Photosynthesis is the reverse of Cellular Respiration.

The main end products of respiration are CO2 (carbon dioxide) and water, which are used as the starting material for Photosynthesis, and photosynthesis converts them into glucose and O2 (oxygen).

Photosynthesis is the ultimate source of all energy rich carbon compounds used by all organisms; it is responsible for the continual supply of atmospheric O2 (oxygen), without which all the aerobic organisms, that use oxygen would not exist.

Green plants, algae, some unicellular green flagellates and 2 bacteria groups are the only organisms that photosynthesize. Each year they release half of all the O2 (oxygen) in the atmosphere.

Plants use CO2 (carbon dioxide) when they produce O2 (oxygen). CO2 is converted to O2 during photosynthesis. At the same time, animals through their respiration process use this O2 from their metabolism and replace it with CO2, which is then used by plants to begin the cycle again.

Photosynthesis is a solar powered process. SUNLIGHT is a key component of the process.

Light is a form of ELECTROMAGNETIC ENERGY. When light meets matter, it can be reflected, transmitted or ABSORBED.

PIGMENT absorbs light. Plant pigment, CHLOROPHYLL (the main light-absorbing molecule of green plants), is a pigment that absorbs LIGHT ENERGY.

Chlorophyll is found in specialized structures called CHLOROPLAST; they give plants their green color. Each chloroplast contains all the chlorophyll and enzymes needed to complete the complex chemical reactions of photosynthesis.

Chlorophyll participates directly in LIGHT REACTIONS.

The site of photosynthesis is typically the leaf of green plants. Each cell has about 30 to 40 chloroplast.

The large amount of chlorophyll in the leaves of plants allows it to produce most of their own FREE ENERGY, by using photosynthesis.

Cells of green leaves-> Contain chloroplast organelles-> Filled with chlorophyll molecules-> Absorb light energy during photosynthesis

Photosynthesis involves 2 linked sets of chemical reactions:
1. The 1st is called the LIGHT-DEPENDENT REACTIONS
2. The 2nd set, which does the actual synthesizing of chemicals, is called LIGHT-INDEPENDENT or the CALVIN CYCLE.

In these 2 processes green organisms use energy from sunlight to make sugar.

Photosynthesis = Light-dependent reactions (produce energy) + Calvin Cycle (produce sugar)

– Light-Dependent Reactions are the conversion of light energy into chemical energy.
– In the first set of reactions, the chlorophyll absorbs energy that is striking the plants surface from sunlight. The Light-Reactions absorb the energy of sunlight and converts it to energy that is stored in chemical bonds.
– Once the light is absorbed the electrons of the chlorophyll become excited (a process where an electron gains energy). This energy absorption agitates the electrons within the chlorophyll. Some of these energized electrons are transferred where they can be used by the organism.
– The energy released from the electrons in the chlorophyll is used to do 2 things:
1. Split water molecules. When the water molecule is split, O2 (oxygen) is released into the atmosphere.
2. Make ATP. Some of the energy from the electrons in chlorophyll is used to change ADP to ATP.
– This energy is passed along until it reaches a particular pair of molecules that can process the energy. The energy released by the transferred electrons helps add a phosphate group to ADP, creating more ATP.
– Some of the produced ATP provides energy to run the 2nd stage of photosynthesis, the Calvin Cycle.
– As a result of the Light-Dependent Reactions, water is split and O2 (oxygen ) is given off. The plant uses some of the O2 for CELLULAR RESPIRATION and some is released into the atmosphere.

– The 2nd stage, called the Calvin Cycle, uses the ATP given off by the 1st set of reactions.
– This step involves the storage of chemical energy into sugar molecules.
– It is called a “CYCLE” because it begins and ends at exactly the same point: Carbon Dioxide (CO2) molecules.
– The Calvin Cycle takes place in the chloroplast. The simple inorganic molecules of CO2 (carbon dioxide) is used to make a complex organic molecule.
– In this step, CO2 (carbon dioxide) is chemically reduced from hydrogen ions and turned into a carbohydrate (sugar molecule/glucose).

CO2 (Carbon Dioxide) + H (Hydrogen Ions) = CH2O (Carbohydrate)

– One sugar molecule is to be used by the plant cell.
– Many plants make more sugar than they need; this sugar is converted to starch and stored in the roots, tubers and fruits of plants, food that other organisms eat.
– Most organisms need the food manufactured by green plants in the process of photosynthesis.

The following reaction summarizes the chemical process of Photosynthesis:

6 CO2(Carbon Dioxide) + 6 H2O(Water){REACTANTS} -> C6 H12 O6(Glucose) + 6 O2(Oxygen) + 6 H2O(Water){PRODUCTS}


Cellular Respiration

Where does the energy come from that power the recharging of the ATP molecule?

Cellular Respiration is a chemical process that occurs in all living cells, when trapped energy in the bonds of food molecules are converted to the stored energy in ATP molecules.

Cellular Respiration is a series of chemical reactions that frees the energy in food molecules, making it available to cells.

The chemical process of Cellular Respiration starts when a food molecule (i.e. glucose) enters the cell and is acted upon by the enzymes in the cytoplasm of the cell.

The steps of Cellular Respiration are controlled by ENZYMES.

This process takes place in the MITOCHONDRIA, in the presence of oxygen and is called AEROBIC RESPIRATION (oxygen requiring).

Respiration is generally defined as OXYGEN-REQUIRING; but respiration can also occur WITHOUT OXYGEN (ANAEROBIC RESPIRATION).

There are 2 steps to the Cellular Respiration Process:
– Glycolysis is the 1st series of chemical reactions in cellular respiration, in which glucose is converted to pyruvic acid.
– The entire process can take place whether or not oxygen is present. So Glycolysis is sometimes referred to as ANAEROBIC RESPIRATION.
– It is a series of reactions that take place in the CYTOPLASM of the cell.
– Each chemical reaction is catalyzed (to cause an action to begin) by an enzyme.
– The chemical reactions of glycolysis are anaerobic, because they occur without oxygen.
– All organisms can carry on glycolysis.
– Once GLUCOSE is present in the cell, its chemical bonds are broken down by glycolysis, with the help of enzymes, releasing free energy to make ATP.
– Glucose is not the only cellular fuel. ALL SIMPLE SUGARS in the diet are catabolized (process by which complex substances are converted to simpler compounds) and used in cellular respiration.
– To break down glucose, a small amount of energy is needed to get the reactions started, 2 ATP molecules supply this energy.
– In the initial reaction a glucose molecule is broken up into 2 new molecules of PYRUVIC ACID.
– Energy is released as the bonds of the glucose are broken to produce the 2 pyruvic acid molecules.
– During glycolysis one 6-carbon glucose molecule is broken down into two 3-carbon (pyruvic acid) molecules. Two ATP molecules are also produced.
– (1) 6-carbon glucose molecule -> (2) 3-carbon (pyruvic acid) molecules + (2) ATP molecules
– After the process of glycolysis has occurred, only about 10% of all available energy within the glucose molecule has been used.
– More energy can be extracted from the molecule, by using AEROBIC RESPIRATION.
– The KREB CYCLE is the aerobic process of cellular respiration.
– If oxygen is not present, the final product of glycolysis, PYRUVATE, is FERMENTED into ethanol and lactate.

2. There are 2 stages to AEROBIC RESPIRATION

– The 2 pyruvic acid molecules enter the Krebs cycle.
– The Krebs cycle takes place in the MITOCHONDRIA of the cell, where the enzymes that run the reactions of the Krebs cycle are located.
– The Krebs cycle is a repeating cycle of aerobic reactions that breakdown the pyruvic acids produced by glycolysis.
– The Krebs cycle rotate twice, once for each of the pyruvic acid molecules and produces 2 ATP molecules, several CO2 (carbon dioxide) molecules, and HYDROGEN-CARRIER MOLECULES.
– The hydrogen-carrier molecules move to the ELECTRON TRANSPORT CHAIN in the mitochondria.

– The molecules of the electron transport chain carry high-energy electrons from the hydrogen atoms down to lower and lower energy levels, releasing considerable amounts of energy along the way.
– A total of 34 more ATP molecules are produced from the electron transport process. The electron transport chain does not produce ATP directly, it produces a PROTON.
– The transported electrons, now deplete of most of their energy, are transferred to an OXYGEN ATOM.
– The oxygen atom combines with 2 hydrogen ions an creates WATER (H2O).
– C6 H12 O6 + 6 O2 -> 6 CO2 + 6 H2O + 36ATP
Glucose + Oxygen -> Carbon Dioxide + Water + Free Energy

When there is no oxygen available to complete the breakdown of glycolysis (the Krebs cycle requires oxygen) fermentation occurs.

Fermentation is the chemical release of energy from food without the use of oxygen.

The chemical process of fermentation does not release any more energy from the food (like the Krebs cycle and the electron transport chain) it only frees up molecules for continued respiration.

The process of converting pyruvate into ethanol and lactate is called fermentation.

Cellular Energy

Energy is the ability to do work.

All cells get their energy from their metabolism (food).

Energy required for motion is called KINETIC ENERGY.

Stored energy is called POTENTIAL ENERGY.

Energy can neither be created or destroyed (the 1st LAW OF THERMODYNAMICS), so the amount is always constant (the same).

Energy can be converted from one form to another. When energy is converted from one form to another, some of the energy ends up as heat (the 2nd LAW OF THERMODYMANICS).

– ATP is a molecule present in living organisms, it shuttles energy within the cells.
– ATP is one of the major energy-providing molecules that initiates biochemical reactions throughout the body.
– It is a source of potential chemical energy for most enzyme reactions.
– In the cell’s mitochondria, ATP is constantly generated from food.
– All chemical reactions are the transfer of energy from one molecule to another.
– The chemical bonds connecting each phosphate molecule to the adenosine molecule hold energy.
– Energy is stored when bonds are formed to connect a phosphate molecule to an adenosine molecule. When these bonds are broken the energy is released.
– When a cell needs an ATP’s molecules energy, the last phosphate group breaks off and the energy in the bond is released for use by the cell.
– ATP molecules bind to chemicals within the cell that need the energy. This ensures that the energy is transferred from the ATP molecule to the proper place for use.
– Specialized proteins, called ENZYMES, use the energy released from ATP to do all the work of the cell.
– Enzymes are important biological catalysts; they function in lowering the activation energy needed for chemical reaction to occur.
– Enzymes are neither changed nor used up in the reaction.

– Once the ATP molecule has released energy by breaking off a phosphate molecule, the ATP molecule only has 2 phosphate molecules and is called ADP (ADENOSINE DIPHOSPATE).
– ADP is like an uncharged battery, it has no energy.
– ADP can have another phosphate molecule join it and become an ATP molecule again.

Types of Tissue

Tissues are groups of cells with a common structure and function.

They work together to perform a particular task.

– Organs are a collection of 2 or more of the basic body tissue types.
– Multiple tissues adapt as a group to perform specific functions and form structures called ORGANS.

– A collection of 2 or more of the organs that together perform some complex body function.
– The human body is a cooperative of organ systems that are interdependent upon one another, either chemically or physically.

There are 4 main CATEGORIES OF TISSUE:
1.  EPITHELIAL TISSUE (covers and lines the body)
2.  CONNECTIVE TISSUE (binds and supports other tissue)
3.  MUSCLE TISSUE (is involved with movement)
4.  NERVOUS TISSUE (forms a communication network)


Epithelial tissue is covering and lining tissue, it covers body surfaces in general and lines cavities within the body.

It has little or no intercellular material between its cells.

The free surface of this tissue is exposed either to air or fluid.

The base of the cell is attached to a BASEMENT MEMBRANE (a dense layer of extra cellular material).

The cells are closely joined and may act as a barrier against injury, microbial invasion or fluid loss.

These cells may be specialized for absorption or secretion of chemical solutions.

Epithelial tissue is categorized by the number of LAYERS and the SHAPES of the free surface of the cells.

LAYERS can be:
1. SIMPLE: one layer of cells.
2. STRATIFIED: multiple tiers of cells.
3. PSEUDOSTRATIFIED: one layer that appears multiple because the layers vary in length.

SHAPES include:
SIMPLE SQUAMOUS epithelial tissue is thin and leaky.
– These cells aid in the exchange of material by diffusion.
– They line blood vessels and air sacs in the lungs.
STRATIFIED SQUAMOUS tissue regenerates rapidly near the basement membrane.
– New cell are pushed to the free surface as replacements for the cells that are continually sloughed off.
– Stratified Squamous tissue is located on surfaces that are subject to abrasion, like the outer skin.

– They are like a cytoplasm filled water balloon.
– They are found where secretion or active absorption of substances is an important function, like the intestines, where they secrete digestive juices or absorb nutrients.
STRATIFIED COLUMNAR epithelial tissue line the inner surface of the urinary bladder.
PSEUDOSTRATIFIED CILIATED COLUMNAR epithelial tissue line the nasal passage.

SIMPLE CUBOIDAL epithelial tissue is specializes for secretion.
– They can be found in the kidney tubules, the thyroid gland and the salivary glands.


Connective tissue binds and supports other tissue.

It has a sparse cell population scattered throughout an extensive extracellular matrix;  it has a lot of intercellular material between its cells.

The matrix contains long, slender rods and connective tissue fiber in a substance similar to soft-set gelatin.

This fiber helps connective tissue to do its job, to directly or indirectly connect body parts together.

3 types of FIBERS make up the various types of connective tissue:
– They are bundles of fibers containing 3 collagen fibers each.
– These fibers are strong and resist stretching.
– The parallel lines on the palm of your hand are collagen bundles.

– They are long threads of the protein, elastin.
– If stretched, this tissue can return to its original shape.

– They are branched and tightly woven.
– They join connective tissue to neighboring tissue.

There are 6 CATEGORIES of connective tissue:
– Contains all 3 fiber types; collagen, elastin and reticular.
– Holds organs in place and attaches the epithelium to underlying tissue.
– Contains 2 types of cells:
1. FIBROBLASTS: secrete proteins of extracellular fibers, like collagen.
2. MACROPHAGES: act as the “attack dogs” of the body’s immune system.

– It is a loose connective tissue that is specialized to store fat.
– The fat is stored in adipose cells distributed throughout its matrix.
– Each adipose cell stores one fat droplet, which can vary in size.
– The stored fat insulates the body and is used for fuel when needed.

– Large numbers of collagenous fibers in parallel bundles makes this tissue very dense.
– This density gives it the great strength needed for tendons (to attach muscle to the bone) and ligaments (to attach bone together at joints).

– It is the strong and flexible connective tissue found in the skeleton of all vertebrate embryos.
– Most vertebrates convert the cartilage to bone, but they retain cartilage in the nose, ears and trachea.
– It is composed of collagenous fibers embedded in chondroitin sulfate (a protein-carbohydrate).

– Bone is hard, but not brittle or completely solid.
– It is mineralized connective tissue.
– OSTEOBLASTS (bone-forming cells) deposit a matrix of collagen and calcium phosphate that hardens into the mineral hydroxyapatite.

– Blood is the only liquid connective tissue in the body.
-It is a liquid extracellular matrix of plasma containing water, salt and proteins.
– Blood contains RED BLOOD CELLS (that transport oxygen), WHITE BLOOD CELLS (for the immune system) and PLATELETS (which are cell fragments that help in the clotting of blood).
– Blood cells are made in the red marrow of long bones.
– Blood vessels and nerve cells occupy slender canals in the bone tissue call HAVERSAIN CANALS.


There is more muscle tissue available in the human body than any other type of tissue.

It consist of long, slender muscle fibers, that contract or shorten to create body movement.

There are 3 types of muscle:
– It is multinucleated and is usually attached to bones by tendons.
– Contractions are voluntary.
– This muscle appears striated under the microscope.

– It is found in the walls of the internal organs and arteries.
– The spindle-shaped, uninucleated cells contract involuntarily.

– It is located only in the wall of the heart.
– The cells are striated, uninucleated, and are joined by intercalated disks.
– Contractions are involuntary.

– It is the major tissue for communication and control within the body’s internal environment.
– It is designed to sense stimuli.
– It communicates by means of NEURONS (nerve cells).
– The neuron conducts impulses or bioelectric signals.
– It transmits signals from one part of the organism to another.

Cell Division (Cellular Reproduction) Part 4 of 4

– Prokaryote cells represent the most primitive living form of cells.
– They divide in a less complex manner the Eukaryote cells, called BINARY FISSION.
– It is not enough to just divide in half; each cell must pass along its’ genetic information to future generations of cells.
– When a cell reproduces, each daughter cell must receive a complete copy of all of the essential genetic material.
– Before a cell divides, the parent cell produces a copy of all the required genetic information. This duplication of the genetic material is called REPLICATION.
– Prokaryote cells have one circular chromosome, prior to cell division, the single chromosome replicates. The 2 strands move to opposite ends of the cell.
– The cell doubles in size, the plasma membrane grows inward, producing a new cell wall as it goes.
– When the new cell wall is in place it “pinches” off and the cell divides into 2. Producing 2 genetically equal daughter cells. Each daughter cell contains a entire set of genetic material.
– Binary Fission is fast, under ideal conditions it can be completed in 20 – 30 minutes.

Cell Division (Cellular Reproduction) Part 3 of 4


The exchange of genetic material between two cells is a sexual union.

Cells exchange or mix their genetic material together, producing unique, yet related cells.

The exchange is accomplished by a sexual union of 2 cells that separate after the genetic exchange occurs.

The process of genetic-recombination between 2 cells is know as CONJUGATION.

GAMATES are the sex cells found in multicellular sexual organisms. There are 2 types of sex cells, MALE and FEMALE.

Sex cells divide in a special process called MEIOSIS.

Meiosis is a longer process than mitosis.

Meiosis only occurs in the germ cells (gametes) of sexually reproducing organisms.

Meiosis is a process of cellular division where the genetic material is reduced by half in the newly created cells.

Sex cells have half the number of chromosomes as the DIPLOID CELL (all cells that have a full number of chromosomes are called diploid) or parent cell and are called HAPLOID CELLS.

Meiosis forms 4 haploid cells that contain half as many chromosomes as the parent cells.

When each parent donates half of the chromosomes, the offspring will have the full number of needed chromosomes.

In sexual reproduction, genetic material from the male and female are put together, a process called FERTILIZATION, to produce a new cell, called a ZYGOTE (a diploid cell that has the full number of needed chromosomes). The new cell must have the same number of chromosomes as each parent. Meiosis ensures that each parent donates only half of the needed chromosomes.

Meiosis allows for genetic variability among organisms.

There are 2 divisions in Meiosis and each includes 4 stages; Prophase, Metaphase, Anaphase and Telophase.

The 2 divisions separate attached chromosomes and produce a total of 4 haploid nuclei.

The actions of Interphase, during the cell cycle are the same for sex cells. DNA replication only occurs once during the Interphase before Meiosis I.

Meiosis I is call the reduction division stage because it separates HOMOLOGOUS chromosomes(matched copies of chromosomes) into 2 different daughter nuclei.

1. Prophase I
– The chromosomes begin to coil-up and condense.
– The homologous chromosomes move next to each other, a process called SYNAPSIS. This action forms a four-part structure called a TETRAD, consisting of 2 sets of sister CHROMTIDS (a chromatid is one copy of a doubled chromosome).
– At the time of the synapsis, genetic material may recombine into a new arrangement, a process called GENETIC RECOMBINATION.
– Also during synapsis the chromatids may exchange genetic material, a process called CROSSING OVER. This is another way that the genes are shuffled, ensuring that each offspring has a random combination of traits from both parents.

2. Metaphase I
– The homologous pairs prepare for separation.
– The homologous pairs line-up at the METAPHASE PLATE/equatorial plane (the center of the cell).
– Spindle fibers help move the chromatids into position and attach to the sister chromatids.

3. Anaphase I
– One chromatid from each of the homologous pairs moves toward a separate pole.
– The attached spindle fibers pull the chromatid toward the poles.
– The homologous pairs separate with sister chromatids remaining together.
– As a result each daughter cell will have half the number of chromosomes of its parent cell.

4. Telophase I
– During Telophase I there is some uncoiling of the chromosomes. The nuclear membrane reappears and cytokinesis produces 2 daughter cells.
– 2 new daughter cells are formed, with each daughter cell containing only one chromosome of the homologous pair.
– The 2 new daughter cells each have half the number of chromosomes of the original parent cell.
– Even though the chromosome number is halved, there is still double the amount of chromosomes necessary for the final product. This is why the cell undergoes the 4 stages; prophase, metaphase, anaphase and telophase, one more time in MEIOSIS II.
– Meiosis II reduces the sister chromatid to a single chromosome.

A brief period of rest called INTERKENSIS separates Meiosis I from Meiosis II.

It is sometimes called INTERPHASE II, however no DNA is replicated, because the chromosomes are already doubled.

The 2nd stages of Meiosis are called; Prophase II, Metaphase II, Anaphase II and Telophase II.

These 4 stages ensure that each of the 4 cells created, has a single copy of each chromosome.

Sister chromatids become separated into different nuclei during Meiosis II.

1. Prophase II
– The chromosomes condense and move toward the equatorial plane (the center of the cell), where the centromeres will attach to the spindle fibers.

2. Metaphase II
– The chromosomes line-up along the metaphase plate/equatorial plane.
– The chromosomes attach to the spindle fibers and are moved into position at the center of the cell.

3. Anaphase II
– The centromeres split and the sister chromatids move toward opposite poles.

4. Telophase II
– The chromosomes unwind, the nuclear membrane reforms and the cell divides.
– Cytokinesis ends the process with 4 separate haploid cells forming.
– Both cells from the beginning of Meiosis II were products of a single cell that began at the start of Meiosis I. Since both of these cells divided again, the end result of Meiosis is: From one cell we get 4 cells.
– Each of the 4 cells is a haploid cell (a cell with half the number of chromosomes).

Cell Division (Cellular Reproduction) Part 2 of 4


Division of Eukaryote cells involves a series of steps that are different from the process that Prokaryote cells go through to divide, a process called BINARY FISSION.

Cell division is more complicated in Eukaryote cells. The cells are larger and more complex.

The material must be distributed evenly and each daughter cell must have a new nuclear membrane.
Cell division may occur by either mitosis or meiosis, depending on what type of cell is involved.

All one cell organisms reproduce by mitosis.

Mitosis is used by multicellular organisms for growth and repair of all its cells, except sex cell or GAMATES.

The division of Eukaryote cells into daughter cells occurs in 2 stages:
– 1. The nuclear contents are divided by mitosis or meiosis, a process called KARYOKINESIS.
– 2. The cell division of the rest of the cell, a process called CYTOKINESIS.


Mitosis is the process where the genetic material of the cell is equally divided into 2 complete cells.

Mitosis is divided into 4 stages; PROPHASE, METAPHRASE, ANAPHASE and TELOPHASE.

1. Prophase
– Prophase is the longest stage of Mitosis.
– For cell division to occur, the already replicated chromosome must be pulled apart.
– The chromosome that was doubled during S phase of Interphase, begins to coil, thicken and shorten, in order to be more easily moved during the process of cell division.
– A chromosome at Prophase becomes “X” shaped. It consists of joined CHROMITIDS, which are the doubled DNA structures from the S phase of Interphase.
– The structure that joins the chromatids is called a CENTROMERE.
– While the chromosomes are recoiling (pulling apart), the nucleoli and nuclear membrane are disappearing.
– At the same time spindles are forming that will help to align and move the chromosomes.
– The CENTRIOLES being to move to opposite ends of the cell.
– The centrioles line-up long, thin, wire-like structures called SPINDLE FIBERS across the length of the cell. (These spindle fibers will help line-up the chromosomes during the next phase of mitosis, Metaphase).
– The chromosomes move toward the middle of the cell.
– By the end of Prophase the nuclear membrane is broken down.

2. Metaphase
– In Meta phase the doubled chromosomes line up at the center of the cell.
– The centromeres divide in two.
– Metaphase last only as long as the chromosomes remain lined-up along the center of the cell.

3. Anaphase
– In Anaphase the 2 complete sets of chromosomes being to move toward opposite corners (poles) of the cell.
– Each chromosome appears to be dragged along by its centromere, which is attached to a spindle fiber.
– The division of the cytoplasm, or CYTOKINESIS, begins at the end of Anaphase.

4. Telophase
– Telophase is the last stage of mitosis.
– The chromosomes reach their respective sides (poles) of the cell. While this is occurring the cell’s plasma membrane pinches in from both sides, enclosing the chromosomes, creating two separate cells.
– The chromosomes then uncoil and the nucleus reappears.

Mitosis ends when the new daughter cells go their separate ways.

Cell Division (Cellular Reproduction) Part 1 of 4

The ability of all life to replicate itself for future generations originates in the reproduction of cells.

All cells arise from other cells.

Cells have a limited life span.

During cell division, one cell becomes split into 2 cells. The original cell is called the PARENT CELL. The 2 cells resulting from the division are called DAUGHTER CELLS.

– The cell cycle is the entire lifespan of a cell, starting with its production from a previous parent cell and ending with its division into 2 new daughter cells.
– Compared to the rest of the cells’ life, cell division is a brief and distinct stage in the cells’ life.
– The cell cycle is composed of an orderly sequence of phases that are controlled by the DNA of the cells’ nucleus.
– It is composed of an INTERPHASE where the cell is growing larger and replicating its DNA. Then there is nuclear division, called MITOSIS, that has 4 stages; prophase, metaphase, anaphase and telophase. Mitosis ends with the division of the cell into 2 separate daughter cells.

– Interphase is not part of cell division. It is a stage when the cell is growing, metabolizing and replicating its DNA.
– All cells spend most of their lives (about 90%) in Interphase. Some cells never leave the stage of interphase.
– Interphase provides enough time for the cell to grow large enough to eventually divide into 2 daughter cells.
– Interphase is divided into 3 stages; G1 phase, S phase and G2 phase.

1. G1 phase or Gap phase
– The cell experiences growth in volume and carries on its normal processes.
– If centrioles (small granules outside the nuclear membrane) are present, they begin to replicate.
– It is the longest phase.

2. S phase
– During Interphase the nucleus exist as a distinct organelle, bound by the nuclear membrane.
– Inside the nucleus are long, thin, unwound strands of chromosomes. These chromosomes influence the activity of the cell.
– This single set of chromosomes replicates itself.
– The genetic information (DNA) is doubled, providing the correct amount of this material for equal distribution during cell division.

3. G2 phase
– In the final stage of Interphase, the nucleus is still well defined.
– Replication of the centrioles is completed.
– The spindle apparatus that helps move the chromosomes during mitosis begins to be assembled.
– The cell chemically prepares for the cell division by replicating organelles and creating the chemicals needed for the actual division process.

Types of Transport: Movement through the Cell Membrane

Transport systems within the cell are like a highway system, they provide for the constant movement of molecules, in and out of the cell.

Transport systems are needed because the cells membrane is “selectively permeable”. Some molecules can pass through (permeate) the cell membrane, while others cannot.

– Because cells naturally move and collide, passive transport requires no energy to move molecules into or out of the cell.
– They move on their own.

1. DIFFUSION (Simple)
– The movement of molecules from an area where they are highly concentrated to an area where they are less concentrated or more spread out.
– Molecules move across the cell membrane from an area of high concentration to an area of low concentration. It stops when the concentration is evenly distributed or equal.

– It is simple diffusion of water ONLY.
– -OSOMOTIC PRESSURE (the pressure exerted by dissolved particles in water) moves the water across the cell.
– Water moves from where the osmotic pressure is low to where the osmotic pressure is high.
– The osmotic pressure is always working to make the solution on both sides of the cell membrane equal.
– When two solutions of different concentrations are compared the solution with the higher concentration is called HYPERTONIC and the solution with the lower concentration, HYPOTONIC. When two solutions have the same concentration they have EQUILIBRIUM.
– Equilibrium: when the osmotic pressure is equal on both sides. When the osmotic pressure is the same on both sides of the cell membrane it is ISOTONIC or ISOSMOTIC. Both sides of the cell membrane have the same amount of particles and pressure, so there is no movement on either side.
– HYPERTONIC or HYPEROSMOTIC: when a cell is in an area of higher concentration. A higher osmotic pressure is placed on the cell, so the water will move out of the cell into the surrounding area.
– HYPOTONIC or HYPOOSMOTIC: when a cell has a higher concentration of particles inside the cell then are in the solution that the cell is in. The water will move into the cell to try to make both sides of the membrane equal.

– It is diffusion that is helped by the use of protein carrier molecules.
– It works in both directions, in and out of the cell.
– It is similar to simple diffusion, but it allows larger molecules, that need extra help to get across the cell membrane.
– Ex: Glucose molecules are too large to cross the cell membrane. So a glucose carrier protein, that is located in the cell membrane, combines with the glucose molecule and helps it cross the cell membrane.
– The molecule is picked up on the one side of the membrane and released on the other side.

– Movement of molecules, which do not normally move in this direction, from an area of low concentration to an area of high concentration.
– The cell must use energy to move these molecules.
– Like facilitated diffusion, active transport uses protein carrier molecules.
– The active transport system uses the high energy molecule (ATP) ADENOSINE TRIPHOSPHATE.
– ATP is split during active transport providing free energy to power the transportation process.

– A way for cells to move very large molecules into a cell.
– The cell membrane surrounds the molecule and forms a vacuole. The vacuole will move the molecule into the cell.

– The active transport that moves molecules out of a cell.
– The molecule is surrounded and pushed out of the cell.
– This process is the exact reverse of endocytosis.

Cell Structure

All cells have a similar structure.

The small structures found in cells are called organelles.

– It is the control center of the cell, it tells the cell what to do.
– It is found in both plant and animal cells.
– It contains the genetic information of the cell.
– Reproduction of DNA and RNA takes place in the nucleus.
– It controls the chemical activities that take place in the cell.

CELL MEMBRANE (also called the Plasma Membrane)
– It is made up of proteins and lipids
– It is a structure that surrounds the cell and controls the flow of material into and out of the cell.
– It helps regulate the flow of materials in and out of the cell. Smaller particles can pass through the membrane and larger particles can’t.
– It defines the size and shape of the cell and provides protection and strength to the cell.

CELL WALL (found in plants, bacteria and fungi)
– It is a supportive, protective structure that surrounds the cell membrane.
– Materials can easily pass through this wall.

– It is a gel-like substance that fills the entire cell’s volume.
– All of the other organelles live in the cytoplasm.
– It is made up of 90% water, sugar, amino acids and salts.
– It provides a liquid environment for chemical reactions to take place.
– All of the cells chemical reactions take place in the cytoplasm.

– It is the collection of membranes that form channels throughout the cytoplasm.
– It is a tiny network in the cytoplasm that carries materials around the cell, like a miniature highway system.
– The channels separate sections of the cell where specific chemical reactions take place.
– The surface of the channels provide space for enzymes to perform chemical reactions.
– The channels also help move chemicals to their destinations inside the cell.
– There are 2 types of endoplasmic reticulum:
– 1. ROUGH ENDOPLASMIC RETICULUM (It is lined with protein ribosomes on it’s surface. The ribosomes are where protein is synthesized).
– 2. SMOOTH ENDOPLASMIC RETICULUM (It has no ribosomes. It is where lipids are synthesized).

– They are the smallest organelle in the cell.
– They are tiny granules that can exist as free floating organelles in the cytoplasm or on the surface of the rough endoplasmic reticulum.
– They are the site of protein synthesis.
– They are involved in building proteins from amino acids.
– They usually exist in two parts; they come together when it is time to work.
– They contain 3 main types of RNA.
– The RNA found in the ribosomes function in protein synthesis and is called rRNA (ribosomal RNA).

– They are made up of stacks of flattened membranes that package chemicals for removal from the cell.
– They function in areas of the cell where the products of the endoplasmic reticulum, like proteins or lipids are stored and packages for transport to their final destination outside the cell.
– The proteins and lipids are enclosed in small membranes for travel.
– It is the site of protein modification into more complex molecules.

– They are a bag-like structure in the cytoplasm.
– They store food in both plant and animal cells.
– They are usually large in plants and small in animals.
– They store water and other nutrients used by plant and animal cells.
– Different kinds of vacuoles have different functions, ex: some store sap (maple, pine trees) others store toxins.

– They are single layered membrane-enclosed storage vesicles that contain digestive enzymes.
– It dissolves large food molecules and breaks up old and damaged cell structures into the organic molecules that they are made of. These molecules are then reused by the cell.

– It is the power house of the cell, where aerobic respiration and energy production take place.
– It is often one of the largest organelles in the cytoplasm.
– It is found in both plant and animal cells.
– It contains DNA and ribosomes, it is semi-autonomous and it can replace itself.
– It is enclosed in a double membrane.
– The smooth outer membrane is highly permeable to small items but it blocks the passage of larger items.
– The inner membrane has many folds that have enzymes that help with cellular respiration.
– It is oval shaped and contains the enzymes to aid the cell in getting energy from food.
– It converts food to usable energy,
– The energy released from food is stored in a high energy molecule called ATP (adenosine triphosphate).
– ATP supplies the cell with chemical energy.

– It is the skeleton of the cell, it gives the cell its rigidity and support.
– It consist of hallow microtubules and solid microfilaments.
– They are the support structures of the cell; they support the shape of the cell, like a skeleton.
– They are small, thin support tubes that cross the inside of the cell membrane to membrane.
– They have many functions, including movement (cell mobility) and the separation of chromosomes during cell division.
– They are tiny threads of long protein fibers.
– They provide cellular support, when they combine with other proteins.
– They participate in muscle contractions.
– During cell division they form a ring that pinches the cell in 2.