Endosymbiosis and the Origin of Mitochondria and Chloroplasts

What are prokaryotic cells?

• Single-celled organisms with a cell membrane

• Multi-celled organisms with a nucleus

• Single-celled organisms with a nucleus

• Multi-celled organisms with a cell wall

Answer explanation

Prokaryotic cells are single-celled organisms characterized by the absence of a nucleus. They are enclosed by a cell membrane which defines their structure. Hence, the correct answer to the question is 'Single-celled organisms with a cell membrane'. Other options mentioned either a nucleus or multiple cells, which are not characteristics of prokaryotic cells.

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Ava, Aiden, and Ethan are having a debate about how prokaryotes divide. Ava thinks it's through mitosis, Aiden believes it's binary fission, Ethan is convinced it's meiosis, and their teacher suggests it might be budding. Which is correct?

• Mitosis

• Binary fission

• Meiosis

• Budding

Answer explanation

Prokaryotes, like bacteria, reproduce asexually. They do not use mitosis or meiosis, which are processes used by eukaryotes. Instead, prokaryotes use a process known as binary fission, during which a single cell divides into two identical cells. This process is faster and simpler than mitosis and meiosis. Therefore, the correct answer to the question is 'Binary fission'.

What is the process by which mitochondria and chloroplasts divide?

• Mitosis

• Binary fission

• Meiosis

• Budding

Answer explanation

The question asks about the division process of mitochondria and chloroplasts. The correct answer is 'Binary fission'. This is because both these organelles divide independently of the cell wherein they reside, and this process of division is similar to the binary fission performed by bacteria.

Harper, Evelyn, and Lily are on a quest to discover the secrets of human genetics. They stumble upon a riddle: 'From whom do humans inherit mitochondria?' Can you help them solve it?

• Both parents

• Only from their father

• Only from their mother

• Neither parent

Answer explanation

Mitochondria is inherited only from the mother. This is due to mitochondrial DNA, which is only passed down from the mother. The sperm's mitochondria gets destroyed by the egg cell after fertilization. So, the answer to the question 'From whom do we inherit mitochondria?' is 'Mother only'.

What is the function of plasmids in prokaryotes?

• Carry genetic material for mitosis

• Provide protection to the cell

• Store extra DNA outside the chromosome

• Facilitate cellular respiration

Answer explanation

Plasmids play a crucial role in prokaryotes as they store extra DNA outside the chromosome in prokaryotes, and outside the nucleus in eukaryotes. These small, circular DNA molecules are independent of the chromosomal DNA and are capable of self-replication. They are not involved in carrying genetic material for mitosis, providing protection to the cell, or facilitating cellular respiration, making the correct choice 'Store extra DNA outside the chromosome'.

Charlotte, Olivia, and Jackson are having a debate about cells. Charlotte thinks that prokaryotic ribosomes are larger, while Olivia believes that eukaryotic ribosomes are larger. Jackson, on the other hand, thinks that one type is more efficient than the other. Can you help them settle this debate? What is the main difference between prokaryotic and eukaryotic ribosomes?

• Charlotte is right, prokaryotic ribosomes are larger

• Olivia is right, eukaryotic ribosomes are larger

• Jackson is right, prokaryotic ribosomes are more efficient

• Jackson is right, eukaryotic ribosomes are more efficient

Answer explanation

The main difference between prokaryotic and eukaryotic ribosomes lies in their size. Prokaryotic ribosomes are smaller in size, typically 70S, while eukaryotic ribosomes are larger, typically 80S.

Maya, David, and Abigail are looking into the endosymbiotic theory about mitochondria and chloroplasts. Can you help them understand why these organelles have a double membrane?

• Is it because it provides protection to the organelles?

• Or, does it allow for increased energy production?

• Could it be a result of endocytosis during evolution?

• Or, is it to separate the organelles from the cytoplasm?

Answer explanation

The double membrane in mitochondria and chloroplasts is significant due to a process called endocytosis during evolution. This phenomenon involves the engulfment of one cell by another, resulting in the formation of organelles with a double membrane. It does not primarily aim at protection or separation from the cytoplasm or increased energy production.

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Where is the electron transport chain located in mitochondria?

• Outer membrane

• Inner membrane

• Intermembrane space

• Matrix

Answer explanation

The electron transport chain is located in the inner membrane of the mitochondria. Here, a series of protein complexes perform redox reactions, transferring electrons from donors to acceptors, and using the released energy to form ATP. The inner membrane is the correct location because it provides the right environment for these processes, while the outer membrane, intermembrane space, and matrix do not.

What is the term for a close relationship between two organisms where both benefit?

• Symbiosis

• Parasitism

• Commensalism

• Predation

Answer explanation

The term for a close relationship between two organisms where both benefit is known as 'Symbiosis'. Other options like 'Parasitism' refers to a relationship where one organism benefits at the expense of the other, 'Commensalism' refers to a relationship where one organism benefits and the other is neither harmed nor benefited, and 'Predation' refers to a relationship where one organism kills and feeds on the other.

How do we know that mitochondria and chloroplasts were once independent prokaryotic cells? Choose all that apply.

• They have their own plasmids and ribosomes

• They have a double membrane

• They divide by binary fission

• They have both nucleoids and nuclei.

Answer explanation

The answer to the question about how we know that mitochondria and chloroplasts were once independent prokaryotic cells is 'All of the above'. This is because they have their own plasmids and ribosomes, they have a double membrane, and they divide by binary fission, all of which are characteristic features of prokaryotic cells.

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