Plant cell
Before you start
A plant cannot walk to find food or move into the shade, so many of its leaf cells make food from light, while other cells have different tasks. The plant also needs to stay upright without a skeleton and survive changes in the water supply. On the animal cell page, we meet a nucleus, mitochondria, endoplasmic reticulum and a Golgi apparatus; a plant cell has all of these too, so you do not need that page first. The differences are the parts that solve the plant’s own problems: a stiff wall, a large water-filled vacuole, and chloroplasts that capture light.
Our model represents a leaf cell with chloroplasts. Notice the two outer layers: the cell wall gives firm support, while the cell membrane just inside it controls the movement of many substances. They are close together but are not the same layer. The large central vacuole connects to the water supply and support mentioned above; the surrounding chloroplasts connect to making food using light. When selecting a structure, keep the plant’s particular need in mind. Its shape, position and job can then help you remember one another.
The setupThis is an enlarged leaf cell, cut open and coloured so that each kind of structure can be told apart. Select a structure in the model or from the list to read its name, its job and how to recognise it; Look closer moves in to its detail. The cutaway switch closes the cell to show its outside, and the list can still select structures hidden inside.
What to do and noticeStart at the boundary and work inwards. Select the cell wall and then the plasma membrane just inside it, and notice that they are two different layers. Next, find the large central vacuole and the chloroplasts pressed around it, and use Look closer on a chloroplast to see its stacked discs. Finally, find a mitochondrion: plant cells release energy by respiration too, even though they also make food from light.
Predict firstA plant cell has a wall and a membrane outside. Which one controls what enters, and which one mainly supports the cell?
Plasma membrane
A cell must take in materials without letting everything enter or leave freely, so it needs a selective boundary. The membrane mainly contains phospholipids and proteins. A phospholipid has a water-friendly end and a water-avoiding part. In water, the water-avoiding parts turn inward and pair up, so the water-friendly ends face the water on both sides. The two layers belong to one membrane, not two separate membranes. Proteins in the membrane can provide passages or help particular substances cross.
The thin membrane surrounding the cell contents. In cells that have a wall, the wall lies outside this membrane. Animal cells have no cell wall.
Follow one set of protein instructions
The cell model shows where structures are. This separate construction shows what “DNA information is used to make protein” means. DNA stores the instructions, and the working copy is made of messenger RNA. Advance one step at a time; nothing moves on by itself.
Each numbered square stands for the information specifying one amino-acid unit, and each circle stands for the unit itself. An amino acid is one small bead in the chain of a protein. Matching colours let us follow the order from the information to the chain. These are instruction markers, not pictures of DNA or RNA molecules. Distances and the number of units are chosen to make each step visible.
Locate the boundary, follow one set of instructions for a protein, then examine the structures that distinguish this cell.
Prerequisites: A cell is a basic unit that carries out life processes. It must take in materials, build its parts and keep information for making them. We will start with these needs and introduce the structures one at a time.Start with two boundaries
Predict firstA plant cell has a wall and a membrane outside. Which one controls what enters, and which one mainly supports the cell?
The thick cell wall is the outermost layer of a plant cell, and the plasma membrane lies just inside it. The wall mainly supports the cell; the plasma membrane is the thin boundary that controls what enters and leaves. As water enters, the contents press outwards, and the firmer wall limits swelling. The cutaway opening lets us see inside; a living cell does not have this large hole.
How to observe
- Start with the boundaries, then explore inside; distinguish a wall from a membrane.
- Select a structure, read what it does, then use Focus to inspect its detail.
- Inspect the grana in chloroplasts, then find mitochondria: plants respire too.
What this model simplifies
Sizes, counts and colours are adjusted for teaching; this is not a raw microscope image. Cellular organization is dynamic. Each model represents one example, not every member of its group; bacterial accessory structures, plant chloroplasts and fungal forms particularly vary.
