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.

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 adolescence is and how it differs from puberty, which is part of it.

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

State whether these statements are true or false and justify your answer: a) girls usually start puberty somewhat earlier than boys; b) in old age the body stops changing; c) full physical maturity is reached in youth.

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.

Sexual characteristics are classified into primary and secondary. Explain the difference between the two groups and classify: appearance of armpit hair, development of the testes, widening of the hips, voice change (voice cracking), 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.

Explain why the first menstruation in girls and the first ejaculations in boys appear at puberty, relating these facts to the maturation of the reproductive systems.

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.

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

Compare the sleep needs of a baby, a teenager, and an older adult, and explain why sleeping well is especially important during the stages of growth.

Explain what 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.

In a decision-making experiment, 14-year-olds and 25-year-old adults were evaluated in a driving simulator with yellow 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 yellow 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:

• Olivia 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.

During puberty, hormonal changes naturally cause an increase in adipose tissue in girls (essential for the maturation of the reproductive system) and rapid musculoskeletal development in boys. However, many adolescents resort to extremely restrictive diets to mimic unrealistic standards of thinness seen on social media.

1. a) Biologically justify why maintaining an adequate percentage of body fat is essential for the proper functioning of the reproductive axis and the regulation of hormonal cycles.
2. b) Predict what physiological consequences severe caloric restriction sustained during puberty can have on growth in height, bone density, and fertility.

Over the past century and a half, the average age of menarche (girls' first menstruation, one of the milestones of puberty) has advanced from 16-17 years to 12-13 years in developed countries. In contrast, the average age for becoming independent and starting a family has been delayed beyond the age of 30.

1. a) Justify what biomedical and nutritional factors explain the earlier onset of reproductive maturity compared to the 19th century.
2. b) A friend claims: “If the body is already fertile at age 13, it means that biologically we are already full adults”. Refute this statement by providing two biological arguments (one concerning skeletal ossification and the other regarding the development of the nervous system).

A 14-year-old boy in the middle of his pubertal growth spurt is offered anabolic steroids (synthetic testosterone derivatives) at the gym to speed up muscle mass gain.

1. a) Sex hormones regulate both muscle development and the closure of epiphyseal plates (growth plates of long bones). Predict the irreversible consequence that taking anabolic steroids would have on his final height and explain why.
2. b) Knowing that the endocrine system self-regulates through negative feedback mechanisms, explain what will happen to the natural synthesis of testosterone in his own testicles if his body detects a massive presence of external synthetic hormone.