RBSE Solutions Class 12 Biology Chapter 2 Male and Female Gametophyte: Structure and Development

RBSE Class 12 Biology Chapter 2 Multiple Choice Questions

Question 1. What is the role of the innermost wall layer, the tapetum in pollen sac?
(a) Dehiscence
(b) Safety
(c) Nutrition
(d) Mechanical
Answer: (c) Nutrition
In simple words: The tapetum is the inner layer of the pollen sac that provides all the necessary food and nutrients for the developing pollen grains to grow properly.

🎯 Exam Tip: Remember that the tapetum is crucial for pollen development; its primary function is nourishment, which is often tested.

Question 2. Ubisch bodies are formed by -
(c) Tapetum
Answer: (c) Tapetum
In simple words: Ubisch bodies are created by the tapetum, which is a layer of cells within the pollen sac.

🎯 Exam Tip: Associate Ubisch bodies directly with the tapetum, as this connection is key to understanding pollen wall formation.

Question 3. How many meiotic divisions are required for the production of 100 pollen grains in Pollen sac/pollen chamber?
(a) 100
(b) 75
(c) 50
(d) 25
Answer: (d) 25
In simple words: Each meiotic division makes four pollen grains. So, to get 100 pollen grains, you need to divide 100 by 4, which gives 25 meiotic divisions.

🎯 Exam Tip: Recall that one meiotic division produces a tetrad of four microspores, which develop into pollen grains. Use this 1:4 ratio for calculations.

Question 4. Female Gametophyte is -
(a) Embryo
(b) Embryo sac
(c) Endosperm
(d) Accessory cells
Answer: (b) Embryo sac
In simple words: The female gametophyte in flowering plants is called the embryo sac. It contains the egg cell ready for fertilization.

🎯 Exam Tip: Distinguish between embryo (the young plant), endosperm (food storage), and embryo sac (female gametophyte) to avoid confusion.

Question 5. In mature Polygonum type of embryo sac, these are found -
(a) Seven cells and eight nuclei
(b) Seven nuclei and eight cells
(c) Eight cells and eight nuclei
(d) Seven cells and seven nuclei
Answer: (a) Seven cells and eight nuclei
In simple words: A fully grown Polygonum embryo sac has seven cells, but inside these cells, there are a total of eight nuclei.

🎯 Exam Tip: Remember the specific numbers for the Polygonum type embryo sac: three antipodal cells, two synergids, one egg cell, and one large central cell with two polar nuclei, totaling 7 cells and 8 nuclei.

Question 6. How many male gametes are formed in pollen grain in Angiospermic plants -
(b) Two
Answer: (b) Two
In simple words: Each pollen grain in flowering plants usually forms two male gametes. These two gametes are important for double fertilization.

🎯 Exam Tip: It is important to know that two male gametes are formed, one for fusing with the egg and the other for fusing with the central cell (polar nuclei).

RBSE Class 12 Biology Chapter 2 Very Short Answer Questions

Question 1. How many types of tapetum are there? Write their name.
Answer: There are two main types of tapetum found in flowering plants. These are the amoeboid, also known as plasmodial, and the secretory, also known as glandular. Both types help provide food to the growing pollen grains.
In simple words: There are two kinds of tapetum: amoeboid (plasmodial) and secretory (glandular).

🎯 Exam Tip: Clearly state both types of tapetum and mention their common function of nourishment.

Question 2. What is pollen kit?
Answer: Pollen kit is an oily, sticky layer found on the outer surface of pollen grains that are carried by insects. This layer gives the pollen a special color and smell, helping insects find and pick it up. It makes the pollen stick to the insect's body.
In simple words: Pollen kit is a sticky, oily layer on insect-pollinated pollen that gives it color and smell, helping it attach to insects.

🎯 Exam Tip: Emphasize that pollen kit is specific to insect-pollinated pollen and plays a role in attracting insects and adhesion.

Question 3. From which place pollen tube comes out of pollen grain?
Answer: The pollen tube emerges from small, thin areas on the otherwise thick and tough outer wall (exine) of the pollen grain. These specific areas are called germ pores. The pollen tube grows out through one of these germ pores.
In simple words: The pollen tube grows out from small, thin spots on the pollen grain's hard outer wall, called germ pores.

🎯 Exam Tip: Remember that germ pores are critical weak points on the exine that allow the pollen tube to emerge during germination.

Question 4. What is the egg apparatus?
Answer: The egg apparatus is a group of three cells found at one end of the embryo sac. It includes one egg cell and two synergids that are present alongside it. These three cells work together in the process of fertilization.
In simple words: The egg apparatus is a group of three cells in the embryo sac: one egg cell and two synergids next to it.

🎯 Exam Tip: Know the components of the egg apparatus (egg cell and synergids) and their location at the micropylar end of the embryo sac.

Question 5. How the secondary nucleus is formed?
Answer: The secondary nucleus is formed when two polar nuclei, which are located in the center of the embryo sac, combine or fuse together. This fusion happens before fertilization.
In simple words: The secondary nucleus is made when two polar nuclei join together.

🎯 Exam Tip: Understand that the secondary nucleus is diploid and results from the fusion of two haploid polar nuclei, distinguishing it from other nuclei.

Question 7. Where is megaspore mother cell formed?
Answer: The megaspore mother cell is formed in a specific area called the hypodermal region of the nucellus. This happens at the micropylar end of an ovule. The nucellus is the main part of the ovule that provides nutrients.
In simple words: The megaspore mother cell grows inside the ovule's nucellus, near the micropyle.

🎯 Exam Tip: Precisely locate the megaspore mother cell within the ovule, noting the nucellus and micropylar end as key terms.

Question 8. How many nuclei are formed in the monoscopic embryo sac?
Answer: In a monoscopic embryo sac, there are typically eight nuclei formed. These nuclei are arranged in a specific way to prepare for fertilization.
In simple words: A monoscopic embryo sac usually has eight nuclei inside it.

🎯 Exam Tip: For the monoscopic embryo sac (like Polygonum type), remember the 8-nucleate, 7-celled structure.

Question 9. What type of ovule is found in a majority of angiosperms?
Answer: Most flowering plants (angiosperms) have an anatropous ovule. This type of ovule is inverted, meaning it is turned upside down. It is also sometimes called the inverted type.
In simple words: Most flowering plants have an anatropous ovule, which is an inverted type.

🎯 Exam Tip: Know that the anatropous ovule is the most common type and understand its inverted orientation.

Question 10. What is meant by the term dithecous?
Answer: The term "dithecous" refers to an anther that has two lobes. Each of these lobes typically contains two pollen sacs. So, a dithecous anther is a bilobed anther.
In simple words: Dithecous means an anther has two lobes.

🎯 Exam Tip: Remember "di-" means two; dithecous implies a bilobed anther, which is a common characteristic.

Question 11. How many pollen chambers are formed in the anther?
Answer: A typical anther has four pollen chambers. These chambers are where pollen grains develop and are stored before release.
In simple words: A normal anther has four pollen chambers inside it.

🎯 Exam Tip: Understand that each of the two lobes in a dithecous anther contains two pollen chambers, summing up to four in total.

Question 12. Name different layers of the wall of the anther.
Answer: The wall of the anther consists of four distinct layers. These layers are: 1. Epidermis, 2. Endothecium, 3. Middle layers, and 4. Tapetum.
In simple words: The anther wall has four layers: epidermis, endothecium, middle layers, and tapetum.

🎯 Exam Tip: List the four anther wall layers in order from outermost to innermost for a complete answer.

Question 14. Define the terms - Hilum, Funicle and Chalaza.
Answer:
1. Hilum - The hilum is the exact spot where the main body of the ovule connects to its stalk, called the funicle. It's like the belly button of the ovule.
2. Funicle - The funicle is the stalk that attaches the ovule to the placenta, which nourishes the ovule.
3. Chalaza - The chalaza is the bottom or basal part of the ovule. This is the area from which the protective coverings (integuments) of the ovule begin to grow.
In simple words: Hilum is where the ovule joins its stalk (funicle). The funicle is the stalk. Chalaza is the base of the ovule where the coverings start.

🎯 Exam Tip: Clearly define each term, highlighting its specific location and role within the ovule structure.

Question 15. How many pollen tetrads will be formed by the meiotic division of 16 pollen mother cells?
Answer: If there are 16 pollen mother cells, then 16 pollen tetrads will be formed. This is because each pollen mother cell undergoes one meiotic division to produce a single tetrad of four microspores.
In simple words: Each pollen mother cell makes one pollen tetrad. So, 16 cells will make 16 tetrads.

🎯 Exam Tip: Remember the 1:1 ratio between pollen mother cells and the tetrads they produce after meiosis.

Question 16. How many megaspores are formed from the meiotic division of one megaspore mother cells?
Answer: From the meiotic division of one megaspore mother cell, four megaspores are formed. However, in most cases, only one of these four megaspores develops into the functional embryo sac.
In simple words: One megaspore mother cell makes four megaspores after meiosis.

🎯 Exam Tip: While four megaspores are formed, highlight that typically only one becomes functional, with the others degenerating.

RBSE Class 12 Biology Chapter 2 Short Answer Questions

Question 1. Write functions of the tapetum.
Answer: Tapetum cells have several important functions. They provide food and nutrients for the developing pollen grains. They also help deposit a tough substance called sporopollenin, which forms the outer protective layer of the pollen. If the tapetum cells break down too early, before pollen grains are fully formed, the pollen grains will not be able to develop properly and will become sterile or unable to function. This shows how crucial the tapetum is for healthy pollen.
In simple words: The tapetum feeds pollen, forms its outer protective layer, and ensures the pollen develops properly; without it, pollen can become sterile.

🎯 Exam Tip: Mention the two primary roles of tapetum: nutrition and contribution to sporopollenin formation, emphasizing its importance for pollen viability.

Question 2. Write in detail, the structure of pollen grain.
Answer: Pollen grains in flowering plants are typically single-celled, have one nucleus, and are haploid (half the number of chromosomes). They are usually round and cannot move on their own. Each pollen grain has a two-layered wall. The outer layer is tough and called the exine. It is made of sporopollenin, a very resistant substance that protects the pollen from harsh conditions like strong acids or high temperatures. The exine has small openings called germ pores, where sporopollenin is absent. The inner layer is thin and soft, called the intine, made of cellulose and pectin. Inside the intine, there is cytoplasm and a nucleus. A mature pollen grain has two cells: a large vegetative cell and a smaller generative cell. The vegetative cell has lots of food stored, and the generative cell will later divide to form male gametes.
In simple words: A pollen grain is a small, non-moving cell with a tough outer wall (exine) and a soft inner wall (intine). It has two cells inside: a big one for food and a small one that makes male reproductive cells.

🎯 Exam Tip: Describe both wall layers (exine and intine) and their composition, then explain the two cells (vegetative and generative) found within a mature pollen grain.

Question 3. What are Ubisch bodies?
Answer: Ubisch bodies are small, fatty structures that are released by the tapetal cells. These bodies then get deposited on the wall of the developing pollen grain. They help in forming the exine, which is the tough outer layer of the pollen grain, by depositing sporopollenin.
In simple words: Ubisch bodies are tiny, fatty parts from tapetal cells that help build the strong outer wall of pollen grains.

🎯 Exam Tip: Connect Ubisch bodies to tapetal cell secretions and their crucial role in sporopollenin deposition and exine formation.

Question 4. Draw a well-labelled diagram of a typical ovule.
Answer: A typical ovule in flowering plants is an anatropous ovule, meaning it is inverted. Below is a simplified representation of its structure:

In simple words: The picture shows a typical ovule, which is like a small seed part. It has an outer and inner covering, a central part called the nucellus, and an embryo sac inside where the egg cell is. It connects to the plant by a stalk.

🎯 Exam Tip: Focus on accurately labeling the micropyle, chalaza, funicle, hilum, integuments, nucellus, and embryo sac, as these are the crucial parts of an ovule diagram.

Question 5. Draw a well-labelled diagram of Polygonum type of embryo sac.
Answer: The Polygonum type embryo sac is the most common type and develops from a single functional megaspore. It is characterized by having eight nuclei but only seven cells. Below is a simplified representation:

In simple words: The diagram shows the embryo sac with three small cells at the top (egg apparatus), two nuclei in the middle (polar nuclei), and three cells at the bottom (antipodal cells).

🎯 Exam Tip: Accurately draw and label the three antipodal cells, the two polar nuclei in the central cell, and the egg apparatus (one egg cell and two synergids) at their respective positions.

Question 6. Differentiate between orthotropous and anatropous ovule.
Answer:
Orthotropous Ovule: In this type of ovule, all parts - the funicle (stalk), chalaza (base), and micropyle (small opening) - are aligned in a straight line. The ovule stands upright on the placenta.
Anatropous Ovule: In contrast, the anatropous ovule is inverted. The main body of the ovule is turned 180 degrees. Because of this inversion, the micropyle and the hilum (where the funicle attaches) end up lying very close to each other. This is the most common type of ovule in flowering plants.
In simple words: An orthotropous ovule is straight, with its stalk, base, and opening in a line. An anatropous ovule is upside down, so its opening and stalk connection are very close.

🎯 Exam Tip: When differentiating, clearly describe the alignment of funicle, chalaza, and micropyle for each type, highlighting the inverted nature of the anatropous ovule.

Question 7. Write a brief account of the structure of ovule of angiosperms.
Answer: A mature ovule in flowering plants is usually oval-shaped and has several parts. The main body of the ovule is called the nucellus, which is protected by two outer layers called integuments. These integuments start growing from the base of the ovule. At the top end, the integuments do not completely cover the nucellus, leaving a tiny opening called the micropyle. The ovule is attached to the plant by a stalk called the funicle. The point where the ovule's body connects to this stalk is known as the hilum. The very bottom part of the ovule, where the integuments begin, is called the chalaza.
In simple words: An ovule is an oval structure with a central nucellus covered by two integuments. It has a small opening (micropyle), a stalk (funicle), a connecting point (hilum), and a base (chalaza).

🎯 Exam Tip: Systematically describe each part of the ovule (nucellus, integuments, micropyle, funicle, hilum, chalaza) and its anatomical relation to others.

Question 8. Describe the structure of the female gametophyte of angiosperms.
Answer: The female gametophyte of flowering plants is also known as the embryo sac. A typical embryo sac is usually monoscopic and follows the Polygonum type of development. It starts with four nuclei at the micropylar end and four nuclei at the chalazal end. At the micropylar end, three nuclei arrange themselves to form the egg apparatus, which consists of one egg cell and two synergids. The remaining nucleus from this end moves to the center and becomes a polar nucleus. Similarly, three nuclei at the chalazal end develop into antipodal cells. The fourth nucleus from the chalazal end also moves to the center, becoming the second polar nucleus. These two polar nuclei then fuse to form a secondary or definitive nucleus, which is important for double fertilization. The synergids help guide the pollen tube to the egg cell. The role of the antipodal cells is not fully understood, but they may be involved in regulating fertilization.
In simple words: The female gametophyte, or embryo sac, typically has seven cells and eight nuclei. It contains an egg cell and two helping cells at one end, three cells at the other end, and two central nuclei that fuse to form a secondary nucleus.

🎯 Exam Tip: Detail the 7-celled, 8-nucleate structure, explaining the arrangement and function of the egg apparatus, polar nuclei, and antipodal cells.

RBSE Class 12 Biology Chapter 2 Essay Type Questions

Question 1. Describe in detail the structure of pollen sac with the help of well-labelled diagrams.
Answer: Each pollen sac, or microsporangium, acts as a chamber for pollen development. It is surrounded by a wall that matures into four distinct layers. Inside these wall layers is a mass of cells called sporogenous cells, which divide to form microspore mother cells. These mother cells then undergo meiosis to produce microspores, which develop into pollen grains. Thus, the pollen sac is filled with pollen grains surrounded by its protective wall layers. The four layers of the pollen sac wall, from outside to inside, are:
1. Epidermis: This is the outermost protective layer. As the anther grows, its epidermal cells stretch and flatten, providing overall protection.
2. Endothecium: Located just beneath the epidermis, these cells have thick walls and are elongated. Their internal walls have deposits of cellulose, forming U-shaped fibrous bands. These cells are hygroscopic, meaning they absorb water. When dry, they create tension, which helps the anther split open (dehiscence) to release pollen.
3. Middle Layers: These layers are found below the endothecium and consist of two to three rows of thin-walled cells.
4. Tapetum: This is the innermost layer and is crucial for nourishing the developing pollen. Tapetal cells also contribute to forming the exine (outer wall) of the pollen grain by depositing sporopollenin. Without a functional tapetum, pollen grains cannot mature and become sterile. The tapetum can be amoeboid (plasmodial) or secretory (glandular), with secretory being common in most dicots. Tiny fatty structures called Probisch bodies are found in tapetal cells, which later become Ubisch bodies after sporopollenin deposition.

In simple words: The pollen sac wall has four layers: epidermis (outermost protection), endothecium (helps in opening), middle layers (between endothecium and tapetum), and tapetum (provides food and makes the pollen's outer skin). Inside, sporogenous cells make pollen.

🎯 Exam Tip: Clearly describe each of the four wall layers of the anther, detailing their position, structure, and specific function, especially the tapetum and endothecium.

Question 2. Write in detail, the structure of pollen grain.
Answer: Pollen grains in flowering plants (angiosperms) are typically unicellular, uninucleate, haploid, and non-motile structures that are normally round. The wall of the pollen grain is made of two main layers. The outer layer, called the exine, is very tough and made of sporopollenin, which protects the pollen from strong acids, high temperatures, and other environmental damage. The exine is not smooth all over; it has small, thin areas called germ pores where sporopollenin is absent. These germ pores are where the pollen tube will emerge. The inner layer, called the intine, is thin, soft, and elastic, composed mainly of cellulose and pectin. Inside these layers, the pollen grain contains cytoplasm and usually two cells: a large vegetative cell and a smaller generative cell. The vegetative cell has a large, irregular nucleus and stores food. The generative cell, which is spindle-shaped or elliptical, will divide to form two male gametes needed for fertilization. The development of the male gametophyte (which is the pollen grain itself) involves the microspore forming these two cells, eventually producing the male gametes.

1. Tetrahedral: In this arrangement, three microspores can be seen from one side, with the fourth one hidden behind. This is common in most dicotyledonous plants.
2. Isobilateral: All four microspores are arranged in the same flat plane within the tetrad. This type is typical for monocot plants.
3. Decussate: Here, two microspores are arranged on top, and two are at the bottom, perpendicular to each other. When viewed, the upper two are fully visible, but only one from the lower pair is clearly seen. Magnolia plants show this type.
4. T-shaped: In this arrangement, two microspores are positioned side-by-side in a horizontal line (transverse), and the other two are arranged vertically (longitudinal). Aristolochia is an example of a plant with T-shaped tetrads.
5. Linear: In this type, all four microspores are arranged in a single line.
The wall between the microspores is made of callose. This callose wall breaks down due to enzymes, allowing the microspores to separate from each other and become round. At this point, they are called pollen grains and are found freely inside the pollen chamber.
In some plants, pollen grains or microspores stick together in a single mass called a pollinium. For example, Calotropis and some orchids have pollinia.

More commonly, microspores separate individually, but sometimes they remain in groups called tetrads. If more than four microspores are found in a tetrad, this condition is known as Polyspory, seen in plants like Drimys, Anona, Drosera, Elodea, and Typha.
In simple words: A pollen grain has a strong outer wall (exine) and a softer inner wall (intine). Inside are a large food-storing cell and a smaller cell that produces two male gametes. Pollen tetrads can be arranged in different shapes like tetrahedral or isobilateral, which become individual pollen grains.

🎯 Exam Tip: When describing pollen grain structure, include details about the exine (sporopollenin, germ pores) and intine, and explain the roles of the vegetative and generative cells. For tetrads, name and briefly describe each type with an example.

Question 3. Describe types of ovules diagrammatically.
Answer: In flowering plants, six different types of ovules can be found. Each type has a unique orientation and curvature. These are:
1. Orthotropous: The ovule is straight, with the micropyle, funicle, and chalaza all in a straight line. An example is gamopetalous plants.
2. Anatropous: This is an inverted ovule, where the body turns 180 degrees, bringing the micropyle close to the funicle. This is the most common type.
3. Campylotropous: The ovule is curved, causing the micropyle to face the chalaza. The chalaza is positioned at a right angle to the funicle. Examples include members of the Cruciferae and Leguminosae families.
4. Amphitropous (or Transverse Ovule): The ovule is highly curved, making the embryo sac horseshoe-shaped. This is seen in families like Alismaceae and Butumaceae.
5. Hemianatropous: In this type, the nucellus and integuments lie roughly at right angles to the funicle. Examples include families Ranunculaceae and Primulaceae.
6. Circinotropous: The funicle is very long and forms a complete circle around the ovule. The ovule itself is free from the funicle except for a small attachment area at its end. This type is found in Opuntia and other members of the Cactaceae and Plumbaginacea families.

In simple words: Ovules come in different shapes and ways they are attached. Some are straight (orthotropous), some are upside down (anatropous), others are curved (campylotropous, amphitropous), some are at right angles (hemianatropous), and a few have a long, circling stalk (circinotropous).

🎯 Exam Tip: For each ovule type, briefly describe its orientation (straight, inverted, curved, right angle, circling funicle) and mention its defining characteristic, such as the position of the micropyle and chalaza.

Question 4. Describe the development of male gametophyte with the help of well-labelled diagrams.
Answer: The development of the male gametophyte begins with the microspore or pollen grain, which is considered the first cell of the male gametophytic generation. Initially, the microspore increases in size and becomes filled with dense cytoplasm. Its nucleus undergoes mitotic division (karyokinesis) to form two nuclei. After this, a cell wall forms (cytokinesis) between them, creating two unequal cells: a smaller, lens-shaped generative cell and a larger vegetative cell. The vegetative cell has a large, irregularly shaped nucleus and contains abundant food reserves. The generative cell, which is initially attached to the pollen grain wall, later separates and moves into the cytoplasm of the vegetative cell. It may become elliptical or spindle-shaped.
The germination of the pollen grain starts when it lands on the stigma of a flower. The vegetative cell then grows out as a pollen tube, through one of the germ pores. As the pollen tube grows, the vegetative nucleus moves into it, followed by the generative cell. The generative cell then divides mitotically to form two male gametes. These two male gametes, along with the vegetative nucleus, are carried by the pollen tube to the embryo sac for fertilization.

In simple words: The male gametophyte starts as a pollen grain, which divides to form a large vegetative cell and a smaller generative cell. When it germinates, the vegetative cell forms a pollen tube, and the generative cell divides to make two male gametes that travel through this tube.

🎯 Exam Tip: Detail the two key stages: formation of vegetative and generative cells within the pollen grain, and then the development of the pollen tube and male gametes during germination.

Question 5. Describe the development of embryo sac in angiosperm with the help of well-labelled diagrams.
Answer: The megaspore is the initial cell that develops into the female gametophyte, also known as the embryo sac, in flowering plants. The nucleus of this functional megaspore divides three times by mitosis, leading to eight nuclei in total. Initially, two nuclei form, then four, and finally eight nuclei are present within the elongated megaspore cell. Out of these eight nuclei, four are at the micropylar end and four at the chalazal end. At the micropylar end, three nuclei organize to form the egg apparatus, which includes one egg cell and two synergids. The fourth nucleus from this end moves to the center and is called a polar nucleus. Similarly, at the chalazal end, three nuclei differentiate into antipodal cells. The fourth nucleus from this end also migrates to the center, becoming another polar nucleus. These two polar nuclei in the center then fuse together to form a secondary or definitive nucleus \( ( = \) definitive nucleus). Therefore, a mature embryo sac typically contains seven cells and eight nuclei: one egg cell, two synergids, three antipodal cells, and a large central cell with the secondary nucleus. This process ensures the development of the female reproductive structure necessary for fertilization.
In simple words: The embryo sac starts from one cell called a megaspore. This cell's inside part (nucleus) divides many times to make eight smaller parts. Three of these parts near one end become the egg and its helpers. Three parts near the other end become support cells. The two remaining parts meet in the middle to form a special central cell. This whole structure is ready for the plant to make seeds.

🎯 Exam Tip: When describing the embryo sac, clearly explain the roles of the egg apparatus, antipodal cells, and polar nuclei, and specify their location within the sac. Remember the 7-celled, 8-nucleate structure as a key point.