Table: Comparison of Mitochondria and Chloroplasts in Cells
A eukaryotic cell has only three organelles that have a double-layered structure, namely, nucleus, mitochondria, and chloroplast., Here, we will discuss the two organelles of eukaryotic cells , mitochondria and chloroplasts, and their differences. Mitochondria and chloroplast are semiautonomous organelles that share various structural similarities but the major difference is their occurrence. Mitochondria are found in eukaryotic animal cells, whereas chloroplasts are found in plant cells.
Mitochondria
Mitochondria are membrane-bound organelles found in almost all eukaryotic organisms. Their primary function is to generate energy in the form of adenosine triphosphate (ATP). It is commonly called a powerhouse of the cell. Additionally, they are able to generate heat, store calcium for cell signalling activities, cellular differentiation, mediate the cell cycle, and promote cell growth. Each human cell contains on average 100-1000 mitochondria.
Almost all the genetic material is stored in every cell’s nucleus. Mitochondria have their own DNA and ribosomes. In most organisms, the Mitochondrial DNA is inherited maternally. The number of mitochondria varies in different organisms, tissues, and cell types. Usually, there are multiple mitochondria found in one cell depending on its function.
Structure of Mitochondria
Mitochondria have a double-layered membrane. They are rod-shaped or sausage-shaped organelles measuring 0.5-10μm in length. In a typical cell, they occupy almost 25% of the cell volume. Earlier mitochondria were represented as individual isolated organelles, now they form a dynamic connected network also called a reticulum. It has four main compartments mentioned below.
Outer Membrane- It is permeable to certain ions and small molecules.
Intermembrane Space- It has a composition similar to the cytosol.
Inner Membrane- In this, respiratory chain proteins are found and are folded into multiple cristae allowing larger space to hold proteins involved in electron transport chains.
Both outer and inner membranes are made up of phospholipid layers just like the cell’s outer membrane.
Matrix - It is the inner part of the mitochondria, where the metabolic reactions take place.
The mitochondrial DNA resides in its matrix. Also, it is small and circular.
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Functions of Mitochondria
Mitochondria are essential for aerobic metabolism. They are responsible for energy production through oxidative phosphorylation. Almost 90% of the cell’s energy is produced by them. They convert nutrients into Adenosine TriPhosphate (ATP) in the presence of oxygen (aerobic respiration). They maintain, replicate, and transcribe their own DNA. They are also involved in the synthesis of iron-sulfur clusters.
Chloroplasts
Chloroplast is an organelle found in plants and green algae. It is a type of plastid that contains chlorophyll to absorb solar energy. It is green in colour due to the presence of two pigments -chlorophyll a and chlorophyll b. The chloroplast is a double-layered cell organelle. It is a semi-autonomous organelle that has its own DNA. It also contains thylakoids. The number of chloroplasts varies in different cells. Plants growing in shade contain larger chloroplasts in their cells than those which grow in intense light.
Structure of Chloroplasts
Chloroplasts differ in shape being plate-shaped in Chlorella, cup-shaped in Chlamydomonas, and in higher plants, they are spherical or ovoid. They measure 4-6μm in size. The chloroplasts have the following parts:
Outer Membrane - It is a semi-porous membrane, permeable to small molecules and ions. It is not permeable to large proteins.
Intermembrane space
Inner Membrane - It regulates the passage of materials in and out of the chloroplast.
Stroma - It is an aqueous, alkaline fluid that is protein-rich and is present within the inner membrane. The chloroplast DNA, chloroplast ribosomes, starch ribosomes, thylakoid system, and many proteins are found floating in the stroma.
Thylakoid - The thylakoid system is suspended in the stroma and is a collection of membranous sacs called thylakoids. The chlorophyll is stored in thylakoids and is the site for the process of light reactions to take place in photosynthesis. The thylakoids are arranged in stacks known as Grana. Each Grana contains 10-20 thylakoids.
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Functions of Chloroplast
Chloroplasts are the sites for photosynthesis where reactions take place to harness solar energy and convert it into chemical energy. They also carry out functions like the synthesis of fatty acids, amino acids, and membrane lipids. Plants do not have specialized immune cells, all cells participate in plant response.
Mentioned below is the table that enlists the difference between mitochondria and chloroplast based on different parameters.
Difference Between Mitochondria and Chloroplasts
Here, we learned about mitochondria, their structure, and their function. We have also learned about chloroplast structure and function. The difference between these semi-autonomous organelles is also covered in the article.
FAQs on Mitochondria vs Chloroplasts: Differences, Structure & Function
1. What are the main differences between mitochondria and chloroplasts?
The main differences between mitochondria and chloroplasts lie in their function, structure, and presence in cell types.
- Function: Mitochondria perform cellular respiration to produce ATP, breaking down glucose. Chloroplasts perform photosynthesis to create glucose using light energy.
- Occurrence: Mitochondria are found in almost all eukaryotic cells (both plant and animal), while chloroplasts are found only in plant cells and some protists.
- Pigments: Chloroplasts contain chlorophyll and other photosynthetic pigments, giving them a green colour. Mitochondria lack these pigments.
- Energy Source: Mitochondria use chemical energy from organic molecules. Chloroplasts use light energy from the sun.
2. What are the key structural and functional similarities between mitochondria and chloroplasts?
Despite their different roles, mitochondria and chloroplasts share several important similarities, which supports the endosymbiotic theory. Both organelles:
- Are enclosed by a double membrane (an inner and an outer membrane).
- Contain their own circular DNA and 70S ribosomes, allowing them to synthesise some of their own proteins.
- Are involved in energy conversion for the cell.
- Can replicate independently within the cell through a process similar to binary fission.
3. What is the primary function and structure of a mitochondrion?
The mitochondrion is known as the 'powerhouse of the cell'. Its primary function is to carry out cellular respiration, a process that converts the chemical energy in nutrients (like glucose) into adenosine triphosphate (ATP), the main energy currency of the cell. Structurally, it has two membranes. The inner membrane is highly folded into structures called cristae, which increase the surface area for ATP synthesis. The fluid-filled space inside is called the matrix.
4. What is the primary function and structure of a chloroplast?
The primary function of a chloroplast is to conduct photosynthesis. It captures solar energy and converts it into chemical energy in the form of glucose. Structurally, a chloroplast has a double membrane surrounding a fluid-filled space called the stroma. Within the stroma are stacks of flattened sacs called thylakoids; a stack is known as a granum. The thylakoid membranes contain chlorophyll, the pigment that absorbs light energy.
5. How do mitochondria and chloroplasts work together in a plant cell?
In a plant cell, mitochondria and chloroplasts have a complementary relationship essential for life. Chloroplasts act as the 'producers', using sunlight to create glucose and oxygen through photosynthesis. This glucose is then used by the mitochondria, the 'consumers', as fuel for cellular respiration. The mitochondria break down the glucose to produce large amounts of ATP, which powers all other cellular activities. The carbon dioxide released by mitochondria is then used by chloroplasts for photosynthesis, creating a sustainable cycle.
6. Why are mitochondria and chloroplasts called 'semi-autonomous' organelles?
Mitochondria and chloroplasts are called semi-autonomous because they possess their own genetic system and can replicate independently of the cell's nucleus. They contain their own circular DNA and ribosomes (70S type), similar to those found in prokaryotic cells. This allows them to synthesise some of the proteins required for their functions. However, they are only 'semi' autonomous because they still depend on proteins encoded by the cell's nuclear DNA for their complete structure and function.
7. What is the importance of the highly folded inner membrane in mitochondria (cristae) and the stacked thylakoids in chloroplasts (grana)?
The intricate internal structures of both organelles are a perfect example of structure enhancing function.
- In mitochondria, the folded cristae dramatically increase the surface area of the inner membrane. This provides more space for the protein complexes involved in the electron transport chain, maximising ATP production during cellular respiration.
- In chloroplasts, the stacking of thylakoids into grana creates a large surface area for chlorophyll molecules to capture as much sunlight as possible. This arrangement concentrates the machinery for the light-dependent reactions of photosynthesis, making energy conversion highly efficient.
8. Could an animal cell survive if it were to contain chloroplasts?
Hypothetically, it is highly unlikely an animal cell could survive and thrive with chloroplasts. While it might produce some glucose, several fundamental problems would arise. Animal cells lack a cell wall for structural support against osmotic changes from photosynthesis. More importantly, animals are mobile and have opaque tissues (like skin), which would prevent most cells from receiving the consistent, direct sunlight needed for efficient photosynthesis. The organism's overall anatomy and metabolism are not adapted to a photosynthetic lifestyle.
