Biology · Plant Kingdom · NEET
NCERT defines algae as chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic organisms. Learn these 5 words in order because NEET questions are built directly from this line. 'Chlorophyll-bearing' means they have the green pigment, so they can do photosynthesis.
Thalloid means the body is a simple thallus. A thallus is a plant body that is NOT divided into true roots, stems and leaves. So even a large seaweed like kelp has no real root or leaf, it is just one undifferentiated body. This is why algae are called 'simple'.
They can be both. The plant body may be unicellular (like Chlorella), colonial (like Volvox), or filamentous (like Ulothrix and Spirogyra). A few marine forms called kelps form very large bodies. So 'multicellular only' is a wrong idea for NEET.
No. NCERT says 'largely aquatic' (fresh water and marine), but NOT only aquatic. They also grow on moist stones, soil and wood, and in association with fungi (lichens) and even animals (on the sloth bear). So 'algae live only in water' is false.
Autotrophic means they make their own food. Because they carry chlorophyll, algae do photosynthesis and prepare their own food from sunlight, water and carbon dioxide. This is why they are producers and add dissolved oxygen to water. Fungi, in contrast, are heterotrophic.
In the NCERT Plant Kingdom chapter, true algae (green, brown, red) are studied inside Plantae as the first, simplest plants. Note: blue-green algae (cyanobacteria) are NOT true algae; they are prokaryotes placed in Kingdom Monera. So the word 'algae' in Plant Kingdom means only the eukaryotic green/brown/red types.
By three methods: vegetative (mainly fragmentation, where each broken piece grows into a new thallus), asexual (mainly by motile flagellated zoospores), and sexual (fusion of two gametes). Knowing just these three keywords is enough for the 'characteristics' question.
An example of colonial alga is
Which of the following pairs is of unicellular algae?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
'Algae' is plural; the singular is 'alga'. So we say 'one colonial alga is Volvox' but 'algae are autotrophic'.
No. Algae have no true roots, stems, leaves or vascular tissue. Vascular tissue first appears in pteridophytes. This 'simple, thalloid, non-vascular' point is a common NEET distinction.
Chlorophyceae (green algae), Phaeophyceae (brown algae) and Rhodophyceae (red algae). They differ in pigments, stored food and cell wall, which is a very high-yield NEET table.
Algae carry out at least half of all carbon dioxide fixation on Earth by photosynthesis, so they are major primary producers and oxygen sources. NEET tests both this ecological role and their economic products (algin, carrageen, agar).
The zoospore. It is flagellated (motile) and germinates to form a new plant. Remember zoospore = the default asexual answer for algae.
