Question

How would you recognize a primary plastid? It would a. have one envelope membrane. b. have two envelope membranes. c. have more than two envelope membranes. d. lack pigments. e. be golden brown in color.

Short answer

The correct answer is b. A primary plastid would have two envelope membranes.

Step-by-step solution

Identify the Characteristics of a Primary Plastid

A primary plastid has two envelope membranes. This characteristic distinguishes it from other organelles inside the cell.

Match the Options with the Characteristics of a Primary Plastid

Go through all the options one by one and only select those that match with the given characteristic of a primary plastid. After thorough analysis, it becomes clear that the answer is option b - 'have two envelope membranes'.

Key concepts

Cell Organelles

Cell organelles are specialized structures within a cell that perform distinct processes necessary for the cell’s survival and proper functioning. Much like the organs in our bodies, each organelle has a unique role, from generating energy to synthesizing hormones.

For instance, mitochondria are known as the powerhouse of the cell because they produce adenosine triphosphate (ATP), the cell's energy currency. The nucleus holds genetic material and controls the cell's growth and reproduction. Another example is the ribosomes, the site of protein synthesis where amino acids are assembled into proteins according to the genetic code.

Understanding the various organelles within a cell is crucial for recognizing a primary plastid, which is also an organelle found in plant and algal cells. It’s involved in photosynthesis, storage of products like starch, and can contain pigments that give plants their color.

Envelope Membranes

Envelope membranes are layers that encase certain organelles, providing a distinct internal environment by regulating the entry and exit of substances. This function is akin to an exclusive club's bouncer, who controls who gets in and out.

In the context of plastids, these membranes are vital as they not only protect the internal components but also play a role in the synthesis and transport of important molecules. For instance, the double envelope membrane of the primary plastid is an identifying feature that distinguishes it from organelles with single or multiple membranes.

These dual membranes highlight the endosymbiotic origin of plastids, where an ancient free-living photosynthetic bacterium was engulfed by a eukaryotic cell. The two membranes are remnants from the engulfment process, with the outer membrane possibly deriving from the host's phagocytic vesicle, and the inner membrane from the plasma membrane of the symbiotic bacterium.

Plastid Characteristics

Plastids are a group of plant cell organelles that are involved in energy storage and the synthesis of metabolic materials. A primary plastid, which has a dual-membrane structure, is an evidence of the organelle's evolutionary history – a result of a symbiotic relationship between a eukaryotic host cell and photosynthetic bacteria.

Some key features of primary plastids include their ability to perform photosynthesis, thanks to the presence of chlorophyll pigments within them, which often give them a green color. However, not all plastids are green; some, like chromoplasts, contain other pigments and can be red, orange, or yellow. Plastids can also store nutrients such as starch in amyloplasts, or lipids in elaioplasts, demonstrating their versatility within the cell.

It's essential to highlight that primary plastids are found in plants and algae, setting these organisms apart from non-photosynthetic cells which lack such organelles. Recognizing a primary plastid involves identifying its dual-envelope membrane structure, ruling out other possibilities such as single or multiple membrane structures.