Animal Development: We're Just Tubes - Crash Course Biology #16

How many layers of tissue do the most complex animals form during their early development?

• One

• Two

• Three

• Four

What is formed when a sperm cell fertilizes an egg cell?

• A gamete

• A zygote

• A morula

• A blastula

What is the name for the solid ball of 32 cells formed after a zygote divides multiple times?

• Gamete

• Blastula

• Morula

• Gastrula

What is the process called when an indentation forms in a blastula, eventually leading to the creation of a digestive tract?

• Cleaving

• Fertilization

• Gastrulation

• Mitosis

What kind of animal is a deuterostome?

• An animal where the mouth forms first.

• An animal where the anus forms first.

• An animal with only one opening for eating and waste.

• An animal that does not have a digestive system.

What are organisms called if they only develop two germ layers?

• Triploblastic

• Diploblastic

• Monoblastic

• Polyblastic

In animals with three germ layers, what does the ectoderm usually become?

• Muscles and bones

• The digestive tract

• Skin and nerves

• The circulatory system

What did Ernst Haeckel's recapitulation theory claim about an embryo's development?

• Embryos develop randomly without a pattern.

• An embryo's development shows all the evolutionary steps of its species.

• All embryos look exactly the same throughout their development.

• Embryos only develop into fish-like creatures.