Plant Kingdom Class 11 Biology Chapter 3 Notes

Algae

Characteristics of Algae:

Chlorophyll-bearing organisms.
Simple, thalloid (lacking true stems, roots, or leaves) in structure.
Autotrophic, capable of photosynthesis.
Primarily aquatic, found in both fresh water and marine environments.
Can inhabit various other substrates, including moist stones, soils, and wood.
Some algae form symbiotic associations with fungi (lichen) and animals (e.g., on sloth bears).

Diversity in Form and Size:

Algae exhibit significant variability in form and size.
Range from colonial forms (e.g., Volvox) to filamentous forms (e.g., Ulothrix and Spirogyra).
Some marine algae, like kelps, can form massive plant bodies.

Reproduction:

Algae reproduce through vegetative, asexual, and sexual methods.
Vegetative reproduction involves fragmentation, where each fragment develops into a thallus.
Asexual reproduction includes the production of spores, with zoospores being the most common. These are motile and give rise to new plants.
Sexual reproduction occurs through the fusion of two gametes, which can be isogamous (similar in size and flagellated), anisogamous (dissimilar in size), or oogamous (involving a large non-motile female gamete and a smaller motile male gamete). Examples include Ulothrix, Spirogyra, and Volvox.

Significance and Uses:

Algae play a crucial role in carbon dioxide fixation on Earth through photosynthesis.
They increase dissolved oxygen levels in their surroundings due to their photosynthetic activity.
Algae serve as primary producers of energy-rich compounds, forming the foundation of aquatic food chains.
Some species of marine algae, such as Porphyra, Laminaria, and Sargassum, are used as food.
Certain types of algae, particularly brown and red algae, produce hydrocolloids like algin and carrageen, which have commercial applications.
Agar, obtained from Gelidium and Gracilaria algae, is used in microbiological research and in food products like ice-creams and jellies.
Chlorella, a unicellular alga rich in proteins, is used as a food supplement, even by space travelers.
Algae are classified into three main classes: Chlorophyceae (green algae), Phaeophyceae (brown algae), and Rhodophyceae (red algae).

1. Chlorophyceae (Green Algae)

Characteristics of Chlorophyceae:

Commonly referred to as green algae.
Plant body can be unicellular, colonial, or filamentous in structure.
Typically exhibit a grass-green color due to the presence of chlorophyll a and b pigments.
Chlorophyll pigments are localized within distinct chloroplasts.
Chloroplasts can have various shapes, such as discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon-shaped, depending on the species.
Many green algae have one or more storage bodies called pyrenoids within their chloroplasts, which contain protein in addition to starch.
Some green algae store food in the form of oil droplets.
Possess a rigid cell wall composed of an inner layer of cellulose and an outer layer of pectose.

Reproduction:

Vegetative reproduction commonly occurs through fragmentation or the formation of various types of spores.
Asexual reproduction involves the production of flagellated zoospores, typically formed in structures known as zoosporangia.
Sexual reproduction in green algae exhibits significant variation in the type and formation of sex cells.
Sexual reproduction can be isogamous (gametes similar in size and flagellated), anisogamous (gametes dissimilar in size), or oogamous (involving a large, non-motile female gamete and a smaller motile male gamete).

Commonly Found Green Algae:

Chlamydomonas
Volvox
Ulothrix
Spirogyra
Chara

2. Phaeophyceae (Brown Algae)

Characteristics of Phaeophyceae (Brown Algae):

Primarily found in marine habitats.
Exhibit a wide range of variation in size and form.
Variability includes simple branched, filamentous forms like Ectocarpus and large, profusely branched forms such as kelps, which can grow up to 100 meters in height.
Contains a combination of pigments, including chlorophyll a, chlorophyll c, carotenoids, and xanthophylls.
The color of brown algae varies from olive green to shades of brown, depending on the presence of the xanthophyll pigment fucoxanthin.
Food storage occurs in the form of complex carbohydrates, often laminarin or mannitol.
Vegetative cells possess a cellulosic wall, typically covered on the outside by a gelatinous coating of algin.
The protoplast contains plastids, a centrally located vacuole, and a nucleus.
The plant body is anchored to the substrate by a holdfast and typically consists of a stalk (stipe) and leaf-like photosynthetic structures (fronds).

Reproduction:

Vegetative reproduction primarily occurs through fragmentation.
Asexual reproduction in most brown algae is carried out by biflagellate zoospores, which are pear-shaped and possess two laterally attached flagella.
Sexual reproduction can take different forms, including isogamous (gametes similar in size), anisogamous (gametes dissimilar in size), or oogamous (involving a large, non-motile egg and a smaller motile sperm). Union of gametes may occur in water or within the oogonium in oogamous species.
Gametes are pyriform (pear-shaped) and bear two laterally attached flagella.

Commonly Found Brown Algae:

Ectocarpus
Dictyota
Laminaria
Sargassum
Fucus

3.Rhodophyceae (Red Algae)

Characteristics of Rhodophyceae:

Commonly referred to as red algae due to the dominance of the red pigment r-phycoerythrin in their cells.
The majority of red algae are marine, with higher concentrations found in warmer regions.
They are found in both well-lit regions close to the water’s surface and at great depths in the ocean, where there is limited light penetration.
Most red algae have multicellular thalli, and some exhibit complex body organization.
Food is stored in the form of floridean starch, which is structurally similar to amylopectin and glycogen.

Reproduction:

Vegetative reproduction in red algae usually occurs through fragmentation.
Asexual reproduction involves the production of non-motile spores.
Sexual reproduction in red algae is oogamous, involving non-motile gametes.
The sexual reproduction process is accompanied by complex post-fertilization developments.

Commonly Found Red Algae:

Polysiphonia
Porphyra
Gracilaria
Gelidium

Bryophytes

Characteristics of Bryophytes:

Bryophytes comprise mosses and liverworts commonly found in moist, shaded areas, especially in hilly regions.
They are often referred to as the “amphibians of the plant kingdom” because they can grow in soil but rely on water for their sexual reproduction.
Typically found in damp, humid, and shaded environments.
Play a crucial role in plant succession on bare rocks and soil.

Plant Body and Reproduction:

The plant body of bryophytes is more differentiated than that of algae, appearing thallus-like and can be prostrate or erect.
Bryophytes lack true roots, stems, or leaves, but they may possess root-like, leaf-like, or stem-like structures.
The primary plant body of bryophytes is haploid and produces gametes, making it the gametophyte.
The sex organs in bryophytes are multicellular, with the male sex organ called antheridium, which produces biflagellate antherozoids.
The female sex organ, the archegonium, is flask-shaped and produces a single egg. Fertilization occurs when an antherozoid fuses with the egg to form a zygote.
Zygotes do not immediately undergo reduction division (meiosis); instead, they develop into a multicellular structure called the sporophyte.
The sporophyte remains attached to the photosynthetic gametophyte and derives nourishment from it.
Some cells of the sporophyte undergo meiosis to produce haploid spores, which germinate to form new gametophytes.

Economic and Ecological Significance:

Bryophytes, in general, have limited economic importance. Some mosses provide food for herbaceous mammals, birds, and other animals.
Sphagnum mosses, for example, provide peat, which has been historically used as fuel and packing material for trans-shipment of living materials due to their water-holding capacity.
Mosses, along with lichens, are the first organisms to colonize rocks, making them ecologically important. They help decompose rocks, creating a suitable substrate for the growth of higher plants.
Mosses form dense mats on the soil, reducing the impact of falling rain and preventing soil erosion.

Classification of Bryophytes:

Bryophytes are divided into two main groups: liverworts and mosses.

1. Liverworts

Characteristics of Liverworts:

Liverworts are commonly found in moist, shady habitats, such as the banks of streams, marshy areas, damp soil, tree bark, and deep in the woods.
The plant body of a liverwort is typically thalloid, as seen in examples like Marchantia.
The thallus is dorsiventral (with distinct upper and lower sides) and closely appressed to the substrate.
Leafy liverworts have small leaf-like appendages arranged in two rows on stem-like structures.

Reproduction:

Asexual reproduction in liverworts occurs through the fragmentation of thalli or through specialized structures known as gemmae (singular: gemma).
Gemmae are green, multicellular, asexual buds that develop in small receptacles called gemma cups, located on the thalli. These gemmae detach from the parent body and germinate to produce new individuals.
During sexual reproduction, liverworts produce male and female sex organs, which can be found on the same thallus or on different ones.
The sporophyte, which is part of the liverwort life cycle, consists of three parts: a foot, seta, and capsule.
After meiosis, spores are produced within the capsule.
These spores germinate to give rise to free-living gametophytes, thus completing the life cycle.

2. Mosses

Characteristics of Mosses:

The dominant stage in the life cycle of mosses is the gametophyte, which consists of two stages.
The first stage is the protonema, which develops directly from a spore. It is a creeping, green, branched, and often filamentous structure.
The second stage is the leafy stage, which originates from the secondary protonema as a lateral bud. It consists of upright, slender axes with spirally arranged leaves.
Mosses are anchored to the soil through multicellular and branched structures called rhizoids. The leafy stage bears the sex organs.

Reproduction:

Vegetative reproduction in mosses occurs through fragmentation and budding in the secondary protonema.
In sexual reproduction, the sex organs, antheridia (male) and archegonia (female), are produced at the apex of the leafy shoots.
After fertilization, the zygote develops into a sporophyte, which includes three parts: a foot, seta, and capsule. The sporophyte in mosses is more elaborate than that in liverworts.
The capsule contains spores, which are formed after meiosis.
Mosses have an intricate mechanism for spore dispersal.

Common Examples of Mosses:

Funaria
Polytrichum
Sphagnum

Pteridophytes

Characteristics of Pteridophytes:

Pteridophytes encompass horsetails and ferns and are used for medicinal purposes and as soil stabilizers. They are also commonly grown as ornamental plants.
Evolutionarily, pteridophytes represent the first terrestrial plants to possess vascular tissues, namely xylem and phloem.
They are typically found in cool, damp, and shady environments, although some species can thrive in sandy soil conditions.

Life Cycle and Plant Body:

In pteridophytes, the dominant phase in the life cycle is the sporophyte, which is differentiated into true root, stem, and leaves.
These organs possess well-differentiated vascular tissues.
The leaves in pteridophytes can be small (microphylls) as seen in Selaginella or large (macrophylls) as in ferns.
Sporangia, responsible for spore production, are located on the sporophyte and are subtended by leaf-like appendages called sporophylls.
In some cases, sporophylls may form distinct compact structures known as strobili or cones (e.g., Selaginella, Equisetum).
Spores are produced by meiosis in spore mother cells within the sporangia.

Gametophyte and Reproduction:

Spores germinate to produce inconspicuous, small but multicellular, free-living, mostly photosynthetic thalloid gametophytes called prothallus.
Gametophytes require cool, damp, shady environments to grow due to their need for water for fertilization.
Gametophytes bear male and female sex organs, known as antheridia and archegonia, respectively.
Water is essential for the transfer of antherozoids (male gametes) from antheridia to the archegonium, where they fuse with the egg to form a zygote.
The zygote develops into a multicellular and well-differentiated sporophyte, which represents the dominant phase of pteridophytes.

Spore Types:

In most pteridophytes, all the spores are of a single kind, making them homosporous.
Some genera, like Selaginella and Salvinia, produce two types of spores: macrospores (large) and microspores (small), making them heterosporous.
The megaspores and microspores germinate to give rise to female and male gametophytes, respectively.
In heterosporous pteridophytes, female gametophytes are retained on the parent sporophytes for varying durations, and zygotes develop into young embryos within the female gametophytes. This is a precursor to the seed habit, considered an important step in plant evolution.

Classification of Pteridophytes:

Pteridophytes are divided into four classes: Psilopsida (e.g., Psilotum), Lycopsida (e.g., Selaginella, Lycopodium), Sphenopsida (e.g., Equisetum), and Pteropsida (e.g., Dryopteris, Pteris, Adiantum).

Gymnosperms

Characteristics of Gymnosperms:

Gymnosperms are plants in which ovules are not enclosed by an ovary wall and remain exposed both before and after fertilization.
The seeds of gymnosperms are not covered and are considered “naked.”
Gymnosperms include medium-sized trees, tall trees, and shrubs. Some species, like the giant redwood tree Sequoia, are among the tallest trees.
Their roots are typically tap roots, but some genera have fungal associations in the form of mycorrhiza (e.g., Pinus), while others (e.g., Cycas) have specialized roots called coralloid roots associated with N2-fixing cyanobacteria.
Stems can be unbranched (e.g., Cycas) or branched (e.g., Pinus, Cedrus).
The leaves may be simple or compound and are well-adapted to withstand extremes of temperature, humidity, and wind. In conifers, needle-like leaves reduce surface area, and their thick cuticles and sunken stomata reduce water loss.

Reproduction:

Gymnosperms are heterosporous, meaning they produce haploid microspores and megaspores.
Microspores and megaspores are produced within sporangia borne on sporophylls arranged spirally along an axis, forming strobili or cones.
Strobili bearing microsporophylls and microsporangia are called microsporangiate or male strobili.
Microspores develop into a highly reduced male gametophyte, known as a pollen grain, which is confined to a limited number of cells.
The development of pollen grains takes place within the microsporangia.
Cones bearing megasporophylls with ovules or megasporangia are called macrosporangiate or female strobili.
Male and female cones or strobili may be borne on the same tree (e.g., Pinus), but in Cycas, male cones and megasporophylls are on different trees.
The megaspore mother cell is differentiated from one of the cells of the nucellus, forming an ovule.
The ovules are borne on megasporophylls that may cluster to form female cones.
The megaspore mother cell undergoes meiosis to form four megaspores, with one of them developing into a multicellular female gametophyte.
The female gametophyte bears two or more archegonia or female sex organs and is retained within the megasporangium.
Unlike bryophytes and pteridophytes, in gymnosperms, the male and female gametophytes do not have an independent free-living existence. They remain within the sporangia retained on the sporophytes.
Pollen grains are released from the microsporangium, carried by air currents, and come in contact with the openings of ovules borne on megasporophylls.
The pollen tube, carrying the male gametes, grows towards the archegonia in the ovules and discharges their contents near the mouth of the archegonia.
Following fertilization, the zygote develops into an embryo, and the ovules develop into seeds, which are not covered.

Angiosperms (Flowering Plants)

Characteristics of Angiosperms:

Angiosperms, commonly known as flowering plants, are distinct from gymnosperms in that they have specialized structures known as flowers, where pollen grains and ovules are developed.
Unlike gymnosperms, the seeds of angiosperms are enclosed within structures known as fruits.
Angiosperms represent an exceptionally diverse and large group of plants found in a wide range of habitats, from the smallest plants like Wolffia to tall trees like Eucalyptus, which can reach over 100 meters in height.
Angiosperms play a crucial role in human life as they provide food, fodder, fuel, medicines, and various other commercially important products.

Classification of Angiosperms:

Angiosperms are divided into two main classes:
1. Dicotyledons (Dicots): These are angiosperms with seeds that typically have two cotyledons (seed leaves).
2. Monocotyledons (Monocots): These are angiosperms with seeds that usually have a single cotyledon.