Practise plant-transport mechanism questions by tracing root water pathways, explaining transpiration pull and modelling phloem loading and mass flow.
Water absorbed by plant roots travels by different pathways from root hairs to the xylem.
Fig. 6.1 shows these pathways in the root of Ranunculus acris.
Name cell A and pathway B as shown in Fig. 6.1.
cell A
pathway B
Transpiration occurring at the leaves is mainly responsible for movement of water across the root of R. acris.
Explain how transpiration is responsible for the movement of water across the root as shown in Fig. 6.1.
Explain why the movement of water in pathway C is slower than in pathway B.
Fig. 3.1 is a diagram of an area of phloem tissue from a transverse section through the stem of a squash plant, Cucurbita pepo.
Fig. 3.1
Sucrose is formed from the glucose synthesised by mesophyll cells in the leaves of C. pepo. Explain how companion cells are involved in the transfer of sucrose into phloem sieve tubes.
Hydrogen bonding is important in the movement of water in xylem.
Outline how hydrogen bonding is involved in water transport in the xylem of a plant stem.
Nerium oleander is a xerophytic plant. A photomicrograph of a section through the leaf of N. oleander is shown in Fig. 3.1.
Fig. 3.1
The leaf shown in Fig. 3.1 has a number of adaptations to reduce water loss by transpiration. Two of these adaptations are:
- a multilayered epidermis
- stomata only found in depressions, known as stomatal crypts, on the lower surface of the leaf.
Explain how a multilayered epidermis and stomatal crypts will help to reduce water loss in N. oleander.
multilayered epidermis
stomatal crypts
Sucrose, amino acids and other assimilates synthesised in palisade mesophyll cells of N. oleander pass to the vein, where they can be transported within specialised cells from the source to the sink.
Explain the difference between a source and a sink.
One of the enzymes involved in the synthesis of sucrose in the cytoplasm of palisade mesophyll cells is known as cyFBPase. The gene coding for this enzyme is cyFBP.
The importance of cyFBPase in plant growth can be investigated using plants with a mutation in gene c y F B P. These plants cannot synthesise cyFBPase.
Investigations have shown that plants with the c y F B P mutation grow to a much smaller height and have proportionately far less starch stored in their roots than normal plants.
Suggest why plants with the cyFBP mutation will store less starch in their roots.