NEET 2015 Chemistry Question Paper with Answer and Solution

(B) The cardiac cycle produces two primary heart sounds,often described as 'lub' and 'dub'.
$1$. The first heart sound ('lub') is associated with the closure of the atrioventricular $(AV)$ valves (tricuspid and bicuspid valves) at the beginning of ventricular systole.
$2$. The second heart sound ('dub') is associated with the closure of the semilunar valves (aortic and pulmonary valves) at the end of ventricular systole,preventing the backflow of blood from the arteries into the ventricles.
Therefore,the second sound is heard when the semilunar valves close.

(C) The correct composition of blood is: Blood $=$ Plasma $+$ Formed Elements (RBCs,WBCs,and Platelets).
Serum is defined as plasma from which clotting factors like fibrinogen have been removed (Serum $=$ Plasma $-$ Clotting Factors).
Lymph is essentially filtered blood plasma that lacks RBCs and large plasma proteins (Lymph $=$ Plasma $-$ RBCs $-$ Large Proteins).
Therefore,the statement 'Blood $=$ Plasma $+$ $RBC$ $+$ $WBC$ $+$ Platelets' is the most accurate representation of blood composition among the choices provided.

(C) Human urine is typically acidic (pH approximately $6.0$) because the renal tubules,particularly the proximal convoluted tubule $(PCT)$ and the distal convoluted tubule $(DCT)$,actively secrete hydrogen ions $(H^+)$ into the tubular filtrate. This process helps in maintaining the acid-base balance of the body fluids. By secreting $H^+$ ions,the kidneys help regulate the blood pH,and as a result,the urine becomes acidic.

(C) The glenoid cavity is a shallow,pyriform articular surface located on the lateral angle of the scapula.
It articulates with the head of the humerus to form the glenohumeral joint,which is a ball-and-socket joint.
This joint allows for a wide range of movement of the arm.
Therefore,the correct option is $C$.

(D) The pituitary gland is often referred to as the master gland of the body.
However,the posterior pituitary (neurohypophysis) does not synthesize its own hormones.
Instead,it stores and releases two hormones,$Oxytocin$ and $Antidiuretic$ $hormone$ ($ADH$ or $Vasopressin$),which are synthesized in the hypothalamus.
Therefore,$Antidiuretic$ $hormone$ is the correct answer.

(C) The correct answer is $C$.
In the kingdom $Monera$,the organisms are prokaryotic.
Prokaryotic cells lack a well-defined nucleus and membrane-bound organelles.
Therefore,the nuclear membrane is absent in $Monera$.
Option $A$ is correct because $Protista$ includes diverse organisms like algae (photosynthetic) and protozoans (heterotrophic).
Option $B$ is correct because mushrooms like $Agaricus$ are edible.
Option $D$ is correct because animal cells lack a cell wall.

(D) Chrysophytes,which include diatoms and golden algae (desmids),are characterized by cell walls that form two thin overlapping shells that fit together like a soap box.
These walls are embedded with silica,making them indestructible and leading to the formation of 'diatomaceous earth' over billions of years.

(B) $1$. $Neurospora$ is a genus of Ascomycetes fungi widely used as a model organism in biochemical and genetic research.
$2$. Morels and truffles are edible fungi belonging to the class Ascomycetes and are considered delicacies,not poisonous mushrooms.
$3$. Yeast (e.g.,$Saccharomyces$ $cerevisiae$) is a unicellular fungus used extensively in the fermentation process to produce ethanol and $CO_2$.
$4$. $Penicillium$ is a multicellular fungus known for producing the antibiotic penicillin.
Therefore,the statement that morels and truffles are poisonous is incorrect.

(D) true nucleus is a characteristic feature of eukaryotic cells,where the genetic material is enclosed within a nuclear membrane.
$Mucor$ is a fungus,$Vaucheria$ is an alga,and $Volvox$ is an alga; all of these are eukaryotic organisms.
$Anabaena$ is a genus of filamentous cyanobacteria (blue-green algae),which are prokaryotic organisms.
Prokaryotic cells lack a membrane-bound nucleus and other membrane-bound organelles.
Therefore,a true nucleus is absent in $Anabaena$.

(D) The fungi commonly known as imperfect fungi are the $Deuteromycetes$ because only their asexual or vegetative phases are known.
When the sexual forms of these fungi were discovered,they were moved into classes they rightly belong to (either $Ascomycetes$ or $Basidiomycetes$).
$Deuteromycetes$ reproduce only by asexual spores known as conidia.
The mycelium is septate and branched.
Some members are saprophytes or parasites,while a large number of them are decomposers of litter and help in mineral cycling.

(A) The correct answer is $A$.
$1$. $Mucor$ is a member of the class Zygomycetes (Fungi). Fungi in this group reproduce by non-motile spores called sporangiospores or aplanospores. They do not produce flagellated zoospores.
$2$. Haploid endosperm is a characteristic feature of Gymnosperms,formed before fertilization.
$3$. Brown algae (Phaeophyceae) contain chlorophyll $a$,$c$,and the pigment fucoxanthin,which gives them their characteristic brown color.
$4$. Archegonia (female sex organs) are present in Bryophyta,Pteridophyta,and Gymnosperms.

(B) In $Ectocarpus$,which belongs to the class $Phaeophyceae$ (brown algae),the male gametes are motile and possess two laterally attached flagella.
$Anabaena$ is a cyanobacterium (blue-green algae) that reproduces through akinetes or heterocysts,and its gametes are not flagellated.
$Spirogyra$ (green algae) exhibits conjugation,where the gametes are non-flagellated (isogamous or physiologically anisogamous).
$Polysiphonia$ (red algae) is characterized by the complete absence of flagellated stages in its life cycle.

(C) The statement 'Mannitol is stored food in Rhodophyceae' is wrong.
In $Rhodophyceae$ (red algae),the stored food is Floridean starch,which is very similar to amylopectin and glycogen in structure.
Mannitol is the stored food material in $Phaeophyceae$ (brown algae).
$Agar-agar$ is indeed obtained from $Gelidium$ and $Gracilaria$.
$Chlorella$ and $Spirulina$ are unicellular algae rich in proteins and are used as food supplements by space travelers.
$Algin$ (from brown algae) and $carrageen$ (from red algae) are hydrocolloids produced by algae.

(B) In the plant kingdom,specifically among algae,the presence of flagellated male gametes is a characteristic feature of certain groups.
$1$. $Anabaena$ is a cyanobacterium (blue-green algae) that reproduces via akinetes or hormogonia and does not produce flagellated gametes.
$2$. $Ectocarpus$ is a brown alga (Phaeophyceae) that produces biflagellated zoospores and gametes.
$3$. $Spirogyra$ is a green alga (Chlorophyceae) that undergoes conjugation,where the gametes are non-flagellated (isogamous).
$4$. $Polysiphonia$ is a red alga (Rhodophyceae) which is unique because its life cycle completely lacks flagellated stages.
Therefore,$Ectocarpus$ is the correct answer.

(B) Let us evaluate each statement:
$(a)$ Lichens and mosses are indeed the pioneer species in primary succession on bare rocks. This statement is correct.
$(b)$ $Selaginella$ is a heterosporous pteridophyte,not homosporous. This statement is incorrect.
$(c)$ Coralloid roots in $Cycas$ are associated with nitrogen-fixing cyanobacteria ($Anabaena$ or $Nostoc$),not $VAM$ mycorrhizae. This statement is incorrect.
$(d)$ In bryophytes,the dominant phase is the haploid gametophyte,while in pteridophytes,the dominant phase is the diploid sporophyte. This statement is correct.
$(e)$ In gymnosperms,the male and female gametophytes do not have an independent free-living existence; they remain within the sporangia retained on the sporophytes. This statement is correct.
Therefore,statements $(a), (d),$ and $(e)$ are correct.

(B) Viviparous animals are those that give birth to live young ones. Most mammals are viviparous.
$A$. Elephant is a placental mammal and is viviparous.
$B$. Platypus $(Ornithorhynchus)$ is a monotreme,which is an egg-laying mammal (oviparous).
$C$. Whale is a marine mammal and is viviparous.
$D$. Flying fox $(Pteropus)$ is a bat,which is a mammal and is viviparous.
Therefore,the correct answer is $B$.

(A) The kidneys play a vital role in maintaining the $pH$ of the blood.
During the formation of urine,the tubular cells secrete $H^+$ ions,$K^+$ ions,and ammonia into the filtrate.
Specifically,the active secretion of $H^+$ ions into the renal filtrate helps in maintaining the ionic and acid-base balance of body fluids.
Because of this active secretion of hydrogen ions,human urine typically exhibits an acidic $pH$.

(D) The disease $Amoebiasis$ (also known as amoebic dysentery) is caused by the protozoan parasite $Entamoeba$ $\text{histolytica}$.
$Syphilis$ is a bacterial disease caused by $Treponema$ $\text{pallidum}$.
$Influenza$ is a viral disease caused by the influenza virus.
$Blastomycosis$ is a fungal infection caused by the fungus $Blastomyces$ $\text{dermatitidis}$.
Therefore, the correct option is $D$.

(A) The thermal stability of metal carbonates increases as the electropositive character of the metal increases.
The order of thermal stability is: $K_2CO_3 > Na_2CO_3 > CaCO_3 > MgCO_3$.
Since $MgCO_3$ has the lowest thermal stability,it decomposes most easily upon heating to release $CO_2$.
The reaction is: $MgCO_3 \xrightarrow{\Delta} MgO + CO_2$.

(B) In the complex ion $[Fe(CN)_6]^{3-}$:
$1$. The ligand is $CN^-$,which is named as 'cyanido' according to $IUPAC$ nomenclature.
$2$. There are $6$ such ligands,so the prefix is 'hexa-'.
$3$. The central metal atom is iron,and since the complex ion is anionic,it is named as 'ferrate'.
$4$. The oxidation state of $Fe$ is calculated as: $x + 6(-1) = -3$,which gives $x = +3$.
$5$. Combining these,the name is 'Hexacyanidoferrate $(III)$ ion'.

(C) In the complex $[M(en)_2(C_2O_4)]Cl$,let the oxidation state of $M$ be $x$.
Ethylenediamine $(en)$ is a neutral bidentate ligand,so its charge is $0$.
Oxalate $(C_2O_4^{2-})$ is an anionic bidentate ligand with a charge of $-2$.
Chloride $(Cl^-)$ is a counter ion with a charge of $-1$.
The total charge of the complex is $0$,so: $x + 2(0) + 1(-2) + 1(-1) = 0$.
$x - 2 - 1 = 0$,which gives $x = +3$.
The coordination number is calculated as: $2 \times (\text{denticity of } en) + 1 \times (\text{denticity of } C_2O_4^{2-}) = 2(2) + 1(2) = 4 + 2 = 6$.
The sum of the coordination number and the oxidation number is $6 + 3 = 9$.

(D) The complex $CoCl_3 \cdot 3NH_3$ is formulated as $[Co(NH_3)_3Cl_3]$.
In this complex,all three chloride ions are coordinated directly to the central metal atom and are not present as free ions in the ionization sphere.
Therefore,it does not produce a precipitate of $AgCl$ when treated with silver nitrate $(AgNO_3)$.

(D) The correct answer is $D$.
In $Rhodophyceae$ (red algae),the stored food material is Floridean starch,which is very similar to amylopectin and glycogen in structure.
Mannitol is a stored food material found in $Phaeophyceae$ (brown algae),not in $Rhodophyceae$.
$Algin$ is obtained from brown algae and $carrageen$ from red algae,making statement $A$ correct.
$Agar-agar$ is commercially produced from $Gelidium$ and $Gracilaria$,making statement $B$ correct.
$Chlorella$ and $Spirulina$ are unicellular algae rich in proteins and are used as food supplements by space travellers,making statement $C$ correct.