What are three reasons lichens are useful to humans?

Lichens are useful as they act as pollutant indicators, like food and medicines.

Explanation:

In lichens, High SO2 concentrations were said to be the main reason for habitat loss, reductions in some species. The most sensitive lichens are shrubby and leafy. Lichens are very sensitive to pollution such as nitrogen because they receive water and nutrients from wet and dry atmospheric deposition. this property makes them a pollutant indicator.

Lichens provide food and also help algae to produce food. they make of their own food production. Bryoria is a genus of lichen used by native Americans.

Lichens in traditional medicine are generally used for treating skin disorders, wound, and digestive issues.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation: