14. Homeostasis
A section of Biology, 9700
Listing 10 of 131 questions
Woolly foxglove, Digitalis lanata, shown in A, and common oleander, Nerium oleander, shown in B, are plants grown for the attractive flowers that they produce. Both plants are poisonous, as their leaves produce toxic organic compounds known as cardiac glycosides. Cardiac glycosides have a powerful effect on the action of cardiac muscle. A B N. oleander is able to grow in very dry conditions. The leaves have adaptations to reduce water loss by transpiration. State the term used to describe a plant, such as N. oleander, that has adaptations to allow it to grow in conditions where water is in short supply. Aphids are small insects that feed on plant fluids using piercing and sucking mouthparts. When aphids feed on the sap present in vascular tissue of leaves and stems, a sugary liquid called honeydew is passed out of the gut. The honeydew can be analysed to find out what is present in the sap. State the name of the vascular tissue from which the aphids feed. An investigation found that aphids feeding on D. lanata produced honeydew containing cardiac glycosides. Suggest why cardiac glycosides were present in the sap from the vascular tissue. Cardiac glycosides have an effect on the movement of ions into and out of cardiac muscle cells. The outcome is an increased ability for the cells to contract. Investigations into the action of the cardiac glycoside oleandrin, extracted from N. oleander, have shown that it acts to prevent the correct functioning of Na/K‑ATPase, a membrane transport protein. Na/K‑ATPase has a role as an enzyme and as a transport molecule. • ATPase is an enzyme that catalyses the hydrolysis of ATP to ADP and inorganic phosphate. • Energy released from this hydrolysis is used to transport sodium ions (Na+) out of cardiac muscle cells and potassium ions (K+) into the cells. Explain what is meant by the hydrolysis of ATP. Name the type of transport mechanism involved in the transport of Na+ and K+ across the cell surface membrane of cardiac muscle cells. Oleandrin is a non‑competitive reversible inhibitor of ATPase. Describe the mode of action of oleandrin and explain how this will affect ion movement through Na/K‑ATPase transport proteins of the cell surface membranes of cardiac muscle cells. Digoxin, a cardiac glycoside extracted from D. lanata leaves, can be purified and used as a drug to treat some heart disorders. Examples of these heart disorders are: • atrial fibrillation, where the normal rhythmic cardiac cycle is disrupted • heart failure, where cardiac muscle is contracting weakly. Describe the sequence of events occurring in the left side of the heart during one normal cardiac cycle. Include reference to blood pressure changes. The first event in the sequence is described for you. The left atrium fills with blood during relaxation of the left atrium and left ventricle. Suggest how the health of a person with heart failure can be improved by treatment with the drug digoxin.
9700_w18_qp_22
THEORY
2018
Paper 2, Variant 2
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