A Level Biology Modul 3

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TOPIC

NOTES

KEY FACTS

QUESTIONS & EXERCISES

You really should know everything in this section before you sit the exam

heart cycle gaseous transport

CIRCULATION CONTROL OF BREATHING ENERGY & EXERCISE TRANSPORT IN PLANTS ALL

Heart T. Fluid Cycle Q1

summary diag.

Q1 Anaerobic Q1 Q2

Word version of notes

Heart Cycle control The pacemaker is the Sinoatrial node (SAN) which is responsible for the intrinsic heartbeat. Impulses originate from the SAN which causes atria to contract because the cardiac muscle transmits the impulse as it contracts. There is a slight delay of the impulse at the Atrioventricular node (AVN) to ensure that atrial contraction is complete before the ventricles contracts. The impulse passes to the ventricles via specially conductive fibres called Purkinje fibres which are grouped into the bundle of His in the septum and cause the rapid transmission of the impulse to the apex of the heart. From here the impulse spreads through the ventricles, causing them to contract from the apex upwards. The cardiovascular centre in medulla modifies heartbeat. Chemoreceptors in the aortic arch, carotid body and medulla detect [CO2], [O2] and pH. Impulses are sent from these receptors to the cardiovascular centre in the medulla. Depending on the input from these receptors either: Impulses are sent along sympathetic nerves to stimulate the SAN and increase cardiac output OR Impulses are sent along parasympathetic nerves (vagus nerves) to inhibit the SAN and decrease cardiac output

Transport of Gases by blood CO2 Transport: • • • • • • • • •

CO2 diffuses into blood (in solution);some carried in solution as CO2 (about 7%); CO2 diffuses along conc gradient into red cells; where carbonic anhydrase is present which converts CO2 to carbonic acid which dissasociates into hydrogencarbonate ions and H+ hydrogencarbonate diffuses out into blood plasma; this major form of CO2 carried (about 86%); buffering by haemoglobin (of H+) in lungs reactions reversed (due to changes in conc gradients); CO2 diffuses out into alveoli (along conc gradient);

O2 Transport Lung • • •

High partial pressure of oxygen in the lungs haemoglobin in lung capillaries has high affinity for oxygen; therefore becomes saturated with oxygen (Haemoglobin combining with oxygen to give oxyhaemoglobin)

Muscle

• • •

ODC curve shifted to right in muscle (Bohr effect) because of high carbon dioxide concentration/low pH and higher temperature; haemoglobin in muscle therefore has low affinity for oxygen; therefore oxyhaemoglobin dissociates/’gives up’ oxygen readily; therefore more oxygen available for muscle cells;

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Diffusion of oxygen into blood/tissues;

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SUMMARY OF AEROBIC AND ANAEROBIC PATHWAYS OF ATP SYNTHESIS