1. 7th Grade Cells and Heredity (Module A) Unit 1: Cells Lessons 5 & 6
Homeostasis & Cell Processes
Photosynthesis & Cell Respiration

2. Homeostasis
Maintaining a constant internal state (staying in BALANCE) in a changing environment
What makes an environment change?
Cells need to be able to do 4 things
1. obtain and use energy (examples?)
2. make new cells (process?)
3. exchange materials (examples?)
4. eliminate wastes (examples?)

3. 1. Obtain and use energy
Plants, algae and some bacteria use photosynthesis to make their own food
These organisms are called producers because they produce their own food
Happens in the chloroplasts
Capture light energy from the sun and change it to chemical energy in sugars
Use green pigment called chlorophyll
Do pg

4. 1. Obtain and use energy (con’t)
Animals get their energy from consuming other organisms, so we call them consumers
To get this energy out of the organism they consume (eat!) they must break down the sugar stored
This process is called cellular respiration – the process of breaking down food to produce ATP (adenosine triphosphate)

5. More about Cellular Respiration
Both plants and animals do cellular respiration – in mitochondria and cell membrane
Even prokaryotic cells (like bacteria) do it! – in cytoplasm and cell membrane
Read and do pgs

6. Photosynthesis and Cellular Respiration are the reverse process of each other! Read and do pg. 74

7. Q: What are the starting materials of photosynthesis?
A: carbon dioxide and water
Q: What are the products of photosynthesis?
A: Glucose and oxygen
Q: What are the starting materials of cellular respiration?
A: glucose and oxygen
Q: What are the products of cellular respiration?

8. 2. Cells make new cells! All cells grow, divide and die
Some more often than others ex. Skin cells constantly divide, nerve cells can’t divide once they are fully formed
GROWTH occurs when new cells are added
Mitosis (part of the cell cycle)
1. DNA is copied (inside nucleus)
2. DNA organizes into chromosomes
3. chromosomes separate & nucleus splits
(We will study mitosis in more depth later in the year)

9. 3. Cells exchange materials (Like what
3. Cells exchange materials (Like what? Read page 56 1st pgh) cell membranes are semi-permeable – some particles can go in and out
Passive transport – movement across cell membrane without using energy
Diffusion – movement of molecules from high concentration to low concentration
Ex. Tea in tea bag
Osmosis – diffusion of WATER through semi-permeable membrane
If molecule is too large to diffuse, may use protein channels (facilitated diffusion)
Diffusion animation -
Osmosis animation (for advanced classes) -

11. 3. Cells exchange materials (con’t)
Active transport – movement from areas of low concentration to high concentration – REQUIRES ENERGY
Some other examples are endocytosis and exocytosis

12. 3. Cells exchange materials (con’t)
Endocytosis – cell surrounds particle, encloses it, and brings it in to cells
Amoebas use this to eat!
Exocytosis – (reverse of endocytosis) –
particle gets enclosed in a vesicle
Vesicle fuses to cell membrane
Particles released outside of cell

13. SO, how do organisms maintain homeostasis (during temperature changes?
When some organisms (like YOU and ME) get cold ________________
Behavioral adaptations:
Some reptiles ______________________________
Some mammals ____________________________
When it’s cold, some trees _____________________ to reduce the amount of water loss
Some trees also ______________________ because chlorophyll (the green pigment) breaks down