AP Biology Unit 1

What is science?

systematic endeavor aimed at understanding the natural world through observation, experimentation, and logical reasoning

Inquiry

posing questions and seeking answers through systematic investigation

Observations: qualitative and quantitative

quantitative: describing qualities or characteristics

quantitative: involving numerical measurements

Reasoning: inductive and deductive

Inductive: involves making generalizations based on specific observations

deductive: logical inference to predict specific outcomes from general principles

hypothesis: definition and formulation

proposed explanation for a phenomenon or prediction that can be tested through experimentation.

how to write hypothesis

use If(cause), then (effect), because (rationale)

Null Hypothesis (H0)

states that there is no significant relationship between variables being studied

alternative hypothesis

proposes there is a significant relationship between variables studied

hypothesis

educated guess based on prior knowledge and observations, which can be tested through experiments

scientific law

describes an observable phenomenon that occurs consistently under specific conditions, often expressed mathematically

scientific theory

well-substantiated explanation supported by extensive evidence explaining the reasons behind a wide range of observations

Independent variable

the factor that is deliberately manipulated by the researcher

dependent variable

the factor that is measured or observed to assess the effect of the independent variable

positive control

the group is exposed to a treatment known to produce a positive result

negative control

this group is not to the treatment and should not produce a result (helps show external factors that influence outcome)

constants

all the factors that must be kept the same throughout the experiment for all groups

number of trials

having more trials per experiment is better to show how more robust and statistically significant the results will be

Statistics

Branch of mathematics that helps us understand and interpret data

Statistics in biology

used to summarize, describe, and analyze experimental data, helping scientists draw conclusions

Bell shaped curve

represents normal distributions, a common pattern where most data points are concentrated around the middle (mean) value, with fewer data points appearing as you move away from the mean.

Central Tendencies

measures that summarize a set of data by identifying the center point (Mean, Median, and Mode)

Mean

(Average) the sum of all data points divided by the number of data points.

Median

the middle value when the data points are ordered from least to greatest (central point of data)

Mode

most frequently occurring value in data set

variability

measures how spread out the data points are

range

difference between the highest and lowest values

standard deviation

shows how much the data points differ from the mean.

what does higher standard deviation mean

more spread out data (factors other than independent variable are causing the change)

low standard deviation

data points are closer to mean (means independent variable is causing changes)

Standard Error (SE)

measures how accurately the sample mean estimates the population mean (decreases as the sample size increases)

Error Bars

graphical representations of the variability of data on charts and graphs (represent range, standard deviation, or standard error)

Creating error bars

create normal bar graph, but use the mean value for each data set

add error bars above and below each bar to represent the standard error

Overlapping error bars

suggest that the difference between data sets may not be statistically significant

Non-overlapping error bars

suggest a significant difference between data sets

Chi-square (χ²)

a statistical test used to determine if there is a significant difference between observed and expected values in categorical data.

How to perform a chi-square test

1. state hypothesis

2. calculate expected frequencies

determine the expected frequencies based on hypothesis

3. calculate chi-square value

using the formula x²=sum((O-E)²/E)

O = number of observed frequencies

E= expected frequencies

4. determine degrees of freedom

degrees of freedom is the number of categories minus one

5. compare chi-square distribution

null hypothesis

there is no significant difference between the observed and expected frequencies

alternative hypothesis

there is significant difference between the observed and expected frequencies

matter

anything that takes up space and has mass

element

a pure substance that cannot be broken down into simpler substance by chemical means (made up of one kind of atom)

compound

a substance formed when two or more different elements combine in a fixed ratio

essential elements

elements that organisms need in large amounts to survive (CHON— make up of 96% of living matter)

trace elements

elements required by organisms in minute quantities (Fe, I, Zn)

Atomic number

number of protons in nucleus of atom

atomic mass

average mass of an element’s atoms, usually expressed in atomic mass units (amu)

groups

vertical columns that indicate elements with similar chemical properties

Periods

horizontal rows that indicate the number of electrons shells in the atoms of the elements

Bohr Model

represents electrons orbiting the nucleus in fixed energy levels or shells

Lewis Dot Model

Represents valence electrons as dots around the chemical symbol of an element

Octet Rule

Atoms tend to gain, lose, or share electrons to have full outer shell of 8 electrons, achieving stability similar to the noble gases

Electronegativity

A measure of an atom’s ability to attract and hold electrons in a chemical bond

High electronegativity = more attraction of electrons

Electroneg increases moving from left to right on the periodic table

Nonpolar Covalent Bond

electrons are shared equally between atoms

Polar covalent bonds

electrons are shared unequally leading to partial charges on atoms

Single bonds

one pair of electrons shared

Double bonds

two pairs of electrons shared

Triple bonds

Three bonds of electrons shared

Ionic bonds

Formed when one atom donates an electron to another atom, creating positively charged cations and negatively charged anions that attract eachother

Hydrogen bonds

Weak bonds between a hydrogen atom in one molecule and an electronegative atom in another molecule

Acids

substances that increase the concentration of hydrogen ions in a solution. They donate protons when dissolved in water

Bases

substances that reduce the concentration of hydrogen ions in a solution. They accept protons or produce hydroxide ions when dissolved in water

pH 7

neutral (pure water)

pH < 7

Acidic (more H+ ions)

pH > 7

Basic (more OH- ions)

Enzyme activity for pH

optimal pH range in which they function most efficiently, deviations form this range can denature enzymes, reducing their activity

enzymes

proteins that catalyze biochemical reactions

cellular processes with pH

cellular respiration and photosynthesis involve reactions that are pH-dependent

Homeostasis for pH

Organisms that maintain a stable internal pH through buffers, which are substances that minimize changes in pH by absorbing or releasing H+ or OH- ions

Buffers

crucial in biological systems to maintain a stable pH. They are mixtures of weak acids and their corresponding bases

Cohesion

the attraction between water molecules due to hydrogen bonding

Adhesion

the attraction between water molecules and other types of molecules

How do cohesion and adhesion work together in plants?

they facilitate transport from the roots to the leaves through the xylem in a process known as transpiration

What molecule is vital for all life forms and is polar (partial positive charge and partial negative charge)?

Water (H2O)

Capillary Action

ability of water to flow in narrow spaces without the assistance of external forces due to cohesion and adhesion

How does capillary action work in plants?

helps draw water up from the roots through tiny vessels in the replant stem and into leaves, brings nutrients and water from soil to rest of plant

High specific heat

Water can absorb or release large amounts of heat with only a slight change in its own temperature

Evaporative Cooling

When water evaporates, it takes heat away from the surface, cooling the organism. (eg. sweating)

Importance of density in water

the lower density of ice causes it to float on liquid water, insulating the water below and providing a habitat for aquatic life during cold seasons

Solvent

the substance that dissolves other substances to form a solution

Solute

the substance that is dissolved in a solvent

Solution

a homogeneous mixture of solvent and solute

Organic compounds

primarily composed carbon atoms bonded to hydrogen, oxygen, nitrogen, and other elements

Where are organic compounds found?

living organisms and include carbohydrates, lipids, proteins, and nucleic acids (Glucose, DNA, protein, and fats)

Inorganic Compounds

Inorganic Compounds do not primarily consist of carbon-hydrogen bonds. They include minerals, salts, and water

Where are inorganic compounds found?

non-living systems but are vital to life processes

Tetravalency in Carbon

Carbon has four valence electrons, allowing it to form four covalent bonds with other atoms, leading to a variety of complex molecules

Bonding capacity in Carbon

Carbon can form a single, double, and triple bonds, creating a range of molecular structures

Cantenation

Carbon can bond with other carbon atoms to form long chains and rings, essential for creating complex organic molecules

Hydrocarbon Chains

organic molecules consisting entirely of carbon and hydrogen

Types of hydrocarbon chains

single, double, or triple bonds

Importance of Carbon in Living systems