growth (stpm biology topic)

GROWTHGROWTHGROWTHGROWTH

WHAT IS GROWTH?• CHARACTERISTIC OF ALL LIVING

ORGANISMS.• PERMENANT IRREVERSIBLE

INCREASE IN SIZE OF ORGANISM• DUE TO INCREASE IN ITS DRY

MASS.

GROWTH IN UNICELLULAR ORGANISMS

• ORGANISM REACHES CERTAIN SIZE, UNICELLULAR DIVIDE TO FORM 2 SEPARATE CELLS.

• SIZE LIMITED, DUE TO THE DISTANCE OF THE CELL OVER THE AREA OF A NUCLUES CAN EXERT ITS CONTROLLING INFLUENCE.

• THIS DIVISION WILL LEAD TO POPULATION GROWING.

GROWTH IN MULTICELLULAR

ORGANISMS• MULTICELLULAR MANY CELL WITH IS

SPECIALITIES.• HAVE:

– CELL DIVISION (INCREASE CELL MITOSIS)– CELL EXPANSION ( NEW CELL INCREASE IN SIZE,

VOLUME AND MASS FOOD)– CELL DIFFERENTIATION (CHANGES IN CELL

STRUCTURE FOR DIFFERENT FUNCTIONS)– MORPHOGENESIS (DEVELOPMENT OF OVERALL

FORM OF ORGANS AND FORMATION OF MULTICELLULAR ORGANISM)

FACTORS AFFECTING THE PLANT GROWTH

• EXTERNAL FACTORS– LIGHT (PHOTOSYNTHESIS)– TEMPERATURE (ENZYME ACTIVITIES)– OXYGEN (AEROBIC RESPIRATION & SEED GREMINATION)– CARBON DIOXIDE (PHOTOSYNTHESIS)– WATER (METABOLIC PROCESS)– RELATIVE HUMIDITY (TRANSPIRATION)– MINERALS (PLANT METABOLISM, GROWTH &

DEVELOPMENT)– GRAVITY ( DISTRIBUTION GROWTH REGULATORS

GEOTROPISM)– SEASONAL INFLUENCES (DORMANCY, ABSCISION,

REPRODUCTION, PHOTOPERIODISM)– BIOTIC FACTORS ( PATHOGENS, COMPETITION)

CONTINUES…• INTERNAL FACTORS

– GENOTYOE OF PLANT (DETERMINES SYNTHESIS OF SPECIFIC PROTEINS AND ENZYMES, TYPES OF METABOLISM AND SIZE)

– PRESENCE OR ABSENCE OF GROWHT REGULATORS/ PLANT HORMONES.

FACTORS AFFECTING ANIMAL GROWTH

• GENOTYPE• ANIMAL HORMONE• AVAILABILITY OF NUTRIENTS SUCH

AS BALANCED DIET• ENVIRONMENTAL CONDITIONS

SUCH AS LIGHT INTENSITY• BIOTIC FACTORS.

MEASURING THE POPULATION GROWTH OF

UNICELLULAR• Direct cell count

– Counting sample under a microscope– Total number of cell in solution

• Coulter Counter and flow cytometers.

– Disadvantages • Dead cell is not distinguished• Small cell, hard to see• Not suit for cell suspensions of low density bacteria

visible more.

– Liquid • Large cell sample : haemocytometer• Small cell sample : Petroff-Hausser counting chamber.

Continues…• Plant count of viable cells

– Sample undergo series of dilutions– 0.1- 0.2 of the final dilution

transferred onto plate (solidified nutrient agar medium)

– After incubation, count colonies.

Continues…• Determining biomass by measuring the

turbidity using spectrophotometer.– Turbidity or cloudiness of a suspension

scattering of light by the unicellular organisms passing through.

– The amount of light scattered is proportional to the concentration of cells.

– A time correlation between cell concentration and optical density of a culture for the organism must be carried out as a standard reference.

Methods measuring growth of multicellular

organisms

– Advantages

– Disadvantages

Parameter Positive Negative

Height and length

Easy, quickMeasured continually

Measures length in one dimension, don’t measure growth in other directionsAn organisms might have the one that grow sideway

Surface area More accurate

Difficult and impractical if organisms have irregular shape


Volume, size

Suit spherical or cylindrical organism

Rarely in that size.Often difficult to carry out.

Dry mass (the mass of the body after all the water has been removed from it)

Gives more accurate measurement of the organic materials.

Water has to be removed by drying the organism.Organism need to be killed, cannot measured after that.A large number need to be used.Different organisms have different growth rate.


Wet mass or fresh mass

Easy, no need to kill organismGrowth can be measured continuosly.

Inaccurate water fluctuationMore suitable measuring growth in animal not for tree.

Other problem encountered in

measuring growth• parts of the same organism grow at different

rates( allometric growth)• Irregular growth due to fluctuations in diet or

environment.• Accumulation of fats in the body is reversible.

The increase in fat in the body is not considered as growth.

Types of growth curves• Growth curve – obtain using

variety of parameters of growth (mass, height, weight) plotted against set intervals of time.

• Usual shape of the growth curve is sigmoid (S-shaped)

Phases in sigmoid growth curve

1. Lag phase– Growth is slow. – Little or no cell division and cell enlargement.

2. Log phase (exponential growth phase)– Growth proceed exponentially – Growth rate is maximal.– Cell divide and enlarge rapidly as conditions for growth

are at optimum.– Cell division increase– Adequate supplies of nutrients, space and no

accumulation of excretory toxic wastes. – Rate of growth is at its maximum at inflexion point (I)


3. Decelerating phase (linear growth phase)– Growth began to decrease/ at a constant rate.– Limited by external and/or internal factors

4. Equilibrium phase– The organism/ population has achieved

maturity.– Rate of cell division is equal to the rate of cell

mortality. – Net growth rate is zero.


• Plateau phase (stationary phase/ negative growth phase)– Overall growth has ceased.

• In zero growth, the curve flatten out.• In continuing positive growth. (organisms grow

until it dies)• In negative growth, the growth curve declines

(indicating senescence associated with ageing).

Growth parameters

Time

SIGMOID SHAPED ABSOLUTE GROWTH CURVE

12

34

5

Absolute growth curve• Obtained by plotting the data from

any one of the physical parameters against time.

• Shows the overall growth pattern and the extent of growth.

Growth parameter

(x)

Time (t)

Absolute growth rate• Obtained by plotting the change in parameter per unit

time, against time.• The curve shows how the rate of growth changes while

the parameter is being measured.• The growth rate increase with time until it achieves a

maximum level.• The growth rate will decrease until it becomes zero.

Growth rate

(dx/dt)

Time (t)

Relative rate of growth curve

• Obtained by dividing the absolute rate of growth at the beginning by the amount of growth at the beginning of each time period.

• Indicates the efficiency of growth.

% Increase in size

Time (t)

TYPES OF GROWTH CURVE

• HUMAN GROWTH CURVE– Consist of 2 sigmoid growth curve, with 2 main

rapid growth phases1. The infant phase

– Growth rates is very rapid– Irrespective of whether the baby is female or male

3. Adolescent phase– Growth rates is rapid– In earlier part, females have a more rapid growth rate.

Female attain puberty at an earlier age compared to male.4. A slower growth phase can be found in between the

rapid growth phase. (Childhood phase)– Growth rate is slower– Slightly higher for male age 4.

4. Adult phase• Growth rate is zero• Most individual reached maturity.• Starting at age 18 (male) and 16 (female)

5. Ageing phase.• Growth rate is negative• Size will start to decrease. Starting at age

30.

female

male

1 2

34 5

Step like growth curve• Growth limited by the exoskeleton (built from non

living substance = chitin), unable to expand or elongate once it is formed.

• In order to grow, the organism had to remove their old exoskeleton. (process called ecdysis)

• Before the new skin harden, they must absorb air and water as much as possible to increase their body volume.

• So, the growth of this organisms usually happen during ecdysis.

• The young form of the animal that exists between 2 periods of ecdysis = instar.

adult

Growth in terms of size during ecydysis by intake of water/ air

Time (t)

length

Annual woody plant• Shows sigmoid growth curve of dry mass

versus time.• During germination = food stored in

cotyledons used up before first leaves began photosynthesis

• The loss will be replaced later through photosynthesis

• Growth turn rapids until it become constant.

Dry mass

time

Perennial woody plant• Perennial plants of multiple seasons,

hard to reach maximum size.• The overall growth curve will appear

to comprise a series of sigmoid curves represent the growth in a season.

• This growth pattern = continuous growth.

Wet mass

Time (years)

Growth in 1 year

Growth patterns1. Allometric growth (allos ; other .

Metron ; measure)– Different parts of the body grow at

different rates from each other and from the overall rate of the body.

– Produces changes in the size and form of the organism.

Growth patterns2. Isometric growth

• Occurs when an organ grows at the same rate mean rate as the rest of the body of the organism.

• No change in shape or external form when the size of the organism increases.

Growth patterns3. Intermittent growth (discontinuous growth)

• The growth was limited by the hard, inelastic exoskeleton of the animals.

• The periodic shedding of the outer cuticle allows growth to occur for a short period of time.

• Growth prevented when cuticle harden.• Moulting usually occurs about 4-5 times before the

adult stage is reached.• The curve of length against time, will show the

intermittent growth curve.• This may not reflect the real growth.• If growth curve plotted by using dry mass, a

normal sigmoid curve is produced.

Growth patterns4. Limited (definite or determinate) growth.

• The growth does not continue throughout life.• The organisms growth to a predetermined

size within the normal range for the group of organisms. No further growth.

• Occurs in annual plants (fruit, seed and dicotyledons leaves)

• Occurs in mammals, insects and birds.

Growth patterns5. Unlimited (indefinite or

indeterminate) growth.• The growth of the organism

continues throughout life• Growth will continue until the

organism is destroyed by its own size, parasites, predators or natural courses.

exercise• Define the growth term.• Growth rate in organisms is influenced by ________ and ________

factors.• Why cell specification is important in multicellular cell?• Describe each of the growth phase in multicellular organism

– Cell division– Cell enlargement– Cell differentiation

• Differentiate between growth of multicellular and unicellular organism.

• Name 3 methods used to determine growth and list the advantages and disadvantages

• Define dry mass• Why is the height of a tree is not a suitable parameter to

measure growth?

exercises• Define relative growth rate• With the help of sketch graph, show the differences

between absolute growth rate curve and relative growth rate curve.

• Perennial plants will continue to grow until the growth restricted by________

• What is limited growth?• Differentiate between lag phase and log phase.• Explain allometric growth and isometric growth.

Ecdysis • Happen in animal with exoskeleton• The periodic splitting and shedding of

the old inelastic exoskeleton (outer chitinous cuticle)

• In order to grow, they need to change their hard exoskeleton

• Happen several times at fixed intervals to form a new and bigger layer of chitin.

Ecdysis in arthropod• Breathes in a lot of air to expand its body and to break

its old exoskeleton.• Once it free from old exoskeleton, the animal once

again increases its size by breathing in more air before the newly formed layer of chitinous exoskeleton hardens.

• Ecdysis is controlled by ecdysome hormone, secreted by the neurosecretory cells in the brain.

• The ecdysone hormone stimulates the exoskeletal replacement and subsequent growth processes.

• The hormone causes genes to stimulate synthesis of specific enzymes that catalyse the digestion, reabsorption of some materials in the inner part of the old cuticle and the formation of a new soft cuticle.

Metamorphosis• Metamorphosis is a biological process by

which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's form or structure through cell growth and differentiation.

• Some insects, amphibians, molluscs, crustaceans, echinoderms and tunicates undergo metamorphosis, which is usually (but not always) accompanied by a change of habitat or behaviour.

Complete metamorphosis

• Complete metamorphosis has 4 stages of growth, egg, larva, pupa and adult. As the insect grows, its shape changes completely.

• During the pupal (chrysalis) stage, the body undergoes a complete reorganisation, transforming into the adult.

• As the larva looks completely different from the adult, this is termed complete metamorphosis.

• Shown by holometabolic animals such as housefly, butterfly, mosquito.

• Holometabolism, also called complete metamorphism, is a term applied to insect groups to describe the specific kind of insect development which includes four life stages - as an embryo, a larva, a pupa and an imago.

• For example, in the life cycle of a butterfly, the embryo grows within the egg, hatching into the larval stage caterpillar, before entering the pupal stage within its chrysalis and finally emerging as an adult butterfly imago.

Incomplete metamorphosis

• Incomplete metamorphosis has only 3 stages: egg; nymph; and adult. The insects hatch from their eggs looking like miniature adults. These young insects are called nymphs. As they grow, they shed their skin several times before they become adults. At each shedding of the skin, the nymph enters a new "instar", a new stage of growth.

• Shown by hemimetabolic animals such as cockroaches, grasshoppers, locusts termites.

• Hemimetabolic = Hemimetabolism or hemimetaboly, also called incomplete metamorphosis, is a term used to describe the mode of development of certain insects that includes three distinct stages: the egg, nymph, and the adult stage, or imago.

• These groups go through gradual changes; there is no pupal stage. The nymph often resemble the adult somewhat, as they have compound eyes, developed legs and wing stubs visible on the outside.

Influeces of hormone in metamorphosis

• Regulated by the equilibrium of 3 hormones:– Neurosecretory hormone

• Secreted by neurosecretory cells located on the dorsal surface of the brain

• Stored in the corpus cardiatum• Stimulates the secretion of ecdysone from the thorax

gland.– Ecdysone

• Secreted by the thorax gland to initiate ecdysis.– Juvinile hormone

• Secreted and stored in the corpus alatum gland.

DORMANCY• Dormancy is a period in an organism's

life cycle when development is temporarily suspended.

• Its minimizes metabolic activity and therefore helps an organism to conserve energy.

• Dormancy tends to be closely associated with environmental conditions.

• Organisms can synchronize entry to a dormant phase with their environment through predictive or consequential means.

• Predictive dormancy – occurs when an organism enters a dormant

phase before the onset of adverse conditions. – For example, photoperiod and decreasing

temperature are used by many plants to predict the onset of winter.

• Consequential dormancy – occurs when organisms enter a dormant phase after adverse conditions have arisen.

– This is commonly found in areas with an unpredictable climate.

– While very sudden changes in conditions may lead to a high mortality rate among animals relying on consequential dormancy, its use can be advantageous, as organisms remain active longer, and are therefore able to make greater use of available resources.

Plant dormancy • Dormant seeds

– When a mature seed is placed under favorable conditions and fails to germinate, it is said to be dormant.

– There are two basic types of seed dormancy:• embryo dormancy or internal dormancy

– caused by a condition of the embryo which prevents germination.

– The oldest seed that has been germinated into a viable plant was an approximately 1,300-yr-old lotus fruit, recovered from a dry lakebed in northeastern China.

• seed coat dormancy or external dormancy– caused by the presence of a hard seed covering or

seed coat that prevents water and oxygen from reaching and activating the embryo.

Dormancy in animal

• Hibernation– mechanism used by many animals to escape cold

weather and food shortage over the winter. – Hibernation may be predictive or consequential. – An animal prepares for hibernation by building up a

thick layer of body fat during late summer and autumn which will provide it with energy during the dormant period.

– During hibernation the animal undergoes many physiological changes, including decreased heart rate (by as much as 95%) and decreased body temperature.

– Animals that hibernate include bats, ground squirrels and other rodents, mouse lemurs, the European Hedgehog and other insectivores, monotremes and marsupials.

• Diapause– predictive strategy that is

predetermined by an animal's genotype. – Diapause is common in insects, allowing

them to suspend development between autumn and spring,

– In mammals such as the red deer, where a delay in attachment of the embryo to the uterine lining ensures that offspring are born in spring, when conditions are most favorable.

• Aestivation– an example of consequential dormancy

in response to very hot or dry conditions.

– It is common in invertebrates such as the garden snail and worm, but also occurs in other animals such as the lungfish.

– Lungfish : burrows deep into the muddy sand and secretes a layer of mucus that opens at its mouth to allow air to enter lungs. Become inactive until water source back to normal.

EXERCISESEGG

NYMPH

ADULT

LARVA

PUPA

P Q

A

B

C

Y

Xa)What types of metamorphosis are P and Q?

b)What animals exhibit p-type metamorphosis and q-type metamorphosis?

c) Briefly describe the term metamorphosis.

d) Where does ecdysis occur for organisms with p-type metamorphosis and q-type metamorphosis?

1.

Cleavage

M

organogenesis

a) What phase is M?

b) Briefly describe each phase.

c) Why are the parameters, size or fresh mass, prefered over dry mass?

2

a) What is diapause?

b) At which life stage does the insect undergo diapause?

c) Name 2 factors that can cause the insect to undergo diapause.

3.

a) What is dormancy?

b) List two factors that cause dormancy in plant.

c) Name the process that can overcome the dormancy in seed.

4.

Time (days)

Parts

Whole seed

Endosperm

Embryo

0 304 275 3

1 280 260 5

2 272 253 8

3 265 231 20

4 246 207 33

5 220 159 52

5.

a) What may cause the weight loss of the endosperm during the early stages of germination?

b) Calculate the weight loss of the whole seed.

c) The result shows that the dry weight of the whole seed decreased during germination. Why does it occur?

Answer • 1. a) p; complete metamorphosis,

q; incomplete metamorphosis• B) p; butterfly, q; cockroach• C) metamorphosis is the way in

which an insect develops, grows and changes its form.

• d) p=b, q= y

• 2. a ) gastrulation• B) 1. during cleavage, the zygote undergoes repeated

mitotic divisions but there is no increase in mass.• 2. during gastrulation, there is a rearrangement of cells

into disttinct layers.• 3. during organogenesis, the cells develop into tissues

and organs.• C) dry mass can only be measured by killing and drying

the organism. This method is not always possible not ethical. The parameters (size and fresh mass) are easy and convenient and there is no need to kill the organism.

• 3. a) diapouse is a type of dormancy in insects. It can happen at any stage during their life cycle when the environment condition is unfavourable.

• b) diapause can happen at any stage throughout the life cycle of an insect.

• c) draught and low light periods.

• 4. a) dormancy is the period where growth and development of the organism stops. It happen when the environmental condition is not favourable for the organism. It is a way to protect the organism against conditions such as draught and winter.

• b) dormancy in plants is caused by environmental factors such as draught, low oxygen concentration, or internal factors such as low concentration of growth hormone or the accumulation of the growth inhibitory substances.

• c) Stratification and scarification

• 5. a) the weight loss is due to respiration where the storage food is used to produce energy that is required in producing the embryo/

• B ) 304 -220 = 76 g• C) 1. the increase in the weight of embryo is less

compared to the weight loss of the endosperm.• 2. the stored food in the endosperm is used to

produce energy that is used in the formation of embryo. Water is removed during drying process and carbon dioxide is release during respiration.

growth (stpm biology topic)

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