CBSE Class 12 Biology 2025 Sample Paper Solved Set 7

Section – A

Q. No. 1 to 12 are multiple choice questions. Only one of the choices is correct. Select and write the correct choice as well as the answer to these questions.

1 During apomictic seed formation, there is no reduction division and the gametes (both egg cell and the pollen) are diploid.
What is the ploidy of the endosperm formed through apomixis?
A. 2n
B. 3n
C. 4n
D. 6n

Answer : d

2 Which of the following statements describes the difference between placenta and umbilical cord?
A. The placenta secretes hormones whereas the umbilical cord does not.
B. The placenta persists after pregnancy while the umbilical cord is expelled.
C. The placenta is lined with veins and arteries while the umbilical cord is not.
D. The placenta interlocks with foetal tissues whereas the umbilical cord interlocks with the uterine tissue.

Answer : a

3 Billions of years ago, when Earth had a reducing atmosphere containing methane and ammonia along with high temperatures, the organisms that came to existence would have been -
A. aerobic and chemo-autotrophic
B. anaerobic and chemo-heterotrophic
C. aerobic and chemo-heterotrophic
D. anaerobic and chemo-autotrophic

Answer : b

4 Which of the following phenomena significantly contributes to speciation?
P) Natural Selection
Q) Genetic Drift
R) Gene flow
S) Geographic Isolation
T) Stabilizing Selection
A. only Q and S
B. only R and T
C. only P, Q and S
D. only Q, R and T

Answer : c

5 A sample of normal double-stranded DNA was found to have thymine content of 27%. What will be the expected proportion of guanine in thisstrand?
A. 23%
B. 32%
C. 36%
D. 73%

Answer : a

6 If a genetic disease is transferred from a phenotypically normal but carrier female to only some of the male progeny, the disease is
(A) autosomal dominant
(B) autosomal recessive
(C) sex-linked dominant
(D) sex-linked recessive

Answer : d

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