Home / IB DP Biology- B2.2 Organelles and compartmentalization – IB Style Questions For SL Paper 1A

IB DP Biology- B2.2 Organelles and compartmentalization - IB Style Questions For SL Paper 1A -New Syllabus

IBDP Biology SL Paper 1 - All Chapters

Question

Which of the following is considered a cell organelle?

(A) Cell wall
(B) Lysosome
(C) Cytoskeleton
(D) Cytoplasm
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{B}} \)

A lysosome is a membrane-bound cell organelle that contains digestive enzymes used for intracellular digestion and recycling of cellular components. The cell wall is an external supporting structure, the cytoskeleton is a network of protein filaments, and the cytoplasm is the fluid matrix that surrounds organelles.

Question

If the ER (endoplasmic reticulum) is completely removed from a cell, the cell can function normally for a short time but is unable to synthesize new ER during this time. Which of the following is the most likely explanation for this phenomenon?
(A) The genes for ER synthesis are present in the ER.
(B) The ER is not an obligatory organelle in most cells.
(C) The genes for ER synthesis are irreversibly turned off once cell development is complete.
(D) The information required to construct the ER does not reside exclusively in the DNA.

Answer/Explanation

Answer: (D) The information required to construct the ER does not reside exclusively in the DNA.

Explanation:

The endoplasmic reticulum (ER) is an organelle made by the cell using instructions from DNA in the nucleus. However, the ER cannot form completely from scratch without existing ER membranes and proteins to help guide its assembly. This means the cell needs some ER material to build new ER.

Option Evaluation:
A. Incorrect – Genes for ER proteins are located in the nucleus, not in the ER itself.
B. Incorrect – The ER is essential for many cell functions, so it is not non-obligatory.
C. Incorrect – The genes for ER proteins remain active as needed; they are not permanently turned off after development.
D. Correct – Although DNA contains the instructions, the cell also needs existing ER structures to build new ER. Without any ER, the cell lacks the machinery to make new ER from DNA instructions alone.

Question

The diagram represents transcription and translation.

What structures do the letters X and Y represent?

▶️Answer/Explanation

Answer: D

Explanation:

First, understanding what X and Y are based on the image:

X is…

  • A single-stranded molecule coming out of the DNA (which is double-stranded on the right side).
  • It’s clearly not DNA (because DNA is double-stranded).
  • This strand is being read by tRNA during translation → that’s mRNA.

So, X = mRNA

Y is…

  • A three-base sequence on that mRNA.
  • The tRNAs are matching their own sequences (anticodons) to this sequence.
  • That means Y = the triplet on mRNA, which is called a codon.

So, Y = codon

Let’s now break down the options:

OptionXYCorrect?
ADNAanticodonX is not DNA, Y is not anticodon
BmRNAanticodonY is codon, not anticodon
CDNAcodonX is not DNA
DmRNAcodonThis is the correct match

Memory Trick:

  • Codon = on the mRNA (CO-ME… CODON-MRNA)
  • Anticodon = on tRNA, it’s the anti to the codon
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