Biological classification NCERT notes

Biological classification Chapter-2, Class-11th NCERT notes

2 kingdom classification- Carl Linnaeus divided all organisms into Plantae and Animalia

Why was it not used for a long time? Did not distinguish between Prokaryotes and eukaryotes unicellular and multicellular organisms and photosynthetic (green algae) and non-photosynthetic (fungi) organisms. A large number of organisms did not fall into either category.

Five kingdom classification

5 kingdom classification

On what basis did R.H Whittaker classified organisms?

1. Cell structure  2. Body organization  3. mode of nutrition 4. Reproduction

5. Phylogenetic relationships.

1. Monera

1. Prokaryotes (Bacteria), which do not have membrane around nucleus (nuclear membrane absent). Reproduce mainly by fission.

2. Have 4 different types of shapes-

• Coccus- Spherical shaped
• Bacillus- Rod-shaped
• Vibrium- comma-shaped
• Spirillum- spiral-shaped

3. Majority are heterotrophs- depend on other organisms or on dead organic matter for food. Thus, help in the decomposition process.

4. Can also be Autotrophs, i.e., synthesise their own food from inorganic substrates. They can be photosynthetic autotrophic (require sunlight) or chemosynthetic autotrophic (require inorganic substances such as nitrates, nitrites and ammonia).

5. Chemosynthetic autotrophic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production. Help in recycling nutrients like nitrogen, phosphorous, iron and sulphur.

6. Helpful in making curd from milk.

7. Production of antibiotics, fixing nitrogen in legume roots.

8. Cause diseases- Cholera, typhoid, tetanus, citrus canker

9. Archaebacteria

Characteristics of Archaebacteria

10. Eubacteria or true bacteria- Rigid cell wall, and if motile, a flagellum is present.

Cyanobacteria or BGA

• 1. Have chlorophyll a similar to green plants and are photosynthetic autotrophs. Example- Nostoc and Anabaena
• 2. Unicellular, colonial or filamentous, freshwater/marine or terrestrial algae.
• 3. Colonies surrounded by a gelatinous or mucilaginous sheath.
• 4. Form blooms in polluted water bodies.
• 5. Some can fix atmospheric nitrogen in specialised cells called heterocysts, e.g., Nostoc and Anabaena.

11. Mycoplasma- Bacteria that lack cell wall is called Mycoplasma

2. Protista

1. Has single celled eukaryotes.

2. Fresh water as well as in marine environments

3. Reproduce asexually and sexually by a process involving cell fusion and zygote formation

Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds and Protozoans are grouped under Protista

1. Chrysophytes

1. Includes diatoms and desmids (golden algae). Microscopic.

Diatoms- Cell walls form two thin overlapping shells, which fit together as in a soap box. Walls are embedded with silica and thus the walls are indestructible. Thus, diatoms have left behind large amount of cell wall deposits in their habitat; this accumulation over billions of years is referred to as ‘diatomaceous earth’. Being gritty this soil is used in polishing, filtration of oils and syrups.

2. Dinoflagellates

1. They appear yellow, green, brown, blue or red depending on the main pigments present in their cells.

2. Mostly marine and photosynthetic

3. The cell wall has stiff cellulose plates on the outer surface. Most of

them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates.

4. Very often, red dinoflagellates (Example: Gonyaulax) undergo such rapid multiplication that they make the sea appear red (red tides).

5. Toxins released by such large numbers may even kill other marine animals such as fishes.

3. Euglenoids

1. Instead of a cell wall, they have a protein rich layer called pellicle which makes their body flexible.

2. Two flagella, a short and a long one

3. Photosynthetic in the presence of sunlight, when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms.

4. Majorly fresh water organisms found in stagnant water

4. Slime Moulds

1. saprophytic