Cell Proccess
Photosynthesis
Photosynthesis: The conversion of light energy to chemical energy that is stored i sugars or other organic compounds. Occurs in lants, algae, and certain prokaryotes.
There is a reciprocal relationship between chemoheterotrophic nutrition and photoheterotrophic nutrition.
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
Formula for Photosynthesis is 6o2+ 6h2O----- C6H12O6 + 602
Aerobic Respriation: The netabolic process of which most living cells or things which food turns into usable things like ATP or Gluecose.
Formula for Aerobic Respiration: 6CO2+6H2O+ Light energy----- C6H12O6+ 6O2
Mesophyll: The tissue in the interior of the leaf.
This is where the chloroplast is mostly found at in the mesophyll.
All green parts of a plant have chloroplasts, but leaves are the major sites of photosynthesis in most plants.
Stroma: An enveelope of two membranes surrounding a dense fluid.
Suspended within the stroma is a third membrane system., made up sacs called Thylakoids.
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.
Photophosophorylation: The light reactions generates ATP using chemeosis to power the addition of phostate group of ADP.
The light reactions use solar power to reduce NADP+ to NADPH by adding a pair of electrons along with an H+.
Calvin Cycld Synthesis part of photosynthesis.
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.
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.
Wavelength: The distance between the crests of electromagnetic waves.
Wavelengths range from less than a nanometer to more than a kilometer.
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.
Electromagnetic Spectrum: The entire rnge of radiation.
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.
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Celluar Respiration
Celluar Respiration includes both anarobic and aerobic processess.
Aerobic Respiration: The most efficient catabolic pathway in wcih oxygen is consumed as a reactant along with organic fuel.
The cells prokaryotic and Eukaryotic orgamnisms can carry out aerobic respiration .
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.
Fermentation: It is the partial degradation of sugars or other organic fuels that occurs without the use of oxygen.
Redox Oxidation: A transfer of one or more electrons from one reactant to one another.
Oxidation: The loss of electrons from one substance .
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.)
Reducing Agent: reduces the Y which accepts the donated electgron.
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.
Not all redox reactions involve the complete transfer of electrons from one subtance to another , some change the degree of electron sharing in covalent bonds.
Electron Transport chain: Consists of a number of molecules, mostly protiens , built into a the inner membrane of the mitochondria of eukaryotoe cells and the plasma membrane of aerobically respring prokaruotes.
Electron Transfer from NADH to oxygen is an exergomic reaction with a free-energy change.
Glycolysis: Occurs in the cytosol , begins the dehydration process by breaking gluecose into 2 molecules of a compound called pyruvate.
Citric Acid cycle: the pyrvate enters the mitochondrian and it is oxidized to a compound called aceytol CoA.
Some steps of the glycolysis and the citric acid cylce are redox reactions in which dehydrogenases transfer electrons from substances to NaD+, forming NAD+.
Cytochromes: The remaining electron carriers between ubniquinone and oxygen are protiens.
Their prosynthetic group called, a heame group, has an iron atom that accepts and donates electrons.
The electron transport has several types of cytochromes each a different protien with a slightly different electron carrying heme group.
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.
Substarte Level phosphorylation:: The smaller amount of ATP is formed directly in a few reactions of glycolysis and in the citric acid cycle.
Oxidative Phosphorylation: The mode of ATP synthesis.
It is powered by the redox reactions of the electron transport chain.
The mode of ATP synthesis occurs when an enzyme transfer a phospahte group from a substarte molecule to ADP, rather than adding a inorganic phosphate to ADP as an oxidative phosphorylation.
ATP Synthase: The enzyme that actually makes ATP from aDP and inorganic phosphate.
It works like an ion pump , it usually works ATP as an energy soruce to transport ions against their gradeints.
Chemeosis: The process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive celluar work such as the synthesis of ATP synthase.
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BioChemistry
Water and fitness of the eniviroment.
Inner means between molecules.
Intra means within the molecule (actual chemical bonds)
Hydrogen Bonding: A special case of dipole IMFS.
In living cells, the electromagnetic partners are usually oxygen or nitrogen atoms.
A hydrogen bond is not the same as a bonded hydrogen.
A bonded hydrogen is within a watr molecule.
A hydrogen bond is between molecules.
Hydrogen bonding occurs when the H of one molecule is attracted to a highly electromagnetic molecule.
Collid: is a stable suspension of fine particles in a liquid.
A bonded hydrogen atom within a water molecule can shift between 2 water molecules ( from one molecule to another).
The hydrogen atom leaves its electron behind and its transfereed as a proton or hydrogen ion.
Concentration of H+ and OH- are equal in pure water.
ZAn acid in any substance that increases the H+ concentrationj of a soulution.
A base is any substance that reduces the H+ concentration of a soulution.
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.
CArbon and Molecular Diversity
Living organisms consist mostly of carbon based compounds.
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.
Organic compounds range from simple molecules to colossal ones.
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
One phosphate molecule adenosoine triphostae (ATP) is the primary energy that is transferring molecule in the cell.
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.
Cell Parts/Structure
Prokaryotic: Cells without a nucleus or membrane bound organelles
Both eukaryotic and prokaryotic cells are limited.
Eukaryotic: Cells with a nucleus and membrane bound organelles
Nucleus: The dark straining object in the nucleus .
Golgi Apparatus
It modifies the protiens from the endoPlasmic reticulum.
Manufactures certain poly sacchrides.
Contributing to the plasma memebrane.
There is a flow or connection or organelle membranes in the formation of lysosomes.
Vacuoles and vesicles are membrane bound compartments used for storage.
Mitochondria used to phosphate ADP to ATP (energy).
Plastids: located in the chloroplast , it is responsible for photosynthesis
Leukoplast responsible for storage of starch.
A stack of thylakoids is a granum . The matrix is found around the stroma.
Ribosomes: are the qorkbenches for protien synthesis made from RNA.
Both flagella and cilia are covered with the plasma membrane.
Cilia: The nicrotuble contaning extensions that project from some cells.
Flagella: A specialized of arrangement of microtubles.
Centrioles: Functions as a compression resisting girders of the cytoskeleton.
They are each composed of nine sets of triplet microtubles arranged in a ring.
Centtrosomes: In animal cells microtubles grow out from a centrosome a region that is located near the nucleus and it is considered
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
Cell membranes is a dynamic and intriate structure that regulates material transported across the membrane.
All cells have plasma membranes and many of their organelle also have membranes . All membranes are made from a bilayer of phospholipids.
Phospholipids have the ability to move laterallt ut only upon a rare occasuon are able to move also from it.
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.
Cell Communication:
Local Signaling
Paacrine signaling invates a cells of a chemical that indues the difference or behalf
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.
Transduction: ocurs after the reception the cells need to process the cell.
Cell Transport
Cell membranes are permeable tospecific ions and a variety of polar molecules.
These hydrophillic substances can avoid contact with the lipid bilyer by passing through transport protiens.
Some transport protiens , called channel protiens , functions by having a hydrophilic channel that certain molecules or atomic ions use as tunnel through the membranes .
Aquaporins: molecules through the plasma membrane of certain cells is greatly by channel protiens.
Most aquaporins proteins are consisted of 4 identical subunits.
Diffusion: The movement of particles of any substance so that they tend to spread out into the available space.
2 types of diffusion.
Passive Diffusion:
Or tans;rot, is the diffusion of a substance across a bilogical 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
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.
Concentration Gradient: The region along which the density of a substance increases or decreases.
When a substane is more concentrated on one side of a membrane than on the other, there is a tendacy for the substance to diffuse across the membrane down its concentratio gradient.
Example:Dissolve oxygen diffuses into the cell across the plasma membrane.
Exocytosis: The cell secretes certain bilogical molecules by the diffusion of vesicles with the plasma membrane.
A transport vesicle that has budded from the golgi apparatus moves along microtubules of the cytoskelecton to the plasma membrane.
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.
Endocytosis: takes place in molecules and particular mattr by forming new vesicles from the plasma membrane:
Human cells are receptor meditated endocytosis to take in cholesterol for membrane synthesis and the synthesis of other steriods.
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Evolution
Evolution:tHE PROCESS BY WHICH DIFFERENT KINDS OF LIVING ORGANISMS ARE THOUGHT TO HAVE DEVELOPED AND DIVERSIFIED FROM EARLIER FORMS DURING THE HISTORY OF THE EARTH.
Speciation: The process by which one species splits into 2 or more species.b
Speciation explains the features that organisms share( unity of life)
When a species splits, the species that result share many characteristics because they descended from this common ancestor.p
Speciation had surprised Darwin because it had lead to the tremendous diversity of life repeatedly yielding new species that differ from existing ones.
Natural Selection: a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.
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.
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.
Such losses can influence how efficiently a population can adapt to a change in the environment.
Genetic Drifts can cause harmful alleles to becomes fixed. Alleles that are neither harmful nor beneficial can be lost or become fixed entirely by chance through genetic drift.
Genetic Drift can also cause alleles that are slightly harmful to become fixed. When it occurs, the populations survival can be threatened.
Genetics: Is the study of how heritable traits are transmitted from parents to the offsrping.
Allele frequencies can also change by gene flow, the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes.
Allele frequencies can also be affected by chance events that occurred during fertilization.
Because alleles are transferred between populations, gene flow can result in two populations combining into a single population with a common gene pool.
Allele transferred by gene flow can also affect how well populations are adapted to the local environmental conditions.
Artificial Selection: Selecting and breeding individuals that possess desired traits.
PreZygotic Barriers blocks the fertilization from occuring.
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.
Temporal Isolation: Species that breed during different times of the day, different seasons, or different years can not mix their gametes.
Mechanical Isolation: Mating is attempted, but morphological differences prevent its successful completion.
Homology: Similarity resulting from common ancestry is known as homology
Homologous Structures: Represents variations on a structural theme that was present in their common ancestor.
Comparing early stages of development in different animal species reveals additional anatomical homologous not visible in adult organisms.
Mutation: changes in the nucleotide sequence of DNA.
cannot be predicted
most occur in somatic cells and are lost when the individual dies
mutations of the sex cells are the only ones passed to offspring
sexual recombination: produce variations that make adaptations possible- rearranges
alleles into fresh combinations every generation
most phenotypic variation is a result of sexual recombination(allele variation
originates from past mutations)
populations have many possible mating combinations
shuffles alleles but does not change frequencies
Sexual Selection: natural selection for mating success
sexual dimorphism: marked differences between the sexes in secondary sexual
characteristics, which are not directly associated with reproduction
distinctions include differences in size, color and ornamentation
in vertebrates, males are usually the showier sex
intrasexual selelction: selection within the same sex is a direct competition among
individuals of one sex for mates of the opposite sex
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intersexual selection: (mate choice)- individuals of one sex(usually females) are
choosy in selecting their mates from the other sex
usually depends on the showiness of males
female only gains an advantage over other females if she chooses a mate that
enables her to produce more fit offspring
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ecology
Ecology:• Ecology – the Study of Interactions Between Organisms and the Environment
Organisms all live in complex environment that include:
Abiotic components – The nonliving components of the environment such as water, light, temperature, nutrients, soil.
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
Biotic components – the living components of the environment such as other organisms as foods, other resources, or predators.
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 and Bitoic Factors• These environmental factors limit the geographic range (distribution) and the abundance of species.
Behavior and habitat selection – Certain behaviors like mating, reproduction, nest building habits, etc. can eliminate habitats that otherwise would be very suitable. (ex. European corn borer only deposits its eggs on corn although they eat a wide variety of plants)
Ecology is studied on several levels of organization
1: Organism – physiology, evolution, behavior of organisms in relation to environmental factors
2:Population – interactions of individuals of the same species, living in the same environment
3: Community – studies the interactions of all living organisms that are living in the same area
4: Ecosystem – emphasizes energy flow and chemical cycling among organisms and the abiotic environment:
5;Biosphere – includes the entire portion of Earth that is inhabited by life. Studies global effects of climate change, ozone depletion, mass extinction etc.
Dispersal – the movement of organisms from centers of high density or from center of origin to other areas.u
Dispersal can be two kinds:
Natural range expansions – organisms move into previously uninhabited areas as a natural way of expanding the population.
Species transplants – species artificially or accidentally introduced and reproduce in new location.
Climate – Temperature, water, sunlight and wind are the major abiotic components of climate – the prevailing weather conditions in a particular area.
Aquatic Biomes
Biomes – major types of ecological associations that occupy broad geographic regions of land or water.
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 %).
Aquatic biomes are physically and chemically stratified:
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Light intensity decreases sufficiently because water and photosynthetic organisms absorb it.
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
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.
Aquatic biomes can be described by analyzing salinity, oxygen content, organic content, turbulence, light intensity, temperature
Case study on dead zones.
Animal behavior – an action carried out by muscles or glands under control of the nervous system in response to a stimulus. These behaviors are determined by the physiological systems and abilities of the organism.r
Animal behavior is essential part of acquiring nutrients, finding a partner, keeping up homeostasis, raising young, etc.
Because behavior is necessary for reproduction, it also influences and influenced by natural selection. Animal behavior is limited by the given set of genes that animals have but various mutations and changes in behavior can make the population more or less fit to survive in a given environment.
Basics of Animal Behavior-- Animal behaviors can be attributed to two components:
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)
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.
Population – individuals of a species within a given area. They are distributed in space, vary in age and size → population structure.
POPULATION DENSITY AND DEMOGRAPHICS
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.
Patterns of distribution of various populations within a geographic range:
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.
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)
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)
Population Density and Population Change:
Density independent factors – the birth and death rate changes but independently from the size of the population ( natural catastrophy)
Density dependent factors – The birthrate falls with rising density (ex. Lynx population decreases if not enough hares are available)
This is an example of negative feedback mechanism (review)—at increased densities the birth rate declines or the death rate increases or both. Mechanisms that cause this:
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)
Population Dynamics – focuses on complex interactions between biotic and abiotic factors that cause variations in population size.
Over time all populations show fluctuations in 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:
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:
genetics
Sickle Cell Anemia
Bent or twisted shape of the red blood cells.
Causes blood to stop flowing through vessels, thus damaging organs and tissue.
popThe normal allele for hemoglobin is just ONE DNA base change from the sickle cell allele.
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The study of heredity, or how the characteristics of living things are transmitted from one generation to the next. Every living thing contains the genetic material that makes up DNA molecules. This material is passed on when organisms reproduce.
mitosis
interphase
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.
prophase
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.
Mtaphase
The chromosomes are now at the middle of the cell. Spindle fibers
attached to chromatids.
anaphase
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.
mitosis:a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
Subtopic
teleophase
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.
Cytokenis:The cell is divided in two cells and mitosis ends.
In each new cell, the nuclear membrane and other organelles begin to re-assemble and
the chromosomes are 'unwound'.
The result of mitosis is two cells that are identical to each other and the original cell.
Meosis
Meiosis is the type of cell division by which gametes (eggs or sperm) are formed. It
involves two divisions and results in four different daughter cells that have 23
chromosomes. This ensures that, when an egg and a sperm unite during fertilization, the
resulting embryo will have 46 chromosomes - the normal number for a human.
The first meiotic division is called Meiosis I, and the second meiotic division is called
Meiosis II.
Prophase 2: Unlike Prophase I, the chromosomes are not duplicated. Chromosomes
are visible. Sister chromatids are still connected to each other, but thanks
to the process of crossing over (sharing of genetic material), they are no
longer exactly identical.
The centrosomes move to opposite ends of the cell, and microtubules begin
to grow out from them, once again forming a meiotic spindle.
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.
Metaphase 2:
The chromosomes are now lined up along the middle of the cell. Sister
chromatids are attached to microtubules from opposite ends of the cell.
Anaphase 2:The two sister chromatids in each metaphase chromosome are separated
and pulled to opposite ends of the cell. As a result, each of the daughter
cells from Meiosis II ends up with only one copy of each chromosome.
The cell begins to pinch inwards in the middle.
Telpphase 2:
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.
Cytokenis 2:In each new daughter cell, the nuclear membrane and other
organelles begin to re-assemble and the chromosomes are
'unwound'.
The result of meiosis II is four unique daughter cells. Each
daughter cell possesses either a paternal or a maternal copy of
each original chromosome (1 copy each of 23 chromosomes). This
means that each daughter cell possesses only half as many chromosomes as the original
parent cell.