Invertebrate Animals

PRINCIPAL CHARACTERISTICS

Invertebrate animals are alike in one way: they have no inner skeleton or backbone. Invertebrates differ, however, in size, shape and body covering.

SIZE: Most invertebrates are very small, only a few centimetres, but some are enormous, like the giant squid.

Look! This is a picture of a giant squid found near Japan:

BODY SHAPE: Most invertebrates are symmetrical.

• Bilateral symmetry: Two identical halves or planes. For example: insects.

In this picture, you can see a ladybug.

• Radial symmetry: Several planes of symmetry. For example: starfish.

• Asymmetry: The body has no symmetry. It is irregular. For example: sponges.

Look at the following diagram which shows the different kinds of symmetry:

 BODY COVERING: Some invertebrate bodies are protected by shells or exoskeletons (like scorpions or snails), but others have no covering.


WHERE AND HOW INVERTEBRATES LIVE

Invertebrates differ in their habitat and their movement.

• Many invertebrates live in the ocean, but some live in fresh water, and others on land.
• Most invertebrates can move. However, some do not move: they attach themselves to rocks or the ocean floor. Parasites live inside other animals and harm them.

Most invertebrates are oviparous. A larva hatches from an egg. At first, it does not look like the adult. Later, its body changes.


INVERTEBRATE GROUPS

There are many groups of invertebrates. For example:

SPONGES
They have irregular bodies and no symmetry. They cannot move around. They attach themselves to rocks or the ocean floor. They filter sea water and retain the nutritive substances for food.

CNIDARIANS
They have jelly-like bodies, some with radial symmetry. They have tentacles that sting you. They are marine animals. Some, like coral and sea anemone, attach themselves to rocks. Others, such as medusas, can move about.

WORMS
They have soft bodies with bilateral symmetry. Some are cilindrical, but others are flat. Some worms are aquatic; others are terrestrial. Many are parasites.

ECHINODERMS
They have five-way symmetry. They have a skeleton made of hard plates, often with spines. They are covered by a thin skin. All are marine animals.

ARTHROPODS
They have bilateral symmetry. Their bodies are totally coveredby an articulated exoskeleton, like armour. Some are aquatic; otheres are terrestrial.

MOLLUSKS
They have a soft body with bilateral symmetry. Many are covered with one or two shells.

Can you identify the invertebrate animals? Click the image below and play the game!

Parts of the Plant

Click the picture below and label the parts of the plant. When you finish, check your answers.

Plant Classification

There are more than 250,000 plant species on Earth. All of them can be classified into two groups: nonflowering and flowering.

NONFLOWERING PLANTS

They are the smallest group. They never produce flowers or seeds. They reproduce with spores. When the right conditions exist, spores germinate and create a new plant. Examples are mosses and ferns.

Mosses are very short plants with tiny stem, leaf and root structures. They live on rocks, on tree trunks, and on the ground. Moss spores are produced in a capsule at the end of a filament.

Ferns are much larger than mosses. They have thick, underground stems and large leaves. Fern spores form on the underside of the leaves.

Nonflowering plants grow in dark, humid forests.
Here is a picture of Iguazú Falls in Argentina where you can see mosses and ferns.

FLOWERING PLANTS

They form the most numerous, diverse plant group. They produce flowers and seeds to reproduce. They can be classified into two groups:

Gymnosperms
They have small, simple flowers without a corola or calyx. They do not produce fruit. The seeds are grouped together in cones.

Most gymnosperms are trees that have leaves all year. As a result, they are called evergreens. Cypress trees, pines and firs are gymnosperms.

In this photograph you can see a cypress forest in Chubut, Patagonia, Argentina.

Angiosperms
They have large, beautiful flowers. They produce seeds and fruit.
This is the largest plant group. It includes trees, bushes and grasses. Chestnut trees, thyme, and poppies are angiosperms. Angiosperms that lose all their leaves in autumn are called deciduous plants.

Here is a photo of ceibo trees, with their beautiful red flowers.

Did you know that ceibo's flower is Argentina's national flower?

What Living Things are Like

In nature there are nonliving things and living things. Rocks, air and wind are nonliving things. People, animals and plants are living things.

Living or nonliving? Click here to classify the following items.

We can recognize living things because they share the following characteristics:

1. They are born. All living things come from other living things.
2. They eat. All living things need food. The type of food may vary.
3. They grow. All living things increase in size during their lifetime. Sometimes they change in appearance.
4. They react. Living things can perceive what is going on around them, and they react to what they perceive.
5. They reproduce. Living things can create offspring similar to themselves.
6. They die. At some time, all living things stop functioning and cease to live.

Click on the picture below to do a test about living and nonliving things:

How many right answers did you get?

The Solar System

The Universe is made up of celestial bodies. The Sun, the planets and other celestial bodies make up the Solar System.

Some celestial bodies that make up the Universe give off heat and light; others do not.

• Self-luminous celestial bodies give off heat and light that they produce themselves. These are called STARS.

• Nonluminous celestial bodies do not produce light. They reflect light from the Sun or from other stars. PLANETS, SATELLITES and COMETS are nonluminous.

There are eight planets that orbit around the Sun in the Solar System. MERCURY, VENUS, EARTH and MARS are closest to the Sun. For this reason, they receive more heat and light. JUPITER, SATURN, URANUS and NEPTUNE are farther from the Sun. These planets are larger in size.

The Earth is the third planet in the Solar System. It moves around the Sun and it has a satellite, the Moon.

Its shape is spherical, but slightly flattened at the poles.

An imaginary circle called the equator divides the Earth into two halves at its widest part:

- The upper half is the NORTHERN HEMISPHERE.

- The lower half is the SOUTHERN HEMISPHERE.

The Earth rotates on an imaginary axis that goes from the North Pole at the top to the South Pole at the bottom.

Now click the following image to take a journey through time and space. Read about the planets, stars and other celestial bodies in the Universe. Look at the different pictures and discover new facts!