Plant cell structureEdexcel International A Level Biology: Subtopic test

1. 1
   A student examines an electron micrograph of a palisade mesophyll cell from a leaf. The cell has a thick layer outside its plasma membrane, a very large sac occupying most of the cell interior, and several oval organelles containing stacks of flattened membranes.

   (a)

   What is the function of the tonoplast?

   [1 mark]

   • AIt is the membrane around the vacuole and controls the movement of substances into and out of the vacuole
   • BIt cements adjacent cell walls together
   • CIt forms channels through the cell wall that link the cytoplasm of adjacent cells
   • DIt is the site of the light-dependent reactions of photosynthesis

   (b)

   Which structure is found in a palisade cell but not in a human liver cell?

   [1 mark]

   • ARough endoplasmic reticulum
   • BA nucleus
   • CMitochondria
   • DA cellulose cell wall

   (c)

   The cell is placed in distilled water. Explain why it does not burst.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A potato tuber stores energy over the winter. Cells from inside a tuber were stained with iodine solution and viewed under a light microscope. Many organelles in the cells contained dark blue-black granules.

   (a)

   Which organelle contains the stained granules?

   [1 mark]

   • AMitochondrion
   • BGolgi apparatus
   • CAmyloplast
   • DRibosome

   (b)

   Which feature would distinguish an amyloplast from a chloroplast in an electron micrograph?

   [1 mark]

   • AThe amyloplast has no envelope, but the chloroplast has a double membrane
   • BThe amyloplast contains large starch grains and has no stacks of thylakoids (grana)
   • COnly the amyloplast contains DNA
   • DThe amyloplast is found only in animal cells

   (c)

   Explain why the tuber stores energy as starch in amyloplasts rather than as glucose in the cytoplasm.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A researcher injects a fluorescent dye into one parenchyma cell in the stem of a plant. Within minutes the dye is detected in the neighbouring cells, even though the dye cannot cross the plasma membrane. Microscopy shows that where the dye passes between the cells, the cell wall is thin.

   (a)

   Explain how the dye could move from the injected cell into its neighbours.

   [3 marks]

   (b)

   Describe the structure and roles of pits and of the middle lamella.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student studies electron micrographs of three cell types: a parenchyma cell from a potato tuber, a palisade cell from a potato leaf, and a human liver cell.

   (a)

   Compare the structure of the potato tuber cell with that of the human liver cell.

   [6 marks]

   (b)

   In the micrograph of the leaf cell, the student sees three structures. X is an oval organelle with a double membrane enclosing stacks of flattened membrane sacs. Y is a very large sac, bounded by a single membrane, that fills most of the cell. Z is a thick layer outside the plasma membrane. Identify X, Y and Z and, for each, explain how its appearance is related to its function.

   [6 marks]

   Total for question 4: 12 marks

End of questions