Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
1 Question: Are the cells in an elephant bigger, smaller, or about the same size as those in a mouse? 2 Surface area (plasma membrane surface) is determined by A=LxW Volume of a cell is determined by V=LxWxH Therefore, volume increases FASTER than the surface area 3 When the surface area is no longer great enough to get rid of all the wastes and take in enough nutrients, food and water… then the cell MUST divide Therefore, the cells of an organism are close in size 4 Question: Are the cells in an elephant bigger, smaller, or about the same size as those in a mouse? About the same size, but … The elephant has MANY MORE cells than a mouse! 5 •Osmosis is a special case of diffusion •Osmosis involves the diffusion of water through a membrane •The membrane may be: Artificial (non-living) - Cellophane Natural - Cell Membrane •The membrane must allow water molecules to diffuse through. The cell membrane is permeable to H2O. •If a dilute solution is separated from a concentrated solution... water will pass from the dilute to the concentrated solution. dilute solution concentrated solution level falls level rises membrane More water passes from dilute to concentrated ... ...until concentrations become equal Common misconception: Water does happen to pass in BOTH directions... it just passes faster from the dilute to the concentrated solution. Remember... Water molecules undergo diffusion. H2O water membrane sugar solution There are as many water molecules on the right as there are on the left. Many of them on the right are attached to sugar molecules and are not free to move. Because there are more freely moving water molecules on the left, more H2O diffuses through the pores of the membrane from left to right. Next slide Osmosis in Animal Cells Cytoplasm functions as a fairly concentrated solution. There is a greater concentration of free water molecules outside the cell than inside… ...so water diffuses into the cell by osmosis and the cell swells up If osmosis continued, the animal cell would burst! This would be bad news for animals Consequently, there are processes in the animal’s body which control osmosis... This is done by keeping the concentration of body fluids inside the cell the same as it is outside Trout Perch In fresh water fish, blood is more concentrated than the surrounding water As a result the fish takes in water by osmosis Not so much through the skin - (too) thick – but through the gills, which have a very thin membrane The fish gets rid of the excess water by means of its kidneys blood carries water to kidneys gills absorb water by osmosis kidneys expel excess water ... heart ...in the form of dilute urine Found in unicellular protists like paramecia Regulate water intake by pumping out excess H2O(homeostasis) Keeps the cell from lysing (bursting) Contractile vacuole animation 20 A solution can be… 1. 2. 3. Hypotonic Isotonic Hypertonic 21 Hypo = less, (think hypothermia) Tonic = dissolved particles Hypotonic Solution = Solute concentration lower outside than inside the cell The outside of the cell has LESS solute, MORE free H2O Water moves into cell from solution. Cell expands (and may burst) http://www.chem.ufl.edu/~itl/4411/colligative/F G13_022.GIF The concentration of solutes is the same on either side of the membrane. Both sides have the same amount of solutes and free H2O! No NET water movement. This is the ideal situation! Hyper = more (think hyperactive) Tonic = dissolved particles Hypertonic Solution: Solute concentration higher outside the cell than inside the cell. The outside of the cell has MORE solute, LESS free H2O http://cdn.innovateus.net/preset_4/hypertonicbloodcell.png Water moves out of cell into solution. Cell shrinks and becomes shriveled Comprehension Question: What would happen if a nurse gave a patient an IV with a pure water solution? Draw it, explain it! Comprehension Question: Survival Tip: If stranded at sea, people are cautioned not to drink the ocean water, no matter how thirsty they may become. Draw it, explain it! Osmosis and Plant Cells Cytoplasm functions as a fairly concentrated solution. Plant cells are surrounded by a strong, rigid cell wall which prevents the cell from taking on too much water and exploding. •Cell membrane acts as a selectively permeable membrane •Cell wall is freely permeable to water •The vacuole contains a solution of salts and sugars •If there is water outside the cell, it will diffuse by osmosis through the plasma membrane into the vacuole The vacuole will expand, pushing the cytoplasm outwards against the cell wall •The cellulose cell wall cannot stretch, so the vacuole cannot continue to expand •But the pressure of the vacuole against the cell wall makes the cell very firm A plant cell in this condition is said to be turgid If all the cells in the plant are turgid, the plant will be firm and upright and the leaves would be expanded cell wall vacuole The cell absorbs water by osmosis .... cytoplasm and cell membrane ....but the cell wall stops the cell from expanding any more These cells are short of water; the tissue is limp and the plant is wilting The cells have taken up water by osmosis; the cells are turgid and the tissue is firm (1) Limp/ Plasmolyzed (2) turgid The color of cell sap in these two cells differ. What does this say about the concentrations of the cell sap? What will happen? If the concentration of the cell sap is greater in one cell than in its neighbor, water will pass by osmosis from the less concentrated to the more concentrated. cell sap more concentrated cell sap less concentrated Plasmolysis in Red Onion Cell http://www.youtube.com/watch?v=Sw87Q53 NZLI http://www.youtube.com/watch?v=gYbt7hhI xPo http://www.youtube.com/watch?v=x4il3cHhq hY Exposure to extremely hypertonic environments can kill a plant. EX: •Your dog creates spots of dead lawn where he pees. •The urine is hypertonic to the interior of the cells that make up the blade of grass •Large amounts of water are drawn out of the grass, killing it! 1. 2. 3. 4. 5. 6. 7. Osmosis Contractile Vacuole Hypotonic Solution Hypertonic Solution Isotonic Solution Plasmolyzed Turgid