SL Content Statements

• C3.1.1

  System integration

• 
  

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

• C3.1.2

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

• 
  

  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.
  

• C3.1.3

  Integration of organs in animal bodies by hormonal and nervous signalling and by transport of materials and energy

• 
  

  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.
  

• C3.1.4

  The brain as a central information integration organ

• 
  

  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.

• C3.1.5

  The spinal cord as an integrating centre for unconscious processes

• 
  

  Students should understand the difference between conscious and unconscious processes.
  

• C3.1.6

  Input to the spinal cord and cerebral hemispheres through sensory neurons

• 
  

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

• C3.1.7

  Output from the cerebral hemispheres to muscles through motor neurons
  

• 
  

  Students should understand that muscles are stimulated to contract.
  

• C3.1.8

  Nerves as bundles of nerve fibres of both sensory and motor neurons

• 
  

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

• C3.1.9

  Pain reflex arcs as an example of involuntary responses with skeletal muscle as the effector

• 
  

  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.
  

• C3.1.10

  Role of the cerebellum in coordinating skeletal muscle contraction and balance

• 
  

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

• C3.1.11

  Modulation of sleep patterns by melatonin secretion as a part of circadian rhythms

• 
  

  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.
  

• C3.1.12

  Epinephrine (adrenaline) secretion by the adrenal glands to prepare the body for vigorous activity

• 
  

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

• C3.1.13

  Control of the endocrine system by the hypothalamus and pituitary gland

• 
  

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

• C3.1.14

  Feedback control of heart rate following sensory input from baroreceptors and chemoreceptors
  

• 
  

  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.
  

• C3.1.15

  Feedback control of ventilation rate following sensory input from chemoreceptors

• 
  

  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.
  

• C3.1.16

  Control of peristalsis in the digestive system by the central nervous system and enteric nervous system

• 
  

  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.
  

AHL Content Statements

• C3.1.17

  Observations of tropic responses in seedlings
  

• 
  

  AOS: 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.
  

• C3.1.18

  Positive phototropism as a directional growth response to lateral light in plant shoots

• 
  

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

• C3.1.19

  Phytohormones as signalling chemicals controlling growth, development and response to stimuli in plants

• 
  

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

• C3.1.20

  Auxin efflux carriers as an example of maintaining concentration gradients of phytohormones

• 
  

  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.
  

• C3.1.21

  Promotion of cell growth by auxin

• 
  

  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.
  

• C3.1.22

  Interactions between auxin and cytokinin as a means of regulating root and shoot growth

• 
  

  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.
  

• C3.1.23

  Positive feedback in fruit ripening and ethylene production

• 
  

  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.