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PinkMonkey Online Study Guide-Biology

14.3 Kingdom : Plantae

Kingdom Plantae includes all organisms which are truly multicellular and photosynthetic exept for algal protists. They are complex autotrophs preparing food material by photosynthesis for themselves as well as for rest of the other organisms. Hence, they are the chief producers of the world. They are found in all the types of environment: aquatic algae, amphibian mosses, and terrestrial ferns and seed-bearing plants.

The plantae are distinguished by the following characters:

(1) They are multicellular organisms, adapted to carry on photosynthesis, hence autotrophic.

(2) Presence of cell wall of true cellulose, enclosing cytoplasm with large vacuole.

(3) They perform photosynthesis due to chlorophyll present in chloroplasts.

(4) They may show alternation of sexual and asexual generations in life-cycle.

(5) They are non-motile, without definite size and shape.

(6) Growth in these plants is intermittent.

They are classified as follows:

ALGAE

Algae are chlorophyll-bearing unicellular or multicellular plants. When multicellular, they may be colonial or filamentous. Most of them are aquatic, either fresh water, (Volvox), or marine, (Spirogyra). Some are sheet-like (e.g., Ulva). Chlorophyll is present in chloroplasts, the number and shape of which are characteristic of each alga. Besides chlorophyll, they also show various carotenoid pigments which impart different colors to algae. According to the nature of photosynthetic pigments, they are further classified into three divisions such as Chlorophyta (green),. Phaeophyta (brown), and Rhodophyta (red).

Life - cycles

Algae show both a gametophytic (haploid) stage and a sporophytic (diploid) stage, which alternate. The life-cycle mainly shows two types, either haplontic or diplontic.

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Figure 14.29 Types of life - cycles

(a) Haplontic life - cycle, when the plant body is a gametophyte i.e., haploid and is dominant or of long duration, and the zygote is diploid and of short duration.

(b) Diplontic life-cycle, when the plant body is a sporophyte, i.e. diploid and is dominant or of long duration, and the gametophyte is haploid and of short duration.


Green algae (Chlorophyta)

These algae live in wide variety of habitats, marine to fresh water to damp soil.

General Characteristics

(i) These are unicellular (Chlamydomonas), colonial (Volvox) or filamentous. When filamentous they are unbranched (Spirogyra, Ulothrix) or branched (Chara).

(ii) The cell wall consists of an inner layer of cellulose and outer layer of pectic compounds and may be covered by a gelatinous sheath.

(iii) The protoplasm is divisible into cytoplasm and nucleus. Cytoplasm contains one or more vacuoles. Chlorophyll is present in chloroplasts, the shape and number of which are characteristic of each alga.

(iv) Pigments chlorophyll-a and chlorophyll-b are predominant. However, carotene and xanthophyll are also present.

(v) Food reserve is in the form of starch surrounding the proteinaceous refractile bodies called pyrenoids.

(vi) Reproduction is vegetative by mitotic cell division in unicellular forms or by fragmentation in filamentous forms; asexual by formation of spores such as zoospores, aplanospores, hypnospore and akinates and sexual simply by conjugation or by gamete formation by isogamy or anisogamy or oogamy.

(vii) The life-cycle is of haplontic type showing alternation of dominant haploid stage with short-lived diploid stage.

Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Ulva etc.

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Figure 14.30 Types of Chlorophyta

Table of Contents

14.0 Introduction
14.1 Kingdom : Monera
14.2 Kingdom : Protista
14.3 Kingdom : Plantae
14.4 Kingdom : Fungi

Chapter 15





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