Download - Growth Chap 8
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
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
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
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
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
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.
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