Biology & Biomedical Issues

Theory

A personal hunch, casual guess, or suspicion about how or why something happens

Hypothesis

A specific, testable prediction or tentative explanation for a small set of observations

Scientific Theory

A comprehensive framework that explains a wide range of natural phenomena and unifies many facts and tested hypotheses

Homeostasis

Process of maintaining a stable internal environment in a cell or an entire organism

• If you go outside when the air temperature is below freezing, your body doesn't freeze

  • by shivering and other means, it maintains a stable internal temperature.

Organization

Living things have multiple levels of organization

• Their molecules are organized into one or more cells

Cell

Basic unit of structure and function of living things

• Seen as the “building blocks” of living organisms

Metabolism

The total sum of all chemical reactions in the body that convert food and drink into energy and building blocks to keep you alive and functioning

• Divided into two main processes → anabolism & catabolism

Anabolism

The building up of smaller molecules into larger structures needed for growth, repair, and maintenance

Catabolism

The breakdown of complex substances (like food or stored fat) into simpler components to release energy.

Protein

Large, complex molecules made of many small amino acid chains that perform vital work in every cell of the body

Amino acid

Monomer of protein → molecule that bonds with similar/identical molecules to form the larger structure (polymer) which is protein in this example

Adaptation

A characteristic that helps living things survive and reproduce in a given environment

Evolution

A change in the characteristics of living things over time

Gene theory

Theory that the characteristics of living things are controlled by genes that are passed from parents to offspring.

Control group

Assigned to the placebo

Experimental group

Receives the actual treatment

Cell theory

Theory that states:

• all living things are made up of cells

• all life functions occur within cells

• all cells come from pre-existing cells

Unicellular organisms

Living things made up of only one cell that does all the work to stay alive

• Asexual reproduction (split into 2 identical cells)

• Can be prokaryotic (no nucleus) or eukaryotic (with a nucleus)

  • Ex: Amoeba, bacteria, yeast

Multicellular organisms

Living thing composed of more than one cell with specialized functions

• Made of millions to trillions of cells

• Cells contain a membrane-bound nucleus and organelles

• Cells divide and perform specific tasks

  • Ex: Humans, dogs, birds

Is a virus alive based on cell theory?

No

• Viruses are not made of cells

• Cannot reproduce or carry out metabolism

  • Must infect a living cell and use the cells machinery to make more virusses

What is the study of biology?

The scientific study of life and living organisms

What is the scientific method?

A step-by-step process that scientists use to explore ideas, test predictions, and answer questions about the natural world

• Make an observation

• Conduct background research

• Form a hypothesis

• Conduct an experiment

• Analyze the data

• Draw a conclusion

• Share results

Independent variable

The cause or predictor

• Ex: The number of hours you spend studying

Dependent variable

The effect or outcome

• The final test score

Blind experiment

The participants do not know whether they received the placebo or the actual treatment but the researchers know

Double blind experiment

Researchers and participants do not know who received the placebo or treatment

Why is sample size important?

If researchers test a new medication on only 10 people, the results might not accurately represent how it works for thousands of people. Testing it on a larger, appropriately selected group can provide stronger evidence.

Does sample size change at different stages of clinical trials?

Clinical trials generally involve more participants in later phases so researchers can gather stronger evidence about a treatment's effectiveness and safety.

What is an element?

A pure substance made of only one type of atom

• Ex: Gold only made of gold atoms, oxygen only made of oxygen atoms

What is an atom?

The basic building block of all matter in the universe

• smallest unit of an element

• contains protons, neutrons, electrons

  • The number of protons determines which element an atom is, such as every carbon atom has 6 protons.

Neutral atom

No overall charge

• Number of protons = number of electrons

  • Carbon has 6 protons (+) , 6 electrons (-), overall charge is 0

Ion

An atom that has gained or lost electrons

• Loses electrons → positive ion (cation)

• Gains electrons → negative ion (anion)

  • If a sodium atom has 11 protons and 11 electrons → neutral

  • If sodium loses one electron, it becomes a cation (+11 & -11 = +1)

Isotope

Atoms of the same element that have different numbers of neutrons

*The number of protons stays the same because that determines the element

• If one carbon has 6 protons and 6 neutrons and another carbon has 6 protons but 7 neutrons, they are both carbon because they both have 6 protons but are different isotopes since they have different masses

Molecule

Two or more atoms chemically bonded together.

• Can contain atoms of the same element or different elements.

  • O₂ (oxygen gas): 2 oxygen atoms bonded together.

  • H₂O (water): 2 hydrogen atoms and 1 oxygen atom bonded together.

  • CO₂ (carbon dioxide): 1 carbon atom and 2 oxygen atoms bonded together.

Compound

A substance made of two or more different elements chemically combined

• Must contain at least two different elements

  • H₂O (water): hydrogen + oxygen.

  • NaCl (sodium chloride): sodium + chlorine.

  • CO₂ (carbon dioxide): carbon + oxygen.

Molecules vs Compounds

• Molecules: 2 or more ATOMS bonded

• Compound: 2 or more DIFFERENT ELEMENTS

  • O₂ is a molecule but not a compound because it contains only oxygen atoms.

  • H₂O is both a molecule and a compound because its atoms are bonded together and it contains two different elements.

  • NaCl is a compound since it has one sodium bonded to one chlorine

What are the 3 types of chemical bonds?

Covalent, Ionic, Hydrogen

Covalent bonds

Atoms share electrons

• The strongest bonds

Ionic bonds

Atoms transfer electrons, creating charged ions that attract each other

• “Weaker” than covalent bonds

• Result from the attraction of oppositely charged ions, rather

than shared electrons

Hydrogen bonds

The attraction formed between a slightly positively charged hydrogen atom and another slightly negatively charged atom

How many types of chemical bonds exist in water?

1. Covalent bonds within each water molecule

• O and H share electrons.

2. Hydrogen bonds between water molecules

• The slightly positive H of one water molecule is attracted to the slightly negative O of another.

What happens when you add sodium chloride (NaCl) to water?

NaCl dissolves and separates into ions: NaCl → Na⁺ + Cl⁻

• The oxygen end of water is slightly negative, so it attracts Na⁺.

• The hydrogen ends of water are slightly positive, so they attract Cl⁻.

So after adding NaCl, you have three important types of interactions:

1. Covalent bonds → within H₂O

2. Hydrogen bonds → between H₂O molecules

3. Ionic attractions → between Na⁺/Cl⁻ and the charged ends of water

What does it mean that water is polar?

A polar molecule has a positive charge on one side and a negative charge on the other

• A water molecule (H₂O) has an uneven distribution of electrical charge.

  • Oxygen (O) has a slightly negative charge

  • Hydrogen (H) atoms have slightly positive charges

  
  

Why is water's polarity important?

• Water can dissolve many ionic and polar substances, allowing them to mix and move around

• Many chemical reactions in living cells occur in water because substances can dissolve and interact

• Transports nutrients and waste

• Helps regulate temperature

Solute

The substance that gets dissolved, usually present in a smaller amount

• Ex: salt

Solvent

The substance that does the dissolving, usually present in a larger amount

• Ex: water

Solution

The final mixed combination that looks the same throughout, formed by adding a solute to a solvent

• Ex: saltwater

Why does water act as a good solvent?

Its positive and negative ends attract charged particles and other polar molecules.

Saltwater example:

• Salt separates into sodium ions (Na+) and chloride ions (Cl−).

• The slightly negative oxygen ends of water molecules attract the positive sodium ions.

• The slightly positive hydrogen ends attract the negative chloride ions.

• Water molecules surround the ions and help keep them dispersed in the solution.

When writing out chemical equations, does the arrow point towards the reactants or the products?

The arrow in a chemical equation points toward the products

• Reactants → Products

• 2H2​+O2​→2H2​O

What does the pH scale measure?

How acidic or basic a solution is

• 0-6: Acidic (lower pH)

• 7: Neutral (neither acidic or basic, like water)

• 8-14: Basic/Alkaline (higher pH)

What does it mean for something to be acidic?

It has a high concentration of hydrogen ions, commonly represented as hydronium ions (H3​O+) in water.

• a pH value below 7

  • lemon juice

  • vinegar

  • stomach acid

What does it mean for something to be basic?

Has a lower concentration of hydronium ions relative to hydroxide ions (OH−).

• pH above 7

  • Baking soda disolved in water

  • Soap solution

  • Bleach

What is a buffer?

A substance that helps prevent sudden changes in pH when small amounts of an acid or a base are added

• Acids increase the concentration of hydrogen ions.

• Bases reduce the concentration of hydrogen ions or increase hydroxide ions.

• Buffers help resist these changes in pH

How are buffers important for homeostasis?

They help maintain homeostasis by keeping the pH of body fluids relatively stable

• can take up excess H+ and OH – ions

What type of chemistry is “organic” chemistry?

“Organic” refers to life.

• Organic chemistry deals with carbon-containing chemicals.

• Carbon can form covalent bonds with up to four elements.

What is a macromolecule?

A large molecule that is important for the structure and function of living organisms

Four major types:

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Carbohydrates

Organic molecules that provide energy and can also help with energy storage and structural support

• They are made of carbon, hydrogen, and oxygen.

• Ex: starch, bread, rice, pasta, fruit, and potatoes.

Monosaccharide

One sugar molecule. It is the simplest type of carbohydrate.

• Ex: glucose, a sugar that cells use for energy.

Disaccharide

Made when two monosaccharides join together

• Ex: Sucrose (table sugar) = glucose + fructose

Polysaccharide

A large carbohydrate made of many monosaccharides linked together

• Ex: starch, glycogen, cellulose

Proteins

An essential macronutrient and a large, complex molecule made of smaller building blocks called amino acids

• Ex: enzymes, meat

What are examples of different functions of proteins?

• Enzymes: Speed up chemical reactions in the body, such as breaking down food or building molecules

  • Amylase breaks down starch

• Structural support: Provide shape, rigidity, and mechanical support to cells, tissues, organs, hair, and nails

  • Keratin helps form hair and nails

• Regulates gene expression

• Transport/storage: Carry essential molecules and gases through the bloodstream or across cell membranes, or store nutrients

  • Hemoglobin carries oxygen in the blood

What are the different structural levels of a protein?

• Primary: The specific order of amino acids in a chain.

• Secondary: Parts of the chain form shapes such as an alpha helix (coil) or beta-pleated sheet (folded sheet).

• Tertiary: One polypeptide chain folds into its overall three-dimensional shape

• Quaternary: Two or more polypeptide chains come together to form one functional protein

How does the difference in protein side chains change the functionality of the protein or its interaction with water?

Dictates whether a protein loves or fears water, driving how the protein folds into its unique 3D shape and performs its specific function

• Hydrophilic (Water-Loving) Side Chains: These polar or charged side chains contain oxygen, nitrogen, or full electrical charges. They form hydrogen bonds or ionic interactions with surrounding water molecules

• Hydrophobic (Water-Fearing) Side Chains: These nonpolar side chains consist mostly of carbon and hydrogen. They cannot form hydrogen bonds with water. Instead, they disrupt water structure, forcing water molecules to form an ordered "cage" around them.

Lipids

A group of mostly nonpolar, water-insoluble biological molecules that include fats, oils, phospholipids, and steroids

• Store energy and make up cell membranes

What are the types of lipids, and where are they found in the body?

• Triglycerides → Fat cells (adipose tissue) under the skin and around organs.

• Phospholipids → The membranes surrounding virtually all your body's cells and their organelles.

• Steroids → Steroid hormones are produced in organs such as the adrenal glands

Nucleic acids

Store genetic information

• Ex: DNA

Monomer

A small molecular building block that can bond with other molecules to form a larger molecule

• Think of a monomer as one individual LEGO brick.

• Nucleotides are building blocks/monomers used to make DNA.

  
  

Polymer

A large molecule made of many repeating or linked smaller building blocks called monomers

• Think of a polymer as a long LEGO structure made by connecting many individual bricks

• A polymer is a type of macromolecule.

• However, not every macromolecule is a polymer; lipids, for example, are generally not considered true polymers since they are not made up of the same repeating monomer

How does a macromolecule relate to a polymer or monomer?

A polymer is a type of macromolecule and polymers are made up of monomers

Dehydration synthesis

A chemical reaction that joins monomers together to form a larger molecule (polymer) by releasing a water molecule as a byproduct

• A hydrogen atom (H) is removed from one monomer, and a hydroxyl group (OH) is removed from the other monomer.

• The H and OH combine to form a molecule of water (H₂O).

• The remaining parts of the monomers share electrons to form a strong covalent bond

  • Monomer + Monomer→Larger molecule + Water (leftover)

    
    

Hydrolysis

A chemical reaction where water breaks one or more chemical bonds in a compound, splitting it into smaller fragments

• Larger molecule + Water → Smaller molecules

What are the requirements of being a cell?

• Enclosed in a membrane—homeostasis

• Transportation—regulated

• Ability to carry out energy transformations—metabolism

• Information storage and retrieval system—nucleic acids/DNA

• Reproduction—make copies

Organelle

A specialized tiny structure inside a cell that performs a specific job, much like an organ does in the whole body

• The word means "little organ". Organelles keep the cell alive, healthy, and organized

Nucleus

The control center. It stores the cell's genetic information (DNA).

Endoplasmic reticulum (ER)

A network that helps make and transport proteins and lipids (fats).

• Smooth ER

• Rough ER

Smooth ER

Makes lipids, helps detoxify certain chemicals, and stores calcium in some cells.

Rough ER

Has ribosomes; helps make and process proteins destined for secretion, membranes, or certain organelles.

Golgi Apparatus

Modifies, sorts, and packages proteins and lipids for delivery to other parts of the cell or for export outside the cell

Lysosomes

Act as the cell's recycling center and digestive system, breaking down waste, old cell parts, and foreign invaders

Mitochondria

Convert food nutrients (carbohydrates, fats, and proteins) into ATP (adenosine triphosphate), the cell's main energy currency

• “Powerhouse of the cell”

Cytoskeleton

Maintain cell shape, provide mechanical support, and organize the internal contents of eukaryotic cells.

Label parts of the eukaryotic cell

What factors limit cell size?

Surface area-to-volume ratio

• Restricts how efficiently it can exchange nutrients and waste with its environment

• Want large SA:V ratio so nutrients can enter and waste can leave efficiently (small cell)

• Transportation limits size → As a cell gets larger, substances may need to travel farther inside it, making the process slower and longer

Passive transport

Does not require the cell to use energy (ATP). Substances move down their concentration gradient, from higher concentration to lower concentration

• Diffusion

• Facilitated diffusion

• Osmosis

Active transport

Membrane proteins use energy to move substances against their concentration gradients

• Protein pumps

• Endocytosis

• Exocytosis

Diffusion

• Does not use energy

• O2 and CO2 moves

• High to low concentration

Facilitated diffusion

• Does not use energy

• Moves glucose, ions

• High to low concentration

Osmosis

• Does not use energy

• Moves water

• High to low concentration

• Direction is determined by the difference in total solute concentration

  • Lots of solutes in cell, then water will enter cell

  • Lots of solutes in water, then water exits cell

Active transports (pumps)

• Requires ATP energy

• Moves ions, Na+, K+

• Low to high concentration

Endocytosis

• Requires ATP energy

• Large particles, fluids, molecules

• Into the cell

Exocytosis

• Requires ATP energy

• Proteins, hormones, waste

• Out of the cell

Why is it important for a cell to be able to regulate transport?

Transport is needed so that the cell can maintain homeostasis to stay alive and function properly

• Bring in needed substances

• Remove waste

What is tissue and its 4 main types?

Groups of cells that work together to perform a common function.

• Epithelial

• Connective

• Muscle

• Nervous

Where would you find epithelial tissue?

Found covering the outside of the body, lining the inside of organs and body cavities, and forming glands

• Skin

• Digestive tract

• Respiratory tract

• Blood vessels

• Glands

• Kidneys

What are the functions of epithelial tissue?

Acts as a protective covering or lining.

It protects, absorbs, secretes, and helps filter substances throughout the body.

What are the types of connective tissue?

• Loose connective

• Dense connective

• Adipose

• Cartilage

• Bone

• Blood

Loose connective tissue

Found under the skin and around organs; holds tissues together and cushions organs

• Areolar: binds organs and tissues together while providing flexibility and cushioning

Adipose tissue

Stores fat, provides insulation and body cushioning, and serves as an energy reserve

Dense Connective Tissue

Found in tendons and ligaments; provides strength and connects body parts.