Animal cells are the fundamental units of life in protozoa and multicellular animals. Each cell is a wonder in its own right, plus they work together as building blocks for tissues, organs, and organ systems. Animal cells are mostly microscopic, ranging in size from 1 to 100 micrometers. However, some of the largest cells in nature are eggs, which are still single animal cells.
Animal cells are eukaryotic cells, meaning they possess a nucleus and other membrane-bound organelles. Unlike plant cells, animal cells do not have cell walls, allowing for more flexibility in shape and movement. A plasma membrane encloses the cell contents of both plant and animal cells, but it is the outer coating of an animal cell.
Animal Cell Structure: Organelles and Their Functions
Animal cells contain many organelles, which are subunits within the cell that perform specialized functions. The organelles may be membrane-bound (enclosed within a lipid bilayer) or non-membrane bound (free in the cytoplasm). Here is a list of animal cell components and organelles and their functions:
- Cell Membrane: The cell membrane or plasma membrane is a selectively permeable lipid bilayer that encloses the contents of the cell and regulates the transport of materials into and out of it.
- Cytoplasm: The cytoplasm is the jelly-like fluid that gives a cell is shape and contains the molecules the cell needs for its processes.
- Cytoskeleton: The cytoskeleton is a network of protein fibers that provides structural support, maintains cell shape, and enables cell movement. It is composed of three main types of protein filaments: microfilaments, intermediate filaments, and microtubules.
- Nucleus: The nucleus is the control center of the cell, containing DNA and regulating gene expression. It is surrounded by a double-layered nuclear envelope or nuclear membrane that has nuclear pores that allow the exchange of materials between the nucleus and the cytoplasm.
- Nucleolus: Located within the nucleus, the nucleolus is the site of pre-ribosome production.
- Mitochondria: Often referred to as the “powerhouse” of the cell, mitochondria are responsible for generating energy in the form of adenosine triphosphate (ATP) through cellular respiration.
- Endoplasmic Reticulum (ER): The ER is a network of membrane-bound tubes and sacs involved in the synthesis, folding, and transport of proteins and lipids. There are two types of ER: the rough ER, which is studded with ribosomes and involved in protein synthesis, and the smooth ER, which is responsible for lipid synthesis and detoxification.
- Ribosomes: These small structures, composed of RNA and proteins, are the sites of protein synthesis within the cell. They can be found either free-floating in the cytoplasm or attached to the rough ER.
- Golgi Apparatus: The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids for transport to their final destinations within or outside the cell.
- Lysosomes: Lysosomes are membrane-bound organelles containing enzymes that break down waste materials and cellular debris, playing a crucial role in the recycling of cellular components.
- Peroxisomes: These small organelles contain enzymes that neutralize toxic substances and break down fatty acids, contributing to cellular detoxification and energy production.
- Centrosome: The centrosome is an organelle found in animal cells, but not plant cells. It is a small organelle near the nucleus with radiating tubules. The centrosome produces and organizes microtubules and regulates cell division so that the cell contents equally divide between daughter cells.
Types of Animal Cells
Some animal cells are organisms in their own right. For example, an amoeba and a paramecium are animal cells that are also protozoan animals. But, more complex animals consist of many cells that differentiate to serve different purposes. Here are the four types of animal cells:
- Muscle Cells: Muscle cells, or myocytes, are specialized for contraction, allowing for movement and the maintenance of posture. They contain actin and myosin filaments that slide past each other to generate force. Types of muscle cells are cardiac, skeletal, and smooth muscle.
- Nerve Cells: Also known as neurons, these cells transmit electrical impulses throughout the body, facilitating communication between different parts of the organism. Neurons possess specialized structures such as dendrites, axons, and synapses, which are involved in receiving, transmitting, and processing information.
- Epithelial Cells: These cells form continuous layers called epithelia that cover the body’s surfaces, line cavities, and form glands. They function in protection, secretion, absorption, and transportation of substances. Epithelial cells are squamous, cuboidal, or columnar in shape and form either single or multiple layers. Some epithelial cells have cilia. Some secrete products, such as mucus, hormones, or enzymes.
- Connective Tissue Cells: Connective tissue cells provide structural and metabolic support to other tissues in the body. They include fibroblasts, adipocytes (fat cells), chondrocytes, and osteocytes (bone cells), and blood.
Worksheet: Label the Parts of an Animal Cell
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Common Questions About Animal Cells
Do animal cells have a cell wall?
No.
Which organelle contains the genetic material of the cell?
The nucleus contains the genetic material, which is DNA in the form of chromatin.
Which organelle generates energy for the cell?
The mitochondria provide chemical energy for cells.
How is an animal cell different from a plant cell?
Animal cells tend to be round or irregular in shape because they lack a rigid support, while plant cells have a fixed, often rectangular shape because of their cell walls. Plants cells also contain chloroplasts and a central vacuole, which are not features of animal cells. Animal cells have centrosomes, while plants do not.
References
- Alberts, B.; Johnson, A.; et al. (2015). Molecular Biology of the Cell (6th ed.). Garland Science. ISBN 978-0815344322.
- Campbell, N.A.; Williamson, B,; Heyden, R.J. (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 978-0132508827.
- Lodish, H.; Berk, A.; et al. (2004). Molecular Cell Biology (5th ed.). New York: WH Freeman. ISBN 978-0716743668.
- Raven, P.H.; Johnson, G.B. (2002). Biology. McGraw-Hill Education. ISBN 978-0071122610.
- Wallin, Ivan E. (1923). “The Mitochondria Problem”. The American Naturalist. 57 (650): 255–61. doi:10.1086/279919