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

5. Cell Components

Endosymbiotic Theory

General Biology

5. Cell Components

Endosymbiotic Theory

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0:55 minutes

Problem 2

Textbook Question

Biologists think that endosymbiosis gave rise to mitochondria before plastids partly because
a. The products of photosynthesis could not be metabolized without mitochondrial enzymes.
b. All eukaryotes have mitochondria (or their remnants), whereas many eukaryotes do not have plastids.
c. Mitochondrial DNA is less similar to prokaryotic DNA than is plastid DNA.
d. Without mitochondrial CO₂ production, photosynthesis could not occur.

Verified step by step guidance

Understand the concept of endosymbiosis: Endosymbiosis is a theory that explains how eukaryotic cells may have evolved from prokaryotic cells. It suggests that certain organelles, like mitochondria and plastids, originated as free-living bacteria that were engulfed by ancestral eukaryotic cells.

Consider the role of mitochondria and plastids: Mitochondria are involved in cellular respiration, converting oxygen and nutrients into ATP, the energy currency of the cell. Plastids, such as chloroplasts, are involved in photosynthesis, converting light energy into chemical energy stored in glucose.

Evaluate the presence of mitochondria and plastids in eukaryotes: All eukaryotic cells have mitochondria or their remnants, which are essential for energy production. However, not all eukaryotic cells have plastids, as plastids are primarily found in plants and some protists.

Analyze the evolutionary timeline: The presence of mitochondria in all eukaryotes suggests that they were acquired earlier in evolutionary history than plastids. This is because mitochondria are essential for basic cellular functions, whereas plastids are specialized for photosynthesis.

Consider the implications of mitochondrial enzymes: The products of photosynthesis, such as glucose, require mitochondrial enzymes for further metabolism through cellular respiration. This interdependence supports the idea that mitochondria were established before plastids in eukaryotic cells.

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Key Concepts

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

Endosymbiosis Theory

Endosymbiosis is a theory that explains the origin of eukaryotic cells from prokaryotic organisms. It suggests that mitochondria and plastids, such as chloroplasts, originated as free-living bacteria that were engulfed by a host cell. This symbiotic relationship eventually led to the bacteria becoming integral organelles within the eukaryotic cell, providing essential functions like energy production and photosynthesis.

Mitochondria and Plastids

Mitochondria are organelles responsible for producing energy through cellular respiration, while plastids, including chloroplasts, are involved in photosynthesis. The presence of mitochondria in all eukaryotic cells, as opposed to plastids, which are only found in plants and some protists, supports the idea that mitochondria were acquired earlier in evolutionary history. This distinction is crucial for understanding the sequence of endosymbiotic events.

Eukaryotic Diversity

Eukaryotic diversity refers to the wide range of organisms that possess eukaryotic cells, including animals, plants, fungi, and protists. The fact that all eukaryotes have mitochondria, while only some have plastids, suggests that the acquisition of mitochondria was a more fundamental and earlier event in eukaryotic evolution. This helps explain why biologists believe mitochondria appeared before plastids in the evolutionary timeline.

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