Title: Pattern of Human Growth 05 July 2018 Learning question: what can go wrong in meiosis and how can this be detected? Homework: Revise this module – class text next Wednesday

Key words Absolute growth rate Relative growth rate Life cycle

Aims from specification (c) describe, with the aid of diagrams, the pattern of growth during the human life cycle; (d) explain and interpret growth charts for males and females from birth to 18 years of age (HSW5b); (e) distinguish between absolute and relative growth rates; (f) explain that humans are multicellular organisms in which genetically identical cells are organised into tissues, tissues into organs and organs into organ systems; (g) describe the differential growth patterns of lymphatic, reproductive and nervous tissue.

Growth during human life cycle The human life cycle covers the period from conception, through: The fetal growth phase Growth rate is very high Infancy and childhood Growth rate is very rapid at first then the rate of growth slows down to a steadier rate Adolescence Rapid growth spurt due to puberty Adulthood Growth rate falls to zero, as person’s body mass or height stops increasing

Absolute growth rate The graph below shows the mass of a human plotted against age. This is the absolute growth rate of a human and us useful to show overall growth patterns Can also be used to plot height or mass against time to show the rate of growth

Relative growth rate This shows the efficiency of growth, because it compares mass or height with the measurement at the beginning of the time period Relative growth rate is a specific growth rate. It shows the increase compared to the initial height/mass

Different parts, different growth rates Humans are multicellular organisms, growing from a zygote to blastocyst, to embryo, to fetus. Cells start off genetically identical, but differentiate to form different tissues, organs and organ systems. Organ systems comprise several organs that work together to perform a function

Different parts, different growth rates Not all organ systems develop at the same rate The head of a fetus grows rapidly and reaches adult size early. Humans have large brains – need to learn complex skills from an early age Animals with smaller brains are not able to do this Reproductive organs have a slow growth rate Prevents humans from reproducing until they have learned the complex skills they need to look after a very dependant baby

Different parts, different growth rates Describe the growth rate of the nervous system compared to the average of all systems and the reproductive system Can you think of a reason to account for the growth pattern of the lymphatic system?

Different parts, different growth rates The lymphatic system is involved in the immune system. A fetus gets its immunity from antibodies passed from the mother via the placenta (passive immunity) After birth, the baby continues to receive antibodies via breast milk The lymphatic system develops very rapidly in childhood and the immune system is very active in producing antibodies to common childhood pathogens (active immunity) Reproductive system is last to develop, as these organs are not needed until puberty. This occurs between 9-15 years in girls and 10-16 years in boys

Complete questions on page 93