Category Zoology

The nucleus of every human cell carries a set of unique codes for making new cells to build and maintain the body. These instructions are called genes, and they are made of a substance called DNA.

Inside the cell nucleus, there are 46 tiny structures called chromosomes. These are made of tightly coiled strands of DNA, which contain all the information the cell needs to make a new, identical version of itself. Every time a cell divides so the body can grow or repair itself, a DNA strand “unzips” down the middle. Each unzipped half then rebuilds itself into a new DNA strand, identical to the original and carrying all the same codes.

The DNA molecule

Magnified, a strand of DNA looks like a twisted ladder, with two long, thin strands connected by rungs. These rungs are called bases, and are made up of four different chemicals. The bases, and are made up of four different chemicals. The bases interact to form instructions for making proteins – the building materials that make up our organs, muscles, blood, bones and hair.

Chromosome

Inside a cell nucleus there are 46 chromosomes (23 pairs), made of tightly packed DNA.

Histone

This ball-shaped protein acts as a framework for DNA to coil around.

Double helix

The twisted ladder shape of a DNA molecule is known as a double helix.

Backbone

The two long, thin parts of the DNA strand are known together as the backbone.

Pairing up

DNA bases are made up of your chemicals – adenine, cytosine, guanine, and thymine. The bases link together in pairs. The specific order of the base pairs along the ladder gives the instructions for making different proteins.

The order of the base pairs creates different codes to form different proteins. Adenine always links to thymine. Guanine always joins with cytosine.

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The body is made of trillions of cells, each too small to see without a microscope. These cells aren’t all the same. There are about 200 different types, each with its own size, shape, and contents. Each type of cell has a particular task.

Just as the body has organs, such as the heart, the cell has organelles, such as mitochondria. These parts work together to make the cell a living unit. In addition, tiny rods, including microtubes, move organelles and form a kind of “skeleton” that supports and shapes the cell.

Golgi apparatus

The Golgi apparatus processes and packages proteins made on ribosomes, ready for use inside or outside the cell.

Vesicle

This bag takes proteins from the Golgi apparatus and carries them to where they are needed.

Cell membrane

This flexible membrane surrounds the cell and controls what enters and exist. It consists of a double layer of lipid (fat) molecules containing proteins that have different jobs to do.

• Lipid layer: A double layer of lipid (fat) molecules forms main part of the membrane.
• Protein: This protein channel transports substances into and out of the cell.
• Glycoprotein: This “tag” identifies the cell to other cells.

Centrioles

These two bunches of microtubles play a key part in cell division.

ATP synthase

This is where the energy-carrier ATP is made.

Microvilli

These structures increase the area of a cell’s surface so it is better at taking in substances nut not all cells have them.

Rough endoplasmic reticulum

This network of tubes and flattened bags makes and transports proteins and other substances.

Ribosome

This tiny structure makes the many proteins that build and run the cell.

Nucleus

 This tiny structure makes the many proteins that build and run the cell.

Lysosome

This membrane bag contains enzymes that break down unwanted substances and recycle worn-out organelles.

Cytoplasm

A jelly-like fluid in which organelles floats, the cytoplasm contains proteins and other substances.

Microtubes

These structures help to shape the cell and move organelles.

Vacuole

This bag contains water and food taken into the cell.

Mitochondria

These sausage-shaped organelles are the cell’s power stations. They release the energy from glucose and other foods that cells use to drive their many activities.

Inner membrane

A folded membrane provides a large surface for making ATP.

Cell structure

No cell is exactly like the one shown here, but this example shows the features that are found in many body cells. Each busy, living cell consists of an outer membrane, cytoplasm, and different types of organelles. Most cells have a control centre called the nucleus.

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Each type of cell has a shape and size related to its own vital task in the body.

Red blood cells

Red blood cells are doughnut shaped, and this lets them pick up and carry oxygen easily. Hemoglobin is the protein inside red blood cells. It carries oxygen. Red blood cells also remove carbon dioxide from your body, transporting it to the lungs for you to exhale.

Red blood cells are made in the bone marrow. They typically live for about 120 days, and then they die.

Nerve cells

Nerve cells are long, thin, and carry electrical signals over long distances. Essentially, nerve cells, also known as a neurons, are the active component of the nervous system. Neurons communicate with each other as well as with other cells through electric signals (nerve impulses), which in turn allows effector organs to respond to the appropriate stimuli.

Muscle cells

Muscle cells can contract (shorten) and relax to produce movement. Muscle cells, commonly known as myocytes, are the cells that make up muscle tissue. There are 3 types of muscle cells in the human body; cardiac, skeletal, and smooth. 

Epidermal cells

Epidermal cells in the skin fit tightly together to form a protective layer. Epidermal cells include several types of cells that make up the epidermis of plants. Although they serve a number of important functions, their primary role is to protect from a variety of harmful factors (environmental stressors) including microbes, chemical compounds as well as ultraviolet light among others.

Fat cells

Fat cells are filled with droplets of liquid fat as an energy store. Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis.

Cone cells

Cone cells in the eye detect light, enabling us to see. They respond differently to light of different wavelengths, and are thus responsible for color vision, and function best in relatively bright light, as opposed to rod cells, which work better in dim light.

Cell lifespans

Different types of body cell have different lifespans. Some, such as kin cells, are worn away. Other cells wear out and self-destruct. They are replaced with more of their kind by special cells called stem cells.

White blood cells fighting infection: Less than 1 day

Skin cells: 30 days

Liver cells: 12-18 months

Muscle cells: 15 years

Some nerve cells in the brain: A whole lifetime

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Tissues are groups of connected cells. Many tissues are made entirely from one type of cell. The four main types of tissue in the human body are connective, epithelial, muscular, and nervous.

Nerve tissue

Large groups of nerve cells create nervous tissue. This forms the brain, spinal cord, and masses of nerves that wok together in the nervous system, the body’s high-speed communications network.

Epithelial tissue

Made up of three main shapes of cell, epithelial tissue lines and covers surfaces inside and outside the body. It forms skin and the linings of body cavities such as the gut and lungs.

Muscle tissue

Built from long, thin cells, muscle tissue can relax and contract to allow muscles to move bones. It also helps sustain blood pressure and carry blood through the digestive system.

Connective tissue

This dense tissue is the body’s “glue”, filling the space between other tissues and organs, and binding them together. Examples include adipose tissue (fat), bone, and blood.

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Everything in the body id made up of atoms, the tiniest building blocks of matter. Atoms combine to form molecules. Millions of molecules form every cell in the body. There are more than 200 types of cell, with similar cells working in teams called tissues. The body’s many organs and systems are made up of different tissues.

Atoms and molecules

The smallest parts in the body are atoms. These tiny building blocks form the elements in the body, such as carbon. Atoms can also join together in groups called molecules – for example, water is a molecule, made from a combination of hydrogen and oxygen atoms.

Cell

Molecules build up to create body cells. There are about 37 trillion cells in the average human, with different types of cells carrying out a variety of body functions, from transporting oxygen to sensing light and colour in the eye.

Tissue

Cells performing the same function are grouped together to form body tissues, such as skin, fat, or heart muscle. Blood is also a tissue, in liquid form.

Organ

Different kinds of tissue combine to make larger structures called organs. Each organ works like a machine, performing its own role. An example of an organ is the stomach, which plays a part in the process of digesting food.

Body system

Organs are at the centre of 12 internal body systems. Each system has a specific job to keep the body in working order. The stomach is one of the main organs of the digestive system.

Complete human

When this common combination of integrated systems, organs, and tissues works together, the human body is complete. Each individual component plays its part in maintaining a fully functioning body.

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The human body is made from substances containing the element carbon. Called organic compounds, these often contain hydrogen and oxygen, too. Although organic compounds are based on only a few elements, they produce more than 10 million different compounds. Four main types of carbon compound exist inside the human body.

Nucleic acids

The molecules DNA and RNA carry all the instructions for making the proteins that our bodies are made of. They also carry code that controls how cells work and reproduce.

Proteins

Proteins are vital body molecules. Organs such as the brain are made o protein, as well as muscles, connective tissues, hormones that send chemical messages, and antibodies that fight infection.

Fats

Fats are made from carbon and hydrogen atoms. They form the outer barrier of cells. The layer of fat beneath the skin stores energy and helps the body to keep out the cold.

Carbohydrates

Carbohydrates are made of carbon, oxygen, and hydrogen, and are the body’s main source of energy, carbohydrates circulate in the blood as sugars, or are stored in the liver and muscles.

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