Algae are aquatic plants. They are both freshwater and marine. Freshwater includes ponds, streams, moist rocks and bark of trees. Marine forms are present from sea shore to depth upto 100meter. Algae may be:
(a) Epiphytes: These algae grow on the surface of other plants.
(b) Endophytes: These algae live inside the other plants.
(c) Phytoplankton: The free floating algae are phytoplankton.
(d) Sessile: Some algae are attached to the substratum by holdfast.
General structure of Algae
Algae have different body sizes. They are from microscope to macroscopic like seaweeds. Algae have different vegetative
I. Unicellular: These may be motile or non-motile.
- Colonial form: Some algae are multicellular colonial. The cells are held together by a mucilaginous matrix. It forms colonies of different shapes. Some colonies have definite number of cells. Such colonies are called coenobia.
- Filamentous forms: Cell division occurs in single plan in filamentous form. So cells are arranged in linear form in a filament. The filaments may be branched or unbranched. There are different forms of filaments:
(a) Heterotrichous: The filament with prostate (horizontal) and vertical system are called heterotrichous.
(b) Pseudoparenchymatous: Sometimes, filaments are loosely grouped to from pseudoparenchymatous body.
(c) Coenocytic: The filaments without cross walls are called coenocytic filaments.
They have eukaryotic cells. Cell has following parts:
- Cell wall: Cell is surrounded by definite cell wall. Cell wall is chiefly composed of cellulose.
- Cytoplasm: Cytoplasm has different membranous organelles. These organelles are plastids, mitochondria, ribosomes and endoplasmic reticulum. Some motile forms have eye spots. It is sensitive to light. Motile forms have one or more contractile vacuole.
- Nucleus: Nucleus is embedded in cytoplasm. It has central or peripheral position. Nucleus is composed of chromosomes, nucleoplasm and nucleolus.
Algae are classified into different groups on the basis of presence of different pigments. Pigments are present in chloroplasts. Chluroplasts also have pyrenoids. Pyrenoids are used to store reserve food material. Some pigments are:
(a) Chlorophyll a, b, c, d and e: Chlorophyll a is present in all the
algae. Chlorophyll b is present in Chlorophyta and Eugenophyta. Chlorophyll c is present in Bacillariophyta, Chrysophyta etc. Chlorophyll d is present only in Rhodophyta.
(b) Carotene, Xanthophyll, Fucoxanthin, myxozanthin: These pigments are also present in some algae
(c) Phycobilins: These are phycocyanin (blue) and phycoerythrin (red).
Reserve food material
(a) Carbohydrates: The carbohydrate reserve food materials in algae are starch, floridean starch and myxophycean starch. Laminarin, paramylum and leucosin are also present in some algae.
(b) Fats: Fats are also present in some algae. Sterols are also reserve food material in many algae.
(c) Alcohol: Mannitol (polyhydroxy alcohol) is also a food reserve in some algae.
Most of the uniCellular and reproductive cells have flagella. Their number may be two or four. There are two types of flagella: Acronematic with smooth surface and pentonematic with fine hairs. Each flagellum is composed of axial filaments called axonemes.. Axonemes are surrounded by sheath. Flagellum arises fron basal bodies. Basal bodies are connected with each other by transverse fibers called paradesmose.
Following types of life histories are found in algae:
(a) Monophasic Haploid: It is a primit;Ne 1;fc cycle. lc ‘Ilk case, vegetative plant body remains haploid. Gametes are pri ,diced by mitosis Gametes fuse to form diploid zygote. First div ision in zygote is meiosis. It forms haploid vegetative body. Thus zygote is the only diploid stage in such cycles.
(b) Monophasic diploid: It is more advanced life cycle. In this case, vegetative stage is diploid. Haploid gametes are formed by meiosis. These gametes fuse to form diploid zygote. Zygote divides by mitosis to form vegetative body. Thus all life form is diploid except gametes.
(c) Diphasic life cycle: In this case, two types of generation are produced: gametophyte and sporophyte. Both generations alternates with each other. If both generations have similar vegetative structure, then they are called isomorphic. If they have different structures, then they are called heteromorphic. • Gametophyte is haploid generation. It produces gametes by mitosis. Gametes fuse to form diploid zygote. Zygote form diploid sporophyte.
• Sporophyte is diploid generation. It produces spores by
meiosis. Spores germinate to form gametophyte plant.
Algae reproduce vegetatively, asexually and sexually
The reproduction from body parts is called vegetative reproduction. It occurs by simple division in unicellular individuals. In multicellular algae, a pail is detached from the plant body. It grows to form new plant. Some algae produce special propagules. They detach from the plant body and develop new plant. Asexirrepcosim.capn
Asexual . unlit occiirs in favourable 1041 “rmaja—(tteent
types of s es are rsduced during asexual repttluotioas. Spores are prodUcecf by Ifie—division of protoplast dP–telfrefriihty°1are Produced inside the sporangium.
- Zoospores: Motile spores are called zoospores. They have flagella or cilia. They are produced in zoosporangium. Zoospores are produced in water. They are found in most of the algae. 2-16 ‘pores are produced in each cell.
- Aplanospores: The non-motile spores are called aplanospore.
- Hypnospores: In this case, cell secretes a thick wall and become rounded. It becomes hynospore.
- Akinetes: If the original wall of the cell becomes thick, it is called akinete.
- Pa I tuella : Sometimes, spores remains embedded in mucilaginous matrix. Thus a rounded body is formed with many spores. This condition is called Palmella stage.
Sexual reproduction occurs under unfaVourable conditions. It produces a resting stage for passing unfavourable period. Gametes are produced during sexual reproduction. These gametes are prudence’ in gametangia. Gametes fuse to form zygote.. Zygote secrets4r ts– k wall awl become zygospore. Zygospore geimMates duri.ifFia.Voifrable conditions. There are different forms of smival reprocriiaionS in algae.
I. Isoganny: In this case, gametes have similar size and form. Their fiSletriciealled isogamy.
2. Anisogamy: In this case, gametes have similar structures and form but different sizes. The smaller active gamete is called male gamete. The larger less active gamete is called female gamete. They fuse to for zygospore.
- Oogamy: In this case, the gametes have different forms and structures, sizes and behaviors. The small motile gamete is called antherozoid. They are produced in gametangia or antheridia. The non-motile larger gamete is called egg or oosphere. It is produced in oogonium. The male gamete swims in water. It enters into to oogonium. Fertilization occurs. The zygote secretes a thick wall and become oospore.
- Parthenogenesis: Sometimes, oosphere is changed into oosporc without fertilization. It forms parthenospore. This condition is called parthenogenesis.
Alga are divided into different divisions (phylum) on the basis of pigments and reserve food material:
1. Chlorophyta: They have grassy green colour. Four pigments are present in them. These are chlorophyll a, b, carotene and Xanthophyll. Pyrenoid is present in them. Reserve food material is
starch. Motile cells have 2-4 flagella. Sexual reproduction is isogamy or oogamy. Example: spirogyra
2. Xanthphyta: A large amount of yellow pigment Xanthophyll is esent in them. Chlorophyll a, b, and carotene are also present. So they are yellow green in colour. Food reserve is oil. Starch is absent. Cell wall is rich in pectic compounds. Their body is composed of two tightly overlapping pieces. Motile cells have two flagella. Sexual reproduction is isogamy. Example: Vaucheria
- Charophyta: The plant body has erect braches. These blanches have nodes and intemodes. Pigments are chlorophyll a, b, carotene and Xanthophyll. Asexual reproduction is absent. Adult plant develops protonema stage. Antherozoid is spirally coiled. Example: Chars
- Bacillariophyta (diatom): These are yellow green or golden brown. Pyrenoids are present. Food reserve is fats. Starch is absent. Cell wall contains pectic substances with silica. They have two overlapping valves. Axuospore or endospore is formed.82Master Success Text Book of Botany A
Sexual reproduction occurs by union of cells. Example: Pinnularia
- Paaeophyta: (brown algae): They have excessive brown pigment fucoxanthin. Food reserve is mannitols, laminarin and fats. They have large body sizes. Reproductive cells have two unequal flagella. Sexual reproduction is isogamy or oogamy. Example: Laminaria
- Rhodophyta (red algae): They contain red pigment phycoerythrin and blue pigment phycocyanin. Pyrenoids are present. Food reserve is floridean starch. Flagella are entirely absent. Sexual reproductive is oogamous. Special spores carpospores are produced in them.
- Euglenophyta: Their pigments are chlorophyll a, b, and carotene. Food reserve is paramylon or fats. All the members are naked (without cell wall). They have 1-3 flagella. Reproduction occurs by cells division. Sexual reproduction is almost absent. Example: Euglena
Economic importance of algae
Algae have following beneficial effects:
I. Source of food: Most of photosynthesis is carried out by fungi in fresh water and marine water. Therefore, they store a large amount of energy.
- Some green algae like ulva are directly eaten by man.
- Dried Spirogyra and oedogonium are also eaten by man.
- Kelps (Brown algae) are eaten in China and Japan.
- Chlorella is used in the preparation of cakes and pastries.
- Porphyra are eaten by man. These are also used in puddings and soups.
- Diatoms are major source of food for marine fishes. These fishes are consumed by human.
2. Drugs and medicines: Different algae gives following drugs:
- An antibiotic chlorellin is obtained from Chlorella. It is affective against gram positive bacteria.
- Agar-agar is obtained from Gelidium. It is used a laxative.
- Chara plants are used to kill mosquito larvae.
3. Uses of diatomaceous earth: Diatomaceous earth is formed by the death of diatoms. It has following uses:
- Pt is used to polish metal and automobile.• 83Kingdom Protista: Algae
- It is used in tooth and tooth pastes.
- It is used as fire proof material.
- It is used to filter oils and syrup in sugar industries
- It is used as absorbent in dynamites.
- Light weight bricks are prepared from it. These bricks are used for building fire proof houses.
4. Uses of &gin: Algin is obtained from different algae. It has
- It is used as adhesive structure in artificial silk.
- It is used in ice creams.
- Algin is used as moisture retainer in many types of
- It is used in paints and many pharmaceutical products.
- It is used in processing of natural and synthetic rubbers.
5. Uses of gelatin: Gelatin is obtained from red algae. Gelatin is used as bases in shoe polishes, shaving creams, cosmetics, shampoos, glue, jellies, candles and tooth paste.
Harmful effects of algae
Algae have following harmful effects:
I. Algae grow excessively along the shore of ponds and oceans. It makes the environment unhygienic.
- Algae cause algal bloom. Algae cover the upper surface of swimming pools. It produces foul smell.
- Algae damage the tea and other subtropical rain plants.
- Algae cause eutropMeation in ponds and lakes. It causes the death of many fishes due to oxygen deficiency.
- Some species of marine algae destroy the ships.