3.1 The diagrams below represent the growth responses of two different plant organs to external stimuli - NSC Life Sciences - Question 3 - 2018 - Paper 1

(a) The external stimulus at A is light.

(b) The external stimulus at D is gravity.

Plant organ B is a stem because it shows upward growth, which is characteristic of stems that grow towards light, exhibiting positive phototropism.

The growth response observed in plant organ C involves auxin concentration changes. Auxins accumulate on the side of the plant organ that is darker (in this case, the side away from the light source), causing uneven growth. This uneven distribution results in bending towards the light source, demonstrating positive phototropism.

Pathway A represents a reflex arc.

Pathway A directly connects sensory neurons to motor neurons without involvement of the brain, which is characteristic of reflex arcs.

Reflex actions are important as they allow for rapid responses to stimuli, protecting the body from harm by minimizing injury from potentially dangerous situations, such as pulling away from a hot surface.

The part of the nervous system represented by 1 is the spinal cord.

The myelin sheath is important because it acts as an insulator, speeding up the transmission of nerve impulses along the axon and preventing the loss of electrical signals.

If the axon of neuron 2 was cut, the person would be unable to feel the stimulus because the impulse would not be transmitted to the effector, resulting in a lack of response.

Pathway B illustrates the route an impulse takes when traveling to the brain. The impulse moves from the sensory neuron to the brain, then to a motor neuron, which finally provides a response.

Immediately after a meal is eaten, the blood glucose concentration increases.

Eating many small meals per day helps a diabetic person maintain a more stable blood glucose level. When consuming fewer larger meals, there is a larger glucose influx which can trigger a disproportionate insulin response. Smaller meals reduce the risk of spikes in blood sugar levels.

Person A was exercising.

1. Person A has a higher skin surface temperature at 37.2 °C compared to Person B's 36.6 °C, indicating increased metabolic activity during exercise.
2. Person A may also exhibit perspiration due to increased body heat generated while exercising.

One hormone that would have the same effect on the blood vessels is adrenaline.

The skin temperature of person A was higher after 10 minutes due to increased blood flow to the skin and sweat production as a result of physical activity. This vasodilation allows more blood, which is warmer, to reach the surface, raising the surface temperature.