Organization of Algal Thalli

Algal thalli exhibit a diverse range of organizational structures, varying from unicellular microscopic forms to large macroalgae like giant kelp, exceeding one hundred feet in length.

Chlaymdomonas

1. Unicellular Thalli

   • Simple motile unicell: Chlamydomonas
   • Non-motile unicell: Chlorella

2. Colonial Organization

   • Cells are grouped into colonies.
     • Motile colonies: Volvox
     • Non-motile colonies: hydrodictyon
     • Definite-shaped colony: Coenobium (e.g., Volvox)

3. Filamentous Thalli

   • Unbranched filaments: Ulothrix
   • Simple branched filaments: Cladophora
   • Complex filaments: Ectocarpus, Polysiphonia, Sargassum, and Laminaria

4. Parallelism Among Different Divisions

   • No single thallus type is restricted to a specific division.
   • Striking parallelism is observed among different algal divisions.

Types of Cell Structures in Algae

A. Prokaryotic Cell Organization (Class Cyanophyceae/Mixophyceae)

• Presence of a primitive or incipient nucleus
• Lack of nuclear membranes and histones
• DNA is organized into fibrils.
• Chlorophyll in photosynthetic lamellae or thylakoids
• Absence of chloroplast, mitochondria, Golgi body, and endoplasmic reticulum

1. Characteristic Features of Prokaryotic Algae
   • Simple cells lacking the nuclear membrane, mitochondria, and plastids
   • Reproduction without mitosis
   • Cell wall composition: mucopeptide (specific to Cyanophyceae)

B. Eukaryotic Cell Organization

• Presence of a well-organized nucleus
• Membrane-bounded organelles: plastids, mitochondria, and Golgi bodies

1. Membrane-bound Organelles in Eukaryotes
   • Nucleus
   • Plastids
   • Mitochondria
   • Golgi Bodies

Examples of Eukaryotic Algae

• Ectocarpus
• Polysiphonia
• Sargassum
• Laminaria

Flagella in Algae

Flagella, singularly known as flagellum, are thread-like structures crucial for cell movement and are present in almost all classes of algae, excluding Rhodophyceae and Cyanophyceae.

1. Flagellar Structure

   • Each flagellum consists of:
     • 2 central fibrils
     • 9 peripheral double fibrils (9+2 arrangements)

2. Types of flagellaA.Whiplash or Acronematic Flagella:Flagella with a smooth surface

   B. Tinsel Flagella or Pleuromematic Flagella: flagella with a surface covered with fine hair-like appendages called mastigonemes.

   Mastigonemes arrangement types:

   (i) Pantonematic: Two opposite rows of mastigonemes;

   (ii) Pantocronematic: Terminal fibril;

   (iii) Stichonematic: Mastigonemes develop only on one side of the flagellum.

3. Isoknot and Heteroknot

• If the flagella of a cell are similar, it is known as isoknot.
• If the flagella are dissimilar, it is called heterooknot.

1. Characteristic Features of Flagella

   • Size, number, and arrangement are specific to the class of algae or genera.

2. Flagella in Different Algal Classes

   • Chlorophyceae:
     • Motile stages possess two or four anteriorly inserted whiplash flagella of equal length.
   • Phaeophyceae and Xanthophyceae:
     • Have one whiplash and one tinsel flagellum of unequal length.

Axonemes, Basal Bodies, and Their Structure

1. Axoneme:

   • The axoneme is a structural component found in the core of eukaryotic flagella and cilia.
   • It is responsible for the beating and movement of flagella or cilia.

   Structure of Axoneme:

   
   
   

   • Microtubule Arrangement:

     • The axoneme is primarily composed of microtubules, which are tubular structures made of protein.
     • Microtubules are arranged in a characteristic pattern, usually in a "9+2" arrangement.
     • This arrangement consists of a central pair of microtubules surrounded by nine doublets.

   • Dynein Arms:

     • Dynein arms are molecular motor proteins attached to the microtubules.
     • They generate force during the sliding movement between adjacent microtubules, causing the bending and flexing of the axoneme.

2. Basal Bodies:

   • Basal bodies are cylindrical structures located at the base of cilia and flagella.
   • They serve as the anchoring point and organizing center for the formation of axonemes.

   Structure of Basal Bodies:

   • Microtubule Arrangement:

     • Similar to axonemes, basal bodies also have a microtubule arrangement, often in a "9+0" pattern.
     • The central pair found in axonemes is absent in basal bodies, giving them a "9+0" structure.

   • Transition Zone:

     • The region where the microtubules transition from the basal body to the axoneme is known as the transition zone.

   • Role in Flagellar/Ciliary Function:

     • Basal bodies play a crucial role in the initiation and organization of axonemal microtubules.
     • They anchor and organize the microtubules, providing structural support for the growth and movement of flagella or cilia.

3. Composition:

• Both axonemes and basal bodies are composed of protein structures, with microtubules being a fundamental component.
• Other associated proteins, such as dynein arms, contribute to the mechanical movement of the axoneme.

✅ MCQs on Organization of Algal Thalli

(With Answers + Explanations)

---

1. Algal Thallus Organization

1. Which organism represents a simple motile unicellular alga?

(a) Chlorella
(b) Volvox
(c) Chlamydomonas
(d) Ulothrix

Answer: c
Explanation: Chlamydomonas is a single-celled alga with two flagella → motile.

---

2. Chlorella is an example of:

(a) Motile unicell
(b) Non-motile unicell
(c) Filamentous alga
(d) Branched alga

Answer: b
Explanation: Chlorella is unicellular and lacks flagella → non-motile.

---

3. Volvox is a:

(a) Motile colony
(b) Non-motile colony
(c) Filamentous alga
(d) Branched thallus

Answer: a
Explanation: Volvox forms motile spherical colonies with coordinated flagella.

---

4. Hydrodictyon is a:

(a) Motile colony
(b) Non-motile colony
(c) Unicellular alga
(d) Branched filament

Answer: b
Explanation: Hydrodictyon forms a fixed net-like non-motile colony.

---

5. A colony with a definite shape is called:

(a) Coenocyte
(b) Coenobium
(c) Thallus
(d) Zoospore

Answer: b
Explanation: Coenobium = fixed-shaped colony (e.g., Volvox).

---

6. Ulothrix is an example of:

(a) Unbranched filament
(b) Branched filament
(c) Parenchymatous thallus
(d) Coenobium

Answer: a

---

7. Cladophora possesses:

(a) Unbranched filaments
(b) Simple branched filaments
(c) Complex false parenchyma
(d) Coenocytic filaments

Answer: b

---

8. A complex type of filamentous alga is:

(a) Ulothrix
(b) Chlamydomonas
(c) Polysiphonia
(d) Chlorella

Answer: c
Explanation: Polysiphonia shows multiaxial intricate filaments → complex.

---

9. Parallelism in algal thalli means:

(a) Each division has its own unique thallus
(b) All thalli are identical
(c) Similar thallus types appear in different divisions
(d) None of these

Answer: c

---

2. Prokaryotic (Cyanophyceae) Cell Structure

10. Cyanophyceae cells lack:

(a) Chlorophyll
(b) Nuclear membrane
(c) Cell wall
(d) Ribosomes

Answer: b
Explanation: Cyanobacteria have incipient nucleus (no nuclear envelope).

---

11. Cell wall of Cyanophyceae is made of:

(a) Cellulose
(b) Pectin
(c) Mucopeptide
(d) Chitin

Answer: c

---

12. Cyanophyceae lack all except:

(a) ER
(b) Mitochondria
(c) Golgi bodies
(d) Photosynthetic lamellae

Answer: d

---

13. Cyanophyceae reproduce without:

(a) Binary fission
(b) Mitosis
(c) Fragmentation
(d) Hormogonia

Answer: b
Explanation: They lack mitotic spindle → no true mitosis.

---

14. DNA in Cyanophyceae occurs as:

(a) Chromosomes
(b) Fibrils
(c) Nucleosomes
(d) Histone-wrapped chromatin

Answer: b

---

3. Eukaryotic Algal Cell Structure

15. Eukaryotic algae contain all except:

(a) Plastids
(b) True nucleus
(c) Mitochondria
(d) Mucopeptide wall

Answer: d
Explanation: Mucopeptide is unique to Cyanophyceae (prokaryotes).

---

16. An example of eukaryotic alga:

(a) Nostoc
(b) Oscillatoria
(c) Polysiphonia
(d) Anabaena

Answer: c
Explanation: Red, brown, green algae all are eukaryotic.

---

4. Flagella in Algae

17. Flagella are absent in:

(a) Chlorophyceae
(b) Phaeophyceae
(c) Rhodophyceae
(d) Xanthophyceae

Answer: c
Explanation: Red algae completely lack flagella.

---

18. What is the typical structure of a eukaryotic flagellum?

(a) 9+0
(b) 9+2
(c) 3+1
(d) 13+0

Answer: b

---

19. Whiplash flagella have:

(a) Hairs
(b) Smooth surface
(c) One-sided appendages
(d) Two rows of hairs

Answer: b

---

20. Tinsel flagella contain:

(a) No hairs
(b) Mastigonemes
(c) Cellulose plates
(d) Stigma

Answer: b

---

21. Mastigonemes arranged in two opposite rows are called:

(a) Stichonematic
(b) Pantocronematic
(c) Pantonematic
(d) Pleuromonematic

Answer: c

---

22. Algae with equal flagella exhibit:

(a) Isoflagellation
(b) Isoknot
(c) Homokaryon
(d) Homothallism

Answer: b

---

23. One whiplash + one tinsel flagellum is characteristic of:

(a) Chlorophyceae
(b) Phaeophyceae
(c) Cyanophyceae
(d) Rhodophyceae

Answer: b

---

5. Axoneme & Basal Body

24. Dynein arms in axoneme function in:

(a) Energy storage
(b) Bending movement
(c) Cell division
(d) Protein synthesis

Answer: b

---

25. Basal bodies exhibit which microtubule pattern?

(a) 9+2
(b) 9+1
(c) 9+0
(d) 13+2

Answer: c

---

26. The region where basal body transitions into axoneme is called:

(a) Connecting zone
(b) Transition zone
(c) Emergence point
(d) Initiation zone

Answer: b

---

27. Basal bodies are structurally similar to:

(a) Ribosomes
(b) Centrioles
(c) Nucleus
(d) Plastids

Answer: b
Explanation: Both have 9× triplet microtubule pattern.

---

28. The core of a flagellum is known as:

(a) Stroma
(b) Axoneme
(c) Matrix
(d) Thallus

Answer: b

---

6. Class-wise Flagellar Arrangement

29. Chlorophyceae motile stages show:

(a) One tinsel + one whiplash
(b) No flagella
(c) Two or four equal whiplash flagella
(d) Only tinsel flagella

Answer: c

---

30. Rhodophyceae are unique because:

(a) They have tinsel flagella
(b) They have 4 flagella
(c) They completely lack flagella
(d) They have 9+0 axoneme

Answer: c

___________________________________________________________

🌊 Algal Organization Quiz 🌊

20s

Results