1. Cellular Transport & the Cell Cycle
Chapter 8
Cellular Transport & the Cell Cycle

2. 8.1 Cellular Transport-Osmosis
Diffusion- the movement of particles from an area of higher concentration to an area of lower concentration (review)
Osmosis-the diffusion of water across a selectively permeable membrane
The water will move from the area of higher water concentration to an area of lower water concentration
The difference in concentrations across the semi-permeable membrane is called a concentration gradient

3. 8.1 Osmosis & Solution Types
Isotonic Solution- a solution in which the concentration of dissolved substances outside the cell is the same as the concentration of the dissolved substances in the cell
Hypotonic solution- a solution in which the concentration of dissolved substances outside the cell is lower than the concentration of the dissolved substances in the cell
Hypertonic Solution- a solution in which the concentration of dissolved substances outside the cell is higher than the concentration of the dissolved substances in the cell

4. 8.1 Cell Response
The cell will respond differently depending on the type of solution it is in:
In an isotonic solution, there will be no visible changes because water is moving in both directions across the membrane at the same rate
In a hypotonic solution, the water will move into the cell, causing the cell to increase in size
In a hypertonic solution, the water will move out of the cell, causing the cell to decrease in size

5. 8.1 Passive Transport
Passive transport is the movement of substances across the cell membrane without the use of energy
Water moving across the plasma membrane is considered to be simple diffusion and is classified as passive transport
In facilitated diffusion, carrier or channel proteins move substances across the membrane with the concentration gradient and is also considered passive transport

6. 8.1 Active Transport
Active transport is the movement of materials across a membrane that requires energy
Carrier proteins that move substances across a membrane against the concentration gradient are exhibiting active transport
In this process, carrier proteins bind to the substance, then change shape in order to release the substance on the other side, before returning to their original shape.

7. 8.1 Transport of Large Particles
Cells can also absorb or release substances without using the plasma membrane to do so:
Both are considered to be active transport, as they require energy
Endocytosis: a process by which a cell surrounds and takes in a material from its environment
Exocytosis: a process by which materials are expelled or secreted from a cell

8. 8.2 Cell Growth & Reproduction
Most cells are between 2 and 200 micrometers (1 micrometer = 1 millionth of a meter)
Cell efficiency is related to cell size
Larger cells are less efficient
This is because they have a smaller surface area to volume ratio
Smaller cells are more efficient
This is because they have a larger surface area to volume ratio

9. 8.2 Cell Size The amount of DNA can limit the size of a cell
If there is not enough DNA to support the needs of the cell, the cell does not grow
As a cell gets bigger, the plasma membrane has to move exponentially increasing amounts of substances into and out of the cell
Eventually, the plasma membrane won’t be able to keep up

10. 8.2 Cell Division
Cells will divide before they get too big in order to prevent the problems associated with being too big
Cell division is the process by which new cells are produced from one cell
It results in 2 cells that are identical to the first cell
Cell division must take place in order to replace the cells that are dying

11. 8.2 Chromosomes
Chromosomes were first observed as short, stringy structures that appeared suddenly and vanished right after cell division
These structures contain DNA, which is copied and passed from generation to generation
Most of the time, they are chromatin, strands of DNA wrapped around histones, a type of protein
The chromatin must organize before cell division can occur

12. 8.2 The Cell Cycle
The cell cycle is the sequence of growth and division of a cell
There are 2 general phases in the cell cycle
Interphase- when a cell grows and carries on metabolism
Interphase occurs during most of a cell’s lifespan
Mitosis- cell division when 2 daughter cells are formed
The cytoplasm divides after mitosis to separate the 2 new cells

13. 8.2 Interphase Interphase is divided into 3 parts:
The cell grows rapidly and produces lots of protein
The cell copies its chromosomes (DNA synthesis & replication)
The cell manufactures organelles, and Centrioles replicate

14. 8.2 Mitosis When cells reach their maximum size, they undergo mitosis
Mitosis has 4 phases:
Prophase
Metaphase
Anaphase
Telophase

15. 8.2 Prophase Prophase is the 1st phase of mitosis (and the longest)
In prophase:
The chromatin coils into chromosomes, which have 2 halves, called sister chromatids, held together by a centromere
Sister chromatids contain 2 exact copies of the DNA
The nucleus, nucleolus, and nuclear envelope begin to disappear
By the end of prophase, they are gone
In animal cells: centrioles move to opposite ends of the cell and the spindle forms between them
In plant cells: the spindle forms without the presence of centrioles

16. 8.2 Metaphase Metaphase is the 2nd phase of mitosis In metaphase:
The doubled chromosomes attach to the spindle fibers by the centromeres
The chromosomes line up at the middle of the spindle with one sister chromatid pointing to each side of the cell

17. 8.2 Anaphase Anaphase is the 3rd phase of mitosis
Anaphase starts with the separation of the sister chromatids
In anaphase:
The centromeres split apart and the chromatid pairs separate
They are pulled apart due to the shortening of the microtubules in the spindle fibers

18. 8.2 Telophase Telophase is the 4th phase of mitosis In telophase:
It starts when the chromatids reach the opposite sides of the cell
The chromosomes unwind
The spindle disappears
The nucleolus reappears and the nuclear envelope starts forming around each set of chromosomes
A new membrane starts to form between the 2 new nuclei

19. 8.2 Cytokinesis
Following telophase, the cell undergoes cytokinesis, when the cell’s cytoplasm divides
In plants: a cell plate forms in telophase and forms new cell walls
In animals: the plasma membrane folds in to touch in the center

20. 8.2 Results of Mitosis
In unicellular organisms: after mitosis, they remain as single cells
In multi-cellular organisms: after mitosis, cell growth and reproduction results in the specialization of cells to form tissues, which form organs, which work together to form organ systems, which are necessary for multi-cellular organisms

21. 8.3 Regulating the Cell Cycle
The cell cycle is regulated by a combination of enzymes, called cyclins, and proteins that are activated when they attach to the cyclin
The cell cycle can run out of control if the body does not produce the right enzymes, produces too much or too little of a certain enzyme, or produces enzymes at the wrong time

22. 8.3 Cancer Cancer is the result of uncontrolled cell division
Scientists believe that one or more of the genes that produce the enzymes or proteins involved in the cell cycle changes
This uncontrolled cell division usually starves surrounding cells of their nutrients
While scientists can’t pinpoint a cause of cancer, it appears to be a combination of environmental and genetic factors
They do agree, however that a diet low in fats and high in fiber can reduce the risk