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NMT Biomechanics Why is it better to be seaweed better than to be phytoplankton?

Paul Calvert's picture

This is an introductory post to a discussion on the advantages of multicellular organisms over single-celled eukaryotes from an energy harvesting viewpoint.  It is intended for the New Mexico Tech biomechanics class but others can play.

As engineers we should seek for a numerical measure (or some measures) that allows us to decide how close an organism is to the optimum.  Consider two cases: a seaweed in comparison to a single-cell photosynthetic eukaryote and a herbivore in comparison to a single-celled eukaryotic animal.

Comment on the possible answers, problems with the answers you previously gave or improve on the question.  You will be graded on the quality of your comments over the next two weeks.

 

PDC

 

 

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Paul Calvert's picture

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The advantage to having a body is the
safety all the single cells have, as well as the work load of the
cells being shared with massive amounts of cells.

It is better to be a photosynthetic
seaweed attached to a rock becuase the vulnerability you face is a
lot less than if you were a single celled algae on the same rock. The
work is a lot more, but in comparison to vulnerability, the work
would be worth it.

Having a body gives greater protection
from the elements and predators for the seaweed. Being anchored to
the rock allows the seaweed to obtain resources relatively
consistently as it wont easily be moved by currents.

The seaweed has to carry out more
photosynthesis, but it's larger surface area allows for more
photosynthesis to take place because it can absorb more. It is an
assumption without calculation, but I am assuming that the seaweed
can photosynthesize more than the algae can, relatively.

There are advantages for being both
multicellular piece seaweed and a single cell organism living on a
rock. One advantage to being seaweed by the ocean is that if there is
a powerful storm that rolls through the area the multicellular
seaweed has a better chance to survive because is one cell dies then
there are millions of other cells left. If the single cell living on
a rock has one cell dies then the entire organism dies.

A body allows for a mobile living
environment. Since an environment can become unstable, an entire
species could be wiped out if it's energy sources or living
conditions change to drastically. For instance, the volcanic vents,
which provide energy to a photon empty environment, can turn off
randomly. If the creatures surviving off of it were unable to move,
they would die.

A seaweed is much better rooted to it's
environment. While mobility allows for a change of environment, at
the bacterial level it's motion is outside of the control of the
bacteria. The seaweeds complex system allows for it to take advantage
of the changing environment of tides and weather.

A larger mass means (as stated in the
presentation) less worry of being pulled away from the sun. Perhaps a
bonus is that the larger body size leads to bigger surface area which
in turn leads to a better spread to obtain the UV coming from the sun
(for the seaweed case).

The advantage to having a body is
having function that is more complex. This means the ability to catch
food and therefore energy more quickly. A plant, on the other hand,
is stationary and can be defenseless to the environment in many
aspects.

A reason it could be better to be
seaweed rather than a single-celled algae is that the systems to
deliver and capture energy allow for the plant to grow and expand and
reproduce more easily. The complexity of seaweed could also allow
potential to develop functions that are much more complex and
advantageous in the future.

Single-celled organisms cannot get far
so they have to work to get good, much harder than a joined together
mass of organisms. Seaweed is substantially more efficient because
the plant can grow up and shade other organisms. Single-celled
bacteria and other organisms on their own are essentially also being
tossed around and washed around the ocean decreasing their chance of
survival and means for nutrients as well. Seaweed can remain
relatively stable due to its slick and sticky features that allows it
to remain close to the surface to receive the appropriate amount of
sunlight as well. It is also more efficient and more protective
always to form a protective grouping or barrier which seaweed can be
described as. Its kind of like an army or group of warriors that
have developed a formation for survival. It is easier to protect and
survive to fight off other threats such as environmental or
predators. Seaweed is a perfect demonstration of bacterial symbioses
to beneficially interact to provide support for each single-celled
bacteria it is composed of. They have a stable and specific
relationship and share mutualist ecological benefits together that
contributes so much more than providing for themselves on their own.

I'd
like to add on to my previous answer. Having thought about it more, I would say
that the main advantage to having a body is the ability to adapt to
environmental changes. An organism with multiple cells has a larger, tougher
strutcture and can potentially adapt to small to moderate changes in
temperature or salinity in the water easier, whereas a small single-celled
organism might die to the slightest change in environment. Of course this
depends on the single-celled organism because some archae are extremophiles and
can handle temperatures and saline levels that even animals cannot.

Also,
multi-celled organisms such as the seaweed have more specialized cells whereas
the single-celled algae's cell has to do all of the work for all of its
functions. Having multiple cells that specialize in different functions
maximizes the energy efficiency of the organism.

Some
of the responses above mentioned vulnerability, and I think that single-celled
organisms are vulnerable to environmental conditions, but if that vulnerability
is to predation, I would have to disagree. Yes, a seaweed is larger and tougher
and can repair damage (a seaweed can take some damage and repair itself while a
single-celled algae probably would die from damage), but the single-celled organism
is much smaller and can evade predation easier. This is especially true if the
rock that these organisms are on is porous or cratered. Maybe there is
something that I am missing in terms of predation, so let me know.

Many
of the same observations could be held true for the herbivore vs. single-celled
animal.

 -Sarah
Bryant

Well, from an
engineering standpoint, complex systems will always be the more stable.
Comparing seaweed
to a single cell may be viewed with the same
advantages as a solar panel. While the single cell could have a larger surface
to volume ratio, the seaweed has a larger overall reception area, as well as
the option of shape preference. In this case, a flat shape which maximizes its
own the surface area to volume ratio. So already, the seaweed is at least effective
as a single cell. Then you add the other benefits, like cell job selectivity.
Some cells can focus on the storage and movement of energy and store for
potential changes to environment. This gives it the ability to attempt to adapt
to new environments. A good analogy for this would be a company versus a single
person business. While the single person business may be easier to manage, the
growth potential and risk factor increases. If the owner gets sick, the
business fails, but as long as he is not sick the business operates at full
functionality. We may say the same for the seaweed, one cell or cell group may
be damaged, but the overall system can continue as it repairs.

The same strengths
apply to the herbivore system. The multicellular system can move easier, as a
result of the increased size plus the cell diversity allowing for tendon
covered bone. Any advantage that allows for easier acquisition of food
increases the efficiency of the system. Increasing efficiency allows for excess
energy, which leads to growth potential. When comparing the system efficiency
and environmental security of a multicellular system, the multicellular system
outperforms consistently. With complexity comes problems, in the cause of
organisms this might include disease, malformation defects, or injury. Even
with these concerns, the mechanical and chemical energy advantages of the single
cellular system are inherently higher than a multicellular, but the abundance
of resources enables the initial waste of energy to create a more efficient long-term
system. As long as there is an abundance of natural resources to support the
organism’s life, the multicellular organism will continue to outperform. It is
when resources are sparse that we see the single cell become more advantageous.

On the note of an herbivore versus a single celled eukaryotic animal, I argue a couple of ways the herbivore would have the advantage. First, there is the idea of potential. By being a mass of cells with various functions and specialties, there is more potenital for the animal to expand and adapt. On a large scale, the worlds atmosphere changes, and on a smaller scale an animals environment changes in regard to food, predators, and natural disasters. The animal can relocate and can traverse large areas to find food, whereas the sincle celled animal may be subject to die off quickly.

However, I could see it being argued that the single celled organism can replicate more quickly and perhaps adapt to environmental changes in a quicker time frame, which in certain environmental changes could be more of a benefit than the type of adaptability the herbivore has.

Second, I would argue another advantage of the herbivore over the single cell in relation to mechanics. With a large collection of cells there is potential to create structures that have higher stiffness, higher toughness, more flexibility, and so on. These could be argued to be necessary factors to allow the herbivore to function in the first place, but we can also see in nature that these factors can combine to give the animal special abilities beyond simple function. These added functions open up larger sources for food. For example, an herbivore being able to climb and jump across trees to eat berries and foliage.

For the case of a seaweed versus single celled eukaryote, a similar mechanical advantage could be argued. However, the range that seaweed can move is limited. The seaweed can adapt large complex structures to resist the environment, but as it was previously stated in other comments, the single cell could just as easily evade changes depending on the situation. Overall, I would say that added stiffnesses, flexibility, and complex structures allow for more food sources like that of the herbivores (as in agreement with other comments as well). 

 

 

   The two cases in which need to be compared are seaweed in
comparison to a single-cell photosynthetic eukaryote and an herbivore in
comparison to a single-celled eukaryotic animal.

   In response to the comparison for the seaweed versus the
single-cell eukaryote, it can be said that one is more optimal than the other.
The biggest concern for both is safety. Some form of safety is a huge concern
in any form of survival. The seaweed is able to protect itself from the
environment because it is able to flex and bend, and adapt to the environment. Seaweed
is more optimal than a single-cell eukaryote. The single-cell eukaryote is more
vulnerable to any type of damage, and the environment is much harsher on it.
The other concern that arises though is that the single-cell eukaryote is small
enough to adapt to smaller environments that have smaller threats and the cell
is small enough to adapt to allow for less vulnerability, whereas the seaweed
is larger and it is longer in length to be damaged from harm of larger threats.

   In response to the herbivore and the single-celled
eukaryotic animal, the same form of safety arises. No organism, no matter size,
ca survive if its existence is threatened and the larger the threat the more
danger that organism is in. It’s relative to size. The herbivore has the
ability to adapt and potentially be a threat to other organisms, showing
dominance and no longer having safety as an issue. The single cell though has
the ability duplicate faster than an herbivore and that can be argued as a
strong point, in the fact that its ability to adapt is quicker, but the
herbivore is larger and can adapt on a larger scale. From a mechanical
standpoint it can be argued that the herbivore is more optimal due to the
ability to be stronger and have a higher stress rate in comparison to a smaller
single celled organism.

   Both single celled and multi celled organisms have the
ability to strive, but I feel that the environment and safety is the biggest
factor for optimization. The cells either single or multiple, are only optimal
due to its ability to survive in the environment it is located in. 

Single-cell organisms, such as bacteria and protozoa, have been so successful in adapting to a variety of different environments that they comprise more than half of the total biomass on earth. Unlike animals, many of these unicellular organisms can synthesize all of the substances they need from a few simple nutrients, and some of them divide more than once every hour.  

Multicellularity enables a plant, for example, to become physically large; to have roots in the ground, where one set of cells can take up water and nutrients; and to have leaves in the air, where another set of cells can efficiently capture radiant energy from the sun. Specialized cells in the stem of the plant form channels for transporting water and nutrients between the roots and the leaves. Yet another set of specialized cells forms a layer of epidermis to prevent water loss and to provide a protected internal environment.  The plant as a whole does not compete directly with unicellular organisms for its ecological niche; it has found a radically different way to survive and propagate. 

Expanding more upon some of the other answers as well, a main difference requires the understanding of cellular and molecular biology level of these organisms.  If a multicellular organism has a higher number of cells, which it does, than the jobs and tasks performed by each cell can be specific.  They can delegate tasks efficiently and in a more timely manner than compared to a singe-celled organism who's one cell has to know when and how to perform and delegate all the tasks that are necessary to sustain life.  This can be compared with animals and bacteria as well. Animals adapted to their environments to benefit from motility, animals are much longer-living organisms compared to short-lived bacteria and unicellular organisms, due to this more complex state and structure.  The unicellular organisms have much less back-up in responding to external stimulus and adapting to changes in environment (which has also been discussed) and this may also be a reason that multicellular organisms have longer lifespans as well.  

Multicellular organisms also have a better and more developed reproductive system to continue to produce offspring to continue to provide life.  Seaweed have a much more complicated sexual reproduction than compared to unicellular phytoplankton. Some forms of seaweed algae even produce sexual pheremones that results in the attraction of another seaweed to reproduce.  This reproduction enables multicellular organisms to also provide a better lifestyle to sustain nutrients and also produce more cells to respond to stimuli better.  

However one instance I can think of when "more" could be considered a disadvantage is the proliferation and growth of cells at a higher and uncontrolled rate, like for instance with cancer.  I think single-celled organisms are less susceptible to the damage from the over growth of cells because there is only one cell and if this cell were to become damaged the cell would not be able to support the organism and the organism would die.  With the ability of having "many" cells there are multiple issues that can grow wrong involving DNA sequencing and other information that is provided by the cell to replicate.  

 This comes to a point to consider both the intricacies of single-celled organisms who without having back-up and other resources, still manage to survive on their own, and the complexities of multicellular organisms who provide structure and adaptation to survive more efficiently and longer.   I think the most feasible and logical design of a biomaterial would be to take advantage of this complex, yet intricate and simple design.  To harnass both capabilities of both simple and complex to provide for the issue and a design to control something like overgrowth and proliferation of cells with a mechanism from a single-celled design as well provide the structure and stability of a multi-ceullular organism.  

 

 

Mika Myers

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