NOTA BIOLOGY SEM1 2021_2022

DIFFERENTIATE BETWEEN ISOMETRIC GROWTH & ALLOMETRIC GROWTH

Isometric Growth Allometric Growth

 Isos: same; metron: measure  Allos: other; metron: measure

 Growth in which the various organs within an organism • Growth in which the various organs / parts within an

grow at the same rate as the rest of the body. organism grow at different rate as the rest of the body.

 The organism increase in size without changing its • As the size of organism increase, the shape will
shape. changes.

 Example : growth in fish. • Example : growth in human organs and tissue

Intermittent Growth Curve

• Also known as discontinuous growth.
• Occurs in arthropods (invertebrate with inelastic exoskeleton) & certain insects (which undergo

incomplete metamorphosis).
• Arthropods & certain insects grow in step-like pattern.
• This is due to present of hard exoskeleton surrounding their body which cannot expand.
• To allow growth & development, arthropods & certain insect will shed their hard exoskeleton.
• The process is called ecdysis / moulting.
• Ecdysis : Periodic shedding / moulting / casting off the hard exoskeleton to allow growth &

development in arthropod & certain insect.
• Since the new exoskeleton is soft, arthropods will take in air or water to expand the soft

exoskeleton as much as possible.
• Causes a sudden increase in length but not in mass because during moulting, it cannot feed itself.
• Increase in length during moulting at vertical line is not consider as actual growth.
• When exoskeleton is harden, it leaving the some space within the new exoskeleton for the tissue

to growth, & arthropod start to feed again.
• The space inside the exoskeleton will be gradually filled up with body tissue, such as muscle.
• Actual growth occurs at flat horizontal lines (instar), even though there is no increase in length.
• A stage between two sequential ecdysis is called instar stage ( or the developmental stage of an

arthropod between moults).

Incomplete metamorphosis

• Refer to a type of metamorphosis in which certain insects hatches from an egg, then goes through
several nymphal stages (instar stage) & the adult stage.

• There is no pupal stage.
• Each nymphal stage looks like a small version of the adult but getting slightly bigger with age.
• At the final nymphal stage the insect then moults / ecdysis into the adult form.