The Big Discussion on Cells

Living Things All living things – “organisms” have a cellular organization, contain similar chemicals, use energy, grow and develop, respond to their surroundings, and reproduce. These are the 7 major characteristics of life!

What is a Cell? All organisms are made of small building blocks called cells. A cell is the basic unit of structure and function in an organism.

Cell Sizes can vary Most cells are small, about 40 human cells would fit on the dot of this letter i. Some cells are big, the yolk of a chicken egg is a single cell. The smallest cells are so tiny that you could fit over a million of them on the period at the end of this sentence.

Cell Size Cells are made of molecules Molecules are tiny particles of matter. Molecules are made up of atoms. The atom is the basic fundamental unit of matter. Atoms are made up of protons, neutrons and electrons.

How Many Cells Make Up Organisms? Organisms can be composed of only one cell or many cells. Unicellular or single celled organisms include bacteria the most numerous organisms on Earth. Multi-cellular organisms are composed of many cells. You are made up of trillions of cells. You have specialized cells in your body that perform specific functions.

Chemicals of Life The most abundant chemical in cells is water. Water can dissolve more chemicals than any other substance on Earth. Other chemicals are called carbohydrates and these are the energy source for the cell. Two other chemicals are proteins and lipids which are the building materials for cells, much like wood and bricks are the building materials of houses. Finally nucleic acids are the genetic material.

Cells use Energy The cells of organisms use energy to do what living things must do, such as grow and repair injured parts. Cells are always hard at work. Right now your cells are busy not only with your eyes and brain but your blood cells are moving chemicals around your body. White Blood Cells are pictured to the right!

How do we look at Cells? The invention of the microscope made it possible for people to discover and learn about cells. A microscope is an instrument that makes small objects look larger. A light microscope that has more than one lens is called a compound microscope. The Top 10 Microscope IMAGES!!! Cool Microscopic Images

Who discovered that we have Cells? One of the first people to observe cells was the English scientist Robert Hooke. In 1663, Hooke observed the structure of a thin slice of cork using a compound microscope. To Hooke the cork looked like rectangular rooms, which he called cells.

Who discovered that we have cells? At about the same time that Robert Hooke made his discovery, Anton van Leeuwenhoek also began to observe tiny objects with his microscope. Leeuwenhoek was a Dutch scientists and when he looked at water from a pond he saw tiny single celled organisms.

The Cell Theory Observations from Hooke and Leeuwenhoek led to the development of the cell theory. The cell theory states: All living things are composed of cells. Cells are the basic unit of structure and function in living things. All cells are produced from other cells.

Looking Inside Cells Cells contain even smaller structures inside of the cell called organelles. Organelles were called organelles because early scientists thought they looked like “inner organs” kind of like our heart, kidneys, or brain.

The Importance of Cells Think about every time you need energy to move your cells have to actively be working so that you can move. Think about every time you breathe in your individual cells have to take in oxygen and use it to make energy. All of our energy needs are met by small tiny parts of our body that we barely even think of.

Cells &Tissue A group of similar cells that perform the same function is a tissue. There are four basic types of tissue: muscle, nervous, connective, and epithelial. Muscle tissue can contract, or shorten - this helps you move! Connective tissue provides support and connects the parts of your body (ex: bone, fat, and blood) Nervous tissue carries messages back and forth between your brain and other parts of your body – it directs and controls the body. Epithelial tissue covers the surfaces of your body ( ex: skin and the lining of the digestive system)

Organs & Organ Systems An organ system is a group of organs that work together to perform a major function. Your heart and the blood vessels are parts of the circulatory system. All organ systems work together and depend on each other. An organ is a structure that is composed of different kinds of tissue. An organ’s job is usually more complex than that of a tissue. For example, the heart is an organ that pumps blood throughout the body.

Respond to their Surroundings A change in an organism’s surroundings that causes the organism to react is called a stimulus. An organism reacts to a stimulus with a response – an action or change in behavior. Ex: change in temperature, light, moisture, etc… What are some ways that you respond to a stimulus?

Development and Reproduction All living things need four things to stay alive: food, water, living space, and stable internal conditions. Living things grow and develop. Growth is the process of becoming larger. Development is the process of change that occurs during an organism’s life to produce a more complex organism. Another characteristic of organisms is the ability to reproduce, or produce offspring that are similar to the parents. Living things arise from living things through reproduction.

Homeostasis Because conditions in their surroundings can change, organisms must be able to keep the conditions inside their bodies constant. The maintenance of stable internal conditions despite changes in surroundings is called homeostasis.

Homeostasis All systems of the body work together to maintain homeostasis, the body’s tendency to keep an internal balance. Sometimes, things can happen to throw off homeostasis. As a result, your heart may beat rapidly or your breathing may quicken. These are signs of stress, the reaction of your body to potentially threatening, challenging, or disturbing events. When stress is over, homeostasis is restored, and the body returns to its normal state.