Coordination and Response: Biology 0610 (Cambridge O Level / IGCSE)

A chef checks on a roast by opening a very hot oven. As the chef closes the oven door, the back of one hand briefly brushes against the hot metal door frame. The hand jerks away from the door before the chef consciously feels any pain.

This rapid, automatic response is a simple reflex action, coordinated through a reflex arc.

Which row shows the correct order in which structures are involved, from the stimulus to the response?

A planetarium usher spends each show inside the dimly lit projection dome, guiding visitors to their seats by torchlight. Between shows, the usher steps out into the brightly lit foyer to greet the next group of visitors.

(a) State the name of the eye structure that: (i) refracts light as it enters the eye (ii) contains the light receptors (iii) carries impulses from the eye to the brain [3]

(b) Describe how the diameter of the usher's pupils changes as they step from the dim dome into the bright foyer, and explain why this response is useful. [3]

A lifeguard at a busy swimming pool spots a swimmer struggling in the deep end and immediately prepares to dive in for a rescue. In the few seconds before diving in, the lifeguard's heart pounds faster, their breathing quickens, and their pupils widen.

(a) Name the gland that releases the hormone responsible for these changes, and name this hormone. [2]

(b) State two of the effects described above that this hormone produces on the lifeguard's body. [2]

(c) The lifeguard's nervous system also plays a part, sending nerve impulses to the leg muscles so the lifeguard can run and dive. Compare the speed of action and the duration of effect of this nervous response with the hormonal response described in (a) and (b). [2]

A marathon runner has been running for over three hours without eating. Partway through the race, their blood glucose concentration begins to fall below its normal set point.

(a) Explain what is meant by homeostatic control by negative feedback, using the runner's falling blood glucose concentration as an example. [3]

(b) Name the pancreatic hormone that would be released to raise the runner's blood glucose concentration back towards the set point, and describe the role of the liver in this response. [3]

A greenhouse manager arranges a row of young tomato seedlings in trays under a single fluorescent strip light fixed along one side of a growing tent, with no light reaching the seedlings from any other direction. After one week, every shoot tip has curved noticeably towards the strip light, and each stem is longer down its shaded side than down the side facing the light.

(a) Name the plant hormone responsible for this curvature, and state where in the shoot it is made. [2]

(b) Explain, in terms of the distribution of this hormone and its effect on cells, why the shaded side of each stem grows longer than the illuminated side, causing the shoot tip to bend towards the light. [4]

A researcher records electrical activity along a sensory neurone as it carries an impulse towards the spinal cord. Just before the impulse reaches a relay neurone, the researcher notes that the sensory neurone does not actually touch the relay neurone, a very narrow gap separates the two cells.

(a) Name this junction between two neurones, and name the narrow gap found within it. [2]

(b) Describe how an impulse arriving at the end of the sensory neurone is passed across this junction to the relay neurone. [3]

(c) Explain why this junction allows impulses to travel across it in one direction only, from the sensory neurone to the relay neurone. [1]

Which of the following is an example of a reflex action rather than a voluntary action?

A student closes one eye and holds a pencil at arm's length in front of the open eye, keeping it in focus as they slowly bring it closer to their face.

(a) Name the muscles that control the shape of the lens, and name the structures that connect these muscles to the lens. [2]

(b) Describe how the shape of the lens changes as the pencil moves closer to the eye, and explain how the muscles and structures named in (a) bring about this change. [3]

(c) State how the shape of the lens differs when the student instead focuses on a distant object across the room. [1]

Which statement correctly describes a hormone?

A student places a young bean seedling on its side inside a dark box for two days, so that its root and shoot both lie horizontally. When the student checks the seedling, the root has curved downwards and the shoot has curved upwards.

(a) State the name given to this growth response to gravity, and state whether the root and the shoot each show a positive or a negative form of this response. [2]

(b) The plant hormone auxin accumulates on the lower side of both the horizontal root and the horizontal shoot. Explain, in terms of the effect of auxin on cell elongation, why the root curves downwards while the shoot curves upwards. [4]