Comparing Plant and Animal Cells

Plant and animal cells are both eukaryotic cells with a nucleus, mitochondria and a cell membrane, but plant cells also have a cell wall, chloroplasts and a large central vacuole. In brief: plant cells are usually fixed in shape and rectangular, and they can make food by photosynthesis, while animal cells are more flexible, often rounder, and must obtain food from outside. A leaf cell has chloroplasts, but a human skin cell does not.

Comparing the two types is one of the standard tasks in introductory biology. This guide lists the structures that the cells share and those that differ, compares them in a table, describes how to prepare and view cells under a microscope, works through a drawing-and-identification example and corrects the mistakes that are made most often.

What are the features of an animal cell?

An animal cell is surrounded only by a flexible cell membrane. It has a central nucleus, and the cytoplasm contains mitochondria, ribosomes, endoplasmic reticulum, a Golgi apparatus and lysosomes. Animal cells also have centrioles, which help to organize the spindle during cell division. Higher plants usually lack centrioles.

Because there is no wall, animal cells can change shape, which allows them to move, engulf particles and form tissues of many types. They store energy as glycogen and have many small vacuoles, if any.

What are the features of a plant cell?

A plant cell has all of the basic structures of the eukaryotic cell, and some additional ones.

• Cell wall: A rigid layer of cellulose outside the cell membrane. It gives the cell a fixed shape, supports the plant and prevents the cell from bursting when it takes in water.
• Chloroplasts: Organelles with chlorophyll in which photosynthesis occurs. Only the green parts of the plant have them.
• Large central vacuole: A fluid-filled sac that can fill most of the cell. It stores water and ions, and the pressure inside it keeps the cell firm.
• Plasmodesmata: Tiny channels through the walls that connect the cytoplasm of neighboring cells.
• Starch grains: A storage form of carbohydrate.

Plant and animal cells compared

Why do the differences exist?

The differences reflect how plants and animals live. Plants are fixed in place and make their own food, so they need chloroplasts and walls that support a stationary body against gravity and wind. A large vacuole and the pressure inside it give flexible green parts their firmness, and a wilting plant has cells that have lost this pressure.

Animals move and eat other organisms. They need flexible cells that can contract, change shape and ingest particles, which a rigid wall would prevent. Nervous and muscle tissue, for example, rely on cells that can change shape and conduct signals.

Worked example: identifying cells under the microscope

A student prepares two slides. Slide 1 is a thin layer of skin from the inside of an onion scale leaf, stained with iodine. Slide 2 is cells from the inside of the cheek, stained with methylene blue. Decide what the student should see and how to tell them apart.

1. Onion cells: They appear as a regular pattern of rectangular boxes with distinct walls. A round nucleus is visible in each, usually near the wall. There are no chloroplasts, because the inner bulb is not exposed to light.
2. Cheek cells: They are small, flat and irregular, without a regular pattern. Each has a cell membrane but no clear wall, and a central nucleus stained dark blue.
3. Distinguish them: A clear boundary with a straight, thick edge and a regular box shape indicates a wall, which means a plant cell. An irregular outline without a thick border indicates an animal cell.

For the drawing, use a sharp pencil, draw the outlines with single clean lines, label the visible parts and add a scale or magnification. Calculating the actual size uses the formula: actual size = measured size in the drawing ÷ magnification. For example, a cell drawn 40 mm across at ×400 magnification has an actual size of 40 ÷ 400 = 0.1 mm, which is 100 micrometers.

How were the differences discovered?

The cell wall was the first plant structure observed, by Hooke in 1665. The nineteenth-century cell theory of Schleiden and Schwann noted that plants and animals are both made of cells but differ in the presence of walls. Chloroplasts were described in the 1800s, and electron microscopy in the twentieth century revealed internal membranes. The shared structures support the idea that plants and animals evolved from a common eukaryotic ancestor.

Why does the comparison matter?

The difference between wall-bearing and wall-less cells underlies many technologies. Plant cell walls are the source of fiber for paper, textiles and dietary fiber. Herbicides can target processes that exist only in plant cells, such as photosynthesis, which makes them relatively safe for animals when used correctly. Medicine uses animal cell cultures to test drugs, and plant cell cultures are used to produce some compounds and to clone plants.

Which mistakes are common?

Mistake 1: Saying plant cells lack mitochondria

Plant cells have mitochondria and use them for respiration. Chloroplasts are an addition and not a replacement.

Mistake 2: Confusing the cell wall with the cell membrane

The wall is a rigid outer layer in plants. The membrane lies just inside it, and is present in all cells.

Mistake 3: Thinking every plant cell has chloroplasts

Root cells and the inner cells of a bulb have none. Chloroplasts occur where light reaches.

Mistake 4: Giving animal cells a fixed shape in drawings

Animal cells are flexible and take many shapes. A drawing should avoid straight, regular edges unless the cell type calls for it.