Topic 7.5

You must control an experiment. You can test only one variable at a time. (How does the amount of water effect plant growth? Keep the light, containers, soil and plants the same.) Controls are kept the same in all trials. A Control Group is the set-up that isn’t changed. (One plant gets the normal amount of water!). The independent variable is the thing you change (amount of water). The dependent variable is the result of the change you made(height of plant in cm.). Controls: Light, type of plant, amount of soil, pot, temperature.

Independent variable: Amount of water given in mm. Dependent variable: Plant growth in cm.

The Conclusion must be supported by the data and results you gather. To be valid, each experiment needs a large sample size (grow 2000 plants in each experiment) and must be repeated many times in order to prove the Hypothesis (grow 2000 plants 100 times). If you are collecting samples, in an experiment, do it randomly. Don’t take them all from one place. Yes!No!

Reading Graphs and Making Calculations Some TAKS questions ask students to analyze graphs or do basic math calculations to solve problems or draw conclusions. The Independent Variable on a graph is on the X-axis. The Dependent variable is on the Y-axis.

Line graphs represent change over time. The steeper the slope of a line, the faster the change in time is occurring. Pie graphs represent %’s of a whole.

Pipetting

 Liquid volumes are measured in Liters (L), milliliters (mL) or microliters (  L)  A liter is slightly more than a quart  A microliter is 1/1000 of a mL or smaller than a tiny drop  Depending on the volume to be measured, 3 options: graduated cylinder, pipet or micropipet

 Bigger units left  Smaller units right  Move decimal point to the right if converting big units to small units  Move decimal point to the left is converting small units to big units

 1.25 L is equal to how many mLs?  1250 mL  How many liters is 60 mLs?  0.06 L  250 uL is how many L?  L

 Typically 0.1 mL to 25 mL  Plastic disposable or glass pipets  Pipette roller or pipette bulb is needed  Commonly used pipettes are:  1mL, 5mL, 10mL, and 25 mL  Pipets are named by the maximum they deliver

 Graduations: lines marked on volume measuring devices that indicate volume  Meniscus: a curve formed by the surface of liquids confined in a narrow space, such as in a measuring device

 Never mouth pipette  Hold the bottom of the roller and the top of the pipette when you are assembling them  Always keep the pipette vertical when there is fluid in it  Always keep the tip of the pipette sterile and take care to not touch surfaces

 There are 4 parts to a micropipet  Plunger button  Ejector button  Volume display (setter)  Dispensing Tip

 Plunger button  Typically there are 2 stops  The first evacuates the air in the micropipet  The second stop evacuates the volume plus another 50% or so.  Practice to feel the difference

 Bad pipet tip: leaks, clogged tip  Damaged pipetor  Wrong size tip for pipet size  Bubbles in your tip due to poor technique  Liquid not at room temperature or it may be viscous