Endosperm Questions in English

(D) In $Coconut$ $(Cocos \, nucifera)$, the endosperm is unique because it exhibits both nuclear and cellular types. The primary endosperm nucleus undergoes successive nuclear divisions to form free nuclei (liquid endosperm or coconut water), and later, cell wall formation occurs at the periphery, resulting in cellular endosperm (coconut meat). This combination is often referred to as double endosperm.

(A) In angiosperms,the endosperm is formed by the fusion of one male gamete $(n)$ with two polar nuclei $(n+n)$ or a secondary nucleus $(2n)$.
Given:
Female plant is diploid $(2n)$,so the polar nuclei are $n$ each. The secondary nucleus is $2n$.
Male plant is tetraploid $(4n)$,so the male gamete produced is $2n$.
Endosperm ploidy = (Male gamete) + (Secondary nucleus) = $2n + 2n = 4n$ (Tetraploidy).

(A) In a maize seed,which is a monocotyledonous seed,the seed coat is membranous and generally fused with the fruit wall. The endosperm is bulky and stores food. The embryo is small and situated in a groove at one end of the endosperm. Therefore,the endosperm occupies the largest region of the maize seed.

(A) The liquid endosperm of coconut is known as free-nuclear endosperm. During the development of the coconut,the primary endosperm nucleus undergoes successive nuclear divisions without cytokinesis,resulting in the formation of thousands of free nuclei suspended in the liquid. This is a classic example of free-nuclear endosperm.

(D) In angiosperms,the process of double fertilization involves the fusion of one male gamete with two polar nuclei to form the Primary Endosperm Nucleus $(PEN)$.
This fusion occurs within the central cell of the embryo sac.
Following this,the central cell containing the $PEN$ is referred to as the Primary Endosperm Cell $(PEC)$.
The $PEC$ undergoes repeated divisions to form the endosperm tissue,which provides nutrition to the developing embryo.
Therefore,the Primary Endosperm Cell $(PEC)$ is the first cell of the endosperm tissue.

(D) The coconut fruit is a drupe. In a coconut,the edible part is the endosperm. The liquid part is the free-nuclear endosperm,and the white kernel is the cellular endosperm.

(D) In flowering plants,seeds are formed from ovules after fertilization.
All seeds typically contain a seed coat,an embryonal axis,and one or two cotyledons.
However,the endosperm is not present in all seeds.
Seeds in which the endosperm is completely consumed by the developing embryo during seed maturation are called non-albuminous or ex-albuminous seeds (e.g.,pea,bean,groundnut).
Seeds that retain a part of the endosperm are called albuminous or endospermic seeds (e.g.,wheat,maize,castor).
Therefore,the endosperm is not a universal structure in all seeds.

(C) The given diagram represents a maize grain,which is a monocot seed. The structure labeled '$P$' is the endosperm.
In angiosperms,the endosperm is formed by the process of double fertilization,specifically by the fusion of one male gamete $(n)$ with two polar nuclei $(n + n)$.
This process is known as triple fusion,resulting in a primary endosperm nucleus $(PEN)$ which is triploid $(3n)$.
Therefore,the ploidy of the endosperm is $3n$.

(D) In the seeds of cereals such as maize,wheat,and rice,the endosperm is bulky and stores food.
The outer covering of the endosperm separates the embryo by a protein-rich layer known as the $Aleurone \text{ Layer}$.
This layer is specialized for the synthesis of enzymes during seed germination.

(C) The liquid endosperm of coconut, also known as coconut water, is a classic example of a free-nuclear endosperm.
During the development of the coconut endosperm, the primary endosperm nucleus undergoes repeated mitotic divisions (karyokinesis) without being followed by cell wall formation (cytokinesis).
This process results in the formation of a large number of free nuclei suspended in the central fluid, making the endosperm multinucleate.
Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

(D) The provided figure represents the structure of a castor seed.
In the castor seed,the part labelled as '$X$' represents the endosperm.
The endosperm is the nutritive tissue that stores food for the developing embryo.
Castor seeds are albuminous or endospermic seeds,meaning the endosperm is retained in the mature seed.

(C) The correct matching is as follows:
$1$. Cellular endosperm: In this type,the primary endosperm nucleus divides and is immediately followed by a cell wall formation. Example: $Petunia$.
$2$. Nuclear endosperm: In this type,the primary endosperm nucleus undergoes repeated free nuclear divisions without wall formation. Example: $Coconut$ (liquid endosperm).
$3$. Helobial endosperm: This is an intermediate type where the first division is followed by a wall,dividing the cell into a large micropylar and a small chalazal chamber. Example: $Asphodelus$.
Therefore,the correct match is $i-c, ii-a, iii-b$.

(A) In the $Nuclear$ type of endosperm development,the primary endosperm nucleus undergoes successive nuclear divisions without cytokinesis,giving rise to a large number of free nuclei.
Subsequently,a large central vacuole develops in the center of the embryo sac,which pushes the free nuclei towards the periphery of the cytoplasm.
This is the most common type of endosperm development,seen in plants like coconut (liquid endosperm).

(C) The endosperm of a seed is triploid $(3n)$,therefore $3n = 21$.
This implies that the haploid number $(n)$ is $21 / 3 = 7$.
The secondary nucleus (or definitive nucleus) is diploid $(2n)$,formed by the fusion of two polar nuclei.
Therefore,the chromosome number in the secondary nucleus is $2n = 2 \times 7 = 14$.

(C) The nucellus is a diploid $(2n)$ tissue in the ovule.
Given that the number of chromosomes in the nucellus is $2n = 24$,the haploid number $(n)$ is $24 / 2 = 12$.
The endosperm in angiosperms is formed by the fusion of one male gamete $(n)$ with two polar nuclei $(n + n)$,resulting in a triploid $(3n)$ structure.
Therefore,the number of chromosomes in the endosperm is $3n = 3 \times 12 = 36$.

(C) In coconut,the endosperm development is unique. The primary endosperm nucleus undergoes successive free nuclear divisions,which give rise to free nuclear endosperm (the coconut water). Subsequently,the endosperm becomes cellular towards the periphery,forming the white kernel (cellular endosperm). Therefore,coconut contains both free nuclear and cellular endosperm.

(A) The correct answer is $A-51$.
In flowering plants,the gametes are haploid $(n)$. Given that the chromosome number of gametes in apple is $n = 17$.
The Primary Endosperm Nucleus $(PEN)$ is formed by the fusion of two polar nuclei $(n + n)$ and one male gamete $(n)$,making it triploid $(3n)$.
Therefore,the chromosome number in the $PEN$ is $3 \times 17 = 51$.

(B) In angiosperms,the primary endosperm nucleus $(PEN)$ is formed by the fusion of two polar nuclei (each $n$) and one male gamete $(n)$,resulting in a $3n$ (triploid) structure.
Therefore,the primary endosperm cell is triploid.