realizată de Jazmyn Richmond 7 ani în urmă
517
Mai multe ca aceasta
The two sister chromatids from each metaphase chromosome are now at opposite ends of the cell. At the site of the metaphase plate, the cytoplasm begins to pinch inwards.
The chromosomes are now lined up along the middle of the cell. Sister chromatids are attached to microtubules from opposite ends of the cell.
As the spindle fibers grow, they once again attach to the chromosomes. As in mitosis, each chromatid becomes attached to one spindle. The spndles direct the chromosomes towards the middle of the cell.
The two sister chromatids from each metaphase chromosome are now at opposite ends of the cell. At the site of the metaphase plate, the cytoplasm pinches inward.
The two sister chromatids are separated and pulled to opposite ends of the cell. As a result, each of the daughter cells from mitosis ends up with one copy of every chromosome that was in the original cell. The cell begins to pinch inwards in the middle.
The chromosomes are now at the middle of the cell. Spindle fibers attached to chromatids.
The chromosomes become visible. The two identical copies of each chromosome are called chromatids. Each chromatid pair is joined together, forming an 'x-shaped' structure called a metaphase chromosome. The nuclear membrane, nuculeolus, endoplasmic reticulum and Golgi complex break up. The centrioles move to opposite ends of the cell, and spindle fibers begin to grow out from them.
The chromosomes are duplicated just before mitosis, so there are two identical ('sister') copies of each one. This gives a total of 2 x 46 chromosomes (92). They remain in their 'unwound' state, and are therefore invisible.
The centrioles, a pair of cylindrical structures, are also duplicated. Each set of centrioles is surrounded by a tubule-making zone; the centrioles and the zone together make up a centrosome.
Smaller, invertebrate animals can have an even more fluctuating population number. Environmental factors affect them even more, more predators or even in some cases cannibalism can decrease the population while laying very large number of eggs can quickly increase the population numbers:
Fluctuation of numbers of large mammal populations can be caused by harsh winter or increasing predator numbers, but they are usually seem to be relatively stable:
Over time all populations show fluctuations in numbers.
Competition for resources Territoriality Health (increased transmission rate of a disease) Predation Toxic metabolic wastes Intrinsic factors (physiological factors that drop reproduction – later maturation, aggressive interactions among individuals)
Patterns of distribution of various populations within a geographic range:
Random – occurs in the absence of strong attractions or repulsions among individuals of the population. The position of each individual is fairly independent on the other individuals. (ex. Wind blown seed disposal for trees or other plants)
Uniform – the individuals in the population are evenly spaced (ex. Plants release chemicals that inhibit the germination and growth of other organisms, territoriality among animals, artificially planted trees)
clumped – the individuals aggregated in patches (ex. Plants, fungi, pack of wolves) because of patchy environmental conditions or food sources, carnivorous animals may be more successful of hunting in packs or herbivorous animals may be more successful of surviving attacks of carnivores in herds, mating behaviors also may call for clumped dispersion.
Members of the same population rely on the same resources, are influenced by the same environmental factors, interact and reproduce with each other.
Population density – the number of individuals per unit area or volume (can be determined directly by counting or by sampling)
Population dispersion – the pattern of spacing among individuals of the populations.
Learned behaviors – Results from experiences of the animal. Learned behaviors can modify innate behaviors. Learning behavior also may not follow the exact same pattern every time.
Examples of learned behaviors:
Classical conditioning – animals associate one stimulus with another (Ex. dog salivate when gets food, can be taught to salivate when hears a bell – Pavlov) Habituation – response to the stimulus decreases when it is repeated with no apparent effect (Ex. Drug habituation in humans; harbor seals get used to hearing local killer whale calls and do not respond to it) Imprinting behavior – during a critical period, an animal can adopt a behavior by latching on to the stimulus (Ex. Mallard chicks follow the first organism who they see right after hatching – Lorenz) Operant conditioning – or trial and error learning – animal is rewarded or punished after chance behavior.
innate behavior -- behavior determined by the "hard-wiring" of the nervous system. It is genetically predetermined, usually inflexible, a given stimulus triggering a given response. These behaviors frequently follow a classical, rigid pathway called a fixed-action pattern (FAP) where a releaser (some type of stimulus) triggers an operation of the innate releasing mechanism in the nervous system. This trigger results in the same set of actions every time the response is initiated. (Ex. Mating dances of birds triggered by the presence of a female; the egg rolling behavior of many waterfowl species; kelp gull chicks peck on a red spot on mother’s beak to initiate regurgitation of food etc.)
Examples of innate behaviors:
Reflexes – knee-jerk reflex, withdrawal reflex Taxis – movement in response to the direction of the stimulus toward (positive) or away (negative) from the stimulus Kinesis – Random movement of the animal in no particular direction (Ex. Pill bugs move more when the humidity is low) Instincts (stereotyped behavior) – more complex behaviors than reflexes that repeat the same way every time (Ex. Shaking water from wet fur, newly hatched sea turtles move toward the ocean)
Photic zone – has sufficient light for photosynthesis
Aphotic zone – does not have sufficient light for photosynthesis
Benthic zone – the bottom of all aquatic biomes, mostly made up of sand and organic and inorganic sediments.
Thermocline – narrow zone of rapidly changing temperature that separates the warm upper and cold lower layers of lakes and oceans
Aquatic biomes can be described by analyzing salinity, oxygen content, organic content, turbulence, light intensity, temperature Case study on dead zones.
Lakes are the most important standing water biomes. Oligotrophic lakes are deep lakes that are usually poor in nutrients (organic materials) but rich in oxygen with lower temperatures, and low phytoplankton concentration.
Light intensity decreases sufficiently because water and photosynthetic organisms absorb it.
Aquatic biomes account for the largest part of the biosphere in terms of area. Ecologists usually distinguish between fresh water biomes (salt concentration is less than 1 %) and marine biomes (salt concentration is more than 3 %).
Species transplants – species artificially or accidentally introduced and reproduce in new location.
Natural range expansions – organisms move into previously uninhabited areas as a natural way of expanding the population.
Biotic Factors – Some host species may be necessary for parasites to reproduce in new areas or pollination cannot occur without certain pollinator species, specific nutrient requirements may be necessary (ex. Koalas only eat eucalyptus leaves; parasites that cause malaria need the Anopheles mosquito to infect humans)
Abiotic factors – Temperature – affects biological processes such as germination or enzyme activities. Water – some organisms can tolerate only fresh water, while others only sea water (different osmoregulation). Terrestrial organisms face a constant threat of dehydration. Sunlight – Driving force of photosynthetic organisms and also influence the daily activities of other organisms (photoperiod regulation). Wind – influence temperature control, growth of plants and water loss. Rocks and soil – its composition, pH limit the distribution of plants and of the animals that feed on them.p
intersexual selection: (mate choice)- individuals of one sex(usually females) are choosy in selecting their mates from the other sex
female only gains an advantage over other females if she chooses a mate that enables her to produce more fit offspring
usually depends on the showiness of males
pop most obvious in males
in vertebrates, males are usually the showier sex
distinctions include differences in size, color and ornamentation
shuffles alleles but does not change frequencies
populations have many possible mating combinations
most phenotypic variation is a result of sexual recombination(allele variation originates from past mutations)
Such barriers typically act in one of 3 ways: by impending members of different species from attempting to mate, by preventing an attempted mating from being completed successfully, or by hindering fertilization if mating is completed successfully.
Mechanical Isolation: Mating is attempted, but morphological differences prevent its successful completion.
Temporal Isolation: Species that breed during different times of the day, different seasons, or different years can not mix their gametes.
Allele transferred by gene flow can also affect how well populations are adapted to the local environmental conditions.
Allele frequencies can also be affected by chance events that occurred during fertilization.
Overtime, natural selection can increase the match between organisms and their environment and their environment.
If an environment changes, or if individuals move to a new habitat , natural selection may result in adaptation to these new conditions, sometimes giving a rise to the new species.
Biogeography: the scientific study of the geographic distributions of species.
Endemic: Referring to a species that is confined to a specific geographic area.
Darwin described it that in most Islands species are closely related.
Homology: Similarity resulting from common ancestry is known as homology.
Organisms share many characteristics, leading Darwin to perceived unity of life. He attributed the unity of life to the descent of all organisms from ancestor that lived in the remote past.
Problems after birth may cause hybrids to be infertile or may decrease their chance of surviving long enough to reproduce.
Postzygotic Barriers Overcomes prezygotic barriers and fertilizes an ovum from another species, may contribute to reproductive isolation after the hybrid zygote is formed.p
He had also thought the descendants of that ancestral organism lived in various habitats over millions of years, they accumulated diverse modifications or adaptations, that fit them specific ways of life.
Reduced Hybrid Viability: the genes of a different parent species may interact ways that impair the hybrids development or survival in its development.
Reduced Hybrid Fertility: Even if hybrids are vigorous they may be sterile. If the chromosomes of the 2 parent species differ in number or sturcture, meosis in the hybrids may fail to produce normal gametes.
Human cells are receptor meditated endocytosis to take in cholesterol for membrane synthesis and the synthesis of other steriods.
when the vesicle membrane and plasma come into contact , specific proteins rearrange the lipid molecules of the 2 bilayers so that the two membranes fuse together.
Example:Dissolve oxygen diffuses into the cell across the plasma membrane.
Facilitated diffusion
many polar molecules and ions are pumped by the lipid bilayer of the membrane diffusion passively with the help of transport proteins than span the membrane.
Active Transport/ Diffsion:
A solute across a membrane against its gradient reuires work, the cell must expand energy.
Therefore, it enables a cell to maintain internal concentrations of small solutes that differ from concentration in its enviroment
Passive Diffusion:
Or tans;rot, is the diffusion of a substance across a bilogical membrane .
Transduction: ocurs after the reception the cells need to process the cell.
Direct contact can occur between cells that have cell junctions. These junctions allowed direct contact between the cytoplasm od adajacent cells.
Reception: Begins with the signal interacting with a receptor site located on the outside surface of the lasma membrane.
Memranes are more fluid when they contain more unsatturated fatty acids within their phospholipids. more satturated gfatty acids results in increased distance between the lipids.
Cholesterol: Is found in the cell membranes of animals but not plants . It affects the fluidity of the membrane.
They are constructed of a triplet microtubls.
Ceell walls: Most cells hae materials external to the plasma membrane.
Cell walls are found in prokaryotes, plants fungi and some protists.
Plasmodesmata are chemicals between plant cells that allow direct flow from one cells cytoplasm
Centtrosomes: In animal cells microtubles grow out from a centrosome a region that is located near the nucleus and it is considered
They are each composed of nine sets of triplet microtubles arranged in a ring.
Ribosomes: are the qorkbenches for protien synthesis made from RNA.
ATP consists of an organic molecule called adensoine.
The versatality of carbon makes possible the great diversity of organic molecules.
Variation at the molecule level lies at the foundation of all biological diversity.
Most organic compounds contain hydrogen atoms in addition to carbon atoms with O, N and d among others thrown in from tim to time.
HydroCarbons: are orgnic molecules consisting of only carbon and hydrogen componets
CArbon is unparalled to its ability to form large complex and diverse molecules.
Isomers: Are compounds with the same molecular formula but differet structures.
Functional Groups: the componets of organic molecules that are most commonly involved in chemical reactions.
Buffers: are subtances that resist changes in concentration of H+ and OH-0 in a soulution.
C)2 is that main product of a fossil fuel combustion.
Example: As seawater acidifies H+ ions compete with carbonate tons to produce.
The hydrogen atom leaves its electron behind and its transfereed as a proton or hydrogen ion.
A hydrogen bond is not the same as a bonded hydrogen.
Hydrogen bonding occurs when the H of one molecule is attracted to a highly electromagnetic molecule.
A hydrogen bond is between molecules.
A bonded hydrogen is within a watr molecule.
Intra means within the molecule (actual chemical bonds)
It is powered by the redox reactions of the electron transport chain.
Glycolysis releases less than a quarter of the chemical energy in gluecose that can be harvested by ells: most of the energy remains stockpiled in the 2 moecules of pyruvate.
Citric Acid cycle: the pyrvate enters the mitochondrian and it is oxidized to a compound called aceytol CoA.
Cytochromes: The remaining electron carriers between ubniquinone and oxygen are protiens.
The electron transport has several types of cytochromes each a different protien with a slightly different electron carrying heme group.
Their prosynthetic group called, a heame group, has an iron atom that accepts and donates electrons.
Some steps of the glycolysis and the citric acid cylce are redox reactions in which dehydrogenases transfer electrons from substances to NaD+, forming NAD+.
Oxidizing Agent: oxidizes Xe by removing its electron.
Because an electron transfer requires both a donor and an acceptor, oxiditation and reduction always go together
Acetyl CoA: feeds its aceytol group into the citric acid cycle for further oxidatie.
Reduction: is the addition of electrons to another substance.
NAD+: The hydrogen atoms are not transferred directly to oxygen, but instead are usually passed first to an electron carrier .(niicotinamide adenine dinucleotide.)
Some prokayotes use subtances other than oxygen as reactants in a similar process that harvests chemical energy without oxygen. This process is called anarobic respiration.
The cells prokaryotic and Eukaryotic orgamnisms can carry out aerobic respiration .
The segment most importamt to life is the narrow band from about 380 nm to 750 nm in wavelength.
This radiation is also known as the visible light because it can be detected as various colors by the human eye.
Photons: The model of light as waves explains many of the lights properties, but in certain respects light behaves as though it consists of discrete particles.
To convert CO2 to carbonhydrate, the calvin cycle also requires chemical energy in the form of ATP, which is also generated by the light reaction.
The Calvin Cycle is the one that really makes ATP but it can do only with the help of the NADPH and ATP produced by the light reactions.
Carbon Fixation: The initial incorporation of carbon into organic comppunds .
The calvin cycle then reduces the fixed carbon to carbonhydrte by the addition of electrons.
Chlorophyll: The green pigment that gives leaves their color resides in the thylakoid membranes of the thylakoid.
It is the light energy absorbed by the chlorophyll that drives the synthesis of organic molecules in the chloroplasts.
All green parts of a plant have chloroplasts, but leaves are the major sites of photosynthesis in most plants.
Formula for Aerobic Respiration: 6CO2+6H2O+ Light energy----- C6H12O6+ 6O2
The process of photosynthesis imost likely originated in a group of bacteria that had infolded regions of the plasma membrane containing clusters of such molecues
