Question
The diagram refers to questions 2 and 3 . It shows a heterotrophic, unicellular, freshwater organism that has been placed in distilled water. The short arrows show movement of water and the long arrows show a sequence of steps.
What life function is illustrated?
A. Nutrition
B. Homeostasis
C. Endocytosis
D. Response
▶️Answer/Explanation
Answer: B. Homeostasis
Explanation:
What’s going on in the diagram?
- This is a unicellular heterotroph in distilled water (means the water outside is super dilute, so water will move into the cell by osmosis).
- The short arrows show water rushing into the cell (osmosis).
- The circle marked with X is likely a contractile vacuole (common in protists like Paramecium).
- That vacuole fills with excess water, then contracts to pump it out→ which prevents the cell from bursting.
So, what life function is this?
It’s not nutrition (no food here), not endocytosis (no engulfing), and not just a response. This is all about maintaining water balance inside the cell.
Question
The giant alga Acetabularia has a feature that suggests it is an exception to the cell theory. What feature is this?
A. It lacks a nucleus.
B. It lacks a cell wall.
C. It has only one mitochondrion.
D. It lacks subdivision into separate cells.
▶️Answer/Explanation
Answer: D. It lacks subdivision into separate cells.
Explanation:
Cell theory states that:
All living organisms are made of one or more cells.
The cell is the smallest unit of life.
All cells come from pre-existing cells.
Acetabularia is a giant unicellular alga that can grow up to 5 cm long, yet it is a single cell, not divided into smaller cells. This makes it an exception to cell theory because it appears like a multicellular organism due to its size and structure, but is actually just one large cell, challenging the idea that all life is built from tiny, microscopic cells.
Option Evaluation:
A. Incorrect – Acetabularia does have a nucleus located in its rhizoid (base). The presence of a nucleus supports cell theory.
B. Incorrect – Acetabularia has a cell wall, like other algae and plant-like organisms.
C. Incorrect – It is not limited to one mitochondrion. Large cells like Acetabularia have many mitochondria to support their energy needs.
D. Correct – Acetabularia is not subdivided into smaller cells. Despite its large size, it remains a single, continuous cell, which makes it an exception to the usual interpretation of cell theory
What provides evidence for the endosymbiotic theory?
A. Mitochondrial DNA in eukaryotic cells
B. 70S ribosomes in prokaryotic cells
C. Gene transfer from prokaryotic cells to eukaryotic cells using plasmids
D. Prokaryotic cells (Escherichia coli) in the large intestine digest proteins
▶️Answer/Explanation
Answer: A. Mitochondrial DNA in eukaryotic cells
Explanation:
The endosymbiotic theory states that mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells and became permanent, functioning organelles.
A. Correct – Mitochondria have their own circular DNA, similar to bacteria, supporting the idea they were once independent prokaryotes.
B. Incorrect – 70S ribosomes are found in prokaryotes, but this alone does not support endosymbiosis unless found in organelles like mitochondria.
C. Incorrect – Plasmid-based gene transfer is used in labs and does not explain the origin of mitochondria or chloroplasts.
D. Incorrect – E. coli in the intestine is mutualism, not endosymbiosis inside a cell.
Question
What best describes stem cells?
A. Cells found only in the early embryo.
B. Multipotent embryonic cells that can differentiate into all cell types.
C. Totipotent stem cells that are found in specific niches in adults.
D. Pluripotent stem cells that may differentiate into blood cells.
▶️Answer/Explanation
Answer: D. Pluripotent stem cells that may differentiate into blood cells.
Explanation:
Stem cells are undifferentiated cells that have the ability to self-renew (divide and make more stem cells) and differentiate into specialized cell types. They are classified based on their potential to become different types of cells:
- Totipotent – Can form all cell types, including embryonic and extra-embryonic tissues (e.g., zygote).
- Pluripotent – Can form any cell type in the body, but not extra-embryonic tissues (e.g., embryonic stem cells).
- Multipotent – Can form a limited range of cells (e.g., adult stem cells like those in bone marrow).
Now let’s evaluate each option:
A. Incorrect – Stem cells are not only found in the early embryo; adult stem cells also exist in specific tissues (e.g., bone marrow, skin).
B. Incorrect – Embryonic stem cells are pluripotent, not multipotent. This option incorrectly describes their potency.
C. Incorrect – Totipotent cells are only found in the very early embryo (e.g., zygote to 8-cell stage), not in adult niches. Adult stem cells are typically multipotent.
D. Correct – Pluripotent stem cells (like embryonic stem cells) can give rise to many cell types, including blood cells. This best matches the correct definition.
Question
The graph shows the concentration of the lipid lecithin in the amniotic fluid surrounding the fetus during normal gestation. This lipid is produced in the lungs of the fetus and acts as a surfactant.
What problem may occur in a baby born before 34 weeks gestation?
A. Type I pneumocytes do not produce sufficient surfactant for lungs to inflate.
B. There are no type II pneumocytes.
C. The alveolar walls stick together.
D. The alveoli are too large.
▶️Answer/Explanation
Answer: C. The alveolar walls stick together.
Explanation:
What the graph shows:
- It tracks lecithin concentration (a surfactant lipid) in amniotic fluid over weeks of pregnancy.
- From 12 to 30 weeks, the lecithin levels stay super low.
- Around 30–34 weeks, there’s a sharp increase.
- After 34 weeks, levels go up rapidly and plateau near 10 mg/100 ml.
Important Concepts:
- Lecithin = surfactant that prevents alveoli (air sacs) from sticking together.
- Surfactant is made by type II pneumocytes.
- Without surfactant, lungs can collapse because the alveolar walls stick together after each breath.
Let’s break down the options:
A. Wrong: Type I pneumocytes are for gas exchange, not surfactant production.
B. Also incorrect: Type II pneumocytes exist earlier but just aren’t active enough yet.
C. Correct! This is what happens without enough surfactant – alveoli collapse after exhalation because the surface tension is too high.
D. Irrelevant: The issue is about alveolar function, not size.
Question
In mammals, mature red blood cells are specialized in that they lack nuclei, mitochondria or ribosomes. Which statement applies to red blood cells?
A. No chemical reactions take place within their cytoplasm.
B. They cannot produce new enzymes.
C. Materials cannot enter red blood cells.
D. Materials cannot exit red blood cells.
▶️Answer/Explanation
Answer: B. They cannot produce new enzymes.
Explanation:
Mature red blood cells in mammals are highly specialized for transporting oxygen. To maximize space for hemoglobin, they lack a nucleus, mitochondria, and ribosomes. Because of this:
- They cannot divide (no nucleus).
- They do not produce ATP via aerobic respiration (no mitochondria).
- They cannot synthesize new proteins or enzymes (no ribosomes).
Despite these limitations, chemical reactions still occur (e.g., binding and releasing oxygen), and materials can still move in and out via the plasma membrane.
Option Evaluation:
A. Incorrect – Chemical reactions like oxygen binding to hemoglobin still occur in RBCs. Metabolism is limited, but not absent.
B. Correct – Without ribosomes, RBCs cannot produce new enzymes or proteins.
C. Incorrect – RBCs have a plasma membrane that allows the transport of gases and ions, so materials can enter.
D. Incorrect – Materials like CO₂ and O₂ exit the cell regularly during gas exchange, so exiting is possible.
Question
The micrograph shows two types of blood cell.
What determines the differences between the two types of cell?
A. Different number of mitotic cycles
B. Different expression of some genes
C. Reaction to oxygen of red blood cells
D. Reaction to antigens of white blood cells
▶️Answer/Explanation
Answer: B. Different expression of some genes
Explanation:
All body cells in an organism contain the same DNA. However, different types of cells express different sets of genes, depending on their role. This is known as differential gene expression. It allows a stem cell to specialize into a red blood cell, white blood cell, muscle cell, etc., each with distinct functions and structures.
Option Evaluation:
A. Incorrect – The number of mitotic divisions does not determine the type or function of a mature blood cell.
B. Correct – Differences between red and white blood cells are due to different expression of genes, even though they have the same genetic material.
C. Incorrect – Red blood cells do react to oxygen, but that’s a function, not the cause of their structural differences.
D. Incorrect – White blood cells do react to antigens, but again, this is a result of their differentiation, not the reason they became white blood cells.
Question
Which graph represents the change in cell surface area to volume ratio with increasing cell diameter?
▶️Answer/Explanation
Answer: B
Explanation:
As a cell increases in diameter, its:
- Surface area grows with the square of its radius (∝ r²)
- Volume grows with the cube of its radius (∝ r³)
So, the SA:V ratio = surface area / volume = r² / r³ = 1 / r
What this means:
As the cell diameter increases, the SA:V ratio decreases and not linearly, but steeply at first, then gradually flattens out.
Which graph shows this?
Let’s check them:
- A: Straight line down = Not accurate; it’s linear, not curved.
- B: Curved downward, starting high and flattening = Yes! Matches 1/r
- C: Goes up with size = Wrong direction.
- D: Line going up = Opposite of what we want.
Final Answer: B
So, as cells get bigger, their SA:V ratio decreases, making it harder for them to exchange nutrients and waste efficiently which is why cells tend to stay small or become flattened/elongated.