What Is an Animal Cell?
Your body contains roughly 37 trillion cells. Every muscle you move, every thought you think, and every beat of your heart depends on animal cells working together. Like all living cells, animal cells are surrounded by a cell membrane and filled with cytoplasm, but they have their own unique set of features.
Animal cells are eukaryotic — they have a true nucleus enclosed by a membrane. This is what separates them from bacteria, which have no nucleus at all.
Main Parts of an Animal Cell
Cell membrane — The outer boundary of the cell. It is made of a double layer of fat molecules (a lipid bilayer) with proteins embedded in it. The membrane is selectively permeable — it allows some substances in and keeps others out.
Nucleus — The largest organelle in most animal cells. It contains the cell's DNA packaged into structures called chromosomes. The nucleus directs cell activities and controls reproduction.
Cytoplasm — The watery, gel-like fluid inside the cell membrane. It suspends all the organelles and is the site of many chemical reactions.
Mitochondria — Often called the "powerhouses" of the cell. Mitochondria break down glucose and oxygen to release energy in a process called cellular respiration. Cells with high energy needs (like muscle cells) have more mitochondria.
Ribosomes — Tiny structures that build proteins from amino acids following instructions from the nucleus.
Endoplasmic reticulum (ER) — A network of folded membranes. Rough ER has ribosomes on its surface and processes proteins. Smooth ER processes fats and detoxifies chemicals.
Golgi apparatus — Acts like the cell's post office: it packages proteins and sends them to the right destinations inside or outside the cell.
Lysosomes — Small sacs containing digestive enzymes that break down old or damaged cell parts and foreign material.
Animal cells do not have a cell wall, which is why they come in many irregular shapes. Red blood cells are disc-shaped, nerve cells have long branching extensions, and muscle cells are long and thin.
What Animal Cells Lack Compared to Plant Cells
Animal cells do not have a cell wall, chloroplasts, or a large central vacuole. Because there is no rigid wall, animal cells are flexible — important for cells like red blood cells that must squeeze through tiny blood vessels.
Without chloroplasts, animal cells cannot make their own food. Animals must eat other organisms to obtain energy.
A common mistake: students often say animal cells have "no vacuole." Animal cells do have small vacuoles, but they are tiny compared to the large central vacuole in plant cells.
Specialised Animal Cells
Different jobs require different cell shapes. Nerve cells are very long so they can carry messages across the body. Red blood cells are packed with a protein called haemoglobin to carry oxygen. Sperm cells have a tail (flagellum) for swimming. In each case, the cell's shape matches its function.
Real world: Cancer and uncontrolled cell division
Cancer occurs when animal cells malfunction and divide uncontrollably, forming tumours. Because animal cells lack a rigid cell wall, cancer cells can change shape and invade surrounding tissue more easily. Understanding animal cell structure — especially the nucleus, which controls cell division — is fundamental to cancer research and treatment.
Real world: Blood cells and oxygen delivery
Red blood cells are highly specialised animal cells — they have no nucleus (to make more room for haemoglobin) and are disc-shaped to maximise surface area for oxygen absorption. Doctors look at blood cells under a microscope to diagnose conditions like anaemia, where there are too few healthy red blood cells.
Real world: Microscopy in science class
Using a light microscope to look at cheek cells (animal cells scraped gently from the inside of your mouth) is a classic school experiment. You can see the cell membrane, nucleus, and cytoplasm — the three features common to all animal cells.
Where do you see this in real life? Every time you eat, drink, or breathe, trillions of your animal cells are taking in nutrients, producing energy, and carrying out their specialised functions. A blood test at the doctor's provides information about millions of your cells — their size, shape, and number all tell the doctor about your health.
Practice Problems
What is the function of mitochondria in an animal cell?
Show answer
Why are animal cells more flexible in shape than plant cells?