Of all the plastids that are known to us, the Chloroplast steals the limelight. Why so?
They are the one that are responsible for sustaining life on this planet. Albeit, there are many more reasons and Chloroplasts are one those reasons.
Why are we saying so?
Ah! You are a curious devil it seems! Find out the answer to the question in this exhaustive list of chloroplast facts that can aid you with your biology lessons.
Chloroplast Facts: 1-4 | Introduction
1. Chloroplasts are the plastids which contain chlorophyll pigment in the plant cells.
2. They help in photosynthesis, synthesis and storage of food in the form of carbohydrates, proteins, and lipids.
3. Chloroplasts are generally termed as “Kitchens of the cells” because they synthesize and store the food.
4. They contain DNA, RNA, and ribosomes and hence they can replicate themselves and they are termed as “semi-autonomous organelles”.
Chloroplast Facts: 5-25 | History
5. Nehemiah Grew and Antonie van Leeuwenhoek described chloroplasts in the 17th century.
6. Joseph Priestly was the first person to give a demonstration that plants produce oxygen. He did that in the years 1771 to 1772.
7. A Dutch physician, Jan Ingen-Housz went further and formulated the equation of the photosynthesis in 1779.
CO2 + H2 = O2 + Organic Matter
8. In 1782, Jean Senebier, a Swiss pastor, demonstrated that fixed air or carbon dioxide is necessary for the production of oxygen by the plants.
9. In 1804 Nicholas Theodore de Saussure demonstrated that water is also a necessity for the production of oxygen.
10. He also correlated light requirement to production of oxygen and uptake of carbon dioxide.
11. In 1837, Dutrochet showed that chlorophyll is important for making oxygen.
12. In the same year, Hugo von Mohl described chloroplast as discrete bodies within the plant cell.
13. In 1843, Liebig, a German biochemist, told that carbon dioxide is the source of the organic compounds formed by the plants.
14. Sachs, in 1862, proved that plants produced starch in a light-dependent reaction (photosynthesis).
15. In 1883, Meyer described the structural details of chloroplasts.
16. In 1884, Eduard Strasburger adopted the term “chloroplast”.
17. In 1913, Wilstatter and Stoll succeeded in isolating chlorophyll and determined the structure of chlorophyll.
18. Thunberg, in 1923, understood that carbon dioxide was reduced and water was oxidized in photosynthesis.
19. In 1932, California Institute of Technology’s Robert Emerson and William Arnold conducted an experiment on Chlorella and concluded that not all chlorophyll molecules in a chloroplast are involved in converting light energy to chemical energy.
20. This experiment helped in discovering the reaction centers of the pigment chlorophyll.
21. In 1936, Wood and Werkman differentiated between light reaction and dark reaction.
22. Hill, in 1936, found that chloroplasts release oxygen when they are illuminated.
23. In 1947, K. Porter and S. Granick defined the ultrastructure of grana of chloroplast.
24. Melvin Calvin was awarded a Nobel prize for botany for elucidating the dark reaction process with the help of his colleagues James Bassham and Andrew Benson in 1961.
25. To honor Melvin Calvin for his discovery, the dark reaction is named after him and is called the Calvin cycle.
Chloroplast Facts: 26-27 | Distribution
26. Mostly chloroplasts are homogeneously distributed in the cytoplasm. But in some cells, chloroplasts are concentrated near the nucleus or underneath the plasma membrane.
27. The chloroplasts are motile organelles and hence show passive and active movements.
Chloroplast Facts: 28-37 | Morphology
28. Chloroplasts of higher plants are usually biconvex (convex on both sides) or plano-convex (convex on one side).
29. But in different plant cells, chloroplasts have different shapes like filamentous, spheroid, ovoid, saucer-shaped, discoid or club like.
30. They have vesicles (a tiny cavity) and have no color at the center.
31. Size of chloroplasts varies from species to species. They are usually 2 to 3 μm in thickness and 5 to 10 μm in diameter.
32. Chloroplasts of polyploid plant cells (cells which have more than two homologous chromosomes) are larger than chloroplasts of diploid plant cells (cells which have two homologous chromosomes).
33. Chloroplasts of plants grown in sunlight are smaller and lesser in comparison to the chloroplasts of plants which grow in shade.
34. The number of chloroplasts varies from cell to cell and even from species to species.
35. Most of the times it remains constant for a specific plant cell.
36. An alga has a single, huge chloroplast and cells in higher plants have around 30 to 200 chloroplasts.
37. When the chloroplasts’ number is less, they increase the number by dividing and when the chloroplasts’ number is more, they decrease the number by degeneration.
Chloroplast Facts: 38-44 | Chemical Composition
38. Chloroplasts are composed of carbohydrates, proteins, chlorophyll, carotenoids, lipids, ribosomes, DNA, RNA, some enzymes and co-enzymes.
39. Some metallic atoms like Iron, Copper, Manganese, Zinc, etc. are also present in chloroplasts.
40. The most common carbohydrates in chloroplasts are starch and sugar phosphates. Otherwise content of carbohydrates is very low in chloroplasts.
41. Lipids make up around 20% to 30% of the chloroplasts (of its dry weight).
42. Proteins constitute around 35% to 55% of the chloroplast.
43. Chlorophyll is the green pigment which is responsible for the green color of the leaves, young stems etc.
44. Carotenoids are carotenes and xanthophylls (carotenoids are related to vitamin A).
Chloroplast Facts: 45-78 | Ultrastructure
45. Chloroplasts consists of three main components. They are:
Chloroplast Facts | Envelope
46. The chloroplast is covered by an envelope which is a double bound membrane.
47. Both the membranes i.e. outer membrane and inner membrane are semi permeable to smaller molecules.
48. Outer membrane is not permeable to larger proteins. Outer membrane has more lipids than proteins (in 3:1 ratio).
49. Inner membrane borders the stroma. As said earlier, inner membrane is also semi permeable.
50. It is also the place where lipids, fatty acids, carotenoids are synthesized. Intermembrane space is the space present between outer membrane and inner membrane. It is about 10 to 20 nanometers.
Chloroplast Facts | Stroma
51. It is also called the matrix. It makes up most of the volume of the chloroplasts.
52. It is somewhat like a gel-fluid which surrounds the thylakoids. The stroma is alkaline.
53. 50% of the proteins of chloroplasts are present in the stroma. Ribosomes and DNA are also present in stroma.
54. The ribosomes (17 nanometers) present in chloroplasts are smaller i.e. two-thirds of the size of the ribosomes (25 nanometers) present in the cytoplasm.
55. Plastoglobuli (plural form of plastoglobulus) present in stroma are the bubbles of lipids and sometimes even proteins.
56. The plastoglobuli increases when the cell is under stress or when it is aging and the chloroplast is transforming into a gerontoplast.
57. They are also common in etioplasts but decrease in number when etioplasts transform into chloroplasts.
58. Plastoglobuli contain proteins and enzymes required for the synthesis and metabolism of lipids.
59. Plastoglobuli are considered to be attached to thylakoids so that the contents can be exchanged between plastoglobuli and thylakoids.
60. In normal or young chloroplasts, you can see that the plastoglobuli are present singularly but in old or stressed chloroplasts, the plastoglobuli are interconnected with each other.
61. Plastoglobuli are more on stromal thylakoids and less on granal thylakoids.
62. Starch granules are also present in stroma. They take up 15% of the chloroplasts’ volume.
63. Starch granules are not bound by any membrane. They grow in the day because the chloroplasts synthesize sugar and are consumed at night for the function of respiration.
64. Location and composition of starch granules vary from species to species.
65. In aglae and hornworts, there is an almost spherical and refractive structure called pyrenoids.
66. They are absent in higher plants. They are the sites for starch accumulation in plants.
67. Reduction of carbon dioxide and synthesis of starch, sugar, proteins and fatty acids take place in stroma. These syntheses or pathways are controlled by many factors like light, temperature, photoperiods (day length).
Chloroplast Facts | Thylakoids
68. Thylakoids are flattened and membranous closed sacs.
69. The space inside each thylakoid is called interthylakoid space.
70. Thylakoid word originated from Greek word “thylakos” which means sack.
71. Collection of thylakoids in groups (piled up on one another) of 20 to 60 thylakoids is called grana.
72. Each chloroplast consists of 20 to 60 of granal clusters.
73. The grana are interconnected with each other via a structure called intergranal lamellae. They are also called the stromal lamellae.
74. Stromal lamellae are present between the thylakoids. They are known for lateral extension from one thylakoid to connect another, thereby creating an interconnecting membranes’ network.
75. There are two types of thylakoids. The first one is granal thylakoid and the second one is stromal thylakoid (which are basically stromal lamellae).
76. Granal thylakoids are the ones which are arranged in grana and the stromal thylakoids are the thylakoids which are in contact with stroma.
77. Granal thylakoids are disc-shaped or pancake-shaped structures having a diameter of about 300 to 600 nanometers.
78. Stromal thylakoids are like helicoid sheets that spiral around the granal thylakoids.
Chloroplast Facts: 79-80 | Pigments
79. The pigments present in chloroplasts are chlorophyll a, chlorophyll b, chlorophyll c, chlorophyll d, carotenoid, phycobilin, etc.
80. Of all the pigments, chlorophyll is the most important.
Chloroplast Facts: 81-90 | Functions
81. Chloroplasts act as guard cells near the stomata (a pore present in the epidermis of leaves or young stems which helps in respiration).
82. Chloroplasts have a role in immune system too. When the plant is attacked by any pathogen, chloroplasts responds in either of the two ways mentioned below.
83. The first way is the hypersensitive response whereby the chloroplasts undergo programmed cell death and hence killing any pathogen present inside the cell.
84. The second way is the systemic acquired resistance where the chloroplasts produces certain type of enzymes which serve as warning signs to other cells about the invasion of the pathogen.
85. The other cells start preparing defense molecules against the pathogen.
86. The most important work of chloroplasts is definitely the photosynthesis.
87. Thylakoids contain enzymes and protein complexes which help in light reaction and dark reaction.
88. Solar energy is converted into chemical energy. Oxygen is produced by splitting of water molecule in the presence of light. This light reaction takes place in thylakoid membranes.
89. In Calvin cycle or the dark reaction, the chemical energy in the form of ATP (Adenosine Triphosphate) is used in converting carbon dioxide to carbohydrates.
90. The Celvin cycle is also called carbon fixation and it takes place in stroma of the chloroplasts.
The total process of photosynthesis which are C3 cycle, C4 cycle and photorespiration is explained in details in our upcoming e-book (store opening shortly).
Sources: 1. alevelbiology.co.uk 2. microscopemaster.com 3. sciencedirect.com 4. wikipedia.org 5. plantcellbiology.masters.grkraj.org