Line 1: Mitochondria (sing.: mitochondrion), unless specifically stained, are not easily visible under the microscope.
Explanation: This line introduces mitochondria and highlights that they are challenging to see under a microscope without special staining techniques due to their small size and colorless nature.
Line 2: The number of mitochondria per cell is variable depending on the physiological activity of the cells.
Explanation: This line explains that the number of mitochondria in a cell can vary significantly. Cells with high energy demands (e.g., muscle cells) have more mitochondria compared to less active cells.
Line 3: In terms of shape and size also, considerable degree of variability is observed. Typically it is sausage-shaped or cylindrical having a diameter of 0.2-1.0µm (average 0.5µm) and length 1.0-4.1µm.
Explanation: This line describes the typical shape and size of mitochondria. They can be sausage-shaped or cylindrical, with a diameter ranging from 0.2 to 1.0 micrometers (µm) and a length of 1.0 to 4.1 µm (average diameter: 0.5 µm).
Line 4: Each mitochondrion is a double membrane-bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments, i.e., the outer compartment and the inner compartment.
Explanation: This line describes the basic structure of a mitochondrion: It’s a double membrane-bound organelle. The outer membrane is the outermost boundary. The inner membrane folds inward, creating compartments: Inner compartment (matrix): Filled with a dense substance. Outer compartment (intermembrane space): The space between the two membranes.
Line 5: The inner compartment is filled with a dense homogeneous substance called the matrix.
Explanation: This line focuses on the inner compartment (matrix): It contains a dense and uniform material called the matrix.
Line 6: The outer membrane forms the continuous limiting boundary of the organelle.
Explanation: This line clarifies the role of the outer membrane: It defines the overall shape and external boundary of the mitochondrion.
Line 7: The inner membrane forms a number of infoldings called the cristae (sing.: crista) towards the matrix (Figure 8.7). The cristae increase the surface area.
Explanation: This line describes the inner membrane and its unique feature: It has inward folds called cristae (singular: crista). These folds significantly increase the inner membrane surface area, which is crucial for its function.
Line 8: The two membranes have their own specific enzymes associated with the mitochondrial function.
Explanation: This line highlights the importance of membranes: Both the outer and inner membranes have specific enzymes embedded in them. These enzymes play essential roles in various functions of the mitochondria.
Line 9: Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell.
Explanation: This line explains the primary function of mitochondria: They are the cellular powerhouses responsible for aerobic respiration. Aerobic respiration is a process that uses oxygen to convert glucose (sugar) into cellular energy in the form of ATP (adenosine triphosphate).
Line 10: The matrix also possesses single circular DNA molecule, a few RNA molecules, ribosomes (70S) and the components required for the synthesis of proteins.
Explanation: This line describes the contents of the matrix: It contains a single circular DNA molecule (mitochondrial DNA). It has some RNA molecules needed for protein synthesis. Interestingly, it also has ribosomes (smaller 70S type) and components for protein synthesis. This suggests some level of protein synthesis within the mitochondria.
Line 11: The mitochondria divide by fission.
Explanation: This line mentions the reproduction method for mitochondria: They reproduce by fission, a process where a single mitochondrion divides into two daughter mitochondria. This concludes the breakdown of the passage on mitochondria.
Line 1: Plastids are found in all plant cells and in euglenoids. These are easily observed under the microscope as they are large. They bear some specific pigments, thus imparting specific colours to the plants.
Explanation: This line introduces plastids and highlights their key features: They are present in all plant cells and some protists (euglenoids). Unlike mitochondria, they are large and easily visible under a microscope due to their size and pigments. These pigments contribute to the various colors seen in plants.
Line 2: Based on the type of pigments plastids can be classified into chloroplasts, chromoplasts and leucoplasts.
Explanation: This line introduces the three main types of plastids based on their pigments: Chloroplasts: Contain chlorophyll and carotenoid pigments, essential for photosynthesis. Chromoplasts: Contain fat-soluble carotenoid pigments (like carotene, xanthophylls) responsible for yellow, orange, or red colors in plants. Leucoplasts: Colorless plastids with various shapes and sizes, used for storing nutrients (starch, oils, proteins).
Line 3-4 (Chloroplasts):
Explanation: These lines delve deeper into chloroplasts, the most common type of plastid: They contain chlorophyll and carotenoid pigments, crucial for capturing light energy during photosynthesis. They are typically lens-shaped, oval, spherical, or even ribbon-like, with a variable size (length: 5-10 µm, width: 2-4 µm). Their number can vary significantly, from one per cell in a green alga (Chlamydomonas) to 20-40 per cell in plant leaf mesophyll (tissue containing photosynthetic cells).
Line 5-6 (Chloroplast Structure):
Explanation: These lines describe the structure of chloroplasts: Similar to mitochondria, they are double membrane-bound organelles. The inner membrane is less permeable than the outer membrane. The space enclosed by the inner membrane is called the stroma.
Line 7-8 (Thylakoids):
Explanation: These lines introduce thylakoids, a key component within the chloroplast: The stroma contains numerous flattened membranous sacs called thylakoids. Thylakoids are arranged in stacks like coins (grana) or as intergranal thylakoids (individual thylakoids connecting grana).
Line 9-10 (Thylakoid Lumen):
Explanation: This line describes another important chloroplast structure: The thylakoid membrane encloses a space called the lumen.
Line 11 (Stroma Contents):
Explanation: This line mentions the contents of the stroma: It contains enzymes required for carbohydrate and protein synthesis. It also has small, double-stranded circular DNA molecules and ribosomes (smaller 70S type).
Line 12 (Pigment Location):
Explanation: This line clarifies the location of pigments in chloroplasts: Chlorophyll pigments are specifically located within the thylakoids.
Line 13 (Ribosome Size):
Explanation: This line highlights a difference between chloroplast and cytoplasmic ribosomes: Chloroplast ribosomes are smaller (70S) compared to ribosomes found in the cytoplasm (80S).