WHAT IS PLANTAE
- Plantae is the kingdom which constitutes all the plants present on the earth.
- With more than 250,000 species, they are the second largest group in size after Arthropoda.
- There are a wide variety in shapes and sizes of plants around us, from tiny creeping plants to tall forest trees.
GENERAL CHARACTERISTICS OF PLANTAE
- Plants are multicellular eukaryotes.
- Plants contain both cell wall and cell membrane.
- Cell walls constitute the outermost boundary whereas cell membrane is found inner to the cell wall.
- Plant cells are distinguishable by the presence of a large central vacuole. The nucleus in plant cells lies peripheral due to presence of central vacuole.
- Plants are autotrophs meaning they can prepare their own food through photosynthesis. Plants contain photosynthetic pigment in the form of plastids.
- They are primarily non-motile and are anchored to a substrate throughout their entire life.
- They can reproduce by both sexual and asexual means.
- For sexual reproduction, the plant bears specialized reproductive organs, which are responsible for the production of male and female gametes. These gametes fuse to form an embryo which then develops to give rise to a new individual.
- Plant cells have a unique mechanism of cell division which is not seen in other eukaryotes.
- During mitosis, the plant cell forms a structure called a phragmoplast.
- Plants show alternation of generation, meaning the life cycle of plants consists of alternating haploid gametophyte and diploid sporophyte generation.
- Plants are responsible for the production of oxygen and the absorption of carbon dioxide.
CLASSIFICATION OF PLANTAE
The plant kingdom is divided into two groups
- Cryptograms are non seed bearing and non flowering plants and they are further classified as follows,
- Thallophyta are thalloid plants and consist of algae, fungi and lichens.
- Thallophytes are a diverse group of aquatic organisms which contain chlorophyll and are able to conduct photosynthesis.
- However, they lack the traditional structures of plants i.e. stem, roots, leaves etc.
- Seaweeds such as kelp
- Pond scum
- Algal blooms in lakes.
- Bryophytes consist of small flowerless green plants which lack true roots, stem and leaves.
- Bryophytes are nonvascular and do not contain xylem and phloem.
- Common liverwort
- Mountain fern moss
- Pteridophytes are plants that reproduce by spores and possess vascular tissue, roots, stems, and leaves.
- They include ferns, horsetails, and club mosses
- They are sometimes termed as “cryptogams”, which means that their mode of reproduction is hidden.
- Phanerogams are seed bearing and flowering plants and are classified as follows,
- The term gymnosperm literally means “naked seed”
- Gymnosperms are a group of plantae that have seeds unprotected by an ovary or fruit. Rather, they are exposed on the surface of leaf-like structures called bracts.
- Angiosperms are vascular plants that possess true stems, roots, and leaves.
- Unlike some gymnosperms such as conifers and cycads, angiosperm’s seeds are present within a flower.
ALTERNATION OF GENERATION
- Alternation of generations is a form of life cycle found in terrestrial plants and some algae in which successive generations of individuals alternate between haploid and diploid organisms.
- It is also called as metagenesis or heterogenesis.
- It comprisesof alternation of a sexual phase and an asexual phase in the life cycle of an organism
- These two phases, or generations, are often morphologically distinct.
- The sexual phase is called the gametophyte generation as it produces gametes or sex cells.
- Whereas the asexual phase is known as sporophyte generation as it produces spores asexually.
- On the basis of Chromosome, the gametophyte is haploid (has a single set of chromosomes), and the sporophyte is diploid (has a double set).
- Among bryophytes, such as mosses and liverworts, the gametophyte is the dominant life phase.
- Whereas in angiosperms and gymnosperms, the sporophyte is the dominant phase.
IMPORTANCE OF PLANT SPECIES
- Plants act as a primary source of food to nearly all terrestrial organisms, including humans.
- Humans eat either plants or other organisms that rely on plants as a source of nutrition. Hence, plants form an important component of the food chain.
- Plants maintain balance between the atmospheric constituents. They release oxygen into the environment and absorb carbon dioxide during photosynthesis.
- Oxygen is significant for cellular respiration in all aerobic organisms.
- It also maintains the ozone layer which protects Earth’s life from damaging UV radiation.
- Plants recycle organic matter in biogeochemical cycles and maintain the environmental balance.For example, through transpiration, plants move huge amounts of water from the soil to the atmosphere.
- Plants such as peas consist of bacteria that fix nitrogen. This makes nitrogen available to all plants, which transfer it on to consumers.
- Plants produce many products which are beneficial for humans, such as firewood, timber, fibers, medicines, dyes, pesticides, oils, and rubber.
- Plants create habitats for various organisms.
- A single tree can act as food and shelter to various species of insects, worms, small mammals, birds, and reptiles.
- Arihant’s handbook of biology. Plant Kingdom. Page no: 24-42.
- NCERT biology; textbook for class 11. Plant Kingdom. Page no: 46-62.