Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

20. Development

Animal Development

General Biology

20. Development

Animal Development

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2:44 minutes

Problem 6

Textbook Question

In humans, identical twins are possible because
a. Extraembryonic cells interact with the zygote nucleus.
b. Convergent extension occurs.
c. Early blastomeres can form a complete embryo if isolated.
d. The gray crescent divides the dorsal-ventral axis into new cells.

Verified step by step guidance

Understand the context: Identical twins, also known as monozygotic twins, occur when a single fertilized egg splits and develops into two embryos.

Consider the options: Each option describes a different biological process or concept. We need to identify which one is related to the formation of identical twins.

Option a: Extraembryonic cells are involved in forming structures like the placenta, not in splitting the zygote.

Option b: Convergent extension is a process during gastrulation that involves cell movement and tissue elongation, not related to twin formation.

Option c: Early blastomeres are cells formed during the early stages of embryonic development. If these cells are isolated, they have the potential to develop into a complete embryo, which is the basis for the formation of identical twins.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Identical Twins Formation

Identical twins, or monozygotic twins, occur when a single fertilized egg, or zygote, splits into two separate embryos. This splitting usually happens during the early stages of embryonic development, leading to two genetically identical individuals. The process is distinct from fraternal twins, which result from two separate eggs being fertilized by two different sperm cells.

Blastomeres

Blastomeres are the cells formed by the division of the fertilized egg during the early stages of embryonic development. In some species, including humans, early blastomeres have the potential to develop into a complete embryo if they become isolated. This totipotency is crucial for the formation of identical twins, as it allows the separated cells to develop independently into two embryos.

Embryonic Development

Embryonic development is the process by which a fertilized egg transforms into a fully formed organism. It involves multiple stages, including cleavage, blastulation, gastrulation, and organogenesis. Understanding these stages is essential for comprehending how identical twins can form, as the splitting of the embryo typically occurs during the early cleavage stage, when cells are still totipotent.

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Textbook Question

Which of the following is common to the development of both birds and mammals?

a. Holoblastic cleavage

b. Epiblast and hypoblast

c. Trophoblast

d. Gray crescent

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The archenteron develops into

a. The mesoderm.

b. The endoderm.

c. The placenta.

d. The lumen of the digestive tract.

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Textbook Question

What structural adaptation in chickens allows them to lay their eggs in arid environments rather than in water?

a. Extraembryonic membranes

b. Yolk

c. Cleavage

d. Gastrulation

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Textbook Question

If an egg cell were treated with EDTA, a chemical that binds calcium and magnesium ions,

a. The acrosomal reaction would be blocked.

b. The fusion of sperm and egg nuclei would be blocked.

c. The fast block to polyspermy would not occur.

d. The fertilization envelope would not form.

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Textbook Question

Cells transplanted from the neural tube of a frog embryo to the ventral part of another embryo develop into nervous system tissues. This result indicates that the transplanted cells were

a. Totipotent.

b. Determined.

c. Differentiated.

d. Mesenchymal.

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Textbook Question

You obtain an egg cell from the ovary of a white mouse and remove the nucleus from it. You then obtain a nucleus from a liver cell from an adult black mouse. You use the methods of nuclear transplantation to insert the nucleus into the empty egg. After some prompting, the new zygote divides into an early embryo, which you then implant into the uterus of a brown mouse. A few weeks later, a baby mouse is born. What color will it be? Why?

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Textbook Question

In an experiment, a researcher colored a bit of tissue on the outside of a frog gastrula with an orange fluorescent dye. The embryo developed normally. When the tadpole was placed under an ultraviolet light, which of the following glowed bright orange? (Explain your answer.)

a. The heart

b. The pancreas

c. The brain

d. The stomach

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Textbook Question

In an embryo, nerve cells grow out from the spinal cord and form connections with the muscles they will eventually control. What mechanisms described in this chapter might explain how these cells 'know' where to go and which cells to connect with?

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