Samacheer Class 8 Science - Plant Kingdom

The naming of an organisms with two words are known as Binomial Nomenclature. For example, the binomial name of mango is Mangifera indica. Here the first word Mangifera refers to the genus name and the second word indica to the species name.

Seed has two cotyledons.
Plants have tap root system, leaves with reticulate venation.
Flowers are tetramerous or pentamerous. Calyx and corolla are well differentiated.
Pollination occurs mostly by insects.

Mushrooms contain rich protein, minerals and are edible. Example: Agaricus.
The antibiotic penicillin is got from the fungus penicillium notatum other antibiotics like gentamycin, erythromycin are also got from fungi.

In this system, plants are classified on the basis of several characters. Bentham and Hooker’s classification is an example of Natural System of Classification.
This system of classification is based on morphological.
This classification is widely used in many Herbaria and botanical gardens all over the world.
Bentham and Hooker published their Natural system of Classification in their book named Genera Plantarum in 3 volumes.

1. Agriculture : Some of the blue green algae are essential for the fixing of atmospheric nitrogen into the soil, which increases the fertility of the soil, example Nostoc, Anabaena.
2. Agar Agar : Agar Agar is extracted from some red algae, namely Gelidium, Gracillaria, etc., which is used to prepare growth medium in laboratories.
3. Iodine : Iodine is obtained from brown algae like Laminaria (kelp).

Algae:
Algae are autotrophs.
It has pigments.
Reserve food material is starch.
Some algae are prokaryotic in nature, example: Cyanobacteria (Nostac, Anabenae)
Fungi:
Fungi are heterotrophs.
It has no pigments
Reserve food materials are glycogen and oil.
All are eukaryotic nature, example: Agaricus

The main plant body is sporophytes, which is the dominant phase, differentiated into true root, stem and leaves.
Sporophytes reproduce by means of spores. Spores are produced in sporangium.
The sporangia bearing leaves are called sporophyll.
Most of the plants produce only one type of spore, it may be either microspore or megaspore (homosporous).

Outline of Bentham and Hooker’s system of classification:
Seeded plants (Division):
(i) Dicotyledonae (Class I)
1. Polypetalae (Sub class I)
Thalamiflorae
Disciflorae
Caliciflorae
2. Synpetalae (Sub class II)
Inferae
Heteromerae
Bicarpellatae
3. Monochlamydeae (Sub class III)
Series 8 Family 36)
(ii) Gymnospermae (Class II) (3 families)
(iii) Monocotyledonae (Class III) (Series 8 Family 36)

Monocots:
Seeds have a single cotyledon.
Leaves show parallel venation
They have fibrous root system.
Flowers are trimerous. Example : Paddy
Dicots:
Seeds have two cotyledons.
Leaves show reticulate venation.
They have tap root system.
Flowers are tetra or pentamerous. Example : Mango

Gymnosperm:
They reproduce by production of cones.
Pollination is by wind.
They are naked seed bearing plants.
The xylem lacks vessels and phloem lacks sieve tubes.
They have two phases in its life cycle. (Sporophyte & Gametophyte).
Angiosperm:
They produce flowers.
Pollination takes place by wind, water, insects etc.
They are closed seed bearing plants.
Xylem and phloem and well developed.
The sporophyte is the dominant phase. Gametophytic phase is much reduced in angiosperms.

Woods of many conifers are used in the paper industries, example Pinus, Agathis.
Conifers are the sources of soft wood for construction, packing and plywood industry example Cedrus, Agathis.
Turpentine is an essential oil used for paint preparation extracted from the resin of Pinus. It is also used medicinally for relief from pain and bronchitis etc.
Seeds of Pinus gerardiana are edible.
Ephedrine is an alkaloid extracted from Ephedra. It cures asthma and respiratory problems.
Araucaria bidwillii is an ornamental plant.

Medicinal plants and their uses:
1. Acalypha indica (Kuppaimeni):
The paste obtained from the leaves of this plant is used to cure the bums on the skin.
The juice of this plant leaves is mixed with lemon juice to cure ringworm.
2. Aegle marmelos (Vilvam):
The unripe fruit of this tree is used to treat indigestion.
It is used to cure chronic, diarrhoea and dysentery.
3. Solanum trilobatum:
The leaves and fruits of this plant cure cough and cold.
It is widely used in the treatment of tuberculosis and bronchial asthma.
4. Phyllanthus amarus (Keezhanelli):
The entire plant is used for the treatment of jaundice.
It gives additional strength to human liver and used to treat other liver disorders.
5. Aloe vera (Sothu katrazhai):
Leaves of this plant is used to cure piles and inflammations on the skin.
It cures peptic ulcer.