Origins of Photosynthetic Life

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Questions and Answers

What is a key requirement for temporary endosymbiotic relationships to evolve into permanent ones?

They must exist only within non-photosynthetic organisms.

They must be reversible and dynamic.

They must occur in organelles without genomes.

They must be heritable and stable within the host cells. (correct)

Which of the following provides scientific evidence that chloroplasts share a common ancestry with bacteria?

Both have circular genomes similar to those found in bacteria. (correct)

Both contain a double membrane structure.

Both are involved in aerobic respiration.

Both engage in photosynthesis and respiration.

How do chloroplasts contribute to the ecosystem beyond photosynthesis?

They solely recycle carbon dioxide in the atmosphere.

They generate organic sugars that provide energy to other organisms. (correct)

They solely produce oxygen as a waste product.

They decompose organic matter to release nutrients.

Why is it advantageous for cells to have distinct organelles?

They allow specific biochemical functions to take place without interference from incompatible processes. Signup and view all the answers

Which organelle is primarily responsible for photosynthesis?

Chloroplast Signup and view all the answers

What process is disrupted by the absence of chloroplasts in non-photosynthetic organisms?

Photosynthesis Signup and view all the answers

What occurs to chloroplasts when a host cell divides?

They are distributed evenly between two daughter cells. Signup and view all the answers

What is a consequence of increased membrane surface area in organelles?

It increases the potential metabolic capacity and reaction efficiency. Signup and view all the answers

What is the significance of the appearance of the first photosynthetic cells during the Proterozoic eon?

They enabled the production of oxygen and changed the Earth's atmosphere. Signup and view all the answers

Which of the following structures is primarily responsible for photosynthesis in eukaryotic cells?

Chloroplasts Signup and view all the answers

Which statement best describes the difference between prokaryotic and eukaryotic cells?

Eukaryotic cells have a true compartmentalized nucleus. Signup and view all the answers

What evidence supports the endosymbiotic theory regarding the origins of mitochondria and chloroplasts?

Mitochondria and chloroplasts share similar structures with prokaryotic cells. Signup and view all the answers

How do mitochondria contribute to cellular energy production?

They convert food energy into ATP, which powers cellular functions. Signup and view all the answers

What role did early eukaryotes play in the evolution of complex life forms?

Their complex organelles enabled increased metabolic capabilities. Signup and view all the answers

Which statement best describes the interaction between unicellular organisms prior to the emergence of eukaryotes?

They developed mutualistic relationships to survive harsh conditions. Signup and view all the answers

What characteristics do chloroplasts share with prokaryotic cells that support the endosymbiotic theory?

Presence of double membranes and their own DNA. Signup and view all the answers

What is one implication of the endosymbiotic theory regarding the evolution of eukaryotic cells?

Eukaryotic cells developed from a combination of prokaryotic cells through a symbiotic relationship. Signup and view all the answers

Which characteristic is common to all eukaryotic cell types according to the endosymbiotic theory?

Presence of mitochondria. Signup and view all the answers

What evidence supports the endosymbiotic theory regarding chloroplast origins?

Living examples of eukaryotes acquiring photosynthetic capabilities from engulfing bacteria. Signup and view all the answers

Why might anaerobic ancestral eukaryotes have initially engulfed aerobic bacteria?

To utilize the energy produced through aerobic processes. Signup and view all the answers

Which of the following describes a temporary endosymbiotic relationship?

Corals living symbiotically with dinoflagellates. Signup and view all the answers

What was a significant feature of the early Earth atmosphere that influenced the development of life?

It was a hostile environment. Signup and view all the answers

Which process is suggested as the first step in the origin of plastids based on endosymbiotic theory?

Phagocytosis by an early eukaryote. Signup and view all the answers

How does the genetic material of modern-day mitochondria provide evidence for the endosymbiotic theory?

It replicates independently from the host cell's DNA. Signup and view all the answers

Study Notes

Photosynthesis and Early Life

First photosynthetic cells marked a critical point in life's history; eukaryotes evolved during the Proterozoic eon.
Unicellular organisms began co-existing and becoming interdependent as a response to harsh environmental conditions.
Eukaryotic cells possess a true nucleus, internal membranes, and membrane-bound organelles; prokaryotic cells lack a nucleus and have fewer organelles.

Evolution of Cells

Most of Earth's history was marked by unicellular life with nearly no oxygen until photosynthetic cells emerged.
Prokaryotes emerged over 2 billion years ago; eukaryotic cells followed, showcasing more complexity.
Early eukaryotes featured organelles that performed distinct functions within internal membrane systems.

Organelles: Chloroplasts and Mitochondria

Chloroplasts: Present in plant cells and photosynthetic protists; crucial for converting light energy into chemical energy.
- Enclosed by a double membrane containing thylakoids organized in stacks called grana, containing pigments for photosynthesis.
Mitochondria: Found in both animal and plant cells; generate ATP and convert food energy into cellular energy. Malfunctioning mitochondria can lead to exhaustion.

Endosymbiotic Theory

Proposes all cells descended from ancient prokaryotes, with subsequent evolutionary modifications leading to eukaryotes.
Compartmentalization, facilitated by cell membranes, allowed genetic information to be stored in nuclei and regulated more efficiently.
Eukaryotes integrated aerobic or photosynthetic prokaryotes (modern mitochondria and chloroplasts) into their cells.

Scientific Evidence Supporting Endosymbiotic Theory

Living examples of endosymbiotic relationships, such as eukaryotes that engage in photosynthesis after engulfing photosynthetic bacteria.
Green algae like Cymbomonas showcase photosynthetic bacteria that benefit from the host.
Temporary symbiotic relationships observed in corals and sea slugs emphasize evolutionary significance; corals house dinoflagellates, while sea slugs retain chloroplasts from consumed algae.

Organelles and Cellular Function

Organelles compartmentalize cellular functions, enhancing metabolic capacity and efficiency.
- Each organelle has a distinct set of enzymes and products, ensuring optimized biochemical functions.
- Chloroplasts facilitate photosynthesis, while mitochondria are responsible for aerobic respiration, keeping incompatible processes separate.

Energy Functionality of Chloroplasts

Chloroplasts convert light energy and carbon dioxide into organic sugars and oxygen, essential for nourishing the ecosystem.
Non-photosynthetic organisms depend on energy derived from plants or animals that consume plants.
Energy from chloroplasts flows through food chains, with organisms utilizing sugars to synthesize ATP for energy needs, such as athletes requiring energy for muscle function.

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Description

Explore the significant developments in the history of life, focusing on the emergence of the first photosynthetic cells, especially eukaryotes in the Proterozoic eon. This quiz examines the interactions between unicellular organisms and their adaptation to harsh environments.