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The Cell Wall

A detailed research project on the cell wall organelle.

Made By: Sarah Jisri | Course Code: SBI 4U0 | Class: Grade 12 University Prep. Biology | Project: Assignment #1 – Organelle Research Project

The organelle I chose is, as suggested above, the cell wall.

A picture of the cell wall visible in a plant cell

Brief Description:

Picture of the cell wall

Image: Close-up, microscopic image of moss leaf cells showing cell walls and chloroplasts.

Source:Thought Co.

  • Cell walls are found in plant cells, animal cells only contain the cell membrane.
    • Certain prokaryotes, algae, slime molds, water molds & fungi also have cell walls (Staehelin, 2019).
  • The cell wall borders the plasma membrane of plant cells.
  • It provides strength and protection against stresses such as mechanical stress and osmotic stress (Staehelin, 2019).
  • It also allows cells to develop turgor pressure (the pressure of the cell contents against the cell wall) (Nature, n.d.).

Location

  • The cell wall is found on the edge of the cell, it surrounds all the organelles located within the cell.
  • It is what separates the inside contents of the cell with the outer fluids.
  • It is located outside of the plasma membrane.
  • It does not move around, instead it stays in its place.

When is it found?

  • It is present and in the cell 24/7, it is always there.
  • It does not leave/exit the cell, nor does it move around.

How many are found?

  • There is only one cell wall organelle present in a cell.
  • However, there are layers to the cell wall. In all cell walls there are 2 main layers and most plants produce an additional layer (Staehelin, 2019).
    • The middle lamella
      • Acts as a cementing layer between the primary walls of adjacent cells (Staehelin, 2019).
    • The primary cell wall
      • It is the layer containing cellulose made by the dividing/growing cells. For cell wall expansion during growth, these walls are thinner & less rigid than cells that stopped growing (Staehelin, 2019).
      • Have a structural & supportive role only when the vacuoles are filled with water to where they exert turgor pressure against the cell wall (Staehelin, 2019).
    • + The secondary wall
      • A grown plant cell might keep its primary cell wall and sometimes thickening it, or it might make an additional, rigid layer, which is the secondary cell wall (Staehelin, 2019).
      • Responsible for most of the plant’s mechanical support and properties (Staehelin, 2019).
Picture of the layers of a cell wall exluding the secondary wall.

Functions

Major Function

  • There are many important functions of a cell wall, however the cell wall mainly functions as a barrier or wall between the inner cell contents and the outer contents, providing protection and stability/support to the cell.

Minor Functions

  • Helps the cell maintain it’s shape and rigidity
  • As previously stated, it also allows cells to develop turgor pressure (the pressure of the cell contents against the cell wall) (Nature, n.d.).
    • Turgor pressure is important because it prevents wilting and it helps with maintaining structure of the plant (Nature, n.d.).
  • Provides a porous medium for the diffusion, circulation & distribution of water, minerals, and other small nutrients (Staehelin, 2019).
  • Provides rigid and strong building blocks that can be used to make stable-higher order structures, including leaves and stems (Staehelin, 2019).
  • Provides a storage site of regulatory molecules which sense the presence of pathogens and control tissue development (Staehelin, 2019).
  • Provides cell – cell communication through the plasmodesmata (Bailey, 2019).
    • Plasmodesmata: Pores between plant cell walls that allow molecules & communication signals to pass between individual plant cells (Bailey, 2019)​.

What could happen should the organelle be removed from the cell?

  • The cell might become weaker, less stable and lose its shape.
  • It will not have the same protection as it used to, which means unwanted and potentially harmful substances can get in which might weaken the cell even further or cause the cell to collapse and eventually die.
  • Due to turgor pressure being absent, the cell will not handle the concentration of solution – whether it be a hypotonic or hypertonic solution – and will burst (Topper Learning, n.d.).
  • Important substances might not be able to enter and exit the cell which might also cause weakening and death.
  • If the cell wall is removed from the cell then all the functioning of all the cell organelles inside the cell would be affected because the diffusion of various substances would not happen (Topper Learning, n.d.).

Interaction with other organelles

  • Vesicles: They carry substances in and out of the cell, and so when they import substances into the cell they interact with the cell wall to deliver to the other organelles in the cell (Mentzer, 2019).
  • Plasma membrane: During synthesis and remodeling, the cell wall physically anchors to the plasma membrane through the cellulose fibrils & plasma membrane proteins that interact with cell wall components (Liu & Persson & Sánchez-Rodríguez, 2015).
  • Plasmodesma: Cell wall works with plasmodesma in apoplastic transport, which is transport through the layer outside the plasma membrane (apoplast), to transport gases (E.x. Carbon dioxide), or plant hormones and pheromones (biolabxy, n.d.) .

Why?

  • Vesicles: They have this interaction because vesicles bring in necessary substances to keep the cell running.
  • Plasma Membrane: This interaction is important for proteins to retain their localization at the plasma membrane for cell wall synthesis, remodeling & for signal transduction (Liu & Persson & Sánchez-Rodríguez, 2015).
  • Plasmodesma: They generate connections between the neighboring cells. They allow intercellular movement of molecules such as transcription factors, hormones, and sugars ( Hernández-Hernández & Benítez & Boudaoud, 2019).

What type of molecules is it composed of?

A picture of a glucose monomer and cellulose
  • The basic structural component of plant cell walls is primarily cellulose which is a carbohydrate. (Staehelin, 2019)
    • The cellulose fibers found in the cell wall are long and linear polymers of several thousand glucose molcules linked together (Staehelin, 2019).
      • The chemical links between individual glucose monomers give cellulose molecules a flat, ribbonlike structure which allows adjacent molecules to band together into microfibrils with lengths from 2 – 7 μm (micrometres) (Staehelin, 2019).
      • The cellulose fibrils are made by enzymes floating in the cell membrane (Staehelin, 2019).
    • The bonds present in cellulose and fiber molecules are Beta Glycosidic Bonds.
  • However cellulose is not the only component, the cell wall also consists of a water-saturated matrix of other polysaccharides and structuralglycoproteins (Staehelin, 2019).
    • The 2 major classes of matrix polysaccharides are hemicelluloses and pectic polysaccharides (a.k.a. pectin) (Staehelin, 2019).
      • Both of which are synthesized in the Golgi apparatus or Golgi body. They are then transported to the cell wall in vesicles, and secreted into the cell wall (Staehelin, 2019).
      • Hemicelluloses: Include glucose molecules connected together with the addition of short side chains of xylose & other uncharged sugars.
      • Pectic Polysaccharides: The linear backbone of all pectic polysaccharides is formed by negatively charged galacturonic acid residues & rhamnose sugar molecules. Attached to these are complex, branched sugar side chains (Staehelin, 2019).
        • Their negative charge allows them to bind tightly to positively charged ions (cations).
  • Bacterial cell walls contain peptidoglycan (Staehelin, 2019).
  • Algal cell walls are similar to plant cell walls. Many contain specific polysaccharides which are useful for taxonomy (Staehelin, 2019).
  • Fungal cell walls don’t have cellulose, instead they contain chitin (Staehelin, 2019).
Fungal cell wall which contains chitin instead of cellulose

How might they be important to the function of the cell.

  • Cellulose is important to the cell wall because it is important in aiding with keeping a cell stable and stiff and make sure it remains upright (BBC, 2019).
  • It helps the cell keep its rigidity and shape (ALevelBiology, 2020).
  • This is what makes a plant’s stem, leaves and branches strong (Study, n.d.).
  • In addition to the above, because of the strong cellulose fibers in the cell wall, plant cells don’t burst like animal cells when they’re in a hypotonic solution (ALevelBiology, 2020).
    • Hypotonic solution: A solution in which the concentration of the solute is higher inside the cell than outside. This causes water to diffuse into the cell resulting in the expansion of the cell.
    • The cellulose helps keep the cell alive and functioning properly.
  • Hemicelluloses: They have been shown to regulate and control the rate at which primary cell walls expand during growth (Staehelin, 2019).
  • Pectic Polysaccharides: They help with cell adhesion and wall hydration, and the pectin crosslinking plays a part in wall porosity and plant morphogenesis (Xiao & Anderson, 2013).

Analogy

The cell wall is similar to a screen door in a house.

Picture of a screen door
Picture of a screen door
Pictures of screen doors

Explanation

  • The screen door seems to represent the cell wall fairly well in terms of general functions in real life examples which is why I chose it.
  • However, it also doesn’t check all the boxes for the functions of the cell wall, especially the specific functions. This leaves a balance between the strengths and weaknesses and room to possibly have a stronger comparison.
  • In this case, the house represents the inside of the cell and the screen door represents the cell wall.

Strengths

  • The screen door acts a barrier/wall between the inside of the house and the outside of the house.
  • The screen door filters substances and things through, it only allows certain things inside while other things can’t enter. For example, Oxygen and air can enter the house; animals like birds, squirrels, & flies will not be able to come in through a functioning screen door.
  • Offers some sort of protection to the inhabitants of the house by keeping animals and possibly strangers out.

Weaknesses

  • Screen doors do not really act as strong structural support, they are more of an addition or a side door to the main door which has more necessity.
  • Does not offer turgor pressure or any sort of pressure for any purpose.
  • Does not provide storage for anything
  • Does not work as a “building block” for anything
  • Does not work as a way of communication as a cell wall does.

Deeper Organelle Interaction Research – Plasma Membrane

The Interactions Between The Cell Wall & The Plasma/Cell Membrane

PICTURE 1: Shows the different proteins located on the plasma membrane which help out and interact with the cell wall.

The synthesis and remodeling of the cell walls are membrane-related procedures. There is a continuous exchange of lipids, proteins & other cell wall components between the cytosol and the plasma membrane. This material exchange and the localization of cell wall proteins at specific spots in the plasma membrane rely on a particular composition of the membrane (refer to PICTURE 1). Also, sensors at the plasma membrane detect changes in the cell wall build, and activate cytoplasmic signaling schemes and cell wall remodeling. The apoplastic polysaccharide matrix is crucial for preventing proteins diffusing in the membrane uncontrollably (Liu & Persson & Sánchez-Rodríguez, 2015) .

Therefore, the cell wall–plasma membrane interaction is important for plant development and responses to external activities (Liu & Persson & Sánchez-Rodríguez, 2015).

What happens to the cell wall during Telophase in mitosis?

Picture showing what role the cell wall plays during telophase of mitosis.
  • Plants cells must develop new cell walls between the daughter cells during cell division (Lumen, n.d.).
  • However, before getting into telophase, it should be know that during interphase, the Golgi apparatus collects enzymes, structural proteins, & glucose molecules before breaking into vesicles and spreading out throughout the dividing cell (Lumen, n.d.).
  • Now, during telophase, these Golgi vesicles are transported on microtubules to form a phragmoplast – a vesicular structure – at the metaphase plate (Lumen, n.d.).
  • Then, the vesicles fuse and combine from the center toward the cell walls, this is now called a cell plate (Lumen, n.d.).
    • More vesicles will continue to fuse causing the cell plate to increase in size, then causing the cell plate to merge with the cell walls at the periphery of the cell (Lumen, n.d.).
  • Enzymes use accumulated glucose between the membrane layers to build the new cell wall (Lumen, n.d.).
  • The Golgi Membranes become parts of the plasma membrane on either side of the new cell (Lumen, n.d.).

Works Cited

Below are all my references in APA format: