IB Biology HL C3.1 Integration of Body Systems Questions

Practise IB Biology HL C3.1 by tracing reflex pathways and explaining feedback control, endocrine signals, ventilation and plant responses.

Exam points

Explain emergent system properties as interacting components are organized from cells through tissues and organs.
Identify brain-region functions and use lesion, fMRI or movement evidence to explain integrated responses.
Trace a rapid withdrawal reflex from sensory input to motor output and skeletal-muscle response.
Explain darkness-triggered melatonin secretion and its role in circadian sleep timing.
Explain epinephrine effects on heart rate, ventilation and respiratory-fuel availability during stress.
Explain hypothalamic-pituitary endocrine control and interpret hormone-response data such as leptin's effect on appetite.
Explain medullary feedback control of heart rate and ventilation in response to blood-pressure and CO₂/pH signals.
Explain how peristalsis moves food through the intestine from the stomach toward the large intestine.
Explain positive shoot phototropism through auxin transport, shaded-side redistribution and acid-growth-driven elongation.
Identify auxin and cytokinin as phytohormones and relate their roles to plant growth and gene expression.
Explain ethylene-driven fruit ripening as positive feedback affecting nearby fruit.

Covered syllabus points

C3.1.1—System integration C3.1.2—Hierarchy in multicellular organisms C3.1.3—Integration of organs C3.1.4—Brain as information integration organ C3.1.5—Spinal cord C3.1.6—Input through sensory neurons C3.1.7—Output through motor neurons C3.1.8—Nerves as bundles C3.1.9—Pain reflex arcs C3.1.10—Cerebellum role C3.1.11—Melatonin and sleep C3.1.12—Epinephrine (adrenaline)C3.1.13—Hypothalamus and pituitary control C3.1.14—Heart rate feedback control C3.1.15—Ventilation rate feedback control C3.1.16—Peristalsis control C3.1.17 (HL)—Tropic responses in seedlings C3.1.18 (HL)—Positive phototropism C3.1.19 (HL)—Phytohormones C3.1.20 (HL)—Auxin efflux carriers C3.1.21 (HL)—Auxin promotes cell growth C3.1.22 (HL)—Auxin and cytokinin interactions C3.1.23 (HL)—Ethylene and fruit ripening

[Maximum number: 1]

A computer model simulation was proposed to assess the removal of extracellular polymeric substances (EPS) from biofilms by using a detachment-promoting agent (DPA).

Simulations on a 60-day-old biofilm after 6 minutes of treatment with DPA and on the same biofilm after 84 minutes of treatment with DPA are shown as a 3D view and a cross section. Dark grey represents bacteria and light grey shows the EPS.

State one reason, other than the formation of an EPS, for the high resistance to antimicrobial agents in biofilm microorganisms.

[Maximum number: 1]

Though a single nerve cell does not think, millions of them organized as a brain result in thinking. What kind of property does thinking represent?

Anatomical

Adaptive

Extracellular

Emergent

[Maximum number: 3]

The diagram shows the liver and its main blood vessels.

Outline the circulation of blood through liver tissue.

[Maximum number: 1]

The following images identify brain activity associated with a specific function.

Label the indicated areas on the images.

X:
Y:

[Maximum number: 1]

The spinal cord is involved in the coordination of involuntary actions such as the pain reflex.

Where are synapses between sensory neurons and interneurons found?

Spinal-cord cross section with pointers A to a swelling outside the cord at left, B to the small central opening, C to the upper right part of the butterfly-shaped inner region and D to a lower outgoing pathway.

[Maximum number: 6]

Explain how the eye detects stimuli and sends information to the brain.

[Maximum number: 1]

What is the main role of nerves in human movement?

To cause muscles to stretch

To move joints

To transport pain signals that indicate muscle injuries

To stimulate muscle contraction

[Maximum number: 3]

List the sequence of the components of a reflex arc for a pain withdrawal reflex.

[Maximum number: 1]

State a function of each of the following parts of the human brain.

Cerebellum

[Maximum number: 2]

Melatonin helps to control circadian rhythms in the body. The graph shows the mean levels of melatonin in the body in day and night workers over 24 hours.

(a)

State where melatonin is produced in the body.

[ 1 ]

(b)

Deduce, with a reason, what time of day would be a good time to take melatonin if you have travelled over several different time zones and are jet-lagged on your arrival.

[ 1 ]

[Maximum number: 2]

The diagram shows a G protein, bound to a G protein-coupled receptor (GPCR), a transmembrane receptor which responds to epinephrine (adrenaline).

Describe two ways in which epinephrine in the body facilitates intense muscle contraction. [2]

1.

2.

[Maximum number: 1]

State the pathway by which hormones travel from the hypothalamus to the anterior pituitary gland.

[Maximum number: 6]

Outline how the rate at which the heart beats is controlled.

[Maximum number: 8]

There is a relationship between form and function in the diversity of molecules and of systems.

Explain the causes of a decreased blood pH and its effects on the ventilation rate in humans.

a. increased (cellular) respiration can increase $\mathrm{CO}_{2}$ levels in blood

OR

anaerobic (cellular) respiration produces lactic acid;

b. due to exercise/lack of oxygen;

c. (aqueous) carbon dioxide reacts to form carbonic acid $/ \mathrm{H}^{+}$ ions (and $\mathrm{HCO}_{3}{ }^{-}$ ions) OR

increased $\mathrm{CO}_{2}$ levels in blood cause a decrease in pH / acidosis

OR

lactic acid in blood can release $\mathrm{H}^{+}$ ions / can cause a decrease in pH /acidosis;

d. in the presence of carbonic anhydrase (enzyme);

e. chemoreceptors detect levels of carbon dioxide (in the blood)

OR

chemoreceptors monitor (blood) $\mathrm{pH} / \mathrm{H}^{+}$ (in blood);

f. (chemoreceptors) found in aorta/carotid arteries;

g. (chemosensors/chemoreceptors) send information to respiratory centre in brain OR

to the medulla/brainstem;

h. (medulla) sends nervous impulses to the external intercostal muscles;

i. (medulla) sends nervous impulses to the diaphragm;

j. through intercostal/phrenic nerve;

k. increasing breathing/ventilation rate;

l. increasing volume of the lungs (during inhalation)/ increasing depth of breathing;

Marking guidance:

8 max

[Maximum number: 3]

Fluids inside unicellular and multicellular organisms allow materials to be moved.

Outline how food is moved from the stomach to the large intestine.

[Maximum number: 4]

Hormones are produced in plants and animals and cause changes in the organism.

Describe the role of the plant hormone auxin in phototropism.

[Maximum number: 2]

(a) Explain how the pressure potential and solute potential change inside a plant root cell when it is placed into a solution that is more hypotonic than the cell's cytoplasm.

The photograph shows a seedling (young plant) of the family Fabaceae. The shoot and roots have been labelled.

Photograph of a Fabaceae seedling with a shoot rising to a young leaf and several branching roots below; pointers label shoot and roots.

State the name and site of production of two phytohormones that regulate the growth of seedlings.

Blank two-row answer table with column headings name of phytohormone and site of production.

Hormone	Site of production
Auxin	Shoot (tip)
Cytokinin	Root (tip)

[Maximum number: 6]

Auxin can be used to promote the development of roots from stem and leafy cuttings in some plants. In a study into the distribution of auxin in the development of these roots, scientists measured the amount of auxin in different leaves of a shoot tip of Petunia hybrida.

The figure indicates the numbering of leaves on the shoot, from L1 as the youngest and smallest to L6 as the largest and oldest leaf. The developmental stage of L5 and L6 was very similar, so L5 was not analysed. The stem base is the lowest part of the cutting where roots may form.

The graph shows the auxin concentration in the different leaves.

(a)

N-1-naphthylphthalamic acid (NPA) is an inhibitor used to block auxin transport. NPA was sprayed onto the leaves of a set of cuttings for 14 days. Development of the roots in control (non-treated) and NPA-treated cuttings was measured 14 days after taking the cuttings. The table shows the influence of NPA on rooting.

Analyse the effect of NPA on the formation of roots.

[ 2 ]

a. NPA decreased the «mean» number of roots per rooted cutting «by about $5 \times$ »
b. NPA decreased the «mean» length per root «by more than half»
c. NPA decreased the «mean» total root length per planted cutting «to about 2 % of control»
d. NPA inhibited the formation of roots
OR
decreased all three measures

(b)

The scientists also measured the changes in auxin concentration in L6 and the stem base during the early period of root formation. They recorded the concentration in the control and NPA-treated cuttings for 24 hours after taking the cuttings.

[ 4 ]

(i)

Compare and contrast the changes in auxin concentration in the stem base over time for the control and NPA-treated cuttings.

[ 2 ]

(ii)

Deduce the effect of NPA on auxin transport between L6 and the stem base.

[ 2 ]

[Maximum number: 2]

Plants have cell walls composed of cellulose.

When a plant cell grows, the cell wall must expand. Explain the role of auxin in cell wall expansion.

[Maximum number: 1]

What plays a direct role in promoting the ripening of fruit?

Oestradiol

Auxin

Cytokines

Ethylene

All question bank results loaded

a	quorum sensing;
b	high biomass density;
c	low/no cell division;
d	limited supply of nutrients;
e	less penetration/diffusion of substances;
f	emergent properties;

Covered syllabus points

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