My Science School

 

 

Our world is home to many millions of living things. From the hot, dry deserts to the frozen Polar Regions, at the depths of the oceans, and even inside the bodies of other creatures! All living things are specially adapted to enable them to survive in their different environments.

Living things may look very different, but they all share some basic characteristic: they need oxygen and ‘nutrients’ for nourishment; they move and grow; they get rid of waste substances; they react to things around them; and they can also reproduce.

 

 

 

 

 

Polar bears are specially adapted to live in the cold extremes of the Polar Regions.

 

 

 

 

 

 

 

Chameleons change the colour and pattern of their skin, to blend in with their surroundings and protect themselves from attack.

 

 

 

 

 

 

 

Lions are camouflaged in the hot, dry plains of Africa.

Imagine you were looking at a waxwork model of a child. They model might confuse you at first. It may look very realistic and even share many of the physical features of a child. But you would soon be able to tell that the waxwork was not a living thing.

A real child can move. A child needs to eat and breathe to survive, and gets rid of waste materials, like faeces and urine, from its body. A child can see and hear things happening nearby and will act accordingly. Eventually the child will grow and may even have children of its own. The waxwork model may appear to be very lifelike but it can do none of these things.

Living things can move about, sometimes very quickly, like these human sprinters.

 

 

 

Living things need nutrients for nourishment. This hummingbird is feeding on flower nectar, a good source of sugar. In turn, the flower has been feeding on sunlight and nutrients from the soil.

 

 

 

 

 

 

 

 

We plant many kinds of trees, shrubs and flowers in public places and in our gardens.

There are about two million different types of living things today! Although they share similar features, there are also great differences between them. People have found it useful to sort living things into groups. The two largest groups are the plant and the animal kingdoms.

 

Within these groups there are many different types, or ‘species’. So scientists divide the plant and animal kingdoms into smaller groups. Animals are firstly divided into those that have backbones, the ‘vertebrates’, and those that do not, the ‘invertebrates’. Plants have also been divided into many different groups that distinguish between their structure and their leaf or flowering cycles.

 

The animal kingdom

Most animals are invertebrates (without a backbone). For example, earthworms, butterflies, spiders and crabs are just a few invertebrates. Vertebrates can be put into five groups: fish, amphibians (vertebrates which spend part of their lives in water and part on land), birds, reptiles and mammals. Mammals are the only animals which produce milk to feed their young.

 

Continue reading "THE VARIETY OF LIFE"

Where did all the different types of living things come from? Nobody knows for certain, but many scientists think that plants and animals have gradually developed, or ‘evolved’, over millions of years. As they have changed, they have become better adapted to survive.

For example, millions of years ago plants had no flowers. They relied solely on the wind and the rain to transport their pollen to other plants, so that new seeds could develop. But over time, plants developed simple flowers to attract insects. Insects accidently pick up sticky pollen as they feed on flower nectar, and carry it to nearby plants, helping the flowers to reproduce.

 

 

Human beings may have evolved from ape-like animals. These developed the ability to stand upright on just two feet, so that they could then use their hands for other things. Over millions of years they learnt how to use tools and developed these to become successful hunters.

 

 

 

 

 

 

Fossils are the remains of plants and animals that have been preserved in rock. They give us clues about the life of ancient living things. Scientists can work out the age of fossils by dating the rocks in which they are found.

 

 

 

 

 

Insect-pollinated plants tend to have fragrant, brightly coloured flowers to attract insects.

All living things are made up of tiny building blocks called ‘cells’. Cells are too small to see without a microscope. Some living things have one cell, but the human body consists of about a hundred trillion cells!

Almost all cells contain a nucleus. The nucleus is very important as it controls everything that happens inside the cell. Around the nucleus is a jelly-like substance called ‘cytoplasm’. Here, lots of chemicals are stored. Around the cytoplasm is a very thin ‘skin’ called the cell membrane? This holds the contents of the cell together and controls what enters and leaves the cell. Plants and animals have different types of cells. These cells are all designed for a particular job.

 

 

 

 

 

Plant cells

Plant cells are each surrounded by a ‘cell wall’ made of cellulose, which gives the plant structure and support. They each have a nucleus and cytoplasm. Plant cells usually have a very regular shape.

Animal cells

Animal cells don’t have any cell walls (just a cell membrane). This is because animals use other ways of supporting themselves, such as skeletons. Animal cells are usually irregular in shape.

 

 

 

 

 

 

Special cells have caused pigmentation in these zebras’ coats, creating a striped camouflage.

 

 

 

 

 

 

 

A leaf under a microscope clearly shows the structure of a plant cell.

Living things need certain substances to move, grow and keep themselves alive. Animals eat plants or other animals as their main source of nutrition.

This food is chemically complicated and must be reduced to simpler materials by a process called “digestion”. Chemicals in the body break down the nutrients in food, which the body then uses for growth and energy. Waste materials are then excreted by the body.

 

 

 

 

Photosynthesis

Plants and animals depend on each other for feeding and breathing. Plants take carbon dioxide from that air and absorb water and minerals from the soil. They use the Sun’s energy to convert these simple substances into sugars and starches and produce oxygen. This is called “photosynthesis”.

Animals, like gorillas, use plants as a source of food. They also breathe in the oxygen that plants release. Animals produce carbon dioxide which they breathe out and they excrete waste water and chemicals from their bodies. Plants depend on all these substances.

 

 

 

 

 

Plants need oxygen in order to carry out certain life processes. Plants use photosynthesis to produce oxygen but they also absorb oxygen from the soil (through their roots) and from the air (through small holes in their leaves).

 

At night, plants take oxygen from the air because there is not enough sunlight for photosynthesis to take place. During the day plants produce their own oxygen – much more than they need. This excess oxygen is released into the air.

 

Plants provide oxygen for humans and animals to breathe.

 

 

 

 

Squirrels need to eat about a pound of food a week to maintain an active life.

Most animals have to move to find their food and to avoid predators and other dangers. Many of these animals have muscles to help them move. Muscles help fish to swim, birds and insects to fly and many animals to walk and run.

Plants move by growing in different directions. When water is in short supply, plant roots grow deeper into the soil to find it. Shoots grow taller to find more sunlight. Plants also need to move their pollen and seeds. Pollen and seeds are ‘dispersed’ – spread around – from their parent plant so that they have their own space to grow. They may be carried by animals, water or the wind.

 

 

 

 

Most snakes get from place to place by throwing their bodies into curves. When a snake moves, waves of muscular contraction flow from head to tail. Its sides also push against irregularities on the ground (represented by the orange arrows in the diagram).

 

 

 

 

 

 

 

Virtually every part of a cheetah’s body has been adapted to maximize its running speed.

 

 

 

 

 

 

 

Climbing plants, like ivy, use walls for support, and grow towards the sunlight.

 

In order to survive, living things must be able to detect changes in their environment and react to them. This includes adapting to changing weather conditions and the threat of living things that may approach them.

Animals have up to five senses – sight, smell, hearing, taste and touch – to help them to detect changes around them. A dog may react to the smell of food by running towards it; an earthworm will react to light by burrowing underground; and a chameleon changes its skin colour and patterns to match its background. Plants don’t have senses of this kind but they can still detect changes in their environment.

 

Plants can react to certain changes in their environment. We have seen how plants grow towards light and water. This sunflower gradually turns as it follows the path of the Sun during the day. Some flowers, such as lilies, open during the day and close at night. Plants are remarkably sensitive to heat; light, drought, certain chemicals and gravity, but they have no special organs for detecting change.

 

 

 

 

 

 

 This sea anemone reacts to touch by retracting its tentacles.

 

 

 

 

 

 

An Arctic fox’s fur turns from brown to white in winter to camouflage it in the snow.

When we react to a changing environment, conditions inside our bodies change. Your body’s main instinct is survival, so it reacts to potentially dangerous situations.

When you exercise, most of the energy in your body is released as heat energy and your temperature rises. To lower your body temperature, blood moves to the surface of your skin where it can cool down. Water also evaporates from your skin as sweat, helping to cool your body. During the winter months, physical changes can also help an animal to hibernate, whilst food is scarce.

 

 

 

 

In the winter months, some animals, like dormice, are no longer able to find food. Their bodies are able to adapt, and they “hibernate”. The animal “sleeps” for the winter. Its body gradually gets colder, its heartbeat slows down and it breathes less often. In this condition animals use little energy. They can survive without eating and live off stores of fat inside their body.

 

 

 

 

 

 

 

In the fall, many birds migrate to a warmer winter climate.

 

 

 

 

 

 

It is important to drink after exercise to replace fluid lost through perspiration.

 

 

As plants and animals develop, they grow and get larger and heavier. How does this growth take place? We know that living things take substances, like food, into their bodies. Some of these substances become part of body cells. Cells get bigger until they cannot grow anymore and they divide into two. As more cells are formed, a living thing grows.

 

When living things are fully developed they are able to ‘reproduce’ and create new members of their species. Most living things in the animal world reproduce when special ‘sex cells’ from the mother and father join together. As this cell grows and divides, a new living thing develops.

 

 

 

 

This cell is ready to divide. The threads inside its nucleus, called “chromosomes”, have been duplicated. The nucleus now starts to divide and each new nucleus gets a complete set of chromosomes. The cell membrane then divides to form two separate cells. These are identical to the original cell with the same number of chromosomes. They will grow and eventually divide themselves into two new cells.

 

 

 

 

 

 

 

This calf will grow and develop for up to seven years before it becomes fully-grown.

 

 

 

 

 

 

 

Yew trees take 1,000 years to mature, while pine trees only take 30 years.

Many living things can pass information to each other – they ‘communicate’. The expression on the face of a cat may show that it is angry or frightened. Bees perform complicated dances to tell each other where to find good sources of food, and monkeys show each other affection by grooming each other and cuddling their young.

Some animals communicate by producing chemicals. Cheetahs mark out their territories by spraying urine and scent onto plants. Birds and mammals also communicate by making sounds. Humans, as the most intelligent of all animals, have developed the most complicated and successful form of communication – speech.

 

 

We usually associate communication with animals, but some plants can communicate. For example, some trees produce poison in their leaves when they are attacked by insects. Some of these trees can also warn nearby trees by passing a chemical signal through the air, enabling trees downwind to prepare for attack. In a similar way, plants also communicate with insects. If corn, cotton or tobacco plants are attacked by caterpillars they emit chemicals that simultaneously attract parasitic wasps. These wasps eat the caterpillars and discourage other worms and moths from laying their eggs on the plants.

 

 

 

 

Monkeys use a number of vocal, visual and tactile forms of communication.

 

 

 

 

 

 

Dolphins communicate using a system of whistles, squeaks, moans and clicks.

 

 

 

 

 

 

Elephants show aggression by locking tusks and wrestling with their trunks.

A living thing cannot live alone. It depends on the other living things to supply the materials it needs to survive. We have seen how animals rely on plants for their food. Animals that only eat plants are called ‘herbivores’. Animals that eat other animals are called ‘carnivores’. A series of living things that feed on each other make up a “food chain”. If one of the members of the chain is removed all the others may be affected.

Often, several food chains interlink as many animals feed on a variety of plants or animals. The chains together make a ‘food web’.

 

 

 

 

 

 

 

 

 

 

 

 

Continue reading "LIVING WITH EACH OTHER"

 

Genes and chromosomes

Inside the nucleus of a human cell are 23 pairs of chromosomes. Along these chromosomes are “genes”. Genes control everything about you, including the way you look. Each of your cells has the same genes. You inherit two copies of every gene – one from your mother and one from your father. That is why you look like your parents.

 

 

 

 

Inheriting eye colour

The gene for brown eyes is known as a “dominant” gene – you only need to inherit one brown eye colour gene for your eyes to be brown. The gene for blue eyes is weaker. In general, a child will only have blue eyes if both inherited eye colour genes are blue. A man carries a gene for brown eyes and a gene for blue eyes, while the woman carries only a gene for blue eyes. One of their daughters has blue eyes because she has inherited two blue eye colour genes. The other daughter has brown eyes because she has inherited at least one brown eye colour gene.

 

 

 

 

 

There are different seashores all over the world. Some seashores are hot and some are icy cold. The animals found on icy seashore can live where it is very cold. They keep warm by having thick fur or oily feathers and a layer of fat under their skin.

 

 

 

 

These birds are looking for food in the mud.

When rivers reach the sea they spread out into wide, muddy seashore called an estuary. Huge flocks of birds feed on muddy estuaries. They hunt for worms, shellfish or crabs in the mud. When the sea flows into the estuary and covers the mud, the birds fly ashore and wait until it goes out again.

 

 

 

 

These penguins live on cold, icy seashore.

In very cold parts of the world, the seashore is icy. Penguins nest on the icy seashores of the Antarctic. It is so cold that they huddle together to keep warm. They keep their egg on top of their feet to stop it from freezing on the ice.

 

 

 

 

 

This seashore is in a hot part of the world.

Coral reefs grow in warm, shallow seas. Coral reefs are made by small animals that live close together. They protect themselves by building hard cases. It is the hard cases that form the coral reef. Coral reefs are important because they are home to many animals.

The waves that crash on to a seashore are very strong. Seashore plants and animals must hold on tight to keep themselves safe. If they let go, they could be washed away or smashed on the rocks.

 

 

These limpets are holding on to a rock.

Seashore animals have different ways of holding on. Limpets use their strong foot to grip tightly on to rocks and stop them from being washed away. Some animals, like sea urchins, cling on to rocks with lots of tiny feet that look like tubes. Mussel shellfish anchor themselves down to rocks with tough threads.

 

 

 

 

This seaweed grips on tightly to the rocks.

Seaweeds anchor themselves on to rocks to stop them from being washed away by strong waves. Large seaweeds grip on to rocks with strong, finger-like rootlets called holdfasts. During storms, seaweed is ripped off rocks.

 

 

 

 

 

Sea otters wrap themselves in seaweed.

When sea otters sleep, they wrap themselves in giant kelp seaweed. They grab a floating end of kelp and spin around in the water. The kelp wraps around the otter and anchors it down. It stops the sea from carrying the sea otter away in its sleep.