Plant cells are organised in the same way as animal cells. There is a hierarchy, or "order" involved. 


In this section we will look at this. In plants, in just the same way as animals, cells are grouped into tissues, tissues are grouped into organs and organs are grouped into organ systems.


The organs in the plants are such things as the stems, roots and leaves, and are made of tissues such as:


  • Epidermal tissue which covers the whole plant.
  • Palisade mesophyll tissue which is the part of the leaf where most of the photosynthesis takes place.





  • Spongy mesophyll tissue which is also in the leaf and contains large air spaces to allow gases (carbon dioxide and oxygen and so forth) to diffuse in and out of the cells.

  • Xylem and Phloem which are tube like structures designed to transport food, mineral ions and water around the plant.

  • Meristem tissue which is found at the growing tips of shoots and roots, this is able to differentiate into lots of different types of plant cells allowing the plant to grow, not unlike stem cells in animals.


The leaf is an organ system made up of several types of tissue:




  • The epidermal tissues are covered with a waxy cuticle which helps to reduce water loss by evaporation.


  • The upper epidermis is transparent so that light can pass through to the palisade layer.

  • The palisade layer has lots of chloroplasts which are the small structures where photosynthesis takes place, they are close to the top of the leaf where they can receive the most light.

  • The Xylem and Phloem form a network a bit like a venous system in your body, which delivers water and other nutrients to the entire leaf and takes away the glucose produced by photosynthesis. 


If you think about it the circulatory system in humans does a similar thing, the arterial system takes blood to the organs and the venous system takes the deoxygenated blood back to the lungs. 



The tissues of the leaves are also adapted for very efficient gas exchange, the lower epidermis is full of little holes called stomata which under a microscope look like little mouths. These "mouths" open and close under the control of Guard Cells which respond to changes in environmental conditions. If it helps, you can think of the guard cells as similar to the doormen at the entrance to a nightclub, supervising the entry and exit to the premises.


The Stomata allow Carbon Dioxide to diffuse directly into the leaf, where photosynthesis uses this to produce Glucose and Oxygen.






The air spaces in this spongy mesophyll layer allow for an increase in the rate of gas diffusion, so you can see that the structure of the leaf is ideally adapted for its purpose.