by Animal cells are eukaryotic cells characterized by the absence of a cell wall and enclosed by a plasma membrane. The plasma membrane surrounds cell organelles, including the nucleus. In contrast, plant cells possess a rigid cell wall.
Animals, constituting a vast and diverse group of organisms, account for three-quarters of all known species. They exhibit mobility, responsiveness to stimuli, adaptability to environmental changes, and diverse modes of feeding, defense, and reproduction. These functions are facilitated by specialized cellular components.
Animals, unlike plants, do not possess the capacity for autotrophic nutrition and rely on plants directly or indirectly for sustenance.
All living organisms, whether unicellular or multicellular, are composed of cells, which serve as the fundamental structural and functional units of life. The cell wall, present in most cells, imparts shape and rigidity.
The absence of a rigid cell wall in animal cells grants them the capacity to differentiate into a wide array of cell types, tissues, and organs. This diversity allows for the development of specialized cells, such as nerve and muscle cells, enabling mobility an attribute not observed in plant cells.
Animal cell Size and Shape
Animal cells vary in size and shape, depending on their specific functions and locations within the organism.
Size:
- Microscopic:
Most animal cells are too small to be seen with the naked eye. They typically range from about 10 to 30 micrometers in diameter.
- Variability:
The size of animal cells can vary widely. For example, red blood cells are about 7-8 micrometers in diameter, while some nerve cells can be as long as several centimeters.
Shape:
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Spherical (Round):
Some animal cells, like red blood cells, are spherical in shape. This allows for flexibility and efficient transport through narrow blood vessels.
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Irregular:
Many animal cells have irregular shapes. For instance, cells in connective tissues can have elongated, irregular forms to provide structural support.
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Flattened:
Cells in epithelial tissues are often flattened, which helps them form protective layers in organs like the skin.
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Long and Branched:
Nerve cells, or neurons, can have long, branching structures called dendrites and axons that facilitate communication within the nervous system.
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Cuboidal or Columnar:
Cells in glandular tissues and the lining of organs like the intestines can be cuboidal (cube-shaped) or columnar (tall and narrow) to aid in secretion and absorption.
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Stellate or Star–shaped:
Some specialized cells, like certain immune cells called microglia, have a stellate or star-shaped morphology.
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Fibrous:
Cells in muscle tissues are elongated and have a fibrous appearance to allow for contraction.
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Amoeboid:
Some cells, like white blood cells known as macrophages, have an amoeboid shape, allowing them to change their form for tasks like phagocytosis (engulfing foreign particles).
List of 16 Animal cell organelles
- Nucleus:
Contains genetic material (DNA) and controls cellular activities.
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Nucleolus:
Produces ribosomes within the nucleus.
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Cytoplasm:
Gel-like substance that surrounds organelles and houses various cellular activities.
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Endoplasmic Reticulum (ER):
- Rough ER: Involved in protein synthesis and processing.
- Smooth ER: Synthesizes lipids and detoxifies harmful substances.
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Golgi Apparatus:
Modifies, sorts, and packages proteins and lipids for transport.
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Mitochondria:
Produces energy (ATP) through cellular respiration.
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Ribosomes:
Sites of protein synthesis in the cell.
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Lysosomes:
Contain enzymes for intracellular digestion and waste removal.
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Peroxisomes:
Involved in detoxification and breakdown of fatty acids.
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Centrosome (Centrioles):
Involved in cell division and formation of microtubules.
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Microfilaments and Microtubules:
Provide structural support and play a role in cell movement.
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Cytoskeleton:
Network of protein filaments that maintain cell shape and allow for cellular movement.
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Plasma Membrane:
Forms the outer boundary of the cell and regulates the passage of substances in and out of the cell.
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Vesicles and Vacuoles:
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Vesicles: Small membrane-bound sacs involved in transport and storage.
- Vacuoles: Larger sacs that store nutrients and waste products in plant cells.
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Endosomes:
Membrane-bound compartments involved in sorting and transporting materials within the cell.
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Flagella and Cilia:
Appendages used for cellular movement or the movement of materials over the cell surface.
Animal Cell Structure
The structure of an animal cell is a complex and organized arrangement of various organelles and cellular components. Structures found in an animal cell:
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Plasma Membrane:
- Outer boundary of the cell.
- Composed of a phospholipid bilayer with embedded proteins.
- Regulates the entry and exit of substances into and out of the cell.
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Cytoplasm:
- Gel-like substance filling the cell interior.
- Contains various organelles and cellular structures.
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Nucleus:
- Central organelle containing genetic material (DNA).
- Surrounded by a double membrane called the nuclear envelope.
- Regulates cellular activities and contains the nucleolus, which produces ribosomes.
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Nucleolus:
- Found within the nucleus.
- Produces ribosomal RNA (rRNA) and assembles ribosomal subunits.
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Endoplasmic Reticulum (ER):
- Network of membrane-bound tubules and sacs.
- Rough ER: Studded with ribosomes, involved in protein synthesis and processing.
- Smooth ER: Synthesizes lipids and detoxifies substances.
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Golgi Apparatus:
- Stack of flattened membrane sacs (cisternae).
- Modifies, sorts, and packages proteins and lipids for transport.
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Mitochondria:
- Double-membraned organelles.
- Site of cellular respiration, producing ATP (energy) through metabolic processes.
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Ribosomes:
- Small, spherical organelles or free-floating in the cytoplasm.
- Sites of protein synthesis.
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Lysosomes:
- Membrane-bound sacs containing digestive enzymes.
- Involved in intracellular digestion and waste removal.
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Peroxisomes:
- Membrane-bound organelles containing enzymes.
- Involved in detoxification and breakdown of fatty acids.
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Centrosome (Centrioles):
- Region near the nucleus.
- Contains a pair of centrioles involved in cell division and organization of microtubules.
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Microfilaments and Microtubules:
- Protein filaments and tubules in the cytoplasm.
- Provide structural support and facilitate cellular movement.
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Cytoskeleton:
- Network of protein filaments (microfilaments, intermediate filaments, microtubules).
- Maintains cell shape, provides structural support, and allows for cellular movement.
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Vesicles and Vacuoles:
Membrane-bound sacs for transport and storage of materials.
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Endosomes:
Membrane-bound compartments involved in sorting and transporting materials within the cell.
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Flagella and Cilia:
- Hair-like projections extending from the cell surface.
- Involved in cellular movement or the movement of materials over the cell surface.
Animal Cell Organelles
Animal cells contain various specialized structures called organelles, each with specific functions. Major organelles found in animal cells:
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Nucleus:
- Contains genetic material (DNA) and controls cellular activities.
- Surrounded by a double membrane called the nuclear envelope.
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Nucleolus:
- Found within the nucleus.
- Produces ribosomal RNA (rRNA) and assembles ribosomal subunits.
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Cytoplasm:
- Gel-like substance filling the cell interior.
- Contains various organelles and cellular structures.
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Endoplasmic Reticulum (ER):
- Network of membrane-bound tubules and sacs.
- Rough ER: Studded with ribosomes, involved in protein synthesis and processing.
- Smooth ER: Synthesizes lipids and detoxifies substances.
-
Golgi Apparatus:
- Stack of flattened membrane sacs (cisternae).
- Modifies, sorts, and packages proteins and lipids for transport.
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Mitochondria:
- Double-membraned organelles.
- Site of cellular respiration, producing ATP (energy) through metabolic processes.
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Ribosomes:
- Small, spherical organelles or free-floating in the cytoplasm.
- Sites of protein synthesis.
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Lysosomes:
- Membrane-bound sacs containing digestive enzymes.
- Involved in intracellular digestion and waste removal.
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Peroxisomes:
- Membrane-bound organelles containing enzymes.
- Involved in detoxification and breakdown of fatty acids.
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Centrosome (Centrioles):
- Region near the nucleus.
- Contains a pair of centrioles involved in cell division and organization of microtubules.
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Microfilaments and Microtubules:
- Protein filaments and tubules in the cytoplasm.
- Provide structural support and facilitate cellular movement.
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Cytoskeleton:
- Network of protein filaments (microfilaments, intermediate filaments, microtubules).
- Maintains cell shape, provides structural support, and allows for cellular movement.
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Plasma Membrane:
- Outer boundary of the cell.
- Composed of a phospholipid bilayer with embedded proteins.
- Regulates the entry and exit of substances into and out of the cell.
-
Vesicles and Vacuoles:
- Membrane-bound sacs for transport and storage of materials.
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Endosomes:
- Membrane-bound compartments involved in sorting and transporting materials within the cell.
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Flagella and Cilia:
- Hair-like projections extending from the cell surface.
- Involved in cellular movement or the movement of materials over the cell surface.
Plasma Membrane (Cell membrane)
The plasma membrane, also known as the cell membrane, is a crucial structure that surrounds the outer boundary of both animal and plant cells. It plays a vital role in cellular physiology and is essential for the overall functioning of a cell. Characteristics and functions of the plasma membrane:
Structure:
- Composition:
The plasma membrane is primarily composed of a phospholipid bilayer. Phospholipids are molecules with a hydrophilic (water-attracting) “head” and hydrophobic (water-repelling) “tails.”
- Proteins:
Embedded within the phospholipid bilayer are various proteins, which may be integral (spanning the membrane) or peripheral (associated with the membrane’s surface). These proteins have diverse functions, including transport, signaling, and structural support.
Functions:
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Cellular Barrier:
The plasma membrane acts as a selective barrier that separates the internal environment of the cell from the external surroundings. It controls the entry and exit of substances into and out of the cell.
- Transport of Molecules:
The membrane is selectively permeable, allowing certain molecules, such as small ions and non-polar molecules, to pass through via processes like diffusion, facilitated diffusion, and active transport.
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Cell Recognition:
Glycoproteins and glycolipids on the surface of the membrane are involved in cell recognition, immune responses, and cell signaling. They help cells identify and communicate with each other.
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Receptor Sites:
Integral membrane proteins can serve as receptors for signaling molecules like hormones, allowing cells to respond to external signals.
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Cell Adhesion:
Proteins in the membrane are responsible for cell-to-cell adhesion and attachment to the extracellular matrix, contributing to tissue structure and stability.
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Endocytosis and Exocytosis:
The plasma membrane facilitates processes like endocytosis (internalization of materials) and exocytosis (release of substances), crucial for nutrient uptake and waste removal.
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Maintaining Cell Shape:
The plasma membrane, along with the underlying cytoskeleton, helps maintain the cell’s shape and integrity.
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Communication and Signaling:
Proteins in the membrane allow for cell-cell communication and signaling, enabling coordinated responses to changes in the environment.
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Electrical Potential:
The plasma membrane maintains an electrical potential across its surface, which is essential for processes like nerve impulses and muscle contractions.
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Protection and Defense:
The plasma membrane acts as a protective barrier, shielding the cell’s internal contents from potentially harmful external substances.
Animal Cell Functions
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Energy Production:
Animal cells generate energy through cellular respiration, which takes place in the mitochondria. This process produces adenosine triphosphate (ATP), the cell’s primary energy currency.
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Metabolism:
Animal cells carry out various metabolic processes, including the breakdown of nutrients to generate energy, the synthesis of molecules needed for cellular activities, and the removal of waste products.
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Cellular Respiration:
Animal cells use oxygen to convert glucose into ATP through a series of biochemical reactions. This process occurs in the mitochondria.
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Protein Synthesis:
Ribosomes in animal cells are responsible for the synthesis of proteins, which are crucial for various cellular functions, including enzyme activity, structural support, and signaling.
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Cellular Communication:
Animal cells communicate with each other through cell signaling pathways. This allows for coordination of activities and responses to external stimuli.
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Cell Division:
Animal cells undergo cell division to grow, repair damaged tissues, and replace old or dying cells. This process is crucial for growth and development.
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Transport of Molecules:
The plasma membrane regulates the entry and exit of molecules into and out of the cell. Various transport mechanisms, such as diffusion, facilitated diffusion, and active transport, are involved.
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Response to Stimuli:
Animal cells are capable of responding to changes in their environment. For example, nerve cells can transmit electrical signals in response to stimuli.
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Endocytosis and Exocytosis:
Animal cells use processes like endocytosis to take in materials from the external environment and exocytosis to release substances from the cell.
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Immune Response:
Specialized cells of the immune system, which are derived from animal cells, play a crucial role in defending the body against pathogens and foreign substances.
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Maintenance of Homeostasis:
Animal cells work together to maintain stable internal conditions, allowing the organism to function optimally, regardless of external fluctuations.
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Cell Adhesion and Tissue Formation:
Animal cells adhere to each other, forming tissues and organs. This structural organization is crucial for maintaining the integrity and functionality of tissues.
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Reproduction:
Animal cells are involved in the reproductive processes of the organism, including gamete formation, fertilization, and embryonic development.
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Excretion:
Animal cells eliminate waste products through various cellular processes, including the action of lysosomes and excretion of metabolic byproducts.
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Specialized Functions:
Differentiated animal cells in specific tissues and organs perform specialized functions. For example, nerve cells transmit electrical impulses, muscle cells contract, and blood cells transport oxygen.
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