Definitions [3]
Define - Thallus.
Thallus refers to a plant body that is not differentiated into roots, stems, and leaves. Example: Algae.
Define taxonomy.
The theoretical study of classification which includes its basic principles, procedures and rules.
Definition: Nomenclature
Nomenclature is the system of assignment of names to organic compounds.
Key Points
Divisions of Algae and their Main Characteristics
| Classes | Common Name | Major Pigments | Stored Food | Cell Wall | Flagellar Number and Position of Insertions | Habitat |
|---|---|---|---|---|---|---|
| Chlorophyceae | Green algae | Chlorophyll a, b | Starch | Cellulose | 2–8, equal, apical | Fresh water, brackish water, salt water |
| Phaeophyceae | Brown algae | Chlorophyll a, c, carotenoids, xanthophylls | Mannitol, laminarin | Cellulose and algin | 2, unequal, lateral | Fresh water (rare), brackish water, salt water |
| Rhodophyceae | Red algae | Chlorophyll a, c, r-phycoerythrin | Floridean starch | Cellulose, pectin and polysulphate esters | Absent | Fresh water (some), brackish water, salt water (most) |
Classification of Sub-Division Algae
| Feature | Chlorophyceae (Green) | Phaeophyceae (Brown) | Rhodophyceae (Red) |
|---|---|---|---|
| Body form | Unicellular/colonial/filamentous | Simple to large complex forms | Mostly multicellular |
| Pigments | Chlorophyll a, b | Chlorophyll a, c, fucoxanthin | Chlorophyll a, d, phycoerythrin |
| Stored food | Starch | Mannitol, laminarin | Floridean starch |
| Cell wall | Cellulose | Cellulose + algin | Cellulose + pectin |
| Reproduction | Zoospores (2–8 equal flagella) | Zoospores (2 unequal flagella) | Non-motile spores/gametes |
| Habitat | Fresh, brackish, marine | Mostly marine | Mostly marine |
| Examples | Chlamydomonas, Spirogyra | Laminaria, Sargassum | Polysiphonia, Porphyra |
Key Points: Sub-division Algae
- Algae are simple, chlorophyll-containing, autotrophic organisms, mostly found in aquatic habitats.
- They have a thallus body without true roots, stems, and leaves.
- Algae show different forms, such as unicellular (Chlamydomonas), colonial (Volvox), and filamentous (Spirogyra).
- Reproduction occurs by vegetative, asexual, and sexual methods, including fragmentation and spore formation.
- Algae play an important role in CO₂ fixation and oxygen production, supporting aquatic ecosystems.
- They have economic importance, providing food, agar, algin, carrageenan, and protein-rich supplements like Spirulina.
Key Points: Division II - Bryophyta
- Bryophytes are called amphibians of the plant kingdom as they live on land but need water for reproduction.
- They are found in damp, humid, and shaded places and lack true roots, stems, and leaves.
- The plant body is thallus-like and attached to the substratum by rhizoids.
- The gametophyte is the dominant phase, which produces male (antheridia) and female (archegonia) gametes.
- Fertilisation requires water, forming a zygote that develops into a sporophyte (foot, seta, capsule).
- Reproduction occurs by vegetative (fragmentation), asexual (gemmae), and sexual methods.
- Economic importance: prevents soil erosion, acts as a pioneer species, provides peat (fuel), and has medicinal uses.
Key Points: Division III - Pteridophyta
- Pteridophytes are vascular plants with true roots, stems, and leaves; the sporophyte is the dominant phase.
- They are the first terrestrial plants with vascular tissues (xylem and phloem).
- Leaves may be microphylls (small), as in Selaginella, or macrophylls (large), as in ferns.
- Sporangia produce spores and are present on sporophylls, often forming cones (strobili).
- Spores germinate into a haploid gametophyte (prothallus), which is small, independent, and photosynthetic.
- Fertilisation requires water, and the zygote develops into a new sporophyte.
- Some pteridophytes show heterospory (microspores and megaspores), which is an important step towards a seed habit.
Key Points: Phanerogams > Division I-Gymnosperms
- Naked seeds - Gymnosperms have ovules not enclosed by the ovary wall; seeds remain exposed before and after fertilisation.
- Vegetative features - Stem branched (Pinus) or unbranched (Cycas); leaves are needle-like with thick cuticle and sunken stomata to reduce water loss; roots are tap roots.
- Special roots - Pinus has mycorrhiza (fungal association); Cycas has coralloid roots with N₂-fixing cyanobacteria.
- Reproduction - Reproductive structures are strobili (cones); plants are heterosporous - male strobilus has microsporophylls (produce pollen); female strobilus has megasporophylls (bear ovules); pollination is by air (wind).
- Fertilisation - Pollen tube carries male gametes to archegonium → fuses with egg → zygote → embryo; ovule develops into seed; life cycle is diplontic (sporophyte dominant).
- 4 groups - Cycads (Cycas), Conifers (Pinus, Cedrus), Ginkgoales (Ginkgo biloba), Gnetales (Ephedra, Gnetum).
- Economic importance - Ephedrine (from Ephedra) for respiration; Taxol (from Taxus) for cancer; sago from Cycas; timber, resins, turpentine and paper pulp from conifers.
Key Points: Division II - Angiosperms
- Angiosperms are flowering plants with seeds enclosed in fruits.
- They show great variation in size, from small (Wolffia) to large trees (Eucalyptus).
- Classified into monocots and dicots.
- Double fertilisation occurs, forming a zygote and a triploid endosperm.
- After fertilisation, the ovary becomes a fruit, and the ovule becomes a seed.
- Life cycle is diplontic with a dominant sporophyte and a reduced gametophyte.
Key points: Nomenclature of Carbon Compounds
- The IUPAC system provides a unique, systematic way to name carbon compounds based on structure, replacing confusing common names.
- An IUPAC name has three parts: prefix, parent, and suffix, reflecting the carbon chain and functional group.
- The parent name is based on the longest carbon chain, and its ending changes to –ane, –ene, or –yne depending on the number of bonds.
- Functional groups are shown as prefixes or suffixes, and the chain is numbered to give them the lowest possible number.
- If the suffix begins with a vowel, the final ‘e’ in the parent alkane name is dropped (e.g., propane → propanone).
