. Nucleus and Nucleolus:

• Nucleus: The membranous control center of the cell, housing the genetic material (DNA) organized into chromosomes. It regulates cell activities and protein synthesis.
• Nucleolus: A dense region within the nucleus where ribosome subunits are assembled.

8. Endoplasmic Reticulum (ER):

• Smooth ER: A network of tubules lacking ribosomes, involved in lipid synthesis, detoxification, and calcium storage.
• Rough ER: A network of tubules studded with ribosomes, responsible for protein synthesis and modification.

9. Golgi Apparatus:

• A series of flattened sacs that processes, packages, and distributes proteins and other molecules for secretion or transport within the cell.

10. Metabolic Organelles:

• Lysosomes: Membrane-bound sacs containing digestive enzymes that break down cellular waste, foreign materials, and old organelles. (Not found in plant cells)
• Peroxisomes: Membrane-bound sacs containing enzymes that break down toxic molecules like hydrogen peroxide and participate in lipid metabolism.
• Vacuoles: Large, membrane-bound sacs with diverse functions depending on the cell type. In plant cells, they store water, nutrients, and waste products.

11. Chloroplast:

• A double-membraned organelle found in plant cells, containing chlorophyll pigments. It captures sunlight energy and converts it into chemical energy (ATP) through photosynthesis.
• Thylakoid: Flattened membrane sacs within the chloroplast where light-dependent reactions of photosynthesis occur.

12. Mitochondrion:

• A double-membraned organelle, often called the “powerhouse” of the cell. It breaks down glucose molecules through cellular respiration to produce ATP, the cell’s energy currency.
• Cristae: Folds in the inner membrane of the mitochondrion that increase surface area for ATP production.

13. Central Vacuole:

• A large, fluid-filled sac that occupies most of the space in a plant cell. It maintains turgor pressure, stores nutrients and waste products, and helps with detoxification.

14. Cytoskeleton:

• A network of protein fibers that provides structural support, shape, and movement to the cell. It consists of:
  • Microtubules: Hollow tubes that form the mitotic spindle during cell division and provide tracks for organelle movement.
  • Microfilaments: Thin, solid fibers involved in cell movement, shape changes, and organelle anchoring.
  • Intermediate filaments: Provide structural support and maintain cell shape.

15. Cilia vs. Flagella:

• Both are hair-like structures projecting from the cell surface, but flagella are longer and responsible for cell locomotion (e.g., sperm), while cilia are shorter and function in movement or sensory perception (e.g., lining of respiratory tract).

16. Endosymbiotic Theory:

This theory proposes that mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by larger host cells and formed a symbiotic relationship. Over time, they evolved into specialized organelles within the eukaryotic cell, contributing to its energy production and photosynthesis capabilities.

17. Evidence for Endosymbiotic Theory:

• Mitochondria and chloroplasts have their own DNA and ribosomes, similar to bacteria.
• They divide by binary fission, like bacteria.
• They have double membranes, suggesting an engulfed prokaryotic origin.

18. Chloroplast and Photosynthesis:

• Chloroplasts give plant cells their green color due to chlorophyll pigments.
• Photosynthesis occurs inside the chloroplast, converting light energy into chemical energy (ATP) and sugar molecules.

19. Plant Cell vs. Bacterial Cell:

• Plant cells are more closely related to animal cells than bacterial cells. They share similar features like a nucleus, membrane-bound organelles, and endomembrane system, suggesting a common eukaryotic ancestor.

20. Lysosomes and Plant Cell Nutrition:

• Lysosomes are not found in plant cells because they acquire nutrients through photosynthesis instead of engulfing food particles. Plants use chloroplasts for energy production and absorb nutrients from the soil and air.