Animal cells are eukaryotic cells that make up the tissues and organs of 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 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.
Key Takeaways: Animal Cell
- Animal cells are eukaryotic cells, meaning they contain a nucleus and membrane-bound organelles.
- Major animal cell structures include the cell membrane, nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, cytoskeleton, and centrosome.
- Animal cells do not have a cell wall or chloroplasts, which helps distinguish them from plant cells.
- Different animal cells have specialized shapes and structures suited to their functions.
- Most animal cells are microscopic, typically measuring about 10 to 100 µm across.
- You can download labeled and unlabeled animal cell diagrams for studying, teaching, or use as worksheets.
What Is an Animal Cell?
An animal cell is the basic structural and functional unit of an animal. It is a type of eukaryotic cell, so its DNA is primarily enclosed within a nucleus and many cellular processes occur within specialized membrane-bound organelles.
Animal cells share the basic features of other eukaryotic cells, including a plasma membrane, cytoplasm, ribosomes, mitochondria, and a cytoskeleton. However, they lack some structures characteristic of plant cells, particularly a cell wall and chloroplasts.
There is no single shape or size that defines an animal cell. Cells become specialized for different functions, so a neuron looks very different from a muscle cell, red blood cell, or epithelial cell.
Animal Cell Structure: Organelles and Their Functions
Animal cells contain many organelles, which specialized structures that carry out the processes necessary for life. The organelles may be membrane-bound (enclosed within a lipid bilayer) or non-membrane bound (free in the cytoplasm).
Here are the major parts of an animal cell 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 includes the cytosol, organelles, and other structures between the plasma membrane and nucleus. The cytosol is the gel-like fluid portion where many metabolic reactions occur.
- 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: The nucleolus is a dense region within the nucleus where ribosomal RNA (rRNA) is produced and combined with proteins to begin assembling ribosomal subunits.
- Mitochondria: Often referred to as the “powerhouse” of the cell, mitochondria generate energy in the form of adenosine triphosphate (ATP) through cellular respiration. They also participate in calcium signaling, metabolism, and programmed cell death.
- 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. Rough ER is studded with ribosomes and synthesizes many proteins destined for secretion, membranes, or organelles. Smooth ER lacks attached ribosomes and functions in lipid synthesis, calcium storage, carbohydrate metabolism, 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. Their enzymes also produce and break down hydrogen peroxide, helping protect cells from potentially harmful reactive molecules.
- Centrosome: The centrosome is the primary microtubule-organizing center in many animal cells. It usually contains a pair of centrioles surrounded by pericentriolar material. The centrosome helps organize the cytoskeleton and forms the poles of the mitotic spindle during cell division. Most higher plant cells lack centrosomes with centrioles and organize their microtubules differently.
- Vesicles: Vesicles are small membrane-bound sacs that transport and store substances within the cell. They move proteins, lipids, and other materials between organelles and participate in endocytosis and exocytosis.
- Vacuoles: Animal cells may contain small vacuoles that store or transport water, nutrients, wastes, and other substances. Unlike plant cells, animal cells generally do not contain one large central vacuole.
Print an Animal Cell Diagram
Download and print these animal cell diagrams for studying, teaching, quizzes, or classroom activities. Choose a labeled animal cell diagram for reference or an unlabeled diagram for students to identify and label the organelles themselves.
Animal Cell Organelles at a Glance
| Cell Part | Main Function |
|---|---|
| Cell membrane | Controls movement into and out of the cell |
| Cytoplasm | Contains organelles and is the site of many reactions |
| Nucleus | Stores DNA and regulates gene expression |
| Nucleolus | Produces rRNA and assembles ribosomal subunits |
| Mitochondria | Produce ATP through cellular respiration |
| Ribosomes | Synthesize proteins |
| Rough ER | Synthesizes and processes many proteins |
| Smooth ER | Synthesizes lipids and performs other metabolic functions |
| Golgi apparatus | Modifies, sorts, and packages proteins and lipids |
| Lysosomes | Digest and recycle cellular materials |
| Peroxisomes | Carry out oxidative reactions and break down fatty acids |
| Cytoskeleton | Provides structure and enables movement |
| Centrosome | Organizes microtubules and helps form the mitotic spindle |
| Vesicles | Transport materials within or out of the cell |
Types of Animal Cells
Multicellular animals contain many specialized types of cells. During development, cells differentiate and acquire structures that help them perform particular functions. For example, neurons specialize in communication, muscle cells specialize in contraction, and epithelial cells form protective and functional surfaces.
Animal tissues are traditionally grouped into four basic types: muscle, nervous, epithelial, and connective tissue. Each tissue contains characteristic cell types.
- 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 tissues contain diverse cell types that provide structural, metabolic, defensive, and transport functions. Examples include fibroblasts, adipocytes (fat cells), chondrocytes in cartilage, osteocytes in bone, and blood cells such as red blood cells and white blood cells.
Worksheet: Label the Parts of an Animal Cell
[Google Apps worksheet][worksheet PDF][worksheet PNG][answers PNG]
How Animal Cells Get Energy
Animal cells obtain chemical energy from nutrients such as glucose and fatty acids. Through cellular respiration, cells transfer energy stored in these molecules into ATP, a molecule that powers many cellular processes.
Glycolysis begins in the cytosol, while mitochondria carry out later stages of aerobic respiration, including the citric acid cycle and oxidative phosphorylation. Cells then use ATP to power processes such as active transport, movement, biosynthesis, and cell signaling.
Animal Cell vs Plant Cell
Animal and plant cells are both eukaryotic cells and share many structures, including a nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, ribosomes, cytoplasm, and a cell membrane. However, several important structures differ.
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Cell membrane | Yes | Yes |
| Cell wall | No | Yes |
| Nucleus | Yes | Yes |
| Mitochondria | Yes | Yes |
| Chloroplasts | No | Usually present in photosynthetic tissues |
| Vacuoles | Usually small | Typically one large central vacuole in mature cells |
| Centrosome with centrioles | Common | Usually absent in higher plants |
| Typical shape | Variable or flexible | Often more regular because of the cell wall |
The easiest way to distinguish a typical plant cell from an animal cell is to look for a cell wall, chloroplasts, and a large central vacuole. These structures characterize typical plant cells but not animal cells.
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 and plant cells are both eukaryotic, but plant cells have a cell wall and typically contain a large central vacuole. Photosynthetic plant cells also contain chloroplasts. Animal cells lack cell walls and chloroplasts and commonly have centrosomes containing centrioles. Because animal cells lack a rigid cell wall, their shapes are generally more variable than those of plant cells.
Do animal cells have a cell wall?
No. Animal cells have a plasma membrane but do not have the rigid cell wall characteristic of plants, fungi, and many other organisms.
Do animal cells have chloroplasts?
No. Animal cells do not contain chloroplasts and do not perform photosynthesis.
Do animal cells have vacuoles?
Yes. Animal cells can contain small vacuoles and vesicles, but they do not normally have the large central vacuole characteristic of mature plant cells.
Do animal cells have mitochondria?
Most animal cells contain mitochondria, but there are exceptions. For example, mature mammalian red blood cells lose their mitochondria during development.
Which organelle contains DNA?
Most of an animal cell’s DNA is contained in the nucleus. Mitochondria also contain a small amount of their own DNA.
What is the largest organelle in an animal cell?
The nucleus is usually the largest organelle in a typical animal cell, although size and organization vary considerably among cell types.
What shape is an animal cell?
Animal cells do not have one characteristic shape. Depending on their function, they may be round, flattened, elongated, branched, or irregular.
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