Unit 3 : Homeostasis and Cell Transport A. Maintaining Homeostasis 1. Homeostasis process of regulating and maintaining a constant internal env. 2. Need to maintain homeostasis of water levels, glucose levels, temperature, and ph 3. ph control: a. Buffers: used to regulate cell ph b. How a buffer works: buffer added to an acidic or basic solution to make it a neutral ph 4. Temperature Control: a. if the organism is too hot : 1. dilation: blood vessels dilate (get bigger) and move closer to the skin s surface to release heat 2. sweating: evaporation of water from the skin to cool the body b. if the organism is too cold : 1. constriction: blood vessels constrict (get smaller) and move away from the skin s surface to conserve (save) heat 2. shivering: body increases heat production by contracting muscles 5. Glucose level control: a. if blood glucose levels are too high - 1. cells in pancreas produce insulin in response to high glucose levels 2. insulin converts glucose (monosaccharide) to glycogen (polysaccharide) and stores the glycogen in the liver 3. lowers the blood glucose level b. if blood glucose levels are too low - 1. cells in pancreas produce glucagon in response to low blood glucose levels 2. glucagon breaks down glycogen into glucose 3. hydrolysis increases the blood glucose level
6. Water balance occurs in the kidneys - a. if there is too much water in the blood - 1. kidneys filter out & produce a large volume of urine 2. urine will have a low solute, will be light yellow in color b. if there is too little water in the blood - 1. kidneys produce a small volume of urine 2. urine will have a high of solutes, urine will be dark orange, B. Plasma (Cell) Membrane 1. Functions of the plasma membrane: a. maintains homeostasis by controlling what enters & leaves the cell b. allows nutrients in & wastes out c. acts as boundary between cell and ts environment 2. Selectively (Semi) Permeable: membrane only allows certain molecules to come in and keeps others out, membrane is selective
3. Membrane Structure: a. Phospholipid Bilayer 2 layers of phospholipids 1. fatty acid tails hydrophobic ( water fearing )fatty acid carbon chains 2. polar heads hydrophyllic ( water loving ) phosphate group attached to the lipid 3. proteins located on the membrane surface or embedded in the membrane to create channels for movement of molecules through the membrane or receptors for attachment of molecules b. diagram: c. Fluid Mosaic Model flexibility of bilayer allows molecules in / out while maintaining membrane structure 4. Embedded Membrane Proteins: (help movement in/out) a. hormone binding sites holds hormones to cell b. enzymes facilitates reactions c. protein channels for passive transport allows solutes to flow from high to low in/out of cell d. protein pumps for active transport using energy to move solutes from low to high 5. Cell Recognition lipids & proteins in the membrane help cells to identify each other examples : immune system & antibodies rejection of transplanted tissues (organs) blood type recognition of blood cells C. Cellular Transport all cell transport (movement in/out) is based on a gradient Concentration gradient: Existence of high of a substance on one side of the membrane and a low of a substance on the other side
1. Active Transport Substances move from low to high a. ATP (energy in the cell) is required b. equilibrium will not be reached 2. Passive Transport Substances move from high to low a. No energy is required to move b. Equilibrium will be reached c. Three types of passive transport: 1. Diffusion movement of solutes from high to low (Solute: a substance that can be dissolved, ex. salt, sugar, iodine, Ca++) 2. Facilitated diffusion movement of large solute molecules through the membrane with the aid of transport proteins 3. Osmosis movement of water molecules from high to low (a type of diffusion) Direction Active Transport Move against gradient Passive Transport Move with the gradient Movement From low to high From high to low Energy ATP required Not required Equilibrium Not reached Reached
D. Osmotic Pressure: (osmosis) 1. hypotonic: a. Higher of water outside the cell b. Higher of solute inside the cell c. Water will move into the cell d. Cell will swell (increase) in size e. In plant cells, increase in turgor pressure - membrane will push against the cell wall making the cell appear very firm (turgid). f. In animal cells, increase can cause the cell to burst when water pushes against the membrane. 2. Hyp e rtonic: a. Higher of solutes outside the cell b. Higher of water inside the cell c. Water will move out of the cell d. Cell will shrink (decrease) in size e. Freshwater plant in saltwater will cause cells to shrivel or freshwater fish in saltwater will cause cells to shrivel (dehydration) 3. Isotonic: a. Equal of both solutes and water on inside and outside of cell b. Water will move in & out of cell through membrane at same rate c. Dynamic equilibrium shape of cell stays the same even though water is moving through the membrane at an equal rate
% Solutes Water flows? Animal cell Plant cell Solution type 8 3 More solute in cell, so water moves in Swells, could burst Swells, but does not burst b/c of cell wall Hypotonic 2 4 4 7 More solute out of cell, so water moves out Solute inside equals solute outside, water moves in & out at equal rate Cell shrinks, dehydration Cell stays same size (homeostasis) (firm fruit) Cell shrinks but wall keeps it from collapsing (plasmolysis) Cell stays same size (squishy fruit) Hypertonic Isotonic