describe how gases(oxygen and carbon dioxide)enter and leave human cells?

Answer 1

Diffusion

The gases move from an area of higher concentration to an area of lower concentration with the help of the hemoglobin in your blood.

When you inhale, the air you breathe is 78% N2 and 21% O2. The air you exhale is 16% O2. That means that there is a higher concentration of O2 in the air coming into your lungs. The hemoglobin in your blood attracts the higher concentration of O2 into the blood - the iron in the hemoglobin "rusts" and joins with the O2.

When the blood reaches the body cells, the concentration of O2 in the blood is higher than the concentration of O2 in the cells. The hemoglobin releases the O2 for it to diffuse into the cells.

At the same time, the concentration of CO2 is higher in the body cells due to respiration occuring there. The CO2 diffuses from the cell to the blood.

The blood carries the CO2 to the lungs. The concentration of CO2 in the air you inhale is lower than the concentration in the blood, so the CO2 diffuses out of the blood and into the air being exhaled.

NOTE:
In the case of CO (carbon monoxide) poisoning, the CO is more attracted to the hemoglobin in your blood than O2 is. The hemoglobin joins with the CO and refuses to carry O2. This is why CO poisoning is so dangerous. You get less and less O2 to the body cells and can die if not treated soon enough.

Answer 2

Oxygen molecules diffuse into the cell, through the cell membrane via the capillaries. Capillaries contain blood which contain red blood cells (erythrocytes). These red blood cells consist of haemoglobin which carries the oxygen molecules (inhaled from the lungs). Carbon dioxide molecules diffuse out of the cell, though the cell membrane, to the capillaries (capillaries are only one cell thick, so diffusion is easy). Haemoglobin also carries the carbon dioxide, back to the lungs (through the alveolar wall) to be exhaled.

Note: Haemoglobin carries 4 molecules of oxygen - O2 (8 atoms of oxygen).

Answer 3

The respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. A diaphragm pulls air in and pushes it out.


The respiratory system consists of the airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. Within the alveolar system of the lungs, molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation. The system also helps to maintain the acid-base balance of the body through the efficient removal of carbon dioxide from the blood.

Answer 4

http://www.awesomescreenshot.com/0182mgvad8

Answer 5

As stated before we breath in "air" which is a solution containing 78% N2 and 21% O2 and about 1% CO2 along with other impurities. The partial pressure of oxygen in the air is higher then that in venous blood, and the CO2 is higher in the venous blood then in the air (actually most CO2 travels as H2CO3 which then breaks down into CO2 and H2O) consequently CO2 diffuse out through the blood-air barrier (wall of the alveoli+basement membrane+ capillary membrane+ membrane of the red blood cells) It is then transported to the peripheral tissue and in the capillary the flow of blood is reduced in ordered to have ample time for the diffuse process. The unloading of CO2 from Hemoglobin is regulated by 2,3-bisphosphoglycerate (2,3-BPG) which increase as O2 utilization increases and helps in the "unloading" of O2 from Hemoglobin. When one O2 is removed it induces a conformational change make it easier and easier for the rest of the oxygen molecules to unload and diffuse into the cells. CO2, a byproduct of cellular respiration diffuse out of the cells (actually much more rapidly then O2) * about 80% – 90% is converted to bicarbonate ions HCO3− by the enzyme carbonic anhydrase in the red blood cells.
* 5% – 10% is dissolved in the plasma and as carbonic Acid (H2CO3.) This then ionizes accounting for a slightly lower pH in venous blood
* 5% – 10% is bound to hemoglobin as carbamino compounds
Because most cell metabolism operates at a constant rate under a given condition, hypoventilation (slow your breathing) results in decreased pH : respiratory acidosis and hyperventilation (increased breathing) expelles the CO2 rapidly and causes respiratory alkalosis (increase in the pH of the blood.)
The respiratory rate is regulated by the dorsal and ventral respiratory centers of the medulla oblongata, this is sensitive to changes in CO2, H+ in the arterial blood, as they increase they stimulate the dorsal and ventral respiratory center neurons to increase there rate of firing and this increase the respirtory rate. It i also regulated by chemoreceptors in the aortic and carotid bodies of the aortic arch and the carotid artery which are sensitive to changes in O2 in key positions (that is the blood which comes immediately out of the Left Ventricle) if the O2 is low this sends and impulse to the medulla to increase the respiration also. These process help to ensure that the levels of O2 and CO2 remain relatively constant in the the circulation which in turn ensures that the cells get their much needed O2.

Answer 6

see in detail about respiration:-
Cellular respiration describes the metabolic reactions and processes that take place in a cell to obtain biochemical energy from fuel molecules. Energy is released by the oxidation of fuel molecules and is stored as "high-energy" carriers. The reactions involved in respiration are catabolic reactions in metabolism.

Fuel molecules commonly used by cells in respiration include glucose, amino acids and fatty acids, and a common oxidizing agent (electron acceptor) is molecular oxygen (O2). There are organisms, however, that can respire using other organic molecules as electron acceptors instead of oxygen. Organisms that use oxygen as a final electron acceptor in respiration are described as aerobic, while those that do not are referred to as anaerobic.

The energy released in respiration is used to synthesize molecules that act as a chemical storage of this energy. One of the most widely used compounds in a cell is adenosine triphosphate (ATP) and its stored chemical energy can be used for many processes requiring energy, including biosynthesis, locomotion or transportation of molecules across cell membranes. Because of its ubiquitous nature, ATP is also known as the "universal energy currency", since the amount of it in a cell indicates how much energy is available for energy-consuming processes.

Aerobic respiration

Aerobic respiration requires oxygen in order to generate energy (ATP). It is the preferred method of pyruvate breakdown from glycolysis and requires that pyruvate enter the mitochondrion to be fully oxidized by the Krebs cycle. The product of this process is energy in the form of ATP (Adenosine Triphosphate), by substrate-level phosphorylation, NADH and FADH2. The reducing potential of NADH and FADH2 is converted to more ATP through an electron transport chain with oxygen as the "terminal electron acceptor". Most of the ATP produced by cellular respiration is by oxidative phosphorylation, ATP molecules are made to the chemiosmotic potential driving ATP synthase. Respiration is the process by which cells obtain energy when oxygen is present in the cell.

36 ATP molecules can be made per glucose during cellular respiration, however, such conditions are not realized due to losses as the cost of moving pyruvate into mitochondria. Aerobic metabolism is more efficient than anaerobic metabolism (which yields 2 mol ATP per 1 mol glucose). They share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. The post glycolytic reactions take place in the mitochondria in eukaryotic cells, and in the cytoplasm in prokaryotic cells.


Simplified Reaction: C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) ΔHc -2880KJ

Glycolysis
Glycolysis is a metabolic pathway that is found in the cytoplasm of cells in all living organisms and does not require oxygen. The process converts one molecule of glucose into two molecules of pyruvate, and makes energy in the form of two net molecules of ATP. Four molecules of ATP per glucose are actually produced; however, two are consumed for the preparatory phase. The initial phosphorylation of glucose is required to destabilize the molecule for cleavage into two triose sugars. During the pay-off phase of glycolysis four phosphate groups are transferred to ADP by substrate-level phosphorylation to make four ATP and two NADH are produced when the triose sugars are oxidized. Glycolysis takes place in the cytoplasm of the cell. The overall reaction can be expressed this way:

Glucose + 2 ATP + 2 NAD+ + 2 Pi + 4 ADP → 2 pyruvate + 2 ADP + 2 NADH + 4 ATP + 2 H2O

Oxidative decarboxylation of pyruvate
Produces acetyl-CoA from pyruvate inside the mitochondrial matrix. This oxidation reaction also releases carbon dioxide as a product. In the process one molecule of NADH is formed per pyruvate oxidized.

Citric Acid cycle/Krebs cycle
When oxygen is present, acetyl-CoA is produced from pyruvate. If oxygen is not present the cell undergoes fermentation of the pyruvate molecule. If acetyl-CoA is produced the molecule then enters the citric acid cycle (Krebs cycle) inside the mitochondrial matrix, and gets oxidized to CO2 while at the same time reducing NAD to NADH. NADH can be used by the electron transport chain to create further ATP as part of oxidative phosphorylation. To fully oxidize the equivalent of one glucose molecule two acetyl-CoA must be metabolized by the Krebs cycle. Two waste products, H2O and CO2 are created during this cycle.

Oxidative phosphorylation
In eukaryotes, oxidative phosphorylation occurs in the mitochondrial cristae. It comprises the electron transport chain that establishes a proton gradient (chemiosmotic potential) across the inner membrane by oxidizing the NADH produced from the Krebs cycle. ATP is synthesised by the ATP synthase enzyme when the chemiosmotic gradient is used to drive the phosphorylation of ADP.

Theoretical yields

The yields in the table below are for one glucose molecule being fully oxidized into carbon dioxide. It is assumed that all the reduced coenzymes are oxidized by the electron transport chain and used for oxidative phosphorylation.
Step coenzyme yield ATP yield Source of ATP
Glycolysis preparatory phase -2 Phosphorylation of glucose and fructose 6-phosphate uses two ATP from the cytoplasm.
Glycolysis pay-off phase 4 Substrate-level phosphorylation
2 NADH 4 Oxidative phosphorylation. Only 2 ATP per NADH since the coenzyme must feed into the electron transport chain from the cytoplasm rather than the mitochondrial matrix.
Oxidative decarboxylation 2 NADH 6 Oxidative phosphorylation
Krebs cycle 2 Substrate-level phosphorylation
6 NADH 18 Oxidative phosphorylation
2 FADH2 4 Oxidative phosphorylation
Total yield 36 ATP From the complete oxidation of one glucose molecule to carbon dioxide and oxidation of all the reduced coenzymes.

Although there is a theoretical yield of 36 ATP molecules per glucose during cellular respiration, such conditions are generally not realized due to losses such as the cost of moving pyruvate (from glycolysis), phosphate and ADP (substrates for ATP syhthesis) into the mitochondria. All are actively transported using carriers that utilise the stored energy in the proton electrochemical gradient.

* The pyruvate carrier is a symporter and the driving force for moving pyruvate into the mitochondria is the movement of protons from the intermembrane space to the matrix.
* The phosphate carrier is an antiporter and the driving force for moving phosphate ions into the mitochondria is the movement of hydroxyls ions from the matrix to the intermembrane space.
* The adenine nucleotide carrier is an antiporter and exchanges ADP and ATP across the inner membrane. The driving force is due to the ATP (-4) having a more negative charge than the ADP (-3) and thus it dissipates some of the electrical component of the proton electrochemical gradient.

The outcome of these transport processes using the proton electrochemical gradient is that more than 3 H+ are needed to make 1 ATP. Obviously this reduces the theoretical efficiency of the whole process. Other factors may also dissipate the proton gradient creating an apparently leaky mitochondria. An uncoupling protein known as thermogenin is expressed in some cell types and is a channel that can transport protons. When this protein is active in the inner membrane it short circuits the coupling between the electron transport chain and ATP synthesis. The potential energy from the proton gradient is not used to make ATP but generates heat. This is particularly important in a baby's brown fat, for thermogenesis, and hibernating animals.

Anaerobic respiration
Without oxygen, pyruvate is not metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion, but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. This serves the purpose of oxidizing the hydrogen carriers so that they can perform glycolysis again and removing the excess pyruvate. This waste product varies depending on the organism. In skeletal muscles, the waste product is lactic acid. This type of fermentation is called lactic acid fermentation. In yeast, the waste products are ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation.

Anaerobic respiration is less efficient at using the energy from glucose since 2 ATP are produced during anaerobic respiration per glucose, compared to the 36 ATP per glucose produced by aerobic respiration. This is because the waste products of anaerobic respiration still contain plenty of energy. Ethanol, for example, can be used in gasoline (petrol) solutions. Glycolytic ATP, however, is created more quickly. For prokaryotes to continue a rapid growth rate when they are shifted from an aerobic environment to an anaerobic environment, they must increase the rate of the glycolytic reactions. Thus, during short bursts of strenuous activity, muscle cells use anaerobic respiration to supplement the ATP production from the slower aerobic respiration, so anaerobic respiration may be used by a cell even before the oxygen levels are depleted, as is the case in sports that do not require athletes to pace themselves, such as sprinting.