Respiration, Muscles and the Internal Environment flashcards

Topic 7: Respiration, Muscles and the Internal Environment

Substrate level vs oxidative phosphorylation

Substrate level: ATP made by transferring a phosphate group from a substrate directly to ADP. Oxidative: ATP made using energy from electrons passing along the electron transport chain, with oxygen as the final acceptor.

Glycolysis in steps

Glucose is phosphorylated using 2 ATP; the hexose bisphosphate splits into two 3C molecules; these are dehydrogenated, reducing NAD; 4 ATP are made by substrate level phosphorylation; two pyruvate form. Net 2 ATP. In the cytoplasm.

Products of the Krebs cycle per turn

2 CO₂, 3 reduced NAD, 1 reduced FAD and 1 ATP per turn. The cycle turns twice per glucose. The acetyl group joins a four-carbon compound, which is regenerated.

Oxidative phosphorylation in steps

Reduced NAD and FAD give up hydrogen. Electrons pass along carriers in the inner membrane, losing energy that pumps H⁺ into the intermembrane space. H⁺ flows back through ATP synthase, making ATP. Oxygen accepts electrons and H⁺, forming water.

What happens to lactate after anaerobic respiration?

It travels in the blood from muscle to the liver, where it is converted to pyruvate, then oxidised in the Krebs cycle or converted to glucose or glycogen. This needs oxygen, so oxygen uptake stays above resting level after exercise.

Respiratory quotient (RQ) values

RQ = CO₂ produced ÷ O₂ consumed. Lipid about 0.7; protein about 0.9; carbohydrate 1.0; yeast respiring partly anaerobically: above 1.

Flexor vs extensor muscles; tendon vs ligament

Flexor contracts to bend a joint; extensor contracts to straighten it (an antagonistic pair; muscles only pull). Tendon: inelastic, joins muscle to bone. Ligament: slightly elastic, joins bone to bone.

Slow twitch vs fast twitch fibres

Slow twitch: slow, sustained contraction; slow to fatigue; aerobic; many mitochondria and much myoglobin. Fast twitch: fast, powerful; fatigue quickly; anaerobic glycolysis and phosphocreatine; fewer mitochondria, little myoglobin.

Sliding filament theory: the role of Ca²⁺ and ATP

An action potential along the T tubules makes the sarcoplasmic reticulum release Ca²⁺, which binds troponin; tropomyosin moves to expose binding sites on actin. Myosin heads bind and make a power stroke. ATP binds to detach the head, and its hydrolysis re-sets it.

ECG: P wave, QRS complex and T wave

P wave: atrial depolarisation. QRS complex: ventricular depolarisation. T wave: ventricular repolarisation. Heart rate = 60 ÷ R-to-R time in seconds.

Stroke volume and cardiac output

Stroke volume = end-diastolic volume − end-systolic volume. Cardiac output = stroke volume × heart rate.

Thermoregulation: responses when too hot vs too cold

Detected by the hypothalamus and skin thermoreceptors. Too hot: vasodilation of skin arterioles, sweating. Too cold: vasoconstriction, shivering, less sweating, raised metabolic rate.

How is urea formed?

Excess amino acids are deaminated in the liver. The amino group becomes ammonia, which is combined with carbon dioxide to form urea, carried in plasma to the kidneys.

Role of the loop of Henle

The descending limb is permeable to water, which leaves by osmosis. The ascending limb is impermeable to water and ions leave it (actively in the thick part), so the medulla becomes concentrated. This countercurrent gradient lets the collecting duct reabsorb water.

ADH response when plasma is too concentrated

Osmoreceptors in the hypothalamus shrink and stimulate neurosecretory cells; ADH is released from the posterior pituitary; aquaporins are inserted into collecting duct membranes; more water is reabsorbed, giving a small volume of concentrated urine.

Steroid vs peptide hormones in switching genes on

Steroid: lipid-soluble; diffuses across the membrane and binds a receptor inside the cell; the hormone–receptor complex is itself a transcription factor. Peptide: water-soluble; binds a receptor on the cell surface membrane; a second messenger cascade activates transcription factors.