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Psychology (9,983)
PSYA02H3 (979)
John Bassili (149)
Chapter 12

Chapter 12 textbook notes

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Department
Psychology
Course Code
PSYA02H3
Professor
John Bassili

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Chapter 12
LIFESPAN DEVELOPMENT
- We recognize now that development does not stop at the end of childhood.
- Growing older is a matter not only of aging, but also of changing personally,
intellectually, and socially
- Developmental psychologists study both the similarities and the differences among
people as they develop and change
- Since they study change, developmental psychologists employ special strategies of
research
- Cross-sectional study individuals of different ages are simultaneously compared
with respect to some test or observation
- ex) a developmental psychologist might present mathematical problems to
groups of five-, seven-, and nine-year-olds to measure the childrens grasp of
the concept of negative numbers
- In contrast, a longitudinal study compares observations of the same individuals at
different times of their lives
- a longitudinal study of childrens grasp of negative numbers might test a
group of children when they were five years of age, and then repeat the test
on the same children at seven and then at nine
- Cross-sectional studies are usually more convenient to carry out, and they avoid
the problems associated with repeatedly testing or observing the same individuals
- However, they contain a subtle problem in interpretation
Prenatal Development
- The prenatal period extends over the approximately nine months between
conception and birth
- During the pregnancy (266days or 38 weeks), development depends on two factors
whose effects characterize themes of this chapter
-There is the genetic contribution from egg and sperm that determines the
genotype of the new individual
- Genetic material can replicate, producing descendants that are genetic copies of
this single cell
- A child develops from this single source of genetic “instructions”
- Prenatal development, however, is not simply a matter of cellular replication
producing copies of the original fertilized egg
- Although all cells of an individual (with the exception of reproductive cells) have the
same genetic content, they obviously differ
- ex) blood cells are not the same as neurons and muscle cells are not the
same as those that produce bone
- Some factor must direct the mechanisms of replication during the prenatal period
so that cells that are genetically identical will develop along different paths
- X chromosome inactivation is one example of this factor at work
- One of the two X chromosomes that women bear is “silenced early in
development, such that most of its genes do not synthesize the proteins they
normally would
www.notesolution.com
- Inactivation of one X chromosome is important because it limits the total
amount of proteins produced by genes located on the X chromosome
- Without this limit, the metabolism of a developing female would be very
different from that of a developing male (who has only one X chromosome)
- X chromosome inactivation occurs early in the development of females and
affects all subsequent cellular reproduction the “silenced chromosome is
passed along to descendant cells, but it remains silenced
- X chromosome inactivation is one example of an epigenetic modification, a
modification of cell inheritance that is not due to alteration of the DNA sequence it
self
Stages of Prenatal Development
- The union of the ovum (egg) and sperm, conception, is the starting point for
prenatal development
- During the zygote stage which lasts about two weeks, the zygote, or the single
new cell that is formed at conception, divides many times, and the internal
organs begin to form
- By the end of the first week, the zygote consists of about a hundred cells
- Many of the cells are arranged in two layers, one for the skin, hair, nervous
system, and sensory organs and the other for the digestive and respiratory
systems and glands
- Near the end of this stage, a third layer of cells appears that will eventually develop
into muscles and the circulatory and excretory systems
- The embryonic stage of prenatal development, the second stage, begins at aabout
two weeks and ends about eight week s after conception
- During this stage, the zygote is transformed into an embryo and
development occurs at an incredibly rapid pace
- By a month after conception, a heart has begun to beat, a brain and spinal cord
have started to function, and most of the major body structures are beginning
to harm
- By the end of this stage, the major features that define the human body- arms,
hands, fingers, legs, toes, shoulders, head, and eyes are discernible.
- Behaviorally, the embryo can react reflexively to stimulation
- ex) if the mouth is stimulated, the embryo moves its upper body and neck
- Because so many changes depend on a delicate chemical balance, the
embryo at this stage is most susceptible to external chemical influences,
including alcohol and other drugs, or toxins produced by diseases such as
rubella
- These substances are teratogens (any substance, agent, or event that can
cause birth defects)
- The beginning of sexual development occurs during the embryonic stage
- The 23rd chromosome pair determines the sex of the embryo
- The female partner contributes and X to this pair at conception, whereas the male
partner contributes either an X or a Y chromosome
www.notesolution.com
- If the male partner contributes a Y chromosome, the embryo will become a
male (XY); if he contributes an X, the embryo will become a female (XX)
- Early in prenatal development, the embryo develops a pair of gonads that will
become either ovaries or testes
- If a Y chromosome is present, a gene located on it causes the production of
a chemical signal that makes the gonads develop into testes
- Otherwise, the gonads become ovaries
- The presence or absence of testes determines the development of the other sex
organs
- If testes are present, they begin to secrete a class of sex hormones known
as androgens
- The most important androgen is testosterone
- Androgens bring about the development of the male internal sex organs, the
penis, and the scrotum
- The development of female sex organs (uterus, vagina, and labia) occurs naturally;
it does not need to be stimulated by a hormone
- The fetal stage is the final period of prenatal development and lasts about seven
months
- It officially begins with the appearance of bone cells and ends with birth
- At the end of the second month of pregnancy, the fetus is about 4cm long and
weighs about 30g
- By the end of the third month, the development of major organs is completed and
the bones and muscles are beginning to develop
- The fetus is now 8cm long and weighs about 90g
- The fetus may show some movement, especially kicking
- By the end of the fourth month, the fetus is about 15cm long and weighs about
170g.
- It is also now sleeping and waking regularly
- Fetal movements also become strong enough to be felt by the mother, and the
heartbeat is loud enough to be hear through a stethoscope
- Sound and light sensitivity will emerge within a few weeks
- During the sixth month, the fetus grows to more than 30cm long and weighs about
700g
- The seventh month is a critical month because if the fetus is born prematurely at
this point, it has a fair chance of surviving
- A newborn at this age would almost certainly require help breathing
- However, fetuses mature at different rates, and some seven-month-old
fetuses may be mature enough to survive premature birth while other may
not
- During the last two months of prenatal development, the fetus gains weight at the
rate of about 250g per week
- On average, the fetus is about 50cm long and weighs about 3.5kg at the
end of this period
- The fetus is ready to be born
Threats to Normal Prenatal Development
www.notesolution.com

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Description
Chapter 12 LIFESPAN DEVELOPMENT - We recognize now that development does not stop at the end of childhood. - Growing older is a matter not only of aging, but also of changing personally, intellectually, and socially - Developmental psychologists study both the similarities and the differences among people as they develop and change - Since they study change, developmental psychologists employ special strategies of research - Cross-sectional study individuals of different ages are simultaneously compared with respect to some test or observation - ex) a developmental psychologist might present mathematical problems to groups of five-, seven-, and nine-year-olds to measure the childrens grasp of the concept of negative numbers - In contrast, a longitudinal study compares observations of the same individuals at different times of their lives - a longitudinal study of childrens grasp of negative numbers might test a group of children when they were five years of age, and then repeat the test on the same children at seven and then at nine - Cross-sectional studies are usually more convenient to carry out, and they avoid the problems associated with repeatedly testing or observing the same individuals - However, they contain a subtle problem in interpretation Prenatal Development - The prenatal period extends over the approximately nine months between conception and birth - During the pregnancy (266days or 38 weeks), development depends on two factors whose effects characterize themes of this chapter -There is the genetic contribution from egg and sperm that determines the genotype of the new individual - Genetic material can replicate, producing descendants that are genetic copies of this single cell - A child develops from this single source of genetic instructions - Prenatal development, however, is not simply a matter of cellular replication producing copies of the original fertilized egg - Although all cells of an individual (with the exception of reproductive cells) have the same genetic content, they obviously differ - ex) blood cells are not the same as neurons and muscle cells are not the same as those that produce bone - Some factor must direct the mechanisms of replication during the prenatal period so that cells that are genetically identical will develop along different paths - X chromosome inactivation is one example of this factor at work - One of the two X chromosomes that women bear is silenced early in development, such that most of its genes do not synthesize the proteins they normally would www.notesolution.com - Inactivation of one X chromosome is important because it limits the total amount of proteins produced by genes located on the X chromosome - Without this limit, the metabolism of a developing female would be very different from that of a developing male (who has only one X chromosome) - X chromosome inactivation occurs early in the development of females and affects all subsequent cellular reproduction the silenced chromosome is passed along to descendant cells, but it remains silenced - X chromosome inactivation is one example of an epigenetic modification, a modification of cell inheritance that is not due to alteration of the DNA sequence it self Stages of Prenatal Development - The union of the ovum (egg) and sperm, conception, is the starting point for prenatal development - During the zygote stage which lasts about two weeks, the zygote, or the single new cell that is formed at conception, divides many times, and the internal organs begin to form - By the end of the first week, the zygote consists of about a hundred cells - Many of the cells are arranged in two layers, one for the skin, hair, nervous system, and sensory organs and the other for the digestive and respiratory systems and glands - Near the end of this stage, a third layer of cells appears that will eventually develop into muscles and the circulatory and excretory systems - The embryonic stage of prenatal development, the second stage, begins at aabout two weeks and ends about eight week s after conception - During this stage, the zygote is transformed into an embryo and development occurs at an incredibly rapid pace - By a month after conception, a heart has begun to beat, a brain and spinal cord have started to function, and most of the major body structures are beginning to harm - By the end of this stage, the major features that define the human body- arms, hands, fingers, legs, toes, shoulders, head, and eyes are discernible. - Behaviorally, the embryo can react reflexively to stimulation - ex) if the mouth is stimulated, the embryo moves its upper body and neck - Because so many changes depend on a delicate chemical balance, the embryo at this stage is most susceptible to external chemical influences, including alcohol and other drugs, or toxins produced by diseases such as rubella - These substances are teratogens (any substance, agent, or event that can cause birth defects) - The begrdning of sexual development occurs during the embryonic stage - The 23 chromosome pair determines the sex of the embryo - The female partner contributes and X to this pair at conception, whereas the male partner contributes either an X or a Y chromosome www.notesolution.com
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