IB Biology HL Paper 1 Question Bank

1.) The components of a nucleosome are:

A. ribosomal RNA and DNA
B. 8 histone proteins and DNA
C. 8 histones proteins in a ball + 1 further histone
D. 9 histone proteins and DNA

Solution: D
Explanation: There are 9 histone proteins and DNA in a nucleosome

2.) Which of the following statements are correct about the structure of DNA?

A. The purine base cytosine is linked to the pyrimidine base guanine through three
hydrogen bonds.
B. The sugar-phosphate strands are antiparallel and linked by complementary base
C. The bases are linked to each other through a 3’–5′ linkage.
D. Complementary base pairing of guanine with cytosine and adenine with uracil
means that the two sugar-phosphate strands lie parallel.

Solution: B
Explanation: Complementary base pairing is the phenomenon wherein DNA, guanine always binds to cytosine and adenine always binds to thymine.

3.) What does DNA replication consist of?

A. The enzymes DNA ligase and RNA primase can be found on the lagging strand.
B. Okazaki fragments are produced by DNA polymerase I and DNA polymerase III
on the leading strand.
C. On the lagging strand, the RNA primer is synthesised by RNA primase and then
converted into a DNA strand with the enzyme DNA polymerase III.
D. The enzyme DNA polymerase III uses deoxynucleoside triphosphates to build a
new DNA strand only on the leading strand.

Solution: A
Explanation: DNA ligase fuses together Okazaki fragments on the lagging strand during replication.

4.) What type of bond holds together the two strands of DNA?

A. Hydrogen bonds
B. Covalent bonds
C. Ionic bonds
D. Van der Waals forces

Solution: A
Explanation: The two strands of DNA are held together by hydrogen bonds between the nitrogenous bases. Adenine (A) pairs with thymine (T) through two hydrogen bonds, while guanine (G) pairs with cytosine (C) through three hydrogen bonds.

5.) What is the function of the alveoli in the respiratory system?

A. To transport oxygen to the lungs
B. To filter the air we breathe
C. To warm and humidify the air we breathe
D. To exchange gases with the bloodstream

Solution: D
Explanation: The alveoli are tiny air sacs located in the lungs where gas exchange occurs between the lungs and the bloodstream. Oxygen from the air diffuses into the bloodstream, while carbon dioxide diffuses out of the bloodstream and into the alveoli to be exhaled.


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6.) Which of the following statements about the link reaction and Krebs cycle is correct?

A. Pyruvate in the mitochondrial matrix is oxidised to acetyl CoA.
B. At the end of the link reaction, coenzyme A is recycled back into the cytoplasm
to combine with another pyruvate molecule.
C. During one rotation of the Krebs cycle there are three decarboxylation reactions.
D. The link reaction occurs in the mitochondrial matrix and Krebs cycle occurs on the
mitochondrial cristae.

Solution: A
Explanation: Pyruvate—three carbons—is converted to acetyl CoA, a two-carbon molecule attached to coenzyme A.

7.) Which of the following statements accurately describes the function of the electron transport chain during cellular respiration?

A. It converts glucose into ATP
B. It oxidizes NADH and FADH2 to produce ATP
C. It reduces oxygen to produce ATP
D. It produces ATP through substrate-level phosphorylation

Solution: B
Explanation: The electron transport chain is the final stage of aerobic cellular respiration, where most of the ATP is produced. During this process, electrons from NADH and FADH2 are transferred through a series of electron carriers (such as cytochromes and flavoproteins) to oxygen, the final electron acceptor, creating a proton gradient across the inner mitochondrial membrane. The energy from this gradient is then used to drive ATP synthesis by ATP synthase.

8.) A fruit fly of genotype GgTt was test crossed. The off spring genotype ratio was 1 : 1. The reason for this was:

A. The genes are assorted independently.
B. The genes were linked and crossing over occurred.
C. The genes were linked and no crossing over occurred.
D. Non-disjunction had taken place.

Solution: A
Explanation: The Principle of Independent Assortment describes how different genes independently separate from one another when reproductive cells develop.

9.) What is an example of defense?

A. During the process of blood clotting, thrombin causes the release of clotting factors
from the platelets.
B. Active immunity occurs as a result of the body being challenged by antigens.
C. Monoclonal antibodies are produced by fusing a hybridoma cell with a myeloma cell.
D. As a result of vaccination, the primary responsibility of the body will be greater when it
is invaded by an antigen.

Solution: B
Explanation: When there is exposure to disease, active immunity occurs as a result of the body being challenged by antigens.

10.) Which of the following statements about muscles and movement is correct?

A. During muscle contraction, the distance between Z lines decreases, and the dark bands
get wider but the light bands get narrower.
B. Bones are held together at a joint by tendons, which also protect the joint.
C. Synovial fluid, secreted by the cartilage, lubricates the joint to prevent friction.
D. The elbow is an example of a ball-and-socket joint.

Solution: A
Explanation: A sarcomere is defined as the distance between two consecutive Z discs or Z lines; when a muscle contracts, the distance between the Z discs is reduced.

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