GROWTH RATE. By the end of the lesson the students should be able to: (i) Describe absolute (actual) growth curve (ii)Describe absolute growth rate curve

GROWTH RATE

By the end of the lesson the students should be able to: (i) Describe absolute (actual) growth curve(ii) Describe absolute growth rate curve

1Types of Growth CurvesObjectives

2Growth RateThe Types

The absolute (actual) growth curve

• the data obtained from the study of growth in an organism can be analysed by plotting graphs.

The absolute growth rate curve

3Growth RateThe Absolute Growth Curve

• the most common graph plotted for growth

• the curve is of sigmoid shape @ S-shaped

• obtained if any suitable parameter, e.g. dry mass (m), is plotted against time (t)

• applicable in the study of growth of microbemicrobe populationpopulation or any large plant/animallarge plant/animal


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• it shows the overall growth patternthe overall growth pattern and• the overall growth periodthe overall growth period

• for most organisms, the growth pattern are the the samesame

i.e. initiallyinitially, the growth is slow slow

then, it grows faster faster

.finallyfinally, it slows slows down again

Growth RateThe Absolute Growth Curve

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• most organisms will continue to grow, able it at the slow rate

• but for human and other vertebrates, the growth stops when the maximum adult size is achieved


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• can be divided into five phases:

The lag phase (AB)

The log phase (BC)

The retardation phase (CD)

The stationary phase (DE)

The negative growth (EF)


Lag phase Logarithmic phase

Retardation phaseStationary phase

Death phase

AB

C

D E

F


AB BCCD

DEEF

AB

C

D E

F

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The lag phase (AB)

• very little growth

• cell division, enlargement slowly

• the organism is adapting to the new sources/ environment


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The log phase (BC)

AB BCCD

DEEF

AB

C

D E

F


• the growth accelerates

• and remains for a certain period of time

• until the sources become limited

• @ exponential growth

AB BCCD

DEEF

AB

C

D E

F

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The retardation phase (CD) @ Linear

• the growth is limited by:

• internal factors: • organism maturity

• the growth slows down

• external factors:

• food supply • space • competition


AB BCCD

DEEF

AB

C

D E

F

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The stationary phase (DE)

• no further growth

• @ equilibrium / stable

• nett growth rate = 0

• the parameters studied becomes constant

• the organism matures

• the rate of cell division = the rate of cell death


AB BCCD

DEEF

AB

C

D E

F

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The negative growth phase (EF)

• badly deficient in nutrient sources and spaces

• ageing stage

• or the ability to get nutrients or to compete for spaces worsens


• growth rate falls drastically

13Growth RateThe Absolute Growth Rate Curve

• obtained by plotting changes/ differences in parameter, dx/dt, against timetime

• dx = increase in size • dt = the time taken to increase

• absolute growth rate = total of changes in growth time taken for the overall growth

• measure of increase in size over a series of equal time intervals.

time

. Absolute growth rate = dx , dt where: dx = size increased dt = period of time

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• the curve is bell-shaped• it shows the changes in growth ratechanges in growth rate against time

Growth RateThe Absolute Growth Rate Curve

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• i.e. it shows that the highest growth rate in the absolute growthabsolute growth curve is equivalent to the part where the slope is the highest in the absolute rate growthabsolute rate growth curve


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• at the peak of the curve is the inflection point• the point where the growth rate

begins to decline• i.e. the organism is reaching adulthood

Inflection point


17Growth RateThe Absolute Growth Rate Curve

Types of Growth Curves

Example: Growth of Maize Plant • parameter = height (cm) # of days after

plantedheight of plant

(cm)growth rate forevery 10 days

10 2 220 7 530 20 1340 40 2050 75 3560 110 3570 140 3080 150 1090 155 5

100 160 5110 160 0120 160 0

sigmoid curve bell-shaped curve

• the growth rate of an organism or a population increase with the time until it achieves a maximum level, after which the growth rate decrease until it become zero.

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19Growth Rate The Absolute Growth Rate Curve

GROWTH

GROWTH UNDER EXTREME CONDITION

Objectives

To explain and give example of:

seed dormancy (legumes)

hibernation (polar bear)

aestivation (lung fish, insects)

diapause (insects)

Occur in animals and plants at certain intervals (temporarily) during their life cycles

during which growth slows or stops

because of extremely low metabolic rate

Resting stage

Can occur in the adult, egg, pupa, spore or seed stage

Dormancy 1

Dormancy

Purposes

organisms able to survive in unfavorable conditionsunfavorable conditions– insufficient food supply, cold weather (winter), hot

and dry weather (drought)

It is control by hormones that– Response to physiological in plants and animals– Effecting the behavior in animals

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Seed Dormancy

It is a phenomenon in certain seeds in which they would not germinate if not given an optimal condition ( water, oxygen, optimum temperature ).

• Can be seen in seeds ( eg: legumes ), buds, spore & food storage organs (tubers).

Dormancy 3

due to structure of seed coat - waxy cuticles, suberine layer (cuticle like layer) and lignified sclereids which are impermeable to water; prevent imbibition

( passive uptake ) of water

- hard, lignified seed coat which are too strong to allow the

penetration of radicle (out of seed)

Dormancy in PlantsSeed Dormancy

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• Due to many factors include:

i. Lack of oxygen

ii. Dryness

iii. Presence of substances that inhibit germination

Some seeds will not germinate - must undergo certain internal changes

- to ensure that premature germination does not occur.

Special mechanism need to ensure germination does not occur before time [inmature seed germination]:- involve the testa or outer coat – impervious ( impossible to

penetrate) to water also the presence of inhibitor (ABA/ absicic acid)


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in order to break the dormancy, stratification (softening or injury of the seed coat) have to occur

chemical reaction in animal’s digestive tract or by physical abrasion (in order to remove the seed coat)


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• occur during winter (cold weather)

• is a state of inactivity (do not consume much energy) which are characterized by lower body temperature, lower metabolic rate (decrease heart rate, respiration), low growth and development.

Dormancy in AnimalHibernation

• to conserve the food stored because of food scarce/ deficiency

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• in preparation for hibernating, animals store food as body fat (brown fat) which is utilized during winter

• pregnant polar bears hibernate in ice dens (similar to igloo); sleep straight through winter

Example:

polar bear

or

white bear


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• other male and non-pregnant polar bears do not sleep straight through winter.

• they wake up once in a while, walk around and eat before they go back to sleep.


• Others:- small mammals in rodents (ground squirrels, hamster).

• Some store up food in their nests and feed on them if they wake up when the temperature rises.

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Invertebrate and vertebrate animals are known to enter this state to avoid damage from high temperatures and the risk of desiccation. Both terrestrial and aquatic animals undergo aestivation.

• Seasonal dormancy;

• similar to hibernation but, during hot weather

• increase in temperature and lack of water – drought

• e.g. lungfish Protopterus and Lipidiseren in Africa and South America

Dormancy in AnimalAestivation (summer sleep)

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• burying itself in mud formed at the surface of a dried up lake Can continues to live even when the lake has become dry.

• secretes mucus at its mouth to allow air to enter its lungs

• becomes inactive (low metabolism – slow breathing and heartbeat rate) Until its water source is back to normal.

Dormancy in AnimalAestivation

• In addition, stored fat and some of the muscle tissues in the bodies of these animals are lost during the aestivation period.

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• occur in insects– during winter when the

temperature is low and there is no food & water.

• an insect resting stage during which developmental process is temporarily blocked (at any stage of its life cycle)

Dormancy in AnimalDiapause

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• Insects diapause is caused by the caused by the deficiency of certain deficiency of certain hormoneshormones– from the brain – the secretion of

these hormones is controlled by controlled by external stimuli external stimuli such as drought and long days.

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• The hormones secretion depends on the period of exposure to light, – i.e. it behaves in a photoperiodic manner, similar

to the process in plants.

• When the light period drops below a certain critical level, diapause is initiated.

• Diapause can be overcome when the light period increases until it exceeds the critical light period.

• Some insects require a low temperature in order to be released from diapause.

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e.g. • some butterflies and moths - diapause occur during larval stage• white cabbage butterfly - diapause occur during pupae stage• colorado potato beetle - diapause occur during adult


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Operophtera brumata (L.) Eggs diapause during winter

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Documents

GROWTH RATE. By the end of the lesson the students should be able to: (i) Describe absolute (actual) growth curve (ii)Describe absolute growth rate curve