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Patterns in Life: Diversity and Classification 237 12.6.4 Kingdom Plantae — Multicellular, autotrophic eukaryotes with a cell wall Plantsaremulticellular,autotrophicorganismsthatperformphotosynthesis. Grade 7 Their cells have a rigid cell wall primarily made up of cellulose, which Curiosity Chapter 10 provides support and protection. All plants belong to the kingdom Plantae. Plants form the base of most of the food chains and release oxygen which is essential for life on the Earth. Kingdom Plantae is further divided into five classes. Plantae Class Thallophyta Bryophyta Pteridophyta Gymnosperm Angiosperm Thallophyta (algae) — Primitive plants Thallophytes (thallos means undifferentiated body and phyton means plant) are among the simplest plant forms and are mostly found in water or moist environments. They form a thallus, a simple body that allows direct exchange of gases, nutrients and water with the surroundings. They are well-adapted to aquatic habitats. An example of Thallophyta is Spirogyra (Fig. 12.9). Bridging Science and Society Have you ever seen white-green patches on the tree trunk, damp walls or Fig. 12.9: Spirogyra stones? What do you think about these patches? Visit a village and talk to an elderly person about these patches. They recognise these patches as an indicator of a pollution-free environment. In fact, the lichens change their colour with air pollutants. Based on their colour, researchers can find out the concentration of pollutants in the air. Therefore, they are natural bioindicators for the measurement of air quality. Villagers also collect these as forest produce for utilisation in their daily life. Some types of lichen, commonly called patthar ke phool are used as a spice, while some are used as medicines, and also for making dyes since ancient times to give maroon, violet, or burgundy colour to woollen and silk fabrics. Biologically, these are symbiotic (mutual associations of two organisms) — one partner is an autotrophic alga and the other one is a heterotrophic fungus. Fungal partners provide protection, and algal partners photosynthesiseandprovidefood.Somelichensarepoisonous,soitisimportant to classify and identify them properly for safe and proper utilisation. Bryophyta — First steps on land, still need water (a) Marchantia Bryophytes(bryonmeansmossandphytonmeansplant),suchasmossesand liverworts (Fig. 12.10), which represents an important shift from water to land. You might have seen them as large green mats on damp rocks or even on the walls of some old buildings, or even on soil surfaces as green mats. Bryophytes have a more differentiated body as compared to thallophytes. They have root-like structures called rhizoids, and may possess stem-like and leaf-like simple structures. Bryophytes survive in moist and shady (b) Moss places, growing as green mats on the soil, especially during the monsoons. Fig. 12.10: Members Examples of Bryophytes include Marchantia and moss (Fig. 12.10). of class Bryophyta