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Cell Structure and Function
Cells are the smallest living units of an organism. All cells, regardless of type, share
three common components:
A cell membrane that separates the cell's interior from its environment.
Cytoplasm, a jelly-like fluid filling the cell.
DNA, the cell's genetic material.
Cells are broadly categorized into two types: eukaryotic and prokaryotic.
Eukaryotic Cells
Eukaryotic cells are more complex and advanced, found in plants and animals. They
possess:
Organelles: Specialized parts, including the nucleus.
Prokaryotic Cells
Prokaryotic cells are simpler and typically unicellular, like bacteria. They lack:
A nucleus or membrane-enclosed organelles.
Genetic material not contained within a nucleus.
Organelles: The Cell's Miniature Organs
Organelle: Literally meaning "little organ," an organelle is a specialized
part of a cell with a unique job.
Nucleus: The Control Center
Contains DNA or genetic material.
DNA dictates the cell's functions.
Chromatin: Tangled, spread-out form of DNA within the nuclear membrane.
When a cell divides, DNA condenses into chromosomes.
Nucleolus: A structure within the nucleus where ribosomes are made.
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Ribosomes: Protein Synthesizers
Responsible for synthesizing, or making, proteins.
They either wander freely in the cytoplasm or attach to the endoplasmic
reticulum.
Endoplasmic Reticulum (ER): The Transportation Network
A membrane-enclosed passageway for transporting materials, like proteins.
Two types:
Rough ER: Has ribosomes attached.
Smooth ER: Lacks ribosomes.
Golgi Apparatus (Golgi Body): The Customization Center
Receives proteins and other materials from the ER in small vesicles.
Customizes proteins into usable forms by:
Folding them into usable shapes.
Adding lipids or carbohydrates.
Vacuoles: Storage Units
Sac-like structures for storing various materials.
In plant cells, the central vacuole stores water.
Lysosomes: Garbage Collectors
Take in damaged or worn-out cell parts.
Filled with enzymes that break down cellular debris.
Mitochondria: Powerhouses of the Cell
Carry out cellular respiration to produce ATP molecules.
ATP provides energy for all cellular activities.
Cells needing more energy have more mitochondria.
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Cytoskeleton: Maintaining Cell Shape
A network of protein fibers that supports and shapes the cell.
Includes:
Microfilaments: Thread-like structures made of protein.
Microtubules: Thin, hollow tubes.
Chloroplasts: Capturing Sunlight
Found in plant cells and other photoautotrophic organisms.
Site of photosynthesis.
Contain chlorophyll, a green pigment.
Cell Wall: Protection and Support
Found outside the cell membrane in plant cells.
Provides shape, support, and protection.
Animal cells do NOT have a cell wall.
Unique Cellular Structures
Some cells have unique structures for specific functions.
Cilia: Microscopic hair-like projections that move in waves. Found in the human
respiratory tract to trap and expel inhaled particles.
Flagella: Tail-like structures that aid in movement. Found in bacteria and sperm
cells.
Cell Summary
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Eukaryotic Cells (Plant and Prokaryotic Cells (e.g.,
Feature
Animal) Bacteria)
Nucleus Present Absent
Membrane-Enclosed
Present Absent
Organelles
Cell Wall Present in Plant Cells Present in most
Mitochondria Present Absent
Chloroplasts Present in Plant Cells Absent
All cells have a cell membrane, cytoplasm, and genetic material. While only plant
cells have chloroplasts, both plant and animal cells have mitochondria.
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