1. Sample description

Broccoli leaves have a deep and dark green shade. The upper side of the leaf is smooth and waxy, while the lower side is duller in color and slightly rough. 

Sample 1: Cubicle of broccoli leaf
The leaf cubicle can be easily separated as a thin, transparent layer from other layers. This layer consists of many stomata that can be observed as coffee bean-shaped cells. A stoma is a hole that comprises two cells, which allow air and water exchange when they shrink, and stop this process when they swell up. 


Sample 2: Palisade mesophyll of the broccoli leaf
Palisade mesophyll is the thickest layer of the leaf and home to stomata. It can be sampled by slicing a thin piece after peeling off the leaf cubicle. The obtained sample is dark green, resulting from the high density of chloroplasts.

1. Background

Classification:

Broccoli (Brassica oleracea L. var. italica) is a variety of the species Brassica oleracea L., which belongs to the genus Brassica L., family Brassicaceae Burnett, order Capparales, class Magnoliopsida, division Magnoliophyta and kingdom Plantae. 

Broccoli originated in the Eastern Mediterranean and Anatolia. It was mainly grown and  bred by artificial selection in Italy before being introduced to England and the USA in the XVIII century. 

Biological characteristics:

Broccoli is an annual plant that can grow up to 90 cm in height. Growing outward from the tree trunk are the branches, whose tips hold the broccoli heads. Broccoli heads not only grow on the branches but also on the top of the main trunk. They are made up of small broccoli flowers that cluster together, which are commonly mistaken as leaves due to their dark green color. Broccoli heads can also be found, but rarely, in other colors, such as violet, yellow or white. Broccoli thrives in cool climates (18°C to 24°C). Its flowers are unisexual, and pollinated by insects. 

In terms of nutritional value, broccoli is largely considered a superfood due to its high content of vitamins A, C, K, folic acid, and minerals. It also contains glucosinolate and isothiocyanates that decelerate cancer progression, a flavonoid that prevents cardiovascular diseases, and glucoraphanin which is the bio-precursor of the antioxidant sulforaphane.

1. Other facts

• Both broccoli and cabbage belong to the mustard family and originated from the same ancestor plant, the wild mustard Brassica Oleracea. Due to the forces of evolution, the wild mustard plant has altered its physical properties to adapt and subsequently given rise to many Brassica species: broccoli, cauliflowers, kale, kohlrabi, brussels sprouts,...
• Broccoli head can last a long time if stored in a plastic bag in the refrigerator. People are advised against eating raw broccoli due to the potential risk of consuming toxins like tannins, saponins, and protease inhibitors or cooking it at a high temperature as it may diminish nutrition. The safest and healthiest ways to prepare broccoli are boiling or steaming, which can cook it through while retaining nutrients.