The main difference between plant and human cells is that plant cells have a cell wall as well as a cell membrane and that some plant cells have chlorophyll. Another difference is that while there are several types of cells in the human body, there are only three types of plant cells. Rather than being classified according to tissue type, plant cells are classified according to their cell walls.
In humans, the cell membrane allows items to pass into and out of the cell. In plants, the cell membrane does the same thing. The cell wall, made of cellulose, creates a stiff barrier that holds liquid inside. It's located outside the plant's cell membrane.
When a plant has sufficient water, the cell walls make the stems and leaves stand up nicely. A plant that needs water will wilt. Humans have skeletons, so cell walls are not needed.
Chlorophyll is what gives plants their green color. Through photosynthesis, plants take in carbon dioxide, nutrients and water and, with the help of the sun, convert these items into sugars and oxygen. The sugars are stored in the plant, and the oxygen is released into the atmosphere. Humans take in oxygen and release carbon dioxide, but don't create their own food.
The three types of plant cells are parenchyma, collenchyma and sclerenchyma. Parenchyma cells are found in the inner parts of leaves, roots and stems. These cells divide, helping with plant growth, food storage and photosynthesis. The human equivalent would be the cells in an organ that make that organ function.
Collenchyma cells provide structural support to leaves and shoots. Sclerenchyma cells are also used for structural support and for transporting water and sugars throughout the plant. It is the equivalent of the human circulatory system, but with a stiff outer wall.