All Seawater Pro water makers include an automated fresh water rinse timer. In order to maintain optimum performance of your membrane and to eliminate odors in your water, the rinse timer will automatically flush the filters, pump, and all the membranes. 8' Diameter End Port Fiberglass PROTEC Membrane Housings Protec ariswa pressure vessels are designed for continuous use as housing for membrane filtration elements to purify typical waters at any positive pressure ratings from 150 PSI up to 1200 PSI. Single-ply membrane roofing does not have a hard-top layer to protect the synthetic rubber from dropped tools, gravel or loose screws from being pushed into the rubber membrane. This kind of damage could create holes in the rubber and insulation and be vulnerable to leaks.
Learning Objectives
By the end of this section, you will be able to:
- Name examples of prokaryotic and eukaryotic organisms
- Compare and contrast prokaryotic cells and eukaryotic cells
- Describe the relative sizes of different kinds of cells
Cells fall into one of two broad categories: prokaryotic and eukaryotic. The predominantly single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes (pro– = before; –karyon– = nucleus). Animal cells, plant cells, fungi, and protists are eukaryotes (eu– = true).
Components of Prokaryotic Cells
All cells share four common components: 1) a plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment; 2) cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found; 3) DNA, the genetic material of the cell; and 4) ribosomes, particles that synthesize proteins. However, prokaryotes differ from eukaryotic cells in several ways.
Figure 1. This figure shows the generalized structure of a prokaryotic cell.
A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle. We will shortly come to see that this is significantly different in eukaryotes. Prokaryotic DNA is found in the central part of the cell: a darkened region called the nucleoid (Figure 1).
Unlike Archaea and eukaryotes, bacteria have a cell wall made of peptidoglycan, comprised of sugars and amino acids, and many have a polysaccharide capsule (Figure 1). The cell wall acts as an extra layer of protection, helps the cell maintain its shape, and prevents dehydration. The capsule enables the cell to attach to surfaces in its environment. Some prokaryotes have flagella, pili, or fimbriae. Flagella are used for locomotion. Pili are used to exchange genetic material during a type of reproduction called conjugation. Fimbriae are protein appendages used by bacteria to attach to other cells.
Eukaryotic Cells
In nature, the relationship between form and function is apparent at all levels, including the level of the cell, and this will become clear as we explore eukaryotic cells. The principle “form follows function” is found in many contexts. For example, birds and fish have streamlined bodies that allow them to move quickly through the medium in which they live, be it air or water. It means that, in general, one can deduce the function of a structure by looking at its form, because the two are matched.
A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles, which have specialized functions. The word eukaryotic means “true kernel” or “true nucleus,” alluding to the presence of the membrane-bound nucleus in these cells. The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.
Cell Size
At 0.1–5.0 µm in diameter, prokaryotic cells are significantly smaller than eukaryotic cells, which have diameters ranging from 10–100 µm (Figure 2). The small size of prokaryotes allows ions and organic molecules that enter them to quickly spread to other parts of the cell. Similarly, any wastes produced within a prokaryotic cell can quickly move out. However, larger eukaryotic cells have evolved different structural adaptations to enhance cellular transport. Indeed, the large size of these cells would not be possible without these adaptations. In general, cell size is limited because volume increases much more quickly than does cell surface area. As a cell becomes larger, it becomes more and more difficult for the cell to acquire sufficient materials to support the processes inside the cell, because the relative size of the surface area through which materials must be transported declines.
Figure 2. This figure shows the relative sizes of different kinds of cells and cellular components. An adult human is shown for comparison.
Section Summary
Prokaryotes are predominantly single-celled organisms of the domains Bacteria and Archaea. All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles. Many also have polysaccharide capsules. Prokaryotic cells range in diameter from 0.1–5.0 µm.
Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membrane-bound organelles that allow for compartmentalization of functions. Eukaryotic cells tend to be 10 to 100 times the size of prokaryotic cells.
Additional Self Check Question
1. Describe the structures that are characteristic of a prokaryote cell.
Answer
With today’s economy, property owners and managers face the daunting task of keeping their facility running safe and in decent shape. One of the most critical systems in a commercial facility is the roofing system. So, why jump into an investment without knowing the advantages and disadvantages of single-ply membrane roofing?
At West Roofing Systems, we have over 40 years of commercial roofing experience; we work with customers every day to decide what kind of roof is best for their facility.
While the choice is ultimately up to the building owner, we want to point out a few pros and cons to Single-Ply Membrane Roofing Systems.
The Basics
EPDM Roofing System
Single-Ply Membranes are sheets of rubber and other synthetics that can be ballasted or chemically adhered to insulation to create a layer of protection for your commercial facility.
There are two main types of single-ply membrane commercial roofing: Thermoplastic Polyolefin (TPO) and Ethylene Propylene Diene Terpolymer (EPDM). They differ in their chemical makeup, how they are installed and their energy efficiencies.
Read More: Single-Ply Membrane Commercial Roofing: Installation and Performance
Pros of Single-Ply Membrane Roofing
Proven Track Record
EPDM roofing has been used for commercial flat roofing for over 60 years. This amount of time on the market has allowed various laboratory and field studies to be performed and tracked. That’s why single-ply membrane roofing has a proven track record for being a high-performance roofing option.
TPO, while having more market share than EPDM, has not been on the market as long as EPDM. This means that TPO single-ply membrane roofing is still under testing and evolving into a more reliable roofing membrane.
Options for Insulation Materials
Since single-ply membrane roofing does not include the insulation factor, as a customer you have more options to choose from to insulate your facility’s roof. There are a few types of insulation options the facility manager/owner can to choose from:
- Polyisocyanurate (Polyiso) – The most used insulation type for roofing applications, Polyiso is more expensive but pay off with a higher R-value rating.
- Expanded Polystyrene (EPS) – With the highest R-value per dollar, EPS is used for roof, wall and floor insulation. EPS can be used for ground contact and does not retain water over time.
- Extruded Polystyrene (XPS) – Usually defined by the blue, green or pink color, XPS falls in-between Polyiso and EPS in the range of price and performance. XPS is semipermeable with a perm rating of 1.
Membrane Proxy
Choice of Reflective or Retentive Properties
TPO is fast growing in popularity across the commercial roofing market. Also, known as “White Roofs,” TPO is generally manufactured white and highly reflective. TPO is also available in tan, gray, green, blue and red.
On the other side of the spectrum, EPDM is often described as “Black Roofs,” due to the natural dark color of the membrane. This high-performance rubber compound provides excellent weatherability and heat retention beneficial for facilities located in climates with lower “cooling days”.
Easy Installation
Unlike the complexities involved with processing spray polyurethane foam roofing, installing single-ply membrane roofing is relatively simple.
After the existing substrate is prepared, either by cleaning or removing the existing roof, the insulation layers are installed and covered by a cover board.
There are three ways to attach the membrane to the cover board: ballasted, with an adhesive or mechanically fastened.
The significant difference between TPO and EPDM comes when it is time to adhere the membrane seams together. TPO uses a hot-air gun to melt down the membrane at the seams and fuse them together. EPDM is joined together with a seam tape.
Lightweight and Flexible
Even though there are multiple layers, and you can choose the thickness of the membrane installed on your roof. Overall single-ply membrane roofing is lightweight compared to other commercial flat roof systems. This relieves stress that’s put on your building’s structure. (Excluding ballasted systems)
The flexibility of the single-ply membranes allows the contractor to accommodate unique roof designs. This flexibility also allows the roofing systems to stay intact with expanding and contracting buildings.
Cons of Single-Ply Membrane Roofing
Membrane is Easily Punctured
While we explained in the paragraph above that single-ply membrane roofing is lightweight and flexible, that also leads us to our first con, the thin layers are easily punctured.
Single-ply membrane roofing does not have a hard-top layer to protect the synthetic rubber from dropped tools, gravel or loose screws from being pushed into the rubber membrane. This kind of damage could create holes in the rubber and insulation and be vulnerable to leaks.
Roofing Accessories
Membrane Protein Structure
TPO Single-Ply Membrane around Roof Penetration
Most commercial roofing systems have accessories attached such as A/C units, skylights, air vents, plumbing vents and more. These penetrations on the roof can be in the way of rolling out a straight section of membrane.
When the contractor approaches these penetrations with single-ply membrane roofing, they need to cut smaller membrane pieces to size and essentially building up the roof around the vents/units which takes up more time and is not as reliable in terms of being waterproof.
Seams are Vulnerable to Leaks
We covered in the installation explanation how the rubber membrane is rolled out, overlapped and fastened with either heat, mechanical fasteners, adhesives or tapes. Although these seams are sealed, they are more vulnerable to leaks than other roofing systems.
UV Rays
UV rays shine directly on the roof can degrade the adhesives quickly over time. This is what can make those seams vulnerable to leaks. If there’s a puncture, tear or other damage to the roof, the UV rays coming into the adhesive layer can cause more damage with the adhesives deteriorating.
Single-Ply Roofing Systems take up over half of the roofing systems for commercial, industrial, and manufacturing facilities that’re looking for a sustainable, economically efficient option.
At West Roofing Systems, our goal is to get you a long-lasting roof that’ll protect your facility. That includes working with our award-winning team to choose the best roofing systems to meet your needs.
Contact West Roofing Systems today to talk to our expert staff about your future Single-Ply Membrane Roofing System.
Author: Rufus West
Rufus West is a commercial roofing expert! You may see him on the West Roofing website and also on the West Roofing social media pages, giving fun facts and tips about the company and roofing industry.
Just like West Roofing System’s roof solutions, he isn’t bothered by water—it simply rolls off of his back!