Ch. 4 Cell Processes Materials enter and leave the cell by one of three methods. 1. Diffusion – process by which molecules of a substance move from areas of higher concentration to areas of lower concentration The cell membrane is selectively permeable.

This means it permits only certain substances, mainly oxygen, water, and food molecules, to diffuse into the cell. Waste products such as carbon dioxide are allowed to diffuse out.

2. Osmosis – The diffusion of water into or out of the cell. Water molecules move from a place of higher concentration to lower concentration.

Diffusion and osmosis just happen whenever there are unequal concentrations inside and outside the cell. Neither of these processes use up any energy reserves.( No energy required)

3. Active transport – special transport molecules in the cell membrane actually pick up the substance outside the cell and pull it through the cell membrane. Active transport requires the cell to use some of its energy reserves.

2 types of Active Transport Endocytosis – brings something into the cell Exocytosis – releases something from the cell P. 89

The Cell Cycle 1. Interphase – the time when a cell spends most of its time growing and carrying out all of its normal activities.

3 parts to Interphase G = Growth S = Synthesis G 1 – the cell increases in size and organelles S – when chromatin replicate G 2 – the cell gets ready to divide; it is known at this stage as a parent cell

2. Mitosis – It has four phases A. Prophase B. Metaphase C. Anaphase D. Telophase

Prophase Centrioles split and move to opposite ends of the cell called poles Chromosomes appear The nuclear membrane and nucleolus disappear Spindle fibers form between the centrioles

Metaphase Chromosomes attach to the spindle fibers and line up in the middle of the cell

Anaphase The chromosomes separate and the daughter chromosomes start moving toward the poles

Telophase Begins when the chromosomes reach the poles The spindle fibers disappear Two nuclear membranes and nucleoli reform around the groups of chromosomes The chromosomes uncoil to return to chromatin

Cytokinesis The cell divides the cytoplasm to form two new daughter cells Animal Cells – the cytoplasm divides by constricting in the middle until the membrane separates Plant Cells – a cell plate grows in the middle toward the cell wall until division is complete

Key Definitions Parent Cell – the cell before it divides Daughter Cell – reference to the newly created cell Chromatin – thread-like materials that are located in the nucleus during interphase and is composed of DNA and protein Centriole – the cell organelle that controls the movement of chromosomes during mitosis

Synthesis – to create or make Replicate – to make an exact copy Chromosomes – do not appear until mitosis; it is a super coil of DNA and protein; they are located in the nucleus Chromatid – two single chromosomes that are attached at a point called the centromere Centromere – the point of attachment within two chromosomes

Poles – the directed ends of a cell