Category Environtal Studies

WHAT IS GESTATION?

Gestation is the length of time between conception — the fertilization of an egg by a sperm — and the birth of the baby that grows from the fertilized egg. The length of gestation varies according to the species.

Gestation, in mammals, the time between conception and birth, during which the embryo or fetus is developing in the uterus. This definition raises occasional difficulties because in some species (e.g., monkeys and man) the exact time of conception may not be known. In these cases the beginning of gestation is usually dated from some well-defined point in the reproductive cycle (e.g., the beginning of the previous menstrual period).

The length of gestation varies from species to species. The shortest known gestation is that of the Virginian opossum, about 12 days, and the longest that of the Indian elephant, about 22 months. In the course of evolution the duration of gestation has become adapted to the needs of the species. The degree of ultimate growth is a factor, smaller animals usually having shorter periods of gestation than larger ones. Exceptions are the guinea pig and related South American rodents, in which gestation is prolonged (averaging 68 days for the guinea pig and 111 days for the chinchilla). The young of these species are born in a state of greater maturity than are those of the rat with its period of 22 days. Another factor is that, in many species with restricted breeding seasons, gestation is adjusted so that birth coincides with the period when food is most abundant. Thus the horse, a spring breeder with 11 months’ gestation, has its young the following spring, as does the sheep, a fall breeder with a five months’ gestation. Animals that live in the open tend to have longer gestations and to bear young that have reached a state of greater maturity than do animals that can conceal their young in underground burrows or in caves. Marsupials generally have short gestations—e.g., 40 days for the largest kangaroos. The young, born in an extremely immature state, transfer to the pouch in which gestation may be said to continue.

Embryos of some species experience an arrest in development that greatly prolongs gestation. This is especially true of the fur-bearing carnivores the martens and weasels. Embryos of the European badger and American marten, which breed in July and August, develop for a few days, and then lie dormant in the uterus, being implanted in January. Birth occurs in March. Of the total gestation period of 250 days, growth occurs during only 50. Delayed implantation also occurs in mice and other small rodents that become pregnant while they are still suckling a litter.

Either a single factor or a great number of minor factors, all culminating at or near one date, determine the length of gestation. Several minor variations are known: in man, gestation for males is three to four days longer than that for females; and in cattle, bulls are carried about one day longer than heifers. In both species gestation of twins is five to six days less than for singlet’s. In animals such as the rabbit or pig, which bear many young at a time, gestation is shorter for larger litters than for smaller ones. Heredity also influences gestation; in cattle the mean gestation period for Holstein-Friesians is 279 days; for Brown Swiss, 290 days; other breeds fall between these extremes. When hybrids are produced by crossing two species with different gestation periods, the hybrid is carried for a period lying somewhere between those of the two parents and tending toward the mother’s species. Thus a mare carries a mule foal (fathered by a jackass) about 10 days longer than the normal period for the horse (about 337 days). For human gestation, see pregnancy.

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WHAT ARE THE LONGEST ANIMAL LIFE SPANS?

Human beings are far from being the longest-living animals. The giant tortoise can reach 150 years, while several aquatic creatures, such as the killer whale and some species of sea anemone, can survive for well over 80 years. At the other end of the scale, the adult mayfly lives for less than two days. The plant kingdom has far longer-living species. Several trees, such as the yew and giant sequoia, live for thousands of years.

There are tortoises alive today that were 25 to 50 years old when Charles Darwin was born. There are whales swimming the oceans with 200-year-old ivory spear points embedded in their flesh. There are cold-water sponges that were filter-feeding during the days of the Roman Empire. In fact, there are a number of creatures with life spans that make the oldest living human seem like a spring chicken in comparison.

Greenland shark: This shark lives in Arctic waters and slowly grows to an average length of 16 feet. It scavenges for its food and is attracted to the smell of rotting meat in the ocean. It’s also known to primarily live in deeper ocean depths compared to other sharks. A group of scientists conducted radiocarbon testing on the eye lens of 28 female sharks and determined its life span to reach at least 272 years. They concluded that the Greenland shark is the longest-living vertebrae known to man.

Geoducks: These large saltwater clams that are native to the Puget Sound and have been known to live for at least 160 years. They are characterized by their long ‘necks’, or siphons, which can grow to more than 1 meter long.

Tuatara: The word “dinosaur” is commonly used to describe an old person, but when it refers to tuataras, the term is perfectly metaphorical. The two species of tuatara alive today are the only surviving members of an order that flourished about 200 million years ago — they are living fossils. They are also among the longest-lived vertebrates on Earth, with some individuals living for between 100 and 200 years.

Lamellibrachia tube worms: These colorful deep sea creatures are tube worms (L. luymesi) that live along hydrocarbon vents on the ocean floor. They have been known to live 170 years, but many scientists believe there may be some that have lived for more than 250 years.

Red sea urchins: The red sea urchin or Strongylocentrotus franciscanus is found only in the Pacific Ocean, primarily along the West Coast of North America. It lives in shallow, sometimes rocky, waters from the low-tide line down to 90 meters, but they stay out of extremely wavy areas. They crawl along the ocean floor, using their spines as stilts. If you discover one, remember to respect your elders — some specimens are more than 200 years old.

Bowhead whales: Also known as the Arctic whale, the bowhead is by far the longest living mammal on Earth. Some bowhead whales have been found with the tips of ivory spears still lodged in their flesh from failed attempts by whalers 200 years ago. The oldest known bowhead whale was at least 211 years old.

Koi: Koi are an ornamental, domesticated variety of the common carp. They are common in artificial rock pools and decorative ponds. Amazingly, some varieties are capable of living more than 200 years. The oldest known koi was Hanako, a fish that died at the age of 226 on July 7, 1977.

Tortoises: Tortoises are considered the longest living vertebrates on Earth. One of their oldest known representatives was Harriet, a Galápagos tortoise that died of heart failure at the age of 175 years in June 2006 at a zoo owned by the late Steve Irwin. Harriet was considered the last living representative of Darwin’s epic voyage on the HMS Beagle. An Aldabra giant tortoise named Adwaita died at the rumored age of 250 in March 2006.

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HOW DO LIVING THINGS GROW AND AGE?

Two things affect the way in which living things grow and age. The first is their genetic make-up — the genes that they have inherited from their parents. The DNA in their chromosomes controls the way that cells divide to cause the growth of the young organism, its coming to maturity and its aging. The other important factor is the environment and conditions that the organism experiences — how much of the right kind of food it eats, where it lives, the climate and the kinds of events and accidents that happen to it.

Every living organism begins life as a single cell. Unicellular organisms may stay as one cell but they grow too. Multicellular organisms add more and more cells to form more tissues and organs as they grow.

The Growth and development of living organisms are not the same things. Growth is the increase in size and mass of that organism. Development involves the transformation of the organism as it goes through the growth process.

Think of a newly born baby. It has all the features of a fully-grown adult, but they are very tiny. As the years go by, they become big and become a young person like you, and later on, into a fully grown adult, maintaining all the features that they are born with. This is growth. But in their mummy’s tummy, they started off as a single cell and transformed into a zygote and into a foetus before transforming into a tiny baby.

In some organisms, growing involves drastic transformation. Think of a butterfly for instance. It starts off as a cell (egg). Then it transforms into a caterpillar, then into a pupa (chrysalis), and then pops out as a beautiful butterfly.

Plants often start from a tiny seed, and grow into a big tree. One thing common to all organisms is that they grow or develop to look just like their parent species, even though there may be some slight variations resulting from the mixing of cells by the parents. 

Cell growth and development include its repair. As cells grow old, they wear off. Sometimes they suffer injury and bruises, but they are able to repair themselves by growing new cells in a process called Mitosis.

As living things grow, they undergo a process called aging (age). As they get close to the end of their lifespan, their ability to carry out life functions reduces. Eventually, they die to end the process of life.

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Whole world call for Reduce – Reuse – Recycle, what is that?

You can help to make the world a safer, cleaner place. Just remember to: Reduce, Reuse and Recycle.

Reduce waste by only buying the things you need. Try to reuse items or find new uses for them.

Recycle anything you cannot reuse.

 

Buy local foods and reduce packaging.

Reduce rubbish by encouraging your family to buy goods in local markets. Supermarkets often buy their foods from far-away countries. Lots of packaging is needed to protect the goods on the long journey. Foods grown locally often have less packaging, so why not buy them instead.

 

 

Reuse pots and containers.

All kinds of boxes, pots and bottles can find new uses at home. Cardboard boxes can be used to store books, toys or CDs. Plastic ice cream tubs can become lunch boxes. Glass bottles and jars can be used to hold pencils or flowers, or you can use them to grow plants. Decorate them with bright paints or stick on pictures from magazines.

 

Recycle old clothes.

Clothes you have grown out of can be taken to a local charity shop. They may be sold to raise money for the charity, or sent to a developing country.

Unwanted books, toys and household items can also be recycled at charity shops. Even old vinyl records can be recycled —they can be melted down and turned into bank cards.

 

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How do they recycle Plastics material and cloths?

Plastic is cheap, tough and hard-wearing. No wonder so many things are made of plastic these days!

Plastic does not rot, however. So it often ends up in landfills. There are many different kinds of plastic. Some are hard to recycle.

Cloth is easier to recycle. It can be cut up and put into mattresses.

These sheets are made from recycled plastic.

A single bottle may contain several different types of plastic. So, at the recycling plant, plastics are sorted by hand or machine. The plastic is shredded into tiny flakes, which are melted and made into new things.

 

 

Your boots may contain recycled plastic.

Recycled plastic has many uses. Some is used to make garden chairs, fence posts, waterproof boots or new bottles. Other plastics provide stuffing for pillows and duvets or are made into fleecy coats.

 

Old clothes are cut into rags. They can be used for cleaning.

Worn-out clothes and other textiles can also be recycled. You can reuse them as cleaning cloths at home or send them for recycling.

Some old clothes are cut into rags and used to wipe machinery. Other clothes are ripped up and the threads woven to make new clothes or used to stuff seats and mattresses.

 

If you use cloth bags it cuts down on litter.

Most supermarkets hand out plastic bags to their customers to carry home their shopping. Because the bags are free, we often just throw them away at home.

Some supermarkets have started charging for the bags. This encourages people to reuse them or to use strong cloth or canvas bags instead. This cuts down on the litter and waste caused by old plastic bags.

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Do you know something about recycling of metal?

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.

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