RBSE Solutions Class 11 Biology Chapter 21 Flower

RBSE Class 11 Biology Chapter 21 Multiple Choice Objective Questions

 

Question 1. Which of the following have syngenesious condition of stamens?
(a) China Rose
(b) Sun flower
(c) Cucumber
(d) Beans
Answer: (b) Sun flower
In simple words: In a syngenesious condition, the anthers of the stamens are joined together, while their filaments remain separate. This arrangement is common in sunflowers.

🎯 Exam Tip: Remember key examples for each type of stamen cohesion to quickly identify the correct option in MCQs.

 

Question 2. Aestivation in which edges touch each other but do not overlap
(a) Valvate
(b) Twisted
(c) Imbricate
(d) Vexillary
Answer: (a) Valvate
In simple words: Valvate aestivation means that the edges of petals or sepals meet without any overlapping, just touching each other at the margins. Think of a simple door meeting its frame.

🎯 Exam Tip: Visualizing the arrangement of petals in different flowers can help you remember the various aestivation types.

RBSE Class 11 Biology Chapter 21 Very Short Answer Questions

 

Question 1. Write three part of stamen.
Answer: The three main parts of a stamen are the filament, connective, and anther. The anther is where pollen is produced.
In simple words: A stamen has three parts: a thin stalk called the filament, a small part called the connective that joins the stalk to the anther, and the anther itself, which holds the pollen.

🎯 Exam Tip: Knowing the parts of a stamen is basic knowledge for understanding flower reproduction; ensure you can label a diagram too.

 

Question 2. What do you mean by complete flower?
Answer: A complete flower has all four essential parts, also known as whorls: the calyx (sepals), corolla (petals), androecium (stamens), and gynoecium (pistil). The presence of all these structures makes it a complete flower.
In simple words: A complete flower has all four main parts: sepals, petals, male parts (stamens), and female parts (pistil).

🎯 Exam Tip: Understanding the terms "complete" and "incomplete" for flowers is crucial for classifying different plant species.

 

Question 3. What do you mean by perianth?
Answer: The perianth refers to the collective term for the sepals and petals of a flower when they are similar in size and color, making it hard to tell them apart. This forms a single protective and attractive layer around the reproductive organs.
In simple words: Perianth is when the sepals and petals of a flower look so much alike that you can't tell them apart, forming one cover.

🎯 Exam Tip: Identify whether a flower has a distinct calyx and corolla or a fused perianth to help determine its family.

 

Question 4. Explain monoadelphous condition in China Rose?
Answer: In a monoadelphous condition, all the filaments of the stamens are fused together to form a single tube or bundle, but their anthers remain free. This fusion often creates a noticeable column around the pistil, as seen in the China rose.
In simple words: Monoadelphous means all the little stalks of the stamens are joined into one group, but their pollen-holding tops are separate. China rose is a good example.

🎯 Exam Tip: Remember that monoadelphous refers to *one* bundle of fused filaments, a key characteristic in certain plant families.

 

Question 5. What do you mean by tetradynamous condition?
Answer: The tetradynamous condition describes a specific arrangement of stamens where there are six stamens in total: four of them are long, and two are distinctly shorter. This unique setup is typical in plants like mustard.
In simple words: Tetradynamous means a flower has six stamens, but four are tall and two are short. You can see this in mustard plants.

🎯 Exam Tip: Count the number of stamens and note their relative lengths to identify this specific condition in flowers.

 

Question 7. What do you mean by Pistillate flower?
Answer: A pistillate flower is one that contains only the female reproductive part (pistil or gynoecium) and lacks the male reproductive parts (stamens or androecium). Such flowers are considered incomplete, as they cannot self-pollinate.
In simple words: A pistillate flower is a flower that only has the female part (pistil) and no male parts.

🎯 Exam Tip: Distinguish between pistillate (female only) and staminate (male only) flowers to understand plant reproductive strategies.

 

Question 8. What do you mean by petaloid perianth?
Answer: A petaloid perianth occurs when the tepals (which are sepals and petals that look alike) are brightly colored and resemble true petals. This makes the perianth visually attractive and functionally similar to petals, as seen in the onion flower.
In simple words: A petaloid perianth means the sepals and petals look alike and are colorful, like petals. Onions have this type of flower part.

🎯 Exam Tip: The term "petaloid" indicates that a part resembles a petal, even if its origin is different, highlighting its function in attracting pollinators.

RBSE Class 11 Biology Chapter 21 Short Answer Questions

 

Question 1. Explain marginal placentation with labeled diagram.
Answer: Marginal placentation is the simplest type of placentation where the placenta develops along the fused margins of the carpel, forming a ridge on the ventral suture of the unilocular ovary. The ovules are arranged in two rows on this ridge, as typically observed in a pea pod.
In simple words: Marginal placentation means the seeds are arranged in two lines along the inner edge of the ovary, like peas in a pod.

🎯 Exam Tip: When drawing placentation diagrams, ensure the arrangement of ovules within the ovary matches the specific type being depicted.

 

Question 2. Differentiate twisted and imbricate aestivation with the help of diagram and examples.
Answer:
(i) Twisted or Contorted Aestivation: In this type, one margin of each sepal or petal regularly overlaps the margin of the next one in a spiral fashion, like a twisted wheel. For example, twisted aestivation is clearly seen in China rose, lady's finger, and cotton.
In simple words: Twisted aestivation is when each petal overlaps the next one on one side, making a spiral pattern, like in a China rose flower.

(ii) Imbricate Aestivation: This type is characterized by irregular overlapping of sepals or petals, where one sepal/petal is completely internal, one is completely external, and the remaining petals have one margin overlapped and the other margin overlapping. There are several forms of imbricate aestivation:
    a. Descending Imbricate or Vexillary: Found in pea and bean flowers, it has five petals. The largest, outermost petal (standard) overlaps two lateral petals (wings), which in turn overlap the two smallest, innermost anterior petals (keel). This specific arrangement is known as vexillary aestivation.
    b. Ascending Imbricate: Here, the posterior petal is completely overlapped by other petals, making it the innermost one. This is seen in plants like Cassia and Bauhinia.
    c. Quincuncial: This is a modification of imbricate aestivation where, out of five petals, two are completely internal (overlapped on both sides), two are completely external (overlapping on both sides), and the fifth petal has one margin internal and the other external. Murraya is an example of this.
In simple words: Imbricate aestivation means petals or sepals overlap in a way that isn't regular or twisted. Sometimes one petal is fully inside, one fully outside, and others are partly in and out. Vexillary (like in peas) and quincuncial (like in Murraya) are examples of this.

🎯 Exam Tip: Pay close attention to the specific patterns of overlap in each aestivation type, as this is the key distinguishing feature. Use mnemonic devices or draw quick sketches during revision.

 

Question 4. What do you mean by androphore? Explain it.
Answer: An androphore is a stalk-like elongation of the thalamus (the part of the flower to which the floral organs are attached) that occurs specifically between the corolla (petals) and the androecium (stamens). This extended internode elevates the stamens, a feature notably observed in flowers like the Passion flower.
In simple words: An androphore is like a small stem that grows between the petals and the male parts of a flower, making the stamens stand taller, as seen in the Passion flower.

🎯 Exam Tip: Identify the specific position of the androphore between the corolla and androecium, as distinct from a gynophore (between androecium and gynoecium).

 

Question 5. What is Bract? Write names of its type.
Answer: A bract is a small, modified leaf-like structure found at the base of a flower or a cluster of flowers. These can sometimes be colorful and serve to protect or attract pollinators. Smaller, leaf-like structures on the pedicel (flower stalk), distinct from the main bract, are called bracteoles. When bracteoles form a whorl around the base of the calyx, they are known as an epicalyx, a characteristic feature of the Malvaceae family, which includes the China rose.
In simple words: A bract is a special leaf found at the bottom of a flower. Smaller ones on the flower stem are bracteoles, and if many bracteoles form a ring, it's called an epicalyx, like in the China rose family.

🎯 Exam Tip: Bracts and bracteoles are important taxonomic features; observe their presence, position, and form when identifying plant species.

 

Question 6. Explain cohesion of stamens.
Answer: Cohesion of stamens refers to the fusion or union of stamens among themselves. While stamens can be free from each other (a condition called polyandrous), they often fuse in various ways, categorized into five main types:
1.  Monoadelphous: All the filaments of the stamens are united into a single bundle or tube, but their anthers remain free. Examples include China rose, Althaea, cotton plant, and lady's finger.
In simple words: All stamen stalks join into one group, but their pollen tops are separate.

2.  Diadelphous: The filaments of the stamens are united into two distinct bundles or groups, while their anthers remain separate. This arrangement is typical in pea flowers.
In simple words: Stamen stalks join into two separate groups, with individual pollen tops.

3.  Polydelphous: The filaments of all stamens are fused into more than two bundles or groups, while their anthers remain distinct. This condition is observed in citrus plants.
In simple words: Stamen stalks are fused into many bundles, but their pollen tops are separate.

4.  Syngenesious (Synantherous): In this case, the filaments of the stamens are free, but their anthers are fused together, forming a tube around the style. Sunflowers and Tridax are common examples.
In simple words: The pollen tops of stamens are joined together, but their stalks are separate.

5.  Synandrous: Both the filaments and the anthers of the stamens are completely fused, forming a solid, complex structure. This condition is seen in plants like Cucurbita.
In simple words: Both the stalks and the pollen tops of the stamens are completely fused into one solid unit.

🎯 Exam Tip: When describing cohesion of stamens, clearly state whether filaments, anthers, or both are fused, and provide a relevant example for each type.

 

Question 7. Describe the features and representation of the mother axis in a floral diagram.
Answer: A floral diagram is a highly illustrative representation that shows most features of a flower and its parts, including:
    *  Symmetry: Whether the flower is regular (actinomorphic) or irregular (zygomorphic).
    *  Sexuality: If it's unisexual or bisexual.
    *  Number of floral parts: The count of sepals, petals, stamens, and carpels.
    *  Cohesion and adhesion: How floral parts are joined (cohesion) or attached to different parts (adhesion).
    *  Aestivation: The arrangement of sepals or petals in the bud stage.
    *  Anther details: Number of anthers and whether they are monothecous (one lobe) or dithecous (two lobes).
    *  Gynoecium details: Number of carpels, locules (chambers in the ovary), and placentation type.
The mother axis, which is the main stem upon which flowers are borne, is represented by a small black spot or dot at the top of the floral diagram. When flowers grow laterally on this axis, the side of the flower facing the mother axis is considered the posterior side, while the side away from it (towards the bract) is the anterior side. This helps in understanding the orientation of the flower.
In simple words: A floral diagram is a map of a flower showing its shape, how many parts it has, and how they are arranged. The main stem from which the flower grows, called the mother axis, is shown as a dot at the top of the diagram.

🎯 Exam Tip: Focus on understanding how each floral feature is represented symbolically in a floral diagram, particularly the position of the mother axis and bract.

 

Question 8. Differentiate regular flower with irregular type of flower.
Answer:
Regular Flower (Actinomorphic): A regular flower can be divided into two equal halves along any plane that passes through its central axis, much like a radial pattern. All the whorls (sepals, petals, stamens, carpels) have the same number of members, and these members are similar in shape and arranged at equal distances. An example is the mustard flower.
Irregular Flower (Zygomorphic): An irregular flower can only be divided into two equal halves along one specific plane, typically a vertical one. The floral whorls or their members are unequal in size, shape, or number. The pea flower is a classic example of an irregular flower.
In simple words: A regular flower can be cut in half in many ways and still look the same on both sides, like a star. An irregular flower can only be cut in half one way to be symmetrical, like a butterfly.

🎯 Exam Tip: The key difference lies in the number of planes of symmetry: multiple for regular (radial) and only one for irregular (bilateral).

 

Question 9. Explain bracteate flower and ebracteate flower with suitable examples.
Answer:
Bracteate Flower: A flower is called bracteate if it has a bract, which is a small, leaf-like structure, at the base of its pedicel (flower stalk). The bract may protect the young flower or provide other functions. Many plants, such as bougainvillea, have bracteate flowers, where the bracts are often brightly colored and mistaken for petals.
Ebracteate Flower: Conversely, a flower is termed ebracteate if it lacks a bract at the base of its pedicel. These flowers grow directly from the stem without any accompanying leaf-like structures. Most members of the Brassicaceae family (e.g., mustard) typically have ebracteate flowers.
In simple words: A bracteate flower has a small, leaf-like part called a bract at its base, while an ebracteate flower does not have this bract.

🎯 Exam Tip: The presence or absence of bracts is a simple yet important characteristic used in botanical descriptions and classification.

 

Question 10. Explain position of stamens on the basis of cohesion of stamens in China rose and pea flower with labeled diagram.
Answer: The cohesion of stamens refers to the fusion of filaments or anthers within a flower. In China rose and pea flowers, distinct types of stamen cohesion are observed:
1.  Monoadelphous (China rose): In China rose, the filaments of all stamens are fused together to form a single tube or bundle around the style, while their anthers remain separate and free. This single bundle is characteristic of the monoadelphous condition, making it easy to identify.
In simple words: In China rose, all the stamen stalks are joined into one group, but their pollen tops stay separate.

2.  Diadelphous (Pea flower): In pea flowers, the filaments of the stamens are fused into two distinct bundles. Typically, nine stamens form one bundle, and the tenth stamen remains free, forming the second bundle. Their anthers are always separate. This arrangement allows for efficient pollen transfer.
In simple words: In pea flowers, the stamen stalks are joined into two groups, often nine in one group and one alone in the other.

🎯 Exam Tip: Clearly state the specific fusion pattern for each example (single bundle vs. two bundles) and how it affects the anthers.

RBSE Class 11 Biology Chapter 21 Essay Type Questions

 

Question 1. Explain hyogynous, epigynous and perigynous flowers with labeled diagram.
Answer: The position of the ovary relative to the other floral parts (calyx, corolla, and androecium) on the thalamus determines whether a flower is hypogynous, perigynous, or epigynous. This classification is crucial for understanding floral morphology:
1.  Hypogynous Flower: In a hypogynous flower, the gynoecium (ovary) occupies the highest position on the thalamus, meaning it is superior. The other floral parts—sepals, petals, and stamens—are attached below the ovary. This arrangement ensures the ovary is well-protected and prominently positioned for fertilization. Examples include China rose, mustard, and brinjal.
In simple words: In a hypogynous flower, the female part (ovary) sits on top, and all other flower parts are attached below it.
2.  Perigynous Flower: A perigynous flower has a cup-shaped or saucer-shaped thalamus, with the ovary situated in the center. The sepals, petals, and stamens are attached around the rim of this cup, appearing to be at almost the same level as the ovary. In this case, the ovary is said to be half-inferior. Examples include plum, rose, and peach.
In simple words: In a perigynous flower, the ovary sits in the middle, and all other flower parts are attached around it on a cup-like base.
3.  Epigynous Flower: In an epigynous flower, the margin of the thalamus grows upward, completely enclosing the ovary and fusing with its wall. The sepals, petals, and stamens then arise from the top of the ovary. This makes the ovary appear inferior, meaning it is positioned below all other floral parts. Guava, cucumber, and the ray florets of sunflower are examples.
In simple words: In an epigynous flower, the ovary is hidden below all other flower parts, which grow out from the top of the ovary.

🎯 Exam Tip: Focus on the relative position of the ovary (superior, half-inferior, inferior) with respect to the attachment point of other floral whorls on the thalamus.

 

Question 3. What do you mean by placentation? Explain its types with labeled diagram and examples.
Answer: Placentation is the arrangement of ovules inside the ovary of a flower. This arrangement is important for classifying plant families and ensuring successful seed development. There are several main types of placentation:
(i) Marginal Placentation: This is the simplest type, found in monocarpellary (single carpel) ovaries that are unilocular (one chamber). The placenta develops along the fused ventral suture of the carpel, forming a ridge, and the ovules are arranged in two rows on this ridge. Examples include pea, bean, and gram.
In simple words: Ovules grow in two lines along one edge of the ovary, like peas in a pod.

(ii) Axile Placentation: This type occurs in syncarpous pistils where the ovary is partitioned into two or more chambers (multilocular) by septa. The ovules are attached to a centrally placed axis that forms at the junction of these septa. Examples include China rose, tomato, and onion.
In simple words: Ovules are attached to a central column in an ovary that has many separate sections.

(iii) Parietal Placentation: In this arrangement, the ovary is unilocular (single-chambered) but composed of two or more fused carpels. The ovules develop on the inner walls of the ovary or on peripheral placentae. The ovary does not have partitions. Examples include mustard and poppy.
In simple words: Ovules grow on the outer walls inside a single-chambered ovary.

(iv) Free Central Placentation: Here, the ovary is unilocular, and the ovules are borne on a central axis that rises from the base of the ovary. Crucially, there are no septa (partitions) to divide the ovary into chambers. Examples include Primula and Dianthus.
In simple words: Ovules are attached to a central stalk in the middle of a single-chambered ovary, with no walls separating them.

(v) Basal Placentation: In this type, the ovary is monocarpellary and unilocular, with a single ovule attached at the very base of the ovary. This simple arrangement ensures that a single large seed develops efficiently. Examples include sunflower and marigold.
In simple words: Only one ovule grows at the very bottom of the ovary.

(vi) Superficial Placentation: This type is characterized by ovules being borne on the entire inner surface of the partition walls within a multilocular ovary. It is similar to axile placentation but with more extensive ovule attachment surfaces. This is seen in aquatic plants like Nymphaea (water lily).
In simple words: Ovules grow all over the inner walls of an ovary that has many chambers.

🎯 Exam Tip: When explaining placentation types, always include the nature of the ovary (locules, carpels), the arrangement of ovules, and a clear example for full marks.

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