Orcas, or killer whales, are natural predators of sea otters. it has been observed that in regions where the sea otters are not present, sea urchins grow rapidly and destroy much of the natural kelp vegetation. which of these statements is correct in this context?

a) kelp is the keystone species because their survival is key to the survival of the entire ecosystem.

b) sea otters cannot be considered the keystone species because they are not the top predators in the ecosystem.

c) sea urchins are the keystone species because they multiply rapidly in the absence of their natural predators.

d) sea otters are a keystone species as they prevent a herbivorous species from completely destroying a plant species.

 D)  Sea otters are a keystone species as they prevent a herbivorous species from completely destroying a plant species.

The removal of a keystone species could cause their natural prey to multiply and destroy the dominant vegetation of the ecosystem. Kelp is the foundation species in the ecosystem. Sea urchins consume the kelp. If the sea urchin numbers are not kept in check by the sea otters, they will rapidly multiply and destroy the kelp vegetation. Therefore, sea otters are a keystone species as they prevent the herbivorous species from completely destroying a plant species.

~USATestprep~

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: