Morphology of Flowering PlantsClass 11 Biology NCERT Solutions
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Q1Exercises
How is a pinnately compound leaf different from a palmately compound leaf?
Solution
The difference between a pinnately compound leaf and a palmately compound leaf is based on the arrangement of leaflets on the petiole.
| Feature | Pinnately Compound Leaf | Palmately Compound Leaf |
|---|---|---|
| Arrangement of Leaflets | The leaflets are present on a common axis called the rachis, which is a continuation of the midrib. | The leaflets are attached at a common point at the tip of the petiole, resembling the fingers of a palm. |
| Example | Neem | Silk Cotton |
Q2Exercises
Explain with suitable examples the different types of phyllotaxy.
Solution
Phyllotaxy is the pattern of arrangement of leaves on the stem or a branch. There are three main types of phyllotaxy:
-
Alternate Phyllotaxy: In this type, a single leaf arises at each node in an alternate manner. This arrangement prevents the shading of lower leaves and allows maximum exposure to sunlight.
- Examples: China rose, mustard, and sunflower plants.
-
Opposite Phyllotaxy: In this type, a pair of leaves arise at each node, lying opposite to each other. This creates a symmetrical appearance along the stem.
- Examples: Calotropis and guava plants.
-
Whorled Phyllotaxy: In this type, more than two leaves arise at a node and form a circle or a whorl around the stem. This type is less common.
- Example: Alstonia.
Q3Exercises
Define the following terms:
(a)
aestivation
(b)
placentation
(c)
actinomorphic
(d)
zygomorphic
(e) superior ovary
(f) perigynous flower
(g) epipetalous stamen
Solution
(a) Aestivation: The mode of arrangement of sepals or petals in a floral bud with respect to the other members of the same whorl is known as aestivation.
(b) Placentation: The arrangement of ovules within the ovary is known as placentation. The placenta is the cushion-like tissue to which the ovules are attached.
(c) Actinomorphic: A flower that can be divided into two equal radial halves in any radial plane passing through the centre is said to be actinomorphic. It exhibits radial symmetry. Examples include mustard, datura, and chilli.
(d) Zygomorphic: A flower that can be divided into two similar halves only in one particular vertical plane is called zygomorphic. It exhibits bilateral symmetry. Examples include pea, gulmohar, and bean.
(e) Superior Ovary: In a hypogynous flower, the gynoecium occupies the highest position on the thalamus, while the other floral parts (calyx, corolla, androecium) are situated below it. The ovary in such a flower is described as superior. Examples include mustard and brinjal.
(f) Perigynous Flower: A flower in which the gynoecium is situated in the centre, and the other floral parts are located on the rim of the thalamus almost at the same level. The ovary in this case is said to be half-inferior. Examples include plum, rose, and peach.
(g) Epipetalous Stamen: Stamens that are attached to the petals are called epipetalous. This condition is an example of adhesion between two different floral whorls. An example is the brinjal flower.
Q4Exercises
Differentiate between
(a)
Racemose and cymose inflorescence
(b)
Apocarpous and syncarpous ovary
Solution
(a) Difference between Racemose and Cymose Inflorescence
| Feature | Racemose Inflorescence | Cymose Inflorescence |
|---|---|---|
| Main Axis Growth | The main axis has indeterminate growth and continues to grow. | The main axis has determinate growth and terminates in a flower. |
| Flower Arrangement | Flowers are borne laterally in an acropetal succession (older flowers at the base, younger ones at the apex). | Flowers are borne in a basipetal order (the terminal flower is older, and younger ones develop below it). |
| Example | Mustard | Solanum |
(b) Difference between Apocarpous and Syncarpous Ovary
| Feature | Apocarpous Ovary | Syncarpous Ovary |
|---|---|---|
| Carpel Fusion | The gynoecium is composed of two or more carpels that are free (not fused). | The gynoecium is composed of two or more carpels that are fused together. |
| Example | Lotus, Rose | Mustard, Tomato |
Q5Exercises
Draw the labelled diagram of the following: (i) gram seed (ii) V.S. of maize seed
Solution
Since drawing is not possible, the labeled parts of each seed are described below, based on Figures 5.14 and 5.15 in the textbook.
(i) Gram Seed (Dicotyledonous Seed)
A gram seed is a typical dicot, non-endospermic seed. Its main parts are:
- Seed Coat: The outermost protective layer, which is made of two layers: the outer, hard testa and the inner, thin tegmen.
- Hilum: A scar on the seed coat where the developing seed was attached to the fruit.
- Micropyle: A small pore located just above the hilum, which facilitates the entry of water during germination.
- Embryo: It consists of an embryonal axis and two cotyledons.
- Cotyledons: These are two in number, often fleshy and full of reserve food materials.
- Embryonal Axis: It has two ends: the radicle (which develops into the root) and the plumule (which develops into the shoot).
(ii) V.S. of Maize Seed (Monocotyledonous Seed)
A maize seed is a typical monocot, endospermic seed. Its main parts are:
- Seed Coat and Fruit Wall: They are membranous and fused together to form a single protective layer.
- Endosperm: A bulky tissue that stores food. It is separated from the embryo by a proteinaceous layer called the aleurone layer.
- Embryo: It is small and situated in a groove at one end of the endosperm.
- Scutellum: A single, large, and shield-shaped cotyledon.
- Embryonal Axis: It consists of a plumule and a radicle.
- Coleoptile: A protective sheath that encloses the plumule.
- Coleorhiza: A protective sheath that encloses the radicle.
Q6Exercises
Take one flower of the family Solanaceae and write its semi-technical description. Also draw their floral diagram.
Solution
A semi-technical description of a flower from the family Solanaceae (e.g., Solanum nigrum) is as follows:
Floral Characters:
- Inflorescence: Solitary, axillary or cymose.
- Flower: Bisexual, actinomorphic.
- Calyx: Consists of five sepals, which are united (gamosepalous). They are persistent and show valvate aestivation. Represented as .
- Corolla: Consists of five petals, which are united (gamopetalous). They also show valvate aestivation. Represented as .
- Androecium: Consists of five stamens that are epipetalous (attached to the petals). Represented as .
- Gynoecium: It is bicarpellary (two carpels), obligately placed, and syncarpous (carpels are fused). The ovary is superior and bilocular, with a swollen placenta containing many ovules. The placentation is axile. Represented as .
Floral Formula:
The floral formula for Solanaceae is:
- : Actinomorphic (radial symmetry)
- : Bisexual flower
- : Calyx with 5 fused sepals
- : Corolla with 5 fused petals, and 5 stamens that are epipetalous (adhesion shown by the arc)
- : Gynoecium with 2 fused carpels and a superior ovary
Floral Diagram:
(As described in Figure 5.17 f)
The floral diagram shows:
- The mother axis is represented by a dot at the top.
- The outermost whorl is the calyx, showing five united sepals with valvate aestivation.
- The next whorl is the corolla, showing five united petals with valvate aestivation, alternating with the sepals.
- The androecium consists of five stamens, shown attached to the corolla (epipetalous condition).
- The innermost part is the gynoecium, represented by a central diagram of the transverse section of a superior, bicarpellary, syncarpous ovary with axile placentation.
Q7Exercises
Describe the various types of placentations found in flowering plants.
Solution
Placentation refers to the arrangement of ovules within the ovary. The different types are:
-
Marginal Placentation: The placenta forms a ridge along the ventral suture of the ovary, and the ovules are borne on this ridge, forming two rows. This is characteristic of the family Leguminosae.
- Example: Pea.
-
Axile Placentation: The placenta is axial (in the center), and the ovules are attached to it in a multilocular ovary (an ovary with multiple chambers or locules). The ovary is divided by septa.
- Examples: China rose, tomato, lemon.
-
Parietal Placentation: The ovules develop on the inner wall of the ovary or on its peripheral part. The ovary is one-chambered, but it may become two-chambered due to the formation of a false septum (replum).
- Examples: Mustard, Argemone.
-
Free Central Placentation: The ovules are borne on a central axis, and the septa are absent, making the ovary unilocular.
- Examples: Dianthus, Primrose.
-
Basal Placentation: The placenta develops at the base of the ovary, and a single ovule is attached to it.
- Examples: Sunflower, marigold.
Q8Exercises
What is a flower? Describe the parts of a typical angiosperm flower.
Solution
A flower is the reproductive unit in the angiosperms. It is a modified shoot that is specialized for sexual reproduction. The shoot apical meristem changes to a floral meristem, the axis gets condensed, and the internodes do not elongate.
A typical angiosperm flower consists of four different kinds of whorls arranged successively on the swollen end of the stalk (pedicel), called the thalamus or receptacle.
The four parts (whorls) of a typical flower are:
-
Calyx: This is the outermost whorl of the flower. Its individual members are called sepals. Sepals are typically green and leaf-like, and their primary function is to protect the flower in the bud stage.
-
Corolla: This is the whorl located inside the calyx. Its individual members are called petals. Petals are usually large and brightly coloured to attract insects and other animals for pollination.
-
Androecium: This is the male reproductive part of the flower, located inside the corolla. It is composed of stamens. Each stamen consists of a slender stalk called a filament and a terminal structure called an anther. The anther produces pollen grains.
-
Gynoecium: This is the female reproductive part of the flower and forms the central part of the flower. It is made up of one or more carpels. A carpel consists of three parts: the stigma (receptive tip for pollen), the style (a tube connecting the stigma to the ovary), and the ovary (the enlarged basal part containing ovules).
The calyx and corolla are considered accessory organs, while the androecium and gynoecium are the essential reproductive organs of the flower.
Q9Exercises
Define the term inflorescence. Explain the basis for the different types inflorescence in flowering plants.
Solution
Inflorescence is defined as the arrangement of flowers on the floral axis of a plant.
The basis for classifying inflorescences into different types is whether the apex of the floral axis gets converted into a flower or continues to grow. Based on this, there are two major types of inflorescences:
-
Racemose Inflorescence:
- In this type, the main floral axis (peduncle) continues to grow and does not terminate in a flower. It has indeterminate growth.
- The flowers are borne laterally in an acropetal succession, which means the older flowers are found at the base of the axis, and the younger flowers and buds are found towards the apex.
-
Cymose Inflorescence:
- In this type, the main floral axis terminates in a flower, which limits its growth. It has determinate growth.
- The flowers are borne in a basipetal order, which means the oldest flower is at the apex, and younger flowers develop from the lateral buds below it.
Q10Exercises
Describe the arrangement of floral members in relation to their insertion on thalamus.
Solution
Based on the position of the calyx, corolla, and androecium in respect to the ovary on the thalamus, flowers are described as hypogynous, perigynous, and epigynous.
-
Hypogynous Flower:
- In a hypogynous flower, the gynoecium occupies the highest position on the thalamus, while the other floral parts (calyx, corolla, and androecium) are inserted below the ovary.
- The ovary in such flowers is said to be superior.
- Examples: Mustard, china rose, and brinjal.
-
Perigynous Flower:
- In a perigynous flower, the gynoecium is situated in the centre, and the other floral parts are located on the rim of the thalamus, which is almost at the same level as the ovary. The thalamus forms a cup-like structure around the ovary.
- The ovary here is said to be half-inferior.
- Examples: Plum, rose, and peach.
-
Epigynous Flower:
- In an epigynous flower, the margin of the thalamus grows upward, completely enclosing the ovary and fusing with its wall. The other floral parts (calyx, corolla, and androecium) arise above the ovary.
- The ovary in such flowers is said to be inferior.
- Examples: Guava, cucumber, and the ray florets of sunflower.