<span>LD
means lethal dose. LD50 is the amount of a material, administered at once to
cause the death of half (50%) of a group of test organisms. A test which shows that LD50 of a certain
chemical is 20 mg per kg means that 20 milligrams of that chemical for every 1
kilogram body weight of the test animal when administered in one dose, causes
the death of 50% of the test group.</span>
Answer: The effects of which are devastating to human life, flora and fauna, which depend on these resources for their survival. Contamination of water causes disruptions of food chains and destruction of ecosystems. A deadly by-product of this water pollution is the spread of water-borne diseases such as cholera, typhoid etc.
Explanation:
Answer:
Dermal and vascular tissue
Explanation:
The dermal system of plants works together with the vascular system to carry out sweating.
The dermal tissue is wound by the epidermis and periderm. The epidermis is varied in its structure and function, among which its main function is that of protection and vegetal covering. These cells are covered by a cuticle, responsible for providing an impermeable characteristic to the cell. In this region, there is the presence of guard cells, which are responsible for the process of closing and opening pores, called stomata. This structure serves to control the plant's internal gases, such as the entry and exit of water vapor, CO2 and oxygen. The periderm, in turn, is the secondary protective tissue in vegetables. It has a loose organization, allowing an aeration of the internal tissues of the roots and stems. It is in this region that we find mainly the suber, the best known being cork, which is a classic example of periderm.
The vascular system is formed by xylem and phloem. Xylem is the main conductive tissue of water, nutrients and minerals. Its composition is formed by dead cells, with lignin impregnation. It is found more internally in relation to phloem, also acting as an important supporting tissue, as it has special cells called tracheids and vessel elements. Both are elongated cells that have points on their wall to communicate with one cell to another. Phloem, in turn, is formed by living cells, being the main responsible for transporting elaborate sap from the leaves to the stem and roots. It is located just below the plant's bark, formed by a special cell called sieving elements, because that cell has sieving areas, through which the protoplasm of the adjacent cells bind. This region is known as the riddled plaque. These sieved tube elements also have the characteristics of being associated with special parenchymal cells called companion cells.
