Are chemical signals that, instead of being secreted into the bloodstream, are introduced by animals into their habitats. they can be used to attract mates and mark territories.

The model illustrates a process by which a substance is taken up by a cell

Which process of living things produces water that enters the water cycle

Which of these is true of the cytoplasm of an unfertilized egg? a. it is an unevenly distributed mixture of mrna, proteins, organelles, and other substances. b. it does not contain substances that are important in directing development. c. these substances are supplied by the sperm. d. it does not contain substances that are important in directing development. e. development is directed solely by the surrounding cells. f. it is a homogeneous mixture of mrna, proteins, organelles, and other substances. g. it does not contain substances that are important in directing development. h. these substances are produced by the dna of the fertilized zygote.