Discuss the selected characteristics of living cells. PDF

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Summary

• Discuss the selected characteristics of living cells.
• Compare and contrast prokaryotic and eukaryotic cells, and explain the impact that viruses have on them.
• Discuss eukaryotic sub-cellular structure and organelles.


SECTION TWO
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Description

The cell is the smallest structural and functional unit of living organisms, which can exist on its own. Cells carries out seven processes of life such as animals and plants. Eukaryotic cells contain a number of membrane-bound organelles. These structures play important roles in the normal functioning of cells. Cell membranes is a wall around the cell it allows beneficial substances in and waste products out. Cytoplasms is a liquid inside the cell in here food materials change into materials that needed for energy and growth. The sausage shaped organelle called the mitochondria it converts food into energy it is like the cells power-plant. An other organelle inside the cells is endoplasm reticulum. This is a network of channels that moves materials within the cells. Ribosome it is an other cell organelle which is attached to the outside of endoplasm reticulum. Nucleolus has a key role, it produces protein. Golgi body distribute proteins and other materials through out of the cells. Lysosome are sacks which filled with digestive enzymes. They digest worn out cells parts or cells debris such as dead cells or foreign micro organisms. Nucleus controls what the cells does yet not all cells has nuclei. Such as single cells organisms like bacteria has not. Some cells in the body also do not have nuclei such as red blood cells. Most cells has a nucleus which is surrounded by a tow layered membrane and is filled with a liquid called nucleoplasm. Nucleus also contains all of the organisms genetic information DNA or deoxyribonucleic acid. DNA made from long strands of chemical bases that have been paired in a specific order. The stands of DNA are tightly wound in chromosomes. Chromosomes contains many genes which carries the instructions of making proteins. Each proteins controls a specific trade in the organisms. Cell characteristics: Movement - they can move and change their position. Reproduction – they can make more of the same kind of organism as themselves. Sensitivity – they can detect or sense stimuli and respond to them. Growth - they can permanently increase their size or dry mass by increasing the number or size of their cells. Respiration – they can create chemical reactions that break down nutrient molecules in living cells to release energy. Excretion – they can excrete toxic materials, waste products of metabolism, and excess substances (note that excretion is not the same as egestion). Nutrition - they can take in and absorb nutrients such as organic substances and mineral ions. These nutrients contain the raw materials or energy needed for growth and tissue repair. Living organisms can also control their internal conditions, such as their temperature or water content. Prokaryotic and eukaryotic cells originate from the same common ancestor ,so they have some features in common. They both have cytoplasm, a cell membrane, ribosomes and DNA. Cytoplasms where is all of the reactions and enzymes can take their place, all of the dissolved chemicals and substances. Cell membrane surrounding both cells , this is the barrier what controls what enters and exits the cells and also controls the shape of the cells. Ribosomes in the eukaryotic cells found in a certain places. Prokaryotes they tend to be just floating around. They there to aid in protein translations. All Prokaryotes have cells wall, while only some Eukaryotes have cells wall.

Prokaryotic are a lot smaller and simple than eukaryotic. They are the oldest cell types. Lack of nucleus. Lack of organelle. Single celled. The DNA of a prokaryotic is organised as a single , circular chromosomes. Prokaryotic cells has flagella, helps it swim and move through various environments. Eukaryotic has evolved from prokaryotic. Are bigger cells in size and more complex. They have membrane bound organelle such as the mitochondrion or nucleus, these aren't present in prokaryotic. They contain organelle. Single-celled or multicellular. The DNA of a eukaryotic is organised as linear chromosomes. Some eukaryotic cells has tails like human sperm cells. Viruses sub-microscopic infectious agent unable to grow or reproduce outside of another living host cell. They are not alive. They live within the cell of other organisms, including human tissue cells. Existing as a protein capsule that contain all the chemicals the virus needs to reproduce within the cell of its host. They can not reproducers it's own. The protein capsules is unique for every virus and cause the body cells to react against it as an immune response while trying to fight off the disease that the virus has produced. Viruses called bacteriophages are able to infect bacterial cells and use them as hosts to make more viruses. Viruses cause a number of diseases in eukaryotes. Cell membrane act as a barrier that control what passes into and out of the cells and organelles. It can control what can exactly enter and leave the cells. In order to sustain life , there must be exchange of substances between cells and the environment. Cell membrane is made up of a two layers phospholipids, it is called the phospholipid bilayer. Each single one of phospholipid molecules have a hydrophilic phosphate head and two hydrophobic fatty acid tail. Hydrophilic is called water attractive, it attracts water. Hydrophobic means water repelling. In a condition where is water present for example in our cells and body the phospholipids arrange themselves in a type of bilayer form because hydrophilic phosphate head face the outside world because they like water and they form the two outer rows. The hydrophobic tails protect themselves in a core all together as a cluster trying to avoid the water, the tails clustering together in the center of two layers. So they exclude any water that is found there, so the water will leave the area. So it is creates a partially permeable barrier which allows certain substances to pass through, for example Oxygen and Carbon dioxide, it is important for respiration. This is know as simple diffusion. It does not need any energy to force these molecules in or out. It is a type of passives transport. Inside the cells membrane also there are some transport proteins, intrinsic protein and extrinsic protein, these membrane are usually involved transport of substances across the membrane. Some transport proteins act as a channels. It is helping to molecules that may be to big to cross the membrane on their own. This is know as facilitated diffusion. It is also does not need energy so it is a type of passives transport. It moves with the flow, moves with the concentration gradient of high to low. Transport protein helps to pass through to charged ions, like Na+ ( Sodium ion) ,H+ (Hydrogen ion) and also glucose needs the help to pass through. In osmosis for water to travel in a fast rate across the membrane, it is passes through a protein channels called, aquaporins. Also example of facilitated diffusion, type of passives transport. Cholesterol molecules are also present in the cell membrane, give the structure stability to it.

Movement within the cell can involve endocytosis, exocytosis and active transport. Movement of molecules from low to high concentration takes energy because it is against the flow. It is required ATP energy ( adenosine triphosphate) ATP can power Active Transport to force those molecules to go against the concentration gradient, a great example is Sodiumpotassium pump. They catalyse (speed up) the breakdown of ATP into ADP and Pi. This releases the energy to allow a change in shape and pump the molecule across the membrane. Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalised is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Exocytosis is the reverse direction of Endocytosis, this is when molecules exit. Exocytosis can be used to get rid of cell waste. Respiration is a process that happens continuously in all living cells, cells are constantly supplied with energy. Respiration transfer energy to the cell so it can move and grow. In the case of animal cells, chemical energy is changed into kinetic energy and heat energy when movement is involved. The process of respiration also generates heat energy. Respiration is exothermic , this means that energy is released to the environment when respiration takes place. Two types of respiration are anaerobic and aerobics respiration. Aerobics respiration uses oxygen. Anaerobic does not use any oxygen. Similarities that they both catalysed by enzymes. Both of these reactions need to break down glucose to get energy and this is done with specific enzymes. In cellular respiration organisms use the breakdown organic compounds like glucose to fuel metabolic processes. Metabolic processes are the necessary chemical reactions in living organisms. Glucose broken down and the energy release is use of basic life processes. This enables organisms to grow and move around. Aerobics respiration uses oxygen and glucose and it takes place in mitochondria. Mitochondria is present in our cells. Aerobics respiration is the most efficient way of transferring energy from glucose. The reaction take place is glucose+oxygen -> carbon dioxide+water The Kerbs Cycles is the third stage of aerobic respiration and it takes place in the mitochondria matrix. In the Kerbs Cycles a series of enzyme catalysed reactions occur to oxidise the Acetyl-CoA produced in the links reaction. In Kerbs Cycles ATP molecules and reduced coenzyme, such as reduced NAD and FAD , are produced and carbon dioxide is released. Protein synthesis has three steps. Transcription the first stage happens in the cell nucleus. The process of transcription involves forming a single-stranded mRNA from a double-stranded DNA. Transcription is when we going to transcribe the DNA into a message. Messenger RNA consist of a message made of RNA that has been based on the DNA. mRNA is read three basis at a time and these are called codons. So the mRNA going out from the nucleus into the cytoplasm. Activation, step two occurs in the cytoplasm. Translation , step three occurs at the ribosome. The mRNA attaches to the ribosome. Ribosome made from RNA and protein. Ribosomes makes protein that read the mRNA and adding amino acid using tRNA. tRNA stands for transfer RNA. mRNA is important because it is going to direct which tRNAs come in and therefore which amino acids are transferred. One end of the tRNA there is an anti-codon which will match specific codon on the mRNA and has a specific amino acid on the other end. These three parts will take the translation happen.

mRNA attaches to the ribosome and a start code will be read , usually AUG. tRNA bring the first amino acid. The anti-codon on the tRNA matches it up the codon on the mRNA. The next tRNA molecule comes in and matches with the mRNA codon while the amino acid form a peptide bond. Then the previous tRNA detaches and the mRNA moves for the next tRNA molecules comes in. The protein grows until a stop codon is reached. The protein is formed and ready to become functional. This is the end of protein synthesis. Reference: Fullick, A. & Bircher, P. (2015), A level Biology for OCR, Oxford University Press (Accessed: 18 July) Gerard Vargas ,2011, Prokaryotes, Eukaryotes, and Viruses. Available from: https://www.youtube.com/watch?v=Bu75WMnYR_E (Accessed: 18 July) Miss Estruch, 2019, A-level EUKARYOTIC CELLS- The structure and function of the organelles found in eukaryotic cells, Available from: https://www.youtube.com/watch?v=JXTFjP1QArM (Accessed: 18 July) What is up, 2018, Cell Membrane Transport - Transport Across A Membrane - How Do Things Move Across A Cell Membrane, Available from: https://www.youtube.com/watch? v=J5pWH1r3pgU (Accessed: 19 July) Crash Course, 2012, ATP & Respiration: Crash Course Biology #7, Available from: https://www.youtube.com/watch?v=00jbG_cfGuQ (Accessed: 19 July) Khan Academy, 2018, Introduction to nucleic acids and nucleotides, Available from: https://www.youtube.com/watch?v=hI4v7v8AdfI (Accessed: 19 July) Khan Academy, 2009, Embryonic stem cells, Available from: https://www.youtube.com/watch?v=-yCIMk1x0Pk (Accessed: 21 July) Khan Academy, 2015, Cell cycle phases, Available from: https://www.youtube.com/watch? v=U5vAO_f2LDQ (Accessed: 21 July)...