Answer:
They have helical thickening of lignin in their walls to prevent collapse
Explanation:
the primary function of Xylem and its conducting vessels tracheids is to provide support and tranport water and minerals in plants.
Xylem vessels have layers of dead materials in the walls called LIGNIN. Lignin is a polymer; a very strong, hard materials that stop water passage through it,because it contains dead cells,
Therefore the presence of deposit of these strong impermeable, ligified walls in its walls prevent its collapse during mass flow of water of transpiration pull.
Answer: It is called Parasitism.
Explanation:
Parasitism is symbiotic relationship where an organisms lives in or on it's host thereby feeding and causing harm on it host. Examples of such relationship is parasites like roundworm, ticks, fleas that feed on humans and cause harm.
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Answer:
Offspring of a horse and donkey are unable to reproduce.
Explanation:
The biological concept of species states that:
A species is a group of organism with similar characteristics, that can interbreed and have a fertile offspring.
Horse + donkey = mule. A mule is a hybrid and is not fertile.