Home / IB DP Biology Topic 2: Molecular biology 2.9 Photosynthesis Question Bank HL Paper 1

IB DP Biology Topic 2: Molecular biology 2.9 Photosynthesis Question Bank HL Paper 1

IB Biology HL (HIGHER level)- 2024 – Practice Questions- All Topics

Topic 2.9 Photosynthesis

Topic 2 Weightage : 10% 

All Questions for Topic 2.9- Photosynthesis, Light Spectrum, Chlorophyll, Action Spectrum, Photosynthetic Reactions, Chromatographs, Limiting Factors, Oxygenation of Earth, Chloroplasts, Chloroplasts

Question

The graph shows atmospheric oxygen levels over time.

About 2.5 billion years ago, a significant rise in atmospheric oxygen occurred. What was the cause of this rise?

    1. Photosynthesis by non-vascular land plants

    2. Photosynthesis by vascular land plants

    3. Oxygen produced by photosynthetic bacteria being released from the ocean into the atmosphere

    4. Volcanic activity

▶️Answer/Explanation

Ans: C

Photosynthetic bacteria played a crucial role in the evolution of oxygen on Earth. Cyanobacteria, which are photosynthetic bacteria, evolved the ability to produce oxygen through photosynthesis about 2.5 billion years ago. This led to the rise of oxygen on Earth and facilitated the development of aerobic respiration and complex multicellular life. Its thought that a key event in the evolution of oxygenic photosynthesis was the development of proteins that could bind and utilize water molecules. This allowed bacteria to access the energy in water molecules, which they used to produce oxygen.

Question

If a plant is exposed to light, which colour of light would lead to the lowest rate of oxygen release by a green plant?

    1. Blue

    2. Red

    3. Green

    4. White

▶️Answer/Explanation

Ans: C

Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.
Plants have a pigment called chlorophyll that gives them their green color and helps them absorb energy from light. Chlorophyll absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green. Therefore, green light is the least effective for plants because they cannot use it to photosynthesize.
So, if a plant is exposed to the light, which colour of light would lead to the lowest rate of oxygen release by a green plant? The answer is green light because it is mostly reflected by the plant and not used for photosynthesis.

Question

What do chloroplasts and mitochondria have in common?

    1. Both are found in the cells of Filicinophyta.

    2. Both contain grana.

    3. Both occur in all eukaryotic cells.

    4. Both are found in a Paramecium.

      ▶️Answer/Explanation
      Phylum filicinophyta Fonds (pinnate leaves) Sporangia Rhizoid Roots

      Mitochondria and chloroplasts are organelles that are involved in energy production in eukaryotic cells. Mitochondria break down fuel molecules and capture energy in cellular respiration, while chloroplasts capture light energy and make sugars in photosynthesis. Both organelles have their own DNA and ribosomes, and are thought to have evolved from bacteria that were engulfed by larger cells.

      Flilicinophyta is another name for ferns, a group of vascular plants that reproduce by spores. Ferns have both mitochondria and chloroplasts in their cells, as they are photosynthetic plants that also need to respire. Ferns belong to the clade Polypodiopsida, which is a sister group to seed plants.

Question

What does the Rf value in thin layer chromatography represent?

    1. The distance travelled by the pigment front in a fixed time period

    2. The distance from the origin to the solvent front at the end of the experiment

    3. The ratio of distances travelled by the pigment and solvent fronts

    4. The concentration of the pigment applied to the chromatography plate

▶️Answer/Explanation

Ans: C

RF value stands for retardation factor or relative front. It is a ratio of the distance travelled by a solute (the substance being separated) to the distance travelled by the solvent (the liquid carrying the solute) on a chromatography paper. It is a characteristic of the solute and can be used to identify it in a chromatographic system.

The RF value formula is: Distance travelled by the solute divided by the distance travelled by the solvent

The RF value is important because it indicates how well the solute is separated by the solvent and how strongly it interacts with the stationary phase (the paper or other material that does not move) and the mobile phase (the solvent that moves) . Different solutes have different RF values depending on their polarity, relative mass, and relative solubility. The RF value can also be affected by factors such as temperature, solvent composition, and paper quality.

Question

The action spectra for two different types of photosynthetic organisms are shown. Ulva, or sea lettuce, is a green marine alga composed of two layers of cells. The action spectrum for crop plants was plotted from an average of 22 species of plants.

What describes photosynthesis in these organisms?

A. Ulva photosynthesizes more than crop plants at red wavelengths.

B. Crop plants photosynthesize more than Ulva in green light.

C. Photosynthesis by Ulva is highest in red light while that of crop plants is highest in blue.

D. Both have zero photosynthesis at 750nm.

▶️Answer/Explanation

Ans:B

Crop plants are more efficient than green marine algae in performing photosynthesis because they have evolved to optimize their photosynthetic efficiency for the specific conditions of their environment. In contrast, green marine algae have evolved to survive in a wide range of environments and therefore have not optimized their photosynthetic efficiency for any specific environment. However, it is known that photosynthetic efficiency in higher plants is far from having reached its maximum.

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