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Cell
division 4.
Growth (e.g. of children),
cell division, development and understanding how to read percentile charts
of growth
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Doc Brown's biology exam revision notes suitable for students of UK
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page on cell-division updated
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Sub-index for biology notes on many of
cell division
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(4) Cell division, growth (e.g. of children), development and reading percentile charts
Growth of any multicellular organism
involves increase in size and mass.
Plants and animals grow and develop by
various processes:
Cell differentiation is the
process in which a cell becomes specialised for a particular function -
this increases the efficiency and viability of multi-cellular organisms
to survive. (See
cell specialisation notes)
Cell division by mitosis
(previously described
in part 2)
The two points above apply to any
multicellular organisms, but plants can also grow by cell elongation
- plant cells can expand to grow bigger so the whole plant increases in
size.
Animal growth and development
All growth in animals occurs by cell
division, and most growth happens when the animal is young.
After full growth to be an adult, the
animal stops growing.
Therefore when an animal is young you
get the fastest rates of cell division - fastest growth rates.
In adulthood most cell division is
for 'body repairs', that is growing new cells to replace damaged or dead
cells.
In most animals cell differentiation
is lost at a relatively early age of development.
Percentile charts and monitoring
growth of young children
Growth charts (development graphs) are used to
monitor a child's development in size or weight to see if there appears
to be any problem.
Example 1. Babies and young children
Its normal to monitor a baby's growth
after birth to see if it is growing normally - three common measurements
are used - length, mass ('weight') and head circumference.
You should immediately bear in mind
the wide variety of 'sizes' in young children - we are talking
'statistics'.
Doctors will be called in to
investigate if the baby's/child's size or weight is above the top percentile or below the
bottom percentile - in other words - is there abnormal growth in some
way - too much or too little?
Also, if a baby's growth increases or
decreases by two or more percentile lines, or the growth pattern is
inconsistent, then a medical investigation may be needed.
Using thousands of data sets from
many babies you can plot growth charts.
Growth charts are plotted as a series
of 'percentile' graph line e.g.
a 50th percentile line will show that 50% of babies/children will have
reached a particular value or less of height or weight etc.
Statistically, the 50th percentile
line is the median (middle value) of the data set.
The data for boys and girls weight aged 1 to 4 years are shown in the
percentile charts above.
Example of percentile chart
interpretations:
At age 3, 50% of boys have
reached a weight of up to 14.5 kg, so 50% will have a weight of over
14.5 kg..
At age 2, 50% of girls have
reached a weight of up to 11.5 kg, so 50% will have a weight
of over 11.5 kg..
Example 2. Young children and
teenagers
The percentile data on height in cm for
boys aged 9 to 18 years (note the 'acceleration' due to puberty, and then a
levelling off of the graph into adulthood).
Example of percentile chart
interpretation: 75th percentile line
At age 14, 75 % of boys have grown to a
height of 168 cm or less, so 25 % of boys are taller than 168 cm aged 14
years.
The percentile data on height in cm for
girls aged 8 to 18 years (note the 'acceleration' due to puberty, and then a
levelling off of the graph into adulthood).
Example of percentile chart
interpretation: 25th percentile line
At age 14, 25 % of girls have grown to a
height of 157 cm or less, so 25 % of girls are taller than 157 cm aged 14
years.
The percentile data on weight in kg for
boys aged 9 to 18 years (note the 'acceleration' due to puberty, and then a
levelling off of the graph into adulthood).
Example of percentile chart
interpretation:
At age 13, 50 % of boys have grown to a
weight of 43 kg or less, so 50 % of boys have a weight greater of 43 kg aged
13 years.
The percentile data on weight in kg for
girls aged 8 to 18 years (note the 'acceleration' due to puberty, and then a
levelling off of the graph into adulthood).
Example of percentile chart
interpretation:
At age 16, 75 % of girls have grown to a
weight of 62 kg or less, so 25 % of girls have a weight greater of 62 kg
aged 16 years.
Example 3. Comparing percentile
trends with each other
You can also do comparison charts of
one percentile versus another.
This is another diagnostic approach to looking for
overweight (obese) boys and girls aged 2 to 18
For lots of examples of growth charts
from the UK see
and
https://www.rcpch.ac.uk/resources/uk-who-growth-charts-0-4-years
https://www.rcpch.ac.uk/sites/default/files/Boys_2-18_years_growth_chart.pdf
https://www.rcpch.ac.uk/sites/default/files/Girls_2-18_years_growth_chart.pdf
for downloads to study and from which I prepared the chart
diagrams in this section.
Key points -
Summary of ideas - much of this on cell division is covered already in
other sections 1-4
Based on
the syllabus-specifications for students taking the AQA, Edexcel and OCR
GCSE level biology examinations (~US grades 9-10).
Revision Notes:
Cell Division, Growth & Development, and Understanding Growth Charts
1.
Cell Division
Cell division is essential
for growth, repair, and reproduction. There are two key types:
Mitosis
-
Produces
two genetically identical
diploid daughter cells
-
Used for
growth, repair, and asexual
reproduction
-
Stages:
Interphase, Prophase, Metaphase,
Anaphase, Telophase,
Cytokinesis
-
Ensures new cells have
the same genetic material as the parent
Meiosis
-
Produces
four genetically unique
haploid cells
-
Occurs in
gamete (sex cell) formation
-
Leads to
genetic variation
-
Two rounds
of division: Meiosis I and
Meiosis II
2.
Growth and
Development in Children
Growth occurs due to
mitosis and changes in cell size and number. Factors influencing growth
include:
-
Genetics
(inherited traits from parents)
-
Nutrition
(balanced diet supports cell function)
-
Hormones
(growth hormones regulate body size)
-
Health
(diseases can impact development)
Growth Patterns
in Boys and Girls
-
Boys tend to
grow taller later in adolescence
-
Girls begin
puberty earlier and experience earlier growth spurts
-
Growth curves
typically flatten after puberty
3.
Understanding
Percentile Charts
Percentile charts help
compare a child’s growth to population averages. Key terms:
-
Percentiles
indicate position in comparison to others (e.g., 50th percentile =
average)
-
Growth trends
allow doctors to assess normal development
-
Abnormal
deviations may
indicate growth issues
How to Read
Growth Charts
-
Find age
on the x-axis
-
Locate
height/weight on the y-axis
-
Follow the curve for
percentile information
-
Compare boys
vs. girls charts, as they differ
4.
Graphical
Representation of Growth
-
Line graphs
show changes over time
-
Bar graphs
compare different groups (e.g., boys vs. girls)
-
Scatter plots
reveal trends in individual growth patterns
Exam Tips
Summary of
learning objectives and key words or phrases
Be able to correlate cell division with the growth of
children.
Be able to read, understand and interpret percentile
charts graphs of growth of boys and girls compared
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