Question

Question 1 (1 point)

Adhesion molecules in choanoflagellates serve the same function as those in their sister group, the animals. This suggests that:

Question 1 options:

	animals and choanoflagellates likely evolved adhesion molecules independently
	gap junctions allow animal cells to communicate effectively with each other
	choanoflagellates evolved from complex multicellular animals
	evolution adapted unicellular tools for multicellular purposes

Question 2 (1 point)

Plasmodesmata:

Question 2 options:

	are channels in the plasma membrane of plant cells made of transmembrane proteins that allow ions and small molecules to pass between adjacent cells
	are channels in the plasma membrane of animal cells made of transmembrane proteins that allow ions and small molecules to pass between adjacent cells
	provide points of structural support between adjacent plant cells
	are holes in the cell wall through which the plasma membrane and endoplasmic reticulum of adjacent cells are connected

Question 3 (1 point)

Which of the following would provide the BEST evidence that an early form of targeted cell-cell communication was present BEFORE the evolution of complex multicellular organisms?

Question 3 options:

	discovery of an amoeba that forms connections between its plasma membrane and the plasma membrane of another amoeba
	cell adhesion molecules present in plant cells also discovered in fungi
	discovery of transmembrane proteins in a variety of bacteria
	finding plants that use a combination of plasmodesmata and gap junctions

Question 4 (1 point)

Comparing human and chimpanzee DNA sequences reveals 98.8% similarity. This is amazing for species that look so different! Which of the following BEST explains the differences in appearance despite similarities in sequence?

Question 4 options:

	humans undergo cell differentiation but chimpanzees do not
	chimpanzee chromosomes are circular compared to human linear chromosomes
	selective gene expression allows for similar genomes to produce diverse phenotypes
	their proteins use a different 1.2% of amino acid building blocks

Question 5 (1 point)

Stem cells highlight the power of regulatory genes for all of the following reasons EXCEPT:

Question 5 options:

	different combinations of genes are activated and repressed in cells that ultimately serve different functions
	stem cells have a greater diversity of regulatory genes than other kinds of cells
	different combinations of proteins are expressed in different cells resulting from mitosis
	developing cells change location, shape, and function in response to transcriptional products

Question 6 (1 point)

A NASA scientist receives satellite data indicating that a newly discovered planet contains no oxygen gas in its atmosphere. From this information she concludes that complex multicellular organisms are UNLIKELY to exist on that planet. This is because:

Question 6 options:

	complex multicellular life cannot exist once photosynthesis has evolved
	unicellular organisms consume multicellular organisms when oxygen levels are low
	endosymbiosis requires high oxygen concentrations for evolution to proceed
	other electron acceptors (like iron) are unlikely to be readily available and abundant

Question 7 (1 point)

The wide diversity of arthropod body plans can be attributed to:

Question 7 options:

	mutations in genes that regulate the development of limbs, mouthparts, wings, etc.
	acquisition of mitochondria through endosymbiosis of proteobacteria
	specific coordination between embryonic cells through plasmodesmata
	flexibility in metabolism that lets them use a variety of carbon and energy sources

Answer 1

1. Ans: Evolution adapted unicellular tools for multicellular purposes.

Coanoflagellates are unicellular free living eukaryotes which are considered to be the closest living relative of animals. Having the same function for adhesion molecules in both unicellular coanoflagellates and multicellular animal cells suggest that unicellular organism used its raw materials to 1st form colonies and gradually attained multicellularity.

2. Ans : Plasmodesmata are holes in the cell wall through which the plasma membrane and endoplasmic reticulum of adjacent cells are connected.

Plasmodesmata are microscopic channels through which cytoplasm passes through to connect between two adjacent cells. These are formed when parts of endoplasmic reticulam gets trapped at the middle lamella forming pits/holes in the cell wall .

3. Ans : discovery of an amoeba that forms connections between its plasma membrane and the plasma membrane of another amoeba

Amoeba is an unicellular organism and which interact with its adjacent amoeba cells through their plasma membrane. This exact phenomenon is seen in multicellular organism like animal cells where plasma membrane is used for intercellular exchange. So it can be said that targeted cell-cell communication is evolved from the primitive unicellular connections.

4. selective gene expression allows for similar genomes to produce diverse phenotypes.

A genome expression depends on multiple factors such as transciptional factors, environmental factors, epigenetics. So similar genome can be expressed differently producing variety of phenotypes. For eg within human species where almost 100% genome similarity is observed, we can see multiple phenotypes like facial shape, height, colour etc.