Notes
What makes something alive
Living things are made of cells, use energy, grow and develop, reproduce, respond to stimuli, keep homeostasis, have DNA, and evolve as populations.
Doing science
- A hypothesis is a testable explanation. An experiment changes one independent variable and measures a dependent variable.
- Controlled variables stay the same; the control group gets no treatment.
- Repeat trials for reliable data. A theory is a well-supported explanation.
Water
Water is polar and forms hydrogen bonds, giving it cohesion, adhesion, a high specific heat, and the ability to dissolve many substances. Ice floats. pH below 7 is acidic, above 7 is basic.
Macromolecules
| Molecule | Monomer | Main jobs |
|---|---|---|
| Carbohydrates | Monosaccharides (glucose) | Quick energy, storage, plant structure |
| Lipids | Glycerol and fatty acids (fats) | Long-term energy, insulation, membranes |
| Proteins | Amino acids | Enzymes, structure, transport, defense |
| Nucleic acids | Nucleotides | Store and transmit genetic information |
Enzymes
Enzymes are protein catalysts that lower activation energy. A substrate binds the active site. Extreme temperature or pH denatures an enzyme.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Everything except light should be kept the same in each group.
Adhesion is water sticking to other surfaces.
Fats and oils are lipids, which do not dissolve in water.
Proteins are chains of amino acids.
Each enzyme has an optimal pH; far from it the enzyme loses shape and activity.
Plants and many other organisms are alive but do not move from place to place.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A student adds the same amount of hydrogen peroxide to five test tubes, each with the same amount of liver (which contains the enzyme catalase). The tubes are kept at 10°C, 25°C, 37°C, 50°C and 70°C. The student measures the height of oxygen bubbles formed in 1 minute: 1 cm, 3 cm, 5 cm, 2 cm and 0 cm.
(a) Identify the independent variable and the dependent variable.
Show the answer and scoring guide
The independent variable is temperature. The dependent variable is the height of oxygen bubbles (the amount of oxygen produced), which measures enzyme activity.
Check off the points you earned:
(b) Name two variables that should be controlled.
Show the answer and scoring guide
The amount of hydrogen peroxide, the amount of liver, the time allowed (1 minute), and the size of the test tubes should all stay the same.
Check off the points you earned:
(c) Explain why almost no bubbles formed at 70°C.
Show the answer and scoring guide
At 70°C the high heat denatured catalase. Its shape, including the active site, changed so hydrogen peroxide could no longer bind, and the reaction was not sped up.
Check off the points you earned: