Excell at Cells
Welcome to “Excell” At Cells. We think that cells are “excellent” and we hope that when you are through with this activity you will be a cell “cellebrity”. There are fun experiments along with facts to make your brain cells “excell.” We hope you enjoy this activity so much that you’ll want to “cellebrate.
By: Jim V., Catie Leigh L. & Keagan A.
(adapted by Joan Nievas, 2014)
What is a cell?
A cell is the very smallest unit of living matter. All living things including plants and animals are made up of cells. There are many different kinds of cells. The two kinds you are most likely to be familiar with are animal and plant cells. Some of the differences between them are that plant cells have a cell wall and chloroplasts.
Cells have different sizes, shapes, and jobs to do. Did you know that the yoke from an ostrich’s egg is the biggest cell? Even the cells in a single organism may have different shapes, sizes, and jobs. Organisms like humans are made up of trillions of cells. There are also one celled organisms (unicellular) such as euglenas, amoebas, and bacteria.
All cells have some parts in common. One part found in all cells is the cell membrane. The cell membrane surrounds the cell, holds the other parts of the cell in place, and protects the cell. Molecules can pass in and out of the cell membrane. Inside the membrane, all cells, except for bacterial cells, contain a nucleus and cytoplasm. The nucleus is a dark structure located in the middle of the cell. It controls the cell’s activities, and acts like the cell’s brain. Inside the nucleus there is DNA which contains genetic information. The cytoplasm is a jelly-like substance inside the cell where most of the cell’s activities take place. It’s made out of water and other chemicals. All cell parts, except the nucleus, are located in the cytoplasm.
Like all living things, cells die. If you watched a clock for one minute, about three billion cells in your body die. In that same minute, about three billion cells divided so that all the cells that died were replaced. Dead skin cells flake off and dead cells from internal organs will pass through and out of the body with waste products. The length of time cells live can vary. For example, white blood cells only live for thirteen days, red blood cells live for about one hundred and twenty days, liver cells live about eighteen months, and nerve cells can live up to one hundred years. That is a very big difference!
Basically, each cell was made from an already existing cell. New cells are made through a process called cell division or mitosis. One cell turns into two cells and then two cells turn into four cells, etc. Even humans started life with only one cell. Most of the cells in many celled organisms use mitosis to reproduce. The animation shows the basic steps in mitosis which are:
- At the start of mitosis chromosomes are in the nucleus.
- The chromosomes in the nucleus will then make a copy of themselves
- Next the cell divides.
- Last one set of chromosomes goes to the new cell and one set remains in the parent cell.
One of the most important tools that scientists use to study cells is the microscope. An optical microscope can magnify a cell up to two thousand times. If an ant were to be magnified at two hundred thousand times, it would be more than two and one half miles (four kilometers) long. Electron microscopes can magnify a cell by one million times. But even with such large magnifications, the very detailed parts of some cells can’t be seen. If you would like to see real photographs of cells viewed through the lens of an electron microscope, make sure you visit the Nanoworld Image Gallery (you’ll need to register in order to view the gallery).
Scientists also put dyes in cells to make certain parts look bright under a microscope. Another way that scientists use to examine cells is to separate them into their parts by using a machine called a centrifuge. It spins substances at really high speeds. First scientists grind up cells in a tube, and then they place the tube in the machine. After whirling around in the centrifuge, the parts of the cell that weigh more sink, while the lighter parts stay on top. That makes it easier for the scientist to study the parts.
Plant cells are cells that are in plants and algae. Plant cells are like animal cells, but they have a cell wall and chloroplasts. Here’s a labelled picture of a plant cell. You will see all the main parts of the cell. Listed below are definitions of those words. Read on to learn more about photosynthesis.
- Cell Membrane: A thin layer that surrounds the cell.
- Cell Wall: A rigid layer that surrounds the cell membrane of a plant cell.
- Chloroplast: (KLOR-o-plast) A cell structure in which photosynthesis takes place, and it contains the chloropyll.
- Chlorophyll: (KLOR-a-fil) A green substance in plant cells that helps to make food.
- Cytoplasm: (SIGH-ta-plaz-em) The jellylike liquid in cells where activities take place.
- Nucleus: (NEW-kle-us) The dark structure inside the cell that controls the cell’s activities and contains material such as DNA.
- Photosynthesis: (foto-SIN-thi-sis) The process when plants use lights energy to make food.
A very special process that takes place inside of the chloroplasts in plant cells is called photosynthesis. Photo means “light” and synthesis means ” putting things together.” In photosynthesis, green plants actually make their own food. That is so cool! Imagine if we could make our own food. I wonder what we’d make? Personally, I would make pizza. Plants seem to have the right idea since they make sugar. This amazing process is responsible for everything we eat. That’s because animals eat plants, and we eat the animals and the plants.
If you would like to see an actual photograph of a chloroplast viewed through the lens of an electron microscope, visit the Nanoworld Image Gallery (you’ll need to register in order to view the gallery).
In photosynthesis, the chloropyll (KLOR-a-fil) takes in energy from sunlight. The energy comes in the form of a tiny bundle known as a photon. The photon hits a molecule of water inside the chlorophyll. The photon’s energy splits the water molecule into hydrogen and oxygen. The hydrogen combines with carbon dioxide (which the plant has absorbed from the air) to make sugars or glucose. The oxygen is released back into the atmosphere to give us more air. Did you know that the largest suppliers of oxygen in the whole world are tiny plants known as photoplankton? They are found in the oceans and are really important to giving us the oxygen needed to keep life going on our planet.
Believe it or not, a plant uses only about one-sixth of the energy it gets from the sun to nourish itself. The rest of the energy is stored in the glucose until it is eaten by other animals or humans. What an amazing process!
Animal cells are the cells found in animals. You are made up of trillions of animal cells. These are the basic parts of an animal cell:
- Cell Membrane: A cell membrane works like a screen. It lets the good things in like nutrients and lets the bad things out like waste. It is like a sieve.
- Cytoplasm: Cytoplasm is the jelly-like part of the cell where the action takes place. It is where the nutrients are used.
- Nucleus: The nucleus is the brain of the cell. It controls the cell, and tells it what to do. The nucleus also contains the DNA which is like a blueprint. A blueprint is a plan that people use when they build. A cell’s blueprint is the plan the cell uses when it reproduces.
One of the most important ways that animal cells are different from plant cells is that animal cells can’t make their own food. Plant cells make their own food in a process called photosynthesis. Animal cells can’t do that. Instead, animals must eat food. The animal cells use the food to make the energy they need to reproduce and carry out basic functions. This process takes place in a part of the cell called the mitochondrion.
If you would like to see an actual photograph of a pig cell or of mitochondrion viewed through the lens of an electron microscope, visit the Nanoworld Image Gallery (you’ll need to register in order to view the gallery).