AIIMS 1982 Biology Question Paper with Answer and Solution

(A) According to the Histogen theory proposed by Hanstein,the apical meristem of the root is divided into three distinct zones or histogens:
$1$. Dermatogen: The outermost layer which gives rise to the epidermis (or epiblema in roots).
$2$. Periblem: The middle layer which gives rise to the cortex.
$3$. Plerome: The central core which gives rise to the stele (vascular tissues like xylem and phloem,and pith).
Therefore,the correct answer is the epidermis.

(D) The Histogen theory,proposed by $Hanstein$,suggests that the root and shoot apices consist of three distinct meristematic zones or histogens: $Dermatogen$,$Periblem$,and $Plerome$.
$Dermatogen$ is the outermost layer of the apical meristem.
It is responsible for the formation of the epidermis and the epidermal tissue system in plants.
Therefore,the correct option is $D$.

(A) The cell wall is a non-living,rigid,and freely permeable layer that allows the movement of water and dissolved mineral salts without any selective barrier.
In the root,water and minerals from the soil enter the periplasmic space (the space between the cell wall and the plasma membrane) of the root hairs by passing through the cell wall.
Since the cell wall does not restrict the entry of these substances,it demonstrates its permeable nature.
In contrast,the movement from root hairs to cortical cells or further into the pericycle involves crossing the plasma membrane,which is a semipermeable (selectively permeable) barrier.
Therefore,the passage from soil into the periplasmic space of root hairs best illustrates the permeable nature of the cell wall.

(A) The $Plasmalemma$ (or plasma membrane) is a selectively permeable membrane that regulates the movement of specific solutes and solvents into and out of the cell.
While other membranes like mitochondrial and chloroplast membranes are also selectively permeable,the $Plasmalemma$ is the primary example of a biological membrane that exhibits selective permeability to maintain cellular homeostasis.

(A) Short-day plants $(SDP)$ require a continuous,uninterrupted dark period that exceeds a specific critical duration to initiate flowering.
If this dark period is interrupted by even a brief exposure to light,the physiological process required for flowering is inhibited.
Therefore,the plant will not flower at all under these conditions.

(C) At normal body temperature,the $Na^+-K^+$ pump (an active transport mechanism) maintains a high concentration of $K^+$ ions inside the $RBC$ compared to the plasma.
When blood is stored at a low temperature $(4^{\circ}C)$,the metabolic activity of the $RBC$ membrane is significantly reduced.
This low temperature inhibits the $Na^+-K^+$ pump,causing active transport to cease.
As a result,$K^+$ ions move down their concentration gradient from the $RBC$ into the plasma,eventually leading to ionic equilibrium.

(D) Perisperm is the persistent,nutritive tissue derived from the nucellus that remains in the seed after fertilization. In some seeds,such as black pepper and beet,the nucellus is not completely consumed by the developing embryo and persists as a thin layer known as perisperm.

(D) Let the dominant gene for haemolytic jaundice be $H$ and the normal recessive allele be $h$.
The man is heterozygous $(Hh)$ and the woman is homozygous normal $(hh)$.
The cross is: $Hh \times hh$.
The offspring genotypes are $50\% \ Hh$ and $50\% \ hh$.
Only the individuals with the genotype $Hh$ carry the dominant gene.
According to the problem, only $10\%$ of those carrying the gene develop the disease.
Probability of having the genotype $Hh = 1/2$.
Probability of developing the disease given the genotype $Hh = 10\% = 1/10$.
Total probability of a child developing the disease = $P(Hh) \times P(\text{disease}|Hh) = (1/2) \times (1/10) = 1/20$.

(C) Interferons $(IFNs)$ are a group of signaling proteins made and released by host cells in response to the presence of several viruses.
They act as a communication signal between cells to trigger the protective defenses of the immune system that eradicate pathogens.
Interferons are low molecular weight proteins that prevent further viral replication in neighboring healthy cells,thereby providing innate immunity against viral infections.

(D) Flax fibre is a type of bast fibre or phloem fibre obtained from the stem of the plant $Linum \text{ } usitatissimum$.
It is a member of the family $Linaceae$.
These fibres are known for their strength and are widely used in the textile industry for making linen fabric.
$Cannabis \text{ } sativa$ provides hemp fibre, $Crotolaria \text{ } juncea$ provides sunn hemp, and $Cocos \text{ } nucifera$ provides coir fibre.