highschool/Grade 10/Science/SNC2DZ/Unit 2: Biology.md

Unit 2 Biology

• Tissues
• Organs
• Systems of living things

Cellular Biology

A person contains roughly 100 trillion cells - Cells are roughly 20 μm (micrometer, \(`10^{-6}`\) m), around 250 cells / cm

Cell Theory

1. All living things are composed of cells
2. Cells are the basic units of living organisms
3. All cells came from pre-existing cells

Eukaryotic versus Prokaryotic Cells

Prokaryotic cell: Meaning before/lacking nucleus

Eukaryotic cell: Means complete nucleus

Part Of Cell	Prokaryotic	Eukaryotic
DNA	In nuclear region	Usually in membrane, bound nucleus
Size	Usually smaller	Usually larger
Organelles	Not membrane-bound, smaller	Membrane-bound, more complex
Organization	Usually singlecelled	Often multicelled
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