Complete Notes: Algae (NEET Biology)

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🌱 Algae Notes

πŸ“– Introduction

  • Term β€œAlgae” was given by Linnaeus.
  • Phycology – study of algae.
  • Father of Phycology β†’ Fritsch (Structure & Reproduction of Algae).
  • Father of Indian Phycology β†’ M.O.P. Iyengar.

🌊 Nature

  • Algae are mostly aquatic, found in both fresh water and marine water.
  • Most algae have a dominant haploid plant body.
  • Forms: unicellular, colonial, filamentous; some marine β†’ parenchymatous & massive; some multinucleated siphonaceous.
  • Surrounded by mucilaginous sheath; beneath lies cell wall = cellulose (inner) + pectin (outer).
  • Tissue system absent.

🌍 Habitats of Algae

  • Terrestrial: in moist soil & wall β†’ Terrentofolia.
  • Epiphytes: present on plants β†’ Protococcus.
  • Endophytes: inside plants β†’ Coleochaete (in Nitella).
  • Epizoic: on animals β†’ Cladophora (on Mollusca shell), on sloth bear (symbiotic).
  • Endozoic: inside animals β†’ Zoochlorella, Zooxanthellae (in Hydra).
  • Parasitic: Cephaleuros β†’ red rust disease of tea.
  • Thermophilic: hot water β†’ Chlorella.
  • Cryophilic: polar/low temperature β†’ Chlamydomonas spp., Haematococcus nivalis (red snow).
  • Cryptophytic: under soil β†’ Nostoc.
  • Saprophytic: on soil surface β†’ Vaucheria.
  • Epiphloephytes: on bark of trees.

πŸ” Reproduction

1. Vegetative:

  • Binary fission: cell divides into two; nucleus by mitosis (unicellular).
  • Fragmentation: filaments break into pieces (all filamentous algae).

2. Asexual:

  • By motile flagellated zoospores.
  • In unfavourable conditions β†’ aplanospores, hypnospores, cysts.

3. Sexual:

  • Isogamous β†’ Chlamydomonas debaryanum, Ulothrix, Ectocarpus, Spirogyra.
  • Anisogamous β†’ Chlamydomonas brunii.
  • Oogamous β†’ Chlamydomonas coccifera, Volvox, Fucus, Sargassum, Chara.

πŸ’‘ Special Notes:

  • Chlamydomonas β†’ complete evolution of sexual reproduction.
  • Ulothrix zonata β†’ shows origin of sexual reproduction.
  • Sex organs β†’ unicellular & jacketless (except Chara β†’ multicellular & jacketed).
  • In Chara: male = globule, female = nucule.

πŸ”„ Life Cycle

  • Plant body haploid β†’ zygotic meiosis β†’ haplontic.
  • Brown algae β†’ diplohaplontic.
  • Fucus β†’ diplontic.
  • Red algae (Polysiphonia) β†’ triphasic (diplohaplontic).
  • No embryo formation in algae.

πŸ§ͺ Classification

Based on photosynthetic pigments, cell wall, stored food:

  1. Chlorophyta – Green algae.
  2. Phaeophyta – Brown algae.
  3. Rhodophyta – Red algae.
  4. Xanthophyta – Yellow-green algae.

Chlorophyta (Green Algae)

  • Most advanced algae; ancestor of higher plants.

Thallus forms:

  • Unicellular:
    • Chlamydomonas β†’ motile unicell (flagella).
    • Chlorella β†’ non-motile unicell; Calvin Cycle discovered on it.
    • Acetabularia β†’ largest unicell; Hammerling’s experiment.
  • Coenocytic: multinucleated β†’ Caulerpa.
  • Colonial:
    • Motile β†’ Volvox.
    • Non-motile β†’ Hydrodictyon (water net).
  • Filamentous:
    • Unbranched β†’ Ulothrix (pond wool), Spirogyra (pond silk).
    • Branched β†’ Cladophora, Stigeoclonium, Fritschiella.
    • Heterotrichous β†’ Fritschiella tuberosa (resembles land plants).
  • Parenchymatous: Ulva (sea lettuce).

Cell features:

  • Cell wall: inner cellulose + outer pectose.
  • Pigments: Chl-a, Chl-b; Ξ²-carotene; luteaxanthin; violaxanthin.
  • Pyrenoids: protein bodies, surrounded by starch, in chloroplasts.

Stored food:

  • Starch (true starch, stored in pyrenoids inside chloroplasts).
  • Associated with protein bodies.

Reproduction:

  • Vegetative β†’ fragmentation.
  • Asexual β†’ zoospores (2–8 flagella).
  • Sexual β†’ iso-, aniso-, oogamous.

Life cycles:

  • Haplontic β†’ Ulothrix, Spirogyra, Chlamydomonas.
  • Diplontic β†’ Caulerpa.
  • Haplo-diplontic β†’ Ulva, Cladophora.

Economic importance:

  • Food: Codium, Ulva, Chlorella, Spirulina.
  • Antibiotic: Chlorellin from Chlorella.
  • Space research: Chlorella.
  • Parasitic: Cephaleuros β†’ red rust of tea.

Phaeophyta (Brown Algae / Kelp / Seaweeds)

  • Mostly marine & multicellular.
  • Lower forms: filamentous (Ectocarpus).
  • Higher forms: parenchymatous (Fucus, Macrocystis, Sargassum, Laminaria).
  • Largest β†’ Macrocystis (60–100 m).

Body differentiation:

  • Lamina: photosynthetic.
  • Stipe: with trumpet hyphae (like sieve tubes).
  • Holdfast: attachment.

Pigments:

  • Chl-a, Chl-c.
  • Ξ²-carotene.
  • Fucoxanthin (brown).

Why Brown Algae Look Brown (Phaeophyta)

  • Brown algae contain the usual chlorophyll-a and chlorophyll-c, plus Ξ²-carotene.
  • The dominant pigment is fucoxanthin (a xanthophyll carotenoid).
  • Fucoxanthin masks the green colour of chlorophyll, giving the thallus its distinct brown to olive-green colour.
  • Intensity of brown colour depends on fucoxanthin concentration in the chloroplasts.

Stored food:

  • Laminarin, Mannitol.
  • Laminarin (a Ξ²-1,3 glucan polysaccharide).
  • Mannitol (a sugar alcohol, serves as both storage and transport form).

Phycocolloids:

  • Phycocolloids are water-absorbing polysaccharides in algae cell walls (mainly brown & red algae)
  • Chemically including fucinic acid, alginic acid, fucoidin (protective).

Uses of phycocolloids:

  • Ice cream, dental mould, paper-making.

Reproduction:

  • Vegetative β†’ fragmentation.
  • Asexual β†’ zoospores (pear-shaped, biflagellate, lateral flagella).
    • Unilocular sporangia β†’ haploid spores.
    • Plurilocular sporangia β†’ diploid spores.
  • Sexual β†’ iso-, aniso-, oogamous.

Life cycle:

  • Diplohaplontic or diplontic (Fucus).

Special forms:

  • Postelsia β†’ sea palm.
  • Ancyclonema β†’ ice bloom.
  • Sargassum β†’ gulf weed (Sargasso Sea).
  • Laminaria β†’ devil’s apron.
  • Others: Ectocarpus, Dictyota, Fucus.

Economic importance:

  • 70% species used as fodder.
  • Alginates (Laminaria, Fucus, Macrocystis) β†’ soaps, ice-cream, polish, plastics.
  • Source of iodine & bromine.

Rhodophyta (Red Algae)

  • Ancient after blue-green algae (BGA).
  • Mostly marine, warm waters.
  • No motile stages.
  • Mostly multicellular; exception = Porphyridium (unicell).
  • Predominantly marine, mostly in warm seas.
  • Freshwater red algae: Batrachospermum.
  • Terrestrial red algae: Porphyridium.
  • Some become calcified: Corallina, Lithothamnion.

Cell features:

  • Pseudoparenchymatous thallus.
  • Cell wall: cellulose, pectin, xylan, mannan, galactose, polyuronic acids, polysulphate esters.
  • Pit connections between cells.

Pigments:

  • Chl-a, Chl-d.
  • Ξ²-carotene.
  • Phycobilins: R-phycoerythrin (red), R-phycocyanin (blue).
  • Gaudikov’s effect: colour of red algae varies with depth.
  • Surface red algae: R-phycocyanin is relatively more abundant (surface zone).
  • Deep-water red algae: phycoerythrin is relatively more abundant (deep zone).
  • PDF note (verbatim): β€œUltra-violet and violet light have high penetration power so these light reach at the deepest zone.”

Stored food:

  • Floridean starch.
  • Floridean starch (branched polysaccharide, glycogen-like, cytoplasmic).
  • Often associated with floridoside (a sugar alcohol derivative).

Reproduction:

  • Vegetative β†’ fragmentation.
  • Asexual β†’ non-motile spores (monospore, carpospore, tetraspore).
  • Sexual β†’ oogamous.
    • Female: carpogonium with trichogyne.
    • Male: spermatangia, spermatia (non-motile).

Life cycle:

  • Polysiphonia β†’ triphasic (gametophyte, carposporophyte, tetrasporophyte).

Economic importance:

  • Bromine source: Polysiphonia, Rhodomela.
  • Parasitic: Harveyella.
  • Food: Porphyra.
  • Agar: Gelidium, Gracilaria.
  • Carrageenin: Chondrus crispus (Irish moss).
  • Glue: Gloiopeltis.
  • Haematococcus nivalis β†’ red snow.

Xanthophyta (Yellow-Green Algae)

  • Acellular, coenocytic (siphonaceous thallus).
  • Found in moist soil.

Pigments:

  • Chl-a, Chl-e.
  • Ξ²-carotene.
  • Many xanthophylls β†’ yellow colour.

Stored food:

  • Leucosin (a carbohydrate reserve, similar to starch).
  • Oil droplets.

Reproduction:

  • Vegetative β†’ fragmentation.
  • Asexual β†’ zoospores, synzoospores (multinucleated).
  • Example: Vaucheria (shows synzoospore type).

Examples:

  • Vaucheria, Botrydium, Tribonema.

Phycocolloids

What are they?

  • Phycocolloids are hydrophilic (water-loving) polysaccharides present in the cell walls of certain algae, especially brown algae (Phaeophyta) and red algae (Rhodophyta).
  • They act as colloidal substances, making the thallus slimy, flexible, and resistant to desiccation.

Major Chemicals (from Brown & Red Algae)

From Brown Algae (Phaeophyta):

  • Fucinic acid
  • Alginic acid (alginates)
  • Fucoidin (fucosan)

From Red Algae (Rhodophyta):

  • Agar (agar-agar) β†’ obtained from Gelidium, Gracilaria.
  • Carrageenin β†’ obtained from Chondrus crispus (Irish moss).
  • Funori (a glue-like substance) β†’ from Gloiopeltis.

βœ… Functions in Algae

  • Provide mechanical protection to the thallus.
  • Form a gel-like sheath β†’ helps in water retention and prevents desiccation (drying).
  • Maintain flexibility and resistance in marine conditions (e.g., waves).

βœ… Economic Uses (Human Applications)

  • Alginates β†’ ice-cream, jelly, cosmetics, paper, polish, textiles, plastics, dental moulds.
  • Agar β†’ microbial culture medium, food industry (jellies, puddings, ice-cream), pharmaceuticals.
  • Carrageenin β†’ thickener, stabilizer in dairy & bakery products, toothpaste, cosmetics.
  • Funori (glue) β†’ adhesives.

Practice Questions

Q1.
Assertion (A): Algae are mostly aquatic and found in both fresh and marine water.
Reason (R): The plant body of algae is always diploid.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (c)

Q2.
Assertion (A): Red algae can grow at the greatest depths in the sea.
Reason (R): R-phycoerythrin can absorb light of shorter wavelengths (violet & UV), which penetrates to great depths.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (a)

Q3.
Assertion (A): In brown algae, laminarin and mannitol are the reserve food.
Reason (R): Fucoxanthin pigment is responsible for the brown colour of these algae.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (b)

Q4.
Assertion (A): The cell wall of green algae is made up of inner cellulose and outer pectin layer.
Reason (R): In red algae, calcium carbonate may be present in the cell wall.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (b)

Q5.
Assertion (A): In Chlamydomonas, sexual reproduction may be isogamous, anisogamous or oogamous.
Reason (R): Chlamydomonas shows complete evolution of sexual reproduction.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (a)

Q6.
Assertion (A): Volvox is a motile colonial alga.
Reason (R): Motility in Volvox is due to numerous cilia covering the cell surface.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (c) (motility is due to flagella, not cilia)

Q7.
Assertion (A): Alginates are commercially obtained from brown algae.
Reason (R): Alginates are salts of alginic acid present in the cell wall of brown algae.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (a)

Q8.
Assertion (A): Cephaleuros virescens is a parasitic alga.
Reason (R): It causes red rust of tea.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (a)

Q9.
Assertion (A): Brown algae are the largest algae.
Reason (R): Macrocystis, a brown alga, may grow up to 100 meters in length.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (a)

Q10.
Assertion (A): Floridean starch is the reserve food material in red algae.
Reason (R): Floridean starch is structurally similar to glycogen and amylopectin.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Answer: (a)

Q11. Consider the following statements about algae:
I. Algae are mostly aquatic, found in both fresh and marine water.
II. Algae possess a well-developed vascular tissue system.
III. Sex organs in algae are mostly unicellular and jacketless.
IV. Algae can be unicellular, colonial, filamentous or parenchymatous.

(a) I, III and IV are correct
(b) Only II is correct
(c) I and II are correct
(d) All are correct

Answer: (a)

Q12. Consider the following about Green Algae:
I. They contain chlorophyll a and b.
II. They store food as starch.
III. Their cell wall has inner cellulose and outer pectin layer.
IV. Their reserve food is mannitol.

(a) I, II and III are correct
(b) Only IV is correct
(c) I and IV are correct
(d) All are correct

Answer: (a)

Q13. Regarding Brown Algae, which statements are correct?
I. They contain fucoxanthin pigment.
II. They store food as laminarin and mannitol.
III. They are the largest algae, e.g., Macrocystis.
IV. Their zoospores have equal flagella.

(a) I, II and III are correct
(b) Only IV is correct
(c) I and IV are correct
(d) All are correct

Answer: (a)

Q14. Which of the following statements about Red Algae are correct?
I. They contain chlorophyll a and d.
II. They store food as floridean starch.
III. They always possess motile reproductive stages.
IV. Calcium carbonate deposition may occur in some forms.

(a) I, II and IV are correct
(b) Only III is correct
(c) II and III are correct
(d) All are correct

Answer: (a)

Q15. Which of the following is/are correct about Volvox?
I. It is a motile colonial alga.
II. The number of cells in its colony is fixed.
III. It belongs to Rhodophyceae.
IV. Motility is due to flagella.

(a) I, II and IV are correct
(b) Only III is correct
(c) I and III are correct
(d) All are correct

Answer: (a)

Q16. About Chlamydomonas, which statements are correct?
I. It is a motile unicellular green alga.
II. It shows isogamous, anisogamous and oogamous reproduction.
III. It moves with the help of cilia.
IV. It exhibits complete evolution of sexual reproduction.

(a) I, II and IV are correct
(b) Only III is correct
(c) I and III are correct
(d) All are correct

Answer: (a)

Q17. Consider the following statements about Cephaleuros:
I. It is a parasitic green alga.
II. It causes red rust of tea.
III. It is an endozoic alga.
IV. It is economically important as a food source.

(a) I and II are correct
(b) II and III are correct
(c) III and IV are correct
(d) All are correct

Answer: (a)

Q18. Regarding Ulothrix, which statements are correct?
I. It is filamentous and called pond wool.
II. It reproduces by conjugation.
III. It shows haplontic life cycle.
IV. Its sex organs are multicellular and jacketed.

(a) I and III are correct
(b) II and IV are correct
(c) I, II and III are correct
(d) All are correct

Answer: (a)

Q19. Which of the following statements about economic importance of algae are correct?
I. Agar is obtained from Gelidium and Gracilaria.
II. Carrageenin is obtained from Chondrus.
III. Alginates are obtained from brown algae.
IV. Penicillin is obtained from Chlorella.

(a) I, II and III are correct
(b) Only IV is correct
(c) II, III and IV are correct
(d) All are correct

Answer: (a)

Q20. Which of the following statements about Batrachospermum are correct?
I. It is a freshwater red alga.
II. It may appear bluish in colour.
III. It contains phycoerythrin pigment.
IV. It is the largest unicellular alga.

(a) I, II and III are correct
(b) Only IV is correct
(c) I and IV are correct
(d) All are correct

Answer: (a)

Q21.
If red algae can grow at greater depths compared to green algae, the most appropriate reason is:
(a) They contain R-phycoerythrin which absorbs blue/green light efficiently.
(b) They have fucoxanthin pigment.
(c) They have motile reproductive stages.
(d) They store food as laminarin.
Answer: (a)

Q22.
Which of the following best explains why brown algae can grow very large (e.g., Macrocystis up to 100 m)?
(a) Presence of fucoxanthin pigment
(b) Presence of trumpet hyphae for conduction
(c) Storage of mannitol and laminarin
(d) Calcium carbonate deposition in thallus
Answer: (b)

Q23.
In Chara, sex organs are multicellular and jacketed, unlike most algae. This feature indicates:
(a) Adaptation towards advanced sexual reproduction similar to land plants
(b) Regression of sexual reproduction
(c) Lack of differentiation in gametangia
(d) Presence of only vegetative reproduction
Answer: (a)

Q24.
Polysiphonia exhibits a triphasic life cycle (gametophyte β†’ carposporophyte β†’ tetrasporophyte). The adaptive significance of this cycle is:
(a) To reduce gamete formation
(b) To enhance post-fertilization development and spore output
(c) To avoid alternation of generations
(d) To ensure absence of diploid phase
Answer: (b)

Q25.
Ulothrix and Spirogyra show haplontic life cycle, whereas Fucus shows diplontic. This indicates:
(a) Algae show uniform life cycles across groups
(b) Evolutionary diversity in life cycle strategies
(c) Only red algae are haplodiplontic
(d) Diplontic life cycle is primitive in algae
Answer: (b)

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