Question
How do autotrophs living in an aquatic ecosystem obtain carbon?
▶️Answer/Explanation
Autotrophs (like algae and cyanobacteria) in aquatic ecosystems obtain carbon in the form of:
- Dissolved carbon dioxide (CO₂)
- Hydrogen carbonate ions (HCO₃⁻)
These forms of carbon are naturally dissolved in water, and autotrophs absorb them by diffusion across their cell membranes. Once inside, the carbon is used in photosynthesis to produce organic molecules like glucose.
Why the other options are incorrect:
B. Autotrophs don’t feed on other organisms that’s what heterotrophs do.
C. Carbon dioxide uptake happens through diffusion, not active transport, and aquatic autotrophs don’t absorb it directly from the air.
D. Autotrophs don’t ingest organisms; they make their own food via photosynthesis.
Question
▶️Answer/Explanation
- Prokaryotic cells, like bacteria, lack membrane-bound organelles. That means they do not have compartments such as a nucleus, mitochondria, or endoplasmic reticulum.
- Eukaryotic cells, on the other hand, are compartmentalized — they have internal membranes that divide the cell into different organelles with specialized functions (like the nucleus for DNA storage).
Why the other options are incorrect:
B. Incorrect: Both prokaryotic and eukaryotic cells have ribosomes. Ribosomes are not membrane-bound and are present in all living cells to synthesize proteins.
C. Incorrect: Prokaryotic cells do have DNA, but it’s not enclosed in a nucleus. It is found in the nucleoid region.
D. Incorrect: While many prokaryotic cells do have a cell wall, so do some eukaryotic cells, like plant cells and fungi.
Question
The image depicts a potato (Solanum tuberosum) plant at the start of the growing season.
Which visible structures serve as sources and sinks?
▶️Answer/Explanation
Answer: C
Explanation:
In plants, “sources” are tissues that produce or release sugars (like sucrose), and “sinks” are tissues that consume or store sugars for growth or storage.
At the start of the growing season in a potato plant:
- Potato tuber (the underground storage organ) acts as a source:
- It stores starch from the previous season.
- During sprouting, it breaks down starch into sucrose and exports it to support new growth (developing stems and leaves).
- Developing stems and shoots act as sinks:
- These parts cannot photosynthesize yet.
- They need sugars and nutrients to grow, so they receive sucrose from the tuber.
Later in the growing season:
- Mature leaves become the main source (through photosynthesis).
- Growing tubers then act as sinks again, storing sugars as starch for future use.
Summary Table:
| Plant Part | Function at Start of Season |
|---|---|
| Potato tuber | Source (releases stored nutrients) |
| Developing stems | Sink (receives nutrients for growth) |
| Leaves (early) | Not active yet; become sources after full development |
Question
The dichotomous key displays the general characteristics of four vertebrate classes. Which letter corresponds to most fish?
▶️Answer/Explanation
Answer: B
Explanation:
We’re starting with vertebrates, and the key divides them based on:
Skin type →
- “No scales, soft skin” → goes to A
- “Scales present” → goes further into fertilisation type
Scales present → two more options:
- External fertilisation → goes to B
- Internal fertilisation → further splits into:
- Eggs with soft shell → C
- Eggs with hard shell → D
Now let’s match this with fish:
Most bony fish (like salmon, rohu, goldfish, etc.) have:
- Scales
- External fertilisation (they release sperm and eggs into water)
- Lay soft eggs without hard shells
So they match: Scales present → External fertilisation → leads us to B
BUT WAIT! What about cartilaginous fish like sharks and rays?
- They have scales (placoid scales)
- BUT many of them do internal fertilisation
- And they may lay eggs with soft shells, or give live birth
So, some fish (like sharks) might match C, but…
The question asks: “Which letter corresponds to most fish?“
And most fish on Earth are bony fish (over 95% of all fish species).
They match the B category perfectly.
Question
The foxglove, Digitalis purpurea, was once classified in the figwort family. The figwort family has been reclassified and is now much smaller.
Why were species such as the foxglove moved into other families?
A. The appearance was too dissimilar.
B. The plants are found in different locations.
C. The genera were different.
D. The DNA sequences indicated different ancestry.
Answer/Explanation
Answer: D. The DNA sequences indicated different ancestry.
Explanation:
- Originally, classification of plants like foxglove (Digitalis purpurea) was based mostly on morphological features (how they look).
- With advances in molecular biology, scientists began analyzing DNA sequences.
- These genetic studies revealed that some plants, including foxglove, were not as closely related to others in the figwort family (Scrophulariaceae) as previously thought.
- As a result, Digitalis and other species were reclassified into new or different families to better reflect their true evolutionary ancestry.
Why the other options are incorrect:
A. The appearance was too dissimilar – Morphology can be misleading; unrelated species can look similar due to convergent evolution.
B. The plants are found in different locations – Geographic location does not determine evolutionary relationships.
C. The genera were different – Even within a family, multiple genera can exist. Genus difference doesn’t require family reclassification.
Question
The diagram shows features of three plant phyla.
Answer/Explanation
Ans: D
Explanation:
Venn Diagram Features:
We have 3 overlapping groups showing plant characteristics:
- R
▸ Spores produced by sporangia
▸ No seeds, no fruits
▸ So, these are non-flowering, spore-producing plants S
▸ No fruits
▸ Seeds are present, but ovules are not enclosed in ovaries
▸ Gymnosperms basically!T
▸ Fruits are produced
▸ Seeds are enclosed in ovaries
▸ Definitely angiosperms
Let’s match phyla with groups:
R:
- Produces spores by sporangia
- Has no seeds or fruits
- This fits Filicinophyta (ferns) → Not bryophyta because they don’t have true vascular tissues or sporangia like this.
S:
- Produces seeds, but no fruits
- Ovules not enclosed in ovaries
- This matches Coniferophyta (a gymnosperm)
T:
- Produces seeds and fruits
- Ovules enclosed in ovaries
- That’s Angiospermophyta (flowering plants)
Option D is correct: R → Filicinophyta, S → Coniferophyta, T → Angiospermophyta