Biology 171 Exam 2

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Gleason’s view determining which species exist at a certain site

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- Community found in a particular area is neither stable nor predictable.
- A matter of chance whether a similar community develops in the same area after a disturbance occurs.
- Plant and animal communities are ephemeral associations of species that just happen to share similar climatic requirements.
-, chance and history

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biomass

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organic material that non-photosynthetic organisms can eat.

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• Primary Consumer

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an herbivore, an organism that eats plants or algae or other photosynthetic cells.

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• Detritus

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animals and dead plant tissues (plant litter)

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• Primary Decomposers

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bacteria, archaea, fungi that consume detritus

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Trophic Level

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organisms that obtain their energy from the same type of source are said to occupy the same trophic (feeding) level.

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Food Chain

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connects the trophic level in a particular ecosystem

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Grazing food chain

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the collection of organisms that eat plants, along w/ the organisms that eat herbivores.

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Secondary Consumers

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consumers that eat herbivores

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Decomposer Food Chain

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– organisms at the top trophic level in a food chain are not killed and eaten by any other organisms but enter the decomposer food chain when they die – along w/ biomass from dead primary producers and other consumers

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Food chains vs food webs

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Food chains are almost always embedded in more complex food webs b/c most organisms eat more than one type of food.

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- Food Webs

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a compact way of summarizing energy flows and documenting the complex trophic interactions that occur in communities

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food chain limited:• Hypothesis 1 Energy Transfer

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As energy is transferred up a food chain, a large fraction of that energy is lost. By the time energy reaches the top trophic level, there may not be enough left to support an additional suite of consumers. (Limited by productivity)

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food chain limited:• Hypothesis 2 Stability

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Long food chains are unlikely to persist in a variable environment b/c long food chains are easily disrupted by droughts, floods, other disturbances, etc. Length of food chain should increase w/ stability of the environment.

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food chain limited: • Hypothesis 3 Environmental Complexity

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Food-chain length is a function of an ecosystem’s physical structure. 3-D ecosystems should have longer food chains that 2-D ones.

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Gross primary productivity

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the total amount of photosynthesis in a given area and time period.

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Gross photosynthetic efficiency

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the efficiency with which plants use the total amount of energy available to them.

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Secondary Production

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production of new tissue by primary consumers

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productivity

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measure of energy that is at each trophic level--> usually measured using carbon

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why are most food chains short?

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there is a max # of trophic levels that can be supported in on system. most systems have 3 -4 trophic levels. b/c of constraint of energy flow

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indirect effects

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the effect of species A on species B are mediated thru effects on species C

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trophic cascade

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when energy goes from top to bottom (all the way from top to bottom) -- are caused by indirect effects

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phytoplankton blooms

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happens when overfishing of big fish --
density of phytoplankton is impacted by the top predator.

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omnivore

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eat primary producers AND primary consumers

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how can a predator be a mutualist to its prey?

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if indirect effect is stronger than direct then the predator could be a mutualist of what it eats.

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foundation species

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have dramatic effect on community organization b/c they are extremely abundant. often provide food and shelter for many other organisms. example = sugar maple trees

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ecosystem engineers

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have a dramatic impact on the environment in which other species live. they "engineer" the habitat so that its conditions are very different for the species that live there. example = beavers

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keystone species

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can control populations and thus affect community dynamics and composition, some affect all the way down to the lowest trophic level. example = pisaster.

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Ecosystem

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consists of organisms that live in an area together with their physical, or abiotic, environment.  Ecosystems are composed of multiple communities along w/ their chemical and physical environments.

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Ecosystems have 4 components

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1.) Abiotic environment
2.) Primary producers
3.) Consumers
4.) Decomposers
These 4 components are linked by a flow of energy

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Primary Producer

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an autotroph (literally “self-feeding”) – meaning an organism that can synthesize its own food from inorganic sources. (In most ecosystems, primary producers use solar energy to manufacture their own food via photosynthesis. But where sun does not shine, use chemical energy in inorganic compounds) -- form the basis of ecosystems b/c they transform the energy in sunlight or inorganic compounds into the chemical energy stored in sugars

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Primary Producers use this energy in 2 ways

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1.) Support maintenance or respiratory costs
2.) Makes growth and reproduction possible.

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Net Primary Productivity

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energy that is invested in new tissue
-NPP represents the amt of energy available to 2nd and 3rd components of an ecosystem:

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- Consumers:

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eat living organisms

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- Herbivores

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consumers that eat plants

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- Carnivores:

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: consumers that eat animals

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- Decomposers/Detritivores

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obtain energy by feeding on the dead remains of other organisms or waste products.

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Final component of an ecosystem = abiotic environment

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soil, climate, atmosphere, sun, matter and solutes in water.

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ENERGY FLOW

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Sun/Inorganic compounds  consumers  decomposers  abiotic environ

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NPP dictates

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the amount of energy available to consumers and decomposers and global warming is altering NPP worldwide.

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The overall productivity of terrestrial ecosystems is limited by

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combination of temperature and availability of water and sunlight.

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NPP in marine ecosystems is limited primarily by

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the availability of nutrients and that iron is particularly important in the open ocean.

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Biogeochemical (“life-Earth-chemical”) cycle

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the path that an element takes as it moves from abiotic systems through organisms and back again. – Humans are now disturbing biogeochemical cycles on a massive scale

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humus

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Completley decayed organic matter, b/c it is rich in a family of carbon-containing molecules called humic acids.

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The decomposition rate is influenced by two types of factors

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: abiotic conditions such as temp and precipitation, and the quality of the detritus as a nutrient source for the fungi, bacteria, and archaea that accomplish decomposition. Of the many links in a nutrient cycle, the decomposition of detritus most often limits the overall rate at which nutrients move thru an ecosystem. Until decomposition occurs, nutrients stay tied up in intact tissues

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ecosystem ecology

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the study of interactions between organisms and the scientific world

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entropy

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measure of disorder of the system -- every energy transfer, some of the energy is lost to heat and energy is an unusable source of energy by cells.

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GPP

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measure of all photosynthesis in an area

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ATP

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energy carrying molecule that helps cells to everything that cells need to stay alive

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NPP

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amount of energy that goes into production of new cell tissues in a plant and it can be eaten and used by the primary consumer
NPP = GPP - Respiration

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Secondary production

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amount of new tissue produced by consumers from the foods they ingest during a given time period

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how much energy is actually transferred to the next trophic level?

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about 10% of energy is transfered up to the next trophic level. so 90% of energy is not transfered

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• Human impact on ecosystems

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= farming, logging, burning, soil erosion  accelerate nutrient loss.

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Global Water Cycle

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- Total volume of water in the atmosphere over land is balanced by the amount of rain and other forms of precipitation that occurs on the continents.

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Global Carbon Cycle

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- The movement of carbon among terrestrial ecosystems, the oceans, and the atmosphere.
- Carbon frequently moves in and out of the atmospheric pool thru organisms.
- **Photosynthesis is responsible for taking carbon out of the atmosphere and incorporating it into tissue.
- **Cellular respiration releases carbon that has been incorporated into living organisms to the atmosphere, in the form of carbon dioxide.

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Global Nitrogen Cycle

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- Plants are able to use nitrogen only in the form of ammonium or nitrate ions.
- Vast pool of molecular nitrogen in the air (78%) is unavailable to plants.
- Nitrogen is added to ecosystems in a usable form only when it is reduced or “fixed” meaning when it is converted from N2 to NH3.
- Nitrogen fixation results from lightning-driven reactions in the atmosphere and from enzyme-catalyzed reactions in bacteria that live in the soil and oceans.

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decomposers

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can break down nutrients, and convert them into inorganic molecules that consumers/producers need to grow

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pool

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amount of material in a given compartment

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flux

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measure of amount of material moving among pools.

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the water cycle on a global scale

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evaporation = precipitation
global exchange of water is balanced.

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transpiration

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plants lose water

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Chromosomes

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are the carriers of hereditary material – the instructions for building and operating the cell.

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Gametes

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sperm and eggs (male/female reproductive cells)

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Somatic cells

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other types of cells (literally “body-belonging”)

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meiosis.

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During the type of nuclear division that leads to the production of sperm and eggs, the amount of hereditary material found in the parent cell nucleus is reduced by half. As a result, the daughter cells that become sperm and eggs do not contain the same genetic material as the parent cell.

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Mitosis

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is a division of the genetic material that produces daughter cells that are genetically identical to their parent cell. When new somatic cells form in eukaryotes, the amount of hereditary material in the original cell and the daughter cells remains constant

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Asexual reproduction

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production of offspring that are genetically identical to the parent.

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mitoic M phase (mitosis)

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process that distributes chromosome copies to daughter cells

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interphase - between phase (mitosis)

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a non-dividing phase, Cells spend most of their time in interphase. no dramatic changes occur in this stage, chromosomes are uncoiled into extremely long, thin structures.

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Synthesis Phase-S phase (mitosis)

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DNA synthesis, part of interphase, duplication of the genetic material

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Cell Cycle

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regular alternation between M phase and interphase. Orderly sequence of events that occurs starting from the formation of a eukaryotic cell thru the duplication of its chromosomes to the time it undergoes division itself.

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• Histones

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eukaryotic chromosomes that exist as extremely long, threadlike strands consisting of DNA associated w/ globular proteins.

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• Chromatin

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DNA protein material

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• Chromatid

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each of the DNA copies in a replicated chromosome

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centromere.

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• The 2 chromatids are joined together along their entire length as well as at a specialized region of the chromosome called the

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sister chromatids

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• Chromatids from the same chromosome, represent exact copies of the same genetic info. At the start of M phase, each chromosome consists of two sister chromatids that are attached to one another at the centromere.

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INTERPHASE (between phase) mitosis

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Chromosomes replicate, each chromosome is composed of 2 sister chromatids. Centrosomes have replicated

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PROPHASE (before phase)

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Mitosis begins w/ prophase
Chromosomes condense into compact structures
Formation of mitotic spindle in cytoplasm = a structure that produces mechanical forces that pull chromosomes into the daughter cells during mitosis

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mitotic spindle

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a structure that produces mechanical forces that pull chromosomes into the daughter cells during mitosis.

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PROMETAPHASE (before middle phase) mitosis

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Nucleolus disappears, nuclear envelope breaks down. Spindle fibers from each mitotic spindle attach to one of the two sister chromatids of each chromosome at the kinetochore – located at the centromere region of the chromosome, where sister chromatids are attached to each other.

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METAPHASE (middle phase) mitosis

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Kinetochore microtubules finish moving the chromosomes to the middle of the cell. When metaphase is over, the chromosomes are lined up along an imaginary plane called the metaphase plate. Formation of mitotic spindle is complete. Pulling is occurring on the chromosomes b/c kinetochore spindle fibers are puling each chromosome in opposite directions.

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ANAPHASE (against phase) mitosis

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Centromeres holding sister chromatids together split. Pulled apart equally to create independent chromosomes. Motor proteins pull the chromosomes to opposite poles of the cell.
Replicated chromosomes split into two identical sets of unreplicated chromosomes.

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TELOPHASE (end phase) mitosis

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Nuclear envelope begins to form around each set of chromosomes. Mitotic spindle disintegrates, and chromosomes begin to de-condense. Once two independent nuclei have formed, mitosis is complete.

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Cytokinesis mitosis

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The cytoplasm divides to form two daughter cells, each w/ its own nucleus and complete set of organelles. Normally occurs immediately following mitosis.

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Meiosis leads to

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a halving of chromosome number. Precedes the formation of eggs and sperm in animals.

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sex chromosome.

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12th chromosome = X = associated with the sex of the individual

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autosomes

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1 – 11 chromosomes = a –k = non sex chromosomes

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Homologous (same proportion) chromosomes

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the two chromosomes of each type. Homologous chromosomes are similar in shape, size, and content  carry the same genes

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gene

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a section of DNA that influences one or more hereditary traits in an individual.

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Allele

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different versions of the same gene. (rounder eyes vs narrower eyes/ larger body size vs smaller body size) **Homologous chromosomes carry the same genes, but each homolog may contain different alleles.

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Karyotype

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number and types of chromosomes present

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Diploid

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double form - have 2 versions of each chromosome. *Diploid organisms have two alleles of each gene – one on each of the homologous pairs of chromosomes. (Ex. Of diploids = grasshoppers, humans, cedar trees)

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Haploid

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single from – cells contain just one of each type of chromosome. *Haploid organisms do not contain homologous chromosomes. They have just one allele of each gene. (Ex. Of haploids = bacteria, archaea, algae)

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Haploid Number

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n = number of distinct types of chromosomes in a given cell

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Ploidy

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combination of a number and n

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Diploid cells

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2n b/c two chromosomes of each type are present – one from each parent

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Haploid cells

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n b/c they have just one set of chromosomes – no homologs are observed

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In humans n =? 2n = ?

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n = 23
2n = 46

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- Meiosis I

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The homologs in each chromosome pair separate from each other. One homolog goes to one daughter cell; the other homolog goes to the other daughter cell. End result = daughter cells from meiosis I have one of each type of chromosome instead of two, and thus half as many chromosomes as the parent cell. During meiosis I, the diploid (2n) parent cell produces two haploid (n) daughter cells. Each chromosome still consists of two sister chromatids.

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- Meiosis II

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Sister chromatids from each chromosome separate. One sister chromatid goes to one daughter cell; the other to the other daughter cell. The cell that starts meiosis II has one of each type of chromosome, but each chromosome has been replicated (meaning it still consists of 2 sister chromatids) The cells produced by meiosis II also have one of each type of chromosome, but now the chromosomes are unreplicated.

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Outcome of meiosis

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is a reduction in chromosome number. Meiosis is known as reduction division.

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interphase (meiosis I)

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chromosomes replicate in parent cell, in uncondensed state

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early prophase I (meiosis I)

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chromosomes condense, nuclear envelope breaks up, spindle apparatus forms. synapsis of homologous chromosomes

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late prophase I (meiosis I)

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crossing over of non-sister chromatids (often mulitple cross-overs between the same chromatids)

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metaphase I (meiosis I)

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tetrads migrate to metaphase plate

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anaphase I (meiosis I)

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homologs separate and begin moving to opposite sides of cell

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telophase I (meiosis I) and cytokenesis

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chromosomes move to opposite sides of cell, then cell divides

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prophase II (meiosis II)

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spindle apparatus forms

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metaphase II (meisosi II)

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chromosomes line up at middle of cell (metaphase plate)

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anaphase II (meiosis II)

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sister chromatids separate, begin moving to opposite sides of cell

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telophase II and cytokensis (meiosis II)

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chromosomes move to opposite sides of cell, then cell divides

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1. Separation and distribution create variation

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when pairs of homologous chromosomes line up during meiosis I and the homologs separate, a variety of combinations of maternal and paternal chromosomes can result. Each daughter cell gets a random assortment of maternal and paternal chromosomes.

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2. Crossing over creates variation

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produces new combinations of alleles on the same chromosome – combinations that did not exist in either parent. Known as recombination. Genetic recombination – any change in the combination of alleles on a given chromosome. **Crossing over and the random mixing of maternal and paternal chromosomes ensure that each gamete is genetically unique.

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3. Fertilization – outcrossing creates variation

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– gametes from different individuals combine to form offspring  increases the genetic diversity of offspring b/c it combines chromosomes from different individuals, which are likely to contain different alleles.

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WHY SEX?

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Asexual reproduction is much more efficient than sexual reproduction b/c no males are producded. But asexual individuals are doomed to transmitting all of their deleterious (functions poorly and lowers fitness) alleles to all of their offspring.
*Sexual individuals are likely to have offspring that lack deleterious alleles present in the parent. Natural selection against deleterious alleles is called purifying selection. Over time, purifying selection should steadily reduce the numerical advantage of asexual reproduction.
Sexual reproduction produces genetically diverse offspring.

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nondisjunction

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things failing to seperate.
causes gametes to have abnormal chromosome numbers.

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Recessive

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referring to an allele whose phenotypic effect is observed only in homozygous (having two identical alleles of the same gene) individuals

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Dominant

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referring to an allele that determines the phenotype of a heterozygous (having two different alleles of a certain gene) individual

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particulate inheritance:

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hereditary determinants for traits do not blend together or acquire new or modified characteristics through use. Hereditary determinants maintain their integrity from generation to generation. Instead of blending together, they act like discrete entities or particles.

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Principle of Segregation

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To explain the 3:1 ratio of phenotypes in F2 individuals, Mendel reasoned that the two alleles of each gene must segregate – that is, separate – into different gamete cells during the formation of eggs and sperm in the parents. As a result, each gamete contains one allele of each gene

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Principle of independent assortment

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allele of different genes are transmitted independently of one another.

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sources of genetic variation that sex produces

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crossing over, independent assortment of homologs, random fertilization of gametes

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Linkage

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the physical association of genes that are found on the same chromosome
**If two or more genes are linked, it means that they are located on the same chromosome. If a single gene is sex-linked, it means that it is located on a sex chromosome.

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Incomplete dominance

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heterozygotes have an intermediate phenotype

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Codominance

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heterozygotes have the phenotype associated w/ both alleles present. Both alleles are represented in the phenotype.

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Pleiotropic

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a gene that influences many traits rather than just one trait

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Epistasis

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an allele of one gene masks the effect of an allele at another gene.

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Quantitative traits

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individuals vary by degree (height, weight, skin color)
Quantitative traits are produced by the independent actions of many genes.

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Polygenic Inheritance

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each gene adds a small amount to the value of the phenotype.

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Vestigial Trait

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a reduced or incompletely developed structure that has no function or reduced function, but it is clearly similar to functioning organs or structures in closely related species.
(goose bumps/tail bones in humans)

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1. Natural Selection

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– increases the frequency of certain alleles – the ones the contribute to success in survival and reproduction

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2. Genetic Drift

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causes allele frequencies to change randomly. In some cases, drift may even cause alleles that decrease fitness to increase in frequency.

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3. Gene flow

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occurs when individuals leave one population, join another, and breed. Allele frequencies may change when gene flow occurs, b/c arriving individuals introduce alleles to their new population and departing individuals remove alleles from their old population.

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Balancing selection/heterozygote advantage

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heterozygous individuals have higher fitness than homozygous individuals do.

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Genetic variation

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the number and relative frequency of alleles that are present in a particular population.

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Directional selection

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average phenotype of the populations changed in one direction
**Directional selection tends to reduce the genetic diversity of populations. If directional selection continues over time, the favored alleles will eventually reach a frequency 1.0 while disadvantageous alleles will reach a frequency of 0.0. alleles that reach a frequency of 1.0 are said to be fixed; those that reach a frequency of 0.0 are said to be lost.

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Purifying selection

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disadvantageous alleles decline in frequency

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Stabilizing selection

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selection reduces both extremes in a population. Has 2 consequences:
1. There is no change in the avg value of a trait over time
2. Genetic variation in the population is reduced

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Disruptive selection

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opposite effect of stabilizing selection. Instead of favoring phenotypes near the average value and eliminating extreme phenotypes, it eliminates phenotypes near the average value and favors extreme phenotypes. Overall genetic variation in the population is maintained.
Disruptive selection is important b/c it sometimes plays a part in speciation, or the formation of new species.