Algae
Algae are simple, chlorophyll-bearing, thalloid and autotrophic organisms that live mostly in water. These notes on algae first explain how the plant kingdom is classified: artificial, natural and phylogenetic systems, and the newer aids of numerical taxonomy, cytotaxonomy and chemotaxonomy. They then cover reproduction, the uses of algae, and the three classes with their pigments, stored food, cell walls, flagella and examples. Every point of the NCERT text is covered, and the class comparison table is the part NEET asks most often.
- ★ Must learn Whittaker (1969) gave five kingdoms. Plantae now excludes fungi and walled members of Monera and Protista; cyanobacteria are no longer algae.
- Classification of plants moved from artificial (Linnaeus) to natural (Bentham and Hooker) to phylogenetic systems.
- Numerical taxonomy codes all observable characters; cytotaxonomy uses chromosomes; chemotaxonomy uses chemical constituents.
- ★ Must learn Algae: chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic organisms.
- ★ Must learn Isogamy: Ulothrix, Spirogyra. Anisogamy: Eudorina. Oogamy: Volvox, Fucus.
- Algae carry out at least half of the total fixation on earth.
- Algin comes from brown algae, carrageen from red algae, and agar from Gelidium and Gracilaria.
- Chlorella is a protein-rich unicellular alga used as a food supplement by space travellers.
- ★ Must learn Green algae: chlorophyll a and b, starch, pyrenoids, wall of cellulose (inner) and pectose (outer).
- ★ Must learn Brown algae: chlorophyll a, c and fucoxanthin; laminarin or mannitol; algin coat; holdfast, stipe, frond.
- Red algae: chlorophyll a, d and r-phycoerythrin; floridean starch; no flagella; oogamous.
1. The Plant Kingdom and Its Classification
1.1 What Kingdom Plantae includes
- Whittaker (1969) proposed the Five Kingdom classification: Monera, Protista, Fungi, Animalia and Plantae.
- Kingdom Plantae is popularly called the plant kingdom. These pages deal with its further classification.
- ★ Exam imp Our understanding of the plant kingdom has changed over time.
- Fungi, and members of Monera and Protista having cell walls, are now excluded from Plantae.
- Earlier classifications had placed all of these in the plant kingdom.
- ★ Exam imp So cyanobacteria, also called blue-green algae, are no longer treated as algae.
- Kingdom Plantae now includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
The five plant groups in order: All Bright Pupils Get Admission: Algae, Bryophytes, Pteridophytes, Gymnosperms, Angiosperms.
1.2 Three systems of classification
- The earliest systems used only gross superficial morphological characters: habit, colour, and number and shape of leaves.
- They were based mainly on vegetative characters or on the structure of the androecium.
- The system based on the androecium was given by Linnaeus.
- Such systems were artificial. They separated closely related species, because they used only a few characteristics.
- Artificial systems gave equal weightage to vegetative and sexual characteristics.
- This is not acceptable, because vegetative characters are more easily affected by the environment.
- ★ Exam imp Natural systems are based on natural affinities among organisms.
- They use external features and also internal features: ultrastructure, anatomy, embryology and phytochemistry.
- George Bentham and Joseph Dalton Hooker gave such a natural classification for flowering plants.
- ★ Exam imp Phylogenetic systems are based on evolutionary relationships and are acceptable at present.
- They assume that organisms belonging to the same taxa have a common ancestor.
| System | Basis | Key point |
|---|---|---|
| Artificial | A few gross morphological characters; vegetative characters or androecium (Linnaeus) | Separated closely related species; equal weightage to vegetative and sexual characters |
| Natural | Natural affinities; external and internal features | Bentham and Hooker, for flowering plants |
| Phylogenetic | Evolutionary relationships | Taxa share a common ancestor; acceptable at present |
Order in which the systems developed: A-N-P, read as "A New Path": Artificial, then Natural, then Phylogenetic.
1.3 Other sources of information
- Taxonomists also use information from many other sources to resolve difficulties in classification.
- These sources matter most when there is no supporting fossil evidence.
- Numerical taxonomy: carried out easily using computers and based on all observable characteristics.
- In numerical taxonomy, numbers and codes are assigned to all characters and the data are then processed.
- Each character gets equal importance, and hundreds of characters can be considered at the same time.
- Cytotaxonomy: based on cytological information such as chromosome number, structure and behaviour.
- Chemotaxonomy: uses the chemical constituents of the plant to resolve confusions.
| Branch | Information used |
|---|---|
| Numerical taxonomy | All observable characters, coded as numbers and processed by computer |
| Cytotaxonomy | Chromosome number, structure and behaviour |
| Chemotaxonomy | Chemical constituents of the plant |
Read the stem of the question. Evolution or common ancestor points to phylogenetic. Anatomy, embryology or phytochemistry points to natural. Androecium, habit or leaf shape points to artificial. "Equal importance to every character" points to numerical taxonomy.
2. Algae: General Features
★ Very important Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic organisms. A thallus is a plant body not differentiated into true root, stem and leaves.
- Autotrophic: they make their own food by photosynthesis.
- ★ Exam imp They are largely aquatic, living in both fresh water and marine habitats.
- They also occur in other habitats: moist stones, soils and wood.
- Some live in association with fungi, forming a lichen.
- Some live in association with animals, for example on the sloth bear.
- The form and size of algae are highly variable.
- Colonial forms: Volvox. Filamentous forms: Ulothrix and Spirogyra.
- A few marine forms, such as kelps, form massive plant bodies.
3. Reproduction in Algae
- Algae reproduce by three methods: vegetative, asexual and sexual.
- Vegetative reproduction is by fragmentation. Each fragment develops into a thallus.
- Asexual reproduction is by different types of spores.
- ★ Exam imp The most common spores are zoospores.
- Zoospores are flagellated (motile). On germination they give rise to new plants.
- Sexual reproduction takes place through the fusion of two gametes.
3.1 Isogamy, anisogamy and oogamy
| Type | Gametes | Example |
|---|---|---|
| Isogamous | Similar in size and flagellated | Ulothrix |
| Isogamous | Similar in size but non-flagellated (non-motile) | Spirogyra |
| Anisogamous | Dissimilar in size | Species of Eudorina |
| Oogamous | One large, non-motile (static) female gamete and a smaller, motile male gamete | Volvox, Fucus |
★ Very important Isogamy: fusion of two gametes similar in size. Anisogamy: fusion of two gametes dissimilar in size. Oogamy: fusion of a large non-motile female gamete with a smaller motile male gamete.
Examples from equal to unequal gametes: Use Simple English, Very Fluently. Ulothrix and Spirogyra (isogamy), Eudorina (anisogamy), Volvox and Fucus (oogamy).
Spirogyra has non-motile gametes, yet it is isogamous, because its gametes are similar in size. Oogamy needs both conditions: a large non-motile egg and a small motile male gamete.
4. Uses of Algae
- ★ Exam imp Algae carry out at least half of the total fixation on earth through photosynthesis.
- Being photosynthetic, they increase the level of dissolved oxygen in their immediate environment.
- They are primary producers of energy-rich compounds, which form the basis of the food cycles of all aquatic animals.
- Many species of Porphyra, Laminaria and Sargassum are used as food.
- They are among the 70 species of marine algae used as food.
- Certain marine brown and red algae produce large amounts of hydrocolloids (water-holding substances).
- Hydrocolloids used commercially: algin from brown algae and carrageen from red algae.
- ★ Exam imp Agar is a commercial product obtained from Gelidium and Gracilaria.
- Agar is used to grow microbes and in preparing ice-creams and jellies.
- Chlorella is a unicellular alga rich in proteins.
- Chlorella is used as a food supplement, even by space travellers.
| Product or use | Source | Use |
|---|---|---|
| Food | Porphyra, Laminaria, Sargassum (among 70 marine species) | Eaten as food |
| Algin (hydrocolloid) | Brown algae | Commercial uses |
| Carrageen (hydrocolloid) | Red algae | Commercial uses |
| Agar | Gelidium, Gracilaria (red algae) | Growing microbes; ice-creams and jellies |
| Protein supplement | Chlorella (unicellular green alga) | Food supplement, even for space travellers |
Agar comes from two Gs: Gelidium and Gracilaria. Algin is also the gelatinous coat on brown algal cell walls, so algin comes from brown algae; carrageen comes from red algae.
Which two genera give agar?
Which hydrocolloid comes from red algae?
Name the protein-rich alga used by space travellers.
What is the most common type of asexual spore in algae?
5. Chlorophyceae (Green Algae)
- Members of Chlorophyceae are commonly called green algae.
- The plant body may be unicellular, colonial or filamentous.
- They are usually grass green, because chlorophyll a and b are the dominant pigments.
- The pigments are localised in definite chloroplasts.
- Chloroplasts may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped in different species.
- ★ Exam imp Most members have one or more storage bodies called pyrenoids, located in the chloroplasts.
- Pyrenoids contain protein besides starch.
- Some algae store food in the form of oil droplets.
- Green algae usually have a rigid cell wall: an inner layer of cellulose and an outer layer of pectose.
- Vegetative reproduction usually takes place by fragmentation.
- Asexual reproduction is by flagellated zoospores produced in zoosporangia.
- Sexual reproduction varies greatly in the type and formation of sex cells. It may be isogamous, anisogamous or oogamous.
- Common green algae: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara.
★ Very important Pyrenoids are storage bodies in the chloroplasts of green algae. They contain protein besides starch.
Chloroplast shapes: Do Play Real Cricket Shots Regularly: Discoid, Plate-like, Reticulate, Cup-shaped, Spiral, Ribbon-shaped. Green algae examples: Clean Villages Use Solar Cells: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.
6. Phaeophyceae (Brown Algae)
- Members of Phaeophyceae, the brown algae, are found primarily in marine habitats.
- They show great variation in size and form.
- They range from simple branched, filamentous forms (Ectocarpus) to profusely branched kelps.
- ★ Exam imp Kelps may reach a height of 100 metres.
- Pigments: chlorophyll a, c, carotenoids and xanthophylls.
- Their colour varies from olive green to shades of brown.
- The colour depends on the amount of the xanthophyll pigment fucoxanthin present.
- ★ Exam imp Food is stored as complex carbohydrates: laminarin or mannitol.
- The vegetative cells have a cellulosic wall, usually covered outside by a gelatinous coating of algin.
- The protoplast contains plastids, a centrally located vacuole and a nucleus.
- The plant body is usually attached to the substratum by a holdfast.
- It has a stalk, the stipe, and a leaf-like photosynthetic organ, the frond.
- Vegetative reproduction takes place by fragmentation.
- Asexual reproduction in most brown algae is by biflagellate zoospores.
- These zoospores are pear-shaped, with two unequal, laterally attached flagella.
- Sexual reproduction may be isogamous, anisogamous or oogamous.
- Gametes unite in water, or within the oogonium in oogamous species.
- The gametes are pyriform (pear-shaped) and bear two laterally attached flagella.
- Common forms: Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.
Brown algae examples: Every Day Large Ships Float: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus. Body parts from base to top: Hold, Stand, Feed: holdfast holds, stipe stands, frond feeds by photosynthesis.
Laminarin takes its name from Laminaria, a brown alga. So laminarin, with mannitol, is the stored food of brown algae.
7. Rhodophyceae (Red Algae)
- ★ Exam imp Members of Rhodophyceae are called red algae, because the red pigment r-phycoerythrin predominates in their body.
- Most red algae are marine, with greater concentrations in the warmer areas.
- They occur in well-lighted regions close to the water surface.
- They also occur at great depths in oceans, where relatively little light penetrates.
- The red thalli of most red algae are multicellular. Some have a complex body organisation.
- ★ Exam imp Food is stored as floridean starch, very similar in structure to amylopectin and glycogen.
- Red algae usually reproduce vegetatively by fragmentation.
- They reproduce asexually by non-motile spores and sexually by non-motile gametes.
- Sexual reproduction is oogamous and is accompanied by complex post-fertilisation developments.
- Common members: Polysiphonia, Porphyra, Gracilaria and Gelidium.
Red algae examples: two Ps and two Gs: Polysiphonia, Porphyra, Gracilaria, Gelidium. The two Gs are also the two sources of agar.
Extra Depth: Red algae can grow at great depths partly because r-phycoerythrin absorbs the blue and green light that penetrates deep water.
8. The Three Classes Compared
| Feature | Chlorophyceae | Phaeophyceae | Rhodophyceae |
|---|---|---|---|
| Common name | Green algae | Brown algae | Red algae |
| Major pigments | Chlorophyll a, b | Chlorophyll a, c, fucoxanthin | Chlorophyll a, d, phycoerythrin |
| Stored food | Starch | Mannitol, laminarin | Floridean starch |
| Cell wall | Cellulose | Cellulose and algin | Cellulose, pectin and poly sulphate esters |
| Flagella: number and position of insertion | 2-8, equal, apical | 2, unequal, lateral | Absent |
| Habitat | Fresh water, brackish water, salt water | Fresh water (rare), brackish water, salt water | Fresh water (some), brackish water, salt water (most) |
★ Very important NEET most often asks this table: the pigments, stored food, cell wall and flagella of each class.
Take the classes in the order Green, Brown, Red. The second chlorophyll runs b, c, d: green has a and b, brown has a and c, red has a and d.
Flagella fall from green to red: 2-8 equal at the apex, then 2 unequal at the side, then none. Red algae have non-motile spores and gametes, so they need no flagella.
- Chlorophyll a, c and fucoxanthin
- Laminarin or mannitol
- Cellulose wall with algin coat
- 2 unequal lateral flagella
- Primarily marine; rare in fresh water
- Iso-, aniso- or oogamous
- Chlorophyll a, d and r-phycoerythrin
- Floridean starch
- Cellulose, pectin, poly sulphate esters
- Flagella absent
- Mostly marine; some in fresh water
- Oogamous only
9. Exam Essentials: Traps, Exceptions, Numbers and Pairs
Points NEET builds statements and match lists from:
- Chlorophyll c is listed only for brown algae, and chlorophyll d only for red algae.
- Brown algae store laminarin or mannitol, not starch. Red algae store floridean starch.
- Pyrenoids (protein plus starch) belong to green algae.
- Red algae have no flagella; brown algae have 2 unequal lateral flagella; green algae have 2-8 equal apical flagella.
- Agar comes from red algae (Gelidium, Gracilaria); algin from brown algae; carrageen from red algae.
- Volvox is both colonial and oogamous; Ulothrix is filamentous and isogamous.
Exceptions
- Cyanobacteria are called blue-green algae, yet they are not algae any more.
- Spirogyra gametes are non-motile, yet its reproduction is isogamous, not oogamous.
- Most green algae have pyrenoids; some algae also store food as oil droplets.
- Brown algae are rare in fresh water; red algae occur in fresh water only in some species.
- Asexual reproduction is by biflagellate zoospores in most brown algae, not all.
- Red algae are the only class with no flagellated stage: spores and gametes are both non-motile.
- Red algae are only oogamous; green and brown algae may be isogamous, anisogamous or oogamous.
Numbers to Remember
- 1969: Whittaker's Five Kingdom classification.
- At least half of the total fixation on earth is by algae.
- 70 species of marine algae are used as food.
- 100 metres: the height kelps may reach.
- 3 classes of algae: Chlorophyceae, Phaeophyceae, Rhodophyceae.
- Flagella: 2-8 (green), 2 (brown), 0 (red).
Examples to Remember
| Group or feature | Examples |
|---|---|
| Green algae | Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara; Chlorella |
| Brown algae | Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus; kelps |
| Red algae | Polysiphonia, Porphyra, Gracilaria, Gelidium |
| Colonial / filamentous | Volvox / Ulothrix, Spirogyra; branched filamentous Ectocarpus |
| Isogamous / anisogamous / oogamous | Ulothrix, Spirogyra / Eudorina / Volvox, Fucus |
| Algae eaten as food | Porphyra, Laminaria, Sargassum |
Pairs to Match
| Item | Matches with |
|---|---|
| Linnaeus | Artificial system based on the androecium |
| Bentham and Hooker | Natural classification of flowering plants |
| Numerical taxonomy | All observable characters coded and processed by computer |
| Cytotaxonomy | Chromosome number, structure and behaviour |
| Chemotaxonomy | Chemical constituents of the plant |
| Eudorina | Anisogamy |
| Fucus | Oogamy; air bladders on the frond |
| Pyrenoid | Protein and starch store in green algal chloroplast |
| Fucoxanthin | Olive green to brown colour |
| r-phycoerythrin | Red colour of red algae |
| Floridean starch | Red algae; similar to amylopectin and glycogen |
| Laminarin, mannitol | Stored food of brown algae |
| Algin / carrageen | Brown algae / red algae |
| Gelidium, Gracilaria | Agar |
| Chlorella | Protein supplement for space travellers |
In Fucus, name the swollen gas-filled structures on the frond.
What anchors Laminaria to the substratum?
What are the small colonies inside a Volvox colony called?
In Polysiphonia, what bears the many side branches?
Which brown algal pigment decides its shade of colour?
10. Quick Revision
- Whittaker (1969): five kingdoms; Plantae excludes fungi and walled Monera and Protista.
- Cyanobacteria (blue-green algae) are no longer algae.
- Artificial (Linnaeus, few characters) to natural (Bentham and Hooker) to phylogenetic (common ancestor).
- Numerical taxonomy: all characters coded, equal weight; cytotaxonomy: chromosomes; chemotaxonomy: chemicals.
- Algae: chlorophyll-bearing, simple, thalloid, autotrophic, largely aquatic; also on stones, soil, wood, sloth bear.
- Vegetative: fragmentation. Asexual: spores, mostly motile zoospores. Sexual: fusion of two gametes.
- Isogamy: Ulothrix, Spirogyra; anisogamy: Eudorina; oogamy: Volvox, Fucus.
- At least half of the earth's carbon dioxide fixation is by algae; they raise dissolved oxygen.
- Food: Porphyra, Laminaria, Sargassum; algin (brown), carrageen (red), agar (Gelidium, Gracilaria); Chlorella.
- Green: chlorophyll a, b; starch; pyrenoids; cellulose and pectose wall; 2-8 equal apical flagella.
- Brown: chlorophyll a, c, fucoxanthin; laminarin, mannitol; algin; holdfast, stipe, frond; 2 unequal lateral flagella.
- Red: chlorophyll a, d, r-phycoerythrin; floridean starch; no flagella; oogamous; mostly marine, near the surface and at great depths.
- Classes of algae are based on pigments and stored food.
11. Solved Examples
| List I | List II |
|---|---|
| A. Chlorophyceae | I. Floridean starch |
| B. Phaeophyceae | II. Starch |
| C. Rhodophyceae | III. Laminarin or mannitol |
| D. Cyanobacteria | IV. No longer classed as algae |
(1) A-II, B-I, C-III, D-IV
(2) A-III, B-II, C-I, D-IV
(3) A-II, B-III, C-I, D-IV
(4) A-I, B-III, C-II, D-IV
Answer: (3). Green algae store starch (II), brown algae laminarin or mannitol (III), red algae floridean starch (I). Cyanobacteria, though called blue-green algae, are no longer algae (IV).
A. They possess chlorophyll a, c, carotenoids and xanthophylls.
B. Their cell wall is covered on the outside by a coating of algin.
C. Their zoospores have two equal, apical flagella.
D. The frond is the leaf-like photosynthetic organ.
E. They store food as floridean starch.
Choose the correct answer from the options given below:
(1) A, B, D and E only
(2) A, C and D only
(3) B, C and E only
(4) A, B and D only
Answer: (4). C is wrong: the flagella are unequal and laterally attached. E is wrong: floridean starch is the food of red algae; brown algae store laminarin or mannitol.
A. Phylogenetic systems based on evolutionary relationships
B. Artificial systems based on a few morphological characters
C. Natural systems based on natural affinities
Choose the correct answer from the options given below:
(1) C, B, A
(2) B, C, A
(3) B, A, C
(4) A, C, B
Answer: (2). The earliest systems were artificial (B), natural systems such as that of Bentham and Hooker followed (C), and phylogenetic systems (A) are accepted at present.
(1) Laminaria and Sargassum
(2) Gelidium and Gracilaria
(3) Chlorella and Spirogyra
(4) Fucus and Dictyota
Answer: (2). Agar is a commercial product of the red algae Gelidium and Gracilaria.
(1) Their red colour is due to r-phycoerythrin.
(2) They store floridean starch, which resembles amylopectin and glycogen.
(3) Their asexual spores are biflagellate zoospores.
(4) Sexual reproduction is oogamous with complex post-fertilisation developments.
Answer: (3). Red algae reproduce asexually by non-motile spores; flagella are absent in this class.
Statement I: Numerical taxonomy gives equal importance to every character and can consider hundreds of characters at once.
Statement II: Cytotaxonomy uses the chemical constituents of a plant to resolve confusions.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both Statement I and Statement II are correct
(2) Both Statement I and Statement II are incorrect
(3) Statement I is correct but Statement II is incorrect
(4) Statement I is incorrect but Statement II is correct
Answer: (3). Statement I is correct. Statement II describes chemotaxonomy; cytotaxonomy uses chromosome number, structure and behaviour.
12. Practice Questions
- Match List I with List II.
Choose the correct answer from the options given below:
List I List II A. Eudorina I. Oogamy B. Spirogyra II. Protein-rich food supplement C. Volvox III. Anisogamy D. Chlorella IV. Isogamy with non-flagellated gametes
(1) A-IV, B-III, C-I, D-II
(2) A-III, B-IV, C-I, D-II
(3) A-III, B-I, C-IV, D-II
(4) A-I, B-IV, C-III, D-IIAnswer: (2). Eudorina is anisogamous, Spirogyra isogamous with non-motile gametes, Volvox oogamous, and Chlorella a protein supplement. - Which statements about green algae are correct?
A. Chlorophyll a and b are the dominant pigments.
B. Pyrenoids contain protein besides starch.
C. The outer layer of the cell wall is made of cellulose.
D. Asexual reproduction is by flagellated zoospores formed in zoosporangia.
Choose the correct answer from the options given below:
(1) A and C only
(2) A, B and C only
(3) B, C and D only
(4) A, B and D onlyAnswer: (4). C is wrong: cellulose forms the inner layer and pectose the outer layer. - Arrange the parts of a brown alga from the base upwards.
A. Frond
B. Holdfast
C. Stipe
Choose the correct answer from the options given below:
(1) B, C, A
(2) C, B, A
(3) A, C, B
(4) B, A, CAnswer: (1). The holdfast attaches the plant, the stipe forms the stalk, and the frond sits on top. - Cyanobacteria are no longer placed with the algae because:
(1) they lack chlorophyll
(2) Monera and Protista members with cell walls are now excluded from Plantae
(3) they are not aquatic
(4) they reproduce only sexuallyAnswer: (2). Walled members of Monera, to which cyanobacteria belong, are now excluded from Plantae. - Which pair is NOT correctly matched?
(1) Chlorophyceae: 2-8 equal, apical flagella
(2) Phaeophyceae: cellulose and algin wall
(3) Rhodophyceae: chlorophyll a and c
(4) Rhodophyceae: floridean starchAnswer: (3). Red algae have chlorophyll a and d; chlorophyll a and c belong to brown algae. - Given below are two statements:
Statement I: Bentham and Hooker gave a natural classification of flowering plants.
Statement II: Artificial systems gave more weightage to sexual characters than to vegetative characters.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both Statement I and Statement II are correct
(2) Both Statement I and Statement II are incorrect
(3) Statement I is correct but Statement II is incorrect
(4) Statement I is incorrect but Statement II is correctAnswer: (3). Artificial systems gave equal weightage to vegetative and sexual characters, which is the flaw. - What is the basis of classification of algae?Answer: Mainly the type of pigment and the type of stored food. Cell wall, flagella and habitat also differ between the three classes.
- Write a note on the economic importance of algae.Answer: Algae fix at least half of the earth's carbon dioxide and raise dissolved oxygen. They are primary producers for aquatic food cycles. Porphyra, Laminaria and Sargassum are eaten. Algin (brown), carrageen (red) and agar (Gelidium, Gracilaria) are commercial products. Chlorella is a protein supplement.
- Explain isogamy with a suitable example.Answer: Isogamy is the fusion of two gametes similar in size. The gametes are flagellated in Ulothrix and non-flagellated in Spirogyra.
- Differentiate between red algae and brown algae.Answer: Red: chlorophyll a, d and r-phycoerythrin; floridean starch; wall of cellulose, pectin and poly sulphate esters; no flagella. Brown: chlorophyll a, c and fucoxanthin; laminarin or mannitol; cellulose wall with algin; 2 unequal lateral flagella.
Common Mistakes to Avoid
- Calling cyanobacteria algae. They are blue-green algae by name only and are no longer algae.
- Writing chlorophyll a and c for red algae. Red algae have chlorophyll a and d; brown algae have a and c.
- Saying brown algae store starch. They store laminarin or mannitol; red algae store floridean starch.
- Calling Spirogyra oogamous because its gametes are non-motile. Its gametes are equal in size, so it is isogamous.
- Placing pectose inside the green algal wall. Cellulose is the inner layer and pectose the outer layer.
- Linking agar with brown algae. Agar comes from the red algae Gelidium and Gracilaria.
- Mixing up cytotaxonomy (chromosomes) and chemotaxonomy (chemical constituents).
- Giving red algae flagellated zoospores. Red algae have no flagella at any stage.
Frequently Asked Questions
What are algae?
Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic organisms. They live in fresh water and the sea, and also on moist stones, soils and wood. Some live with fungi as lichens, and some on animals such as the sloth bear. Their form ranges from colonies and filaments to massive kelps.
On what basis are algae divided into three classes?
Algae are classified mainly by the pigments they possess and the food they store. Green algae have chlorophyll a and b and store starch. Brown algae have chlorophyll a, c and fucoxanthin and store laminarin or mannitol. Red algae have chlorophyll a, d and phycoerythrin and store floridean starch.
What is the difference between isogamy, anisogamy and oogamy?
In isogamy the two fusing gametes are similar in size, as in Ulothrix and Spirogyra. In anisogamy they differ in size, as in Eudorina. In oogamy a large non-motile female gamete fuses with a smaller motile male gamete, as in Volvox and Fucus.
Why are cyanobacteria not called algae any more?
Our understanding of the plant kingdom has changed. Fungi, and members of Monera and Protista having cell walls, are now excluded from Plantae. Cyanobacteria belong to Monera, so although they are still called blue-green algae, they are no longer classified as algae.
What are pyrenoids?
Pyrenoids are storage bodies found in the chloroplasts of most green algae. Each chloroplast may have one or more of them. Pyrenoids contain protein besides starch, so they act as food stores inside the chloroplast. Some green algae also store food in the form of oil droplets. Pyrenoids are a typical feature of green algae.
Which algae give agar, algin and carrageen?
Agar is obtained from the red algae Gelidium and Gracilaria and is used to grow microbes and in ice-creams and jellies. Algin is a hydrocolloid from brown algae, and carrageen is a hydrocolloid from red algae. Both are water-holding substances used commercially.
How do natural and phylogenetic classifications differ?
Natural systems group organisms by natural affinities using external and internal features such as anatomy, embryology and phytochemistry; Bentham and Hooker gave one for flowering plants. Phylogenetic systems are based on evolutionary relationships and assume that members of a taxon share a common ancestor.
Which points about algae are most important for NEET?
Learn the class comparison of pigments, stored food, cell wall, flagella and habitat. Learn the examples of each class and of isogamy, anisogamy and oogamy. Also learn the products: algin, carrageen, agar and Chlorella. Match-list and statement questions are usually built from these pairs.
Previous year questions on Algae
2 questions from past papers, each with a step-by-step solution.
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