What is the biggest single-celled organism? - Murry Gans

Summary

The video script explores why there are no unicellular organisms as large as elephants or whales. It explains that as cells grow, their volume increases faster than their surface area, which limits the efficiency of nutrient intake and waste removal. This biological quirk prevents the existence of giant single-celled creatures. The script also highlights exceptions like the neuron and villi in the small intestine, which have adapted to maintain function despite their size. Caulerpa taxifolia, the world's largest single-celled organism at 30 centimeters, is mentioned as an example of a cell that has evolved unique structures to enhance its surface area.

Takeaways

• 🐘 The elephant, despite its massive size, is composed of trillions of microscopic cells.
• 🔬 Most cellular functions occur inside the cell, regulated by the cellular membrane which controls the passage of substances.
• 📏 As cells increase in size, the ratio of surface area to volume decreases, which is a critical biological limitation.
• 🧠 Larger cells have a harder time exchanging materials due to a smaller surface area relative to their volume.
• 🚫 Very large single cells are rare because they cannot efficiently manage the transport of resources and waste.
• 💥 A cell's inability to scale up indefinitely without compromising function is due to the surface area to volume ratio issue.
• 🌿 Some cells, like neurons and intestinal villi, have adapted to overcome size limitations through structural innovations.
• 🌱 Caulerpa taxifolia, a large single-celled organism, uses unique strategies like coenocytic structure and photosynthesis to thrive.
• 🐳 No unicellular organism grows as large as multicellular creatures like elephants, whales, or bears.
• 🌍 The tiny cells within large organisms are essential for their survival and function, highlighting the importance of cellular scale in biology.

Q & A

Why are there no unicellular organisms as large as elephants or whales?

Unicellular organisms can't grow as large as multicellular ones because as a cell increases in size, its volume grows much faster than its surface area, leading to a reduced ability to exchange resources and waste efficiently.

What is the role of the cellular membrane in a cell?

The cellular membrane acts as the doorway into and out of the cell, allowing resources to be consumed and waste products to be expelled.

How does the surface area to volume ratio change as a cell grows?

As a cell grows, its volume increases at a much faster rate than its surface area, resulting in a decreased surface area to volume ratio, which hinders the cell's ability to function efficiently.

What is the significance of a cell being cube-shaped in the context of this explanation?

Using a cube to represent a cell simplifies the mathematical calculations, as a cube has a consistent surface area to volume ratio that changes predictably with size.

How does the surface area to volume ratio affect a cell's ability to function?

A higher surface area to volume ratio allows for more efficient exchange of materials across the cell membrane, which is crucial for the cell's survival and function.

What biological quirk prevents cells from growing to the size of elephants or whales?

The biological quirk is that a cell's surface area does not scale proportionally with its volume as it grows, leading to an inefficient exchange of materials if the cell becomes too large.

What are some adaptations that allow certain cells to be exceptionally large?

Some cells, like neurons and cells in the small intestine, have adapted by being very thin or having highly folded membranes with microvilli to increase their surface area relative to their volume.

What is the significance of Caulerpa taxifolia in the context of unicellular organisms?

Caulerpa taxifolia is believed to be the largest single-celled organism, reaching up to 30 centimeters long, due to its unique adaptations that increase its surface area and allow it to function efficiently despite its size.

How does being coenocytic help Caulerpa taxifolia to be a large unicellular organism?

Being coenocytic means Caulerpa taxifolia has multiple nuclei within a single cell, which allows it to function more like a multicellular organism without the divisions between cells, aiding in its large size.

What is the advantage of having many smaller cells instead of a few large ones in a multicellular organism?

Having many smaller cells provides redundancy and resilience; if one cell is damaged or destroyed, the organism can still function, unlike a large cell that, if compromised, could be more detrimental to the organism's survival.

How do the structures called villi in the small intestine help in increasing the surface area for absorption?

Villi are finger-like projections that increase the surface area of the small intestine, and they are covered in cells with highly folded membranes and microvilli, which further enhance the absorption of nutrients.

Outlines

00:00

🐘 Why Elephants Aren't Made of One Cell

This paragraph explores the biological constraints on the size of cells. It explains that while elephants are massive, they are composed of trillions of microscopic cells. The paragraph delves into the relationship between a cell's surface area and volume, illustrating how larger cells have a smaller surface area to volume ratio, which is less efficient for nutrient intake and waste removal. The example of a cube is used to demonstrate this concept, showing that as a cell grows, its volume increases much faster than its surface area, which would lead to inefficiencies in a very large cell. The paragraph also touches on the advantages of having many smaller cells over a few large ones, such as resilience to damage and the ability of certain large cells to adapt through thinning or increased surface area.

Keywords

💡Epic proportions

The term 'epic proportions' refers to something that is very large or grand in scale. In the context of the video, it is used to describe the size of elephants, which are massive creatures. The script contrasts this with the microscopic nature of cells, highlighting the vast difference in size between the organism as a whole and its individual cellular components.

💡Unicellular species

A 'unicellular species' is an organism composed of a single cell. The video discusses why we don't see large unicellular organisms like elephants or whales, which is a central theme of the video. It points out that while there are millions of unicellular species, most are too small to be seen with the naked eye.

💡Cellular membrane

The 'cellular membrane' is a biological membrane that separates the interior of a cell from its external environment, managing the movement of substances in and out of the cell. The video explains that the membrane acts as a doorway, crucial for the cell's survival as it regulates the intake of resources and the expulsion of waste.

💡Surface area to volume ratio

The 'surface area to volume ratio' is a concept that describes the relationship between the surface area and the volume of an object, such as a cell. The video uses this concept to explain why larger cells are less efficient: as a cell grows, its volume increases faster than its surface area, which can lead to issues with the exchange of materials and waste removal.

💡Micrometers

A 'micrometer' is a unit of length in the metric system, equivalent to one-millionth of a meter. The video uses micrometers to describe the size of cells, emphasizing the tiny scale at which cellular processes occur. It helps to illustrate the vast difference in size between cells and the larger organisms they compose.

💡Cellular functions

Cellular functions refer to the various biochemical processes that occur within a cell to maintain life. The video mentions that most of these functions happen within the cell's interior, enclosed by the cellular membrane, highlighting the importance of the membrane in facilitating these vital processes.

💡Neuron

A 'neuron' is a specialized type of cell that transmits nerve impulses and is a fundamental unit of the nervous system. The video points out an exception to the general rule of cell size, mentioning a neuron that can stretch from the base of the spine to the foot, which is an example of a very long but thin cell that has adapted to the challenges of size.

💡Villi

Villi are small, finger-like projections that increase the surface area of cells in the small intestine. The video uses villi as an example of how cells can adapt to increase their surface area, which is crucial for the absorption of nutrients in the digestive system.

💡Microvilli

Microvilli are tiny, hair-like projections on the surface of certain cells that further increase the surface area for absorption or secretion. The video mentions microvilli as part of the adaptation of cells in the small intestine, which helps in the absorption of nutrients.

💡Caulerpa taxifolia

Caulerpa taxifolia, a type of green algae, is noted as one of the largest single-celled organisms. The video discusses this organism as an exception to the general trend of small unicellular life, highlighting its unique biological adaptations that allow it to be larger than most single cells.

💡Coenocytic

The term 'coenocytic' describes a single cell with multiple nuclei. The video uses this term in relation to Caulerpa taxifolia, explaining that despite being a single cell, it contains multiple nuclei, which is a characteristic that allows it to grow larger than most unicellular organisms.

Highlights

Elephants, despite their massive size, are composed of trillions of microscopic cells.

Unicellular species are mostly too small to be seen with the naked eye.

Cells have a cellular membrane that regulates the intake and output of substances.

Cells' surface area and volume increase at different rates, affecting their functionality.

A one-micrometer cube cell has a surface area to volume ratio of six to one.

A ten-micrometer cube cell has a reduced surface area to volume ratio of 0.6 to one.

Larger cells have less surface area relative to volume, impeding efficient resource and waste exchange.

Giant cells would struggle with waste management and could not survive.

Having many smaller cells is advantageous as the failure of one is less critical.

Exceptionally large cells, like neurons, compensate with thin structures to increase surface area.

Villi in the small intestine have highly folded membranes and microvilli to enhance surface area.

Caulerpa taxifolia, a large single-celled green algae, uses unique structures to maximize surface area.

Caulerpa taxifolia is coenocytic, having multiple nuclei within a single cell.

Even the largest unicellular organisms have size limits and do not reach the scale of multicellular giants.

The multitude of tiny cells within large creatures is essential for their survival and function.

Transcripts

The elephant is a creature of epic proportions,

and yet it owes its enormity to more than 1,000 trillion microscopic cells,

and on the epically small end of things,

there are likely millions of unicellular species,

yet there are very few we can see with the naked eye.

Why is that?

Why don't we get unicellular elephants,

or blue whales,

or brown bears?

To find out, we have to peer into a cell's guts.

This is where most of the cell's functions occur,

enclosed by a cellular membrane

that acts as the doorway into and out of the cell.

Any resources the cell needs to consume,

or waste products it needs to expel,

first have to pass through this membrane.

But there's a biological quirk in this set up.

A cell's surface and volume increase at different rates.

Cells come in many shapes,

but imagining them as cubes will make the math easy to calculate.

A cube has six faces.

These represent the cell membrane, and make up its surface area.

A cube measuring one micrometer on each side,

that's one millionth of a meter,

would have a total surface area of six square micrometers.

And its volume would be one cubic micrometer.

This would give us six units of surface area

for every single unit of volume,

a six to one ratio.

But things change dramatically if we make the cube ten times bigger,

measuring ten micrometers on each side.

This cell would have a surface area of 600 square micrometers

and a volume of one thousand cubic micrometers,

a ratio of only .6 to one.

That's less than one unit of surface area to service each unit of volume.

As the cube grows, its volume increases much faster than its surface area.

The interior would overtake the membrane,

leaving too little surface area for things to quickly move in and out of the cell.

A huge cell would back up with waste and eventually die and disintegrate.

There's another plus to having multitudes of smaller cells, too.

It's hardly a tragedy if one gets punctured, infected, or destroyed.

Now, there are some exceptionally large cells

that have adapted to cheat the system,

like the body's longest cell,

a neuron that stretches from the base of the spine to the foot.

To compensate for its length, it's really thin,

just a few micrometers in diameter.

Another example can be found in your small intestine,

where structures called villi fold up into little fingers.

Each villus is made of cells with highly folded membranes

that have tiny bumps called microvilli to increase their surface area.

But what about single-celled organisms?

Caulerpa taxifolia, a green algae that can reach 30 centimeters long,

is believed to be the largest single-celled organism in the world

thanks to its unique biological hacks.

Its surface area is enhanced with a frond-like structure.

It uses photosynthesis to assemble its own food molecules

and it's coenocytic.

That means it's a single cell with multiple nuclei,

making it like a multicellular organism but without the divisions between cells.

Yet even the biggest unicellular organisms have limits,

and none grows nearly as large as the elephant, whale, or bear.

But within every big creature are trillions of minuscule cells

perfectly suited in all their tininess

to keeping the Earth's giants lumbering along.