This matrix contains a variety of enzymes and mitochondria ribosome’s to aid ATP synthesis and transportation.
Endoplasmic Reticulum (see fig 6) – Is easier to understand if you were to see it as a conveyor belt of a cell, taking proteins etc to and from other organelles within the cell and out of it. Smooth ER looks different to rough ER as it has no ribosome’s attached so quite simply it is called smooth ER because it has a smooth and not rough appearance. Smooth ER looks like layered sacs (fig 26) that have been flattened and it will always be found near or attached to the nucleolus via the nuclear envelope and contains glucose/energy for the other organelles. It is formed in such a way (tubules and vesicles creating a network) this increases the surface area allowing the storage of enzymes and proteins. Vesicles are formed when part of the membrane pinches off the ER to transport to the Golgi. Its main function apart from storage and acting as conveyor belt is the production of lipids and steroids. It also detoxifies certain toxins (drugs)
Lysosomes (see fig 7) are organelles in the cell. They may be small but are vitally important. They are spherical shaped and look like little sacks, each contains a high volume of digestive enzymes. They basically digest/get rid of other bad organelles or redundant parts that could potentially be harmful to the cell itself. Also in white blood cells, Lysosomes digest the bacteria those cells may contain.
Without Lysosomes the host would fill with dead cells and the hosts body would become contaminated which could have a possibly negative affect such as death of the host, whether the host is animal or plant.
Lysosomes work in such a way, when the cell absorbs food the Lysosomes go immediately to work by attaching enzymes and releasing them to break down complex molecules. The enzymes that are attached and used must be kept separate from the rest of the cell and only focused and used on what needs to be digested. This is done by the Lysosome by keeping these enzymes inactive within its sack which also has an alkaline environment.
You will find more Lysosomes within a cell that needs high Phagocyte activity (digestion of waste matter) Lysomomes are perfectly suited for their function, as they contain the material to destroy waste, seperateing this material from the rest of the cell affectivly, but when needed is able to focus upon a spcific body/object and apply the digestive material and destroy it. They are natures perfect little bin.
The Cytoskeleton is a network of protien fibres that mesh and network there way through the cell itself. The Cytoskeleton is found throughout the cell within the cytoplasm, it is attached to the plasma membrane and internal organelles. It is both a muscle and a skeleton, it is not static and changes shape and length with the accordance of what is required from it. The fibres themsleves that make up the cytskeleton structual bases are actually three kinds of protien filaments and micrtubules (Fig 12). Actin filamments(also called microfilaments)Intermediate filaments and microtubles. In reference to the cytoskeleton interestingly enough a cell such as an amoeba (Fig 9) changes shape by dismantling its cytoskelteon and rebuilding it elsewhere.
The cytoskeleton not only gives the cell structure but also helps to protect the cell. It enables the cell to be able to move as needed. This is done by the microtubules within the cystskeleton sliding against each other causing the structure itself to move and bend. These micrtubules and microfilaments within the cytoskeleton also aid the process of exotysosis (the process by which the cell secretes vesicles out of the cell membrane containing proteins etc other parts of the body may need) also the microtubules play a key role in intracellular transportation ( specifically directing proteins to other parts of, or through internal cell structures)
Golgi apparatus (fig 10 also fig 11) modifies simple molecules into more complex molecules and looks like flattened pancakes it is part of the membrane system within the cell. What look like flattened pancakes are actually small sacs that collect process and sort molecules such as proteins from rough ER by enclosing them into Golgi vesicles ready to transport to other parts of the cell or out of the cell in a process that is called secretion.
The Golgi apparatus changes proteins for example and brings them to the cell surface membrane where they can be secreted; the secretion it brings to the surface can vary from hormones, enzymes antibodies and other molecules. It is comparable to a factory, its role is to package and to transport proteins from for example rough ER to the outside if the cell, Golgi bodies are made of membrane bound sacks known as Cisternae. Golgi vesicles are also used in the production of Lysosomes. As well as the functions that have been mentioned here also the Golgi is involved in lipid modification. The Golgi body normally resides between the nucleolus and the cell membrane, making it perfect for its function of transport as well as processing.
The Cell Membrane and its functions
Part2/Unit1 by Kendra Pinder
The Cell surface (Plasma) membrane (Fig 13) is made up if a double layered sheet that is formed from phospholipid molecules. This is called a bi layer which is the main structure of the membrane itself. Each phospholipid molecule has a head and two tails (fig 14) they are hydrophobic and so do not react well to the solution of water. The structure of these molecules forms a hydrophobic interior, protecting the cell itself from the external water outside of its environment. The membrane itself is semi permeable and selective of what it allows in and out through the layer itself.
Phospholipid Molecules are not fixed and are infact moveable, this movement itself is determined by diffusion within their own mono layer. Within the bi-layer itself there are protein molecules, some fix themselves to structures that are contained within the layer (Fig 17) for example surface proteins act as markers to identify a cell to other cells. Transport proteins are used in diffusion. Other molecules float around and used when they are needed and provide their own functions for the cell to make use of. Within the bi-layer you will also find cholesterol which also aids stabilisation to the cell structure as well as providing a protective barrier along with the phospholipid molecules.
By functioning in such a way, not only does the cell membrane allow for import and export of specific chemicals and proteins that each individual cell needs, the construction of the phospholipid molecules and cholesterol are protection from the cells external environment.
Diffusion is the movement of molecules in a random fashion moving through semi permeable membrane (fig 15) the process starts from a high concentration to a low concentration of molecules until they are distributed equally. This is a passive process (no energy needed) for the process of diffusion to take place. But the diffusion rates process itself is affected by other factors. These factors being immediately the membrane surface (steepness of gradient), which determines which molecules by size, etc passes through and what rate. If the surface of the membrane is larger, this allows a denser amount of molecules to pass as one time. Temperature is also a factor in diffusion process, affecting the molecules that trying to pass through than affecting the membrane itself. Molecules and ions have more kinetic energy when the temperature sis higher. This then affects the motion of each molecule from external forces (in this case temperature) means a faster transference through the membrane, meaning faster diffusion.
The size of the molecule will affect the diffusion process; some molecules that are larger in size will need help to pass through the membrane. This is called facilitated diffusion. For example Glucose can not diffuse through a phospholipid bi-layer. It can only cross the membrane by passing through hydrophilic channels; this is done by protein molecules creating channels for this larger molecule to pass through the membrane and into the cell itself. (fig 18) The easiest way to explain this process in basic form, it is literally like someone opening a door to a sealed room to allow entry to just one person.
There are many doorways (channels) into a cell, but only certain molecules are allowed through very specific doorways (channels) controlled and regulated by various proteins. This not only means the membrane itself is selective, but also the channels in which it allows entry to specific molecules.
Osmosis is the movement of water passing through a semi permeable membrane from high solvent (a substance that dissolves another substance) amount of water, to a lower solvent amount of water this is a passive process(fig 19) If the solution has a greater solute (the substance that is within an amount of water) than that of the cell, this is call hypertonic, in other words a greater amount of larger molecules on one side of the membrane than there is inside the membrane, causing an increased pressure to the other side. If the solution has the same solute as that of the cell, the molecules are trying to enter then the rate at which the water moves in and out will be balanced and so no levels to the cells water level will change. If the solution is less solute (more water, less substance) than contained within the cell, the water will move into the cell causing it to expand (fig 20)
Although the osmosis process is the same in both animal and plant cells there are two clear different affects this process has on the animal cell and the plant cell.
Plant cells have a strong cell wall surrounding them (fig) when the process of osmosis takes place the plant cell starts to swell, because of the cells string structure it does not burst instead the pressure builds and the plant cell becomes swollen, appearing hardened. What has happened is because of the pressure inside of the plant cell is now working against the osmosis process. This allows the plant to stand up and absorb sunlight (fig 22) this is part of the process called photosynthesis. And this is the plants way of transforming light energy into chemical energy. If the water levels are lower than is required within the plant cell, then this will cause wilting and thus proving a problem when it comes to photosynthesis and the will die.
An animal cell does not have a wall but a membrane as we have already ascertained and so when the water level is more than the cell requires, the cell itself can burst (fig 20) because unlike the plant cell the membrane cannot work against osmosis. This is why an animal cell must always be enveloped in a solution of the same osmotic strength as its cytoplasm. To deal with this, we have kidneys that aid and ensure this balance is maintained.
Active Transport (fig 23) is needed for the diffusion process to take place against the gradient. For this to happen energy is transferred from respiration (exchanging of gases/consumption of oxygen within a cells environment) this is achieved by using transport proteins like the ones used in facilitated diffusion process (fig 18) However because it is going against the grade (molecules that are larger than the membranes will normally allow to pass through) a carrier molecule that helps produce energy for the cell (ATP) is required (fig 24) The ATP changes the shapes of proteins, allowing for the transfer of larger molecules across the membrane. Active transportation is vital to the diffusion process, as various cells within vital organs such as kidneys need to be reabsorbed into the blood after the filtering process is complete.
Specialised Cell and its Function
A sperm cell is a specialised cell. It has a very specific job to do. This is to reach and fertilise an egg (ovum) and to deliver it to the chromosomes and DNA needed to kick start the process of meiosis. As you can see from the photo (fig) the sperm cell is made up of three main sections.
The head which contains the nucleus is encased in a cell membrane; inside of that membrane surrounding the nucleus itself is cytoplasm. The nucleus of the sperm cell (the control centre) contains information (DNA and Chromosomes) that is stored and then delivered into the ovum after fertilisation to construct the basic building blocks of the embryo. Also at the tip of the head within the membrane are special enzymes. These enzymes are used to help penetrate the eggs cell wall, allowing the sperm cell to enter in the first place.
The second section being the tail, its sole function of this section is to rotate/move in such a fashion as to propel the sperm cell towards the stationary egg.
Conclusion the sperm cell is perfectly suited for its specialised function, because it is preloaded with all the relevant DNA and Chromosomes to put in place the building blocks to create an embryo. It is also armed with enzymes to break down the protective ovum wall, and it is has a built in motor, to propel and move it towards its target!
Bibliography
Study Aids :-
Baggaley.A (ED), 2001, Human Body an illustrated guide, London, Dorling Kindersley ltd
Parker.J,2004, AS&A2 Biology, London, Letts
Images:-
http://www.beyondbooks.com/lif71/images/00016722.jpg
http://www.chemistrypictures.org/v/cell_structure/Nucleolus.jpg.html
http://www.chemistrypictures.org/v/cell_structure/Mitochondrion.jpg.html
http://www.crystalinks.com/fertileggsperm.jpg
http://grapevine.net.au/~grunwald/une/KLAs/science/irrigation-photosynthesis.gif#
http://www.hansenkg.de/english/osmosis.jpg
http://hrsbstaff.ednet.ns.ca/dnichol1/WebQuest/cell%20webquest/mitochondria2.gif
http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion2.gif
http://images.google.co.uk/imgres?imgurl=http://bp2.blogger.com/_g7KcbMxmLEU/Rv4E4M3SPZI/AAAAAAAABwE/6pJeQQcdLAs/s400/amoeba.jpg
http://images.google.co.uk/imgres?imgurl=http://www.ndpteachers.org/perit/osmosis2.gif&imgrefurl=http://www.ndpteachers.org/perit/biology_image_gallery1.htm&h=405&w=630&sz=79&hl=en&start=12&um=1&usg=__jPnXONOk8ztSkDCDQn_Fmzzu_w0=&tbnid=lXidWhGtu5SjGM:&tbnh=88&tbnw=137&prev=/images%3Fq%3Dosmosis%26um%3D1%26hl%3Den
http://images.google.co.uk/imgres?imgurl=http://bp0.blogger.com/_c3XSXrnp9Bg/RbtRuXV-AxI/AAAAAAAAAA4/u6nDdOQslHg/s320/Ribosome.jpg&imgrefurl=http://chaiyahong.blogspot.com/&h=249&w=320&sz=18&hl=en&start=32&usg=__qwbRPlu9H0pzDRaF4L_asQQ6luE=&tbnid=IC3u8PRPBno96M:&tbnh=92&tbnw=118&prev=/images%3Fq%3Dribosomes%26start%3D20%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DN
http://images.google.co.uk/imgres?imgurl=http://bp0.blogger.com/_g5mAeJfqB7c/R1d3trU5__I/AAAAAAAAABY/tj-VLlrMNzo/s320/nakpump.gif&imgrefurl=http://apbio12007.blogspot.com/2007_12_01_archive.html&h=290&w=290&sz=34&hl=en&start=19&um=1&usg=__5a1TkRo6ni0oHxf2coMQMUxYklE=&tbnid=ludFLV8r-DB10M:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dtransport%2Bproteins%26um%3D1%26hl%3Den%26sa%3DG
http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t628/T628746A.jpg
http://library.thinkquest.org/C004535/media/golgi_apparatus.gif
http://www.lce.hut.fi/research/polymer/vesicle4.gif
http://library.thinkquest.org/C004535/media/cell_membrane.gif
http://migration.files.wordpress.com/2007/07/cytoskeleton02.jpg
http://www.natuurinformatie.nl/sites/nnm.dossiers/contents/i004643/exocompleet.jpg
http://www.nsf.gov/news/overviews/biology/assets/interact07.jpg
http://www.nzetc.org/etexts/Bio12Tuat02/Bio12Tuat02_082a(h280).jpg
http://publications.nigms.nih.gov/insidethecell/images/ch1_lysosome.jpg
http://www.seorf.ohiou.edu/~tstork/compass.rose/cell.03/er/rough%20er.jpeg
http://sbcb.bioch.ox.ac.uk/ulmschneider.php_files/membrane.jpg
http://sparkleberrysprings.com/v-web/b2/images/lotc/golgi20.jpg
http://upload.wikimedia.org/wikipedia/en/2/2b/PBB_Protein_ATP5D_image.jpg
http://www.williamsclass.com/SeventhScienceWork/ImagesCellBricks/facilitatedDiffusion.jpg