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# Unit 2 Biology # Unit 2 Biology
- Tissues - Tissues
- Organs, - Organs
- Systems of living things - Systems of living things
## Celular Biology ## Cellular Biology
A person contains roughly 100 tillion cells A person contains roughly 100 trillion cells
- Cells are roughly 20 $`\um`$ (micrometer, $`10^{-6}`$ m), around 250 cells / cm - Cells are roughly 20 `\um` (micrometer, $`10^{-6}`$ m), around 250 cells / cm
## Cell Theory ## Cell Theory
1. All living things are composed of cells 1. All living things are composed of cells
2. Cells are the basic units of living organisms 2. Cells are the basic units of living organisms
3. All cells came from pre-existing cells 3. All cells came from pre-existing cells
## Types Of Cells ## Eukaryotic versus Prokaryotic Cells
`Prokaryotic cell`: Meaning before/lacking nucleus `Prokaryotic cell`: Meaning before/lacking nucleus
`Eukaryotic cell`: Means complete nucleus `Eukaryotic cell`: Means complete nucleus
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|DNA|In nuclear region|Usually in membrane, bound nucleus| |DNA|In nuclear region|Usually in membrane, bound nucleus|
|Size|Usually smaller|Usually larger| |Size|Usually smaller|Usually larger|
|Organelles|Not membrane-bound, smaller|Membrane-bound, more complex| |Organelles|Not membrane-bound, smaller|Membrane-bound, more complex|
|Organization|Usually single-celled|Often multicelled| |Organization|Usually singlecelled|Often multicelled|
|Metabolism|May not need oxygen|Usually needs oxygen to exist| |Metabolism|May not need oxygen|Usually needs oxygen to exist|
## Cellular Organelles
### Cell Membrane
- Controls what substances enter/leave the cell selectively
- Allows nutrients to enter
- Allows waste products to leave
- Surrounds and holds other organelles in cell
### Nucleus
- Holds deoxyribonucleic acid (DNA) in form of chromatin
- DNA is a double helix that make genes
- Genes are a complete set of instructions to make a complete product (typically proteins)
- Chromatin is DNA wrapped tightly in protein
- Chromosomes are even more tightly wrapped chromatin used in cell division only
- Surrounded by a double membrane
- Substances enter and exit the nucleus via nuclear pores
- Messenger RNA (mRNA) is encoded from DNA and sent to ribosomes to produce proteins
### Nucleolus
- Dense region of DNA located in the nucleus
- This area of DNA is specially for ribosomal DNA (rDNA)
- Produce "large" and "small" units of complete ribosomes, which either remain free or mix with endoplasmic reticulum, forming rough endoplasmic reticulum (RER)
- Is *not* surrounded by a membrane, literally is just same as rest of nucleus but denser