Chapter 3: Plant Kingdom Revision Notes Part 1
The five kingdom classification for living organisms was founded by the famous scientist R.H. Whittaker. The living organisms were categorised based on the following different characteristics:
- cell structure
- body organisation
- mode of nutrition
- mode of reproduction
- phylogenetic classification systems.
Based on these characteristics, all organisms were classified into five kingdoms:
Source: Five kingdom
Plant Kingdom Classification
Source: Plant kingdom classification
This chapter will dive into the following groups of the plant kingdom:
Algae are aquatic animals that are simple, thalloid structures.
They have an autotrophic mode of nutrition and have chlorophyll.
They are found in moist habitats like soil, woods, stones, or even in association with some fungi (lichens) and on other animals.
They reproduce vegetatively, sexually, and asexually.
Vegetative Reproduction: Occurs through fragmentation; each fragment becomes a thallus \
Asexual Reproduction: Occusrs through the production of spores (specifically zoospores)
Sexual Reproduction: Fusion between gametes (isogamous, anisogamous, oogamous)
Classification of Algae:
- Commonly referred to as the green algae, their body structure is filamentous.
- They are green in colour, due to the presence of pigments such as chlorophyll a and b. These pigments are located in specific chloroplasts.
- Their cell wall is made up of cellulose and they store food in the form of oil droplets. Pyrenoids containing starch are the storage bodies present in chloroplasts.
- They reproduce vegetatively through fragmentation and asexually through zoospores.
- Sexual reproduction can be oogamous, isogamous or anisogamous.e.g. Volvox, Spirogyra and Chara.
- The members of Phaeophyceae or brown algae are found primarily in marine habitats.
- The plant body is usually attached to the substratum by a holdfast and has a stalk.
- They possess chlorophyll a, c, carotenoids, and xanthophylls. Mannitol and laminarin are stored as food reserve materials.
- The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin, i.e., their cell wall is made up of cellulose and algin.
- Sexual reproduction may be isogamous, anisogamous, or oogamous.
- Union of gametes may take place in water or within the oogonium. The gametes are pyriform and bear two laterally attached flagella. e.g. ectocarpus, fucus, laminaria, macrocystis pyrifera etc.
- Due to the presence of a red pigment, r-phycoerythrin, this class of algae are referred to as the red algae.
- Red algae are found in marine as well as freshwater ecosystems. They are found on the surface of water bodies and at great depths.
- Red algae have a very complex body structure. They possess chlorophyll a, d, and phycoerythrin.
- Food is stored in the form of floridean starch, and its cell wall is made up of cellulose, pectin, and poly sulfate esters. E.g. gracilaria, gelidium, etc
- Bryophytes are found in moist, shaded areas in the hills.
- These plants can live in soil but are dependent on water for sexual reproduction. They usually occur in damp, humid, and shaded localities (like amphibians!)
- They lack roots, stems, or leaves, but they possess stem-like, or leaf-like structures.
- They produce gametes, and are called gametophytes. Their sex organs are multicellular.
- The male sex organ is called the antheridium, which produces biflagellate antherozoids, and the female sex organ is called the archegonium, which produces a single egg.
- An antherozoid fuses with the egg to produce the zygote.
Bryophytic plants are broadly divided into Liverworts and Mosses.
- The plant body of a liverwort is a thalloid. e.g. Marchantia
- In sexual reprocution, the gametes are formed either on the same or different thalli.
- Spores are formed through meiotic division, which then germinate to form gametophytes
- Mosses have two distinct stages in their life cycle – the protonema stage, a creeping, green filamentous stage, followed by the leafy stage that develops from the protonema as a lateral bud. The plant body at this stage consists of upright, slender axes bearing spirally arranged leaves. This stage also produces sex organs.
- Vegatative reproduction occurs through fragmentation, while sexual reproduction occurs through the fertilization of the antheridia and archegonia. This leads to sporophyte formation that ultimately leads to spore formation and spore dispersal