CUET 2026 Biology May 29 Shift 2 Question Paper- Download Answer Key and Solution PDF

Step 1: Understand the term acellular.
Acellular organisms are entities that do not possess a cellular structure.
They lack:
Cell membrane
Cytoplasm
Cellular organelles
Step 2: Examine the given options.
Bacteria are unicellular prokaryotic organisms. \(\times\)
Protozoa are unicellular eukaryotic organisms. \(\times\)
Viruses are acellular infectious particles consisting of nucleic acid enclosed within a protein coat. \(\checkmark\)
Step 3: Identify the correct answer.
Since viruses do not possess a cellular organization, \[ \boxed{Virus} \] is the only acellular microorganism among the given options.
Therefore,
\[ \boxed{(B)} \] is the correct answer. Quick Tip: Viruses are called: \[ \boxed{Acellular\ infectious\ agents} \] They remain inert outside the host cell and replicate only inside living host cells. Remember: \[ Bacteria \rightarrow Cellular \] \[ Protozoa \rightarrow Cellular \] \[ Virus \rightarrow Acellular \]

Step 1: Recall the biofertilizers used in rice cultivation.
Rice fields are waterlogged environments where certain nitrogen-fixing cyanobacteria grow abundantly.
These organisms enrich the soil by converting atmospheric nitrogen into usable forms.
Step 2: Examine the given options.
Rhizobium forms symbiotic associations with leguminous plants, not rice. \(\times\)
Clostridium is a free-living anaerobic bacterium but is not commonly used as a biofertilizer in rice fields. \(\times\)
Anabaena is a nitrogen-fixing cyanobacterium widely used in paddy fields. \(\checkmark\)
Ferrobacterium is not used as a biofertilizer in rice cultivation. \(\times\)
Step 3: Identify the correct answer.
Anabaena fixes atmospheric nitrogen and improves soil fertility in rice fields.
Therefore,
\[ \boxed{Anabaena \] is the correct answer.
Hence,
\[ \boxed{(C)} \] Quick Tip: Important nitrogen-fixing organisms: \[ Rhizobium \rightarrow Leguminous plants \] \[ Anabaena \rightarrow Rice (paddy)\ fields \] \[ Anabaena + Azolla \rightarrow Important\ biofertilizer\ for\ paddy\ cultivation \] A common NCERT fact frequently asked in CUET and NEET examinations.

Step 1: Recall the meaning of nitrogen fixation.
Nitrogen fixation is the process by which atmospheric nitrogen
\[ (N_2) \]is converted into biologically usable forms such as ammonia.
Certain bacteria and cyanobacteria possess this ability.
Step 2: Examine the given organisms.
Azotobacter is a free-living nitrogen-fixing bacterium. \(\checkmark\)
Nostoc is a nitrogen-fixing cyanobacterium. \(\checkmark\)
Anabaena is a nitrogen-fixing cyanobacterium commonly found in paddy fields. \(\checkmark\)
Pseudomonas is mainly known as a phosphate-solubilizing bacterium and is not a nitrogen-fixing organism. \(\times\)
Step 3: Identify the correct answer.
Among the given options,
\[ \boxed{Pseudomonas} \] does not fix atmospheric nitrogen.
Therefore,
\[ \boxed{(A)} \] is the correct answer. Quick Tip: Important nitrogen-fixing microorganisms: \[ Rhizobium \] \[ Azotobacter \] \[ Nostoc \] \[ Anabaena \] Remember: \[ \boxed{Pseudomonas} \] is commonly associated with phosphate solubilization rather than nitrogen fixation.

Step 1: Recall the role of bacteria in food production.
Several food products are prepared through microbial fermentation.
One of the most common examples is curd, which is produced by the activity of lactic acid bacteria (LAB).
Step 2: Understand curd formation.
Lactic acid bacteria such as:
\[ Lactobacillus \] convert lactose present in milk into lactic acid.
The lactic acid coagulates milk proteins and converts milk into curd.
Step 3: Evaluate the options.
Curd \(\rightarrow\) Produced by bacterial fermentation \(\checkmark\)
Ice-cream \(\rightarrow\) Not prepared by bacterial action \(\times\)
Sugarcane juice \(\rightarrow\) Natural plant product \(\times\)
Cold-drinks \(\rightarrow\) Manufactured beverages, not produced by bacterial fermentation \(\times\)
Therefore,
\[ \boxed{Curd} \] is the food product prepared by the action of bacteria.
Hence, the correct answer is:
\[ \boxed{(A)} \] Quick Tip: Lactic Acid Bacteria (LAB): \[ Lactobacillus \] converts: \[ Milk \rightarrow Curd \] LAB also improves the nutritional quality of curd by increasing the availability of Vitamin \(B_{12}\). A very important NCERT fact from Microbes in Human Welfare.

Step 1: Recall the function of LAB.
Lactic Acid Bacteria (LAB), such as:
\[ Lactobacillus \] are beneficial microorganisms commonly present in curd and the human digestive tract.
Step 2: Understand their role in the gut.
LAB help in maintaining a healthy microbial balance in the intestine.
They:
Suppress harmful microbes
Improve digestion
Enhance nutrient availability
Promote overall gut health
Step 3: Evaluate the options.
Beneficial \(\rightarrow\) Correct \(\checkmark\)
Harmful \(\rightarrow\) Incorrect \(\times\)
Neutral \(\rightarrow\) Incorrect \(\times\)
All of these \(\rightarrow\) Incorrect \(\times\)
Therefore,
\[ \boxed{Beneficial} \] is the correct description of LAB in our digestive system.
Hence, the correct answer is:
\[ \boxed{(A)} \] Quick Tip: NCERT states that LAB: \[ Lactobacillus \] present in curd: Improve nutritional quality of food Increase Vitamin \(B_{12}\) content Check disease-causing microbes in the stomach and intestine Therefore, \[ \boxed{LAB\ are\ beneficial\ bacteria} \]

Step 1: Recall how biogas is produced.
Biogas is produced by anaerobic microorganisms called methanogens.
Examples include:
\[ Methanobacterium \]
These microbes decompose organic matter in the absence of oxygen.
Step 2: Understand the requirement of methanogens.
Methanogens are:
\[ \boxed{Obligate anaerobes} \] which means they cannot survive and function properly in the presence of oxygen.
Step 3: Determine the effect of oxygen supply.
If oxygen enters a biogas plant:
Activity of methanogens decreases
Biogas production reduces
Anaerobic digestion is disturbed
Thus, oxygen adversely affects the functioning of the biogas plant.
Therefore,
\[ \boxed{Supply of oxygen has a negative effect} \]
Hence, the correct answer is:
\[ \boxed{(B)} \] Quick Tip: Biogas plants operate under: \[ \boxed{Anaerobic\ conditions} \] Key microorganism: \[ Methanobacterium \] \[ Oxygen\ present \Rightarrow Biogas production decreases \] \[ No oxygen \Rightarrow Maximum\ methane\ production \]

Step 1: Recall the nature of methanogens.
Methanogens are anaerobic microorganisms that belong to the group of archaebacteria.
They are commonly found in:
Marshy areas
Biogas plants
Rumen of cattle
Step 2: Understand their metabolic products.
During anaerobic decomposition of organic matter, methanogens produce gases such as:
\[ Methane (CH_4) \]
\[ Carbon dioxide (CO_2) \] and traces of gases including hydrogen sulfide may be present in biogas.
Step 3: Evaluate the options.
Oxygen \(\rightarrow\) Not produced by methanogens \(\checkmark\)
Methane \(\rightarrow\) Major product of methanogens \(\times\)
Hydrogen sulfide \(\rightarrow\) May occur in biogas mixtures \(\times\)
Carbon dioxide \(\rightarrow\) Produced during anaerobic digestion \(\times\)
Therefore,
\[ \boxed{Oxygen} \] is not produced by methanogens.
Hence, the correct answer is:
\[ \boxed{(A)} \] Quick Tip: Methanogens are: \[ \boxed{Anaerobic\ archaebacteria} \] Major biogas components: \[ CH_4 \; (50\!-\!70%) \] \[ CO_2 \] They function in the absence of oxygen and therefore do not produce: \[ \boxed{O_2} \] A common NCERT-based CUET and NEET question.

Step 1: Recall the meaning of BOD.
BOD stands for:
\[ \boxed{Biochemical\ Oxygen\ Demand} \]
It is a measure of the amount of oxygen required by microorganisms to decompose organic matter present in water.
Step 2: Understand how BOD is measured.
When microorganisms degrade organic pollutants, they consume dissolved oxygen.
Therefore, BOD is determined by measuring:
\[ \boxed{The\ amount\ of\ oxygen\ consumed} \] during microbial decomposition.
Step 3: Interpret the significance of BOD.
\[ Higher BOD \Rightarrow More\ organic\ pollution \]
\[ Lower BOD \Rightarrow Cleaner\ water \]
Thus BOD directly reflects oxygen consumption by microbes.
Therefore,
\[ \boxed{Oxygen\ consumption} \] is the correct answer.
Hence,
\[ \boxed{(D)} \] Quick Tip: Remember: \[ \boxed{BOD\ =\ Oxygen\ consumed\ by\ microbes} \] BOD is used as an indicator of water pollution. \[ High BOD \rightarrow Highly\ polluted\ water \] \[ Low BOD \rightarrow Cleaner\ water \] This is one of the most frequently asked NCERT facts from Microbes in Human Welfare.

Step 1: Recall the meaning of biofertilizers.
Biofertilizers are living microorganisms that enrich soil fertility by increasing the availability of nutrients, especially nitrogen and phosphorus.
Step 2: Examine the given options.
Azolla is a water fern associated with the nitrogen-fixing cyanobacterium Anabaena. It is widely used as a biofertilizer in paddy fields. \(\checkmark\)
BGA (Blue-Green Algae) such as Nostoc and Anabaena are important nitrogen-fixing biofertilizers. \(\checkmark\)
Legume is a plant, not a biofertilizer. \(\times\)
Grasses are not biofertilizers. \(\times\)
Salmonella and E. coli are bacteria, but they are not used as biofertilizers. \(\times\)
Step 3: Identify the correct pair.
Among the given options, only \[ \boxed{Azolla and BGA \] are both used as biofertilizers.
Therefore,
\[ \boxed{(A) Azolla and BGA} \] is the correct answer. Quick Tip: Important biofertilizers from NCERT: \[ Rhizobium \] \[ Azotobacter \] \[ Anabaena \] \[ Nostoc \] \[ Azolla-Anabaena \] For paddy fields, remember: \[ \boxed{Azolla + BGA} \] as a highly important biofertilizer combination.

Step 1: Recall the concept of biofertilizers:
Biofertilizers are microorganisms that improve soil fertility by increasing the availability of nutrients, especially nitrogen.
Step 2: Identify the algae used as biofertilizers.
Blue-green algae (cyanobacteria) such as:
\[ Anabaena \]
\[ Nostoc \]
possess nitrogen-fixing ability and are widely used in paddy fields.
Step 3: Evaluate the given options.
Blue-green algae \(\rightarrow\) Important biofertilizers due to nitrogen fixation \(\checkmark\)
Green algae \(\rightarrow\) Not commonly used as biofertilizers \(\times\)
Yellow algae \(\rightarrow\) Not used as biofertilizers \(\times\)
Red algae \(\rightarrow\) Not used as biofertilizers \(\times\)
Therefore,
\[ \boxed{Blue-green algae} \] act as biofertilizers.
Hence, the correct answer is:
\[ \boxed{(A)} \] Quick Tip: Important blue-green algae used as biofertilizers:
Anabaena
Nostoc They fix atmospheric nitrogen and enrich soil fertility. Remember: \[ \boxed{Blue-green\ algae\ (Cyanobacteria) =\ Biofertilizers} \] This is a very common NCERT-based CUET and NEET question.