My Science School

We make metals by digging up minerals and then heating them in a hot fire or furnace.

Minerals like silver, copper and lead are hard to find. So, people do not usually throw them away. But we do throw away lots and lots of steel and aluminium cans.

Luckily, it is easy to recycle metals, which saves minerals and energy.

This hot furnace is making iron.

Iron is a tough metal made by melting iron ore, limestone and coke from coal in a furnace. By adding carbon and other minerals, iron can be made into even tougher steel. Steel is used to build ships, trains, bridges and buildings.

Valuable metals like iron and steel are often recycled. Most steel objects now contain some recycled metal.

 

This giant magnet picks up steel cans.

Cans to store food and drink are mostly made from steel or aluminium. At the recycling plant, a large magnet is often used to pick out the steel cans. These are reheated in a furnace to make new products. The steel in your empty drink can could end up in a steel support high on a skyscraper, or as a paper clip!

 

 

 

Mines spoil wild places.

Metals are found underground as ores. When ores are mined, wild places are destroyed and huge piles of waste rock are left behind. By recycling metals we can avoid new mines and reduce waste and pollution.

 

 

 

You can use a magnet to test metals.

A magnet can separate different metals because iron and steel are magnetic, so they stick to the magnet. Aluminium is not magnetic, so it does not stick.

 

At home, use a magnet to test cans, bottle tops, foil trays and tin foil to find out if they are magnetic. All of these metal items can be recycled.

Picture Credit : Google

We throw away lots of paper and card each day. But we can recycle this waste to make new books, comics and even banknotes.

When we recycle paper and card, it saves materials and energy. We also help to protect wild forests where animals live.

These trees will be cut down to make paper.

Wood is the main raw material used to make card and paper. Most timber used to make paper comes from conifer trees grown on special plantations.

Wild habitats, such as bogs and heaths, are sometimes cleared to plant these forests. Recycling paper means that fewer timber forests are needed. So, recycling can help to save wild places and the animals that live in them.

 

 

The grey cardboard inside a cereal packet is recycled.

Newspapers and magazines have lots of ink on them. When they are recycled, it is cheaper not to remove all the inks. That is why recycled cardboard is grey! Clean, white paper is the best paper for recycling. It can be made into writing paper.

 

 

 

 

Old newspapers can be made into toilet paper.

All sorts of products, including toilet paper and toilet rolls, are now made from recycled paper.

Look out for recycling symbols that show materials have been recycled. We can also avoid wasting paper by reusing envelopes and writing on both sides of paper. Ask your teacher if paper is recycled at your school.

 

 

You can also recycle your Christmas tree.

Christmas trees are also grown on conifer plantations. Many councils now provide special recycling points where trees can be left after Christmas.

So, instead of dumping your tree, recycle it! The trees are cut into chips to make rich compost which can be put on the garden to fertilise the soil.

Picture Credit : Google

 

Glass is one material that is easy to recycle. Like metal and paper, it is made with raw materials from the natural world.

The more we recycle the fewer raw materials we need. Recycling materials like glass also saves energy.

Glass is made in a furnace.

Glass is made from sand and limestone. These raw materials are mined from the ground and heated in a furnace. They melt to make a hot, runny mixture. This is shaped by being blown or poured into moulds. The red-hot mixture cools to form glass.

 

 

This broken glass is ready to recycle.

Glass can be made from recycled bottles and jars instead of fresh sand and limestone. The used glass is smashed up to form a substance called cullet. The cullet is then reheated. The furnace does not need to be so hot to melt cullet, so recycling glass saves energy as well as raw materials.

 

 

At a bottle bank we sort glass into different colours.

First, wash your used bottles and remove the lids before you take them to the bottle bank. Most bottle banks have separate holes for brown, clear and green glass, so the glass is sorted before it goes to the recycling plant. As well as bottles, recycled glass can be used to make glass bricks, tiles and fibreglass boats or canoes.

 

 

 

Glass can be reused, so avoid plastic bottles.

Reduce waste by asking your family to buy milk and juice in glass bottles instead of plastic bottles or paper cartons.

Glass milk bottles are returned and refilled up to a dozen times. But plastic and paper cartons are used just once before being thrown away, and plastic bottles do not rot.

 

Many people are quick to throw things away. They do not reuse things. Reusing means using old things in new ways.

In developing countries, people waste less. They are better at recycling materials. They often repair and reuse old equipment.

When people reuse or recycle, there is less waste. Less waste means less harm to nature.

This old freezer creates waste and can poison the air.

People in developed countries have money to spend on expensive goods such as cars or computers. We like to bud new things when the old ones break or go out of fashion. All this causes waste and pollution. Scrapped TVs, cookers, fridges and cars may give off chemicals which pollute the natural world.

 

 

 

People reuse the cardboard boxes that this man sells.

In poor communities, people often repair or reuse broken equipment, so less is wasted. Some people sort through rubbish heaps for bottles, tins, plastic, bricks and cardboard that can be sold for recycling. Wood and metal sheets are reused to build shacks.

 

 

 

 

Packaging can make products look nice but it causes waste.

In the United Kingdom, a lot of our rubbish is packaging. This is the paper, card and cellophane used to wrap products or to keep foods fresh. Colourful packaging also helps to sell products. But when we get home, most of this packaging is just thrown away, which is a waste.

 

 

 

 

Some packets have lots of layers!

Next time you visit a supermarket, examine the layers of packaging used on different foods.

Are all the lagers really necessary? Individually wrapped foods are fun, but use a lot of extra packaging. They use up valuable materials, such as paper and plastic, which cost money.

Picture Credit : Google

Rubbish is often solid, like an old can or box. But waste from a power station or factory can also be a liquid or a gas.

Some of this waste is dangerous. It harms nature if people do not clear it up properly.

Cars and homes also produce harmful gases by burning fuel.

Power stations produce waste gases.

Power stations release waste gases as they burn fuels, such as coal, oil and gas, to provide us with electricity. This energy is supplied to our homes, schools and factories to run machines. So, every time we switch on the computer or TV, we are helping to create waste.

 

 

Some factories empty liquid waste into rivers.

When factories make goods such as soap, medicine or paint, they may also produce poisonous chemicals as a waste product. Waste liquids sometimes leak into lakes and rivers, where they harm plants and wildlife such as fish and birds.

 

 

 

These workers’ clothes protect them from toxic (poison) waste.

Some factories produce toxic waste. This is very dangerous and contains chemicals that are harmful to all living things, including people. Toxic waste cannot be released into the air, soil or water.

Toxic waste and nuclear waste from power stations must be stored in sealed containers. This waste is buried under the ground, but it can still cause problems if it leaks out. It can be harmful for hundreds of years.

 

 

Batteries contain poisonous metals or acid.

Batteries contain metals and acids that can poison the environment. Most batteries usually end up in a hazardous waste landfill.

However, they can be recycled. Some towns collect batteries as part of a recycling programme.

One alternative is rechargeable batteries. They can be used many times and can also be recycled when they no longer work.

Picture Credit : Google

Some types of rubbish, such as fruit and vegetable peel, rot away quickly. We say they are biodegradable.

Metals like iron and steel rust. They break into smaller pieces over a long time.

Glass and plastic do not rot. In a landfill, they can stay under the ground for hundreds of years.

Dead animals and plants are food for other living things.

In nature, everything is recycled. Nothing is wasted. Dead plants and animals provide food for living things such as worms, fungi and ting bacteria.

The nutrients (minerals) in rotting plants and animals return to the soil. Here, they help other plants to grow. We sag they fertilise the soil.

 

 

Manure helps crops to grow but it can pollute (dirty) rivers.

Many farmers spread animal manure (dung) and plant waste on their fields to fertilise the soil, so their crops grow well. But too much natural waste can cause pollution. If thick, liquid manure, called slurry, gets into ponds and rivers, it can harm water life.

 

 

 

 

Metal wires and plastics do not rot. They can poison the soil.

Paper, card, cotton, leather and wool are all made from plants or animals. These natural materials rot away. Materials such as metal and plastic do not rot. They remain in a landfill for years and may cause pollution.

 

 

 

 

 

Look for minibeasts that feed on waste.

Lift logs and fallen leaves to find the minibeasts that lurk there. Worms, slugs, insects, woodlice and millipedes all feed on plant or animal remains.

These minibeasts help natural waste to decompose (rot). Other minibeasts, such as spiders and centipedes, feed on the decomposers. Always put the log or leaves back gently when you have finished looking at the minibeasts.

Picture Credit : Google

 

Each week, refuse trucks pick up rubbish from our homes and take it to landfills. Landfills are huge holes in the ground. Refuse trucks tip the rubbish into the hole. Then bulldozers bury the rubbish.

People do not like living near landfills. So some towns burn their waste. They use giant ovens called incinerators.

Refuse trucks collect your rubbish.

In many countries, a refuse truck visits once a week to collect waste. The collectors empty dustbins onto the truck, where the rubbish is squashed so more fits in. The full truck then drives to the landfill site.

 

 

 

The trucks tip the waste into landfills.

Many landfill sites are old quarries. The trucks dump their load, and then bulldozers pack the rubbish down and cover it with soil to prevent it blowing away. Modern landfills have a plastic liner to stop poisonous chemicals from leaking into the soil.

 

 

 

 

This golf course was a landfill. A layer of soil covers the rubbish.

Landfill sites are an easy way to get rid of lots of rubbish, though they are often smell and look ugly. Once a landfill is full, a thick layer of soil is added. The landfill may then become a park or golf course. It may be hard to see that a landfill was ever there!

 

 

An incinerator burns rubbish to make energy.

Paper, plastic and other rubbish give off heat energy when burned. The heat is used to boil water to produce steam. This steam is used to generate electricity. However, incinerators can create poisonous gases that pollute the air.

Rubbish rotting in landfills gives off a gas called methane. This can be burned as fuel. Pipes set into the landfill draw off the methane gas, which flows along a pipe to a power station.

Picture Credit : Google

Every day, we all throw things away — wrappers, bottles, empty cans and waste paper. This rubbish creates a lot of waste. It spoils our surroundings and can harm wildlife.

We don’t have to throw rubbish away. We can recycle it. This means using old things to make new things.

Look how messy litter is!

Our rubbish is collected every week. We forget about it. But rubbish does not just go away. Someone has to deal with it. If you just put your rubbish into a bath it would fill 100 baths every year!

Sometimes, people leave rubbish lying around. This is called litter. Litter spoils the look of the countryside, as well as towns. When litter piles up, it can also smell terrible. Just sniff your dustbin!

 

 

 

Waste can harm wildlife.

Shops, hospitals, farms, factories and power stations all produce different kinds of waste. Some of this waste is poisonous and harmful to wildlife. If waste pollutes (dirties) a beach, it can take years to make it clean again.

 

 

 

 

More people in the world means more waste.

When there were fewer people, waste did not matter so much. Now, big towns and cities are found in most parts of the world. The large numbers of people living everywhere produce lots of waste.

 

 

 

 

 

Look in your dustbin.

The type of rubbish we throw away has changed over the years. About 70 years ago, most of the waste in the bin was ash and dust from coal fires that were used to heat houses. That is how “dust” bins got their name!

A lot of rubbish today is packaging. Many products are wrapped up or put in boxes. Once we take out the product, we throw away the packaging.

Introduction

Waste is anything we no longer have use for. When we throw something away, we create waste.

Activities such as cooking or washing also create waste. Yet, we can recycle waste. Recycling means making waste into something new.

A canoe made from old glass!

You might be surprised what rubbish can be turned into. The glass from bottles and jars can be turned into a material called fibreglass. This mix of strong glue and thin strips of glass can be used to make canoes and boats.

 

We can all learn how to recycle.

How we can turn our rubbish into useful products. However, recycling is just one way to deal with waste. Remember these three words: Reduce, Reuse, and Recycle.

• Try to reduce, or cut down, the amount of waste you produce.

• Reuse items, such as glass and plastic jars or bottles, when you can find a use for them.

• If you cannot reuse something, then recycle it.

 

The rubbish we throw away contains materials we can use again.

At recycling centres, we can separate our rubbish into different materials. Factories can use these materials to make all kinds of new products.

When we recycle, we do not have to bury or burn our waste.

This is a recycling centre. A woman is bringing her old glass bottles.

Many recycling centres have a different container for each type of material:

• Glass bottles (green, brown or clear glass)

• Newspapers and magazines

• Textiles (old clothes)

• Cans

• Cardboard

• Plastic bottles and bags

You can prepare cans, bottles and other containers for recycling by washing them out and removing the tops and labels.

 

 

 

Some families sort their rubbish for recycling.

Some local councils have set up recycling schemes, so people don’t have to visit recycling centres. Families may put all items that can be recycled in a separate bin. This is taken away by the council to recycle.

 

 

 

 

 

Look out for this symbol. It reminds you to recycle.

As well as recycling, it is good to try to reuse things. Reusing everyday items, such as plastic bags and containers, helps to cut down on waste. Old electrical equipment, such as TV sets, can be repaired and used again.

Building materials, such as tiles, bricks and even doors and windows, are sometimes saved and reused to build new houses.

 

DNA is an abbreviation of the name of a chemical: deoxyribonucleic acid. It is DNA that contains the instructions for making and controlling every living thing. Inside the nucleus of a cell, the DNA forms chromosomes. Living things have different numbers of chromosomes. Human beings have 46, arranged in 23 pairs. Each of us has inherited one half of each chromosome pair from our father and the other half from our mother. A gene is a small part of the DNA molecule that can make one of the proteins that the living organism needs.

Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). Mitochondrial are structures within cells that convert the energy from food into a form that cells can use.

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.

Living things are said to be animate. Inanimate things are not living. Metal, plastic and glass, for example, are inanimate. All animate things are able to do six things that inanimate things cannot.

Although seemingly diverse, living things, or organisms, share certain essential characteristics. The most recent classification system agreed upon by the scientific community places all living things into six kingdoms of life, ranging from the simplest bacteria to modern-day human beings. With recent innovations such as the electron microscope, scientists peered inside cells and began to understand the intracellular processes that defined life.

Composition

Cells compose all life, performing the functions necessary for an organism to survive in its environment; even the most primitive of life forms, bacteria, consists of a single cell. While peering through a microscope at slices of cork tissue in the late 17th century, scientist Robert Hooke discovered numerous tiny compartments which he coined “cells.” After several developments regarding cell structure and function, Robert Virchow compiled a book, “Cellular Pathology,” describing the nature of cells in relation to life. He formed three conclusions: cells form the basis of all life, cells beget other cells and cells can exist independent of other cells.

Energy Use

All processes occurring within organisms, whether single-celled or multicellular, expend energy. The method of procuring that energy, however, differs between organisms. Organisms called autotrophs make their own energy while heterotrophs must feed to obtain their energy needs. Autotrophs such as plants and some bacteria produce their own food by converting carbon dioxide and water into sugar with the aid of the sun’s energy via photosynthesis. Other autotrophic bacteria use chemicals such as sulfur to make energy in a process called chemosynthesis. The energy organisms need comes in the form of a molecule called ATP, or adenosine triphosphate. Living things make ATP by breaking down glucose.

Response

Organisms use their senses to obtain information from and have the capability of reacting to stimuli in their environments. Even unicellular organisms such as bacteria and seemingly immobile plants can respond to stimuli. Plants such as sunflowers can sense heat and light, so they turn toward the sun’s rays. Predators such as cats can track their prey with keen senses of vision, smell and hearing and then hunt them down with superior agility, speed and strength.

Growth

Living things grow and change through the process of cell division, or mitosis. In organisms composed of more than one cell, mitosis either repairs damaged cells or replace older ones that have died. Additionally, multicellular organisms grow larger in size by increasing the number of cells in their bodies. Unicellular organisms take in nutrients and enlarge. They grow to a certain point and then must divide into two new daughter cells. The process of mitosis takes place in four phases. Certain signals trigger cells to divide. The cell replicates its genetic information, resulting in two exact copies of the gene-bearing structures called chromosomes. Cellular structures separate the chromosome copies, moving them to different sides of the cell. The cell then pinches itself down the middle, creating a new barrier to separate the two new cells.

Reproduction

For a species or organism to continue existing, members of the species must reproduce, either asexually or sexually. Asexual reproduction produces offspring that exactly resemble the parent organism. Certain members in each of the kingdoms of life can reproduce asexually. Bacteria from Kingdoms Archaebacteria and Eubacteria, amoeba of the Kingdom Protista and yeast of Kingdom Fungi use binary fission to simply divide in two, resulting in two identical daughter cells. Worms called planaria can break off a segment that grows into a new organism. Plants such as potatoes form buds which, when cut off and planted, will produce a new potato plant. Sexual reproduction, which allows a mixing of genes from two individuals of a species, evolved from asexual reproduction because the benefits of sex outweigh its costs.

Adaptation

Since the beginning of life, organisms have adapted and evolved to survive according to their environments. Those individuals unable to adapt to changing conditions will die or be unable to pass on much of their genes to the next generation. Many times in the history of the earth, entire species, including many dinosaur groups, have died out when they failed to respond appropriately to environmental changes such as droughts or cooling climates. The environment selects for those individuals best acclimated to live under specific conditions; these creatures have the best selections of mates and will contribute to a greater percentage of descendants.

All cells have a cell wall, hut in plant cells this is made of a stiff, tough layer of cellulose. Cellulose is made of tiny fibres, layered together to form a strong sheet. Most plant cells also contain organelles called chloroplasts. It is in these that photo-synthesis takes place.

Animal cells and plant cells are similar in that they are both eukaryotic cells. These cells have a true nucleus, which houses DNA and is separated from other cellular structures by a nuclear membrane. Both of these cell types have similar processes for reproduction, which include mitosis and meiosis. Animal and plant cells obtain the energy they need to grow and maintain normal cellular function through the process of cellular respiration. Both of these cell types also contain cell structures known as organelles, which are specialized to perform functions necessary for normal cellular operation. Animal and plant cells have some of the same cell components in common including a nucleus, Golgi complex, endoplasmicreticulum, ribosomes, mitochondria, peroxisomes, cytoskeleton, and cell (plasma) membrane. While animal and plant cells have many common characteristics, they are also different.

Size

Animal cells are generally smaller than plant cells. Animal cells range from 10 to 30 micrometers in length, while plant cells range from 10 and 100 micrometers in length.

Shape

Animal cells come in various sizes and tend to have round or irregular shapes. Plant cells are more similar in size and are typically rectangular or cube shaped.

Energy Storage

Animal cells store energy in the form of the complex carbohydrate glycogen. Plant cells store energy as starch.

Proteins

Of the 20 amino acids needed to produce proteins, only 10 can be produced naturally in animal cells. The other so-called essential amino acids must be acquired through diet. Plants are capable of synthesizing all 20 amino acids.

Differentiation

In animal cells, only stem cells are capable of converting to other cell types. Most plant cell types are capable of differentiation.

Growth

Animal cells increase in size by increasing in cell numbers. Plant cells mainly increase cell size by becoming larger. They grow by absorbing more water into the central vacuole.

Cell Wall

Animal cells do not have a cell wall but have a cell membrane. Plant cells have a cell wall composed of cellulose as well as a cell membrane.

Centrioles

Animal cells contain these cylindrical structures that organize the assembly of microtubules during cell division. Plant cells do not typically contain centrioles.

Cilia

Cilia are found in animal cells but not usually in plant cells. Cilia are microtubules that aid in cellular locomotion.

Cytokinesis

Cytokinesis, the division of the cytoplasm during cell division, occurs in animal cells when a cleavage furrow forms that pinches the cell membrane in half. In plant cell cytokinesis, a cell plate is constructed that divides the cell.

Glyoxysomes

These structures are not found in animal cells but are present in plant cells. Glyoxysomes help to degrade lipids, particularly in germinating seeds, for the production of sugar.

Lysosomes

Animal cells possess lysosomes which contain enzymes that digest cellular macromolecules. Plant cells rarely contain lysosomes as the plant vacuole handles molecule degradation.

Plastids

Animal cells do not have plastids. Plant cells contain plastids such as chloroplasts, which are needed for photosynthesis.

Plasmodesmata

Animal cells do not have plasmodesmata. Plant cells have plasmodesmata, which are pores between plant cell walls that allow molecules and communication signals to pass between individual plant cells.

Vacuole

Animal cells may have many small vacuoles. Plant cells have a large central vacuole that can occupy up to 90% of the cell's volume.

Prokaryotic Cells

Animal and plant eukaryotic cells are also different from prokaryotic cells like bacteria. Prokaryotes are usually single-celled organisms, while animal and plant cells are generally multicellular. Eukaryotic cells are more complex and larger than prokaryotic cells. Animal and plant cells contain many organelles not found in prokaryotic cells. Prokaryotes have no true nucleus as the DNA is not contained within a membrane, but is coiled up in a region of the cytoplasm called the nucleoid. While animal and plant cells reproduce by mitosis or meiosis, prokaryotes propagate most commonly by binary fission.

Other Eukaryotic Organisms

Plant and animal cells are not the only types of eukaryotic cells. Protists and fungi are two other types of eukaryotic organisms. Examples of protists include algae, euglena, and amoebas. Examples of fungi include mushrooms, yeasts, and molds.

Mitochondria are organelles that break up food materials to make energy. Other important organelles are ribosomes, which make proteins, and endoplasmic reticulum. This is a structure, made of double membranes, that is linked to the nucleus and to the cell wall, so that chemicals can be carried around the cell. The cell wall itself is said to be semi-permeable. That means that some chemicals can pass through it into the cell but none can pass out.

Mitochondria are specialized structures unique to the cells of animals, plants and fungi. They serve as batteries, powering various functions of the cell and the organism as a whole. Though mitochondria are an integral part of the cell, evidence shows that they evolved from primitive bacteria. 

All living organisms are built with one fundamental brick: the cell. In some cases, a single cell constitutes an entire organism. Cells contain genetic material (DNA and RNA), and they carry out essential functions, such as metabolism and protein synthesis. Cells are also capable of self-replicating. However, the level of organization varies within the cells of different organisms. Based on these differences, organisms are divided into two groups: eukaryotes and prokaryotes. 

Plants, animals and fungi are all eukaryotes and have highly ordered cells. Their genetic material is packaged into a central nucleus. They also have specialized cellular components called organelles, each of which executes a specific task. Organelles such as the mitochondria, the rough endoplasmic reticulum and the Golgi serve respectively to generate energy, synthesize proteins and package proteins for transport to different parts of the cell and beyond. The nucleus, as well as most eukaryotic organelles, is bound by membranes that regulate the entry and exit of proteins, enzymes and other cellular material to and from the organelle.

Prokaryotes, on the other hand, are single-celled organisms such as bacteria and archaea. Prokaryotic cells are less structured than eukaryotic cells. They have no nucleus; instead their genetic material is free-floating within the cell. They also lack the many membrane-bound organelles found in eukaryotic cells. Thus, prokaryotes have no mitochondria.

Cells certainly are the building blocks of life, but they are very busy building blocks! Inside each cell thousands of chemical reactions are going on, so that the cell can carry out its tasks. A typical cell has a cell wall or membrane surrounding a kind of watery jelly called cytoplasm. Within the cell there are a number of parts called organelles. These do all the work that the cell is designed to do. The nucleus is a particularly important organelle. It controls all the activities of the cell.

A cell is the structural and fundamental unit of life. The study of cells from its basic structure to the functions of every cell organelle is called Cell Biology. Robert Hooke was the first Biologist who discovered cells.

All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells (multicellular).  Mycoplasmas are the smallest known cells. Cells are the building blocks of all living beings. They provide structure to the body and convert the nutrients taken from the food into energy. Cells are complex, and their components perform various functions in an organism. They are of different shapes and sizes, pretty much like bricks of the buildings. Our body is made up of cells of different shapes and sizes.

Cells are the lowest level of organisation in every life form. From organism to organism, the count of cells may vary. Humans have the number of cells compared to that of bacteria. Cells comprise several cell organelles that perform specialised functions to carry out life processes. Every organelle has a specific structure. The hereditary material of the organisms is also present in the cells.

Trees in a forest, fish in a river, horseflies on a farm, lemurs in the jungle, reeds in a pond, worms in the soil — all these plants and animals are made of the building blocks we call cells. Like these examples, many living things consist of vast numbers of cells working in concert with one another. Other forms of life, however, are made of only a single cell, such as the many species of bacteria and protozoa. Cells, whether living on their own or as part of a multicellular organism, are usually too small to be seen without a light microscope.

Cells share many common features, yet they can look wildly different. In fact, cells have adapted over billions of years to a wide array of environments and functional roles. Nerve cells, for example, have long, thin extensions that can reach for meters and serve to transmit signals rapidly. Closely fitting, brick-shaped plant cells have a rigid outer layer that helps provide the structural support that trees and other plants require. Long, tapered muscle cells have an intrinsic stretchiness that allows them to change length within contracting and relaxing biceps.