Question
How do autotrophs living in an aquatic ecosystem obtain carbon?
▶️Answer/Explanation
Answer: A
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.
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).
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.
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.
Explanation:
Originally, classification of plants like foxglove (Digitalis purpurea) was based 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.