Question

Describe the structure of a chloroplast and the functions of the structural components

Answer 1

chloroplast has an inner and outer membrane with an empty intermediate space in between. Inside the chloroplast are stacks of thylakoids, called grana, as well as stroma, the dense fluid inside of the chloroplast. These thylakoids contain the chlorophyll that is necessary for the plant to go through photosynthesis.




The chloroplast are double membrane bound organelles and are the site of photosynthesis The chloroplasts have a system of three membranes: the outer membrane, the inner membrane and the thylakoid system. The outer and the inner membrane of the chloroplast enclose a semi-gel-like fluid known as the stroma. This stroma makes up much of the volume of the chloroplast, the thylakoids system floats in the stroma.


Outer membrane - It is a semi-porous membrane and is permeable to small molecules and ions, which diffuses easily. The outer membrane is not permeable to larger proteins.

Intermembrane Space - It is usually a thin intermembrane space about 10-20 nanometers and it is present between the outer and the inner membrane of the chloroplast.

Inner membrane - The inner membrane of the chloroplast forms a border to the stroma. It regulates passage of materials in and out of the chloroplast. In addition of regulation activity, the fatty acids, lipids and carotenoids are synthesized in the inner chloroplast membrane.

Stroma

Stroma is a alkaline, aqueous fluid which is protein rich and is present within the inner membrane of the chloroplast. The space outside the thylakoid space is called the stroma. The chloroplast DNA chlroplast ribosomes and the thylakoid sytem, starch granules and many proteins are found floating around the stroma.

Thylakoid System

The thylakoid system is suspended in the stroma. The thylakoid system is a collection of membranous sacks called thylakoids. The chlorophyll is found in the thylakoids and is the sight for the process of light reactions of photosynthesis to happen. The thylakoids are arranged in stacks known as grana.

Each granum contains around 10-20 thylakoids.


Thylakoids are interconnected small sacks, the membranes of these thylakoids is the site for the light reactions of the photosynthesis to take place. The word 'thylakoid' is derived from the Greek word "thylakos" which means 'sack'.


Important protein complexes which carry out light reaction of photosynthesis are embedded in the membranes of the thylakoids. The Photosystem I and the Photosystem II are complexes that harvest light with chlorophyll and carotenoids, they absorb the light energy and use it to energize the electrons.

The molecules present in the thylakoid membrane use the electrons that are energized to pump hydrogen ions into the thylakoid space, this decrease the pH and become acidic in nature. A large protein complex known as the ATP synthase controls the concentration gradient of the hydrogen ions in the thylakoid space to generate ATP energy and the hydrogen ions flow back into the stroma.

Thylakoids are of two types - granal thylakoids and stromal thylakoids. Granal thylakoids are arranged in the grana are pancake shaped circular discs, which are about 300-600 nanometers in diameter. The stromal thylakoids are in contact with the stroma and are in the form of helicoid sheets.

The granal thylakoids contain only photosystem II protein complex, this allows them to stack tightly and form many granal layers wiht granal membrane. This structure increases stability and surface area for the capture of light.

The photosystem I and ATP synthase protein complexes are present in the stroma. These protein complexes acts as spacers between the sheets of stromal thylakoids.

Chloroplast Function

Functions of chloroplast:

In plants all the cells participate in plant immune response as they lack specialized immune cells. The chloroplasts with the nucleus and cell membrane and ER are the key organelles of pathogen defense.
The most important function of chloroplast is to make food by the process of photosynthesis. Food is prepared in the form of sugars. During the process of photosynthesis sugar and oxygen are made using light energy, water, and carbon dioxide.
Light reactions takes place on the membranes of the thylakoids.
Chloroplasts, like the mitochondria use the potential energy of the H+ ions or the hydrogen ion gradient to generate energy in the form of ATP.
The dark reactions also known as the Calvin cycle takes place in the stroma of chloroplast.
Production of NADPH2 molecules and oxygen as a result of photolysis of water.
BY the utilization of assimilatory powers the 6-carbon atom is broken into two molecules of phosphoglyceric acid.

Answer 2

Chloroplasts are a type of chromoplasts located in photosynthetic plant cells and in green algae. They are located in the part of the cell that receives the most light. The chloroplast medium is known as stroma, and is formed by a solution of carbohydrates, lipids, nucleic acids, pigments, and salts. Its main function is to take energy from the sun and use it in the formation of organic matter.

Step-by-step explanation:

Chloroplasts are formed by:

-External and internal membrane. The outer one has porins and is very permeable, and the inner membrane is less permeable, it contains transport proteins whose function is to regulate the passage of substances. They have no chlorophyll.

-Intermembrane space. Composition similar to cytosol.

-Tilacoides and grana. They are flattened saccules that form a membranous internal network. Each of these stacks is called grana, with a variable number of bags. These membranes have everything that is needed for photosynthesis.

-Stroma. Central space of the chloroplast. Inside they have: double stranded circular DNA, which encodes the synthesis of chloroplast proteins; 70S ribosomes; enzymes that allow reducing carbon dioxide to organic matter, and enzymes whose function is the replication, transcription and translation of chloroplast DNA.