1. © Fall 2005, Pflugerville ISD, 7th Grade
7th Grade Science
Life Science: Levels of Organization,
Cells and The Cell Theory
© Fall 2005, Pflugerville ISD, 7th Grade

2. It’s Alive!! Or, Is It?
What Do You Think?
What characteristics do all living things have in common?
Unit 2 : Chapter 7 : Section 1

3. There are Six Characteristics of Living Things.
It’s Alive!! Or, Is It?
There are Six Characteristics of Living Things.
Living things have Cells.
Living things Sense and Respond to Change.
Living things have DNA.
Living things Reproduce.
Living things use Energy.
Living things Grow and Develop.
Unit 2 : Chapter 7 : Section 1

4. It’s Alive!! Or, Is It? Living Things Have Cells
Every living thing is made up of one or more cells.
Cells are the simplest collection of matter which has all the properties of life.
Some cells specialize to do specific jobs.
Examples are nerve cells, muscle cells, etc…
Unit 2 : Chapter 7 : Section 1

5. The 3 Basic Components of the Cell Theory :
1. All organisms are composed of one or more cells. (Schleiden & Schwann)( )
2. The cell is the basic unit of life in all living things. (Schleiden & Schwann)( )
3. All cells are produced by the division of preexisting cells. (Virchow)(1858)

6. Modern Cell Theory
Modern Cell Theory contains 4 statements, in addition to the original Cell Theory:
1. The cell contains hereditary information(DNA) which is passed on from cell to cell during cell division.
2. All cells are basically the same in chemical composition and metabolic activities.
3. All basic chemical & physiological functions are carried out inside the cells.(movement, digestion, etc)
4. Cell activity depends on the activities of sub-cellular structures within the cell(organelles, nucleus, plasma membrane)

7. There are 2 main types of cells.
It’s Alive!! Or, Is It?
There are 2 main types of cells.
1. Prokaryotic Cells
- have no nucleus
- found in the kingdom of Monera
- Examples are bacteria.
Unit 2 : Chapter 7 : Pre-AP

8. There are 2 main types of cells (cont…).
It’s Alive!! Or, Is It?
There are 2 main types of cells (cont…).
2. Eukaryotic cells
- have a true nucleus (that contains DNA)
- found in more complex kingdoms (animal, plant, etc…)
Unit 2 : Chapter 7 : Pre-AP

10. Unit 2 : Chapter 7 : Section 1
It’s Alive!! Or, Is It?
Living Things Sense and Respond to Change.
A stimulus is a change that causes the activity of an organism to change.
A stimulus can be internal (from inside).
Examples are fever or vomiting when sick.
A stimulus can be external (from outside).
Example is squinting when the lights are bright.
Unit 2 : Chapter 7 : Section 1

11. Unit 2 : Chapter 7 : Section 1
It’s Alive!! Or, Is It?
Living Things Sense and Respond to Change (cont…).
Homeostasis is the maintenance of a stable internal environment.
- Our bodies are very good at controlling the chemical reactions that keep us alive. These reactions can only take place when conditions are exactly right.
- Even though our outside conditions may change, homeostasis keeps our internal conditions the same.
- Example is body temperature.
Unit 2 : Chapter 7 : Section 1

12. Unit 2 : Chapter 7 : Section 1
It’s Alive!! Or, Is It?
Living Things Have DNA.
DNA stands for deoxyribose nucleic acid.
DNA is the molecule that controls the functions of a cell.
DNA is passed from parent to offspring.
Unit 2 : Chapter 7 : Section 1

13. Unit 2 : Chapter 7 : Section 1
It’s Alive!! Or, Is It?
Living Things Reproduce.
Most living things reproduce by sexual reproduction.
Sexual reproduction requires two parents that produce offspring that share characteristics of both parents.
Sexual reproduction produces more diverse more diverse offspring.
Animals
Unit 2 : Chapter 7 : Section 1

14. Unit 2 : Chapter 7 : Section 1
It’s Alive!! Or, Is It?
Living Things Reproduce (cont…).
Some things reproduce by asexual reproduction.
Asexual reproduction occurs when a single parent produces offspring that are exactly the same as the parent.
This leads to more uniform offspring.
Hydra
Unit 2 : Chapter 7 : Section 1

15. Unit 2 : Chapter 7 : Section 1
It’s Alive!! Or, Is It?
Living Things Use Energy
Metabolism is the total of all of the chemical activities that the organisms performs.
Metabolism includes:
- Making food.
- Breaking down food.
- Building cells.
- Moving materials in and out of cells.
Unit 2 : Chapter 7 : Section 1

16. Unit 2 : Chapter 7 : Section 1
It’s Alive!! Or, Is It?
Living Things Grow and Develop.
You grow as your body gets bigger.
Developing is the process of changing, maturing, and going through different stages.
Growing and developing depends on the environment and the resources available.
Unit 2 : Chapter 7 : Section 1

17. Levels of Organization
biome
largest
ecosystem
community
population
organism
organ system
organ
tissue
smallest
cell
Made from Atoms and Molecules

18. Hierarchy of Structural Organization
Chemical
Cellular
Tissue
Organ
Organ System
Organism
Note: be able to define each!

19. Essential Concepts: The Hierarchy of Structural Organization
Chemical
Atoms & bonds
Carbon, oxygen, hydrogen, etc.
Molecules
small inorganic
small organic
proteins
carbohydrates
lipids
nucleic acids
Cell Organelles - from various molecules

20. Essential Concepts: The Hierarchy of Structural Organization
Cellular level –
Cells – the basic structural and functional units of the organism
Cells are specialized for particular functions, e.g., muscle cells are specialized for contracting
Tissue level
Groups of different cell types cooperate to perform specific functions
GnRH cells
skeletal muscle tissue

21. Essential Concepts: The Hierarchy of Structural Organization
Organ level - two or more different tissue types organized to perform specific functions
System level - connected organs that cooperate in related function(s)

22. Hierarchy of Structural Organization
Organism level - all of the organ systems working together to maintain life constitute the living organism