Plant Cells (Part Two) Flashcards
What is variation in primary cell wall rigidity due to?
Orientation of the cellulose fibres
What keeps the plant upright?
Balance between turgor pressure and the opposing cell wall
What is plasmolysis?
Reversible shrinkage of the plant cell due to reduced turgor pressure in the vacuole.
Describe the microfibrils in the secondary cell wall.
- Microfibrils arranged mostly in the same direction
- Form layers
What does the Cellulose Synthase Complex consist of?
Several isoforms of the CesA protein
What does the Cellulose Synthase Complex form, and where?
Forms a rosette in the plasma membrane
Explain how an elementary cellulose microfibril is formed.
- CesA protein forms a pore in the plasma membrane
- Glucan chain is extruded into the wall
- 36 chains emerge from the rosette
- They grow together to form an elementary cellulose microfibril
Give the speed of motion of a GFP-labelled cellulose synthase complex.
0.3 μm/min
What is the driving force for the movement of the cellulose synthase complex?
The polymerization and crystallization of the cellulose chains
How many plasmodesmata connect adjacent cells?
1,000-10,000
What do plasmodesmata allow the passage of?
Small molecules, such as: - ions - water - sugar - amino acids And, to less extent, some larger proteins.
What is the role of callose?
Regulates or closes plasmodesmata.
How can larger proteins, mRNA and viral genomes pass the plasmodesmata?
With the help of movement proteins that widen it.
How does a cell plate form?
By fusion of vesicles
Where does cell plate formation begin?
In the middle of the cell
When are plasmodesmata formed in the cell cycle?
During cytokinesis
Give the steps to the formation of the cell plate.
- An array of microtubules guides and supports the formation of the cell plate.
- Microtubules guide secretory vesicles to the forming cell plate.
- Vesicles of the cell plate form cell wall in their interior;
they fuse to give rise to the primary cell wall. - Plasmodesmata (4) are spared in the newly forming primary wall.
- Cell plate initiates in the cell centre and expands outward until it fuses with the
existing plasma membrane at the cortical division zone
What is cytoplasmic streaming?
Movement of the cytoplasm
What is the width of a plasmodesmata?
50nm
