N. oleander can survive in very dry habitats. Its leaves show adaptations that lower water loss by transpiration. State the term for a plant, such as N. oleander, that has adaptations enabling it to grow where water is scarce.
Aphids are tiny insects that feed on plant fluids by means of piercing and sucking mouthparts. When aphids feed on the sap in the vascular tissue of leaves and stems, a sugary liquid called honeydew is released from the gut. The honeydew can be tested to determine what is present in the sap. State the name of the vascular tissue from which the aphids feed.
An investigation showed that aphids feeding on D. lanata produced honeydew that contained cardiac glycosides. Suggest why cardiac glycosides were found in the sap from the vascular tissue.
Investigations into the action of the cardiac glycoside oleandrin, extracted from $\textit{N.~oleander}$, have shown that it acts by preventing the correct function of Na/K-ATPase, a membrane transport protein. Na/K-ATPase has a role as an enzyme and as a transport molecule. Explain what is meant by the $\textit{hydrolysis of ATP}$.
Name the transport mechanism responsible for moving $\text{Na}^+$ and $\text{K}^+$ across the cell surface membrane of cardiac muscle cells.
Oleandrin is a reversible non-competitive inhibitor of ATPase. Describe how oleandrin acts and explain how this will affect ion movement through Na/K-ATPase transport proteins in the cell surface membranes of cardiac muscle cells.
Digoxin, a cardiac glycoside obtained from $\textit{D.~lanata}$ leaves, can be purified and used as a drug to treat some heart disorders. Such disorders include atrial fibrillation, in which the normal rhythmic cardiac cycle is disturbed, and heart failure, in which cardiac muscle contracts weakly. Describe the sequence of events that takes place on the left side of the heart during one normal cardiac cycle. Include blood pressure changes in your answer. The first event in the sequence is given for you: The left atrium fills with blood during relaxation of the left atrium and left ventricle.
Suggest how treatment with the drug digoxin can improve the health of a person with heart failure.