Cell Theory and Types of Cells

State the three tenets of cell theory and indicate which of these statements contradicts it, reasoning your choice: a) all living things are made of one or more cells; b) some cells can arise by spontaneous generation from non-living matter; c) the cell is the functional unit of living things; d) all cells come from a pre-existing cell.

Order the following levels of organisation of living matter from lowest to highest complexity and define each with a sentence: organ, cell, tissue, organelle and organism.

Classify the following organisms and cells as prokaryotes or eukaryotes, briefly justifying your choice: a cyanobacterium, an amoeba, a skin cell, yogurt bacterium, a yeast and a green alga.

The diagram compares two types of cellular organisation, A and B. State which corresponds to a prokaryotic cell and which to a eukaryotic cell, identify the structures marked with ? and explain the implication for the cell of the difference observed in the organisation of its genetic material.

Compare a prokaryotic cell and a eukaryotic cell with regard to their typical size, the presence of a nucleus and membrane-bound organelles, and the form of their DNA. Based on this comparison, explain where cyanobacteria carry out photosynthesis if they lack chloroplasts.

The emergence of membrane-bound organelles was a milestone in the evolution of the cell. Explain what advantages dividing the cell interior into membrane-bound compartments offers, and give two specific examples of processes that benefit from it.

In a cell biology laboratory, the effect of two antibiotics on a culture of animal eukaryotic cells is analyzed: cycloheximide (an inhibitor of translation on 80S ribosomes) and chloramphenicol (an inhibitor of translation on 70S ribosomes). The results show that cycloheximide stops protein synthesis in the cytosol but not inside the mitochondria, whereas chloramphenicol specifically blocks mitochondrial protein synthesis without affecting cytosolic synthesis. Based on these data and the framework of the endosymbiotic theory:

1. a) Justify the results observed with both antibiotics and indicate which plant organelle would show a response analogous to that of the mitochondrion when exposed to chloramphenicol.
2. b) A researcher claims that mitochondria are fully autonomous bacteria that could survive and divide indefinitely if isolated in a suitable extracellular medium. Reasonably refute their claim by explaining the evolutionary relationship between the mitochondrial genome and the nuclear genome.
3. c) Predict what fundamental differences are to be expected between the inner and outer mitochondrial membranes regarding their lipid composition and the presence of porins, and explain how this asymmetry supports the endosymbiosis mechanism proposed by Lynn Margulis.
4. d) Point out which specific ancestral bacterial groups molecular phylogenetic analysis points to as the origin of mitochondria and chloroplasts.

In deep-sea sediments, a microscopic entity ("Particle Z") surrounded by a lipid bilayer has been discovered, containing a 1.2 Mb double-stranded DNA genome with genes for synthesizing several amino acids and its own tRNAs. However, it lacks machinery to synthesize ATP, ribosomes, and the ability to divide autonomously outside its cellular host. A science communication headline claims: "New cell discovered that blurs the boundary between viruses and bacteria".

Refute the journalistic headline by rigorously applying the tenets of cell theory and the biological concept of life. Justify why the presence of metabolic genes does not turn this particle into an independent cell, and argue why this type of biological entity is studied within biology.

A group of students attempts to replicate Pasteur's classic experiment: they boil nutrient broth for 10 minutes in a swan-neck flask and leave it undisturbed. After four days, the broth becomes turbid and they detect bacterial proliferation (spore-forming bacilli of the genus Bacillus). One student concludes: "This proves that Pasteur was wrong and that spontaneous generation does occur if the medium is rich enough."

Refute the student's claim by explaining what methodological error they made when replicating Pasteur's design and why the presence of bacterial spores does not validate spontaneous generation. Finally, analyze the apparent paradox posed by the postulate "all cells arise from pre-existing cells" in relation to current scientific theories on the prebiotic origin of the first living cell.