Evolution Of Chloroplasts

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Plant cells have several structures not found in other eukaryotes. In particular, organelles called chloroplasts allow plants to capture the energy of the Sun in energy-rich molecules; cell walls allow plants to have rigid structures as varied as wood trunks and supple leaves; and vacuoles allow plant cells to change size.
What Is the Origin of Chloroplasts?
Like mitochondria, chloroplasts likely originated from an ancient symbiosis, in this case when a nucleated cell engulfed a photosynthetic prokaryote. Indeed, chloroplasts resemble modern cyanobacteria, which remain similar to the cyanobacteria of 3 million years ago. However, the evolution of photosynthesis goes back even further, to the earliest cells that evolved the ability to capture …show more content…
At some point, a eukaryotic cell engulfed an aerobic prokaryote, which then formed an endosymbiotic relationship with the host eukaryote, gradually developing into a mitochondrion. Eukaryotic cells containing mitochondria then engulfed photosynthetic prokaryotes, which evolved to become specialized chloroplast organelles.
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Today, chloroplasts retain small, circular genomes that resemble those of cyanobacteria, although they are much smaller. (Mitochondrial genomes are even smaller than the genomes of chloroplasts.) Coding sequences for the majority of chloroplast proteins have been lost, so these proteins are now encoded by the nuclear genome, synthesized in the cytoplasm, and transported from the cytoplasm into the chloroplast.

What Is the Function of Chloroplast …show more content…
The thylakoids contain the light-harvesting complex, including pigments such as chlorophyll, as well as the electron transport chains used in photosynthesis (Figure 2).

Figure 2: Structure of a chloroplast
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What Is the Cell Wall?

A schematic illustration shows a three-dimensional representation of a plant cell's plasma membrane and cell wall. They are shown from the side, and are cut away to reveal distinct layers. Structures inside each layer are labeled. The plasma membrane is shown on the bottom. The primary cell wall is on top of the plasma membrane, and the top-most layer is the middle lamella. View Full-Size Image Figure 3 : Plant plasma membrane and cell-wall structure
A plant cell wall is arranged in layers and contains cellulose microfibrils, hemicellulose, pectin, lignin, and soluble protein. These components are organized into three major layers: the primary cell wall, the middle lamella, and the secondary cell wall (not pictured). The cell wall surrounds the plasma membrane and provides the cell tensile strength and
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