RBSE Solutions Class 12 Biology Chapter 4 Special Methods of Plant Reproduction

RBSE Class 12 Biology Chapter 4 Multiple Choice Questions

Question 1. Development of new plants without fertilization -
(a) Non-fertilization
(b) Parthenogenesis
(c) Apomixis
(d) Micropropagation
Answer: (c) Apomixis
In simple words: Apomixis is how some plants make new plants without needing seeds or pollen from another plant. It's like making a copy of itself.

🎯 Exam Tip: Remember that apomixis is a form of asexual reproduction, meaning it doesn't involve the usual combining of male and female cells.

Question 2. Embryo development without fertilization of the egg is called -
(a) Haploid parthenogenesis
(b) Diploid parthenogenesis
(c) Adventive embryonic
Answer: (a) Haploid parthenogenesis
In simple words: When an embryo starts growing from an egg cell without being fertilized by sperm, and the embryo has half the usual number of chromosomes, it's called haploid parthenogenesis.

🎯 Exam Tip: Distinguish between haploid and diploid parthenogenesis based on the chromosome number of the resulting embryo and the origin of the egg cell.

Question 3. Formation of more than one embryo sac in ovule is found in which of the following:
(a) Argemone
(b) Aristolochia
(c) Casuarina
(d) Calotropis
Answer: (c) Casuarina
In simple words: In plants like Casuarina, you can find more than one embryo sac inside the ovule, which is unusual as most plants have only one.

🎯 Exam Tip: Examples are crucial in biology. Remember specific plant names associated with unique reproductive features like multiple embryo sacs.

Question 4. Polyembryony is commonly found in -
(a) All monocots
(b) All dicots
(c) Angiosperm
(d) Gymnosperms
Answer: (d) Gymnosperms
In simple words: Polyembryony, which means having many embryos in one seed, is a common thing to see in gymnosperms, a type of plant.

🎯 Exam Tip: Understand that while polyembryony can occur in angiosperms, it is a characteristic and more common feature of gymnosperms.

Question 5. Polyembryony caused by cleavage of zygote or proembryo is called, which polyembryony?
(a) Cleavage polyembryony
(b) General polyembryony
(c) Abnormal polyembryony
(d) Adventive polyembryony
Answer: (a) Cleavage polyembryony
In simple words: When a single fertilized egg or a very early embryo splits apart to form many embryos, it is known as cleavage polyembryony.

🎯 Exam Tip: Differentiate between different types of polyembryony based on their origin and mechanism of embryo formation.

RBSE Class 12 Biology Chapter 4 Very Short Answer Questions

Question 1. Define apomixis.
Answer: Apomixis is a special way plants reproduce. In this method, plants create new individuals without undergoing the usual steps of sexual reproduction, which include meiosis and fertilization. This means no mixing of genetic material from two parents happens.
In simple words: Apomixis is when a plant makes new plants without sex or seeds, by making copies of itself.

🎯 Exam Tip: When defining apomixis, clearly state that it bypasses both meiosis and fertilization, resulting in offspring genetically identical to the parent.

Question 3. List the special methods of plant multiplication.
Answer: Higher plants usually make new plants through seeds, which involves meiosis and fertilization. However, there are special ways plants can multiply without these processes. These special methods are:

• Apomixis
• Agamospermy
• Micro-propagation
• Vegetative reproduction

🎯 Exam Tip: When listing, ensure you provide distinct methods and briefly understand what each one entails, even if not explicitly asked for here.

Question 4. Write two advantages or importance of apomixis.
Answer: Apomixis offers several benefits in plant reproduction:
1. Since it does not involve meiosis or genetic mixing, the new plants produced are exact copies of the parent. This helps maintain genetically similar populations.
2. This method is very useful for creating hybrid seeds. It also helps in producing pure lines of plants (homozygous inbred lines).
In simple words: Apomixis is good because it makes perfect copies of plants, keeping them all the same. It also helps make new types of hybrid seeds and pure plant varieties.

🎯 Exam Tip: Focus on genetic stability and efficiency in breeding as key advantages of apomixis.

RBSE Class 12 Biology Chapter 4 Short Answer Questions

Question 1. Explain non recurrent apomixis and recurrent apomixis.
Answer:
1. **Non-recurrent apomixis:** This is when an embryo forms directly from an egg cell without being fertilized. The egg cell is haploid (has half the usual chromosomes), so the resulting embryo is also haploid. This process is also known as haploid parthenogenesis.
2. **Recurrent apomixis:** In this type, the embryo grows from diploid cells (cells with the full set of chromosomes) either from the nucellus (a part of the ovule) or from a diploid embryo sac that formed without meiosis. This means the embryo will be diploid, just like the mother plant.
In simple words: Non-recurrent apomixis is when an embryo grows from an unfertilized egg that has half the chromosomes. Recurrent apomixis is when an embryo grows from an unfertilized egg or other parts that have the full set of chromosomes, like the mother plant.

🎯 Exam Tip: The main difference lies in the ploidy level (haploid vs. diploid) of the cells from which the embryo develops and whether meiosis occurs in the formation of the embryo sac.

Question 2. Differentiate between generative apomixis and somatic apomixis.
Answer: The distinction between generative apomixis and somatic apomixis is as follows:
* **Generative Apomixis:** This occurs when the embryo develops from a diploid cell within the embryo sac. Since meiosis does not happen correctly, the embryo sac cells have the same number of chromosomes as the parent plant. This leads to the formation of an embryo that is genetically identical to the mother.
* **Somatic Apomixis (Adventive Embryony):** In this type, the embryo forms from diploid cells of the nucellus or integuments, which are outside the embryo sac. These somatic cells directly give rise to an embryo without fertilization. This is also known as adventive embryony.
In simple words: Generative apomixis is when an embryo grows from a special cell inside the embryo sac that has all the chromosomes, without fertilization. Somatic apomixis is when an embryo grows from normal plant cells outside the embryo sac, like the nucellus, also without fertilization.

🎯 Exam Tip: Remember that generative apomixis involves cells *within* the embryo sac, while somatic apomixis involves cells *outside* the embryo sac (nucellus or integuments).

Question 4. Explain cleavage polyembryony.
Answer: Cleavage polyembryony happens when a single fertilized egg (oospore) or a very early embryo (proembryo) divides unusually. This division creates a group of cells, and these cells then split further to form more than one embryo. Sometimes, the proembryo can even grow small buds or outgrowths, and each of these can develop into a new embryo. This branching results in many embryos developing from one initial egg.
In simple words: Cleavage polyembryony is when one baby plant (embryo) splits into many baby plants. It's like one fertilized egg making several identical twins.

🎯 Exam Tip: Highlight that cleavage polyembryony is essentially the splitting of a single zygote or proembryo into multiple independent embryos.

Question 5. Explain the importance of micropropagation.
Answer: Micropropagation is a very useful technique for plants because:

• It helps in making many genetically identical plants quickly. This is useful for producing a large number of copies of a desired plant.
• It can be used to grow plants that are free from diseases.
• This method is often the only way to grow new plants from genetically modified cells.
• It allows for a much larger number of plants to be grown in a small space compared to traditional methods.

🎯 Exam Tip: When discussing the importance of micropropagation, emphasize its role in rapid multiplication, disease elimination, and genetic engineering.

RBSE Class 12 Biology Chapter 4 Essay Type Questions

Question 1. Write a note on apomixis.
Answer: Apomixis is a unique way for angiosperm plants to reproduce without the usual sexual steps of meiosis and fertilization. This means the plant can create seeds or new plants that are genetically identical to the parent. Apomixis can happen in different forms, such as being sporophytic or gametophytic, and non-recurrent or recurrent.

According to its definition, apomixis usually has two main types:
1. **Sporophytic Apomixis (Adventive Embryony):** In this type, the embryo forms directly from cells of the nucellus or integument, or any other diploid cell of the ovule. This process does not involve meiosis or fertilization. Since it starts from diploid cells, the embryo is genetically the same as the parent plant.
2. **Gametophytic Apomixis:** Here, the embryo develops from any cell within the embryo sac. This type has two sub-types:
* If the embryo grows from an unfertilized egg cell, it is called parthenogenesis.
* If the embryo develops from any other haploid cell of the embryo sac, like accessory cells or synergids, this process is known as apogamy.

Prof. Panchanan Maheshwari (1950) further classified apomixis into non-recurrent apomixis and recurrent apomixis. These are then divided into more specific types. We will look at four types briefly:
1. **Non-recurrent Apomixis:** This is when an embryo forms directly from a normal egg cell without fertilization. Since egg cells are haploid, the resulting embryo is also haploid. This is also known as haploid parthenogenesis. This process was first observed by Jorgensen in 1928. If an embryo develops from any other cell of the female gametophyte (not the egg cell), it is called haploid apogamy or endogamy. These types of apomixis are rare but interesting for genetics, found in plants like Datura and Maize.
2. **Recurrent Apomixis:** Also known as gametophytic apomixis, this type happens when meiosis is not completed, resulting in a female gametophyte with a diploid (full set) chromosome number, just like the mother plant. It has two forms.
3. **Adventive Embryonic:** In this process, the embryo develops from any diploid cell of the ovule outside the embryo sac, such as cells from the nucellus or integuments. This is called adventive embryony. Sometimes, a regular embryo inside the embryo sac can develop at the same time, leading to polyembryony. Examples include Lemon, Mango, and Opuntia.
4. **Vegetative Apomixis:** In some plants, like specific types of Allium, Agave, and grasses, vegetative buds (called bulbils or propagules) are produced instead of flowers in the flower cluster. These buds can then grow into new plants directly on the parent plant, making reproduction easy.

**Importance of Apomixis:** Apomixis has several key benefits:
* It ensures that plants obtained are genetically identical to the mother plant, forming clones, because meiosis and genetic mixing do not occur.
* It helps in quickly multiplying genetically similar individuals without the risk of changes or variations.
* It allows for the permanent maintenance of heterosis (hybrid vigor) in crop plants, which means the desirable traits of hybrids can be kept over generations.
* This method effectively utilizes the maternal genetic contribution from one generation to the next.
* It helps in quickly developing homozygous inbred lines, which are pure genetic lines useful in plant breeding.
* Apomixis is valuable for producing hybrid seeds as it prevents the loss of specific desired features.
In simple words: Apomixis is a way plants make new plants without using seeds or mixing genes. It can happen in different ways, like making exact copies from other parts of the plant, or from an unfertilized egg. This method is important because it helps keep good plant qualities, makes many copies fast, and is useful for creating hybrid plants.

🎯 Exam Tip: For essay questions on apomixis, structure your answer by defining it, categorizing its types (sporophytic/gametophytic, non-recurrent/recurrent), and then listing its key significances or advantages.

Question 2. Write a detailed account of polyembryony.
Answer: Polyembryony is the development of more than one embryo within a single seed. Normally, a plant seed contains only one embryo. However, sometimes multiple embryos can develop. This can occur due to various reasons, leading to either cleavage polyembryony or adventive polyembryony.

Polyembryony is a common characteristic in gymnosperms, but it can also happen in angiosperms due to the following reasons:
1. **Cleavage in proembryo:** The early embryo splits into multiple parts, and each part grows into a complete embryo.
2. **Development of any other cell of embryo sac along with egg cell:** Besides the egg cell, other cells in the embryo sac (like synergids or antipodals) can also develop into embryos.
3. **Development of more than one embryo sac in one ovule:** A single ovule can contain multiple embryo sacs, and each can potentially form an embryo.
4. **Overactivity of sporophytic cells of ovules:** Somatic cells of the ovule (like nucellar or integumentary cells) can directly develop into embryos.

**1. Cleavage Polyembryony:**
In this type, the zygote (fertilized egg) or the proembryo (early embryo) divides or cleaves, resulting in the formation of more than one embryo. For example, in Orchids and Eulophia, there are different patterns of cleavage polyembryony.

**2. Development of Embryo from cells of embryo sac other than the egg cell:**
In this type of polyembryony, accessory cells (like synergids) that are either fertilized or unfertilized, develop into an embryo alongside the main embryo from the egg cell. If these cells develop from fertilized cells, they can be diploid (e.g., Aristolochia brachiata). If they develop from unfertilized cells, they are haploid (e.g., Argemone mexicana).

**3. Development of more than one embryo sacs in the ovule:**
Some angiosperm plants, such as Casuarina Montana, develop more than one embryo sac within a single ovule. After fertilization, each egg cell in these multiple embryo sacs forms an embryo. This means several embryos can develop within one ovule.

**4. Adventive Polyembryony:**
This occurs when cells from the nucellus or integument (parts of the ovule outside the embryo sac) get activated and directly form an embryo without fertilization. This is known as adventive embryony. The process is similar to adventive embryony.

**Significance of Polyembryony:** Polyembryony is important in fields like horticulture, cell biology, genetics, and plant breeding for several reasons:
* Adventive embryos that develop from the nucellus are genetically identical to the mother plant, acting as clones.
* Plants grown from embryos derived from nucellar cells are robust and full of vigor.
* Embryos from the nucellus are often disease-free, allowing for the production of healthy plants (e.g., virus-free lemon clones).
* Haploid embryos are significant in cell biology research.
* These haploid embryos can be treated with chemicals like colchicine to produce homozygous lines, which are pure genetic lines very valuable in plant breeding experiments.
In simple words: Polyembryony is when one seed grows more than one baby plant inside it. This can happen if the first baby plant splits, or if other cells in the seed also start growing into new baby plants. It is important because it can make many healthy, identical plants and help grow special types of plants for farming.

🎯 Exam Tip: When detailing polyembryony, explain its definition, list the causes, describe the different types with examples, and finally, outline its practical significance in plant science.