The Bio Brief

Hormones not only control human growth — they also control life cycle changes in animals, especially during metamorphosis.

 Metamorphosis = sudden change from larva (young form) to adult.

 What is Metamorphosis?

Metamorphosis is the process by which a young organism changes its body form to become an adult.

Examples:

• Caterpillar → Silk moth
• Tadpole → Frog

 General Metamorphosis Flow Chart

Egg
 ↓
Larva (young stage)
 ↓
Hormonal changes
 ↓
Metamorphosis
 ↓
Adult form

Insects (Silk Moth) and Hormones

In insects like the silk moth:

• The caterpillar passes through many stages
• Insect hormones control these changes
• Finally becomes an adult moth

 Silk Moth Life Cycle

Egg
 ↓
Larva (caterpillar)
 ↓
Pupa (cocoon stage)
 ↓
Adult silk moth

Each stage change is controlled by insect hormones.

 Frog and Hormones

In frogs, metamorphosis is controlled by the hormone thyroxine.

 Source

• Produced by the thyroid gland

 Function

• Changes tadpole into adult frog

 Frog Metamorphosis Flow Chart

Eggs in water
      ↓
Tadpole (with tail, gills)
      ↓
Thyroxine released
      ↓
Legs develop
Tail shrinks
Lungs develop
      ↓
Adult frog

 Role of Iodine (Very Important)

Thyroxine can be produced only if iodine is present.

 In Tadpoles

• If water lacks iodine → no thyroxine
• Tadpoles cannot become adult frogs

 What About Humans?

 Yes — humans also need iodine.

If diet lacks iodine:

• Thyroxine production decreases
• Thyroid gland enlarges
• Causes goitre

 Importance of Iodised Salt

Iodised salt contains iodine, which helps in:

• Proper thyroid function
• Preventing goitre
• Normal growth and development
• Proper brain development in children

 Why Iodised Salt is Important (Flow Chart)

Eat iodised salt
        ↓
Body gets iodine
        ↓
Thyroid produces thyroxine
        ↓
Normal growth and metabolism
        ↓
Prevents goitre

 Are hormones present in other animals?

Yes.

 Do they play a role in reproduction and life cycle?

 Yes.

Hormones in animals control:

• Growth
• Metamorphosis
• Reproduction
• Body functions

Examples:

• Insect hormones → control metamorphosis in insects
• Thyroxine → controls frog metamorphosis
• Sex hormones → control reproduction in many animals

 Quick Revision

 Metamorphosis = larva to adult change
 Insects use insect hormones for metamorphosis
 Frogs use thyroxine
 Iodine is necessary to make thyroxine
 Lack of iodine causes goitre
 Iodised salt prevents iodine deficiency
 Hormones are present in many animals

 In Simple Words

Hormones control major life changes in animals. In insects, special hormones help the caterpillar become a moth. In frogs, thyroxine helps the tadpole become an adult frog. Thyroxine needs iodine, so both animals and humans must get enough iodine. That is why eating iodised salt is important.