The Cell

The cell is one of the most basic units of life. There are millions of different types of cells. There are cells that are organisms onto themselves, such as microscopic amoeba and bacteria cells. And there are cells that only function when part of a larger organism, such as the cells that make up your body. The cell is the smallest unit of life in our bodies. In the body, there are brain cells, skin cells, liver cells, stomach cells, and the list goes on. All of these cells have unique functions and features. And all have some recognizable similarities. All cells have a 'skin', called the plasma membrane, protecting it from the outside environment. The cell membrane regulates the movement of water, nutrients and wastes into and out of the cell. Inside of the cell membrane are the working parts of the cell. At the center of the cell is the cell nucleus. The cell nucleus contains the cell's DNA, the genetic code that coordinates protein synthesis. In addition to the nucleus, there are many organelles inside of the cell - small structures that help carry out the day-to-day operations of the cell. One important cellular organelle is the ribosome. Ribosomes participate in protein synthesis. The transcription phase of protein synthesis takes places in the cell nucleus. After this step is complete, the mRNA leaves the nucleus and travels to the cell's ribosomes, where translation occurs. Another important cellular organelle is the mitochondrion. Mitochondria (many mitochondrion) are often referred to as the power plants of the cell because many of the reactions that produce energy take place in mitochondria. Also important in the life of a cell are the lysosomes. Lysosomes are organelles that contain enzymes that aid in the digestion of nutrient molecules and other materials. Below is a labelled diagram of a cell to help you identify some of these structures.

There are many different types of cells. One major difference in cells occurs between plant cells and animal cells. While both plant and animal cells contain the structures discussed above, plant cells have some additional specialized structures. Many animals have skeletons to give their body structure and support. Plants do not have a skeleton for support and yet plants don't just flop over in a big spongy mess. This is because of a unique cellular structure called the cell wall. The cell wall is a rigid structure outside of the cell membrane composed mainly of the polysaccharide cellulose. As pictured at left, the cell wall gives the plant cell a defined shape which helps support individual parts of plants. In addition to the cell wall, plant cells contain an organelle called the chloroplast. The chloroplast allow plants to harvest energy from sunlight. Specialized pigments in the chloroplast (including the common green pigment chlorophyll) absorb sunlight and use this energy to complete the chemical reaction:
6 CO2 + 6 H2O + energy (from sunlight) C6H12O6 + 6 O2
In this way, plant cells manufacture glucose and other carbohydrates that they can store for later use.
Organisms contain many different types of cells that perform many different functions. In the next lesson, we will examine how individual cells come together to form larger structures in the human body.

Proyecto EDI Science and Technology

The Skeletal System

The Skeletal system is all of the bones in the body and the tissues such as tendons, ligaments and cartilage that connect them.Teeth are also considered part of your skeletal system but they are not counted as bones. They are made of enamel and dentin. Enamel is the strongest substance in your body.

The main job of the skeleton is to provide support for our body. Without the skeleton the body would collapse into a heap. The skeleton is strong but light. Without bones we would be just a puddle of skin and guts on the floor.

The skeleton also helps protect your internal organs and fragile body tissues. The brain, eyes, heart, lungs and spinal cord are all protected by your skeleton. The cranium (skull) protects our brain and eyes, the ribs protect our heart and lungs and our vertebrae (spine, backbones) protect your spinal cord.

Movement Bones provide the structure for muscles to attach so that our bodies are able to move. Tendons are tough inelastic bands that hold attach muscle to bone.

Babies have more than adults! At birth, you have about 300 bones. As we grow older, small bones join together to make big ones. Adults end up with about 206 bones.

Are bones alive?
Absolutely. Old bones are dead, dry and brittle. But in the body, bones are very much alive. They have their own nerves and blood vessels, and they do various jobs, such as storing body minerals like calcium. Bones are made of a mix of hard stuff that gives them strength and tons of living cells which help them grow and repair themselves.

What is a bone made of?
A typical bone has an outer layer of hard or compact bone, which is very strong, dense and tough. Inside this is a layer of spongy bone, which is like honeycomb, lighter and slightly flexible. In the middle of some bones is jelly-like bone marrow, where new cells are constantly being produced for the blood. Calcium is an important mineral that bone cells need to stay strong so keep drinking that low-fat milk!

How do bones break and heal?
Bones are tough and usually don't break even when we have some pretty bad falls. I'm sure you have broken a big stick at one time. When you first try to break the stick it bends a bit but with enough force the stick finally snaps. It is the same with your bones. Bones will bend a little, but if you fall the wrong way from some playground equipment or maybe your bike or skateboard you can break a bone. Doctors call a broken bone a fracture. There are many different types of fractures.
Luckily, bones are made of living cells. When a bone is broken your bone will produce lots of new cells to rebuild the bone. These cells cover both ends of the broken part of the bone and close up the break.

How do I keep my bones healthy?
Bones need regular exercise to stay as strong as possible. Walking, jogging, running and other physical activities are important in keeping your bones strong and healthy. Riding your bike, basketball, soccer, gymnastics, baseball, dancing, skateboarding and other activities are all good for your bones. Make sure you wear or use the proper equipment like a helmet, kneepads, shin guards, mats, knee pads, etc... to keep those bones safe.
Strengthen your skeleton by drinking milk and eating other dairy products (like low-fat cheese, frozen yogurt, and ice cream). They all contain calcium, which helps bones harden and become strong.

The Muscular System

The human body contains more than 650 individual muscles which are attached to the skeleton, which provides the pulling power for us to move around. The main job of the muscular system is to provide movement for the body. The muscular system consist of three different types of muscle tissues : skeletal, cardiac, smooth. Each of these different tissues has the ability to contract, which then allows body movements and functions. There are two types of muscles in the system and they are the involuntary muscles, and the voluntary muscles. The muscle in which we are allow to control by ourselves are called the voluntary muscles and the ones we can? control are the involuntary muscles. The heart, or the cardiac muscle, is an example of involuntary muscle.
Cardiac Muscle:
The cardiac muscles is the muscle of the brain itself. The cardiac muscle is the tissue that makes up the wall of the heart called the mydocardium. Also like the skeletal muscles, the cardiac muscle is striated and contracts through the sliding filament method. However it is different from other types of muscles because it forms branching fibers. Unlike the skeletal muscles, the cardiac muscle is attached together instead of been attach to a bone.
Skeletal Muscle:
The skeletal muscle makes up about 40 % of an adults body weight. It has stripe-like markings, or striations. The skeletal muscles is composed of long muscle fibers. Each of these muscles fiber is a cell which contains several nuclei. The nervous system controls the contraction of the muscle. Many of the skeletal muscle contractions are automatic. However we still can control the action of the skeletal muscle. And it is because of this reason that the skeletal muscle is also called voluntary muscle.
Smooth Muscle:
Much of our internal organs is made up of smooth muscles. They are found in the urinary bladder, gallbladder, arteries, and veins. Also the digestive tract is made up of smooth muscle as well. The smooth muscles are controlled by the nervous system and hormones. We cannot consciously control the smooth muscle that is why they are often called involuntary muscles.

OTHER SYSTEMS
Digestive:
Major role: To break down and absorb nutrients that are necessary for growth and maintenance.
Major organs: Mouth, esophagus, stomach, small intestine, large intestine,(colon)rectum, and anus.Also two
solid organs: the liver and the pancreas.
Circulatory:
Major role: To transport nutrients, gases (such as oxygen and CO2) hormones and wastes thrpugh the body.
Major organs: Heart, blood vessels
Respiratory:
Major role: To provide gas exchange between the blood and the environment. Oxygen is absorbed from the atmosphere into the body and carbon dioxide is expelled.
Major organs: Larynx, lungs, nose, trachea, masopharinx.
Endocrine:
Major role: To relay chemical messages through the body.In conjunction with the nervous system, these chemical messages help control physiosogical processes such as nutrient absorption, growth, etc.
Major organs: Many glands exist i the body that secrete endocrine hormones. Among these, are the hypothalamus, pituitary, thyriod, pancreas, and adrenal glands.
Nervous:
Major role: To relay electrical signals through the body. It directs behaviour and movement and, alog with the endocrine system, control physiological processes such as digestive, circulation, etc.
Major organs: Brain, spinal cord and peripheral nerves