Question

(A)

Distinguish between the two cells enclosed in a mature male gametophyte of an angiosperm.
Study the diagram given below showing the modes of pollination. Answer the questions that follow.

The given diagram shows three methods of pollen transfer in plants. Examine them carefully and write the technical terms used for pollen transfer methods ‘1’, ‘2’ and ‘3’.
How do the following plants achieve pollination successfully?

Water lily
Vallisneria
Write advantages of pollen transfer in method ‘3’. \begin{center} OR \end{center} (B)

Given below is the diagram of human ovum surrounded by a few sperms. Observe the diagram and answer the questions that follow:

Compare the fate of sperms ‘P’, ‘Q’ and ‘R’ shown in the diagram.
Write the role of Zona pellucida in this process.
Analyse the changes occurring in the ovum after the entry of sperm.
How acrosome and middle piece of a human sperm are able to play an important role in human fertilization?

Hint:

Remember — pollen transfer can occur within the same flower, between flowers of the same plant, or different plants. Similarly, acrosomal enzymes like hyaluronidase and zona lysin aid sperm entry during fertilization.

Answer 1

Step 1 (A):

In a mature male gametophyte of an angiosperm, two cells are enclosed: \begin{itemize}
Generative cell: Divides to form two male gametes (sperms).
Vegetative cell: Forms the pollen tube for gamete transfer. \end{itemize}


Technical terms: \begin{itemize}
1 — Autogamy
2 — Geitonogamy
3 — Xenogamy \end{itemize}
Pollination modes: \begin{itemize}
Water lily: By insects (entomophily)
Vallisneria: By water (hydrophily) \end{itemize}
Advantages of Xenogamy (method ‘3’): \begin{itemize}
Introduces genetic variation.
Helps in evolution and adaptability. \end{itemize} Step 2 (B):

Fate of sperms: \begin{itemize}
P: Fails to penetrate the ovum.
Q: Successfully fertilizes the ovum.
R: Degenerates. \end{itemize}
Role of Zona pellucida: \begin{itemize}
It prevents polyspermy by blocking entry of additional sperms once one sperm has penetrated. \end{itemize}
Changes after sperm entry: \begin{itemize}
Completion of meiosis II.
Formation of female pronucleus.
Zona reaction to block polyspermy. \end{itemize}
Role of acrosome and middle piece: \begin{itemize}
Acrosome: Contains enzymes to digest egg membranes.
Middle piece: Packed with mitochondria providing energy for sperm motility. \end{itemize}