.
In epithelial tissues,these junctions are highly developed to maintain the integrity and functionality of the tissue layer.
$1$. Tight junctions help to stop substances from leaking across a tissue.
$2$. Adhering junctions perform cementing to keep neighboring cells together.
$3$. Gap junctions facilitate the cells to communicate with each other by connecting the cytoplasm of adjoining cells,for rapid transfer of ions,small molecules,and sometimes big molecules.
Therefore,these junctions are characteristic features of epithelial tissue.

(D) In the zygotene stage of prophase-$I$,homologous chromosomes pair up. This process is known as synapsis. One chromosome of the pair is derived from the male parent and the other from the female parent.

(C) In plants,manganese is absorbed in the form of manganous ions $(Mn^{2+})$. It activates many enzymes involved in photosynthesis,respiration,and nitrogen metabolism.
The most well-defined function of manganese is in the splitting of water to liberate oxygen during photosynthesis,which is known as the photolysis of water.

(D) Vital capacity $(VC)$ is defined as the maximum volume of air a person can breathe in after a forced expiration. This includes inspiratory reserve volume $(IRV)$,tidal volume $(TV)$,and expiratory reserve volume $(ERV)$. Mathematically,it is equal to the total lung capacity $(TLC)$ minus the residual volume $(RV)$. Therefore,$VC = TLC - RV$.

(C) Lymph is essentially blood plasma from which most of the proteins and all $RBCs$ have been removed.
It is a clear,colourless fluid that acts as a mobile connective tissue.
Lymph is formed by the filtration of blood through capillary walls into the interstitial spaces.
Microscopic examination reveals that lymph contains a large number of leucocytes,primarily lymphocytes,but it lacks $RBCs$ and blood platelets.

(B) In a hinge joint,the convex surface of one bone fits into the concave surface of another bone,allowing movement in only one plane.
Examples of hinge joints include the knee joint,elbow joint,and interphalangeal joints.

(C) Alzheimer's disease in humans is associated with the deficiency of the neurotransmitter acetylcholine.
Alzheimer's disease is an irreversible,progressive neurodegenerative disorder.
In this condition,brain cells (neurons) deteriorate,which leads to a significant decline in cognitive functions such as memory,judgment,reasoning,movement,coordination,and pattern recognition.
The loss of acetylcholine-producing neurons is a hallmark of the disease,which impairs communication between nerve cells.

(C) The signals for parturition originate from the fully developed foetus and the placenta,which induce mild uterine contractions known as the foetal ejection reflex.
This reflex triggers the release of oxytocin from the maternal pituitary gland,which further stimulates stronger uterine contractions leading to childbirth.

(D) Karl Landsteiner classified human blood into four groups based on the presence or absence of specific antigens on the surface of $RBCs$.
In blood group $A$,antigen $A$ is present.
In blood group $B$,antigen $B$ is present.
In blood group $AB$,both antigens $A$ and $B$ are present.
In blood group $O$,neither antigen $A$ nor antigen $B$ is present on the surface of $RBCs$. The term '$O$' signifies the absence of these antigens,which is why it is not called '$C$'.
Therefore,individuals with blood group $O$ are considered universal donors.

(D) The incorrect statement is that baldness is a sex-limited trait.
$1$. Baldness is a sex-influenced trait,not a sex-limited trait. Sex-influenced traits are autosomal traits that are expressed differently in males and females due to hormonal differences.
$2$. Linkage is indeed an exception to the principle of independent assortment,as linked genes tend to be inherited together.
$3$. Galactosemia is an inborn error of metabolism caused by the deficiency of an enzyme required to break down galactose.
$4$. Small population size leads to random genetic drift,which is a change in allele frequency due to chance events.

(B) In a pond ecosystem,fishes can occupy more than one trophic level. For example,a small fish may feed on zooplankton (primary consumer,trophic level $II$) and also on phytoplankton (primary producer,trophic level $I$),or a larger fish may feed on smaller fish (secondary consumer,trophic level $III$) and also on zooplankton (primary consumer,trophic level $II$). Thus,they function at multiple trophic levels depending on their diet.

(B) The various stages in a hydrosere (succession in water) occur in a specific order as the environment transitions from aquatic to terrestrial.
The sequence is as follows:
$(i)$ Phytoplankton stage: Includes organisms like $Volvox$,diatoms,and blue-green algae.
$(ii)$ Rooted submerged stage: Includes plants like $Hydrilla$ and $Vallisneria$.
$(iii)$ Floating stage: Includes free-floating plants like $Pistia$,$Lemna$,and $Azolla$.
$(iv)$ Reed-swamp stage: Includes emergent plants like $Scirpus$ and $Typha$.
$(v)$ Sedge-meadow stage: Includes grasses and sedges.
$(vi)$ Woodland stage: Includes shrubs and small trees like $Lantana$.
$(vii)$ Forest stage: The climax community,which includes trees like $Quercus$ $(Oak)$.
Therefore,the correct sequence is $Volvox \rightarrow Hydrilla \rightarrow Pistia \rightarrow Scirpus \rightarrow Lantana \rightarrow Oak$.

(B) India has a high degree of biodiversity. Among the options provided, $Mango$ $(Mangifera \text{ } indica)$ exhibits the highest genetic diversity in India, with more than $1,000$ varieties of mangoes found across the country.

(B) The $Montreal$ $Protocol$ on substances that deplete the ozone layer is a landmark international agreement designed to protect the stratospheric ozone layer.
The treaty was originally signed in $1987$ (effective in $1989$) and substantially amended in $1990$ and $1992$.
The $Montreal$ $Protocol$ stipulates that the production and consumption of compounds that deplete ozone in the stratosphere—such as chlorofluorocarbons $(CFCs)$,halons,carbon tetrachloride,and methyl chloroform—are to be phased out by $2000$ ($2005$ for methyl chloroform).