1. Chapter 3
Life Science

2. Organization of Life
A cell is smaller than the period at the end of this sentence, yet a single cell has all the items necessary to carry out life’s activities.
Not all of your cells look or act the same. You have about 200 different kinds of cells, and each type is specialized to do a particular job.
You are made of about 100 trillion cells.

3. Tissues
A tissue is a group of cells that work together to perform a specific job in the body.
Blood, fat, and muscle cells are just a few of the many cells that make tissues in your body.

4. Organs
When two or more tissues work together to perform a specific job, the group of tissues is called an organ.
Some examples of organs are your stomach, intestines, heart, lungs, and skin.
Plants also have different kinds of tissues that work together.
A leaf is a plant organ that contains tissue that traps light energy to make food.
Other examples of plant organs are stems and roots.

5. Organ Systems
Organs work together in groups to perform particular jobs called organ systems.
Your body has several organ systems.
One example is the digestive system.

6. Organisms Anything that can live on its own is called an organism.
If a single cell is living on its own, it is called a unicelluar organism.
You are a multicellular organism. This means that you can exist only as a group of cells and that most of your cells can survive only if they remain a part of your body.

7. Populations Although organisms can live on their own, they rarely do.
A group of organisms that are of the same kind and that live in the same area make up a population.

8. Communities
Two or more different populations living in the same area make up a community.
Your hometown is a community that includes all of the people, dogs, cats, and other organisms living there.

9. Ecosystems
The community and all of the nonliving things that affect it, such as water, soil, rocks, temperature, and light, make up an ecosystem.
Ecosystems on land are called terrestrial ecosystems
Ecosystems in water are called aquatic ecosystems

10. The Cell Theory All organisms are composed of one or more cells.
The cell is the basic unit of life in all living things.
All cells come from existing cells.

11. Cells All cells are surrounded by a cell membrane.
When new cells are made, they receive a copy of the hereditary material of the original cells. This material is DNA.
All cells have chemicals and structures that enable the cell to live, grow, and reproduce. The structures are called organelles.
The chemicals and structures of a cell are surrounded by a fluid called cytoplasm.

12. Cells
You are made up of 100 trillion cells, and it would take 50 of these cells just to cover up the dot on the letter i.
As the cell’s volume increases, its outer surface grows too. But the volume of a cell increases at a faster rate than the area of its outer surface.
Multicellular organisms grow by producing more small cells, not larger cells.

13. Cells
A single cell cannot do all the things that many different cells can do.
Having many different cells that are specialized for specific jobs allows multicellular organisms to perform more functions than unicellular organisms.

14. Cells Cells can be divided into two groups:
Prokaryotic – Cells that do not have a nucleus
Eukaryotic – Cells that do have a nucleus
Prokaryotic cells are also called bacteria.
They are the world’s smallest cells, and they do not have a nucleus.
Bacteria do not have any membrane-covered organelles but they do have tiny, round organelles called ribosomes.
These organelles work like little factories to make proteins.

15. Cells Eukaryotic cells are more complex than prokaryotic cells.
All living things that are not bacteria are made of one or more eukaryotic cells.
This includes plants, animals, fungi, and protists.
An advantage of having the cell divided into compartments is that it allows many different chemical processes to occur at the same time.

16. Cells
Instead of being circular, the DNA molecules in eukaryotic cells are linear.
All eukaryotic cells have a cell membrane, and some of them have a cell wall.
Those that have cell walls are found in plants, fungi, and some unicellular organisms.

17. Difference Between Cells
Prokaryotic Cells
No nucleus
No membrane-covered organelles
Circular DNA
Bacteria
Eukaryotic Cells
Nucleus
Membrane-covered organelles
Linear DNA
All other cells

18. Cells
Cells are so small that the details of their structure could not be seen until better methods of magnifying and staining were developed.
We know that cells are very complex, especially eukaryotic cells.

19. Cell Membrane All cells are covered by a cell membrane.
The job of the cell membrane is to keep the cytoplasm inside to allow nutrients in and waste products out, and to interact with things outside the cell.

20. Cell Wall
The cells of plants and algae have a hard cell wall made of cellulose.
The cell wall provides strength and support to the cell membrane.
When too much water enters or leaves a plant cell, the cell wall can prevent the membrane from tearing.

21. Nucleus
The largest and most visible organelle in a eukaryotic cell is the nucleus.
The nucleus has often been called the control center of the cell.
The nucleus stores the DNA.
The dark spot inside the nucleus is called the nucleolus.

22. Ribosomes
Proteins, the building blocks of all cells, are made up of chemicals known as amino acids.
These amino acids are hooked together to make proteins at very small organelles called ribosomes.
Ribosomes are the smallest but most abundant organells.
Ribosomes are not covered with a membrane.

23. Endoplasmic Reticulum
Eukaryotic cells have an organelle called the endoplasmic reticulum.
The ER is a membrane-covered compartment that makes lipids and other materials for use inside and outside the cell.
It is also the organelle that breaks down drugs and other chemicals that could damage the cell.

24. Mitochondria
ATP can be made at several locations in eukaryotic cells, but most of it is produced at bean-shaped organelles called mitochondria.
The reason you breathe air is to make sure your mitochondria have the oxygen they need to make ATP.
Highly active cells, such as those in the heart and liver, may have thousands of mitochondria, while other cells may have only a few.

25. Chloroplasts
Plants and algae have an additional kind of energy-converting organelle, called chloroplast.
These are flattened, membrane-covered sacs that contain an important chemical called chlorophyll.
Chlorophyll is what makes chloroplasts green.
The energy of sunlight is trapped by chlorophyll and used to make sugar.
This process is called photosynthesis.

26. Golgi Complex
When proteins and other materials need to be processed and shipped out of a eukaryotic cell, the job goes to an organelle called the golgi complex.
The golgi complex looks like the ER, but it is located closer to the cell membrane.

27. Vesicles
All eukaryotic cells have membrane-covered compartments called vesicles.

28. Vacuoles
Most plant cells have a very large membrane-covered chamber called a vacuole.
In plants, large central vacuoles store water and other liquids.

29. Lysosomes Lysosomes are specials vesicles in animal contains enzymes.
Lysosomes destroy warn-out or damaged organs.
They get rid of waste materials and protect the cell from foreign invaders.
Sometimes lysosome membranes break, and enzymes spill into the cytoplasm, killing the cell.
This is what happened to you when you were born. Lysosomes caused the destruction of cells formed the webbing between your fingers.

30. Plant or Animal?
How can you tell the difference between a plant cell and an animal cell?
They both have a cell membrane, and they both have nuclei, ribosomes, mitochondria, endoplasmic reticula, golgi complexes, and lysosomes.
Plan cells have cell wall, chloroplast, and a large vacuole. Animal cells do not have these.