Question
▶️Answer/Explanation
The correct answer is:
**C. Insulin has three disulphide bridges giving it tertiary structure and two polypeptide chains giving it quaternary structure.**
Explanation:
– Insulin is a protein hormone that consists of two polypeptide chains, referred to as the A chain and the B chain, which are linked together by disulphide bridges (S-S bonds).
– The diagram shows the presence of disulphide bridges (S ______ S), which contribute to the tertiary structure of the protein.
– The two polypeptide chains (A and B) give insulin its quaternary structure.
– Insulin does not have a fibrous structure (eliminating option A), and it is not a single continuous polypeptide chain (eliminating option B).
– While the diagram does not explicitly show the three-dimensional shape, insulin does have tertiary and quaternary structures (eliminating option D).
Thus, option C is the most accurate description.
Question
What is the function of tRNA-activating enzymes in protein synthesis?
A. They attach amino acids to tRNA molecules using ATP.
B. They activate tRNA and amino acids during transcription.
C. They synthesise ATP and bind it to specific tRNA molecules.
D. They allow the formation of H bonds between tRNA anticodons and specific amino acids.
▶️Answer/Explanation
Ans. A
Aminoacyl-tRNA synthetases (aaRS) are enzymes that play a central role in protein synthesis by attaching amino acids to tRNAs. This process is called tRNA activation or tRNA charging.
Here’s how tRNA activation works:
- The carboxyl group of an amino acid’s backbone covalently links to the α-phosphate of an ATP molecule. This creates an aminoacyl adenylate intermediate (aa-AMP) and releases inorganic pyrophosphate (PPi).
- The aa-AMP undergoes a nucleophilic attack, attaching an aminoacyl group to the tRNA at the 3′-OH. This frees an AMP molecule and creates aa-tRNA.
The tRNA then carries the amino acid to the ribosome, where it matches the codon in the mRNA with the amino acid it codes for.
Question
The three-toed sloth, Bradypus variegatus, lives in tree tops where it feeds on leaves. It also feeds on algae and fungi which live in its fur.
In which trophic group should the three-toed sloth be classified?
A. Autotroph
B. Consumer
C. Detritivore
D. Saprotroph
▶️Answer/Explanation
Markscheme
B
The three-toed sloth, **Bradypus variegatus**, should be classified as a **Consumer** (Option B).
### Explanation:
– **Consumers** are organisms that obtain their energy and nutrients by eating other organisms. The three-toed sloth primarily feeds on leaves (plant matter), algae, and fungi, all of which are other living organisms. This makes it a consumer.
– **Autotrophs** (Option A) are organisms that produce their own food through photosynthesis (e.g., plants). The sloth does not produce its own food.
– **Detritivores** (Option C) feed on dead organic matter (e.g., decaying leaves or dead animals). While the sloth may incidentally consume some detritus, its primary diet consists of living leaves, algae, and fungi.
– **Saprotrophs** (Option D) are organisms that decompose dead organic matter externally (e.g., fungi). The sloth does not decompose organic matter.
Thus, the sloth is best classified as a **Consumer**.
Question
Which processes occur in an ecosystem?
I. Biomass increases in each successive trophic level.
II. Inorganic nutrients are recycled.
III. Chemical energy is stored in carbon compounds.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
Markscheme
C
The correct answer is:
**C. II and III only**
### Explanation:
– **II. Inorganic nutrients are recycled.**
This is a fundamental process in ecosystems. Inorganic nutrients (e.g., nitrogen, phosphorus) are cycled through biogeochemical cycles (e.g., nitrogen cycle, carbon cycle) and reused by organisms.
– **III. Chemical energy is stored in carbon compounds.**
This is also true. Producers (e.g., plants) convert solar energy into chemical energy through photosynthesis, storing it in carbon compounds like glucose. This energy is then passed through the ecosystem via food chains.
– **I. Biomass increases in each successive trophic level.**
This is **false**. Biomass typically decreases at each successive trophic level due to the **10% rule** of energy transfer. Only about 10% of the energy from one trophic level is transferred to the next, resulting in less biomass at higher levels.
Thus, only **II and III** are correct, making **C** the correct answer.
Question
A hummingbird is shown visiting a large flower.
What makes this a mutualistic relationship?
A. The bird feeds on nectar and transfers pollen to the stamen of a flower of the same species.
B. The bird obtains nutrients and the plant is assisted with pollination for sexual reproduction.
C. The bird requires pollen as a protein source and, while obtaining this, disperses seeds for the plant.
D. The bird transfers pollen to the stigma of flowers of a different species while feeding.
Answer/Explanation
Ans:B
The correct answer is:
**B. The bird obtains nutrients and the plant is assisted with pollination for sexual reproduction.**
### Explanation:
– **Mutualism** is a type of symbiotic relationship where both organisms benefit. In this case:
– The **hummingbird** benefits by obtaining **nectar** (a source of energy) from the flower.
– The **plant** benefits because the hummingbird **transfers pollen** (while feeding) to other flowers of the same species, facilitating **pollination** and sexual reproduction.
– **Why not the other options?**
– **A.** Incorrect because the pollen is transferred to the **stigma** (not the stamen) for pollination to occur.
– **C.** Incorrect because hummingbirds primarily feed on **nectar** (not pollen) for energy, and they do not disperse seeds.
– **D.** Incorrect because pollination typically occurs between flowers of the **same species**, not different species.
Thus, **B** is the correct answer, as it accurately describes the mutualistic relationship between the hummingbird and the flower.