Why are cells so small?
- Surface area to volume ratio
- Allows water/nutrients to enter
- Allows waste to exit
- More surface area→slower diffusion
- Small volume, high surface area is best
- Diffusion limitations
- Things need to go from the outside to the inside
- Smaller in volume→less time for materials to enter
- Smaller in volume→waste leaves faster
- Waste removal: faster waste removal prevents build-up of toxicity
- Nutrient uptake: nutrients diffuse faster into the cell with less volume
Cell membrane
It is a structure that separates the inside of the cell from its environment, the outermost part of
the cell, surrounding it. All cells have cell membranes. It is selectively permeable, so it can
control what goes in and out.
Extracellular matrix (ECM) - space between the cells
Endocytosis: parts of the membrane surround materials, allowing them to enter
● Made of:
○ Lipids - mainly aid in the structure of the membrane
■ Mostly phospholipids
■ Also some cholesterol
○ Proteins - mainly work in transport and communication
■ Integral (transmembrane)
■ Peripheral
■ Glycoprotein (carb attached to protein): can make connections with other
cells, adhesion, helps in immune response
○ Carbohydrates - Usually found on the outside, attached to either proteins or lipids
(glycoproteins/glycolipids). Helps cells recognize each other (does it belong to my
body or not) - important for the immune system. Also provides protection/
cushioning for the membrane, and a physical barrier.
■ Glycoproteins can signal to other cells what kind of cell it is
(native/doesn’t belong)
● Constantly shifting ‘fluid mosaic’ to:
○ Allow nutrients to enter
○ Allow other materials to enter/move:
■ Oxygen, nonpolar - goes straight through phospholipids
- Surface area to volume ratio
- Allows water/nutrients to enter
- Allows waste to exit
- More surface area→slower diffusion
- Small volume, high surface area is best
- Diffusion limitations
- Things need to go from the outside to the inside
- Smaller in volume→less time for materials to enter
- Smaller in volume→waste leaves faster
- Waste removal: faster waste removal prevents build-up of toxicity
- Nutrient uptake: nutrients diffuse faster into the cell with less volume
Cell membrane
It is a structure that separates the inside of the cell from its environment, the outermost part of
the cell, surrounding it. All cells have cell membranes. It is selectively permeable, so it can
control what goes in and out.
Extracellular matrix (ECM) - space between the cells
Endocytosis: parts of the membrane surround materials, allowing them to enter
● Made of:
○ Lipids - mainly aid in the structure of the membrane
■ Mostly phospholipids
■ Also some cholesterol
○ Proteins - mainly work in transport and communication
■ Integral (transmembrane)
■ Peripheral
■ Glycoprotein (carb attached to protein): can make connections with other
cells, adhesion, helps in immune response
○ Carbohydrates - Usually found on the outside, attached to either proteins or lipids
(glycoproteins/glycolipids). Helps cells recognize each other (does it belong to my
body or not) - important for the immune system. Also provides protection/
cushioning for the membrane, and a physical barrier.
■ Glycoproteins can signal to other cells what kind of cell it is
(native/doesn’t belong)
● Constantly shifting ‘fluid mosaic’ to:
○ Allow nutrients to enter
○ Allow other materials to enter/move:
■ Oxygen, nonpolar - goes straight through phospholipids
