Plant Cells (Part Two)

Question 1

What is variation in primary cell wall rigidity due to?

Answer 1

Orientation of the cellulose fibres

Question 2

What keeps the plant upright?

Answer 2

Balance between turgor pressure and the opposing cell wall

Question 3

What is plasmolysis?

Answer 3

Reversible shrinkage of the plant cell due to reduced turgor pressure in the vacuole.

Question 4

Describe the microfibrils in the secondary cell wall.

Answer 4

• Microfibrils arranged mostly in the same direction

- Form layers

Question 5

What does the Cellulose Synthase Complex consist of?

Answer 5

Several isoforms of the CesA protein

Question 6

What does the Cellulose Synthase Complex form, and where?

Answer 6

Forms a rosette in the plasma membrane

Question 7

Explain how an elementary cellulose microfibril is formed.

Answer 7

• 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

Question 8

Give the speed of motion of a GFP-labelled cellulose synthase complex.

Answer 8

0.3 μm/min

Question 9

What is the driving force for the movement of the cellulose synthase complex?

Answer 9

The polymerization and crystallization of the cellulose chains

Question 10

How many plasmodesmata connect adjacent cells?

Answer 10

1,000-10,000

Question 11

What do plasmodesmata allow the passage of?

Answer 11

Small molecules, such as:
- ions
- water
- sugar
- amino acids
And, to less extent, some larger proteins.

Question 12

What is the role of callose?

Answer 12

Regulates or closes plasmodesmata.

Question 13

How can larger proteins, mRNA and viral genomes pass the plasmodesmata?

Answer 13

With the help of movement proteins that widen it.

Question 14

How does a cell plate form?

Answer 14

By fusion of vesicles

Question 15

Where does cell plate formation begin?

Answer 15

In the middle of the cell

Question 16

When are plasmodesmata formed in the cell cycle?

Answer 16

During cytokinesis

Question 17

Give the steps to the formation of the cell plate.

Answer 17

1. An array of microtubules guides and supports the formation of the cell plate.
2. Microtubules guide secretory vesicles to the forming cell plate.
3. Vesicles of the cell plate form cell wall in their interior;
   they fuse to give rise to the primary cell wall.
4. Plasmodesmata (4) are spared in the newly forming primary wall.
5. Cell plate initiates in the cell centre and expands outward until it fuses with the
   existing plasma membrane at the cortical division zone

Question 18

What is cytoplasmic streaming?

Answer 18

Movement of the cytoplasm

Question 19

What is the width of a plasmodesmata?

Answer 19

50nm