RBSE Solutions Class 11 Biology Chapter 20 Inflorescence

RBSE Class 11 Biology Chapter 20 Multiple Choice Objective Questions

Question 1. In Racemose inflorescence growth of floral axis is
(a) Limited
(b) Continous
(c) Unlimited
(d) Discontinuous
Answer: (b) Continous
In simple words: In a racemose inflorescence, the main stalk of the flowers keeps growing without stopping. This allows new flowers to form continuously along its length.

🎯 Exam Tip: Remember that "continuous" growth is the key feature of racemose inflorescence, contrasting with determinate growth in cymose types.

Question 2. Compound raceme is
(a) Mulberry
(b) Wheat
(c) Amaltas
(d) Rye
Answer: (c) Amaltas
In simple words: The Amaltas tree, also known as the Golden Shower tree, is an example of a plant that has compound racemes. This means its main flower stalk branches out, and each branch also carries a cluster of flowers.

🎯 Exam Tip: When identifying compound inflorescences, look for branching on the main floral axis, where each branch itself acts like a simple inflorescence.

Question 4. Colecassia is example of:
(a) Spadix
(b) Spike
(c) Catkin
(d) Spikelet
Answer: (a) Spadix
In simple words: Colecassia, a plant known for its edible parts, shows a spadix type of inflorescence. This flower structure has many small flowers packed onto a thick, fleshy stalk, which is usually covered by a large leaf-like part called a spathe.

🎯 Exam Tip: Spadix inflorescences are characterized by their fleshy axis and the presence of a spathe, which helps protect the dense cluster of small flowers.

Question 5. Which of the following is an example of Corymb inflorescence?
(a) Coriander
(b) Fennel
(c) Fenugreek
(d) Iberis
Answer: (d) Iberis
In simple words: Iberis, often called Candytuft, is a plant that has corymb inflorescence. In this arrangement, the flowers are set up so that their top parts are all at about the same level, making a flat or slightly rounded cluster. The outer flowers have longer stalks to reach this height.

🎯 Exam Tip: For corymb inflorescences, visualize a flat-topped cluster of flowers where the outermost ones have longer stalks to achieve a uniform height.

RBSE Class 11 Biology Chapter 20 Very Short Answer Questions

Question 1. Name the plant which has Umbel inflorescence.
Answer: Plants such as Allium cepa (onion) and Hydrocotyle asiatica are classic examples of those that exhibit an umbel inflorescence. In this type, all the individual flower stalks, which are roughly the same length, grow from a single point on the main stem, spreading out like the spokes of an umbrella.
In simple words: Onion plants (Allium cepa) and Hydrocotyle asiatica have umbel flowers, which look like a small umbrella with all flower stems starting from one spot.

🎯 Exam Tip: Remember the "umbrella-like" shape as a key characteristic to identify umbel inflorescences.

Question 2. How many types of florets are found in Capitullum type of inflorescence? Give examples of Capitullum type of inflorescence.
Answer: In a capitulum type of inflorescence, two main types of small flowers, called florets, are typically found: ray florets, which are usually larger and found around the edge, and disc florets, which are smaller and located in the center. Plants such as sunflower and marigold, which belong to the Compositae (or Asteraceae) family, are excellent examples of this inflorescence type.
In simple words: Capitulum flowers, like sunflowers and marigolds, usually have two kinds of small flowers: ray flowers on the outside and disc flowers in the middle.

🎯 Exam Tip: When describing capitulum, always mention both ray and disc florets and note their arrangement and size differences.

Question 4. What are the differences between racemose and cymose type of inflorescence?
Answer: The main differences between racemose and cymose inflorescences lie in how their main floral axis grows and how new flowers develop and mature.

In simple words: Racemose flowers keep growing taller and making new flowers from the bottom up, so the main stalk never stops. Cymose flowers stop growing taller after the first flower appears, and new flowers grow from the sides.

🎯 Exam Tip: Focus on whether the main axis growth is "determinate" (ends in a flower) or "indeterminate" (continues to grow) to distinguish between cymose and racemose types.

Question 5. Differentiate Scorpioid with helicoids inflorescence.
Answer: Scorpioid and helicoid inflorescences are both types of monochasial (or uniparous) cymes, meaning each main axis produces only one lateral branch. Their primary difference lies in the pattern of these lateral branches:

In simple words: Scorpioid cymes make new side flowers in a zig-zag line, switching from left to right. Helicoid cymes make all new side flowers on the same side, creating a spiral shape.

🎯 Exam Tip: Remember that "Scorpioid" implies a scorpion's tail (zig-zag) and "Helicoid" implies a helix (spiral) to easily recall their distinct branching patterns.

RBSE Class 11 Biology Chapter 20 Short Answer Questions

Question 1. How many types are of Monochasial inflorescence? Give example of each.
Answer: Monochasial inflorescence, also known as uniparous cyme, is a type of cymose inflorescence where the main axis ends in a flower and produces only one lateral branch, which also ends in a flower. Depending on how these single lateral branches develop, uniparous cymes are divided into two main types:
1. Scorpioid cyme (cincinnus or rhipidium): In this type, the successive lateral branches develop on alternate sides of the main axis, creating a distinct zig-zag pattern. Good examples include Ranunculus bulbosus and Heliotropium.
2. Helicoid cyme (drepanium or bostryx): Here, the lateral branches consistently develop on the same side of the main axis, forming a coiled or helix-like structure. Plants like Begonia and Juncus show this type of inflorescence.
In simple words: Monochasial inflorescence has two types: Scorpioid, where side branches grow in a zig-zag way; and Helicoid, where side branches all grow on one side, forming a spiral.

🎯 Exam Tip: When differentiating monochasial cymes, visualize the branching: a zig-zag for scorpioid and a coil for helicoid, along with their representative plant examples.

Question 2. What are the differences between Dichasial and Multichasial inflorescence? Give examples of each.
Answer: Dichasial and Multichasial inflorescences are both types of cymose flower arrangements, characterized by the main floral axis ending in a flower. They differ in the number of lateral branches produced below this terminal flower:
1. Dichasial (or Biparous) Cyme: In this arrangement, the central main stem terminates in a flower, and two lateral branches develop simultaneously below it. Each of these two lateral branches also ends in a flower, and they can further branch in a similar dichotomous pattern. Examples include Ixora, Saponaria, and Dianthus.

2. Multichasial (or Polychasial) Cyme: In this type, the main axis also ends in a flower, but many lateral branches develop below it, instead of just two. Each of these numerous lateral branches also terminates in a flower. This inflorescence can sometimes look like an umbel, but it's distinguished because the central flower opens first. Plants like Calotropis (madar) and Viburnum are common examples.
In simple words: Dichasial flowers have one main flower and exactly two side branches that also end in flowers. Multichasial flowers have one main flower and many side branches, all ending in flowers.

🎯 Exam Tip: The key difference is the number of lateral branches: "Di" for two (dichasial) and "Multi" for many (multichasial). Always include plant examples for clarity.

Question 3. Differentiate Catkin and Spadix with example.
Answer: Catkin and Spadix are both specialized types of spike inflorescences, but they possess distinct structural features:

In simple words: A catkin is a long, hanging flower spike with simple, single-sex flowers that usually fall off all at once. A spadix is a thick, fleshy flower spike with many tiny flowers, often covered by a large leaf-like bract called a spathe.

🎯 Exam Tip: The key differentiators are the shape (long and pendulous vs. thick and fleshy), the type of flowers (unisexual in catkin), and the presence of a spathe in spadix.

Question 4. Differentiate Corymb and Umbel with example
Answer: Corymb and Umbel are both types of racemose inflorescences where the flowers appear to form a flat-topped cluster, but their underlying structures and development patterns are distinct:

In simple words: In a corymb, flowers appear flat-topped because lower flowers have longer stems than upper ones. In an umbel, all flower stems grow from the same point and are about the same length, spreading out like an umbrella.

🎯 Exam Tip: Focus on how the pedicels (flower stalks) vary in length or origin point to differentiate between corymb and umbel inflorescences.

Question 5. Differentiate Hypanthodium and Spadix with example
Answer: Hypanthodium and Spadix are both specialized inflorescence types, but they are very different in their structure and the arrangement of their flowers:

In simple words: Hypanthodium flowers grow hidden inside a special cup-like structure, with male flowers near the opening and female flowers at the bottom. A spadix is a thick flower stalk covered by a large leaf-like part, with tiny flowers packed tightly on it.

🎯 Exam Tip: The defining feature of hypanthodium is its flask-shaped or cup-like receptacle, while spadix is identified by its fleshy axis and surrounding spathe.

RBSE Class 11 Biology Chapter 20 Essay Type Questions

Question 1. Define inflorescence. Explain various types of racemose and cymose type of inflorescence with labeled diagram.
Answer:

Inflorescence:
Inflorescence refers to the specific way flowers develop and are arranged on the main stem or floral axis of a plant. The primary stalk that supports the entire flower cluster is called the peduncle. The individual stalks of single flowers within the cluster are known as pedicels, and flowers possessing these stalks are termed pedicellate. Conversely, if a flower lacks a pedicel and is directly attached to the main axis, it is called sessile. In solitary flowers, there is no distinction between the peduncle and the pedicel, as the single flower is borne directly on the stem. This arrangement helps in efficient pollination and seed dispersal.

Types of Inflorescences:
Inflorescences are broadly categorized into two main types based on the growth pattern of the floral axis: Racemose (indeterminate) and Cymose (determinate).

1. Racemose or Indeterminate Inflorescence:
In this type, the main floral axis continues to grow indefinitely and does not terminate in a flower. New flowers are formed laterally in an acropetal succession, meaning the older or outer flowers are located at the bottom or periphery, while the younger or inner flowers are closer to the apex. This allows the plant to produce flowers over a longer period. There are several forms of racemose inflorescence:

• Raceme: The inflorescence axis is simple and elongated. It bears stalked (pedicellate), bisexual, acropetal flowers. Examples include Larkspur, Brassica (Mustard), Delphinium, and Crotalaria.

• Panicle: This is a modified raceme, often referred to as a compound raceme. The main inflorescence axis (rachis) is branched, and these lateral branches bear additional racemes of flowers. Examples include Amaltas, Gold Mohur, and Yucca.

• Spike: This resembles a raceme, but the individual flowers are sessile (without stalks) and are attached directly to a long peduncle. Flowers develop acropetally. Examples include Adhatoda, Achyranthes, and Piper longum.

• Compound Spike (Spikelet or Locusta): In this variation, the inflorescence axis is branched, and the flowers are arranged in a spike-like manner on these branches. In grasses, the fundamental unit of a compound inflorescence is called a spikelet, which consists of a cluster of one or more flowers and their associated bracts. An example is Amaranthus.

• Catkin (amentum): This is a type of spike inflorescence characterized by sessile, unisexual flowers (either male or female). The inflorescence axis is typically long and pendulous (hanging). A key feature is that the entire catkin often drops off as a single unit after flowering or fruiting. Examples include Morus (Mulberry), Salix (Willow), and Acalypha.

• Corymb: In this racemose inflorescence, the main axis is typically shortened. The flowers possess unequal stalks (pedicels); the lower flowers have significantly longer pedicels than the upper ones. This arrangement allows all the flowers to reach approximately the same horizontal level, forming a flat-topped or slightly convex cluster. An example is Iberis amara (Candytuft) or Prunus cerasus (Cherry).

• Umbel: In this inflorescence, the axis is greatly shortened. All the individual bisexual flowers are borne on pedicels of roughly the same length. These pedicels all arise from a single point at the apex of the peduncle, spreading outwards like the ribs of an umbrella. At the base of these flower stalks, there is typically a whorl of bracts forming an involucre. Examples include Allium cepa (Onion) and Hydrocotyle asiatica.

• Compound Umbel: This is a modified umbel where the inflorescence axis is branched. The primary branches arise from a single point, each bearing smaller umbels called umbellules. Bracts at the base of the primary umbel are called an involucre, and bracts at the base of the umbellules are called involucel. Examples include Coriander (Daucus carota), Fennel (Foeniculum), and other members of the Umbelliferae family.

• Capitulum or Head (Anthodium): In this type, the inflorescence axis is flattened into a more or less convex disc, called the receptacle. A large number of small, sessile flowers (florets) are densely packed on this receptacle in a centripetal manner (older flowers at the periphery, younger at the center). The centrally placed florets are known as Disc florets, while the peripheral ones are Ray florets. The entire inflorescence is surrounded by one or more whorls of bracts, forming an involucre. Examples include Sunflower and Marigold (all members of Compositae family).

• Capitate: In this type, numerous sessile flowers arise from a suppressed (very short) axis, forming a globose (spherical) structure. It differs from a capitulum mainly by the absence of a flattened receptacle. Examples include Acacia and Mimosa.

2. Cymose or Determinate Inflorescence:
In cymose inflorescence, the growth of the main floral axis is checked (limited) because it terminates in a flower. This means the central flower is the oldest. Subsequent lateral branches develop below this terminal flower, and they too eventually terminate in a flower. Flowers develop in a basipetal order (older at the top) and open in a centrifugal order (from center outwards). There are several types of cymose inflorescence:

• Solitary: As the name suggests, only a single flower is present on the floral axis. This can be:

1. Solitary axillary: The single flower arises from the axil of a leaf. Example: China rose.
2. Solitary terminal: The single flower develops at the very apex of the main stem. Example: Rose, Argemone.

• Uniparous or Monochasial Cyme: In this cymose inflorescence, the main axis terminates into a flower, and only one lateral branch develops below it, which also ends in a flower. Depending on the sequence and direction of lateral branching, it is further divided into two types:

1. Scorpioid cyme (cincinnus or rhipidium): A uniparous cyme in which the successive lateral branches develop alternately on opposite sides, creating a characteristic zig-zag pattern. Examples include Ranunculus bulbosus and Heliotropium.
2. Helicoid cyme (drepanium or bostryx): A uniparous cyme in which the lateral branches consistently develop on the same side, forming a coiled or helix-like structure. Examples include Begonia and Juncus.

• Biparous or Dichasial Cyme: In this type of cymose inflorescence, the main axis terminates into a flower, and then produces two lateral branches directly below it. Each of these two lateral branches also ends in a flower. This branching can continue, leading to further pairs of branches. Examples include Ixora, Saponaria, and Dianthus.

• Multiparous or Polychasial Cyme: In this cymose inflorescence, the main axis terminates in a flower, but many lateral branches (daughter axes) are produced below it, each of which also ends in a flower. This arrangement can visually resemble an umbel, but it is distinct because the central flower opens first. Examples include Calotropis (madar) and Viburnum.
In simple words: Inflorescence is how flowers are arranged on a plant stem. Racemose flowers keep growing taller and making new flowers from the bottom up. Cymose flowers stop growing taller after the first flower, and new flowers grow from the sides. Examples for each type show different shapes like spikes, umbrellas, or coils.

🎯 Exam Tip: When explaining inflorescence, clearly define the two main types (racemose and cymose) based on axis growth, then provide specific examples and simple diagrams for each sub-type to score full marks.

Question 2. Explain special type of inflorescence with labeled diagrams.
Answer: Special types of inflorescence are unique flower arrangements that differ from the typical racemose and cymose patterns. These specialized arrangements help in specific pollination methods and seed dispersal.
The following are some of these special types of inflorescences:

• 1. Hypanthodium: In this type, the inflorescence is very small and reduced. It has a cup-shaped base called a receptacle, formed by the joining of five bracts (small leaf-like structures). On the inside surface of this cup, there is usually a yellow gland that produces nectar. A single female flower grows from the center of this cup. This female flower is also very small and grows on a long stalk. The male flowers are very small too and grow in a curved, spiral pattern (scorpioid cyme) from the base of each bract. Examples include the Ficus (Banyan) and Fig tree.

• 2. Cyathium: This is a complex inflorescence that often looks like a single flower. The main stalk (peduncle) ends in one female flower. Many male flowers surround this female flower, arranged in a scorpioid cyme pattern. The female flower is simple, consisting of just one three-part pistil (gynoecium). Each male flower has only one stalked stamen. These male flowers grow from the base (axil) of a small, scale-like bract. The entire inflorescence is enclosed within a cup-shaped structure called an involucre, which often has glands. Euphorbia is an example.

• 3. Verticillaster: Examples of plants with this type of inflorescence include Mentha and Leucas.

In simple words: Special inflorescences are unique ways flowers grow together, often forming a specific shape like a cup. These shapes help the plant in important ways, like attracting certain insects to help with pollination.

🎯 Exam Tip: When explaining special inflorescence types, always remember to describe the structure, the arrangement of male and female flowers, and provide clear examples for each type. Labeled diagrams are crucial for full marks.