Chloroplast Structure and Function

Electromagnetic energy is the same as radiation or light energy. This
type of kinetic energy can take the form of visible light waves, like
the light from a candle or a light bulb, or invisible waves, like radio
waves, microwaves, x-rays and gamma rays. Further, irrespective of where radiation is coming from, it can travel in a vacuum. The electromagnetic energy in plants can be converted to stored chemical energy during photosynthesis. 

Option 'A' is correct.

Chloroplasts are the cell organelles where photosynthesis occurs. The light reactions occur in thylakoid membranes and dark reactions occur in stroma of chloroplasts. These reactions result in synthesis of sugars (glucose) in chloroplasts.

The chloroplast is the cell organelles present in plant cells that are responsible for initiating the process of photosynthesis. Chloroplasts are double-membrane bound structures. The stroma of chloroplast is the jelly-fluid like structure in which another membrane system is presently called the thylakoids. These thylakoids are stacked upon each other to form the structure called grana. The grana are connected with each other by an extension of thylakoids called stroma lamellae. Thylakoid of grana has the photosynthetic pigments embedded in it that perform the trapping of sunlight and begin the light reaction of the photosynthesis.

In photosynthesis, light-independent reactions are known as dark reactions. This process does not depend directly on the presence of light but is dependent on the products of light reaction i.e., ATP and NADPH. The dark reactions occur through Calvin cycle. They take place in the stromal matrix of the chloroplast. Chloroplast stroma contains light independent reaction enzymes which are required for the reaction. Thus, the correct answer is option C.

In the chloroplast, the primary photochemical reactions occur. During photosynthesis, primary reactions like the light-capturing and ATP-generating reactions occur on grana. Grana are stakes of thylakoids. Quantasomes are particles found in grana. During photosynthesis, the light-dependent reactions take place on the thylakoid membranes. The inside of the thylakoid membrane is called the lumen. Light-independent reactions take place in the stroma. 

The green parts of the plants have the chlorophyll pigment containing chloroplasts. The chloroplast is a type of plastid which plays a major role in the photosynthesis process.

Chlorophyll which is an essential factor in photosynthesis was first isolated and namedby Joseph Bienaime Caventou and Peter Joseph Pelletier but the chemical composition of the same was first elucidated by the German chemist Richard Willstatter followed by Hans Fischer.  Carotenoids which are the organic pigments found in the chloroplasts and chromoplasts of plants and other photosynthetic organisms. These  are oil-soluble molecules comprising of 40 branched
carbon units bonded together.

• The thylakoid membrane of chloroplasts contain around 250-400 particles known as quantasomes. They are present on the surface of thylakoid discs in chloroplasts.

The chloroplasts are composed of the carbohydrates, lipids, proteins, chlorophyll, carotenoids (carotene and xanthophylls), DNA, RNA and certain enzymes and co-enzymes. The chloroplasts also contain some metallic atoms as Fe, Cu, Mn and Zn. By chemical analysis, these consist of lipids and proteins basically. Lipids are mainly phospholipid components of the membranes and lamellae. Proteins also contain enzymes, which are fully present in mature plastids. By the chemical analysis, it is observed that chloroplastids contain 90% of water, 5% of proteins, 2% of lipids and 3% of pigments.

Thylakoid is a sheet-like membrane-bound structure which is the site of the light-dependent photosynthesis reactions within the chloroplasts and cyanobacteria. Photosystems are then functional and structural units of protein complexes involved in photosynthesis.

The electron transport chain is a series of the proteins and organic molecules which are found in the inner membrane of the mitochondria. Photolysis is the chemical process by which molecules are broken down into smaller units through the absorption of light.

The synthesis of ATP in chloroplasts, promoted by light, is termed as photophosphorylation

So the correct option is A.

Chlorophyll pigments trap sunlight during the process of photosynthesis but get destroyed on exposure to light of higher intensity. An exposure to high light intensity for even a small duration can be harmful. The destruction of chlorophyll when exposed to light of high intensity is called as solarization. It occurs due to irreversible chemical changes in the structure of chlorophyll molecule.

Photosynthetic units are referred as quantasomes. Quantasomes are particles found in the thylakoid membrane of chloroplasts in which photosynthesis takes place.

Photosynthesis is a redox reaction in which carbon dioxide is reduced to sugars in dark reaction and water is oxidised to release oxygen in light reaction of photosynthesis. $C^{14}$ label was used to trace the path of carbon in the dark reaction in $C _3$ plants by Calvin, Benson and Basham. The $O^{18}$ label was used by Rumen and Kamen to experimentally prove that the source of oxygen released during light reaction of photosynthesis is water.

The process of photosynthesis takes place in the chloroplasts, using chlorophyll, the green pigment involved in photosynthesis. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant. Chloroplasts capture light energy from the sun to produce the free energy stored in ATP and NADPH through a process called photosynthesis.

Chlorophyll absorbs sunlight of particular wavelength that causes spitting of water at water splitting complex of photosystem II and oxygen gas is released. PSI absorbs light below 680nm while PS II is activated by light below 700 nm; so plants exhibit maximum amount of oxygen released when illuminated with simultaneous exposure to red and far red light. Fixation of $CO _2$ occurs during the dark reaction. Thus, the correct answer is B.

Blue green algae are prokaryotic orgnanisms and lack membrane bound organelles. Mitochondria and cholroplast are double membrane bound organelles of eukaryotes that serve as site of aerobic respiration and photosynthesis respectively. Chromatophores are the pigment containing membranous structures that serve as site for photosynthesis in BGA. Correct answer is A.

• Thylakoid (internal photosynthetic membranes) is a membrane-bound compartment present within the cellular organelle called chloroplast, they are also present in cyanobacteria.
  
• It is a site for the light-dependent reactions of photosynthesis. 
• It is made up of a thylakoid membrane which surrounds the thylakoid lumen.
• The term thylakoid was coined by Menke in the year 1962.
  
• So, the correct answer is 'Menke'.

Intact chloroplast from green leaves can be isolated by the acetone isolation method. The membranes of the chloroplast are proteinaceous in nature so it can be easily isolated by acetone. The samples obtained are loaded to the chromatography apparatus, which shows bands on the chromatogram.

So, the correct option is B. 

The chloroplasts are double membrane-bound organelle that is found in the cytoplasm. They have membrane-bound thylakoids in which the photosynthesis takes place. The cytoplasm is thus separated from the intrathylakoid space by 3 membranes. i.e the 2 membranes of the chloroplast, and some membrane of thylakoid.

• A stack of thylakoid discs is organized to form grana.
  
• A thylakoid refers to the membrane-bound internal compartment within the chloroplasts of a plant cell and cyanobacteria.
  
• It is a site for light-dependent reactions of photosynthesis. 
  
• There are about  10 to 100 thylakoid discs within a granum and about 40- 60 grana in a plant cell.
  
• So, the correct answer is 'Stacks of thylakoids'.

• Ulothrix is a genus of filamentous green algae which are found in marine and fresh waters habitats.
  
• They have a single girdle-shaped or band-shaped chloroplast near the peripheral region of the cytoplasm (near the cell wall).
  
• So, the correct answer is 'Girdle-shaped'.

• A thylakoid refers to the membrane-bound internal compartment within the chloroplasts of a plant cell and cyanobacteria.
  
• It is a site for light-dependent reactions of photosynthesis. 
• It is made up of a thylakoid membrane which surrounds the thylakoid lumen.
• A stack of thylakoid disk is organized to form grana.
• Within a chloroplast of a plant cell, there are about 40- 60 grana and each granum are composed of 10 to 100 thylakoids.
• So, the correct answer is '40-60'.

• The chloroplast is a discoid plastid which contains chlorophyll (green pigment) within the thylakoid membranes of the organelle.
  
• This organelle is present in the green parts of plants where photosynthesis takes place.
  
• It is the main site of synthesis of glucose by the process called photosynthesis.
  
• The chlorophyll pigment captures the sunlight and converts it into chemical energy and thus, helps in the process of photosynthesis.
  
• So, the correct answer is 'Discoid'.

• A thylakoid refers to the membrane-bound internal compartment within the chloroplasts of a plant cell and cyanobacteria.
  
• It is a site for light-dependent reactions of photosynthesis. 
• It is made up of a thylakoid membrane which surrounds the thylakoid lumen.
• A stack of thylakoid disk is organized to form grana.
• There are about  10 to 100 thylakoids within a granum and about 40- 60 grana in a plant cell.
• So, the correct answer is '10-100'.

• Quantasomes occur in the Grana/chloroplast.
• Quantasomes can be defined as small particles found in the thylakoid membrane of the chloroplasts.
• These particles are embedded in a paracrystalline form on the surface of thylakoid discs in chloroplasts.
  
• So, the correct answer is 'Grana/chloroplast'.

Plastids are considered as sac-like organelles, generally involved in the formation or storage of food. These are chloroplast, chromoplast and leucoplast and are same in their structure to transform into one another during the requirement.

• Plastids are a pigment containing double membrane-bound organelle which is the site of manufacture and storage of chemical compounds.
  
• The chloroplast is a plastid which contains the green coloured pigment called chlorophyll and are present in the green parts of the plants that take part in the process called photosynthesis.
• The outer chloroplast envelope is made up of lipid (20%-30%).
• So, the correct answer is '20-30%'.

The photophosphorylation reaction involves the conversion of ADP to ATP in the presence of sunlight. This takes place in the thylakoid membrane. The photosystem I and II that involves the electron carriers; are present in the thylakoid membranes of the chloroplast. here the light reaction of photosynthesis takes place.

Stroma, refers to the colourless fluid surrounding the grana within the chloroplast. Within the stroma are grana, stacks of thylakoids, the sub-organelles, where photosynthesis is commenced before the chemical changes are completed in the stroma. The internal space enclosed by the chloroplast double membrane but excluding the thylakoid space. This space, filled with a colorless hydrophilic matrix, contains DNA, ribosomes and some temporary products of photosynthesis also known as chloroplastic stroma.

Photosynthetic or chloroplasts pigments that are found in the thylakoid membrane constitute grana of chloroplasts are the organic molecules that absorb light of specific wavelengths in the visible region due to the presence of conjugated double bonds and are chlorophyll a and b, carotenoids and xanthophylls.

A) Chlorophyll is located within the thylakoid membrane. But chlorophyll is present in both lower (algae) and higher plants and some bacteria as well.
B) The light-dependent reactions use light energy to make ATP and NADPH. This is also seen in lower plants.

Chloroplast of C4 plants is dimorphic chloroplast because it shows two different types of the chloroplast. 

1). The chloroplast with grana

2). Chloroplast without grana and surrounded to the vascular bundle. 

The chloroplast is of 2 different types hence it's called as the dimorphic chloroplast. And it is best seen among sugarcane of the C4 plants.

So, the correct option is 'Sugarcane'.

The cytochrome b₆f complex is an enzyme found in the thylakoid membrane in the chloroplast of plants, cyanobacteria, and green algae, that catalyzes the transfer of electrons from plastoquinol to plastocyanin.

During photosynthetic electron transport, protons (H$^+$) accumulate in the thylakoid space. These protons are released into thylakoid space after each split of water molecule during photooxidation and after each electron transport between PQH$ _2$ to cytochrome-f. Increase in the number of protons in the thylakoid space results in an increase in a proton gradient.

A) The green pigment chlorophyll is located within the thylakoid membrane.

Quantasomes are particles found in the thylakoid membrane of chloroplasts in which photosynthesis takes place. They are embedded in a paracrystalline array on the surface of thylakoid discs in chloroplasts.

Plastocyanin is a copper-containing protein that acts as an electron carrier in the photosynthetic electron transport chain within the chloroplast thylakoid lumen.

During photosynthesis in the light, protons are actively pumped from the stroma into the thylakoid lumen by the electron transport chain. This accumulation of protons in the lumen causes the pH there to drop to its lowest levels.

The light harvesting complexes are made up of hundreds of pigment molecules bound to proteins. Each photosystem has all the pigments (except one molecule of chlorophyll a) forming a  light harvesting system also called antennae. These pigments help to make photosynthesis more efficient by absorbing different wavelengths of light. The single chlorophyll a molecules form the reaction center. Therefore, the reaction center is not a part of antennae. 

A. Chloroplast ribosomes are similar to those found in the prokaryotes that is 70s type. Eukaryotic ribosomes which are found in the cytoplasm are of 80stype.

A chlorophyll molecule has a hydrophobic "tail" that embeds the molecule into the thylakoid membrane. The "head" of a chlorophyll molecule is a ring called a porphyrin. The porphyrin ring of chlorophyll, which has a magnesium atom at its centre, is the part of a chlorophyll molecule that absorbs light energy.

A) The peristomium is the first true body segment in an annelid worm's body in the anterior end.

A) Quantasomes are not involved in respiration.
B) Xylem is involved in the ascent of sap. Quantasomes do not play a part in the ascent of sap.

Paper chromatography is a technique that is used in the laboratories to separate plant pigments. The concept used is that this helps to separate the mixture into its
component molecules. The molecules migrate, or move up the paper, at
different rates because of differences in solubility, molecular mass,
and hydrogen bonding with the paper.