Plant cell structure and celluloseEdexcel A-Level Biology A: Subtopic test

1. 1
   A student examines two plant cells with an electron microscope: a palisade mesophyll cell from a leaf and a cell from a potato tuber. Both cells have a large central vacuole surrounded by a membrane.

   (a)

   Which organelle in the tuber cell stores starch?

   [1 mark]

   • AChloroplast
   • BPlasmodesma
   • CAmyloplast
   • DMiddle lamella

   (b)

   What is the membrane surrounding the large central vacuole called?

   [1 mark]

   • APlasma membrane
   • BTonoplast
   • CMiddle lamella
   • DPlasmodesma

   (c)

   Describe two differences between a chloroplast in the leaf cell and an amyloplast in the tuber cell.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A virus infects a tobacco leaf and spreads through the leaf from cell to cell. Each plant cell is surrounded by a rigid wall, and neighbouring cells are held together by a layer between their walls. Microscopy shows thin channels crossing the walls between neighbouring cells, and thin areas of the wall called pits.

   (a)

   What is the function of the middle lamella?

   [1 mark]

   • ATo make cellulose for the cell wall
   • BTo store starch
   • CTo control which substances enter the cell
   • DTo cement adjacent cells together

   (b)

   Which statement describes plasmodesmata?

   [1 mark]

   • AChannels lined with membrane that pass through cell walls and link the cytoplasm of neighbouring cells
   • BGaps in the cell wall that are open to the outside of the plant
   • CThickened regions of the cell wall that strengthen it
   • DMembrane-bound sacs in the cytoplasm that store sugars

   (c)

   Suggest how the virus could spread from cell to cell even though each cell is surrounded by a rigid cell wall.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Cotton fibres, which are used to make textiles, are almost pure cellulose. Potato tubers store large amounts of starch. Both cellulose and starch are polymers of glucose.

   (a)

   Explain how the structure of starch makes it suitable as a storage molecule in the potato tuber.

   [3 marks]

   (b)

   Explain how the structure of cellulose makes cotton fibres strong.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student places thin strips of fresh potato tuber in distilled water for an hour. The cells become firm but do not burst. She then examines an electron micrograph of a thin section of potato tuber, which shows several adjacent cells.

   (a)

   Explain why the potato cells become firm but do not burst in distilled water, referring to the structure of the cell wall.

   [6 marks]

   (b)

   The student uses the micrograph to identify the middle lamella, plasmodesmata and amyloplasts. Describe how she could recognise each of them and state the function of each.

   [6 marks]

   Total for question 4: 12 marks

End of questions