chapter 10 growth

:

CHAPTER 10.0

GROWTH

(3 hrs)

10.0 Growth (3 hrs)

10.1 Growth phases (½)

10.2 Measurement of growth (½)

10.3 Growth patterns (1½)

10.4 Growth rate (½)

Learning outcomes

At the end of this topic, students should be able to :

a) Define growth.

b) State 3 phases of individual growth:

i. Cell division

ii. Cell enlargement

iii. Cell differentiation

Learning outcomes: 10.1 (a) Define growth

• Is an increase in size of an organism

• Through cell division and cell enlargement

• Over a specific of time

• Irreversible in nature

• Beginning from the

zygote stage to adult

stage.

Height (cm)

Age (year)

Height (cm)

GROWTH

Learning outcomes: 10.1 (a) Define growth

• Growth parameters include :

- biomass

- length

- width

- height

- volume

- cell number

Height (cm)

Age (year)

Height (cm)

Learning outcomes: 10.1 (b) State 3 phases of individual growth:

3 phases of individual growth :

i) cell division

ii) cell enlargement

iii) cell differentiation

Height (cm)

Age (year)

1. Cell division

o Cell divides from new

cell by mitosis

o At root tips/shoot tips

o Daughter cells have

dense protoplasm

o Daughter cells have

same number of

chromosomes/genetic

constitution with the

parent cells


Individual Growth Phases

2. Cell enlargement

o The newly formed cell

absorb water by osmosis

o Resulting in increased

turgidity/expansion/dilation

of the elastic cell wall

o Cell increase in size,

volume and mass

o In the initial stage,

enlargement occurs in all

directions

o Later, enlargement

confined to a specific

directions


3. Cell differentiation

o Cells mature to obtain

a permanent size

o The cell walls grow in

thickness

o Attain specialized

/specific structure

o And performed

particular function


10.0 Growth (3 hrs)



10.3 Growth patterns (1)


10.5 Growth under extreme condition

(½)

Learning outcomes


Explain how growth is measured.

• Growth can be measured by using a certain parameter over a period of time.

• Parameter chosen must be appropriate to the organism whose growth is to be measured.

• Eg: height, appropriate for human but not trees (can’t measure growth of root)

Measurements of Growth

Learning outcomes: 10.2 Explain how growth is measured.




Size Biomass

• Easy & quick to be carried out.

• No need to kill the organism.

• Can be measured continuously to observe growth.

Size

length/height/width

surface area

volume

• Measures in 1 or linear dimension.

• Doesn’t measure/consider growth in other direction or dimension.

Advantage Disadvantage


http://www.biologie.uni-hamburg.de/b-online/virtualplants/cotton3d.avi

• Mass of an organism under normal conditions that is without removal of body water content.

Biomass

Wet/fresh mass Dry mass

• Mass of an organism after removing all its water content from its body by drying.


• Easy to measure, requires little preparation of the sample.

• Doesn’t cause injury to an organism.

• Can be used to monitor growth of an organism over a period of time.

Wet/fresh mass

• Doesn’t measure true growth because it may give inconsistent readings.

• Influenced & fluctuations in water content of the body.



• Accurate measurement of the amount of organic matter present.

Dry mass

• (Many) organisms are killed.

• Growth of the same specimen can’t be measured continuously.

• Need a large number of genetically identical specimen grown under similar condition to measure growth to obtain a representative reflection of growth.

• Can’t be used to monitor growth of an organism over a period of time.

• Time consuming.



10.0 Growth (3 hrs)





10.5 Growth under extreme condition

(½)

Learning outcomes

a) Explain sigmoid growth curve (organism and population).

b) Explain human growth curve.

c) Explain limited growth curve (annual plants) and unlimited growth curve (perennial plants).

d) Explain isometric growth (fish) and allometric growth (human organs).

e) Explain intermittent growth curve (arthropods).

a) Sigmoid Growth Curve

b e a c d

Learning outcomes: 10.3 a) Explain sigmoid growth curve


• Most growth curve of organisms is sigmoid.

• It has S-shaped growth curve.

• Also known as actual / absolute growth curve.

• Growth starts slowly at first, then a rapid period of growth until reach maturity, growth begins to slow down & stops.



Can be plotted when absolute parameter (eg: height or mass) against time.

A growth curve is obtained which has S-shaped or sigmoid curve.


• Sigmoid curve is divided into 5 parts :

1. Lag phase

2. Log phase

3. Decelerating phase / linear growth

4. Stationary / plateau phase

5. Senescense



b e a c d


a) Lag phase

• Slow growth occur due to very few cells at initial

stage.

• These cells are actively dividing but actual increase

in size is small.

b e a c d


b) Log phase/exponential phase

• Growth proceeds exponentially.

• The rate of growth increase & proportional to the

number of cells present.

• There is no limiting factors.

• The rate of growth is maximum.

b e a c d


c) Linear growth phase/ decelerating phase

• Growth becomes limited/slows down/decrease & rate of

growth takes place at constant rate.

• It is limited by internal (matured) or external factors

(food sources, space, competition).

b e a c d


d) Stationary/plateau/equilibrium phase

• The organism has achieved maturity.

• Overall growth ceases/stop

• The rate of cell division = rate of cell mortality.

• Net growth rate is zero.

b e a c d


• When replacement of cells is slower than the death of cells, the curve slopes downward and senescence sets in.

e) Senescense

b) Human Growth Curve

Learning outcomes: 10.3 b) Explain human growth curve.

Pattern of Growth in Human

Prenatal Growth

Postnatal Growth

Infant phase

0 – 3 yrs

Childhood phase

3-12 yrs

Adolescence phase

12 - 18 yrs

Adult phase

> 18 yrs


• There are two growth spurts, one at infancy and the

other at puberty.

•Between these two phases there is a period of

relatively slow growth (steady).


Growth in Human

• When adulthood is reached, the growth process

stops.

• Human growth curves appear as two sigmoid

curves joined together.


Growth in Human

.

4 phases :

a) Infant phase :

Growth rate is very

rapid irrespective of

whether the baby is

male or female.


Human Growth Curve

b) Childhood phase :

Growth rate is

slower. Growth

rate in male is

slightly higher

than to female.


c) Adolescent phase :

Growth is rapid when

sexual maturity is

reached at puberty :

- at ~ 11 years female

have more rapid

growth rate.

- at ~ 14 years male

growth rate becomes

higher than female.


d) Adult phase :

- Growth rate is zero

and most individuals

would have attained

maturity.

- Males achieve this

phase at the age of

about 18 while

females at the age of

about 16.


e) Ageing phase :

Growth rate is

negative, that is, the

size of cells will start

to decrease starting

from the age of

about 30.


c) Limited & Unlimited Growth Curve

Learning outcomes: 10.3 c) Explain limited growth curve and unlimited growth curve.

Limited Growth Curve Unlimited Growth Curve


Limited Growth Curve

• Definite/determinate growth •The growth does not continue throughout life/until death •Organism shows limited growth, up to certain size. • Growth is stopped / declined when a maximum size is achieved. • Eg : annual crops, pea, mammals.



• A slight decrease in dry mass in the initial stage of germination. • Food reserve is used for respiration to provide energy.

Consist of 3 stages (annual plant) :

Stage I

1



Stage II

2

• Large increase in dry mass after 1st week. • The first leaf emerges & start to photosynthesis. • The dry mass increases.



Stage III

3

• Decrease in dry mass before death of plants. • The negative growth is due to senescence (eg : fall of leaves).

Unlimited Growth Curve


• Growth pattern consists of cumulative series of sigmoid curves. • Each sigmoid curve represents 1 year’s growth. • Each sigmoid curve can be divided into 4 parts. • Each part corresponding to a season. • Eg : woody perennials plants.

• Also known as indefinite / indeterminate growth. • Organisms grow continuously throughout its life/until death



In Spring

• Temperature & light intensity are low. • A small increase in the height of plant occurs due to very little photosynthesis.



In Summer

• As the temperature & light intensity increase, the rate of photosynthesis increase. • Results in a large increase in the height of plants.



In Autumn

• Temperature & light intensity are lower than in summer.

• Less photosynthesis occur.

• Small increase in the height of the plants.



In Winter

• Conditions is not suitable for photosynthesis.

• Growth is very slow because there is no/very little photosynthesis.

• The growth curve flattens.



• In the following spring, the entire process is repeated.

• Perennial plants grow continuously, the graphs never flatten.

• Every season, the size & weight keep increasing.

• Except it is restricted by environmental factors.

• Such as the presence of parasites, natural predators, outbreak of diseases which will kill the organism.

d) Isometric and Allometric Growth

Learning outcomes: 10.3 d) Explain isometric growth and allometric growth.

Isos : same; metron : measure

Growth in which the various organs within an organism grow at the same rate as the rest of the body.

The organism increase in size without changing its shape.

Its shape is consistent throughout development.

The relative proportion of the organ & whole body remains the same.

Eg : fish, insects

Growth curve is typically sigmoid

Isometric Growth


Isometric Growth

d) Isometric and Allometric Growth


Allometric Growth

Allos : other

Growth in which the various organs/parts within an organism grow at different rate.

As the size of organism increase, the shape changes.

Occurs in animals & human.

In most animals, the last organ to develop & differentiate are reproductive organ.


Allometric Growth


Allometric Growth

In human, head, lymphoid tissue & reproductive organs grow at very different rate.

Head grows rapidly in the first 5 years after birth.

After that, it doesn’t

grow much.

Lymphoid tissue grows rapidly from birth to early adolescence.

After that, the growth rate decreases to half of its maximum size by adult stage.


Allometric Growth

The risk of infection is high in early life, as immunity has not yet been acquired.


Allometric Growth

Reproductive organs grow very little in the early life but rapidly at puberty.

So, in allometric growth, the head of the baby is much larger relative to the rest of the body as compared to an adult.

e) Intermittent Growth Curve

Learning outcomes: 10.3 e) Explain intermittent growth curve.

Also known as discontinuous growth.

Occurs in arthropods (crustaceans & insects).

Growth curve show a step-like pattern.

Due to the presence of inelastic exoskeleton which must be shed (via a process called moulting / ecdysis) before growth can occur.

Before new exoskeleton hardened, arthropods take in air / water to expand the soft exoskeleton as much as possible.

Causes a sudden increase in length (spurts).

0

5.0

4.0

3.0

2.0

1.0

Time (days)

10 20 30 40 50

Len

gth

(cm

)

5th instar

4th instar

3rd

2nd 1st

Adult

Ecdysis




After the exoskleleton becomes hardened, arthropods decrease to its original size.

Leaving some space within the new exoskeleton for growth to occur.

A stage between 2

sequential ecdysis is

called instar.

Increase in length during ecdysis is due to uptake of water or air.

Which is not consider actual growth.

Actual growth occurs at flat horizontal lines (instar), even though there is no increase in length.

If growth curve is plotted using dry mass, a normal sigmoid curve is obtained (shows true growth which is continuous).



150

125

100

75

50

25

Time (days)

10 20 30 40 50

Mass (

mg

)

0

e) Intermittent Growth Curve.

10.0 Growth (3 hrs)





Learning outcomes


a) Describe absolute growth curve.

b) Describe absolute growth rate curve.

a) Absolute Growth Curve

Learning outcomes: 10.4 a) Describe absolute growth curve.

When a parameter is measured at intervals over a period of time (throughout the growth of an organism).

Absolute / actual growth curve can be plotted.

It is the cumulative increase in size over a period of time.

It shows the overall growth pattern of an organism.

Usually absolute growth curve is S-shaped, sigmoid curve.

a) Absolute Growth Curve.

Learning outcomes: 10.4 a) Describe absolute growth curve.

a) Absolute Growth Rate Curve

Learning outcomes: 10.4 b) Describe absolute growth rate curve.

When an increase in size is measured over a series of equal time intervals

Plotting these increments against time produces an absolute growth rate curve

Usually bell-shaped

Absolute growth rate curve increases up to a maximum, then it decreases

a) Absolute Growth Rate Curve

Learning outcomes: 10.4 b) Describe absolute growth rate curve.

Reference

• Campbell N.A & Reece, J.B., Biology, 6th ed. (2002), Pearson Education, Inc.

• Solomon E.P & Berg, L.R, Biology, 7th ed. (2005) Thomson Learning, Inc.

• Mader, S.S Biology, 8th ed. (2004) McGraw-Hill Companies, Inc.

chapter 10 growth

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