IB Biology SL (Standard level)- 2024 – Practice Questions- All Topics
Topic 2.9 Photosynthesis
Topic 2 Weightage : 20%
All Questions for Topic 2.9- Photosynthesis, Light Spectrum, Chlorophyll, Action Spectrum, Photosynthetic Reactions, Chromatographs, Limiting Factors, Oxygenation of Earth, Chloroplasts, Chloroplasts
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?
Blue
Red
Green
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?
Both are found in the cells of Filicinophyta.
Both contain grana.
Both occur in all eukaryotic cells.
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.
An experiment was set up so that each test tube contained water at a pH of 6.3 and a pH indicator. Test tubes 1 and 2 also contained a common pond autotroph. Carbon dioxide dissolves in water and forms carbonic acid. After three days the four test tubes were found to have these results.
What conclusion can be drawn from test tube 1 and test tube 2?
▶️Answer/Explanation
In test tube 1, if you put an autotroph, such as a plant, and expose it to light, it will undergo photosynthesis. A neutral pH is also present which is a optimum for the process of photosynthesis.
During photosynthesis, carbon dioxide is used to produce glucose and oxygen. The glucose produced can then be used in cellular respiration to produce ATP, which is used by the cell for energy.
During cellular respiration, glucose is broken down into carbon dioxide and water. This process releases energy in the form of ATP, and the CO2 produced is used in photosynthesis.
The test tube 2 is at the pH of 5.5 which is also a optimum pH and is in the dark, they only consume oxygen and emit carbon dioxide. Under dim light, photosynthesis and respiration are the same. Plants absorb and store carbon dioxide produced during photosynthesis, whereas they use up all the carbon dioxide produced during respiration.
During respiration, plants break down glucose to release energy that is used for growth and other metabolic processes.
Question
What is a feature of shorter wavelength visible radiation?
A. It includes violet light.
B. It has less energy per photon than longer wavelengths.
C. It is absorbed by greenhouse gases.
D. It is reflected by chlorophyll.
▶️Answer/Explanation
A
Violet light is visible to humans but ultraviolet rays are not. The lens of the human eye blocks most radiation in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea. Humans also lack color receptor adaptations for ultraviolet rays.
Shorter waves vibrate at higher frequencies and have higher energies. Red light has a frequency around 430 terahertz, while blue’s frequency is closer to 750 terahertz. Red photons of light carry about 1.8 electron volts (eV) of energy, while each blue photon transmits about 3.1 ev.
Question
Oxygen is produced during photosynthesis. What is the source of this oxygen inside the plant?
A. Air spaces in the leaf
B. Carbon dioxide
C. Glucose
D. Water
Answer/Explanation
Markscheme
D
The source of oxygen evolved in photosynthesis is photolysis of water. During photosynthesis, green plants produce carbohydrates by the reactions between atmospheric carbon dioxide CO2 and absorbed soil water and in this process, oxygen is formed as a byproduct. The theory that supports this is called the Z-scheme. It describes how electrons are transferred from water to carbon dioxide during photosynthesis.
Question
Which of the following graphs shows the relationship between substrate concentration and enzyme activity with a fixed concentration of enzyme?
▶️Answer/Explanation
The relationship between substrate concentration and enzyme activity in plants is that an increase in the concentration of the substrate brings about an increase in the activity of the enzyme until all the active sites of the enzyme molecules are saturated with substrate. After this, the rate of enzyme reaction becomes steady and addition of the substrate will not have a positive effect.
Question
Absorption spectra of two photosynthetic pigments are shown. Phycoerythrin is a red pigment found in many marine red algae, while chlorophyll a is the major pigment in green plants and algae.
What do the absorption spectra show about the pigments?
A. Phycoerythrin absorbs mostly red light.
B. Chlorophyll a reflects more green light than phycoerythrin.
C. Chlorophyll a photosynthesizes more at $550 \mathrm{~nm}$ than phycoerythrin.
D. Phycoerythrin does not absorb blue light.
▶️Answer/Explanation
Ans:B
Phycoerythrin reflects red light and can be found in red algae and cyanobacteria and responsible for their red colour. Chlorophyll a absorbs light energy of red and blue wavelengths. Whereas, the green light is not absorbed and is reflected back more than phycoerythrin. Thus, the leaves appear green. The set of wavelengths that a pigment doesn’t absorb are reflected, and the reflected light is what we see as colour.