NCERT Solutions for Class 11 Biology Chapter 3: Plant Kingdom

Algae are primarily classified based on the following criteria:

1. Pigmentation: The type of major photosynthetic pigments present.
   • Chlorophyceae (Green Algae): Chlorophyll a and b.
   • Phaeophyceae (Brown Algae): Chlorophyll a, c, and Fucoxanthin.
   • Rhodophyceae (Red Algae): Chlorophyll a, d, and Phycoerythrin.
2. Stored Food Material: The form in which they store their food.
   • Chlorophyceae: Starch.
   • Phaeophyceae: Mannitol and Laminarin.
   • Rhodophyceae: Floridean Starch.
3. Cell Wall Composition: The chemical makeup of their cell wall.
   • Chlorophyceae: Cellulose (inner layer) and Pectose (outer layer).
   • Phaeophyceae: Cellulose and Algin.
   • Rhodophyceae: Cellulose, Pectin, and Polysulphate esters.
4. Flagellar Organisation: The number and position of flagella on motile cells.
   • Chlorophyceae: 2-8, equal, apical flagella.
   • Phaeophyceae: 2, unequal, lateral flagella.
   • Rhodophyceae: Flagella are absent.

In all these plants, reduction division (meiosis) occurs at the time of spore formation from the diploid sporophyte.

• Liverwort and Moss (Bryophytes): Meiosis occurs inside the capsule of the sporophyte, in the spore mother cells, to produce haploid spores.
• Fern (Pteridophyte): Meiosis occurs in the spore mother cells located within the sporangia, which are often found on sporophylls.
• Gymnosperm: Meiosis occurs in the microsporangia (to form haploid microspores) and megasporangia (to form haploid megaspores).
• Angiosperm: Meiosis occurs in the anther (in microspore mother cells to form pollen grains) and in the ovule (in the megaspore mother cell to form the megaspore).

Three groups of plants that bear archegonia are:

1. Bryophytes (e.g., Mosses, Liverworts)
2. Pteridophytes (e.g., Ferns)
3. Gymnosperms (e.g., *Pinus*, *Cycas*)

Life Cycle of a Bryophyte (Moss):

The dominant phase is the haploid **gametophyte**.

1. Gametophyte Stage: The leafy gametophyte bears the sex organs - **antheridia** (male) and **archegonia** (female).
2. Fertilization: Antherozoids swim in water to reach the archegonium and fuse with the egg to form a diploid **zygote**.
3. Sporophyte Stage: The zygote develops into a multicellular **sporophyte** (foot, seta, capsule), which is dependent on the gametophyte.
4. Spore Formation: Inside the capsule, spore mother cells undergo meiosis to produce haploid **spores**.
5. Germination: Spores germinate to form a juvenile **protonema**, which develops into the mature gametophyte. This life cycle is **Haplo-diplontic**.

• Protonemal cell of a moss: Haploid (n)
• Primary endosperm nucleus in dicot: Triploid (3n)
• Leaf cell of a moss: Haploid (n)
• Prothallus cell of a fern: Haploid (n)
• Gemma cell in *Marchantia*: Haploid (n)
• Meristem cell of monocot: Diploid (2n)
• Ovum of a liverwort: Haploid (n)
• Zygote of a fern: Diploid (2n)

Economic Importance of Algae:

1. Photosynthesis: Perform about 50% of total CO₂ fixation on Earth.
2. Food Source: Species like *Porphyra*, *Laminaria*, and *Sargassum* are edible.
3. Commercial Products: Provide **Agar** (*Gelidium*), **Algin** (brown algae), and **Carrageenan** (red algae) used in food and industries.
4. Supplements: *Chlorella* and *Spirulina* are protein-rich food supplements.

Economic Importance of Gymnosperms:

1. Timber: Conifers like *Pinus* and *Cedrus* provide valuable softwood for construction and paper.
2. Resins: Turpentine and rosin are extracted from conifers.
3. Food: Edible seeds of *Pinus gerardiana* (Chilgoza) and sago from *Cycas*.
4. Medicinal Uses: Ephedrine from *Ephedra* treats respiratory issues.
5. Ornamentals: *Cycas*, *Thuja*, and *Araucaria* are used in gardens.

They are classified separately due to fundamental differences in their reproductive structures:

The name Gymnosperm means "naked seed," while Angiosperm means "enclosed seed," highlighting this key distinction.

Heterospory is the production of two different kinds of spores: smaller microspores (male) and larger megaspores (female).

Significance of Heterospory:

1. Precursor to Seed Habit: It is the most crucial evolutionary step towards the development of seeds.
2. In-situ Germination: The female gametophyte develops and is retained on the parent sporophyte, ensuring better nutrition and protection.
3. Increased Parental Care: This retention provides a secure environment for fertilization and embryo development, increasing the survival chance of the offspring.

(i) Protonema: The juvenile, filamentous gametophyte stage in a moss, developing from a spore. Ex: *Funaria*.

(ii) Antheridium: The multicellular male sex organ in bryophytes and pteridophytes that produces male gametes. Ex: *Marchantia*, *Dryopteris*.

(iii) Archegonium: The multicellular, flask-shaped female sex organ in bryophytes, pteridophytes, and gymnosperms. Ex: *Funaria*, *Ferns*.

(iv) Diplontic: A life cycle where the diploid sporophyte (2n) is the dominant phase. Ex: All seed plants (Gymnosperms, Angiosperms), *Fucus*.

(v) Sporophyll: A modified leaf that bears sporangia. Ex: Cones of *Pinus* consist of sporophylls.

(vi) Isogamy: Sexual reproduction where the fusing gametes are morphologically similar. Ex: *Spirogyra*, *Ulothrix*.

(i) Red algae vs. Brown algae

(ii) Liverworts vs. Moss

(iii) Homosporous vs. Heterosporous pteridophyte

(iv) Syngamy vs. Triple fusion

• (a) *Chlamydomonas*  ->  (iii) Algae
• (b) *Cycas*  ->  (iv) Gymnosperm
• (c) *Selaginella*  ->  (ii) Pteridophyte
• (d) *Sphagnum*  ->  (i) Moss

1. Seed Habit: They bear **naked** seeds, not enclosed within a fruit.
2. Plant Body: The main body is a diploid **sporophyte** (roots, stem, leaves).
3. Roots: Generally have a **tap root system**, some with symbiotic associations (coralloid roots in *Cycas*, mycorrhiza in *Pinus*).
4. Leaves: Well-adapted to extreme conditions (needle-like, thick cuticle, sunken stomata).
5. Reproduction: They are **heterosporous** (microspores and megaspores).
6. Reproductive Structures: Spores are produced in cones or **strobili**.
7. Gametophyte: Gametophytes are dependent and retained on the sporophyte.
8. Pollination: Occurs mainly by **wind (anemophily)**.
9. Fertilization: Water is not required. The endosperm is **haploid (n)**.

The gametophyte (prothallus) of a pteridophyte has two major restrictive requirements:

1. It needs cool, damp, and shady places to grow.
2. It requires a film of water for the transfer of antherozoids (male gametes) to the archegonium for fertilization.

Due to these specific needs, the spread of pteridophytes is limited to regions where these conditions are met.

A frond is a large, often finely divided leaf (a megaphyll) that is characteristic of ferns. It is found in the plant group Pteridophyta.

• Unicellular alga rich in protein: *Chlorella* or *Spirulina*.
• Colonial alga: *Volvox*.

The life cycle of an angiosperm is **diplontic**.

1. The main plant body is the **sporophyte (2n)**, which bears flowers.
2. Inside the anther, meiosis forms haploid **microspores**, which mature into **pollen grains** (male gametophyte).
3. Inside the ovule, meiosis forms a functional haploid megaspore which develops into the **embryo sac** (female gametophyte).
4. **Pollination** transfers pollen to the stigma. The pollen tube grows and carries two male gametes to the embryo sac.
5. **Double Fertilization** occurs:
   • Syngamy: One male gamete (n) + Egg (n) → Zygote (2n).
   • Triple Fusion: Second male gamete (n) + Two Polar Nuclei (n+n) → Primary Endosperm Nucleus (PEN) (3n).
6. The zygote develops into an **embryo**, PEN develops into **endosperm**, the ovule becomes the **seed**, and the ovary becomes the **fruit**.
7. The seed germinates to form a new sporophyte.

(i) Chlorophyceae (Green Algae)

• Major Pigments: Chlorophyll a and b.
• Stored Food: Starch.
• Cell Wall: Cellulose and Pectose.
• Example: *Chlamydomonas*, *Spirogyra*.

(ii) Phaeophyceae (Brown Algae)

• Major Pigments: Chlorophyll a, c, and Fucoxanthin.
• Stored Food: Mannitol and Laminarin.
• Cell Wall: Cellulose and Algin.
• Example: *Laminaria*, *Sargassum*.

(iii) Rhodophyceae (Red Algae)

• Major Pigments: Chlorophyll a, d, and r-phycoerythrin.
• Stored Food: Floridean starch.
• Cell Wall: Cellulose, pectin, and polysulphate esters.
• Example: *Porphyra*, *Gelidium*.

1. Which division of the plant kingdom does this plant likely belong to? Give a reason.

   The plant belongs to **Bryophyta**. The green, velvet-like mat in a moist area, simple body, and a dependent sporophyte (stalk and capsule) on the main gametophyte are key features.

2. What is the ploidy of the main 'leafy plant' and the 'stalk-like structure'?

   The main 'leafy plant' is the gametophyte, so it is **Haploid (n)**. The 'stalk-like structure' is the sporophyte, so it is **Diploid (2n)**.

3. What is the function of the capsule?

   The capsule's function is to produce haploid spores through meiosis and facilitate their dispersal.