|
These are the answers to the quiz. |
||
1) Eukaryote cells contain a nucleus. | ||
| Not answered. It is true. Eukaryote cells have the DNA enclosed by a double membrane known as the nuclear envelope. Both chromatin and the nuclear envelope form the nucleus. | ||
2) The plasma membrane separates the intracellular from the extracellular environment. | ||
| Not answered. It is true. The plasma membrane is also known as the plasmalemma. | ||
3) The cytoplasm consists of organelles, cytosol, and the nucleus. | ||
| Not answered. It is false. The cytoplasm is the interior of the cells, the nucleus excluded. That is, it is the cytosol and the organelles.. | ||
4) A typical eukaryote cell is about 10 to 50 µm in size. | ||
| Not answered. It is true. Although the text page says that normal size is between 10 and 30 µm, it is actually very difficult to establish precise limits. It can be said that most eukaryote cells are between 10 and tenths of µm. | ||
5) Eukaryote cells show a wide variety of forms, from elongated to star-like shapes. Rounded forms are not actually the most common morphology. | ||
| Not answered. It is true. In fact, cells may show highly variable morphologies. However, rounded forms are also observed in many cell types. For instance, in animal cells when dividing by mitosis. | ||
| | ||
6) No cells were visualized before the invention of the light microscope. | ||
| Not answered. It is false. We are considering the question as false because a chicken egg contains cells. However, it was not until way after the invention of the light microscope that researchers were aware that the egg yolk is actually a cell. | ||
7) The first microscopes were invented at the beginning of the XVIIth century. | ||
| Not answered. It is true. The invention of the light microscope is endorsed to Lippershey and Janssen around 1600. | ||
8) R. Hook, in his book Micrographia (1664), gives the name cell to the structures that we nowadays know as cells. | ||
| Not answered. It is true. However, he did not realize that "cells" that he observed in the cork were in fact present in every living organism. | ||
9) The cell theory postulate, "All organisms are made up of units called cells", was posed by Schwann and Schleiden. | ||
| Not answered. It is true. We can accept the answer as correct, although other researchers had previously suggested something similar, such as Wolf, Raspail, Milne-Edwards, or Dutrochet. Therefore, the postulate by Schwann and Schleiden was the result of a long way and intense research carried out by previous researchers. | ||
10) The cell ultrastructure can be observed with compound light microscopes. | ||
| Not answered. It is false. It was not until the invention of the electron microscope, at the middle of the XXth century, that the cell ultrastructure could be clearly visualized. | ||
| | ||
11) The sentence "Cells arise from pre-existing cells" is a postulate of the cell theory. | ||
| Not answered. It is true. However, according to what we know today, it may not be completely true. For example, the first cells emerged on Earth from organic molecules by physicochemical processes. In addition, we can nowadays synthesize prokaryote cells in vitro from scratch. | ||
12) The theories about the origin of cells do not exclude that cells may have appeared on other planets. | ||
| Not answered. It is true. Although we don't know how the first cells on Earth were formed, science accepts that it was by physicochemical processes in an ancient environment under particular chemical and physical features. These features may have been happening on other planets of the universe for a long time, even though they may be happening right now. Therefore, we cannot rule out that life is present on other planets, either as cells or as other entities with similar fundamental features. | ||
13) Organic molecules are only synthesized by living organisms. | ||
| Not answered. It is false. Organic molecules can be synthesized by chemical reactions, which are independent of cells. For example, organic molecules have been found in some Martian meteorites. In addition, it looks like many simple organic molecules are synthesized in the interstellar space. | ||
14) The first cells appeared 350 million years ago. | ||
| Not answered. It is false. The first evidence of living cells was found in rocks formed about 3000 to 35000 million years ago. | ||
15) The organic molecules that were used during the emergence of the first cells may have had extraterrestrial origin. | ||
| Not answered. It is true, or it may be true because we know now that simple organic molecules are continuously generated in interstellar space. In addition, it also happens on other planets. In fact, some Martian meteorites contain organic molecules. | ||
| | ||
16) The laws of the Darwin evolution theory —offspring have variability and individuals are selected by the environment— may have been working before the emergence of the first cells. | ||
| Not answered. It is true. This would be possible if we consider the RNA world theory of the emergence of the first cells. RNA may have the ability of auto-replication by complementary base pairing, and some errors may have occurred during the copy and production of new molecules. Thus, there is variability: molecules with different nucleotide sequences. The less stable molecules, or those that auto-replicate more easily, were selected by the environment. The result is that some RNA molecules would produce more copies and would be enriched in the primordial soup. | ||
17) All current cells are descendants of a common ancestral one. | ||
| Not answered. It is true. It is thought that there was an initial cell, LUCA (the last universal common ancestor), that was the ancestor of all the current cells. The universal genetic code (three particular nucleotides are translated into one particular amino acid) is shared by all current cells studied so far, a fact that supports the idea of LUCA. | ||
18) In the origin of life, the formation of the cell membrane needed the involvement of enzymes. | ||
| Not answered. It is false. Amphipathic lipids similar to those of the cell membrane can be synthesized by physicochemical reactions that do not need the participation of any enzyme. Once they are formed, these lipids may spontaneously assemble into a bilayer membrane in aquatic environments. Cell membranes are actually bilayer membranes. | ||
19) The RNA world is the only theory that explains the evolution of the prebiotic or precellular world. | ||
| Not answered. It is false. There is another theory positing that the first molecular system with the ability to evolve was a complex framework of chemical reactions. This system would have evolved into a cell. This theory is known as "the metabolic world." | ||
20) The genetic code is a fact that supports the idea of a universal common ancestor (LUCA) for all current cells. | ||
| Not answered. It is true. The correspondence of a particular nucleotide triplet with an amino acid, that is, the genetic code, is thought to be arbitrary. Therefore, it is easier to think that all cells inherited this code after it was invented once, instead of it being achieved by many cell lines by chance. | ||
| | ||
21) The autogenous theory explains how mitochondria and chloroplasts appeared in eukaryote cells. | ||
| Not answered. It is false. Chloroplasts and mitochondria are thought to appear in eukaryote cells via endosymbiosis. The autogenous theory only explains the origin of other organelles like the endoplasmic reticulum, endosomes/lysosomes, Golgi apparatus, and vesicles. It shows that these organelles were formed by plasma membrane invaginations that were detached afterward. | ||
22) The endosymbiosis theory posits that the ancestor of mitochondria was incorporated before the ancestor of chloroplasts. | ||
| Not answered. It is true. All eukaryote cells having chloroplasts share the same ancestor, which was the first to incorporate the chloroplast ancestor. It is the same process that has happened to mitochondria. | ||
23) All eukaryote cells having chloroplasts share the same ancestor, which incorporated the chloroplast ancestor. The same process has happened to mitochondria. | ||
| Not answered. It is false. We now know that there are secondary and tertiary endosymbiosis. It means that cells can inherit chloroplasts not directly by cell division from cells having chloroplasts but by engulfing a complete cell that contained chloroplasts. These non-inherited but stolen chloroplasts were kept in the new host cells and started working properly in the cytoplasm. | ||
24) Mitochondria are similar to the current aerobic bacteria.c | ||
| Not answered. It is false. Mitochondria have gone through a long and complex evolution inside the eukaryote cells. Mitochondria have lost the majority of the genes that went to the cell nucleus. In addition, most proteins needed by mitochondria are coded by nuclear genes. But, even if this gene transfer had not happened and the genes were conserved, mitochondria would be more similar to the ancestor than to the current aerobic bacteria. | ||
25) Nowadays, there are associations between eukaryote and prokaryote cells that support the endosymbiosis theory. | ||
| Not answered. It is true. There are many examples of ongoing associations between prokaryotes and eukaryotes. In some of them, the prokaryote cell lives inside a eukaryote cell. In fact, in some species of invertebrates, the prokaryote cell can be transmitted to the offspring because it is inside the gametes. However, the high degree of cellular integration of mitochondria/chloroplasts has not yet been observed in other endosymbiotic associations. | ||
Quiz results
Right answers = 0
Wrong answers = 0
Not answered = 25
Unusefull answers = 0
The score of the quiz (range between 0 and 10) = 0,0