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All organisms originate from 2 special single cells called “gametes”,- eggs and sperms.
When one of the million sperm cells finds an egg cell, then the sperm penetrates her and ejaculates his DNA into her. The egg shudders as if in orgasm and starts to have a life. It eats from its environment and grows until it divides.
Depending on the cell and the need for new cells, a cell divides at a rate from once an hour to once a day for about 50 times before it dies.
In this way each cell can be likened to a human being. In this analogy, the cell wall is the skin, the cell nucleus is the brain and the rest of the cell structure would be the various organs like the stomach and heart.
Other analogies are cells as houses, walled cities, bordered countries, islands, continents, or even the world. In this case the organelles in the cell would be likened to kitchens, stairs, industries, factories, train stations, police and fire stations and armies.
Cells emerged about 4 billion years ago as the building blocks of life. Cells are capable of synthesizing new proteins, which are essential for their cellular activities.
A salty sea called cytoplasm which is 70% water contains the organelles of the cell. Cells are not differentiated by race. The skin cells of negros and the skin cell of whites are the same, they are only colored by different pigments.
A semi permeable membrane made mostly from a double layer of fatty acids envelops the cytoplasm and protects it from the environment. This membrane also envelops and gives structure to all organelles within the cell.
Proteins embedded in the membrane act as guarded doors regulating how much of what moves in and out.
Membranes also contain receptor proteins, and like ears, eyes and hands, allow cells to detect external signaling molecules such as hormones.
The nucleus is like our brain and like our testicles, all in one. It is where DNA replicate and where the instruction code is written in chromosomes so that each cell dances to the same music to make an organism like
a plant, ant, or
DNA also contains the code and the shape to build various proteins such as enzymes and hormones, the cell's primary machinery.
Organelles, like organs in our bodies, carry out one or more vital functions of the cells.
The centrosome is like muscle. It produces fibers like a spider produces spider webs and makes a net called the cytoskeleton that anchors organelles in place and
Like muscle, it can move the flagella, the tails of sperm cells, to make them as mobile as tadpoles.
Ribosomes act as assembly lines to synthesize proteins from amino acids. They take the code from the protein coding genes in the DNA to make proteins. They also take the code from viruses that entered the cell and blindly make copies of them until there are enough of them that break out and kill it.
Golgis process and package macromolecules such as proteins and lipids that are synthesized by the cell.
Endoplasmic Reticulum, (ER) like trucks transports them to specific destinations within the cell.
Lysosomes like stomachs contain enzymes to digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria.
Peroxisomes like garbage collectors have enzymes that rid the cell of toxic peroxides.
Vacuoles store water food and waste.
Mitochondria, in animal cells, and chlorophyll, in plant cells, are self-replicating organelles that act like power generators. Like the bacteria in our stomachs, mitochondria and chlorophyll have their own DNA, and are organisms in their own right.
Like the bacteria in stomachs are needed to break down food into glucose, animal cells need mitochondria to break down glucose into ATP, the fuel used by cells. They split glucose into ATP, much like we split logs to make wood for a fire. Because mitochondria in sperm cells are located in the tails that get left behind when sperms and eggs fuse, mitochondria are passed down only from eggs.
Chlorophyll in plant cells is a green pigment that absorbs energy from light by trapping photons and converting them to electricity.
Types of cells
It all starts with 2 cells called "gametes" or sex cells. Individual they are called "egg" and "sperm". They have only half the DNA of normal cells. When eggs get fused or fertilized by sperms they get the full set of DNA and start the dance of cell division called mitosis that continues and eventually forms an adult organism capable of producing either eggs or sperm.
Our bodies are just a walking and talking blob of different cells which are mostly proteins. There are 210 different types of cells in the human body, from the hair, nail and skin cells on the outside to everything else inside.
During the first 12 hours after conception, the fertilized egg cell remains a single cell. After approximately 30 hours, it divides from 1 cell into 2 and 15 hours later, the 2 cells divide into 4. And at the end of 3 days, the fertilized egg cell has become a berry-like structure made up of 16 cells. Cells on average divide once a day and in 9 months grow into a 3.5kg fetus ready to be born.
Cells can divide about 50 times before they die. White blood cells live for about 13 days and liver cells live about 18 months. Cells in the top layer of the skin live about 30 days and red blood cells live for about 120 days. Once the body attains its normal weight, the cells divide at a rate to replace cells that die.
Adipocytes are cells that store fat. They insulate organs from shock and temperature and like a tank of oil, store energy for later burning.
Bone cells like warehouses store metals. They support the body like steel beams and protect the brain like a helmet. Like a vault, they guard the bone marrow where 500 billion blood cells are produced each day.
85% of the cells in the adult human body are 25 trillion red blood cells. Every 7 days, 2.4 million are produced per second in the bone marrow and circulate for about 100–120 days before their components are recycled. Each circulation takes about 1 minute. Efficient gas transport requires red blood cells to pass through very narrow capillaries, and this constrains their size. They lack a cell nucleus and most organelles, in order to accommodate maximum space for hemoglobin. They can be viewed as sacks of hemoglobin, with a plasma membrane as the sack.
1,000,000 white blood cells are
produced every minute by the stem cells in the bone marrow. Like policemen, white blood cells called leukocytes move to any wound site and kill microorganisms like bacteria that cause infection.
Cancer cells
All types of cells of all types of multi-cellular organisms develop into cancer cells if their genes are sufficiently damaged. Cells with a life span of growing, dividing and dying turn into mobile wandering zombie cells that grow, divide, and never die. It is as if the damaged cells with particular functions revert to the single cell bacteria they evolved from billion of years ago. Their genes are so damaged that only the source code called the survival gene functions. The cell becomes a mobile bacteria that divides profusely like a hardy weed suffocating the other cells. If the different cell types of an organism are compared to machines with different functions, then nerve cells would be the network that connects them all and allows them to work together to keep the organism alive and to keep the nerve cells alive.
All types of cells of all types of multi-cellular organisms develop into cancer cells if their genes are sufficiently damaged. Cells with a life span of growing, dividing and dying turn into mobile wandering zombie cells that grow, divide, and never die. It is as if the damaged cells with particular functions revert to the single cell bacteria they evolved from billion of years ago. Their genes are so damaged that only the source code called the survival gene functions. The cell becomes a mobile bacteria that divides profusely like a hardy weed suffocating the other cells. If the different cell types of an organism are compared to machines with different functions, then nerve cells would be the network that connects them all and allows them to work together to keep the organism alive and to keep the nerve cells alive.
Nerve cells called neurons are a special type of cell found in the bodies of most animals. Only sponges and a few other simpler animals have no neurons. Although plants don't have nerves, plants cells are capable of generating electrical impulses just as nerve cells in animals do. The controlled flow of ions in and out of a cell constitutes electrical signaling in both plants and animals. Neurons, the core components of the nervous system, which includes the brain and the spinal cord, connect to each other like electrical cables to form neural networks resembling underground mycelium of mushrooms.
They transmit information by electrical and chemical signaling. Neurons form many thousands of extensions called axons that can be up to 1 meter long. They are like sensors carrying sensations and connect to other neurons like a cable.
The connections form a multi pathway network much like the internet that carry signals from cells to the brain. The brain processes the signals and reacts by sending suitable signals to the appropriate cells for an appropriate response. That is how we jerk our hand when we touch something too hot.
A number of specialized types of neurons exist. Sensory neurons respond to touch, sound, light and numerous other stimuli affecting cells of the sensory organs that then send signals to the spinal cord and brain. Motor neurons receive signals from the brain and spinal cord and cause muscle contractions.
If the different cell types of an organism are compared to machines with different functions, then nerve cells would be the network that connects them all and allows them to work together to keep the organism alive and to keep the nerve cells alive.
If the different cell types of an organism are compared to machines with different functions, then nerve cells would be the network that connects them all and allows them to work together to keep the organism alive and to keep the nerve cells alive.
With the exception of neural stem cells, neurons do not undergo cell division. These are the only cells in our bodies that do not divide. Brain cells are kept alive as long as the supporting body feeds it enough glucose to fuel it and the sensory organs feed it enough sensations to make it think.
When machines finally replace our bodies and sense organs, then our brains would be able to be kept alive indefinitely, opening the door and paving the way to immortality.
THE END
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