Class 11 PT II Question Paper 2025-26 Biology

CBSE CLASS 11
PT II Question Paper
Session 2025-26

BIOLOGY

Exam CBSE Class 11
Subject Biology
Session 2025-26
Document Type PT II Question Paper

Notes · Sample Papers · Previous Year Papers · Mock Tests

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Question Paper
SECOND UNIT TEST
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SESSION: 2025-2026
CLASS: XI MAXIMUM MARKS: 40
SUBJECT: BIOLOGY TIME: 1HR 30 MINS
General Instructions:
(i) All questions are compulsory.
(ii) The question paper has five sections and 19 questions. All questions are compulsory.

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(iii) Section–A has 8 questions of 1 mark each; Section–B has 4 questions of 2 marks each; Section– C has 5

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questions of 3 marks each; Section– D has 1 case-based question of 4 marks; and Section–E has 1 question
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of 5 marks.

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(iv) There is no overall choice. However, internal choices have been provided in some questions. A student

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has to attempt only one of the alternatives in such questions.

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(v) Wherever necessary, neat and properly labeled diagrams should be drawn.
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SECTION-A
1. Enzymes, which are biological catalysts (most are proteins), increase the rate of a 1
biochemical reaction by:
a. Increasing the concentration of the substrate.
b. Converting a non-spontaneous reaction into a spontaneous one.
c. Decreasing the pH of the reaction environment.
d. Decreasing the activation energy of the reaction.

2. Which sequence correctly describes the mechanism triggered by a significant drop in 1

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glomerular blood pressure (low GFR), leading to blood pressure increase?
a. Angiotensin I→ Renin release → Angiotensin II→ Aldosterone release → DCT

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reabsorption

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b. Fall in glomerular blood pressure → Renin release → Angiotensin I→ Angiotensin
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II→ Increased blood pressure
c. Angiotensin II→ Renin release → Aldosterone → Vasoconstriction
d. JG cells activated → Angiotensin II→ Renin → ADH release

For Q. No. 3 and 4 choose the correct option from the following:
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true and R is not the correct explanation of A
c) A is true, but R is false
d) A is false and R is true

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3. Assertion: C4 plants are able to prevent photorespiration. 1

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Reason: C4 plants have a spatial separation of CO2 fixation, using PEP carboxylase

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em4. Assertion: Most of the enzymes of oxidative decarboxylation are present
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in the mesophyll cells and RuBisCO in the bundle sheath cells.

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a mitochondrial matrix.
Reason: ETS operates on inner membrane of mitochondria.

5. Choose the correct option from the following for catabolism of one molecule of 1
glucose during aerobic respiration:
a) Glycolysis, Transition phase, Krebs cycle & Terminal respiration generates 38
ATP molecules
b) Glycolysis generates 38 ATP molecules

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c) Krebs cycle generates 38 ATP molecules

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d) Terminal respiration generates 38 ATP molecules

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6. Match the following biomolecules with their functions: 1
Biomolecule Function
(i) Collagen (A) Oxygen transport
(ii) Haemoglobin (B) Structural protein in connective tissue
(iii) Insulin (C) Hormonal control of glucose
(iv) Keratin (D) Structural protein in hair/nails
Choose the correct option:-
a) i–C, ii–A, iii–D, iv– B
b) i–A, ii–B, iii–C, iv–D
c) i–D, ii–C, iii–B, iv–A
d) i–B, ii–A, iii–C, iv–D

7. The action spectrum of photosynthesis closely matches the absorption spectrum of chlorophyll 1
a because:

a)� Chlorophyll a is the only pigment involved in absorbing light.
b)� Other pigments inhibit the activity of chlorophyll a.
c)� Chlorophyll a is the primary pigment involved in the light reaction.
d)� Photosynthesis only occurs in red light.

8. Arrange the events: 1
A.� Blood enters via afferent arteriole
B.� Hydrostatic pressure builds in glomerulus
C.� Plasma filtered into Bowman's capsule
D.� Efferent arteriole maintains pressure
Choose the correct sequence of events:-
a)� A-D-C-B
b)� A-D-B-C
c)� B-A-C-D
d)� A-B-C-D
SECTION-B
9. A student compares two nucleic acids and observes that one has thymine and the other 2
has uracil.
a. Identify the two nucleic acids.
b. Mention one more chemical difference between them.

10. Define photorespiration and state one major consequence of this process in C3 plants. 2

11. Which two steps in glycolysis involve the utilization of ATP? 2

12. The Countercurrent Mechanism is essential for concentrating urine. 2
Name the two structural components of the kidney that form the countercurrent flow,
and state one key property of the Ascending Limb of the Loop of Henle that is
critical to this mechanism

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SECTION-C

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13. Observe the graph carefully and answer the following questions. 3

a)� Define Km.

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b)� How inhibitors effect enzyme activity? Explain with the help of example.

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14. Differentiate between cyclic and non-cyclic photophosphorylation based on the 3

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photosystems involved, products formed, and electron flow.

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Calculate thesnet
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moleculelof glucose. Mention the number of NADH and FADH molecules produced a
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15.
2
and their

16. Give reason: 3
a)Ureters do not have valves at their ends opening into the urinary bladder, yet
urine does not flow back into them on the contraction of bladder.
b) Why is left Kidney situated little higher than the right kidney?
c) Why in winter season hypotonic and large volume of urine is passed out? (Any one

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reason)

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Figure of Malpighian corpuscle of nephron is given below. Study the diagram & 3

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answer the following questions-

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A) Identify A & B.

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B) Why is diameter of A larger than that of B?

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SECTION-D
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c. Riya, ofm
climates. During a lab session, her teacher provided her with prepared slides e
s leaf. Under
a high school biology student, was curious about how some plants thrive in 4

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vertical leaf

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cells surrounding the
vascular bundles, while the other lacked this distinct structure.
The teacher explained that one plant follows the C3 pathway and the other follows the C4
pathway, and challenged Riya to analyze how their photosynthetic mechanisms differ,
especially in terms of leaf anatomy and carbon fixation strategies.

a)� What is the name of the ring-like structure of cells observed around vascular bundles in
one of the leaf samples?
b)� Name the primary CO2 acceptor molecule in C4 plants.
c)� List any two advantages C4 plants have over C3 plants in dry, high-temperature

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environments.

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c) Explain why the Calvin cycle (C3 cycle) does not occur in the mesophyll cells of C4
plants.
SECTION-E
19. a)� Write the importance of F0 – F1 particles in ATP production during aerobic 5
respiration.
b)� Identify the location of respiratory electron transport system in a cell. Write
the name of the compound which is the terminal electron acceptor in aerobic
respiration.
c)� Calculate how many NADH2 molecules are produced from one molecule of
acetyl CoA in TCA cycle.
OR
Mention the various steps involved in Glycolysis.

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