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Chloroplast

Definition:

Chloroplasts, which are the small, specialized organelles, are found only in plant and algal cells. These are not found in animal cells. As such, the chloroplasts in plant and some protists will work to convert sunlight energy into sugars that will then be used by the cells. This whole process is termed as “photosynthesis” and it depends on the green molecules in the chloroplasts called “chlorophyll”.

Chloroplast Origin and Structure:

In the plants, the chloroplasts will be most commonly found in guard cells that are present in plant leaves. These guard cells will be surrounded by tiny pores, which are known as “stomata”. The opening and closing mechanism of these stomata will for the gas exchange that is needed for photosynthesis. The chloroplast structures are produced from the cells called proplastids. As such, the chloroplasts will develop from these precursor cells in the presence of light. Each chloroplast will contain various structures with each one having its specialized functions.

The structure of chloroplast includes the following components:

Membrane Envelope:

The membrane envelope contains inner and outer lipid bilayers. The primary function of this membrane envelope is to provide protection to the structure by keeping the chloroplasts enclosed within them. The inner layer will separate the stroma from the intermembrane space. In addition, it would control the entry and exit of molecules into the chloroplasts.

Intermembrane Space:

This represents the space between the inner and outer membrane of the membrane envelope.

Thylakoid System:

The inner membrane consists of flattened sac-like structures called thylakoids. These are the regions of light energy to chemical energy conversion.

Thylakoid Lumen:

This is the compartment present within the thylakoids.

Grana:

These are the densely stacked layers of thylakoids that are acting as the regions of light energy to chemical energy conversion.

Stroma:

This represents the thick fluid that is present within the chloroplasts. This will be found inside the envelope yet outside the membrane of thylakoids. This fluid will act as the region of conversion of carbon dioxide to sugars.

Chlorophyll:

As mentioned earlier, this is the green pigment present in the grana of the chloroplast, which carries out photosynthesis by absorbing light energy.

Role of Chloroplasts in Photosynthesis:

The role of these organelles in photosynthesis is to contain a majority of reaction during photosynthesis. In simple terms, photosynthesis is a process in which the plant takes energy from the sun and creates the sugars. When the light energy from the sun reaches the chloroplast and the chlorophyll pigments, it will be converted into chemical energy that can be seen in the compounds like ATP and NADPH. These compounds would then move to the stroma where the molecular reactions would make sugars and oxygen. These sugars are eventually used by the plants and animals for their food and energy. The oxygen produced here will be released, which will be inhaled by the animals thereafter.

When this process is considered to be a human scenario, the chloroplast can be thought to be a kitchen of a home. All the required materials will be brought to the kitchen to cook and will be placed in the oven to bake and after a while, food will come out. Likewise, chloroplast is where the photosynthesis takes place and the food and energy will be given out as a result.

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