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  • Created by: Laelle
  • Created on: 01-04-16 18:57
What are microscopes?
Instruments that provide a magnified image of an object
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What is the resolving power of light microscopes?
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Resolving power of electron microscopes?
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Why do electron microscopes have a greater resolving power?
Because electron beams have shorter wavelengths than light rays
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What is resolution?
The minimum distance apart 2 objects can be in order to appear as separate items
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What is magnification?
How many times bigger an image produced is compared to the object under the microscope
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Greater resolution means what?
More detail and greater clarity of the image produced
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What happens if you increase magnification?
The image increases in size, and more detail is revealed
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What happens if you increase magnification beyond the resolving power of a microscope?
The object appears bigger, but blurred
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What is cell fractionation?
A process where cells are broken up and organelles isolated
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What is the purpose of cell fractionation?
To study the structure and function of various organelles
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Why is the solution buffered?
To prevent fluctuation of pH, which may affect the cells structure and enzymes activity
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Why is the solution cold?
To reduce enzyme activity that may break down organelles
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Why is the solution isotonic?
To prevent the cells from bursting/shrinking as a result of osmotic gain/loss of water
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What are the 2 stages in cell fractionation?
Homogenation & ultracentrifugation
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Why is the solution homogenised?
Blended: to break cells and release organelles & Filterd: to remove large pieces of debris and unbroken cells
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What is the basis of ultracentrifugation?
Centrifugal force + densities of organelles
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Order of most dense organelles to least?
Nucleus, (chloroplasts in plants), mitochondria, other organelles
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Advantages of the TEM?
High resolution images + allows you to see the ultra structure of cells
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Disadvantages of the TEM?
Specimen must be thin, complex staining process, must be in a vacuum, resolution of 0.1nm is not always achieved
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Advantages of SEM?
Produces a 3D image, specimen doesn't need to be thin
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Disadvantage of SEM?
Has a lower resolution than TEM's of 20nm
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Examples of eukaryotic cells?
Animal, plant, fungal and algal cells
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What additional features do plant cells have (compared to animal cells)?
Cellulose cell wall, chloroplasts + vacuole
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What are fungal cell walls made of?
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What do fungal cells not have, why?
Chloroplast- as they don't photosynthesise
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What is differentiation?
How genetically identical embryonic cells mature and become specialised to perform specific functions
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Which type of organisms have cells that become specialised?
Eukaryotes/multicellular organisms
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How does specialisation occur?
A specific combination of genes in a cell are expressed (switched on) and others repressed (switched off)
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What structural differences make a cell better adapted to its function?
Number of each organelle + shape of cell
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What is a tissue?
A group of similar cells that work together perform a specific fucntion
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Two examples of tissues?
Epithelial tissue, xylem
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What is an organ?
A combination of tissue that work to perform a specific function
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Why are capillaries not organs, whilst arteries and veins are?
Because arteries and veins are made up of a combination of tissues, while capillaries are made up of just one
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What is an organ system?
A group of organs collectively working to perform particular functions more efficiently
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Examples of organ systems?
Digestive system, circulatory systems, respiratory system
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Examples of prokaryotes
Bacteria and viruses
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How are prokaryotes different to eukaryotes?
Smaller, no distinct nucleus, no membrane-bound organelles, smaller ribosome (70s)
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What are bacteria cells successful at?
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What is the cell wall of bacteria made of?
Murein; a polymer of polysaccharides and peptides (peptidoglycan)
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What do bacteria secrete for protection?
A capsule of mucilaginous slim around the murein wall
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What does the capsule also allow?
Bacterial cells to attach together for added protection
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What are plasmids?
Small, circular pieces of DNA
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What other use do plasmids have?
They are vectors for genetic engineering
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What do plasmids do?
They give the bacteria resistance to harmful chemicals e.g. They produce enzymes that break down antibiotics
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Bacterial cells don't have a distinct nucleus, instead...?
A circular strands of DNA
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What does the circular strand of DNA contain?
The genetic information for replication
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What are viruses?
Acellular, non-living particles
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What do viruses consist of?
Nucleic acids (DNA or RNA) surrounded by a protein coat- capsid
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What is the virus HIV further surrounded by?
A lipid envelope
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Where do viruses replicate?
Inside a host cell of another organisms
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How do they attach to host cell?
By attachment proteins on their surface
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What do attachment proteins also allow?
Viruses to identify host cells
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Before mitosis what process occurs?
Interphase- DNA replicates and remains joined at centromere
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Which type of organisms cells undergo mitosis?
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What is mitosis?
Cell division that produces 2 daughter cells genetically identical to the parent cell
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What is mitosis part of?
The cell cycle
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What are the 4 stages of Mitosis?
Prophase, metapahse, anaphase, telophase + cytokinesis
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What type of cell division occurs in prokaryotic cells?
Binary fission
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What results from binary fission?
2 genetically identical daughter cells. Each having a single circular DNA strand and a variable number of plasmids
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Why can't viruses undergo cell divison?
Because they are non-living
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How do viruses replicate?
By attaching to a host cell by their attachment proteins and injecting their viral nucleic acids
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How do the viral nucleic acids affect the host cell?
The genetic info (DNA/RNA) provides instructions for the host cells metabolic processes. They start producing viral components which are assembled to make new viruses
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In multicellular organisms, do all cells have the ability to divide?
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What process do eukaryotic cells unable to divide follow?
The cell cycle
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What are the three stages of the cell cycle?
Interphase (DNA replication), nuclear division (nucleus divides into 2 or 4) + cytokinesis (cytoplasm divides)
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What does uncontrolled cell division lead to?
Tumours and therefore cancer
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What is uncontrolled cell disivion the result of?
A mutation to genes that control mitosis and the cell cycle
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When does a tumour become cancerous?
If it changes from a benign to a malignant
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What is a tumour?
A group of abnormal cells
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What are the features of malignant tumours?
Grow rapidly, less compact + more likely to be life-threatning
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Features of benign tumours?
Grow more slowly, more compact + less-likely to be life-threatning
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Define 'cancer'
A disease caused by growth disorder of cells
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How is cancer often treated?
By disrupting the cell cycle, thus cell division. This ceases the cancer growth
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How do drugs (chemotherapy) disrupt the cell cycle?
1) prevent DNA replication 2) inhibit metaphase stage by interfering with spindle formation
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What's the problem with these drugs?
They also disrupt the cell cycle of normal cells
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Why are drugs more effective at killing cancer cells than normal cells?
It is more effective against rapidly dividing cells + cancer cells have a fast rate of division
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What is the resolving power of light microscopes?



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Why do electron microscopes have a greater resolving power?


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Card 5


What is resolution?


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