Fundamental Concepts in Biology: Cell Organelles and Science Principles

Nature of Science

Science attempts to study and gain information about nature. Science poses hypotheses (usually based on observations) and attempts to explain these hypotheses by observations, inferences, and experimentation.

Hypothesis vs. Theory

A theory is the basis of facts and how they work together. A hypothesis is a question or an educated guess.

Properties of Water

Water is polar. Water is most dense at 4 degrees Celsius.

Cell Organelles and Their Functions

Chromosomes

• Usually in the form of chromatin
• Contains genetic information
• Composed of DNA
• Thicken for cellular division
• Set number per species (e.g., 23 pairs for humans)

Nuclear Membrane

• Surrounds nucleus
• Composed of two layers
• Numerous openings for nuclear traffic

Nucleolus

• Spherical shape
• Visible when cell is not dividing
• Contains RNA for protein manufacture

Centrioles

• Paired cylindrical organelles near nucleus
• Composed of nine tubes, each with three tubules
• Involved in cellular division
• Lie at right angles to each other

Chloroplasts

• A plastid usually found in plant cells
• Contain green chlorophyll where photosynthesis takes place

Cytoskeleton

• Composed of microtubules
• Supports cell and provides shape
• Aids movement of materials in and out of cells

Endoplasmic Reticulum

• Tubular network fused to nuclear membrane
• Goes through cytoplasm onto cell membrane
• Stores, separates, and serves as cell's transport system
• Smooth type: lacks ribosomes
• Rough type (pictured): ribosomes embedded in surface

Golgi Apparatus

• Protein 'packaging plant'
• A membrane structure found near nucleus
• Composed of numerous layers forming a sac

Lysosome

• Digestive 'plant' for proteins, lipids, and carbohydrates
• Transports undigested material to cell membrane for removal
• Vary in shape depending on process being carried out
• Cell breaks down if lysosome explodes

Mitochondria

• Second largest organelle with unique genetic structure
• Double-layered outer membrane with inner folds called cristae
• Energy-producing chemical reactions take place on cristae
• Controls level of water and other materials in cell
• Recycles and decomposes proteins, fats, and carbohydrates, and forms urea

Ribosomes

• Each cell contains thousands
• Miniature 'protein factories'
• Composes 25% of cell's mass
• Stationary type: embedded in rough endoplasmic reticulum
• Mobile type: injects proteins directly into cytoplasm

Vacuoles

• Membrane-bound sacs for storage, digestion, and waste removal
• Contains water solution
• Contractile vacuoles for water removal (in unicellular organisms)