biology

• Annuals: Complete their life cycle in one year or one growing season
• Biennials: Complete their life cycle in two years growing (vegetative and storing food in the first year, flowering and fruiting in second year).
• Perennials: Survives for several years
• Morphology of Root:Radicle comes out/arise from the seed coat in the form soft structure and move toward the soil.
• Roots do not bear Buds
• Roots do not bear nodes and internodes.
• Roots have unicellular root hairs
• The tender apex of the root is protected with a multicellular like structure called root cap.
• In many hydrophytes like Pistia and Eichhornia, root cap is replaced by root pocket.
• The cells of the root cap secrete mucilage for lubricating the passage of root through the soil.
• cell division:It is a small region about 1mm in length.  This is the growing part of the root and is protected by the root cap.
• elongation: It lies just above the meristematic region.
• The cells of the outer layer known as piliferous layer or epiblema produce root hair.
• cell differentiation:It forms the major part of the root.
• Tap Root 1. Storage of food 2. Respiration
• Adventitious Root 1. Storage of food 2. Support 3. Special functions
• Tap Roots or True Roots:  It develops from radicle and made up of one main and other sub branches
• Adventitious roots : In some plants, after sometime of the growth of tap root which arises from radicle, stops and then roots, develop from other part of plant,
• Fusiform roots : These root are thicker in the middle and tappered on both ends.
• Conical roots : These roots are thicker at their upper side and tapering at basal end. eg. Carrot.
• Napiform : These roots become swollen and spherical at upper end and tappered like a thread at their lower end. eg. Turnip (Brassica rapa), Sugarbeet
• Tuberous root : Such roots do not have regular shape and get swollen & fleshy at any portion of roots.eg. Mirabilis
• Halophyte or mangrove grow in oxygen deficient marshy area. Some branches of tap root in these plant grow vertically & comes out from soil in the form of conical spikes. These roots are called pneumatophores through which air entered inside the plant.
• SIMPLE TUBEROUS ROOTS: These roots become swollen and do not assume a definite shape
• FASCICULATED TUBEROUS ROOTS: A cluster of adventitious roots of some plants become thick and fleshy due to the storage of food.
• Stilt roots or brace roots : When root arises from lower nodes and enter in soil obliquely, known as stilt roots eg. Maize, Sugarcane, Pandanus (screwpine)
• Prop root or pillar roots : when root arises from branches of plant and grows downward towards soil. It function as supporting stem for the plant. eg. Banyan.
• Butteress root – Such roots appear from the basal part of stem and spread in different directions in the soil. eg. Ficus, Bombax , Terminalia. It is a characteristic characteristic feature of tropical rain forest
• Climbing roots – These roots arise from nodes and helps the plant in climbing. eg. Money plant (Pothos), Betel, Black pepper, Techoma.
• Foliar roots or Epiphyllous roots – When roots arise from leaf they are called as foliar roots. eg. Bryophyllum, Bignonia.
• Sucking or haustorial roots or Parasitic roots : In parasitic plant roots enter in the stem of host plant to absorbed nutrition from host. eg. Dendrophthoe, Cuscuta,
• Stem is a part of plant which lies above from surface of soil.
• The young stem is green and is capable of performing photosynthesis
• Underground modification : (for storage and vegetative propagation)
• RHIZOME: prostrate, dorsiventral thickened brownish stem, which grows horizontally under the surface of the soil.
• TUBER : are actually the swollen ends or tips of special swollen underground branches, due to the storage of foo (carbohydrate like starch).
• BULB : It is a condensed; disc like underground stem, which itself does not store food material.
• CORM : is a short, stout, fleshy, upright and thickened underground stem.
• Aerial modification (Epiterranean stem) :
• STEM TENDRIL: It is a modification of stem in which axillary bud modifies to form a thin, wiry, and highly sensitive structure called tendril.