During erythropoiesis in the bone marrow, immature cells undergo significant structural modifications to differentiate into mature, functional erythrocytes.

Which of the following statements correctly describe the adaptations or characteristics of mature, functional human erythrocytes?

1. They possess a biconcave disc morphology, which increases the surface-area-to-volume ratio ($SA:V$) to facilitate a higher rate of gas exchange.
2. They lack mitochondria, which ensures they do not consume the oxygen they transport, relying instead on anaerobic respiration for ATP production.
3. They contain a highly developed rough endoplasmic reticulum to continuously synthesise and replace haemoglobin throughout their 120-day lifespan.