Category Zoology

Humans could not survive without all 12 of the body systems – groups of body parts that carry out different tasks. The systems communicate continually by passing instructions to each other, so the body works as one.

The 12 systems are the skin, hair and nails, muscular, skeletal (bones), nervous (brain and nerves), cardiovascular (heart and blood), lymphatic (drainage), immune (defence), respiratory (lungs and breathing), digestive (processing food), urinary (kidneys and bladder), reproductive (sex), and endocrine (hormones) systems.

Working together

Body systems are interdependent, which means they rely on each other to function. Some organs belong to more than one system – the pancreas plays a role in digestion but also releases hormones, so it belongs to both the digestive and endocrine systems.

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From babyhood to old age, the body changes as it grows and ages. At the age of around 20-30, humans reach maximum height, and are physically at their strongest. After that, the body very gradually decreases in power with age. However, the brain actually continues to improve over several more years. As it gains more experience, it gets better at analyzing situations and making decisions.

Making a man

Here are the stages of life for a human man. Size and height are the most obvious changes, but there are many other changes on the way to adulthood and old age.

Baby

Learning to stand and walk is a gradual process for growing babies. Babies have a large head and short arms and legs. By around 18 months, they have gained enough strength and muscle control to stand and start to walk.

Toddler

At about age 2, the arms and legs grow so the head no longer looks as large. The brain develops rapidly, and children learn to talk and use their hands with more precision.

Child

From the ages of 5-10, children continue to grow and learn complex physical skills such as riding a bike and swimming. Milk teeth are replaced by adult teeth by the age of about 11.

Teenager

During puberty, hormones trigger major change: height increases, the body takes on more adult features, and emotional swings are common. A surge in hormones produces a big growth spurt.

Young adult

The body reaches its adult height, and bones stop growing. People are physically capable of reproducing – having children.

Adult

Humans are physically strongest between 20 and 35 years of age. Muscle development is complete and body systems continue to function well.

Middle-aged adult

Between the ages of 50 and 70, the skin becomes less stretchy and wrinkles appear. Muscles weaken. Vision and hearing begin to deteriorate.

Elderly adult

A person gets shorter as they age because their spine shortens. Their muscles also get weaker, and together with stiff joints this can make movement slower.

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When cells reach the end of their natural lifespan, they undergo a process of shrinking and breaking down into small fragments. These pieces are then eaten up by special cleaner cells called phagocytes.

In with the new

The natural breakdown of cells and the clean-up operation by phagocytes leaves room for new cells to replace them.

Use it or lose it

The speed of ageing varies widely between people. Although genetics plays its part, evidence suggests that keeping both mind and body active can help to slow down the ageing process and may help you live longer.

Staying active

Briton Fauja Singh holds many senior running records, including marathons. In 2013, he ran in the Mumbai Marathon at the age of 102.

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We each start out as a single cell. To develop different organs and tissues for the body to grow, our cells must multiply. As adults, cells need to be replaced when damaged or when they complete their life cycle.

Mitosis

The body produces new cells by a process called mitosis. This is when a cell’s DNA, which carries all the instructions to build and run a new cell, duplicates itself. The cell then splits to form two identical cells. This is how cells grow – by making exact copies of themselves.

Checking

The parent cell gets ready for mitosis. It checks its DNA for damage and makes any necessary repairs.

Preparation

The chromosomes duplicate themselves, then the originals join together with their copies.

Lining up

Each doubled chromosome attaches to special tribes, which help them to line up in the centre of the cell.

Separation

The chromosomes break apart at the point where they were attached. Each half is pulled to the opposite end of the cell.

Splitting

A membrane forms around each group of chromosomes. The cell membrane starts to pull apart to form two cells.

Off spring

 Two daughter cells are formed. Each one contains a nucleus with an exact copy of the DNA from the parent cell.

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Throughout life, the human body is constantly changing as it experiences different stages of development. From a single cell, the body goes through a process of cell division and multiplication as it grows and develops. By adulthood the body is fully grown, and cells no longer divide for growth. Instead, they divide to replace worn out or damaged cells.

Stage one: Mimicry

We are born helpless. We can’t walk, can’t talk, can’t feed ourselves, can’t even do our own damn taxes.

As children, the way we’re wired to learn is by watching and mimicking others. First we learn to do physical skills like walk and talk. Then we develop social skills by watching and mimicking our peers around us. Then, finally, in late childhood, we learn to adapt to our culture by observing the rules and norms around us and trying to behave in such a way that is generally considered acceptable by society.

Stage two: Self-discovery

In Stage One, we learn to fit in with the people and culture around us. Stage Two is about learning what makes us different from the people and culture around us. Stage Two requires us to begin making decisions for ourselves, to test ourselves, and to understand ourselves and what makes us unique.

Stage three: Commitment

Once you’ve pushed your own boundaries and either found your limitations (i.e., athletics, the culinary arts) or found the diminishing returns of certain activities (i.e., partying, video games, masturbation) then you are left with what’s both a) actually important to you, and b) what you’re not terrible at. Now it’s time to make your dent in the world.

Stage four: Legacy

People arrive into Stage Four having spent somewhere around half a century investing themselves in what they believed was meaningful and important. They did great things, worked hard, earned everything they have, maybe started a family or a charity or a political or cultural revolution or two, and now they’re done. They’ve reached the age where their energy and circumstances no longer allow them to pursue their purpose any further.

The goal of Stage Four then becomes not to create a legacy as much as simply making sure that legacy lasts beyond one’s death.

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Each of your cells contains a copy of your genome – all the DNA that you inherited from your parents. Just like a fingerprint, everyone (except a identical twin) has a slightly different, unique genome. This means that a criminal who leaves hair, skin, blood, or saliva at a crime scene can be identified by their DNA.

Matching DNA

A DNA fingerprint from a sample is recorded as a series of rungs, similar to a supermarket barcode. Crime investigators use software to search databases of offenders’ DNA to look for a match.

Boy or girl?

A baby’s characteristics – whether it will be tall or short, have curly or straight hair, or brown or blue eyes – are set by the DNA it inherits from its parents. Two special chromosomes, called X and Y, determine whether a baby will be male or female.

Genetic mix

An embryo is created when a sperm cell fertilizes a female egg. All eggs contain an X chromosomes, but a sperm can carry either an X or a Y chromosome. So it is the sperm that determines the baby’s sex.

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