C3.1 Integration of body systems

Question 1

C3.1.1—System integration

Answer 1

This is a necessary process in living systems. Coordination is needed for component parts of a system to
collectively perform an overall function.

Question 2

C3.1.2—Cells, tissues, organs and body systems as a hierarchy of subsystems that are integrated in a
multicellular living organism

Answer 2

Students should appreciate that this integration is responsible for emergent properties. For example, a
cheetah becomes an effective predator by integration of its body systems.

Question 3

C3.1.3—Integration of organs in animal bodies by hormonal and nervous signalling and by transport of
materials and energy

Answer 3

Distinguish between the roles of the nervous system and endocrine system in sending messages. Using
examples, emphasize the role of the blood system in transporting materials between organs.

Question 4

C3.1.4—The brain as a central information integration organ

Answer 4

Limit to the role of the brain in processing information combined from several inputs and in learning and
memory. Students are not required to know details such as the role of slow-acting neurotransmitters.

Question 5

C3.1.5—The spinal cord as an integrating centre for unconscious processes

Answer 5

Students should understand the difference between conscious and unconscious processes.

Question 6

C3.1.6—Input to the spinal cord and cerebral hemispheres through sensory neurons

Answer 6

Students should understand that sensory neurons convey messages from receptor cells to the central
nervous system.

Question 7

C3.1.7—Output from the cerebral hemispheres to muscles through motor neurons

Answer 7

Students should understand that muscles are stimulated to contract.

Question 8

C3.1.8—Nerves as bundles of nerve fibres of both sensory and motor neurons

Answer 8

Use a transverse section of a nerve to show the protective sheath, and myelinated and unmyelinated
nerve fibres.

Question 9

C3.1.9—Pain reflex arcs as an example of involuntary responses with skeletal muscle as the effector

Answer 9

Use the example of a reflex arc with a single interneuron in the grey matter of the spinal cord and a free
sensory nerve ending in a sensory neuron as a pain receptor in the hand.

Question 10

C3.1.10—Role of the cerebellum in coordinating skeletal muscle contraction and balance

Answer 10

Limit to a general understanding of the role of the cerebellum in the overall control of movements of the
body

Question 11

C3.1.11—Modulation of sleep patterns by melatonin secretion as a part of circadian rhythms

Answer 11

Students should understand the diurnal pattern of melatonin secretion by the pineal gland and how it
helps to establish a cycle of sleeping and waking.

Question 12

C3.1.12—Epinephrine (adrenaline) secretion by the adrenal glands to prepare the body for vigorous
activity

Answer 12

Consider the widespread effects of epinephrine in the body and how these effects facilitate intense muscle
contraction.

Question 13

C3.1.13—Control of the endocrine system by the hypothalamus and pituitary gland

Answer 13

Students should have a general understanding, but are not required to know differences between
mechanisms used in the anterior and posterior pituitary

Question 14

C3.1.14—Feedback control of heart rate following sensory input from baroreceptors and chemoreceptors

Answer 14

Include the location of baroreceptors and chemoreceptors.
Baroreceptors monitor blood pressure. Chemoreceptors monitor blood pH and concentrations of oxygen
and carbon dioxide. Students should understand the role of the medulla in coordinating responses and
sending nerve impulses to the heart to change the heart’s stroke volume and heart rate.

Question 15

C3.1.15—Feedback control of ventilation rate following sensory input from chemoreceptors

Answer 15

Students should understand the causes of pH changes in the blood. These changes are monitored by
chemoreceptors in the brainstem and lead to the control of ventilation rate using signals to the diaphragm
and intercostal muscles.

Question 16

C3.1.16—Control of peristalsis in the digestive system by the central nervous system and enteric nervous
system

Answer 16

Limit to initiation of swallowing of food and egestion of faeces being under voluntary control by the
central nervous system (CNS) but peristalsis between these points in the digestive system being under
involuntary control by the enteric nervous system (ENS). The action of the ENS ensures passage of material
through the gut is coordinated.

Question 17

C3.1.17—Observations of tropic responses in seedlings

Answer 17

Application of skills: Students should gather qualitative data, using diagrams to record their observations
of seedlings illustrating tropic responses. They could also collect quantitative data by measuring the angle
of curvature of seedlings.
NOS: Students should be able to distinguish between qualitative and quantitative observations and
understand factors that limit the precision of measurements and their accuracy. Strategies for increasing
the precision, accuracy and reliability of measurements in tropism experiments could be considered

Question 18

C3.1.18—Positive phototropism as a directional growth response to lateral light in plant shoots

Answer 18

Students are not required to know specific examples of other tropisms.

Question 19

C3.1.19—Phytohormones as signalling chemicals controlling growth, development and response to
stimuli in plants

Answer 19

Students should appreciate that a variety of chemicals are used as phytohormones in plants.

Question 20

C3.1.20—Auxin efflux carriers as an example of maintaining concentration gradients of phytohormones

Answer 20

Auxin can diffuse freely into plant cells but not out of them. Auxin efflux carriers can be positioned in a cell
membrane on one side of the cell. If all cells coordinate to concentrate these carriers on the same side,
auxin is actively transported from cell to cell through the plant tissue and becomes concentrated in part of
the plant.

Question 21

C3.1.21—Promotion of cell growth by auxin

Answer 21

Include auxin’s promotion of hydrogen ion secretion into the apoplast, acidifying the cell wall and thus
loosening cross links between cellulose molecules and facilitating cell elongation. Concentration gradients
of auxin cause the differences in growth rate needed for phototropism.

Question 22

C3.1.22—Interactions between auxin and cytokinin as a means of regulating root and shoot growth

Answer 22

Students should understand that root tips produce cytokinin, which is transported to shoots, and shoot
tips produce auxin, which is transported to roots. Interactions between these phytohormones help to
ensure that root and shoot growth are integrated

Question 23

C3.1.23—Positive feedback in fruit ripening and ethylene production

Answer 23

Ethylene (IUPAC name: ethene) stimulates the changes in fruits that occur during ripening, and ripening
also stimulates increased production of ethylene. Students should understand the benefit of this positive
feedback mechanism in ensuring that fruit ripening is rapid and synchronized.