IB DP Biology- A3.1 Diversity of organisms -FA 2025- IB Style Questions For HL Paper 1

Question How do autotrophs living in an aquatic ecosystem obtain carbon?

A. By diffusion of dissolved carbon dioxide and hydrogen carbonate ions

B. By feeding on heterotrophs and obtaining carbon from carbohydrates

C. By active transport of carbon dioxide directly from the atmosphere

D. By ingesting organisms with carbonate shells

▶️Answer/Explanation

Ans: A

Question

The electron micrograph shows the detailed structure of a prokaryotic cell.

How is this cell different from a eukaryotic cell?

A. Eukaryotic cells are compartmentalized, whereas this cell is not.

B. This cell contains ribosomes, whereas eukaryotic cells do not.

C. Eukaryotic cells contain DNA, whereas this cell does not.

D. This cell has a cell wall, whereas eukaryotic cells do not.

▶️Answer/Explanation

Ans: A

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

Ans. C

a potato tuber acts as a source when its buds are sprouting, and developing stems act as sinks in a potato plant:

Part of the plant	Function
Leaves and stems	Source tissues that produce sucrose through photosynthesis
Tubers	Sink organs that store carbon compounds and provide nutrients to developing buds
Developing stems	Sink tissues that receive sucrose transported from the leaves through the phloem

A sink is a part of the plant that uses carbon for growth, storage, and respiration. In a potato plant, the tuber is the primary sink organ.

Potatoes are considered stems because they grow from stolons, which are underground stems. Potato tubers contain buds that produce stems and leaves, which are characteristics that roots lack.

Question

The dichotomous key displays the general characteristics of four vertebrate classes. Which letter corresponds to most fish?

▶️Answer/Explanation

Ans. B

External fertilization in fish is a reproductive process where the male and female gametes fuse outside the body of the female in an aquatic environment:

Spawning: The female releases her eggs and the male releases sperm into the same area at the same time. The process of releasing eggs and sperm is called spawning.

Sperm movement: The sperm swims randomly in the water and comes into contact with the eggs.

Fertilization: The nucleus of the sperm moves into the egg and fuses with it.

External fertilization is common in most fish species, and it also occurs in other aquatic animals, such as crustaceans, mollusks, squid, and echinoderms.

Here are some characteristics of external fertilization in fish:

Water protects eggs

The water protects the eggs from drying out.

Trigger for spawning

Water temperature or the length of daylight can trigger the release of eggs and sperm.

Courtship

Some fish pairs may exhibit courtship behavior before spawning, which allows the female to choose a male.

Multiple paternity

Releasing sperm into the water increases sperm competition, which can lead to multiple paternity.

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

Ans:D

Question

The diagram shows features of three plant phyla.

Answer/Explanation

Ans: D

IB DP Biology- A3.1 Diversity of organisms -FA 2025- IB Style Questions For HL Paper 1

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