All questions of Biological Classification for NEET Exam

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Understanding Protozoan Nutrition
Protozoans are a diverse group of single-celled eukaryotic organisms that exhibit various modes of nutrition. The correct answer to how protozoans obtain their food is option 'D', which states that they can be both predators or parasites (option A) and heterotrophs (option C).

Modes of Nutrition in Protozoans
- Predators:
Many protozoans are active hunters, feeding on bacteria, algae, and smaller protozoans. They utilize specialized structures like pseudopodia, cilia, or flagella to capture and engulf their prey through a process called phagocytosis.
- Parasites:
Some protozoans have evolved to live in or on other organisms, deriving nutrients at the host's expense. For example, Plasmodium, the causative agent of malaria, lives in the bloodstream of its host and absorbs nutrients directly from the host's cells.
- Heterotrophs:
Protozoans cannot synthesize their own food like plants; instead, they rely on organic compounds for energy. They obtain these compounds through the absorption of dissolved nutrients or by consuming other organisms.

Conclusion: A Combination of Strategies
Protozoans exhibit flexibility in their feeding strategies, allowing them to thrive in various environments. By being both predators and parasites, they can exploit multiple food sources, enhancing their survival and adaptability. Thus, it's accurate to say that protozoans obtain their food as both predators or parasites and as heterotrophs, confirming option 'D' as the correct choice.

Overview of Cyanobacteria
Cyanobacteria, commonly known as blue-green algae, are a diverse group of photosynthetic bacteria that play crucial roles in aquatic ecosystems and nitrogen cycling.
Characteristics of Cyanobacteria
- Unicellular, Colonial, or Filamentous:
Cyanobacteria can exist as single cells, in colonies, or in filamentous structures. This versatility allows them to adapt to various environmental conditions.
- Nitrogen Fixation:
They have specialized cells known as heterocysts that enable them to fix atmospheric nitrogen into a usable form. This process is vital for enriching soil and water ecosystems.
Why Other Options are Incorrect
- Heterotrophic Nature:
Option B states that cyanobacteria are heterotrophic bacteria. This is false as they are primarily autotrophic, using sunlight to perform photosynthesis.
- Chlorophyll Presence:
Option C claims they lack chlorophyll, which is incorrect. Cyanobacteria contain chlorophyll a, enabling them to photosynthesize and produce oxygen.
- Habitat Limitations:
Option D asserts that they thrive exclusively in marine environments. In reality, cyanobacteria are found in various habitats, including freshwater, soil, and even extreme environments.
Conclusion
In summary, option A accurately describes cyanobacteria, highlighting their unicellular or filamentous nature and their ability to fix nitrogen in heterocysts. This makes them essential for both aquatic ecosystems and agricultural practices.

Understanding Bacterial Reproduction
Bacteria are unicellular organisms that exhibit unique modes of reproduction. Here’s a breakdown of the statements provided:
Statement A: Bacteria reproduce mainly by fission
- This statement is correct.
- Bacteria primarily reproduce asexually through a process called binary fission, where one cell divides into two identical daughter cells.
Statement B: Bacteria reproduce by production of gametes
- This statement is incorrect.
- Bacteria do not reproduce by gametes (reproductive cells like sperm and egg). Instead, they reproduce asexually, primarily through binary fission.
Statement C: Under unfavourable conditions, Bacteria produce spores
- This statement is correct.
- Many bacteria can form endospores when conditions become unfavorable. This allows them to survive extreme environments until conditions improve.
Statement D: Bacteria reproduce by a sort of sexual reproduction
- This statement can be misleading but is partially correct.
- Some bacteria exchange genetic material through processes like transformation, transduction, and conjugation, which is not true sexual reproduction but allows for genetic diversity.
Conclusion
- In summary, option 'B' is the only statement that incorrectly describes bacterial reproduction. Bacteria do not produce gametes; they mainly reproduce asexually through binary fission, with alternative methods for genetic exchange that do not involve the formation of gametes.

Eubacteria, also called true bacteria, often have a rigid cell wall and flagella for motility. Some eubacteria, such as cyanobacteria, possess chlorophyll (specifically chlorophyll a) and are capable of photosynthesis. Hence, they can fix atmospheric nitrogen, unlike other eubacteria.

Understanding Protozoans
Protozoans are a diverse group of single-celled organisms known for their varied lifestyles and nutritional methods.
Assertion (A): All protozoans are heterotrophs
- Protozoans are primarily heterotrophic, meaning they obtain their food by consuming organic matter.
- They often function as predators, feeding on bacteria, algae, and other small organisms.
- Some protozoans can also be parasitic, deriving nutrients from a host organism.
Reason (R): Protozoans possess chloroplasts that allow them to perform photosynthesis
- Most protozoans do not possess chloroplasts and, therefore, cannot perform photosynthesis.
- While some photosynthetic organisms, like certain algae, may share characteristics with protozoans, they are not classified as true protozoans.
- The presence of chloroplasts is characteristic of plants and certain algae, not protozoans.
Conclusion: Why Option 'C' is Correct
- The assertion is true: all protozoans are indeed heterotrophs.
- The reason is false: protozoans do not have chloroplasts and cannot perform photosynthesis.
- Therefore, the correct answer is option 'C' - Assertion is true, but Reason is false.
In summary, understanding the nutritional modes of protozoans clarifies their ecological role, while recognizing the limitations of their classification helps distinguish them from photosynthetic organisms.

Assertion (A) Explained
Cyanobacteria are indeed capable of photosynthesis and nitrogen fixation. They possess chlorophyll, which allows them to capture light energy and convert it into chemical energy through photosynthesis. Additionally, they have specialized cells known as heterocysts that facilitate nitrogen fixation, converting atmospheric nitrogen into a usable form for the organism.
Reason (R) Explained
The statement that cyanobacteria can only perform photosynthesis in aquatic environments is not accurate. While they thrive in aquatic settings where light is abundant, cyanobacteria can also be found in various terrestrial environments, such as soil and on rocks, where they can still engage in photosynthesis, especially when moisture is available.
Conclusion
Therefore, the correct interpretation is:

• (A) is true: Cyanobacteria can photosynthesize and fix nitrogen.
• (R) is false: Cyanobacteria are not limited to aquatic environments for photosynthesis.

The correct answer is option 'C', indicating that while the assertion is true, the reasoning provided is incorrect. Cyanobacteria's ability to perform photosynthesis is not restricted to aquatic environments, making (R) false.

Causal organisms of sleeping sickness and kala-azar belong to which of the following groups of protozoan protists?

The correct answer is option 'B' - Flagellated protozoans.

Explanation:

Protozoans are a diverse group of single-celled eukaryotic microorganisms that belong to the kingdom Protista. They can be classified into various groups based on their mode of locomotion and other characteristics.

Sleeping sickness and kala-azar are two diseases caused by different species of protozoans. Let's discuss each of them in detail:

1. Sleeping Sickness:
Sleeping sickness, also known as African trypanosomiasis, is caused by the Trypanosoma brucei parasite. This parasite is a flagellated protozoan that belongs to the class Kinetoplastida. Trypanosoma brucei is transmitted to humans through the bite of infected tsetse flies. Once inside the human body, the parasite multiplies in the bloodstream and the lymphatic system, causing a variety of symptoms including fever, fatigue, headaches, and eventually leading to sleep disturbances, neurological problems, and even death if left untreated.

2. Kala-azar:
Kala-azar, also known as visceral leishmaniasis, is caused by the Leishmania donovani parasite. This parasite is also a flagellated protozoan that belongs to the class Kinetoplastida. Leishmania donovani is transmitted to humans through the bite of infected sandflies. Once inside the human body, the parasite invades the cells of the immune system, particularly macrophages, and causes a range of symptoms including prolonged fever, weight loss, enlargement of the spleen and liver, and anemia.

Both Trypanosoma brucei and Leishmania donovani are flagellated protozoans, which means they possess one or more whip-like structures called flagella that enable them to move. These flagella help the parasites to swim through bodily fluids and invade host cells. Therefore, the causal organisms of sleeping sickness and kala-azar belong to the group of flagellated protozoans (option B).

Understanding Archaebacteria
Archaebacteria, also known as archaea, are a distinct group of microorganisms that differ significantly from other bacteria in several ways, particularly in their adaptation to extreme environments.
Cell Wall Structure
- The most defining feature of archaebacteria is their unique cell wall composition. Unlike other bacteria that typically have peptidoglycan in their cell walls, archaebacteria possess pseudopeptidoglycan (or other polymers) that provide structural integrity.
- This unique cell wall structure is essential for survival in extreme conditions such as high temperatures, salinity, or acidity, where many other organisms cannot thrive.
Membrane Lipids
- Archaebacteria also have distinct membrane lipids. Their membranes are composed of ether-linked lipids, which are more stable than the ester-linked lipids found in other bacteria.
- This enhances their ability to withstand extreme heat and harsh chemical environments, contributing to their resilience.
Metabolic Pathways
- Archaebacteria exhibit unique metabolic pathways that allow them to utilize different energy sources, such as hydrogen gas or sulfur, making them versatile in extreme habitats.
- Many archaea are also extremophiles, thriving in environments like hot springs, salt lakes, and deep-sea vents where other forms of life struggle to survive.
Conclusion
In summary, the different cell wall structure of archaebacteria is crucial for their survival in extreme environments, setting them apart from other bacteria. This unique adaptation enables them to thrive in conditions that are inhospitable to most life forms, showcasing the incredible diversity of life on Earth.