Question
The image shows a single Paramecium with food vacuoles that contain ingested cells of the unicellular green alga Chlorella.
What can be deduced about Paramecium?
A. It is an autotroph.
B. It cannot perform all of the functions of life.
C. It carries out heterotrophic nutrition.
D. It is a prokaryote.
▶️Answer/Explanation
Answer: C. It carries out heterotrophic nutrition.
Explanation:
Heterotrophic nutrition is the way some organisms get their energy by eating other organisms or organic matter because they cannot make their own food. Unlike autotrophs (like plants and algae) that use sunlight to make food through photosynthesis, heterotrophs must ingest or absorb food from their environment. Paramecia are single-celled organisms that use cilia to sweep food particles, such as algae or bacteria, into their oral groove where food vacuoles form and digestion takes place.
Evaluating the options:
A. Incorrect – Paramecium is not an autotroph. Autotrophs, like plants or algae, produce their own food using photosynthesis. Paramecia do not perform photosynthesis; instead, they ingest other organisms like Chlorella for food.
B. Incorrect – Paramecia can perform all of the functions of life (e.g., metabolism, growth, reproduction, response to stimuli, homeostasis, and nutrition). Even though it is unicellular, it is still a fully functioning living organism.
C. Correct – Paramecia carry out heterotrophic nutrition by ingesting other organisms like Chlorella and breaking them down in food vacuoles for energy.
D. Incorrect – Paramecium is a eukaryote, not a prokaryote. It has a nucleus and membrane-bound organelles, which are not found in prokaryotes like bacteria.
Question
The image shows the nucleus of a cell from the pancreas that is surrounded by
endoplasmic reticulum.
What describes this nucleus?
A. It is composed of highly folded internal membranes and a liquid matrix.
B. It contains ribosomes and is the main site of protein synthesis in a cell.
C. It contains membrane-bound organelles.
D. It contains chromatin and is surrounded by a double membrane.
▶️Answer/Explanation
Answer: D. It contains chromatin and is surrounded by a double membrane.
Explanation:
The nucleus is the control center of a eukaryotic cell. It contains the cell’s genetic material (DNA), mostly in the form of chromatin — a mix of DNA and proteins. The nucleus is surrounded by a double membrane called the nuclear envelope, which has pores that regulate the exchange of materials (like RNA) between the nucleus and the cytoplasm. The nucleus does not contain organelles but does include structures like the nucleolus, which helps make ribosomes.
Evaluating the options:
A. Incorrect – This describes the endoplasmic reticulum (ER), not the nucleus. The ER is made of folded membranes and has a fluid-filled interior (the lumen), but the nucleus has chromatin and is not made of folded internal membranes.
B. Incorrect – Ribosomes are not found inside the nucleus; they are either free in the cytoplasm or attached to the rough ER. Protein synthesis mainly occurs in the cytoplasm, not the nucleus.
C. Incorrect – The nucleus itself is a membrane-bound organelle, but it does not contain other organelles inside it. This option confuses the nucleus with the whole cell.
D. Correct – The nucleus contains chromatin (DNA and protein) and is surrounded by a double membrane (the nuclear envelope), which controls what enters and leaves the nucleus.
Question
The diagram shows a prokaryotic cell.
What are the structures labelled Y and Z?
▶️Answer/Explanation
Answer: D.
Explanation: The diagram shows a prokaryotic cell, most likely a bacterium.
Structure Y:
- Y is pointing to the region containing a tangled mass of DNA.
- In prokaryotic cells, DNA is not enclosed in a membrane-bound nucleus.
- Instead, it resides in a region called the nucleoid.
So, Y = Nucleoid, not nucleus (which is only found in eukaryotes)
Structure Z:
- Z is pointing to small dots in the cytoplasm.
- These are ribosomes used for protein synthesis.
- Prokaryotic ribosomes are 70S, consisting of a 50S large subunit and a 30S small subunit.
So, Z = 70S ribosome
Why other options are incorrect:
A and C: Both incorrectly list “Nucleus”, which is absent in prokaryotes.
B and C: Both incorrectly list “80S ribosome”, which is found in eukaryotic cells only.
Question
The micrograph of a section through a plant stem shows at least ten different types of cells.
What explains the differences between these cells?
A. Only one gene is expressed in each cell type.
B. Different genes are expressed in each cell type.
C. Only useful genes remain in the DNA of each cell type.
D. Changes in the DNA sequence take place when these cells develop.
▶️Answer/Explanation
Answer: B. Different genes are expressed in each cell type.
Explanation:
In multicellular organisms like plants, all cells come from a single zygote and have the same DNA. However, cells become different from one another through a process called differentiation. This happens because different genes are expressed (turned on or off) in each type of cell. Gene expression means that specific segments of DNA are used to make proteins that give each cell its structure and function for example, xylem cells express different genes than parenchyma cells, even though their DNA is identical.
Evaluating the options:
A. Incorrect – It’s not true that only one gene is expressed in each cell type. Each cell expresses many genes depending on its function, although not all the same ones.
B. Correct – This is the best explanation. All cells have the same DNA, but different genes are expressed in different cell types. This leads to different cell structures and functions, even within the same tissue or organ.
C. Incorrect – All genes remain in the DNA of each cell, including the ones that are not currently useful. Cells do not delete or remove unused genes; they just keep them inactive.
D. Incorrect – The DNA sequence does not change when cells specialize. What changes is which genes are expressed, not the actual genetic code.
Question
What do chloroplasts and mitochondria have in common?
Both are found in the cells of Filicinophyta.
Both contain grana.
Both occur in all eukaryotic cells.
Both are found in a Paramecium.
▶️Answer/Explanation
Answer: A. Both are found in the cells of Filicinophyta.
Explanation:
Chloroplasts and mitochondria are double-membraned organelles found in eukaryotic cells. Mitochondria perform respiration; chloroplasts perform photosynthesis. Only plant cells (like those in Filicinophyta) have both.
Evaluating the options:
A. Correct – Filicinophyta (ferns) are plants, so their cells contain both mitochondria and chloroplasts.
B. Incorrect – Only chloroplasts contain grana; mitochondria do not.
C. Incorrect – Not all eukaryotic cells have chloroplasts; only photosynthetic ones do.
D. Incorrect – Paramecium has mitochondria but no chloroplasts.