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Biology Notes

Cholera
Symptoms
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Muscle and stomach cramps
Vomiting
Fever
Diarrhoea

Cholera bacteria
Cholera is a disease caused by bacteria, Robert Koch finally isolated the cholera bacterium
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Wavelength is
500-650nm
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Thin slice of tissue -> preserved and stained -> sealed
chamber -> air sucked out (vacuum) -> series of magnetic lenses focuses a beam of electrons
through the specimen -> image on screen
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Limitations are you cannot
look at live cells
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Separating cell organelles
Cell fractionation:
Tissue broken up in a homogeniser to burst the cells; suspended in buffer solution which keeps pH
constant, kept cold and has the same water potential as the tissue
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Filtrate is spun in centrifuge at low speed to remove large organelles, e
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nuclei, and they form a
pellet
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g
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Organelle
Cell surface membrane

Main feature
Membrane around the outside
of the cell
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Function
Controls substances coming
into and out of the cell
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Largest organelle, surrounded
by nuclear envelope which
consists of two membranes;
many pores in the envelope
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Contains digestive enzymes
which are separated from the
rest of the cell by the
surrounding membrane
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Made of membranes that form
tubes in the cytoplasm;
covered with ribosomes
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Stack of flattened sacks, each
surrounded by membrane
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Increase surface area
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Produces ATP from
respiration; ATP is the source
of energy
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Assembles protein molecules
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Synthesis lipids
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Forms lysosomes
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Triglyceride is
made up of glycerol and 3 fatty acids
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Lipid test
Dissolve sample in ethanol and pour the solution into water, if a lipid is present then a white
emulsion is formed
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Hydrophobic tail + hydrophilic head
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Fluid mosaic model
‘Fluid’ molecules are free to move around
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Biology Notes
Very small molecules and molecules that dissolve in lipids can easily pass through the bilayer
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Some proteins move freely in the bilayer of the membrane and others are attached to the cell
surface membrane and structures in the cytoplasm
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Carrier proteins that transport substances into and out of the cell
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Carbohydrates are attached to lipids and proteins of cell surface membrane to form glycolipids and
glycoproteins
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Diffusion
The movement of molecules from a high concentration to a low concentration
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Rate of diffusion – the amount diffused through a surface divided by time taken
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Surface area – larger the surface area the faster the rate of diffusion
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Thin exchange surface – this increases the rate of diffusion too
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Carrier proteins have a binding sire on the surface with a specific shape
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Water potential and Osmosis
Water molecules move around randomly and some of them will hit the membrane; this collision
creates pressure on the membrane
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The more water molecules, the greater the water potential
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All other values have a negative value
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Cell surface
membrane is partially permeable – this allows smaller molecules to pass through but not larger
ones
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Now the water potential is higher
outside the cell so water will move via osmosis into the cell
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Biology Notes
Active transport
Movement of molecules from a low to high concentration with the aid of ATP for energy
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ATP comes from mitochondria during respiration
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Water potential in the lumen
is lower than in epithelial cells so water moves into the lumen by osmosis
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Water potential in lumen is now higher than in epithelial cells so water moves out of the
lumen by osmosis
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This part uses
facilitated diffusion
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Glucose moves into the blood via facilitated diffusion
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Choleragen binds to the cell surface
membrane of epithelial cells lining the small intestine; increases active transport of ions into the
lumen
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This means that water moves into the small intestine via osmosis
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ORS – Oral Rehydration Solution
Sachet of glucose and mineral salts is mixed with water which is then consumed by the patient
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Lactose intolerance
Lactose cannot pass through the epithelial cells of the small intestine into the blood, it must be
digested first
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When children are weaned off milk they may no longer drink it
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Undigested lactose passes along the gut to the colon – gut bacteria ferment
this lactose and produce smaller soluble substances e
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methane and carbon dioxide
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