MYP Integrated Sciences Cell Structure Notes

What Makes One Cell Different from Another?

1. Cells look different because they do different jobs.
2. A nerve cell looks nothing like a red blood cell because they have completely different functions.
3. The shape of a cell therefore directly relates to its job:
   1. Red blood cells are concave discs (dimpled on both sides) to maximize surface area for oxygen transport.
   2. Nerve cells on the other hand, are long and thin with branching extensions to transmit electrical signals over long distances.
4. This is what we refer to as the specialization of cells

What Do Animal and Plant Cells Look Like?

1. Shape is the most obvious difference:
   1. Animal cells: irregular, rounded, flexible shape.
   2. Plant cells: regular, rectangular, box-like shape.
2. Plant cells have three structures animal cells don't:
   1. Cell wall - thick, rigid outer layer (outside the cell membrane).
   2. Chloroplasts - green, disc-shaped structures.
   3. Large permanent vacuole - takes up 50-90% of the cell's volume.
3. Both cell types share these structures:
   1. Cell membrane (though you can't see it easily in plant cells because of the cell wall).
   2. Nucleus.
   3. Cytoplasm.
   4. Mitochondria.
   5. Ribosomes.
4. Under a light microscope you can see:
   1. Plant cells: cell wall (as thick outer boundary), nucleus, vacuole (as large clear area), chloroplasts (as green dots).
   2. Animal cells: cell membrane (as thin outer boundary), nucleus, cytoplasm.
5. The vacuole changes plant cell structure:
   1. Pushes the nucleus to the edge of the cell.
   2. Squeezes the cytoplasm into a thin layer around the cell edges
   3. Makes the cell rigid and firm.

What Are the Different Parts of a Cell Called?

1. Cells contain specialized structures called organelles - these are the "organs" of the cell.Some organelles are surrounded by membranes:
   1. Membrane-bound: nucleus, mitochondria, chloroplasts, vacuoles.
   2. Not membrane-bound: ribosomes.
2. Membranes have similar structure throughout the cell:
   1. Made of a phospholipid bilayer (two layers of lipid molecules).
   2. Too thin to see with a light microscope (need electron microscope).
   3. Flexible and fluid, not rigid.
3. Some organelles have double membranes:
   1. Nucleus - surrounded by nuclear envelope (double membrane with pores).
   2. Mitochondria - double membrane with folded inner layer.
   3. Chloroplasts - double membrane plus internal membrane system.
4. Size determines what you can see:
   1. Visible with light microscope: nucleus (5-10 μm), chloroplasts (4-10 μm), cell wall.
   2. Need electron microscope: mitochondria (0.5-1 μm), ribosomes (20-30 nm), membranes (7-10 nm).

Why Do Cells Even Have Compartments?

1. Keep different reactions separate: this prevents reactions from interfering with each other.
2. Specific conditions maintained inside each compartment:
   1. Mitochondria kept at different pH than cytoplasm.
   2. Lysosomes contain digestive enzymes that would damage the cell if leaked.
3. Concentration of reactants: compartments concentrate molecules where needed:
   1. Photosynthesis enzymes concentrated in chloroplasts.
   2. Ribosomes cluster for efficient protein production.
4. Increased efficiency: dedicated spaces = faster reactions:
   1. Mitochondria have folded membranes for more surface area.
   2. Nucleus keeps DNA organized and protected.
5. Protection: some reactions produce harmful substances:
   1. Lysosomes seal away destructive enzymes.
   2. Nuclear membrane protects DNA from cytoplasm reactions.