1. Cell Processes
Middle School Science

2. Moving materials in cells
Cells need energy 24/7
They cannot make their own, but can change energy from one form to another
Cells obtain energy from their environment and convert it to a usable form
Complex process

3. Moving materials in cells
Metabolism
The sum of all activities within a cell
Cannot just happen
Need raw materials
Need to eliminate waste
All material needs to enter and exit through the cell membrane

4. Moving materials in cells
Materials enter and leave a cell by one of three methods:
Diffusion
Osmosis
Active transport

5. Diffusion
Cell membranes in living things need to allow materials to pass through
Selectively-permeable membrane
Substances pass through the pores
Driving force behind the movement of many substances into or out of the cell is diffusion

6. Diffusion
The process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration of that substance

7. Diffusion What causes diffusion to occur? Mainly small molecules
Driving force behind movement
All molecules are in motion
Solids – molecules move slowly
Liquids – move more quickly
Gases – move quickly
Molecules collide with each other, pushing away from one another

8. Diffusion What causes diffusion to occur?
Driving force behind movement
Collisions will continue as molecules spread out evenly

9. Diffusion
Why don’t the organelles and cytoplasm pass through the cell membrane?
Cell membrane is selectively permeable
Permits only certain substances to diffuse
Oxygen, water, and food molecules are permitted to diffuse into the cell
Carbon dioxide and other waste materials are permitted to diffuse out of the cell

10. Osmosis A special kind of diffusion
The diffusion of water across a selectively permeable membrane = osmosis
Water is the most important substance that passes through a cell membrane
About 80% of the cell is water

11. Diffusion and Osmosis
Diffusion and osmosis are types of passive transport
They do not require energy to be able to happen – they just happen

12. Active Transport
What if the cell needs materials that cannot diffuse through the membrane?
Active transport “carries” the materials into or out of the cell
Cells have several forms of active transport
Transport proteins can “pick up” molecules and carry them into or out of the cell
Requires energy
Ex: calcium, potassium, and sodium

13. Active Transport
What if the cell needs materials that cannot diffuse through the membrane?
Transport by engulfing
Another method of active transport
Cell membrane surrounds, or engulfs, a particle
Once surrounded, the cell membrane wraps around the particle and forms a vacuole within the cell
Requires energy

14. Cell Growth and Division
Limits on Cell Growth
Why don’t cells get bigger and bigger?
Has to do with the transportation of materials into and out of the cell
If a cell were to get too large, its membrane would not be able to handle the flow of materials passing through it
The amount of raw materials needed by a large cell couldn’t enter fast enough
The wastes produced couldn’t leave fast enough

15. Cell Division
In order for an organism to grow, the total number of cells must increase
Cell division
One cell divides into two new daughter cells
Occurs in a series of stages, or phases
The process of cell division = mitosis

16. Mitosis Phase 1: Chromosomes are copied Interphase
Cell is performing life functions, not dividing
Chromosomes appear as threadlike coils called chromatin
In animal cells, the two centrioles can be seen outside the nucleus
Most plant cells do not have centrioles

17. Mitosis Phase 1 Near the end, the process of cell division begins
The chromosomes are duplicated
Doubling the normal chromosome number in the cell
Each chromosome and its sister chromosome (copy) are attached at an area called the centromere
At this time the sister chromosomes are called chromatids

18. Mitosis Phase 2: Mitosis begins Prophase Mitosis begins
Mitosis = the process by which the nucleus of a cell divides into two nuclei and the formation of two new daughter cells begins
Threadlike chromatin shorten and form rodlike chromosomes
Centrioles begin to move to opposite ends of cell
Meshlike spindle develops, forming a bridge between opposite ends of the cell

19. Mitosis Phase 3: Chromosomes attach to the spindle Metaphase
The chromosomes begin to attach to the spindle
Chromosomes are attached to the spindle by the centromere, which still connects each chromatid to its identical sister chromatid

20. Mitosis Phase 4: Chromosomes begin to separate Anaphase
The centromere splits
The sister chromatids separate from each other
Chromatids move to opposite ends of cell along the spindle
The chromatids are again called chromosomes at this point

21. Mitosis Phase 5: Two new nuclei form Telophase
The chromosomes begin to uncoil and lose their rodlike appearance
A nuclear membrane forms around the chromatin at each end of the cell
In each nucleus, a nucleolus reappears
At this point, mitosis is complete but the cell still has one phase to go through

22. Mitosis Phase 6: Two daughter cells form Cytokinesis
Final phase of cell division
Involves the division of the cytoplasm
The membrane surrounding the cell begins to move inward until the cytoplasm is pinched in two
Each part contains a nucleus with identical chromosomes
The cell membrane (or cell wall) complete the division

23. Mitosis

24. Mitosis