CBSE Class 9 Science Chapter 5 - Revision Notes - followrudra

• Cell: The basic structural and functional unit of life, discovered by Robert Hooke in 1665. Cells can be classified into two types: prokaryotic and eukaryotic.
• Prokaryotic cells: Primitive cells that lack a well-defined nucleus and membrane-bound organelles. Examples are bacteria and cyanobacteria.
• Eukaryotic cells: Advanced cells that have a well-defined nucleus and membrane-bound organelles. Examples are plant and animal cells.
• Cell membrane: The outermost covering of the cell that separates the contents of the cell from its external environment. It is selectively permeable and allows the entry and exit of some materials by diffusion and osmosis.
• Cell wall: An additional rigid layer present in plant cells, made up of cellulose. It provides shape and support to the cell.
• Nucleus: The control center of the cell that contains the genetic material (DNA) and regulates the cell’s activities.
• Cytoplasm: The jelly-like substance that fills the cell and contains various organelles such as mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, etc.
• Mitochondria: The powerhouse of the cell that produces energy (ATP) by cellular respiration.
• Chloroplasts: The green organelles present in plant cells that perform photosynthesis and produce food (glucose) and oxygen.
• Endoplasmic reticulum: A network of membranous tubes that transport materials within the cell. It can be smooth (without ribosomes) or rough (with ribosomes).
• Golgi apparatus: A stack of flattened sacs that modify, sort, and package proteins and other substances for secretion or storage.
• Lysosomes: The digestive system of the cell that contain enzymes to break down waste materials and foreign invaders.
• Vacuoles: The storage sacs of the cell that store water, food, waste, or other substances. Plant cells have a large central vacuole, while animal cells have smaller vacuoles.