A car can be compared to a plant cell because they both have parts that carry out similar functions. In this case, a cell is not compared to a car in its overall function but instead in the functions of some of its parts.
In this metaphor, the frame of the car, which provides its structure and support, is like the cell wall of a plant, which is responsible for much of the plant's rigidity. The cell membrane, which lies beneath the cell wall and allows select materials in and out of the cell, is like a door in a car, which allows things to enter and exit the car only at certain points.
The driver of the car is much like the nucleus of a cell, which is in control of the rest of the cell. The battery of the car is like the mitochondria, which is the area of the cell that turns food that enters the cell into a usable form of energy. The chloroplasts in a plant cell are like solar panels on a solar-powered car because both chloroplasts and solar panels harvest energy from the sun and use it to make power.
A car trunk is similar to a structure called a vacuole in a plant cell because the vacuole is where water and important nutrients are stored. The ribosomes of a cell are similar to the gas of a car because ribosomes make proteins that fuel the cell, just as gas fuels a car.
The Golgi complex is like the set of pipes found within a car that makes sure that materials are sent to the right place; this is because the Golgi complex is responsible for making sure that proteins are sent to the right place.