D two cells with 12 chromosomes in zero homologus
Answer:
gymnosperms produce male cones and female cones, and the pollen from a male cone fertilize the egg inside a female cone
Answer:
Mechanical digestion begins in the mouth as the food is chewed. Chemical digestion involves breaking down the food into simpler nutrients that can be used by the cells.
Explanation:
Chemical digestion begins in the mouth when food mixes with saliva. Saliva contains an enzyme (amylase) that begins the breakdown of carbohydrates.
Answer:
a. heart development.
Explanation:
As the third week of fetal development starts, the process of formation of blood vessels begins. Also, the splanchnic mesoderm in the head end of the embryo forms heart on days 18 and 19. Since it develops heart, this part of the mesodermal cells is called the cardiogenic area. The underlying endoderm sends the induction signals to these mesodermal cells to form a pair of endocardial tubes that gradually develop into a single primitive heart tube.
This primitive heart begins to beat by the end of the third week of development. Therefore, any drug that affects fetal development during the first 20 days of the pregnancy might affect the development of the heart.