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.

Order the stages of the human life cycle — old age, youth, childhood, adulthood, adolescence — and state which one you are in and one characteristic of the stage that will come next.

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.

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.

Explain what it means that adolescence is a stage of transition between childhood and adulthood, giving one example of this transition in the physical aspect and another in the social one.

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.

Explain what the menopause is, what biological change marks it, and what effects it can have on a woman's health, indicating one habit that helps to prevent each one.

Explain which emotional and social changes are frequent during adolescence and why the group of friends becomes so important at this stage.

Mood swings are frequent in adolescence. Explain them by relating the action of hormones, the remodelling of the adolescent brain and the new social situations experienced at those ages.

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 behaviours (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 $70$-year-old people can be in very different physical shape: one runs fun runs and the other cannot climb stairs. Explain why biological age does not always match calendar age, and which habits influence how we age.

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.

Look at the comparative data from two population groups followed until the end of their life cycle:

• Group A (sedentary habits, regular consumption of ultra-processed foods and tobacco from age 15): Life expectancy = 78,5 years; disability-free life expectancy = 58,0 years.

• Group B (regular physical activity of strength and endurance, Mediterranean diet, and absence of toxic substances from youth): Life expectancy = 84,0 years; disability-free life expectancy = 74,5 years.

1. a) Calculate how many years each group lives with a limiting chronic disease or loss of autonomy, and explain the difference between "extending life" and "extending healthy life years".
2. b) Justify at a cellular and physiological level why bad habits during adolescence (such as damage to the vascular endothelium from smoking or bone mass deficit due to a sedentary lifestyle) have a cumulative impact that manifests at age 70, even if at age 15 the person feels completely healthy.