55 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.3 Cell Membranes And Transport) Flashcards
Why is the model of membrane structure called the “fluid-mosaic” model?
The model of membrane structure is called the ‘fluid-mosaic’ model because:
- The individual phospholipid molecules can move within a layer relative to one another (fluid).
- The proteins embedded in the bilayer vary in shape and size and in their distribution among the phospholipids (mosaic).
Apart from phospholipids and proteins, what are the other biological molecules in plant and animal cell membranes?
Plant and animal cell membranes also contain
1. glycoproteins
2. glycolipids
3. sterols.
What is the sterol in animal cell membranes?
Cholesterol is the sterol in animal cell membranes.
Where is cholesterol located in cell membrane?
It occurs between the phospholipid molecules
How does cholesterol affect the cell membrane?
It makes the membrane more stable at high temperatures and more fluid at low temperatures
What performs the function of cholesterol in plant cell membranes?
Other sterols perform this function in plant cell membranes.
What is the glycocalyx?
The carbohydrate layer around an animal cell is called the glycocalyx.
What are the functions of the glycocalyx?
Some molecules in the glycocalyx have these roles:
- as hormone receptors
- in cell-to-cell recognition
- in cell-to- cell adhesion.
How do small molecules move across the membrane?
Small molecules, e.g. oxygen and carbon dioxide, move between phospholipid molecules and diffuse across the membrane.
How do lipid-soluble substances move across the membrane?
Lipid-soluble substances, e.g. vitamin A, dissolve in phospholipid and diffuse across the membrane.
Which molecules move through the cell membrane more easily? Why?
Lipid soluble molecules.
The phospholipid layer is hydrophobic so lipid-soluble molecules move through the cell membrane more easily than water-soluble substances.
How does water-soluble substances move through the cell membrane?
Water-soluble substances (e.g. glucose, polar molecules, ions) cannot readily diffuse through the phospholipids.
The intrinsic protein molecules form water-filled channels across the membrane.
They must pass through intrinsic protein molecules.
Why is the cell-surface membrane is selectively permeable to water and some solutes?
Water-soluble substances (e.g. glucose, polar molecules, ions) cannot readily diffuse through the phospholipids.
The intrinsic protein molecules form water-filled channels across the membrane.
They must pass through intrinsic protein molecules.
As a result, the cell-surface membrane is selectively permeable to water and some solutes.
The cell membrane should be referred to as ———- and not merely —————-
The cell membrane should be referred to as a phospholipid bilayer and not merely a ‘lipid bilayer”.
Complete the paragraph by filling in the gaps.
The cell membrane is a bilayer made of two layers of ———-molecules.
They have hydrophilic heads pointing outwards and——— tails pointing inwards.
There are two classes of protein in the membrane, intrinsic proteins, which span the membrane, and ————
proteins, on the surface.
The carbohydrates may be bonded to lipid molecules, making glycolipids, or to protein groups, making——–
phospholipid
hydrophobic
extrinsic
glycoproteins
Draw the structure of a biological membrane.
