Cell Structure & Diversity 3- Cell Walls & Respiration Flashcards
What is a plant cell composed of?
Cell wall and protoplast
What is the protoplast?
Cell membrane and everything found inside it
What structures are unique to plant cells?
Cell wall, plasmodesmata, chloroplasts and central vacuole
What is the main component of the cell wall?
Cellulose
What is the structure of cellulose?
A glucose polymer that is highly ordered and forms long ribbon-like structures
How does the structure of cellulose help the cell wall?
The highly ordered structure of cellulose makes it very strong and when multiple cellulose ribbons cross link to from microfibrils it makes a strong and inert structure.
What is the first phase of the cell wall and what is involved?
Crystalline Microfibullar Phase which involves cellulose
What is the second phase of the cell wall and what is involved?
Noncrystalline Matrix which involves pectin and hemicellulose polysaccharides as well as a network extension protein
What is hemicellulose?
A heterogenous group of polysaccharides. A long chain of one type of sugar and a short side chain forms a rigid structure.
What is pectin?
Branched negatively charged polysaccharides which bind water and have gel-like properties.
What is the function of extensin?
Extension cross linking of pectin and cellulose dehydrates the cell wall, reduces extensibility and increases strength.
What is controlled by extension cross linking?
Expanding of cells
Where is the cell wall made?
Outside of the cell
What organelles are needed to make the cell wall?
Golgi complex and rough ER
What are the organelles needed for in making the cell wall?
Coordinating synthesis and delivery of cellulose microfibrils, polysaccharides (pectin and hemicellulose) and cell wall proteins (extensins)
Where are cellulose microfibrils made and what by?
At the plasma membrane by rosettes
Where are the polysaccharides made?
At the Golgi complex and then transported to the cell wall using vesicles
What makes extensions?
Rough ER
How are materials for the cell wall transported?
In vesicles by constitutive exocytosis and the vesicles then fuse to the plasma membrane and release the contents outside
What are rosettes attached to?
Cortical Microtubules
How do rosettes make microfibrils?
Move along the microtubules and joins glucose molecules together to make the cellulose microfibril
What is affected by the way the microtubules are laid?
Where the cellulose is formed and therefore the cell shape
What is the middle lamella?
The sticky portion between the cells which sticks them together
What are the functions of the cell wall?
Regulating the shape, providing structural support and preventing excessive water uptake
What happens if the cellulose microfibrils are randomly orientated?
The cell will expand equally in all directions
What happens if the cellulose microfibrils are laid at right angles to the ultimate longitudinal axis?
Cell will expand longitudinally along that axis
How does the cell wall provide structural support?
The protoplast pushes against the cell wall making the cell wall become rigid and therefore maintaining the plant structure
How does wilting occur?
When the protoplast ins’t pushing against the cell wall
What causes wilting?
When water is lost from the cells it reduces the protoplast volume causing it to not press on the cell wall
What happens when water enters a plant cell?
The protoplast expands and pushes against the cell walls. Equal and opposite pressure of the cell wall pushing back prevents the cell getting too large
What does pressure from the cell do?
Limit the volume of water that can be taken up
What are vacuoles important for and why?
Preventing excessive water uptake because they contain water and make up such a large portion of the protoplast
What is a vacuole?
An organelle surrounded by a highly selective membrane which is similar to the plasma membrane
How does water enter the vacuole?
Passively by osmosis
What is found in high concentration in the vacuole and what does this result in?
Solutes which causes water uptake into the vacuole by osmosis