Animal and Plant Cells

Structure of Plant and Animal Cells

Together with fungal and protozoan cells, animal and plant cells are the main types of Eukaryotic Cells that exist. Even though plant and animal cells have several aspects in common, there are key structural differences that make them behave differently, as we will see later in the article.

The following table details the presence or absence of different important organelles and other key structures in animal and plant cells:

Let's take a closer look at the structures of plant and animal cells. Can you tell how to distinguish both types of cell by looking at the diagram below?

Fig. 1. Differences and similarities between plant and animal cells. Remember that ER is the abbreviation for endoplasmic reticulum.

As you can see from the diagram, plant and animal cells look very different. Thus, there are simple ways to distinguish both of them:

• The shape of the cell: plant cells are usually square or rectangular due to the cell wall, but animal cells can vary significantly in shape because they aren't constrained by the rigid cell wall.
• A lack of a cell wall marks the eukaryotic cell as an animal cell. Not having a cell wall means that animal cells can change shape to adapt to the amount of water exiting or entering the cell, with the risk of bursting or lysing. However, plant cells cannot do this to the same degree. Plant cells have two statuses depending on the amount of water they contain:
  • Turgid: When a plant cell is fully hydrated and contains an excess of water, it becomes turgid and the cell wall prevents further uptake of water. This results in increased pressure within the cell and the cell becomes firm and rigid.
  • Flaccid: When a plant cell loses water, it becomes flaccid. The reduction in pressure within the cell causes the cell wall to collapse and the cell to become limp. This process is called plasmolysis. This status can be reversed by watering a plant.

Fig. 2. Turgid, flaccid and plasmolysed plant cells. Plant cells can transition through these stages depending on the amount of water they can absorb.

• The presence of a big vacuole indicates that the cell is a plant cell. Animal cells do not have a big, permanent vacuole because they do not have cell sap. The permanent vacuole is the largest organelle found in plant cells, whilst in animal cells, the largest organelle is usually the cell nucleus.
• Animal cells do not have chloroplasts. Chloroplasts contain chlorophyll for Photosynthesis. You may recall that photosynthesis is the process by which Plants use light energy to form valuable products such as sugars. Animal cells do not photosynthesise and so do not need chloroplasts. Chlorophyll is a pigment which gives plant leaves their characteristic green colour.

Plant and Animal Cells Labelled Diagrams

It's common for schools to ask students to label a plant and/or animal cell diagram. Each cell has it's peculiarities as we have seen above, but the organelles and other cell structures have such peculiar shapes that you'll be sure to identify each one quickly once you've tried once or twice.

Plant Cell Labelled Diagram

As you can see, a labeled diagram of a plant cell typically includes the following structures: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, mitochondria, endoplasmic reticulum, Golgi apparatus, peroxisomes, and a central vacuole.

Fig. 4. Labelled plant cell diagram. Take note of the shape and location of each organelle and the shape of the cell.

Plant Cell Labelled Diagram

From the diagram below, you can see that a labeled diagram of an animal cell typically includes the following structures: cell membrane, nucleus, cytoplasm, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, centrosomes, and Cytoskeleton.

Similarities Between Plant and Animal Cells

Plant and animal cells have a few similarities, starting with the fact that they are both eukaryotic cells. This means that they both have a nucleus containing the Genetic Information in the form of DNA, and membrane-bound organelles. As we have seen in this article, though, the type and number of organelles can significantly differ between animal and plant cells.

However, as any cell, plant and animal cells tick all the boxes that characterise the basic unit of life:

• Both cell types can reproduce independently via Mitosis and Cytokinesis. Plant cells need to generate new cell wall apart from Plasma Membrane, though.
• Both plant and animal cells respire, i.e. they have catabolic reactions as part of their metabolism. On top of that, most plant cells also photosynthesise.
• Plant and animal cells respond to stimuli, can grow and move, although plant's movement is extremely limited.
• Both plant and animal cells depend and interact with their environment.

Both animal and plant cells are surrounded by a cell membrane, a thin layer that helps protect the cell and regulate what goes in and out. This means that their nucleus is membrane-bound.

Differences Between Plant and Animal Cells

Animal and plant cells create incredibly different organisms, with different characteristics, requirements and abilities. This difference already starts at the cellular level, in particular, it starts at the level of Cell Structure, which we have already covered. The structural differences like the presence of a cell wall in plant cells, or of centrioles in animal cells then end up giving the different functionalities of each cell type.

Other differences between plant and animal cells include motility, Cell Division, photosynthesis capacity and shape.

• Motility: animal cells can move around, slide and bend, whereas plant cells are stationary relative to each other and can't migrate. However, Plants can orientate and bend towards a nutrient source, like a humid plot of land or the rays of the sun. The differences in motility will influence the way each cell type reacts to the environment.
• Cell Division: although both animal and plant cells divide through Mitosis and Cytokinesis, the specific steps for each cell type are different. For example, plant cells need to generate new cell wall to create two daughter cells, while animal cells only have to split the plasma memebrane to prodiuce to daughter cells. Animal cells have centrioles which play a key role in cell division, while plant cells do not have them. In the end, these differences translate into a speedier division for animal cells in general, although we should be careful of making general statements like this as many factors can influence the speed of cell division.

• Photosynthesis: plants have chloroplasts, which allow them to transform sunlight and other inorganic matter into organic matter (glucose) and oxygen. This is why plants are considered "producers" in an ecosystem, because they can create their own "food" from inorganic molecules and light. Other organisms, those that have animal cells among others, can't create their own organic matter and need to consume plants to obtain nutrients and energy.
• Shape: due to the lack of cell wall, animal cells have more irregular shapes compared to plant cells.