DEFINITION
Algae
They are found in wet and damp places.
They are autotrophic.
Some of them are used as food.
For examples, diatoms.
DEFINITION
Uses of algae
Algae are used as food as they are rich in carbohydrates, vitamins and few other inorganic substances. For example, Spirogyra is the chief source of food.
Algae release lot of oxygen into water as a by-product of photosynthesis. This is the source of dissolved oxygen for aquatic organisms.
Agar Agar is used in preparation of ice-cream and jellies. For example, Gelidium.
Algae are chewed instead of tobacco. For example, Rhodomenia.
Algae are used extensively in industries to prepare some products like sugar, soap, cement, rubber blotting paper etc.
Algae are used in agriculture to increase soil fertility. For example, Nostoc, Anabena.
Some algae are used in the preparation of medicines.
DEFINITION
Chlorophyta (green algae)
It contains chlorophyll a and b, which impart them bright green colour.
The main stoarge product is starch and cellulosic cell wall.
Sexual reproduction ranges from isogamous to oogamous.
For example, Chlamydomonas, Volvox, Chlorella.
DEFINITION
Rhodophyta (red algae)
They have water soluble red pigment (phycoerythrin), which masks the green color of chlorophyll a.
The main storage product is floridean starch.
Sexual reproduction is advanced oogamous type. The male organ produces non motile gametes and the female organ has a long receptive neck. After sexual reproduction special spores are produced.
For example, Batrachospermum, Polysiphonia.
SHORTCUT
Phaeophyta (brown algae)
It contain brown carotenoid, fucoxanthin, which masks the green colour of chlorophyll pigment.
Most of them are marine.
The main storage product is laminarin.
Sexual reproduction ranges from isogamous to oogamous. Motile gametes have two laterally attached flagella. Varied types of alternation of generation.
For example, Ectocarpus, Sargassum.
DEFINITION
General characteristics of Bryophyta
The plant body is a gametophyte. They grow in areas which arc in between the aquatic and terrestrial habitats i.e., amphibious zone and hence known as amphibious plants.
They have thalloid or leafy multi cellular green plant body.
The plant body lacks true roots, stem or leaves.
The plants are green and possess chloroplasts.
They show autotrophic mode of nutrition.
Vascular tissues are completely absent.
Sexual reproduction is oogamous.
Male reproductive organ is known as antheridium. It is a club shaped structure being borne by a narrow stalk. It produces biflagellate and motile male gametes or antherozoids.
The female sex organ is known as archegonium. It is a flask shaped structure having a swollen base and a narrow neck.
Water is essential for fertilization.
DEFINITION
Uses of Bryophyta
The uses of Bryophyta are as follows:
Prevention of soil erosion
Soil formation
Water retention
Peat
Used as food for animals, mammals, birds.
DEFINITION
Economic importance of Bryophyta
The uses of Bryophyta are as follows:
Prevention of soil erosion
Soil formation
Water retention
Peat
Used as food for animals, mammals, birds.
DEFINITION
Hepaticopsida (Liverworts)
Many have flattened body called a thallus, but some have a leafy appearance.
They occur on moist shady habitats like marshy ground, damp soil, water banks etc.
For example, Riccia, Marchantia, Porella.
DEFINITION
Bryopsida (mosses)
Gametophytic plant body have thalloid protonema and leafy gametophore.
Sporogenous tissue develops from outer layer of endothecium.
Inner layer forms sterile columella.
For example, Funaria, Sphagnum, Polytrichum.
DEFINITION
General characteristics of Pteridophyta
1. Members of this group are most primitive living vascular plants.
2. The main plant body is a sporophyte. It is differentiated into root, stem and leaves.
3. Plants (sporophyte) reproduce by spores formed in sporangia. Sporangia develop either on the ventral surface or in the axil of leaves.
4. Plants may be homosporous or heterosporous. The development of sporangium may be of eusporangiate or leptosporangiate.
5. Spores develop into a multi-cellular gametophytic body called prothallus - a thalloid structure. It is independent and chlorophyllous. It bears male reproductive organs called antheridia and female reproductive organs called archegonia. Reproductive organs are multi cellular and jacketed.
6. Water is essential to effect fertilization as male reproductive units are flagellated and motile.
7. Seed formation never takes place in living pteridophytes.
8. An embryo develops in situ after fertilization and the sporophyte remains attached to the gametophyte till the development of root.
9. Plants show clear alternation of generations. The sporophyte and gametophyte are independent of each other.
DEFINITION
Classification of Pteridophyta
1) Sub-Division - Psilopsida
These are the oldest known vascular plants. Most of them have become extinct (e.g., Rhynia, Horneophyton). Only two living species, Psilotum and Tmesipteris, are now available.
Plant body is very simple and does not show much differentiation.
Dichotomously branched rhizome takes the place of roots.
Sporangia are directly borne on the stem (i.e., cauline). Either terminal or lateral.
2) Subdivision Lycopsida
Plant body shows differentiation into root, stem and leaves.
Leaves are microphyllous (small) having a single unbranched vein in the midrib region.
Sporangia are borne in the axil of the fertile leaves.
Sporophyll form compact strobili (singular strobilus).
3) Subdivision Sphenopsida
Plant body shows differentiation into nodes and internodes like higher vascular plants.
Leaves microphyllous, and arise in whorls at each node.
Sporangia develop on sporangiophores which form compact cones at the apex of fertile branches (e.g., Equisetum).
4) Subdivision Pteropsida (Ferns)
Plant body shows much advancement towards higher vascular plants, and is well differentiated into root, stem and leaves.
Leaves also show great advancement, and are megaphyllous (large) and pinnately compound.
Sporangia develop on the ventral surface of the sporophylls, and usually aggregated into sori (e.g., Dryopteris, Pteris, Pteridium, Polypodium etc.)
DEFINITION
Reproduction in Pteridophyta
Reproduction in pteridophytes involves production of spores.
Spores are produced inside a special structure called sporangia which occur on the ventral surface of fertile leaves called as sporophylls.
Sporangia may sometimes be found in groups called sori.
DEFINITION
General characteristics of Angiosperms
Angiosperms live in a wide variety of environments, from fresh water to the desert and from the very cold Arctic regions to very hot tropical regions.
The dominant life stage in alternation of generation is the diploid sporophyte.
The haploid gametophyte is small, without chlorophyll, and dependent on the sporophyte.
They are heterosporous and produce microspores and megaspores.
Angiosperms produce seeds that are covered or enclosed within an ovary.
When mature, the ovary constitutes the fruit.
Angiosperms are vascular plants and possess xylem and phloem.
They possess true leaves, true stems and true roots.
DEFINITION
Plant life cycle and alternation of generation
Alternation of generations is a term primarily used to describe the life cycle of plants.
A multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs.
A mature sporophyte produces spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n.
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