Thylakoids are arranged in stacks called
A) cristae.
B) stomata.
C) grana.
D) vacuoles.
The correct answer and explanation is :
The correct answer is: C) grana.
Explanation:
In plant cells, photosynthesis occurs in organelles called chloroplasts. Within chloroplasts, there are specialized internal structures known as thylakoids. Thylakoids are flattened, sac-like membranes that contain chlorophyll and other pigments essential for capturing light energy.
These thylakoid membranes are organized into stacks called grana (singular: granum). Each granum looks like a stack of coins when viewed under a microscope. The grana are connected to each other by structures called stroma thylakoids or lamellae, which are unstacked regions of thylakoid membrane.
The main role of the grana is to optimize the surface area available for light-dependent reactions of photosynthesis. Within the thylakoid membranes, sunlight is captured by chlorophyll and other pigments, initiating a chain of chemical reactions that lead to the production of energy-rich molecules like ATP and NADPH. These energy carriers are then used in the Calvin cycle, which happens in the surrounding fluid called the stroma, to produce glucose.
Let’s briefly look at the incorrect options:
- A) Cristae: These are folds found inside mitochondria, not chloroplasts. They increase the surface area for cellular respiration.
- B) Stomata: These are pores on the surface of leaves that allow for gas exchange (CO₂ in, O₂ out).
- D) Vacuoles: These are storage structures within cells, mainly for water, nutrients, and waste products.
Thus, thylakoids being stacked into grana is crucial for efficient photosynthesis, making C) grana the correct answer.