Algae: General Characteristics, Reproduction, Practice Problems and FAQs

Have you heard about ‘Nori’?

Nori is a dried edible seaweed which is used in Japanese cuisine. Do you know where it comes from? It is made from a species of red algae of the genus Pyropia.

Algae are the simplest photoautotrophic aquatic plants possessing chlorophyll. The term ‘algae’ was given by Carolus Linnaeus and these organisms were put under kingdom Plantae by Whittaker. 

Did you know that algae fix more than half of the total carbon dioxide present on Earth?? They also enhance the dissolved oxygen content of the water bodies which they inhabit. They are widely used for food and other commercial purposes. 

Let’s study more about algae. 

Table of contents

• Evolution of Algae
• Common Characteristics of Algae
• Asexual Reproduction in Algae
• Sexual Reproduction in Algae
• Practice Problems of Algae
• FAQs of Algae

Evolution of Algae

The chemoautotrophs which utilise chemical energy for the synthesis of food are believed to be the first autotrophs to have evolved on the surface of earth. These cells gradually developed chlorophyll and evolved into prokaryotic photoautotrophic cyanobacteria. 

According to the Endosymbiotic theory put forward by Dr. Lynn Margulis, the cell organelles in eukaryotic cells were prokaryotic cells which might have been engulfed by a larger prokaryotic cell. Some of these ingested prokaryotic cells remained undigested, retained their genetic material and formed a symbiotic relationship with the larger cell. This gave rise to membrane bound organelles within eukaryotic cells and with time these organelles become specialised to perform specific functions such as photosynthesis (chloroplasts), respiration (mitochondria), etc.

Based on this theory, it is believed that algae are photosynthetic eukaryotic organisms which have evolved from prokaryotic cyanobacteria. 

Common Characteristics of Algae 

They are eukaryotic photoautotrophic organisms. They are primarily present in marine and freshwater environments but are also found in habitats such as moist stones, wood and soil. Some algae occur as lichens, in symbiotic association with fungi or in association with animals such as sloth bears. Unicellular, filamentous, colonial and multicellular forms present.

The cells possess chlorophyll pigment. Cell walls of algae are made up of cellulose, pectin and hemicellulose. The plant body is a thallus and does not possess true roots, stems and leaves. Vascular tissues are absent. They have a flexible body. They possess mucilage which protects them from decaying in water. They shows both sexual and asexual reproduction.

Asexual Reproduction in Algae

In asexual reproduction a single parent is involved and the offspring produced are genetically identical to the parents. Asexual reproduction in algae can be of two types as follows:

• Vegetative propagation
• Formation of spores

Vegetative Propagation

Vegetative propagation in algae can be by means of fragmentation or binary fission.

Fragmentation

Fragmentation is seen in filamentous algae such as Spirogyra. A part of the body of the alga fragments and separates out to grow into a new individual.

Binary Fission

Binary fission occurs in unicellular forms in which the parent cell divides and produces two daughter cells. It is seen in Chlamydomonas.

Formation of Spores

Zoospores 

These are flagellated and motile spores. Examples include Chlamydomonas.

Aplanospores

These are non-flagellated and non-motile spores. Examples include Ulothrix.

Sexual Reproduction in Algae

Sexual reproduction occurs by the fusion of gametes. It is of three types as follows:

• Isogamy

• Anisogamy

• Oogamy

Isogamy

In isogamy fusing gametes are morphologically similar. They can be motile (e.g., Ulothrix) or non-motile (e.g., Spirogyra).

In anisogamy the fusing gametes are similar in structure but differ in size. Examples include Chlamydomonas. 

In oogamy, a larger non motile female gamete fuses with a smaller motile male gamete. Examples include Fucus and Volvox. 

YOUTUBE LINK: Needs to be created

Practice Problems of Algae

Ques:- Cell wall of algae is made up of all except 

A. Cellulose
B. Hemicellulose
C. Pectin
D. Peptidoglycan

Solution :  Cell walls of algae are made up of cellulose, pectin and hemicellulose. Bacterial cell wall is made up of peptidoglycan. Hence, the correct option is D.

Ques:- Study the given diagram and name the process it represents.

A. Isogamy
B. Anisogamy
C. Oogamy
D. Syngamy

Solution : In anisogamy the fusing gametes are similar in structure but differ in size, as is shown in the diagram. Thus, the correct option is B.

Ques:-Which of the following is not correctly matched?

A. Ulothrix - motile aplanospores
B. Chlamydomonas - motile zoospore
C. Fucus - oogamy
D. Spirogyra - isogamy

Solution : Ulothrix reproduces asexually with the help of non-motile, non-flagellated spores known as aplanospores. Motile asexual spores are known as zoospores and are found in Chlamydomonas. 

Thus, the correct option is A.

FAQs of Algae

Ques:- Write down the differences between algae and fungi?

Ques:-What are zoospores? 

Solution: Zoospores are flagellated and motile asexual spores in fungi. They are commonly produced by algae. Examples include Chlamydomonas.

Ques:-Define Oogamy?

Solution : In oogamy, a larger non motile female gamete fuses with a smaller motile male gamete. Examples include Fucus and Volvox.

Ques:-How do algae reproduce vegetatively?

Solution : Vegetative propagation in algae can be by means of fragmentation or binary fission.

Fragmentation is seen in filamentous algae such as Spirogyra. A part of the body of the alga fragments and separates out to grow into a new individual.

Binary fission occurs in unicellular forms in which the parent cell divides and produces two daughter cells. It is seen in Chlamydomonas.

Ques:-State five general characteristics of algae.

Solution: Five general characteristics of algae are -

• They are eukaryotic photoautotrophic organisms. 
• They are primarily present in marine and freshwater environments. 
• All algae possess various pigments such as chlorophyll, phycoerythrin, fucoxanthin, etc in varying concentrations.
• They exist in unicellular, filamentous, colonial and multicellular forms.
• The plant body of algae is a thallus and not differentiated into true roots, stems and leaves.

Other Related Topics

Other Related Topic Of Biology

• Alternation Generation and Classification
• Phaeophyceae and Rhodophyceae
• Pteridophytes
• Pteridophytes Alternation of Generations
• Bryophytes