Biology Midterm: Units 1, 2, and 3

Scientific Theory

a general explanation of the world supported by a large body of experimental evidence and observations (hypotheses that have withstood testing) and it has the most evidence to support it

Hypothesis

 tentative explanation for one or more observations and is testable through experimentation

Question

 asks something that could be answered in a hypothesis and experiment

Guess

an estimation or assumption made without certainty or evidence. It is a subjective attempt to answer a question or solve a problem based on limited information or intuition.

Hypothesis v. Prediction

A hypothesis is a tentative explanation for one or more observations that is testable through experimentation while a prediction says what will happen in an experiment if the prediction is correct.

Independent Variable

variable that is manipulated to test the hypothesis

Dependent Variables

the result of the experiment, variable expected to change as a result of independent variable

Controlled Variables

all other variables that are kept constant within the experiment

Experimental vs. Control Treatments

The conditions and setup of the treatments are identical, but the researcher deliberately introduces a single variable to the experimental group to see its effect.

Chi-squared test

Compare observed values to expected values. Used with nominal (names) independent variable and discrete (whole number) dependent variable

Population

A group of individuals of the same species in the same place at the same time (that interact) and make up the smallest unit of evolution

3 Ways to Describe a Population

Density, Dispersion, and Demographics

3 Patterns of Dispersion

1. Clumped: individuals are organized in groups, typically clumped around resources

2. Uniform: individuals are evenly spaced, likely to avoid intraspecific conflict

3. Random: individuals are randomly spaced

Method to estimate population size

Mark-Recapture Method: set traps and capture group, note number and mark individuals, release individuals and let them mix with population. Set traps and capture another group, see how many are already marked. Proportion is Total Pop/Number in 1st capture group and mark  = Total captured 2nd group / Number recaptured (already marked)

Birth Rate

increases population (if greater than death rate)

Death rate

decreases population (if greater than birth rate)

Patterns of Survivorship

1. Group 1: Most live to half life and then die off (humans, elephants) - few offspring, good parental care

2. Group 2: constant chance of dying at all age groups (rodents, birds)

3. Group 3:  lots of offspring, few make it out of youth (invertebrates, fish, plants)

Immigration

Increases population; live in a region you are not originally from

Emigration

 decreases population; leave region you are originally from

When would a scientist observe exponential growth?

few limiting factors

When would a scientist observe logistic growth?

many limiting factors, close to carrying capacity

Density dependent limiting factors

the strength of the influence of factors depends on how crowded a population is

1. Predation

2. Disease

3. Competition

4. Territoriality

Density Independent Limiting Factors

1. Temperature

2. Natural disasters

3. Pollutants

Community

Populations of a species that live close enough to interact. All the biotic components of an ecosystem

Ecosystem

All the biotic and abiotic components in an area and how they interact

Two phenomena that reduce intraspecific competition in a community

Resource Partitioning: individuals divide resources into smaller parts instead of pursuing different resources

Character Displacement: evolutionary change that occurs when two similar species inhabit the same environment (traits diverge to avoid competition)

Exploitation

beneficial to one species and detrimental to the other. Examples: Predation (herbivory) and Parasitism

Mutualism

beneficial to both species (bees and flowers)

Commensalism

beneficial to one species and neutral to the other (small fish on sharks)

Competition

detrimental to both species

Why are communities with high biodiversity are more resistant to disturbances such as natural disaster?

Biologically diverse communities are also more likely to contain species that confer resilience to that ecosystem because as a community accumulates species, there is a higher chance of any one of them having traits that enable them to adapt to a changing environment.

• Note:

  1. Species richness: the number of different species in a community

  2. Relative abundance: the proportion of the community made up of each species
     
     
     

Evolution

change in allele frequencies of a population over generations

Natural selection

the process by which individuals with favorable traits survive and reproduce at a higher rate than individuals without those traits, is a mechanism by which evolution occurs

Morphology

Homologous Structures: structural similarities as a result of a common ancestor

Example: Pentadactyl Limb in seals, moles, birds, humans

Vestigial Structures: anatomical structures that have been retained through a species' evolution but have lost most or all of their ancestral function

Example: Tailbone

DNA/protein sequences

If two organisms have similar DNA or protein sequences, they likely evolved from the same ancestor

Biogeography

Closely related are usually geographically close, and related species on different continents could be a result of continental drift (Pangea)

Paleontology

Fossils show forms of animals that have not previously been seen - if these fossils show a similarity to an existing organism, that could be evidence for evolution

Evidence that evolution is ongoing today

antibiotic resistance, pesticide resistance, lactose tolerance in humans, Galapagos finch beak sizes

Four Principles Essential to Natural Selection

Variation

Inheritance

Overproduction

Differential Survival and Reproduction

Variation

difference in DNA among individuals or the differences between populations among the same species

Inheritance

is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction

Overproduction

when living organisms produce more offspring than can survive

Differential Survival and Reproduction

a process of favoring the survival and reproduction of the fittest individuals in a population

Compare and contrast types of natural selection

Directional selection is the selection for ONE extreme trait and away from the other

Stabilizing selection is selection for MODERATE traits and away from both extremes

Disruptive Selection is selection for BOTH extremes and away from moderate traits

Artificial Selection

evolutionary process in which humans consciously select for or against particular features in organisms

Sexual Selection

Traits that appear to be maladaptive (could harm survival) are actually selected for because they increase biological fitness by attracting mates

Distinguish between evolution by natural selection, by genetic drift, and by gene flow.

Evolution by natural selection: Adaptive (non random evolution : individuals with favorable traits survive and reproduce

Evolution by genetic drift: RANDOM CHANGE in allele frequencies in a population from gen to gen (new population forms)

• Examples: Bottleneck and Founder Effects

• Can be facilitated by natural disasters, movement of individuals, chance, etc

Evolution by gene flow: RANDOM MOVEMENT of alleles from one population to another (exchange of genes between existing populations)

Explain the requirements that must be met for a population to be in Hardy-Weinberg equilibrium and why it represents a null hypothesis for evolution.

No Selection

No Mutation

No Migration

Large Population

Random Mating

Null Hypothesis of evolution because allele frequencies remain stable

Biological Species Concept

If animals can interbreed and produce fertile offspring, they are the same species

Pre-zygotic isolating mechanism

Gametic Isolation: sperm cannot fertilize egg

Habitat Isolation

Behavioral Isolation

Temporal Isolation

Mechanical Isolation

Post-zygotic isolating mechanisms

Hybrid Inviability

Hybrid Sterility

Allopatric Speciation

New species develop because of physical separation Ex: other side of cliff

Sympatric Speciation

New species developing within the same location Ex: cell division error

Gradualism

species gradually evolve over time

Punctuated Equilibrium

rapid bursts of speciation followed by relatively little change

Adaptive radiation

a period of rapid evolutionary change in which organisms form many new species with adaptations to different specialized niches (basically punctuated equilibrium) Adaptive radiation is caused by dramatic events in nature such as island colonization and mass extinction

Cladogram/Phylogenetic Tree Features

Root: theoretical last common ancestor

Node: the point where lineage split to give rise to two or more descendant lineages (indicates common ancestor)

Branches: indicate genetic change and shows path of transmission of genetic material

Branch Tip: species

Endosymbiotic Theory

Endosymbiotic theory suggests that a larger prokaryotic cell once engulfed a smaller prokaryotic cell (likely bacteria), which, instead of being ingested, survived and became what we now call organelles. It suggests that these bacteria evolved into mitochondria before other bacteria evolved into chloroplasts. 

Endosymbiotic Theory Evidence

Chloroplasts and Mitochondria…

• Have multiple membranes with structures like prokaryotes

• Are about the same size as prokaryotes

• Have their own DNA in a single ring chromosome like prokaryotes

• Have ribosomes resembling prokaryotic ribosomes

• Can divide in a process similar to binary fission

How does the anatomy of specific organelles (chloroplasts and mitochondria) relate to their specific functions in photosynthesis and cellular respiration?

CHLOROPLASTS

The  membranes around the thylakoids inside the chloroplast have light-harvesting complexes that include chlorophyll

These complexes are used to collect light energy that is used to perform photosynthesis

MITOCHONDRIA

The main function of the mitochondria is to breakdown fuel molecules which produce ATP the main product of cellular respiration

Describe the differences between exergonic and endergonic reactions and give biological example.

Exergonic reaction: releases energy (-ΔG) reaction is spontaneous and happens when bonds are made

Example: Aerobic Cellular Respirtion

Endergonic reaction: energy absorbed (+ΔG) reaction is nonspotaneous and happens when bonds are broken

Example: Photosynthesis

Why is ATP so important in biology?

Energy source for every biological process

What type of biological molecule are enzymes and how do they influence the free energy needed to “activate” a reaction?

Enzymes are proteins (and sometimes RNA’s called ribozymes) that act as catalysts for a reaction. They SPEED UP the reaction RATE by LOWERING THE ACTIVATION ENERGY of the reaction. Enzymes control metabolism (the total of an organism's chemical reactions)

Cellular Respiration summary equation

• C₆ H₁₂O₆ + 6 O₂ --> 6 CO₂ + 6 H₂O + ATP

  • Input: Glucose/other biomolecule (organic) and Oxygen (inorganic: either breathed in or diffused for non-lunged organisms)

  • Output: Carbon Dioxide (waste product), Water (waste product), and ATP (used for function)

Photosynthesis summary equation

• 6 CO₂ + 6 H₂O (light) → C₆ H₁₂O₆ + 6 O₂

  • Input: Carbon dioxide (inorganic) and water (inorganic) and light (inorganic)

  • Output: Glucose (organic) and oxygen

Aerobic cellular respiration vs. Fermentation

• Cellular Respiration: the chemical reaction(s) that break down fuel (food) to make ATP

• Both aerobic CR and fermentation include glycolysis, but aerobic CR also includes Krebs Cycle and the ETC which generates lots of ATP

• Aerobic cellular respiration: oxygen in, carbon dioxide out, also produces 34 ATP by breaking down sugars

  • C6H12O6 + 6O2 → 6H2O + 6CO2 + 34 ATP

• Fermentation:

  • If oxygen is not present after glycolysis in an animal or protist lactic acide fermentation occurs

    • Reactants from Glycolysis, Produces lactic acid + 2 ATP + NAD+ (which can be recycled)

  • If yeast or a plant = alcoholic fermentation

    • Reactants from Glycolysis, Produces 2 ATP + Ethy Alcohol + NAD+

Three steps of Cellular Respiration

1. Glycolysis

   1. Glucose + 2 ATP + NAD+ → 2 pyruvate + Water + NADH (carrying e-) + 4 ATP

   2. (in cytoplasm)

2. Krebs Cycle

   1. Pyruvate + NAD+ +FADH → Carbon Dioxide + NADH + FADH2 (carryng more e-) + 2 ATP 

   2. (mitochondrial matrix)

3. Oxidative Phosphorylation: Electron Transport Chain

   1.  NADH + FADH2 + Oxygen → 34 ATP

   2. (Inner mitochondrial membrane)

Two steps of photosynthesis

1.  Light-Dependent Reactions

   1. H20 → (light) ATP + NADPH + O2

   2. flows through thylakoid membrane

2. Light Independent Reactions (Calvin Cycle)

   1. ATP + NADPH + CO2 → C6H12O6

   2. Stroma of the chloroplasts

What is the role of NADH and FADH2 in cellular respiration? What about NADPH in photosynthesis?

NADH and FADH2 are the electron carriers in cellular respiration which, in the ETC, cause protons to move from inside the mitochondrial matrix to the intermembrane space where they then flow through ATP synthase and generate ATP.

NADPH in photosynthesis is an electron carrier that donates an electron which then allows ATP to be created. Is a product of the first stage that is meant to help fuel the reactions in the second stage of photosynthesis

Why are electron transport chains and the proton gradients generated by them important for cellular respiration? For photosynthesis? What enzyme is critical to these processes?

H+ is the proton gradient. Every time electrons go through ETC, it moves a H+ which then goes through ATP synthase (ATP synthase is the enzyme)

What is chlorophyll? Where is it found in a plant (be as specific as possible!)? Why is it important to photosynthesis?

• The pigment that absorbs sunlight and causes plants to appear green (by absorbing all other light colors and reflecting green)

• Chlorophyll is found within the thylakoid membranes (which are in stacks called granum). Most specifically, they are found in photosystems (light harvesting complexes)

• Without chlorophyll, the plants wouldn’t be able to absorb the light that starts the process of photosynthesis. Chlorophyll is excited by light, causing electrons to jump to a higher energy level

How are the absorption spectra of photosynthetic pigments related to the rate of photosynthesis?

The rate of photosynthesis is maximum in blue and red wavelength of light.

Why is photosynthesis essential to (almost) all life on Earth?

Photosynthesis creates oxygen and without it, life on Earth would be impossible

What do ecologists mean when they say that energy flows but matter cycles in an ecosystem?

Energy flows straight through the ecosystem but some is lost as heat at each step

Matter, however, is recycled (changes form) and not lost from the ecosystem

What two climatic factors influence the geographic distribution of biomes? Why are they so influential?

• Temperature and Precipitation

• These two factors determine what types of plants can grow in a given area and therefore which animals can survive there

Use the 10% Rule to predict the amount of available energy in a particular trophic level given information about a different trophic level.

Explain why this limits how many trophic levels there are in a food web/chain.

At each trophic level only 10% of the energy is transferred to the next level

With less energy at each growing level there is enough for less organisms so eventually there will reach a point where there isn't enough energy for another level

This is why there are so many more primary producers over tertiary consumers

Explain how photosynthesis and cellular respiration are part of biogeochemical cycling.

The carbon cycle is about pathways carbon takes

Cellular respiration releases carbon dioxide into the atmosphere and photosynthesis pulls it out

Cellular respiration and photosynthesis also impact the cycling of water