Cell Structure and Organization
Can you recall? Page No. 44
1. Who observed cells under the microscope for the first time?
Answer: Robert Hooke (1665)
2. Who made the first microscope?
Answer: Leeuwenhoek (late 1600s)
3. How do onion peel cells and our body cells differ?
Answer: Onion peel cells have a cell wall, large central vacuole, and plasmodesmata, but lack centrioles. Human body cells lack a cell wall and central vacuole, but have centrioles (in animal cells).
4. Why bacterial nucleus is said to be primitive?
Answer: Bacterial nucleus (nucleoid) is primitive because it lacks a nuclear membrane and histone proteins, consisting of a single, circular DNA molecule.
Find out Page No. 44
1. How does a combination of lenses help in higher magnification?
Answer: A combination of lenses (e.g., objective and eyepiece) in a compound microscope multiplies their magnifying powers, achieving higher magnification (up to 1000x or more).
2. When do we use plane and concave mirror and diaphragm?
Answer: A plane mirror is used for even light distribution in bright conditions, a concave mirror focuses light in dim conditions, and the diaphragm adjusts light intensity.
3. What is the difference between magnification and resolution?
Answer: Magnification enlarges the image size, while resolution determines the clarity and detail distinguishable in the image.
Find out Page No. 46
Why do basal body of bacterial flagella considered as smallest motor in the world?
Answer: The basal body of bacterial flagella is considered the smallest motor in the world because it functions as a rotary motor, driving the flagellum’s rotation using a proton motive force. Its compact structure, embedded in the cell envelope, enables efficient movement.
Use your brain power Page No. 52
1. Why do we call mitochondria as power house of cell? Explain in detail. Hint: Refer chapter Cellular Respiration.
Answer: Mitochondria are called the powerhouse of the cell because they produce ATP, the cell’s energy currency, through aerobic respiration. The document explains that mitochondria have a double membrane, with the inner membrane forming cristae that house oxysomes (ATP synthase particles). These structures facilitate the Krebs cycle in the matrix and the electron transport chain on the cristae, generating ATP via oxidative phosphorylation, powering cellular activities.
2. Are mitochondria present in all eukaryotic cells?
Answer: No, mitochondria are absent in some eukaryotic cells, such as mature red blood corpuscles (RBCs).
Can you recall? Page No. 54
1. Consider the following cells and comment about the position, shape and number of nuclei in a eukaryotic cell. Add more examples from your previous knowledge about cell and nucleus. – Cuboidal epithelial cell, different types of blood corpuscles, skeletal muscle fibre, adipocyte.
Answer:
- Cuboidal epithelial cell: Single, centrally located, spherical nucleus.
- Blood corpuscles: Mature RBCs lack a nucleus; white blood cells (e.g., lymphocytes) have a single, large, spherical nucleus.
- Skeletal muscle fibre: Multiple, elongated, peripheral nuclei (multinucleated due to syncytium).
- Adipocyte: Single, flattened nucleus pushed to the periphery by fat droplet.
Additional examples:
- Neurons: Single, large, central nucleus.
- Cardiac muscle cells: 1–2 elongated, central nuclei.
- Explanation: The document describes the nucleus in eukaryotic cells (e.g., nuclear envelope, nucleoplasm), and general knowledge aligns with these cell types.
2. Why nucleus is considered as control unit of a cell?
Answer: The nucleus is the control unit because it contains chromosomes (DNA) that store genetic information, regulating protein synthesis, cell division, and heredity. It directs cellular activities via DNA and RNA synthesis.
3. Can cells like Xylem or mature human RBCs be called living?
Answer: Xylem (e.g., tracheids, vessels) and mature human RBCs are not considered fully living because they lack a nucleus and organelles, performing specialized functions (conduction in xylem, oxygen transport in RBCs) without metabolic activity.
4. What is a syncytium and coenocyte?
Answer: A syncytium is a multinucleated cell formed by the fusion of multiple cells (e.g., skeletal muscle fibres). A coenocyte is a multinucleated cell formed by multiple nuclear divisions without cytokinesis (e.g., in some fungi or algae).
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