Exercises: The life cycle

In the timeline, the five stages of the human life cycle are represented from left to right at the positions marked with ?; below, their names appear out of order. Write the name of the stage corresponding to each position (from 1 to 5) and state a physical or psychological characteristic typical of each one.

Explain what puberty is, in which stage of life it occurs, and state two physical changes that take place during it in boys and two in girls.

State whether these statements about adolescence are true or false and justify your answer: a) all adolescents start puberty at the same age; b) during adolescence, both physical and emotional changes occur; c) sexual maturation means that the body is now able to reproduce.

Sexual characteristics are classified into primary and secondary. Explain the difference between both groups and classify: appearance of armpit hair, development of the testes, widening of the hips, voice breaking, maturation of the ovaries, growth of facial hair (beard).

A 12-year-old boy is worried because his classmates have had a "growth spurt" and he has not yet. Explain to him, using biological arguments, why not all adolescents mature at the same time and what factors influence the rate of puberty.

The first menstruation (menarche) usually occurs between the ages of 10 and 15. Explain what it signifies from the point of view of reproductive system maturation and why its arrival does not mean that the rest of physical and emotional development is complete.

In a decision-making experiment, 14-year-olds and 25-year-old adults were evaluated in a driving simulator with amber traffic lights.

• Driving alone: both the 14-year-olds and the 25-year-old adults took a low and very similar level of risk.

• Driving with two peers of the same age in the room: adolescents doubled their risky behaviors (accelerating through amber lights), whereas in adults, the risk did not change.

1. a) Based on the asynchronous development of the brain during adolescence (the emotional and reward limbic system versus the prefrontal cortex for control and planning), justify why the presence of a peer group has such a strong influence on adolescents' risky decisions.
2. b) Design a specific guideline or preventive strategy that a student your age can apply when facing peer pressure to avoid acting impulsively.

Two 75-year-old individuals suffer an identical trip on the street:

• Lucía engaged in strength and moderate-impact exercise during her youth and maintained a diet rich in calcium and vitamin D; her bone mass shows a slight loss typical of old age, and after the fall, she only suffers a bruise.

• Carmen led a sedentary life from adolescence onwards, avoided dairy products, and rarely spent time in the sun; she suffers from advanced osteoporosis and, after the same fall, fractures her hip.

1. a) Explain the concept of "peak bone mass" achieved at the end of growth and justify why lifestyle during adolescence and youth conditions bone fragility in old age.
2. b) A classmate claims: “I don't need to exercise or watch what I eat at 14; when I turn 60, I'll start taking calcium for my bones”. Refute their argument using biological reasons.

A classmate reads that in the 19th century life expectancy in Spain was around 35 years and concludes: “That proves that the human life cycle has changed: in the past, puberty started at age 7, old age was already reached at 20, and our bodies aged twice as fast”.

1. a) Refute their conclusion by explaining precisely the difference between the biological stages of our species' life cycle and the statistical indicator of "life expectancy at birth".
2. b) What demographic phenomenon concentrated in the earliest stages of life drastically lowered that average in the past, even though adults could live to be 70? Mention two biomedical advances that made it possible to raise life expectancy by reducing this phenomenon.