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DIRECTIONS: as a group, read the article linked under your breakout group's number. Then fill in the following columns with information from your reading regarding the organelle you were assigned.

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DIRECTIONS: as a group, read the article linked under your breakout group's number. Then fill in the following columns with information from your reading regarding the organelle you were assigned.

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Cell Membrane

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The plasma membrane, or the cell membrane, provides protection for a cell. It also provides a fixed environment inside the cell, and that membrane has several different functions. One is to transport nutrients into the cell and also to transport toxic substances out of the cell. Another is that the membrane of the cell, which would be the plasma membrane, will have proteins on it which interact with other cells. Those proteins can be glycoproteins, meaning there's a sugar and a protein moiety, or they could be lipid proteins, meaning that there's a fat and a protein. And those proteins which stick outside of the plasma membrane will allow for one cell to interact with another cell. The cell membrane also provides some structural support for a cell. And there are different types of plasma membranes in different types of cells, and the plasma membrane has in it in general a lot of cholesterol as its lipid component. That's different from certain other membranes from within the cell. Now, there are different plants and different microbes, such as bacteria and algae, which have different protective mechanisms. In fact, they have a cell wall outside of them, and that cell wall is much tougher and is structurally more sound than a plasma membrane is.

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The cell membrane, also called the plasma membrane, is found in all cells and separates the interior of the cell from the outside environment.

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Cell Wall

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Cell Wall Definition

A cell wall is an outer layer surrounding certain cells that is outside of the cell membrane. All cells have cell membranes, but generally only plants, fungi, algae, most bacteria, and archaea have cells with cell walls. The cell wall provides strength and structural support to the cell, and can control to some extent what types and concentrations of molecules enter and leave the cell. The materials that make up the cell wall differ depending on the type of organism. The cell wall has evolved many different times among different groups of organisms.

Cell Wall Functions

The cell wall has a few different functions. It is flexible, but provides strength to the cell, which helps protect the cell against physical damage. It also gives the cell its shape and allows the organism to maintain a certain shape overall. The cell wall can also provide protection from pathogens such as bacteria that are trying to invade the cell. The structure of the cell wall allows many small molecules to pass through it, but not larger molecules that could harm the cell.

Cell Wall Structure

Plant Cell Walls

The main component of the plant cell wall is cellulose, a carbohydrate that forms long fibers and gives the cell wall its rigidity. Cellulose fibers group together to form bundles called microfibrils. Other important carbohydrates include hemicellulose, pectin, and liginin. These carbohydrates form a network along with structural proteins to form the cell wall. Plant cells that are in the process of growing have primary cell walls, which are thin. Once the cells are fully grown, they develop secondary cell walls. The secondary cell wall is a thick layer that is formed on the inside of the primary cell wall. This layer is what is usually meant when referring to a plant's cell wall. There is also another layer in between plant cells called the middle lamella; it is pectin-rich and helps plant cells stick together.

The cell walls of plant cells help them maintain turgor pressure, which is the pressure of the cell membrane pressing against the cell wall. Ideally, plants cells should have lots of water within them, leading to high turgidity. Whereas a cell without a cell wall, such as an animal cell, can swell and burst of too much water diffuses into it, plants need to be in hypotonic solutions (more water inside than outside, leading to lots of water entering the cell) to maintain turgor pressure and their structural shape. The cell wall efficiently holds water in so that the cell does not burst. When turgor pressure is lost, a plant will begin to wilt. Turgor pressure is what gives plant cells their characteristic square shape; the cells are full of water, so they fill up the space available and press against each other.

This diagram of a plant cell depicts the cell wall in green, surrounding the contents of the cell.

Algae Cell Walls

Algae are a diverse group, and the diversity in their cell walls reflects this. Some algae, such as green algae, have cell walls that are similar in structure to those of plants. Other algae, such as brown algae and red algae, have cellulose along with other polysaccharides or fibrils. Diatoms have cell walls that are made from silicic acid. Other important molecules in algal cell walls include mannans, xylans, and alginic acid.

Fungi Cell Walls

The cell walls of fungi contain chitin, which is a glucose derivative that is similar in structure to cellulose. Layers of chitin are very tough; chitin is the same molecule found in the rigid exoskeletons of animals such as insects and crustaceans. Glucans, which are other glucose polymers, are also found in the fungal cell wall along with lipids and proteins. Fungi have proteins called hydrophobins in their cell walls. Found only in fungi, hydrophobins give the cells strength, help them adhere to surfaces, and help control the movement of water into the cells. In fungi, the cell wall is the most external layer, and surrounds the cell membrane.

Bacteria and Archaea Cell Walls

The cell walls of bacteria usually contain the polysaccharide peptidoglycan, which is porous and lets small molecules through. Together, the cell membrane and cell wall are referred to as the cell envelope. The cell wall is an essential part of survival for many bacteria. It provides mechanical structure to bacteria, which are single-celled, and it also protects them from internal turgor pressure. Bacteria have higher concentration of molecules such as proteins within themselves as compared to their environment, so the cell wall stops water from rushing into the cell. Differences in cell wall thickness also make Gram staining possible. Gram staining is used for the general identification of bacteria; bacteria with thick cell walls are gram-positive, while bacteria with thinner cell walls are gram-negative.

While archaea are similar in many ways to bacteria, hardly any archaeal walls contain peptidoglycan. There are several different types of cell walls in archaea. Some are composed of pseudopeptidoglycan, some have polysaccharides, some have glycoproteins, and others have surface-layer proteins (called an S-layer, which can also be found in bacteria).

Cell membrane - A membrane found on the outside of all cells that separates them from the outside environment.

Turgor pressure - Water pressure inside cells.

Chitin - A polysaccharide that is a main component of fungal cell walls and also of the exoskeletons of certain animals like insects.

Quiz

1. Which is a function of the cell wall?
A. To maintain turgor pressure
B. To provide support to the cell
C. To control what molecules enter and exit the cell
D. All of the above

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Cell Wall - Definition, Function & Structure | Biology Dictionary

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A cell wall is an outer layer surrounding certain cells that is outside of the cell membrane. All cells have cell membranes, but generally only plants, fungi, algae, most bacteria, and archaea have cells with cell walls.

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Nucleus

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The cell nucleus acts like the brain of the cell. It helps control eating, movement, and reproduction. If it happens in a cell, chances are the nucleus knows about it. The nucleus is not always in the center of the cell. It will be a big dark spot somewhere in the middle of all of the cytoplasm (cytosol). You probably won't find it near the edge of a cell because that might be a dangerous place for the nucleus to be. If you don't remember, the cytoplasm is the fluid that fills cells.

Not all cells have a nucleus. Biology breaks cell types into eukaryotic (those with a defined nucleus) and prokaryotic (those with no defined nucleus). You may have heard of chromatin and DNA. You don't need a nucleus to have DNA. If you don't have a defined nucleus, your DNA is probably floating around the cell in a region called the nucleoid. A defined nucleus that holds the genetic code is an advanced feature in a cell.

The things that make a eukaryotic cell are a defined nucleus and other organelles. The nuclear envelope surrounds the nucleus and all of its contents. The nuclear envelope is a membrane similar to the cell membrane around the whole cell. There are pores and spaces for RNA and proteins to pass through while the nuclear envelope keeps all of the chromatin and nucleolus inside.

When the cell is in a resting state there is something called chromatin in the nucleus. Chromatin is made of DNA, RNA, and nuclear proteins. DNA and RNA are the nucleic acids inside of the cell. When the cell is going to divide, the chromatin becomes very compact. It condenses. When the chromatin comes together, you can see the chromosomes. You will also find the nucleolus inside of the nucleus. When you look through a microscope, it looks like a nucleus inside of the nucleus. It is made of RNA and protein. It does not have much DNA at all.

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Biology4Kids.com: Cell Structure: Cell Nucleus

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The cell nucleus acts like the brain of the cell. It helps control eating, movement, and reproduction. If it happens in a cell, chances are the nucleus knows about it. The nucleus is not always in the center of the cell. It will be a big dark spot somewhere in the middle of all of the cytoplasm (cytosol).

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Cytoplasm

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Definition: What is the Cytoplasm?

In cell biology, the cytoplasm is a highly viscous (gel-like) substance enclosed within the cell membrane. It is composed of water (about 85 percent), proteins (10 to 15 percent), lipids (2 to 4 percent), nucleic acids, inorganic salts and polysaccharides in smaller amounts.

Depending on the cell, cytoplasm may also contain occasional granules of inclusions (e.g. stored nutrients and pigments, etc). Apart from the cell membrane, which encloses all cell components, a majority of cell organelles ( ribosome, Golgi apparatus,
Endoplasmic Reticulum, etc) are located in the cytoplasm. For this reason, most of the metabolic activities occur within the cytoplasm.

* Organelles are also part of the cytoplasm.

* The cytoplasm makes up nine-tenths of the entire cell.

Some of the other functions of the cytoplasm include:

Recent discoveries regarding the cytoplasm:

· Depending on the activity, bacterial cytoplasm can display glass-like properties.

· Yolk segregation from the cytoplasm in fish embryo is crucial for the development of fish larva.

· The "atypical centriole" in the cytoplasm has been associated with infertility, birth defects, and miscarriages.

· Different cell organelles have a different "feel" or experience in the cytoplasm.

As previously mentioned, the cytoplasm is enclosed within the cell membrane as is the case with the other cell components/organelles. With regards to the specific location, however, this is dependent on the type of cell. For instance, in eukaryotic cells, the cytoplasm is located between the cell membrane/plasma membrane and the nuclear membrane.

Unlike prokaryotic cells, eukaryotic cells contain a membrane-bound nucleus. This nuclear envelope separates the nucleus from the other parts of the cell. As a result, the cytoplasm is restricted to the space between the nuclear membrane and the cell membrane.

Prokaryotes, on the other hand, lack a true nucleus ( DNA material contained in a nuclear membrane). As a result, there is no nuclear membrane separating genetic material (DNA) from the other components of the cell.

In prokaryotes, then, the cytoplasm occupies the entire cell environment (within the plasma membrane). In this case, all cellular components/organelles, including the genetic material, are suspended in the cytoplasm.

With regards to location, the cytoplasm is also divided into the two layers. These include the ectoplasm and the endoplasm. For the most part, the two are used to describe the cytoplasm of protozoa ( amoeba in particular) that varies in structure, location, and function.

- This is the outer layer of the cytoplasm in a eukaryotic cell (amoeba). As such, it is located just beneath or adjacent to the plasma membrane. In such cells and amoeba, this layer of the cytoplasm is clearly visible given its location.

Some of the main characteristics of the ectoplasm include:

Non-granulated

Less dense and thus more clear

Thin and superficial

Contains actin filaments in higher numbers (this provides the cell membrane with elastic support)

In amoeba, the ectoplasm plays an important role in locomotion. This is achieved through changes in the acidity and alkalinity of water in the ectoplasm.

Here, changes in alkalinity/acidity of the water cause the amount of water in the pseudopodium to change. As a result, the organism changes direction depending on the elongation or shortening of pseudopodium as a result of the concentration of water.

- Unlike the ectoplasm, the endoplasm is the inner layer of the cytoplasm. As such, it is located deeper in the cell where it surrounds the nucleus. It contains many granules (secretory vesicles) and is, therefore, denser compared to the ectoplasm.

Some of the other components of the endoplasm include:

Given that the endoplasm contains many of the organelles of the endomembrane system; it is the site of most of the processes that occur in a cell. As such, it significantly contributes to the various metabolic activities of the cells as well as cell division.

Like the ectoplasm, the endoplasm also plays an important role in locomotion. Here, the endoplasm flows and fills pseudopodium where it's converted into ectoplasm.

Change in the alkalinity or acidity of this fluid then changes the concentration of water making it possible for the organism to move in a particular direction (depending on the location of food substances).

As the ectoplasm in the pseudopodium cause the amoeba to move in one direction, ectoplasm at the tail end is slowly converted to endoplasm that contains more granules. This allows the cycle to continue making it possible for the organism to change direction depending on its needs.

Definition of Terms

- The cytosol is the intracellular fluid of the cytoplasm. It is largely composed of water (over 70 percent) and surrounds all organelles located/suspended in the cytoplasm. Some of the other components of cytosol include soluble molecules of varying size, proteins as well as dissolved ions.

Characteristics of cytosol:

7.0 -7.4 pH range

Viscosity similar to water

Less than 0.0002 mM of calcium ions concentration

High amount of charged macromolecules

As the intracellular fluid of the cytoplasm, the cytosol is involved in signal transduction originating from the cell membrane. It contributes to the transduction signaling from the plasma membrane to the nucleus (with the nucleus being the effective site).

Apart from its role in signaling, the cytosol is also involved in the transportation of metabolites (e.g. amino acids in eukaryotic cells) in addition to being the site of metabolic chemical reactions in prokaryotes.

* The difference between cytoplasm and cytosol lies in the fact that cytosol is the fluid (intracellular fluid) of the cell while cytoplasm consists of all cell components within the cell membrane (excluding the nucleus).

- Also known as the karyoplasm and nucleus sap, the nucleoplasm is a type of protoplasm contained within the nuclear membrane.

Like cytosol, nucleoplasm is largely composed of water, various molecules as well as dissolved ions. Apart from maintaining the shape and structure of the nucleus, nucleoplasm is also involved in the transportation of various material required for cell metabolism and other functions.

* Compared to cytosol (in the cytoplasm), the nucleoplasm is highly gelatinous.

* Prokaryotic cells do not have a nucleoplasm.

- Described as the basis of life upon its discovery, the term protoplasm is sometimes used to refer to the cytoplasm and the internal components of a cell in general. It consists of proteins, lipids, sugars, and starches (carbohydrates), phosphates, potassium, and sodium (inorganic salts) and water.

* Whereas cytoplasm includes cell components within the cell (excluding the nucleus) the term protoplasm is sometimes used to refer to all components within the cell including the nucleus.

Cytoplasmic Structure

As previously mentioned, the cytoplasm is mostly composed of water (water is the largest component). Apart from water, sugars, inorganic salts and other organic components, the cytoplasm is also composed of various organelles (which also form the endomembrane system) and the cytoskeleton.

The endomembrane system is composed of:

Cytoskeleton is composed of:

Different components of the cytoplasm have different functions that contribute to the proper functioning of the cell. Whereas the endomembrane systems play an important role in the transport of various materials, the cytoskeleton serves to support the structural integrity of the cell.

* Components of the cytoplasm are in continual flux and thus not stable (fixed in place).

Essentially, functions of the cytoplasm can be attributed to its components.

Some of these functions include:

The cytoplasm is involved in several forms of transportation. The endoplasmic reticulum and golgi apparatus, both components of the endomembrane system, are some of the systems involved in the transportation of material (proteins and lipids respectively) from one point to another in the cell.

On the other hand, the cytoplasm is also involved in the transportation and consequent removal of waste products from the cells through structures known as vesicles.

As already mentioned, the cytoplasm is a viscous matrix that is largely composed of water. By exerting an outward pressure (turgor pressure) against the cell membrane, it contributes to the general shape of the cell.

Apart from the pressure exerted by the fluid, the cytoplasm also contributes to the shape and structure of the cell through its cytoskeleton. As mentioned earlier, the cytoskeleton is composed of microtubules and microfilaments (as well as intermediate filaments).

As is the case with the skeletal system in higher animals, the cytoskeleton contributes to the shape of the cell at the plasma membrane.

Consisting of cytosol, a viscous fluid, the cytoplasm protects various components of the cell by acting as a cushion that absorbs some shock that may otherwise damage organelles.

Here, then, the cytoplasm serves to protect the internal components of the cell by acting as the barrier between the internal and external.

Various molecules (lipids, fats, starch, etc) can be found floating in the cytoplasm. Some of these molecules are used to build different structures of the cells. Before they are used, however, these molecules float in the cytoplasm where they are stored.

For this reason, some cells may contain high levels of given molecules in their cytoplasm. Adipocytes, for instance, are good examples of cells that store high amounts of lipids in their cytoplasm.

Several enzymes can be found in the cytoplasm. The cytoplasm, therefore, is also a site of metabolism for a number of substances. These activities, however, occur at a higher rate in such organelles as the mitochondria.

* It is worth noting that like the chloroplast and nucleus, the mitochondria is not part of the endomembrane system.

Some of the other functions of the cytoplasm include:

* When stained with Eosin, in histology, cell cytoplasm will appear pink in color.

More on cell staining here.

More on Prokaryotes and Eukaryotes
Return to Organelles main page Return to Cell Biology main page Return from Cytoplasm to MicroscopeMaster home

References

James N. Weiss. (2001). The Cytoplasm.

Lakna Panawala. (2017). Difference Between Cytoplasm and Nucleoplasm. ResearchGate.

Lakna Panawala. (2017). Difference Between Cytosol and Cytoplasm. ResearchGate.

Scott D. Kobayashi et al. (2003). Cytoplasmic Membrane Systems: Structure,

Function, and Membrane Trafficking.

https://www.sophia.org/tutorials/cytoplasm-structure-and-function

https://resources.saylor.org/wwwresources/archived/site/wp-content/uploads/2010/11/BIO101-Difference-Between-Cytosol-and-Cytoplasm.pdf

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Cytoplasm - Definition, Function, Structure and Location

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In cell biology, the cytoplasm is a highly viscous (gel-like) substance enclosed within the cell membrane. It is composed of water (about 85 percent), proteins (10 to 15 percent), lipids (2 to 4 percent), nucleic acids, inorganic salts and polysaccharides in smaller amounts. Depending on the cell, cytoplasm may also contain occasional granules of inclusions (e.g.

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Mitochondria

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Biology4Kids.com! This tutorial introduces mitochondria. Other sections include plants, animal systems, invertebrates, vertebrates, and microorganisms.

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Chloroplasts

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Chloroplasts are the food producers of the cell. The organelles are only found in plant cells and some protists such as algae. Animal cells do not have chloroplasts. Chloroplasts work to convert light energy of the Sun into sugars that can be used by cells. The entire process is called photosynthesis and it all depends on the little green chlorophyll molecules in each chloroplast.

Plants are the basis of all life on Earth. They are classified as the producers of the world. In the process of photosynthesis, plants create sugars and release oxygen (O ₂). The oxygen released by the chloroplasts is the same oxygen you breathe every day. Mitochondria work in the opposite direction. They use oxygen in the process of releasing chemical energy from sugars.

We'll hit the high points for the structure of a chloroplast. Two membranes contain and protect the inner parts of the chloroplast. They are appropriately named the outer and inner membranes. The inner membrane surrounds the stroma and the grana (stacks of thylakoids). One thylakoid stack is called a granum.

Chlorophyll molecules sit on the surface of each thylakoid and capture light energy from the Sun. As energy rich molecules are created by the light-dependent reactions, they move to the stroma where carbon (C) can be fixed and sugars are synthesized.

The stacks of thylakoid sacs are connected by stroma lamellae. The lamellae act like the skeleton of the chloroplast, keeping all of the sacs a safe distance from each other and maximizing the efficiency of the organelle. If all of the thylakoids were overlapping and bunched together, there would not be an efficient way to capture the Sun's energy.

The purpose of the chloroplast is to make sugars that feed the cell's machinery. Photosynthesis is the process of a plant taking energy from the Sun and creating sugars. When the energy from the Sun hits a chloroplast and the chlorophyll molecules, light energy is converted into the chemical energy found in compounds such as ATP and NADPH.

Those energy-rich compounds move into the stroma where enzymes fix the carbon atoms from carbon dioxide (CO ₂). The molecular reactions eventually create sugar and oxygen (O ₂). Plants and animals then use the sugars ( glucose) for food and energy. Animals also breathe the oxygen gas that is released.

Not all chlorophyll is the same. Several types of chlorophyll can be involved in photosynthesis. You will hear about chlorophyll a and b most often. All chlorophylls are varieties of green and have a common chemical structure called a porphyrin ring.

There are other molecules that are also photosynthetic. One day you might hear about carotenoids in carrots, phycocyanin in bacteria, phycoerythrin in algae, or fucoxanthin in brown algae. While these compounds might be involved in photosynthesis, they are not all green or the same structure as chlorophyll. Accessory pigments such as carotenoids and fucoxanthin pass absorbed light energy to neighboring chlorophyll molecules instead of using it themselves.

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Chloroplasts are the food producers of the cell. The organelles are only found in plant cells and some protists such as algae. Animal cells do not have chloroplasts. Chloroplasts work to convert light energy of the Sun into sugars that can be used by cells.

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Vacuole

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Vacuoles are storage bubbles found in cells. They are found in both animal and plant cells but are much larger in plant cells. Vacuoles might store food or any variety of nutrients a cell might need to survive. They can even store waste products so the rest of the cell is protected from contamination. Eventually, those waste products would be sent out of the cell.

The structure of vacuoles is fairly simple. There is a membrane that surrounds a mass of fluid. In that fluid are nutrients or waste products. Plants may also use vacuoles to store water. Those tiny water bags help to support the plant. They are closely related to objects called vesicles that are found throughout the cell.

In plant cells, the vacuoles are much larger than in animal cells. When a plant cell has stopped growing, there is usually one very large vacuole. Sometimes that vacuole can take up more than half of the cell's volume. The vacuole holds large amounts of water or food. Don't forge that vacuoles can also hold the plant waste products. Those waste products are slowly broken into small pieces that cannot hurt the cell. Vacuoles hold onto things that the cell might need, just like a backpack.

Vacuoles also play an important role in plant structure. Plants use cell walls to provide support and surround cells. The size of that cell may still increase or decrease depending on how much water is present. Plant cells do not shrink because of changes in the amount of cytoplasm. Most of a plant cell's volume depends on the material in vacuoles.

Those vacuoles gain and lose water depending on how much water is available to the plant. A drooping plant has lost much of its water and the vacuoles are shrinking. It still maintains its basic structure because of the cell walls. When the plant finds a new source of water, the vacuoles are refilled and the plant regains its structure.

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Vacuoles are storage bubbles found in cells. They are found in both animal and plant cells but are much larger in plant cells. Vacuoles might store food or any variety of nutrients a cell might need to survive. They can even store waste products so the rest of the cell is protected from contamination.

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A cell wall is the outermost layer of a cell. It separates the rest of the cell from other cells and/or the environment.

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Cytoplasm takes up the space in between other organelles of the cell. It is 90% of the cell and defines the shape.

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Outside the cell.

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The cell wall is generally found in plants, fungi, algae, most bacteria, and archaea.

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Everywhere there isn't an organelle.

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Found in both plant and animal cells. We think.

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Free floating around other organelles

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Mitochondria perform cellular respiration for the cell by breaking down nutrients into energy similar to digestion.

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Nucleus - membrane-bound organelle that contains the cell’s chromosomes.

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Both plant and animal, but more common in plants.

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Holds nutrients and waste.

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Nucleus - center of a cell

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Found within cells; membrane that covers it. Takes up about half of the whole cell.

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Are the food producers of the cell.

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They are located within the cytoplasm

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Mitochondria can be found in both

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Nucleus - Both plant and animal

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Found in plant cells and some protists such as algae.