Development
Unit 2.2
The Continuation of Life
Pre-natal development
After fertilisation, 9 months of development from a single cell to a fully formed baby take
place inside the uterus of a female.
First stages
1. a) Explain the difference between the terms pre-natal and post-natal development.
2 a)(i) What type of cell division happens during cleavage and why is this important?
(ii) Label the diagram and note what the chorion is.
(iii) By what means does the chorion make a space for the
embryo in the uterus wall?
(iv) Explain why it is important that the embryo then forms finger-like projections.
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b) Annotate the diagram of fertilisation to implantation.
c) Explain what is meant by differentiation and the importance of this process.
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Twins
3 a) Distinguish between the terms monozygotic and dizygotic twins with reference to the
gametes from which they arose.
b) Draw a table to compare the development of monozygotic and dizygotic twins with
reference to the number of placentas, chorions and amniotic sacs present in each case.
c) Explain why monozygotic twins must always be the same sex as each other.
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The Placenta and Exchange of material
4a)(i) Useful exchanges between maternal and fetal circulation involve movement of dissolved
gases, glucose and antibodies. Match each of these with one of the following means of
molecular transport: active transport, pinocytosis, diffusion and explain why.
(ii) In terms of the fetal and maternal blood, explain why molecular transport is necessary.
b) The placenta does not form a barrier to harmful substances or pathogens. Four harmful
agents that are able to cross the placenta are listed below. Match these to the possible
adverse effects on the developing embryo.
heroin
congenital defects of eyes and ears
HIV
failure of limbs to develop properly.
rubella
painful post-natal withdrawal symptoms
thalidomide
development of AIDS at an early age.
5 a) (i) Identify the roles played by progesterone and oestrogen during gestation.
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(ii) Describe the sites of production of both hormones throughout pregnancy.
(iii) Describe the role the chorion plays in gestation.
b) (i) Note the function of the hormone prolactin and name the gland that secretes it.
Rhesus factor
6 a) Explain why a Rh+ fetus is regarded as foreign by the immune system of a Rh– mother.
b)(i) Describe the series of events that lead to a Rh– mother becoming sensitised.
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(ii)In the absence of any form of treatment, explain why future Rh+ embryos borne by a
sensitised Rh– mother will be at risk.
(iii) The outcome of this is called haemolytic disease of a new-born. How can this be: -
 treated –
 prevented -
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Birth and post-natal development
After 38 weeks a human fetus is said to be “full-term” and is ready to be born and begin a
lifetime of growth and development.
Birth and beyond
1 a) During labour leading to normal parturition, the amniotic sac bursts and the cervix of
the uterus becomes …………………………. . Contractions of the uterine wall start at the
…………………… of the uterus and travel ……………………………… in waves. The contractions
gradually …………………………….. in power and frequency until the baby is expelled from the
………………………… and delivered through the ………………… .
b) (i) Identify what oxytocin is and which gland secretes it.
(ii) Describe the means by which birth can be induced artificially.
2. a) (i) What other role does oxytocin have?
(ii) Note what colostrum is.
(iii) Explain why it is important that the baby receives colostrums for several days
following the birth.
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b) (i) Identify the components of breast milk that give it a higher energy content
than colostrum.
(ii) Explain why breast milk is regarded as being superior to cows’ milk as a food
source for babies.
c) Note the harmful fat-soluble chemical that some breast milk might be contaminated
with and explain how this could be possible.
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Patterns of growth and growth hormones
3 a)(i) Explain what a growth spurt is.
(ii) Identify and label the two growth spurts that affect humans on the graph below.
(iii) Compare the growth of males and females.
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The graph below compares the growth rates of different parts of the body.
b) Why do you think the brain develops quickest and the reproductive organs slowest?
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Role of growth hormones
4 a) Where is somatotrophin (human growth hormone) produced?
b) Describe TWO ways in which somatotrophin promotes growth.
c) Complete the table to show the effects of differing levels of somatotrophin
production.
production of
somatotrophin
during period of
development
named condition
effects
normal
adolescence
-
normal growth
low
high
high
d) Describe how growth hormone is obtained for use in treating children who show early
signs of pituitary dwarfism.
Puberty
5. a) Major changes to the body occur in males and females at puberty.
List THREE for each sex.
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b) List the chain of events that cause these changes to occur during puberty.
6 a) Testosterone, oestrogen and progesterone are all natural steroid hormones. Explain
how these hormones have their effect.
b) (i) Note what anabolic steroids are.
(ii) Why do some healthy people choose to take these?
(iii) Give ONE possible harmful side effect of anabolic steroids to each sex.
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