1. OBJECTIVE
This experiment deals with the observation of plant cells and aims to identify primary (thin) and secondary (thick) wall structures, pigmentation organelles (chloroplasts and chromoplasts) and communication structures (plasmodesmata). We will mount histological slides using samples of onion cataphyllum with methylene blue dye (to observe the epidermis), pear pulp (to observe stone cells and secondary wall) and tomato epidermis and pulp (to observe chromoplasts in pulp and secondary wall and plasmodesmata in epidermis). With the experiment, the student will learn, in everyday vegetables, how to characterize a plant cell by identifying the cell wall, pigmentation structures and cellular communication, differentiating it from an animal cell.


At the end of this experiment, you should be able to:

Mount plant histological slides;

identify a plant cell;

distinguish thin and thick walls of plant cells;

differentiate pigmentation structures, such as chloroplasts and chromoplasts;

recognize cellular communication structures such as plasmodesmata.

2. WHERE TO USE THESE CONCEPTS?
These contents help students transform common sense information into scientific knowledge. Plant cells are formed by the plasma membrane and the cellulosic wall (the outermost, thickest and rigid layer) which, in addition to providing tissue structure, helps protect against dehydration and desiccation. Thus, it is possible for the student to understand, for example, why a leaf withers instead of drying in the absence of water, as the wall provides structural resistance during the initial development of the plant's body and prevents death in periods of drought. Furthermore, the plant cell surface has small structures that connect the cytoplasm of neighboring cells, the plasmodesmata, allowing the distribution of substances such as elaborated sap, hormones and physiological information across the entire surface of the tissues. In relation to chloroplasts and chromoplasts, it is possible for the student to understand that chromoplasts are pigments found in fruits, flowers and leaves in the process of ripening and aging, unlike chloroplasts, which are present in the initial processes of development of these structures. The conversion of chloroplasts to chromoplasts in fruit ripening is a classic example. In this way, it is possible to understand the reasons, through histology and the microscope, for processes that were previously seen with the naked eye, in the environment.


3. THE EXPERIMENT
In this experiment, you will assemble histological slides: with epidermis samples from one of the cataphyllum leaves stained with methylene blue; with pear pulp dissolved in water, to visualize stone cells and identify the secondary cell wall; and with tomato epidermis and pulp mounted in water, to observe plasmodesmata and chromoplasts, respectively. After observation, you will identify these structures at different magnifications, photograph them and describe them.


4. SECURITY
This practice will be carried out in the laboratory, so the participant must be dressed in long pants (except leggings; preferably, thicker fabrics, such as jeans), closed shoes (that cover the feet and chest) and a lab coat. It is also important to keep your hair tied with an elastic band during practice and while in the laboratory.


5. SCENARIO
The environment for this experiment consists of a bench with an optical microscope, a tray containing Petri dishes for handling samples, tweezers, slides and coverslips, a bowl with filtered water, samples of fresh onion, fresh pear and fresh tomato, paper towel , bottle of methylene blue and razor steel blades, like Gillette.