The word chloroplast easily reminds you of the plant cells. But, it is important to know the chloroplast definition and other details. The term chloroplast is derived from the Greek words- Khloros and plastes. Khloros means green, while plastes refer to something formed.
But, what is chloroplast? Chloroplasts are molecules with high chlorophyll concentration, and they absorb light energy to provide algae and plants with green color. Chloroplasts have evolved from free-living bacteria.
Chloroplasts are generally present in leaves and not in roots- the underground parts of plants. That is why chloroplasts do not receive the light needed for photosynthesis.
What is the function of chloroplasts in the photosynthesis process?
chloroplasts photosynthesis tree
Photosynthesis is the process of storing solar energy into chemical energy stored in glucose form. Water, carbon dioxide, and sunlight play an important role in producing oxygen, water, and glucose. Photosynthesis involves multiple stages- Light reaction and dark reaction.
Light is essential for the light reaction in the chloroplast grana. The pigment chlorophyll forms chemical energy from light energy. Other pigments capable of absorbing light are chlorophyll b, carotene, and xanthophyll.
During the light reaction, sunlight turns into chemical energy in the ATP and NADPH. Protein complexes in the thylakoid membrane facilitate the process of converting light energy into chemical energy. However, NADPH and ATP are also useful for dark reactions.
The dark reaction happens in the stroma, containing enzymes to produce sugar.
Know the structure of chloroplasts
structure of a chloroplast
You can check a chloroplast diagram to have a clear concept. Based on the cross-sectional diagram, the chloroplast structure comprises the following parts-
Membranes
The oval-shaped chloroplasts have inner and outer membranes.
Inner Membrane
It is a protective member to control the molecules. While some molecules get in the structure, other molecules get out of it.
Outer Membrane
As a major covering for chloroplasts, the membrane is highly permeable. That is why small molecules easily pass through it.
Intermembrane Space
There is a minute space between the outer and inner membranes. The width of the membrane ranges from 10 to 20 nanometers.
Stroma
A gel-like fluid is present near the thylakoids, DNA, ribosomes, and plastoglobules.
The Lamella
It looks like bridges and causes the spread of thylakoids. That is why chlorophyll can absorb a high amount of light energy.
Thylakoids
Thylakoids are sacks looking like discs, and they contain chlorophyll found in stack-like setup.
In green algae and vascular plants, the thylakoids remain stacked over one another. The thylakoid stack refers to granum, and its pigments are carotenoids and chlorophylls. Combined with other molecules, these light-absorbing pigments create photosystems.
Enzymes in the stroma make organic molecules for energy storage. As the stroma also has ribosomes and DNA, chloroplasts seem to evolve from free-living bacteria.
It is all about the chloroplast structure, and each of these parts plays an important role.
Facts related to chloroplasts
According to an estimation of scientists, a single square millimeter of a green leaf has almost 500,000 chloroplasts.
The intermembrane, inner membrane and outer membrane together refer to the chloroplast envelope.
Chloroplasts contain chlorophyll, proteins, carbohydrates, ribosomes, carotenoids, lipids, RNA, DNA, co-enzymes, and enzymes. They play a vital role in the photosynthesis process.
Chloroplasts start wiggling around the plant cell to locate the right part for light absorption.
Scientists refer to chloroplasts as the kitchen of the cell, as they store food.
Another name of the stroma is a matrix where the plant synthesizes carbon dioxide, sugar, starch, and fatty acids. However, temperature, light, and several other factors affect it.
When a pathogen attacks a plant, chloroplasts respond to it by turning out some enzymes. Other cells identify it and prevent the effect of the attack.
In some cases, chloroplasts send hypersensitive responses to initiate the programmed cell death process. It closes the system to kill pathogens, while other cells prepare special molecules to remove them.
You can find different views about the discovery of chloroplast. However, in 1905, Konstantin Mereschkowski got the credit for the discovery.
Why are chloroplasts? Greenlight damages chlorophyll and cannot help with absorption. That is why chloroplasts look like green organelles. Greenlight reflects back to the eyes of human beings.
The chloroplast’s shape may vary based on the algae and plant species. The lens-shape chloroplasts are present in terrestrial plants.
Any green part of a plant, including the unripened fruits and stems, has chloroplast. However, the major photosynthetic activities take place in the leaves.
Do chloroplasts have DNA and ribosomes?
Chloroplasts have their unique genome, separated from the plant cell’s DNA. There are circular DNA pieces, known as plasmids. In fact, multiple plasmids are present in chloroplasts to carry almost 120 genes.
Furthermore, the chloroplast comprises 10% of the proteins needed for proper functioning. DNA is the source of the remaining protein.
Chloroplasts have the potential to make ribosomes on their own. They can turn out protein from the messenger RNA. Since ribosomes have protein and rRNA, the genome creates ribosomal RN. The genome has the gene to produce ribulose bisphosphate carboxylase, a type of enzyme. Ribulose bisphosphate has a combination of organic molecules and carbon dioxide gas.
Why do plants need chloroplast?
Chloroplasts let the plants survive and grow properly. They are comparable to solar panels, as they convert light energy into a usable version to facilitate different activities. But, some plants like Rafflesia do not have chloroplasts. They receive nutrients from other plants.
Do animal cells have chloroplasts?
chloroplasts plant vs animal cell
Plant cells contain chloroplasts, whereas animal cells have mitochondria. A plant cannot derive sugar from its food, and that is why it is reliant on sun rays. On the contrary, animals need no chloroplast, as they get sugar from their everyday diet.
However, vacuoles are present in both animal and plant cells. Every plant cell has a big vacuole, and it is useful for storing nutrients and water. It also maintains the cell’s form. But, animal cells have several small vacuoles to store nutrients and water.
There is a cell wall and membrane in plant cells. The cell wall surrounds the membrane to make the plant cells look distinctive. The major function of the membrane is to control the flow of water into a cell. Animal cells have no cell walls but have a cell membrane.
Common traits of chloroplast and mitochondria
Chloroplast and mitochondria are eukaryotic cell organelles with nucleic acids (RNA and DNA)
There are multiple membranes to differentiate the organelles’ interior parts. They help in the formation of organelle parts.
The photosynthesis and cell respiration processes of plant cells involve chloroplast and mitochondria.
Both cell organelles help in transforming energy for eukaryotic cells.
They also comprise a macromolecular machine, like ribosomes.
Interestingly, plant cells have both mitochondria and chloroplasts to undergo cell respiration and photosynthesis. After photosynthesis, plants cause the breakdown of glucose. That is why they need mitochondria for cell respiration.
Mitochondria vs chloroplast- What is the difference?
While mitochondria are present in both animal and plant cells, chloroplasts are found only in plants. Mitochondria turn out energy as ATP, while chloroplast is the photosynthetic site in a plant cell. These cell organelles look different from each other. While mitochondria are bean-shaped, the chloroplast is disc-shaped.
Mitochondria are colorless, whereas chloroplast is green. The major chambers in mitochondria are cristae and matrix. However, chloroplast also has chambers- thylakoid and stroma. Mitochondria are responsible for consuming oxygen, but chloroplasts can release this gas. Furthermore, mitochondria release energy to break down food to produce water and carbon dioxide. On the contrary, chloroplasts rely on carbon dioxide and water for glucose production.
Do fungi have chloroplasts?
Fungal cells are different from plant cells, as they have no chlorophyll and chloroplasts. Some fungi have bright shades ranging from red and black to green. Other cellular pigments result in these colors. The red cap and white patches indicate the poisonous fly agaric. Fungi’s pigments are related to cell walls, and they ensure protection against UV radiation.
Fungal cell walls have polysaccharides known as glucans and chitin. However, insects' exoskeletons also have chitin to provide strength to their cell walls. Predators cannot attack the cells due to the walls. Plasma membranes in fungi are like ones found in eukaryotes.
Fungi do not have chloroplasts, and that’s why they cannot be considered autotrophs. They rely on energy present in organic compounds. For this reason, fungi differ from plants. However, being osmotrophic, fungi are not animals. They derive food due to nutrient absorption from the environment.
Chloroplasts and other plastids
Genome present in plastids and chloroplasts is not different. However, they have variations in function and structure. Chloroplasts are unique, as they have a thylakoid membrane. Other plastids related to plant cell metabolism have two membranes. But, they do not have thylakoid coverings and other photosynthetic components.
Plastids are of multiple types based on the type of pigment they have. Due to the presence of chlorophyll, we call them chloroplast. Chromoplasts do not have a trace of chlorophyll, though it has carotenoids.
That is why they look red, yellow, and orange. Some fruits and flowers have these pigments. Nevertheless, their major role in the cell metabolism process is not clear. Another non-pigmented plastid is the leucoplast intended for storing energy in non-photosynthetic tissues. Some common leucoplasts are elaiplasts and amyloplasts for storing lipids and starch.
Conclusion
From the detailed discussion, you have learned about the parts of chloroplast and the chloroplast function in plant cells. Chloroplast under a microscope can show you the parts present in it.