Question

1. What is a problem that a cell needs to overcome if its volume is very large relative to its surface areas? How have Eukaryotes been able to get around this problem?

2. Do Eukaryotes with chloroplasts lack mitochondria? How does primary endosymbiosis differ from secondary endosymbiosis?  

Answer 1

1. In order to survive,cells must constantly interact with their sorrounding environment. Gases and food molecules that cell require is dissolved in water and must be absorbed and waste products of cellular metabolism must be eliminated. Plasma membrane is the only passage of all materials in and out of cell.

As a cell grows bigger the cell mebrane enlarges also the internal volume increases. The volume increases more rapidly than does the surface area of the membrane , and so the relative amount of surface area available to pass materials to a unit volume of the cell steadily decreases. Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased metabolism occuring in the increased cellular volume. So then the cell must divide into smaller cells with favorable surface area/volume ratios, or cease to function.

To solve the surface-area-to-volume problem and its consequence internal transport problem there many evolutionary adaptations.

• one solution is  to divide into two cells, or development of organelles that perform specific tasks. These adaptations lead to the development of larger and more complex cells called eukaryotic cells.
• Another  solution is multicellularity, where an organism is made of multiple cells with specialized functions.

Cell specialization is required for multicellularity, where different cells carry out different functions from each other and often have different morphologies optimized for carrying out those functions. This is seen mainly in eukaritoes where each system has different functions like circulatory systems bring nutrients and remove waste, while respiratory systems provide oxygen for the cells and remove carbon dioxide from them.

2. Chloroplasts are organelles that conduct  photosynthesis and are found in plant cells and eukaryotic algae. They absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant.The entire process is called photosynthesis.

Mitochondria are membrane-bound cell organelles that generate most of the chemical energy needed to power the biochemical reactions of the cell. Chemical energy produced by the mitochondria is stored in a small molecule called adenosine triphosphate (ATP) and they are present in both plant cell and animal cell.

So eukariotes with cholroplast doesnt lack mitochondria.

Primary endosymbiosis occurs is the process eukaryotic cell engulfing and absorbing a prokaryotic cell, such as a smaller cell that carry out photosynthesis (eg. cyanobacteria).

Secondary endosymbiosis is the process of  eukaryotic cell engulfing and absorbing another eukaryotic cell.

Scinetist believe the endosymbiotic theory is the reason for mitochondria and chloroplasts to evolve in eukaryotic organisms. Before mitochondria and chloroplasts were organelles in a cell, they were prokaryotes that were absorbed by eukaryotic cells.

Primary endosymbiosis is thought to have occurred first. Secondary endosymbiosis occurred second. Both involve the concept of one cell absorbing genetic material from a smaller preexisting organism to increase the complexity of the resulting symbiotic union.