Cells: Smallest Living Structures

SilverStallion · 14-06-2004, 05:20 AM

To understand genetics, you must first be farmiliar with cells and how they multiply.

CELL: THE BUILDING BLOCK OF LIFE

One of the fundamentals of fish biology is to know about the animal cell structure. Cells are the smallest living structure in living organisms, thus is the basic building block of multi-cellular organisms.

This is the organizational map:
Cells -> Tissue -> Organ -> System -> Organism

Here's how it works, using the human as an example:
Human body consist several systems working together. To name a few are the circulatory,respiratory, excretory, nervous, skeletal, muscle and lymphatic.

Each system consist of a series of organs working together, serving the same basic function. For example, the human circulatory system which basic function is to circulate the blood throughout the body is consist of the heart, arteries, veins and capilaries.

The organ is made up of a group if tissues performing a more specific function. For example, the heart is made up of different type of muscular tissues that expands and contract to create a pumping motion to pump the blood.

Finally, each tissue are a group if similar cells working together as a whole functioning unit.

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THE CELL

Now you know how an organism works, let's understand more about the cell itself.

Below is the diagram of cross section view of a generalised animal cell.

A cell mainly consist of three parts, nucleus, cytoplasm and surface membrane.

Nucleus is made up of:

nuclear envelope that surrounds the nucleus which seperates the nucleus contect from the cytoplasm
chromatin which is a network of thread-like structures that contains the heredity materials. They control the activities in the cell and undegoes condensation to become a multi-coiled structure called chromosomes during cell division. And lastly,
nucleolus, which involves in the contruction of proteins in cell.

Thus the nucleus is the control station of the cell which controls the activities of the cell and sent out specific instructions to other parts of the cell. They also contain the genetic materials that give rise to different traits that manifest the organism.

The cytoplasm forms the larger portion of the cell and is where most of the life processes take place. They contain organelles (subcellular structures found in cells which have specific functions):

mitochondria, also known as the "power house" of the cell. They are responsible to the release of energy from broken down food during respiration.
vacuoles, which is a fluid-filled space containing water and fod materials enclosed by a membrane.
a pair of centrioles that plays a vital role in cell divison.

With all these organelles, the cell is able to respire and perform most of the biochemical processes.

Both the nucleus and cytoplasm is envelope by a layer of cell membrane that is partially-permeable. It controls the subtance going in or out of the cell. As it is partially-permeable, only certain subtance can pass through while the rest cannot.

From a basic cell (called stem cell), they can differentiate into more specialised cells that performs specialised functions, thus give rises to different tissues. Some examples of specialised cells are red blood cells, muscle cells and skin cells.

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We've reached the end of the topic. Hope you have a better understanding of the cells and the structures.

Feel free to discuss with me about the topic.

And lastly, the pictures above is either taken or drawn by me, so do ask for permission or credit it of you're gonna use it. Thanks ^_^

Angel

14-06-2004, 06:12 AM

Hi angel...
this is indeed very inspiring...
good science lesson for many bros here.
You seem very well versed in the bio aspects.
Cool...

Anyway with respect to the cell I do have a few questions to ask.
One for freshwater and one for marine apparently.

We all now know the basic structure of cells tissues and systems right.
The first question would be for planted tanks actually here goes.

Plant leaves are covered by a waxy layer called the cuticle, this prevents water loss and protects the plant cells from invasion of pathogenic organisms like bacteria, some protozoanz and plant viruses. The cuticle also acts as a physical barrier to chemical substances. Gaseous exchange in plants is conducted via the stomata of in the leaves of hte plants and even in aquatic plants the spaces in the spongy mesophyll layer after the stomata are also air filled. This prevents loss of ions from the cells and improves osmotic control for the plants. Prevention of direct contact of the cell plasma membrane from the liquid media in this case water, also prevents pathogenic organisms from invading the cell... this is important as the cells in the spongy mesophyll layer are not lined with cuticle since their purpose is actually for gaseous exchange. The cellulose cell wall of plants provide almost no protection against the abovementioned so far as they are actually highly porous. The air space in the mesophyll layers actually makes plants float and grow upwards.

Ok now my question is, we use liquid fertilisers for aquatic plants and understand that not all plants require base fertilisers. It is also understood that many aquatic plants are able to absorb these nutrients through their leaves. What I don't understand is how this is possible. The plasma membrane itself is essentially a phospholipid bilayer and has a hydrophobic core. This actually prevents hydrophilic substances like ions and most other water soluble compounds from passing through the plasma membrane. This is important in control of the cell's osmotic potential and ions will not be lost easily to surroundings. Water however can enter and leave the cell easily. Thus we have plasmolysed and turgid cells at different solutions as learnt in science I think sec2. The liquid fertiliser we add into the water actually consists of many different types of compounds and trace elements dissolved in solution in ionic form. So how is it actually possible for the plant to absorb the nutrients in the fertiliser if ions are not able to pass through the plasma membrane? Is there any mechanism to explain this process? Ions are hydrophilic and logically are not able to pass through your selectively permeable membrane. Also since the plant cells are protected by an air space in the mesophyll layers and the cuticle layer on the leaf surface, even if ions are able to pass through the plasma membrane by some mean which I do not yet understand, how does the ions in the solution contact the permeable region of the leaves? Ions will have to contact the plasma membrane before entering the cell right?

Sorry for the long long post just wanna understand more about liquid fertilisers and how effective they are if not I just add and add and eventually ifd the plant doesn't really absord it I'll accumulate all the fertiliser in my water.

Ermmmm... this post is rather long maybe I'll post my question about the marine one some other time.

SilverStallion · 14-06-2004, 06:19 AM

Quote:

Originally Posted by ryzcris

Hi angel...
this is indeed very inspiring...
good science lesson for many bros here.
You seem very well versed in the bio aspects.
Cool...

Anyway with respect to the cell I do have a few questions to ask.
One for freshwater and one for marine apparently.

We all now know the basic structure of cells tissues and systems right.
The first question would be for planted tanks actually here goes.

Plant leaves are covered by a waxy layer called the cuticle, this prevents water loss and protects the plant cells from invasion of pathogenic organisms like bacteria, some protozoanz and plant viruses. The cuticle also acts as a physical barrier to chemical substances. Gaseous exchange in plants is conducted via the stomata of in the leaves of hte plants and even in aquatic plants the spaces in the spongy mesophyll layer after the stomata are also air filled. This prevents loss of ions from the cells and improves osmotic control for the plants. Prevention of direct contact of the cell plasma membrane from the liquid media in this case water, also prevents pathogenic organisms from invading the cell... this is important as the cells in the spongy mesophyll layer are not lined with cuticle since their purpose is actually for gaseous exchange. The cellulose cell wall of plants provide almost no protection against the abovementioned so far as they are actually highly porous. The air space in the mesophyll layers actually makes plants float and grow upwards.

Ok now my question is, we use liquid fertilisers for aquatic plants and understand that not all plants require base fertilisers. It is also understood that many aquatic plants are able to absorb these nutrients through their leaves. What I don't understand is how this is possible. The plasma membrane itself is essentially a phospholipid bilayer and has a hydrophobic core. This actually prevents hydrophilic substances like ions and most other water soluble compounds from passing through the plasma membrane. This is important in control of the cell's osmotic potential and ions will not be lost easily to surroundings. Water however can enter and leave the cell easily. Thus we have plasmolysed and turgid cells at different solutions as learnt in science I think sec2. The liquid fertiliser we add into the water actually consists of many different types of compounds and trace elements dissolved in solution in ionic form. So how is it actually possible for the plant to absorb the nutrients in the fertiliser if ions are not able to pass through the plasma membrane? Is there any mechanism to explain this process? Ions are hydrophilic and logically are not able to pass through your selectively permeable membrane. Also since the plant cells are protected by an air space in the mesophyll layers and the cuticle layer on the leaf surface, even if ions are able to pass through the plasma membrane by some mean which I do not yet understand, how does the ions in the solution contact the permeable region of the leaves? Ions will have to contact the plasma membrane before entering the cell right?

Sorry for the long long post just wanna understand more about liquid fertilisers and how effective they are if not I just add and add and eventually ifd the plant doesn't really absord it I'll accumulate all the fertiliser in my water.

Ermmmm... this post is rather long maybe I'll post my question about the marine one some other time.

As you know that the plant cells have cell walls (animal cells don't have this) and also the cell membrane. Cell wall functions as a support for the cell and the whole plant. it is fully permeable which means all molecules can pass through it.
next is the cell membrane, which is layer that controls the materials entering and exiting.

At the cell membrane, 2 kinds of tranportation takes place, passive transport and active transport.

Under passive transport, there's 2 forms of Diffusion, simple diffusion and facilitated diffusion

Simple difussion transports molecules small enough to pass through the bi-lipid layer. Those molecule which is highly polar can pass through the membrane with the help of special proteins that forms a channel across the bi-lipid layer. thus polar molecules can pass through the membrane without trouble.

next is facilitated diffusion. Facilitaed difussion moves large, lipid-soluble molecules across the membrane with the aid of protein carriers. the molecule binds to the carriers and initiated a structural change in the protein, thus the molecule is released into the cell.

Lastly, is Active transport process. this is where molecules is "pump" in or out of the cell with the expenditure of energy.

Thus, even when ion/molecules are too polar to pass through the bi-lipid layer, there are mechanisms that allow polar ions/molecules to pass through.

There's more http://www.arofanatics.com/forums/sh...99&postcount=7

Angel

14-06-2004, 06:30 AM

how is active transport carried out by the phospholipid bilayer??

I understand that active transport is only neccessary if the concentration of the ions in the surrounding liquid is lower than that in the cell. What mechanism then does the phospholipid bilayer employ to ensure that there is no backflow of ions back into the surrounding liquid?

The ions in the cytoplasm, how are they stored?

How does the Phospholipid bilayer select what it wants to allow through?

What vital role do the centrioles play in cell division?

I understand that cells divide thru two different means, namely Mitosis and Meiosis. Do the neucleus/centrioles behave differently during these two different cell division process??

Sorryu for bombarding u with these question... just wnted to know the answers... hope I can comprehend ur cheem cheem tecnical answers... lol

SilverStallion · 14-06-2004, 07:21 AM

Quote:

Originally Posted by SGRay

how is active transport carried out by the phospholipid bilayer??

I understand that active transport is only neccessary if the concentration of the ions in the surrounding liquid is lower than that in the cell. What mechanism then does the phospholipid bilayer employ to ensure that there is no backflow of ions back into the surrounding liquid?

The ions in the cytoplasm, how are they stored?

How does the Phospholipid bilayer select what it wants to allow through?

What vital role do the centrioles play in cell division?

I understand that cells divide thru two different means, namely Mitosis and Meiosis. Do the neucleus/centrioles behave differently during these two different cell division process??

Sorryu for bombarding u with these question... just wnted to know the answers... hope I can comprehend ur cheem cheem tecnical answers... lol

how is active transport carried out by the phospholipid bilayer??
Active tranport is carried out by protein carriers found embeded in the phospholipid bilayer. In the presence of ATP (cell's energy currency) and the substance, both ATP and substance will bind to the carrier and with the aid of phosphate, the protein carrier changes comformation and expels the substance into or out of the cell. With the loss of phosphate, the carrier restores to its original structure and the cycle repeats.

I understand that active transport is only neccessary if the concentration of the ions in the surrounding liquid is lower than that in the cell. What mechanism then does the phospholipid bilayer employ to ensure that there is no backflow of ions back into the surrounding liquid?
Substance-protein specificity

The ions in the cytoplasm, how are they stored?
Ions are not stored, they simply cycle in and out of the cell. Ions are important for biochemical processes as they are a form of cellular regulation

How does the Phospholipid bilayer select what it wants to allow through?
Simple Diffusion do not select what enters or not. as long as the molecule is small enough and is non-polar, it can just enter the cell. That is why some toxins can enter the cell without trouble.

and since facilitated diffusion and active transport rely on proteins, the proteins controls the type of molecules moving in and out. This is called Substrate Specificity.

What vital role do the centrioles play in cell division?
Centrioles are an organelle that is made up of microtubules. during cell division, contrioles direct the formation of mitotic spindles. These mitotic spindles will then attach themselves to the chromosomes and "pull" the pair of chromatids apart, to two opposite ends.

I understand that cells divide thru two different means, namely Mitosis and Meiosis. Do the neucleus/centrioles behave differently during these two different cell division process??
Nucleus after mitosis will retain the same number of chromosomes whereas after meiosis, the number of chromosomes will half.
Centrioles generally just functions to seperate and move the chromatids to opposite poles. but at the end of meiosis I, the centrioles will split into 2 pairs and proceeds into meiosis II.

thus, at the end of mitosis, there will be 2 sister cells with the same number of chromosomes as the parent.
whereas at the end of meiosis, there will be 4 gametes with half the chromosome number as compared to the parent cell

14-06-2004, 07:37 AM

substance protein specificity? elaborate pls. My bio not good.

hmm... if the ions are not stored, that means the ions taken in thru active transport can still move out of the cell thru passive transport?this means that the rate of active transport must be so fast that it superceeds that of diffusion? wouldn't that expend a lot of energy?

You studying aborad? how old are u?

SilverStallion · 14-06-2004, 07:41 AM

Quote:

Originally Posted by SilverStallion

As you know that the plant cells have cell walls (animal cells don't have this) and also the cell membrane. Cell wall functions as a support for the cell and the whole plant. it is fully permeable which means all molecules can pass through it.
next is the cell membrane, which is layer that controls the materials entering and exiting.

At the cell membrane, 2 kinds of tranportation takes place, passive transport and active transport.

Under passive transport, there's 2 forms of Diffusion, simple diffusion and facilitated diffusion

Simple difussion transports molecules small enough to pass through the bi-lipid layer. Those molecule which is highly polar can pass through the membrane with the help of special proteins that forms a channel across the bi-lipid layer. thus polar molecules can pass through the membrane without trouble.

next is facilitated diffusion. Facilitaed difussion moves large, lipid-soluble molecules across the membrane with the aid of protein carriers. the molecule binds to the carriers and initiated a structural change in the protein, thus the molecule is released into the cell.

Lastly, is Active transport process. this is where molecules is "pump" in or out of the cell with the expenditure of energy.

Thus, even when ion/molecules are too polar to pass through the bi-lipid layer, there are mechanisms that allow polar ions/molecules to pass through.

Angel

just to add on, the function of the cuticle is to prevent water loss. One of the adaptation of a fullysubmerged water plant is that they show no or little sign of cuticle forming, since it is not a problem for water plants to lose water in their aquatic environments.

as for floating plants,the thick waxy cuticle to repel water, to keep the stomata open and clear. and most of the soluble nutrient absorption is done by the roots.

14-06-2004, 07:46 AM

Quote:

Originally Posted by SilverStallion

just to add on, the function of the cuticle is to prevent water loss. One of the adaptation of a fullysubmerged water plant is that they show no or little sign of cuticle forming, since it is not a problem for water plants to lose water in their aquatic environments.

as for floating plants,the thick waxy cuticle to repel water, to keep the stomata open and clear. and most of the soluble nutrient absorption is done by the roots.

from ryzcris:
Plant leaves are covered by a waxy layer called the cuticle, this prevents water loss and protects the plant cells from invasion of pathogenic organisms like bacteria, some protozoanz and plant viruses. The cuticle also acts as a physical barrier to chemical substances. Gaseous exchange in plants is conducted via the stomata of in the leaves of hte plants and even in aquatic plants the spaces in the spongy mesophyll layer after the stomata are also air filled. This prevents loss of ions from the cells and improves osmotic control for the plants. Prevention of direct contact of the cell plasma membrane from the liquid media in this case water, also prevents pathogenic organisms from invading the cell... this is important as the cells in the spongy mesophyll layer are not lined with cuticle since their purpose is actually for gaseous exchange. The cellulose cell wall of plants provide almost no protection against the abovementioned so far as they are actually highly porous. The air space in the mesophyll layers actually makes plants float and grow upwards.

so aquatic plants have little or no protection against pathogens, protozoans and parasites?

SilverStallion · 14-06-2004, 07:46 AM

Quote:

Originally Posted by SGRay

substance protein specificity? elaborate pls. My bio not good.

hmm... if the ions are not stored, that means the ions taken in thru active transport can still move out of the cell thru passive transport?this means that the rate of active transport must be so fast that it superceeds that of diffusion? wouldn't that expend a lot of energy?

You studying aborad? how old are u?

substance protein specificity? elaborate pls. My bio not good.
If you understand the Lock-and-key theory of enzymes, understanding this is no problem. the protein only reacts when a substrate specific to it is present.

hmm... if the ions are not stored, that means the ions taken in thru active transport can still move out of the cell thru passive transport?this means that the rate of active transport must be so fast that it superceeds that of diffusion? wouldn't that expend a lot of energy?
Related to above, since proteins are substrate specific, the problem of backflow is solved.

14-06-2004, 07:51 AM

I see... being highly specific the proteins can only take in certain kinds of ions. Thus limiting them?

I see, the ions cannot bond with the inner lipid layer... got it.

14-06-2004, 05:20 AM	#1
SilverStallion Dragon Join Date: Jan 2003 Posts: 2,082	Cells: Smallest Living Structures To understand genetics, you must first be farmiliar with cells and how they multiply. CELL: THE BUILDING BLOCK OF LIFE One of the fundamentals of fish biology is to know about the animal cell structure. Cells are the smallest living structure in living organisms, thus is the basic building block of multi-cellular organisms. This is the organizational map: Cells -> Tissue -> Organ -> System -> Organism Here's how it works, using the human as an example: Human body consist several systems working together. To name a few are the circulatory,respiratory, excretory, nervous, skeletal, muscle and lymphatic. Each system consist of a series of organs working together, serving the same basic function. For example, the human circulatory system which basic function is to circulate the blood throughout the body is consist of the heart, arteries, veins and capilaries. The organ is made up of a group if tissues performing a more specific function. For example, the heart is made up of different type of muscular tissues that expands and contract to create a pumping motion to pump the blood. Finally, each tissue are a group if similar cells working together as a whole functioning unit. -------------------------------------------------------------------------------- THE CELL Now you know how an organism works, let's understand more about the cell itself. Below is the diagram of cross section view of a generalised animal cell. A cell mainly consist of three parts, nucleus, cytoplasm and surface membrane. Nucleus is made up of: nuclear envelope that surrounds the nucleus which seperates the nucleus contect from the cytoplasm chromatin which is a network of thread-like structures that contains the heredity materials. They control the activities in the cell and undegoes condensation to become a multi-coiled structure called chromosomes during cell division. And lastly, nucleolus, which involves in the contruction of proteins in cell. Thus the nucleus is the control station of the cell which controls the activities of the cell and sent out specific instructions to other parts of the cell. They also contain the genetic materials that give rise to different traits that manifest the organism. The cytoplasm forms the larger portion of the cell and is where most of the life processes take place. They contain organelles (subcellular structures found in cells which have specific functions): mitochondria, also known as the "power house" of the cell. They are responsible to the release of energy from broken down food during respiration. vacuoles, which is a fluid-filled space containing water and fod materials enclosed by a membrane. a pair of centrioles that plays a vital role in cell divison. With all these organelles, the cell is able to respire and perform most of the biochemical processes. Both the nucleus and cytoplasm is envelope by a layer of cell membrane that is partially-permeable. It controls the subtance going in or out of the cell. As it is partially-permeable, only certain subtance can pass through while the rest cannot. From a basic cell (called stem cell), they can differentiate into more specialised cells that performs specialised functions, thus give rises to different tissues. Some examples of specialised cells are red blood cells, muscle cells and skin cells. -------------------------------------------------------------------------------- We've reached the end of the topic. Hope you have a better understanding of the cells and the structures. Feel free to discuss with me about the topic. And lastly, the pictures above is either taken or drawn by me, so do ask for permission or credit it of you're gonna use it. Thanks ^_^ Angel Last edited by SilverStallion; 14-06-2004 at 01:56 PM.

14-06-2004, 06:30 AM	#4
SGRay Guest Posts: n/a	how is active transport carried out by the phospholipid bilayer?? I understand that active transport is only neccessary if the concentration of the ions in the surrounding liquid is lower than that in the cell. What mechanism then does the phospholipid bilayer employ to ensure that there is no backflow of ions back into the surrounding liquid? The ions in the cytoplasm, how are they stored? How does the Phospholipid bilayer select what it wants to allow through? What vital role do the centrioles play in cell division? I understand that cells divide thru two different means, namely Mitosis and Meiosis. Do the neucleus/centrioles behave differently during these two different cell division process?? Sorryu for bombarding u with these question... just wnted to know the answers... hope I can comprehend ur cheem cheem tecnical answers... lol Last edited by SGRay; 14-06-2004 at 06:40 AM.

14-06-2004, 06:12 AM	#2
ryzcris Guest Posts: n/a	Hi angel... this is indeed very inspiring... good science lesson for many bros here. You seem very well versed in the bio aspects. Cool... Anyway with respect to the cell I do have a few questions to ask. One for freshwater and one for marine apparently. We all now know the basic structure of cells tissues and systems right. The first question would be for planted tanks actually here goes. Plant leaves are covered by a waxy layer called the cuticle, this prevents water loss and protects the plant cells from invasion of pathogenic organisms like bacteria, some protozoanz and plant viruses. The cuticle also acts as a physical barrier to chemical substances. Gaseous exchange in plants is conducted via the stomata of in the leaves of hte plants and even in aquatic plants the spaces in the spongy mesophyll layer after the stomata are also air filled. This prevents loss of ions from the cells and improves osmotic control for the plants. Prevention of direct contact of the cell plasma membrane from the liquid media in this case water, also prevents pathogenic organisms from invading the cell... this is important as the cells in the spongy mesophyll layer are not lined with cuticle since their purpose is actually for gaseous exchange. The cellulose cell wall of plants provide almost no protection against the abovementioned so far as they are actually highly porous. The air space in the mesophyll layers actually makes plants float and grow upwards. Ok now my question is, we use liquid fertilisers for aquatic plants and understand that not all plants require base fertilisers. It is also understood that many aquatic plants are able to absorb these nutrients through their leaves. What I don't understand is how this is possible. The plasma membrane itself is essentially a phospholipid bilayer and has a hydrophobic core. This actually prevents hydrophilic substances like ions and most other water soluble compounds from passing through the plasma membrane. This is important in control of the cell's osmotic potential and ions will not be lost easily to surroundings. Water however can enter and leave the cell easily. Thus we have plasmolysed and turgid cells at different solutions as learnt in science I think sec2. The liquid fertiliser we add into the water actually consists of many different types of compounds and trace elements dissolved in solution in ionic form. So how is it actually possible for the plant to absorb the nutrients in the fertiliser if ions are not able to pass through the plasma membrane? Is there any mechanism to explain this process? Ions are hydrophilic and logically are not able to pass through your selectively permeable membrane. Also since the plant cells are protected by an air space in the mesophyll layers and the cuticle layer on the leaf surface, even if ions are able to pass through the plasma membrane by some mean which I do not yet understand, how does the ions in the solution contact the permeable region of the leaves? Ions will have to contact the plasma membrane before entering the cell right? Sorry for the long long post just wanna understand more about liquid fertilisers and how effective they are if not I just add and add and eventually ifd the plant doesn't really absord it I'll accumulate all the fertiliser in my water. Ermmmm... this post is rather long maybe I'll post my question about the marine one some other time.

14-06-2004, 07:37 AM	#6
SGRay Guest Posts: n/a	substance protein specificity? elaborate pls. My bio not good. hmm... if the ions are not stored, that means the ions taken in thru active transport can still move out of the cell thru passive transport?this means that the rate of active transport must be so fast that it superceeds that of diffusion? wouldn't that expend a lot of energy? You studying aborad? how old are u?

14-06-2004, 07:51 AM	#10
SGRay Guest Posts: n/a	I see... being highly specific the proteins can only take in certain kinds of ions. Thus limiting them? I see, the ions cannot bond with the inner lipid layer... got it.

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