Classifying vertebrates
Vertebrates are animals with a backbone. They are divided into 5 main groups:
1. Fish
Live in water
Have gills to breathe
Body covered with scales
Lay many eggs
Examples: Goldfish, Shark
2. Amphibians
Live on land and in water
Smooth, moist skin
Babies breathe with gills, adults with lungs
Lay eggs in water
Examples: Frog, Salamander
3. Reptiles
Dry skin with scales
Breathe using lungs
Lay eggs on land
Examples: Snake, Lizard, Turtle
4. Birds
Have feathers
Have wings and beaks
Lay hard-shelled eggs
Most can fly
Examples: Sparrow, Eagle
5. Mammals
Have hair or fur
Babies drink mother’s milk
Breathe with lungs
Most give birth to live young
Examples: Humans, Dogs, Cows
Question :
Ans : Why fish eggs don’t float away
Most fish lay eggs in water, but the eggs don’t float away because:
1. The eggs are sticky
Many fish eggs are sticky like glue.They stick to rocks, plants, or sand, so the water cannot wash them away.
2. Some eggs sink to the bottom
Some fish eggs are heavy, so they sink and stay safely on the riverbed or sea floor.
3. Some fish make nests
Fish like tilapia and betta make a nest or a safe place so the eggs stay together.
4. Some parents guard the eggs
A few fish protect the eggs until they hatch so nothing carries them away.
5. Eggs are tiny and in groups
Fish lay hundreds or thousands of eggs together.They stay stuck in a big cluster like a jelly ball
Fun Fact
How sharks breathe
Water goes into the shark’s mouth.
The water flows over the gills.
Inside the gills are tiny parts called gill filaments that take oxygen from the water.
The water then goes out through the gill slits on the sides.
🦈 Do sharks always keep swimming?
Some sharks must keep swimming to push water over their gills — this is called ram ventilation.But some sharks can rest because they use a method called buccal pumping, where they pull water in without moving.
Simple example:
Great white shark → must keep swimming.
Nurse shark → can rest at the bottom and still breathe.