Cell walls Flashcards
What is a cell wall?
A cell wall is a rigid layer that gives protection, support and shape to the cell. The cell membrane in plants, algae, fungi and most bacteria is surrounded by the cell wall.
The cell walls of multiple cells can adhere to each other to help support an entire organism.
What is a cell membrane?
A dell membrane is a double-layer of phospholipids that forms a boundary between a cell and the surrounding environment and controls the passage of materials into and out of a cell.
What are phospholipids?
A phospholipid is molecule that forms a double-layered cell membrane. A phospholipid is composed of a charged phosphate group, a glycerol and two fatty acid chains.
What is the composition of the cell wall?
Cell wall composition varies and is related to the different need of each type of organism. In plants and algae, the cell wall is made of cellulose, a polysaccharide. In fungi, cell walls are made of chitin and In bacteria, they are made of peptidoglycan.
Way do cell walls of plants and algae have openings or channels?
Because molecules cannot easily diffuse across cellulose. Water and other molecules small enough to fit through the channels can freely pass through the cell wall.
What is chitin?
Chitin i a tough, protective polysaccharide that makes up the cell walls of some fungi.
What is peptidoclycan?
Peptidoclycan Isa substance forming the cell walls of many bacteria.
REMEMBER!
Cell walls shape and support individual cells and entire organisms!
- Cell membranes are composed of two phospholipid layers!
- Chemical signals are transmitted across the cell membrane!
How is a phospholipid formed?
The glycerol and the phosphate groups form the head of a phospholipid and the fatty acids form the tail.
Way is the head of a phospholipid polar?
Because it bears a charge. Water molecules are also polar. Therefore, the polar head of a phospholipid forms hydrogen bonds with water molecules. In contrast, the fatty acid tails are nonpolar and cannot form hydrogen bonds with water. The nonpolar tails are attracted to each other and repelled by water.
Way do the properties of polar heads and nonpolar tails cause the phospholipids to arrange themselves in layers?
Becuase the cell membrane touches the cytoplasm inside the cell and the watery fluid outside the cell.
Which molecules are embedded within the phospholipid layers of the cell membrane?
- Cholesterol molecules > They strengthen the cell membrane.
- Some proteins > Extend through one or both phospholipid layers and help materials cross the membrane.
- Other proteins > Are key components of the cytoskeleton.
- Carbohydrates > Attached to membrane proteins they serve as identification tags, enabling cells to distinguish one type of cell from another.
What is the fluid mosaic model?
The fluid mosaic model describes the arrangement of the molecules that make up a cell membrane. This model of cell membrane structure takes its name from two characteristics.
Which are these two characteristics?
- The cell membrane is flexible, not rigid. The phospholipids in each layer can move from side to side and slide past each other. As a result, the membrane behaves like a fluid.
- The variety of molecules studding the membrane is similar to the arrangement of colourful tiles with different textures and patterns that make up a dynamic mosaic.
What is selective permeability?
The cell membrane has the property of selective permeability, which means it allows some, but not all, materials to cross. The terms semipermeable and selectively permeable also refer to this property.
