CHAPTER 8

GROWTH

Growth

Outline Growth phase Measuring growth Types of growth curves Patterns of growth Ecdysis and Metamorphosis Dormancy

Growth Phases

growth – permanent increase in size acquired by organism

can be divided into three distinct process

i. cell division

- basis growth in all organisms

ii. cell enlargement

- increase in size and volume of cell components

iii. cell differentiation

- cells begin to differ to form tissue

Measuring Growth

growth can be estimated by measuring length or height, mass, surface area and volume

the most often used parameter is wet mass but not accurate and inconsistent

dry mass is more accurate because not influenced by body fluid, but need to kill the organisms

measuring surface area and volume are easy but only shows physical growth

Types of Growth CurvesThe growth curves- organism’s measurements plotted against time, growth curve

is S-shape or sigmoid- all organisms (excepts insects) shared similar growth curves,

consists of 5 phases:i. Lag phase - slowly or no growth occurs,

organisms need to adapt to their new environment

ii. Log phase - rapid growth, all requirements are enough and no body wastes accumulate

Types of Growth Curves

iii. Linear - growth rate becomes limited because of maturity, decreased in food supply and space

iv. Steady - constant growth, cell division rate same as death rate, growth rate is zero

v. Stationary - growth is stopped because of senescence, lack of food and

space

Phases of Sigmoid Curve

Types of Growth Curves

The absolute growth rate curve (agr)- enables us to express the growth of organisms in terms of

growth rate- estimating the increase size during successive intervals of time- in most organisms, agr increase steadily until reaches a

maximum, and gradually falls- absolute rate curve is bell-shaped curve

Absolute growth

Types of Growth Curves

Relative growth rate curve (rgr)- percentage growth per day as a function of age - mass increase stated as size percentage obtained at each period

of time- growth rate was maximum at the beginning and gradually slow

down

Relative growth

Patterns of growth

- generally, patterns of growth for most organisms is sigmoid except for several organisms

- can be divided into:i. limitedii. unlimitediii. isometriciv. allometricv. growth in human

Patterns of growth

Limited- only one sigmoid curve and limited growth- most organisms and annual plants- zero growth for newborn, rapid growth for young organisms,

followed by steady growth and slows down towards maturity- start with decreased in growth because seed embryo

harnesses the food supply, rapid growth because of photosynthesis and dies when reach Winter

Patterns of growth

Unlimited- occur in woody perennial plants- trees continue to grow year after year, mostly occurs in

Spring- growth curve is a cumulative sigmoid, each represent one

year’s growth

Unlimited growth

Patterns of growth

Isometric- occurs in organisms such as insect and fish - their organs grow at the same rate as the rest of the body - in insect, shape of nymph same with adult but different in

size- insects has exoskeleton, growth only can occurs when they

shed their outer layer- increase of time will also increase their size and mass

Isometric growth

Patterns of growth

Allometric- occurs when an organ grows at the different rate from the rest

of the body- human, nervous system grow faster for baby than an adult,

reproductive organs grow slowly at childhood then a matured person

- chimpanzees, jaws grow faster than rest of the head

Patterns of growth

Human growth- have two phases, in infancy and in adolescence- steady growth between the two phases, while adulthood is

when growth halts- first phase : continuation of fetal growth period

2nd phase : rapidly during puberty due to action of androgens and estrogens

- girls mature earlier than boys and rate of tissues growth in both sexes are varies

Ecdysis and Metamorphosis

Ecdysis - shedding of the exoskeleton by insects and other arthropods to allow growth

In insects- zygote develops within the eggs into young insects- young insects undergo ecdysis several times before become

adults (4-8, some until 30 times)- stage between molts are called instar- after ecdysis, insects are pale, soft and exoskeleton need 1-2

hours to hardens- to grow to their new size, they require air or water

Ecdysis and Metamorphosis

Metamorphosis - the way that insects develop, grow, and change form

- can be classify into two groups:i. incompleteii. complete

Ecdysis and Metamorphosis

Incomplete Metamorphosis (12% undergo this process)- has 3 stages

i. egg - a female insect lays eggs (covered by an egg case, protects the eggs and holds

them together. ii. nymph - the eggs hatch into nymphs (looks like

small adults, but usually don't have wings)

iii. adult - insects stop molting and they have also grown wings.

Ecdysis and Metamorphosis

Complete Metamorphosis (88%) - has 4 stages

i. egg - a female insects lays eggs. ii. larva - hatch from the eggs (do not look like adult

insect, usually worm-like shape) - caterpillars, maggots, and grubs - they molt their skin several times and they

grow slightly larger.

Ecdysis and Metamorphosis

iii. pupa - larvae make cocoons around themselves and don't eat while inside their cocoons. - bodies develop into an adult shape with wings, legs, internal organs, etc (take 4 days to many months

iv. adult - inside the cocoon, the larvae change into adults- after a period of time, the adult breaks out

of the cocoon.

Incomplete metamorphosis

Complete metamorphosis

Ecdysis and Metamorphosis

Hormones control- hormones influence molting and metamorphosis- immature insect require a larger exoskeleton, sensory input

activates neurosecretory cells in the brain.   - these neurons respond by secreting brain hormone which

triggers the corpora cardiaca to release prothoracicotropic hormone (PTTH)

- this sudden "pulse" of PTTH stimulates the prothoracic glands to secrete molting hormone (ecdysteroids/ecdisone)

Ecdysis and Metamorphosis

Hormones control- high level of ecdysone led to biochemical and behavioral

changes that cause molting to occur - juvenile hormone is secreted by the corpora allata prior to

each molt- this hormone inhibits the genes that promote development of

adult characteristics (e.g. wings, reproductive organs, and external genitalia), causing the insect to remain "immature" (nymph or larva).  

Ecdysis and Metamorphosis

Metamorphosis in frogs- has three stages of growth [premetamorphosis (50 days),

prometamorphosis (21 days) and climaxstage (one week)]- thyroid hormones needed for the larvae to become adults- if thyroid hormones is removed, it will not change into frog- if immature tadpole is fed a thyroid gland, it will become

miniature frog

Dormancy- during dormancy, growth and development are cease- metabolism only just sufficient to keep cell alive- dormancy enables an organism to withstand unfavorable

condition- in plants, dormancy occurs in seeds, buds, spores, eggs and

storage organs- in animal, dormancy is called hibernation, aestivation and

diapauses

Dormancy

Seed dormancy- because of their hard coat, need to be broken or decay before

germination- can occurs because lack of oxygen and inhibitorsHibernation- avoiding the necessity to maintain body temperature during

winter cold- metabolism drops, so food reserves can be used for a long

time- prior hibernation, animals start to stores fats under tissues

Dormancy

Aestivation- seasonal dormancy, same with hibernation but occurs in

summer- lungfish, Protopterus and Lipidiseren have mechanism to

keep their survival in drying-out swamps by forming a jellylike layer on their lips which allow oxygen to enter

- use store fats and muscle tissues for metabolismDiapause- occurs at any stage of insects, may survive for months