Notes
Cell theory
All living things are made of cells, the cell is the basic unit of life, and all cells come from pre-existing cells. Cells stay small to keep a high surface area to volume ratio.
Two kinds of cells
| Prokaryotes | Eukaryotes |
|---|---|
| No nucleus; DNA in nucleoid | DNA inside a nucleus |
| No membrane-bound organelles | Membrane-bound organelles |
| Bacteria and archaea | Protists, fungi, plants, animals |
Both have a cell membrane, cytoplasm, ribosomes and DNA.
Organelles
- Nucleus (control, DNA), ribosomes (proteins), rough ER (protein making), smooth ER (lipids), Golgi (packaging), mitochondria (ATP), lysosomes (digestion).
- Plant cells add a cell wall, chloroplasts, and a large central vacuole.
The membrane and transport
- The membrane is a phospholipid bilayer with proteins (fluid mosaic model). It is selectively permeable.
- Passive transport (diffusion, facilitated diffusion, osmosis) moves substances from high to low concentration with no ATP.
- Hypotonic outside: water enters. Hypertonic outside: water leaves. Isotonic: no net change.
- Active transport uses ATP to move substances from low to high concentration. Endocytosis and exocytosis move large materials.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Yeast is a eukaryote with a nucleus; bacteria have none.
Rough ER makes proteins and the Golgi packages them for release.
Salty water is hypertonic, so the cell loses water.
Moving vesicles to release materials uses energy; the other three are passive.
Materials could not move in and out fast enough to supply the larger volume.
This is the fluid mosaic model; all cells have a membrane.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A student cuts three equal potato cubes and weighs each one. She soaks one in distilled water, one in 0.3 M salt solution, and one in 1.0 M salt solution for 24 hours. The cubes change mass by +8%, 0%, and -15%.
(a) Which process caused the change in mass? Explain what moved.
Show the answer and scoring guide
Osmosis caused the change. Water moved across the potato cells' membranes from the side with lower solute concentration to the side with higher solute concentration.
Check off the points you earned:
(b) Classify each solution as hypotonic, isotonic or hypertonic compared to the potato cells.
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Distilled water is hypotonic (cube gained mass). The 0.3 M solution is about isotonic (no change). The 1.0 M solution is hypertonic (cube lost mass).
Check off the points you earned:
(c) Explain why the cube in distilled water did not burst, even though water entered its cells.
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Plant cells have a rigid cell wall. As the central vacuole fills, the cell presses against the wall (turgor pressure), and the wall stops the cell from bursting.
Check off the points you earned: