chapter 8. the boundary between the cell and its environment controls what enters and exits the...

Cell Transport and the Cell Cycle

Chapter 8

Plasma Membrane

The boundary between the cell and its environment

Controls what enters and exits the cell (selective permeability)

- nutrients, wastes, water

Maintain homeostasis

Plasma Membrane

Diffusion

Movement of particles from high low concentration

Happens because of the random movement of particles

Three things affect the rate of diffusion:- concentration (how much),

temperature, and pressure

Diffusion

Diffusion results in an evenly distributed solution

- when this happens its called dynamic

equilibrium

OsmosisOsmosis is the diffusion of water.

From high low concentration

In a cell, water always tries to reach an equal concentration on both sides of the membrane.

Important in maintaining homeostasis

How Osmosis Affects Cells

Hypotonic Solution:- more water outside the cell

than inside- water moves into the cell- cell swells

Hypertonic Solution:- more water inside the cell than

outside- water moves out of the cell- cell shrinks

How Osmosis Affects Cells

Isotonic Solution:- amount of water is the same

outside and inside the cell- cell stays the same

Passive Transport (Diffusion, Osmosis, Facilitated Diffusion)

Movement of particles across membranes by diffusion

High low concentration

Requires no energy

Passive transport with the help of transport proteins is called facilitated diffusion

Active Transport

Movement of materials through a membrane against a concentration gradient.

Low high concentration

Energy required

Uses carrier proteins

Active Transport

Transport of large particles:endocytosis – cell surrounds and

takes in material from its

environmentexocytosis – expulsion or

excretion of materials from a cell

(wastes, indigestible

particles)

What Limits Cell Size?

Diffusion limits cell size!!- short distances = fast and efficient diffusion- long distances = slow and inefficient

diffusion

DNA limits cell size

Surface area-to-volume ratio- as a cell size increases, its volume

increases faster than its surface area - what does this mean for the cell?

Cell Growth and Reproduction

Chapter 8.2

Cell Reproduction

Remember the cell theory states that all cells come from preexisting cells.

Cell division is the process by which new cells are produced from one cell.

We lose cells constantly throughout the day and they are constantly being replaced.

What are Chromosomes?

Carriers of the genetic material (DNA) that is copied and passed from generation to generation.

Located in the nucleus

Exist as chromatin (uncoiled) for most of its life.

Before cell division, the chromatin (DNA) coils up tightly and is called chromosomes

Chromosome Structure

1. Chromatid2. Centromere3. Short arm4. Long arm

The Cell Cycle

The sequence of growth and division of a cell.

Cells go through two general periods:- growth period (interphase)- division period (mitosis)

Interphase (Growth)

The majority of a cells life is spent here

G1 phase – cell growth S phase – DNA is copied G2 phase – growth and getting ready for

cell division

Mitosis (Division)

Starts with one cell and results in two identical cells (daughter cells)

Four phases of mitosis:1. Prophase (longest phase)

- chromosomes coil up and double- nuclear envelope and nucleolus break down and disappear- spindle fibers form- centrioles migrate to opposite

poles

Mitosis (Division)

2. Metaphase:- chromosomes line-up in

middle- spindle fibers attach to

centromeres of chromosomes

3. Anaphase:- chromosomes separate

and move to opposite poles

Mitosis (Division)

4. Telophase:- chromosomes uncoil (back

into chromatin)- spindle fibers breakdown- nucleolus and nuclear

envelope reappear

Cytokinesis

Division of the cytoplasm

In animal cells, plasma membrane pinches in and forms a cleavage furrow.

In plant cells, a rigid cell plate is formed across the equator of the cell.

Cellular Organization

Cell tissue organs organ system organism

Cancer

Enzymes control the cell cycle

If the cell cycle gets out of control, then cells divide without stopping.

Cancerous cells form masses called tumors