Toothwort (Lathraea squamaria) and mistletoe (Viscum album) are parasitic plants that grow on host trees, such as apple or hazel. They obtain water and organic nutrients directly from the vascular systems of these trees.
Select the term used to describe the tree from which these parasitic plants extract nutrients in this relationship.
Explain why these parasitic plants grow specialized structures (haustoria) directly into the phloem of the host tree.
Scientists investigated two different parasitic plant species growing on a host apple tree (Malus domestica). Toothwort (Lathraea squamaria) is pale cream-white and has no functional leaves, whereas European mistletoe (Viscum album) is green and has fully developed leaves.
They supplied the leaves of the host apple tree with carbon dioxide containing the stable isotope carbon-13 (13C^{13}\text{C}13C). The 13CO2^{13}\text{CO}_213CO2 was not supplied to the parasites.
They then measured:
The table shows their results:
| Species of parasite | Chlorophyll aaa concentration / mg g−1\text{mg }\text{g}^{-1}mg g−1 of tissue | Percentage of sugar in the parasite containing 13C^{13}\text{C}13C (%) |
|---|---|---|
| Toothwort (L. squamaria) | 0.02 | 98 |
| Mistletoe (V. album) | 0.45 | 35 |
Explain why sugars in the tissue of the parasitic plants contain 13C^{13}\text{C}13C.
Explain the relationship between the chlorophyll aaa concentration and the percentage of 13C^{13}\text{C}13C-labelled sugar in each species of parasite.