Respiration in plants. (Hô Hấp)

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Respiration

Respiration is the process that breaks down complex carbon compounds into

simple molecules and simultaneously generates the ATP used to power other metablic processes During respiration, carbon is oxidized Its oxidation state goes from +0 to +4 as electrons are removed by NAD+, which is convert to NADH in the process This is basically the opposite photosynthesis , in which NADPH

carries electrons to carbon, reducing it

The NADH generated by respiration is a good reducing agent, but it is produced in much larger quantities than needed for constructive reduction reactions Plants use mostly NADPH from photosynthesis for their reductions, not NADH, and most of the compounds that animals and fungi consume are already reduced Because NADH contains a great amount of energy, it is selectively advantageous for an organism to be able to oxidize it so as to generate even more ATP

As electrons are added, protons are attracted and incorporate, converting oxygen to water If this reverse analogy were carried one step further, the electron transport chain would have to give off light, but that would be a complete waste of energy; instead, it conserves the energy as high-energy phosphate bonding orbitals of ATP The overall reaction of respiration is:

C6H12O6 + 6O2 6CO2+6H2O+ 38ATP

Breathing provides the mechanism necessary to take in oxygen and give out carbon dioxide that is a waste gas It is a physical process and part of respiration

Respiration is a biochemical and physical process

Oxidation of NADH requires transferring electrons from it onto something else This ideal recipient would be abundant, cheap, and nontoxic after it is used These are also three ideal characteristic of the source of electrons in photosynthesis, and the chemical involed in both processes is water As it turns out, the result of

respiration is the reserve of photosynthesis Electrons are transferred from carbon

in carbonhydrate by meas of reduced NADH, which carries them to an electron transport chain, which in turn deposits them onto oxygen, reducing it In oxidative phosphorylation, the free energy that released as electrons are moved through the

electrons transport chain (ultimately reducing oxygen to water) is used to form ATP from ADP and phosphate

Glycolysis

In glycosis (from glyco-, meaning “sugar”, and lysis, meaning “spliting”), the six-carbon glucose molecule is split into two molecules of pyruvate Glucolysis occurs

in a series of 10 steps, each catalyzed by a specific enzyme This series of reactions

is carried out by vertually all living cells, from bacteria to the eukaryotic cells of plants and animals Glycolysis is an anaerobic process that occurs in the cytosol Biologically, glycosis may be considered a primitive process, in that it most likely arose before the appearance at atmospheric oxygen and before the origin of cellular organelles

Glycolysis is a universal beginning pathway conducted in the cytoplasm of cells for breaking down glucose into chemical energy The energy released from each molecule of glucose is used to attach a phosphate to each of four molecules of adenosine diphosphate (ADP) to produce two molecules of adenosine triphosphate (ATP) and an additional molecule of NADH The energy stored in the phosphate bond is used in other cellular reactions and is often regarded as the energy

"currency" of the cell However, since glycolysis requires the input of energy from two molecules of ATP, the net yield from glycoylysis is only two molecules of ATP per molecule of glucose The glucose itself is broken down during glycolysis into pyruvate Other fuel sources such as fats are metabolized through other

processes, for example the fatty acid spiral in the case of fatty acids, to produce fuel molecules that may enter respiration pathways at various points during

respiration

Types of respiration

Cellular respiration falls into two categories: Aerobic and anaerobic Respiration that requires oxygen as the terminal electron acceptor is aerobic respiration Under certain conditions, oxygen is not available, and an alternative electron acceptor must be used This is anaerobic respiration, respiration without oxygen, often called fermentation Because animals and plants must have oxygen for their

respiration, they are known as obligte or strict aerobes At the opposite extreme are

certain bacteria called obligate anaerobes, which carry out anaerobic respiration exclusively; such as bacteria are actually killed by oxygen Many fungi and certain types of tissues in animals and some plants are faculatively aerobic (or

facultatively anaerobic): If oxygen is present, they carry out aerobic respiration, but when oxygen is absent or insufficient, they switch to anaerobic respiration Although many fungi, espicially yeasts, can live indefinitely anaerobically, plant and animal tisues can survive this way for only a short time They must eventually obtain oxygen and switch back to aerobic respiration or they die

• Aerobic means “with air” This type of respiration needs oxygen for it to occur so it is called aerobic respiration The word equation for aerobic respiration is:

• Glucose + Oxygen Carbon dioxide + Water + Energy

• The chemical equation is:

• C6H12O6 + 6O2 6CO2 + 6H2O + 2900 kJ/mol

• In the above equations we see that glucose is broken down by oxygen to release energy with carbon dioxide and water being produced as by-products of the reaction

Approximately 2900 kJ of energy is released when one mole of glucose is broken down

The released energy is used to make a special energy molecule called Adenosine

triphosphate (ATP) ATP is where the energy is stored for use later on by the body.

• Aerobic respiration occurs in plants as well as animals Oxygen enters plant cells through the stomata Plants produce their food via photosynthesis and release energy from it through the process of respiration Below is a reminder of what the equation for

photosynthesis is:

•

• (Energy via sunlight)

Carbon dioxide + Water Glucose + Oxygen

• Comparing the two equations we can see that aerobic respiration works in the opposite way to photosynthesis During the day both photosynthesis and respiration are taking place at the same time, though photosynthesis is occurring at a faster rate At night when there is no light only respiration takes place.

2 Anaerobic Respiration

Anaerobic means without air (“an” means without) Sometimes there is not enough oxygen around for animals and plants to respire, but they still need energy to survive Instead they carry out

respiration in the absence of oxygen to produce the energy they require this is called anaerobic respiration.

The oxygen supply to plants can also run out, this happens for example if the soil gets waterlogged

In this case they have to obtain their energy via anaerobic respiration Below is the word and

chemical equation for anaerobic respiration in plants:

Glucose Ethanol + Carbon dioxide + Energy

C6H12O6 2C2H5OH + 2CO2 + Energy

When the above reaction occurs in yeast cells it is referred to as fermentation Fermentation is the process used for baking bread and brewing alcohol.

The difference between aerobic and anaeobic pathway:

Oxigen Present Oxigen Absent

Obligate aerobes Aerobic respiration;

able to live

No respiration; death

Obligate anaerobes Oxygen destroys certain

vital metabolites; death

Fermentation; able to live

Facultative Aerobic respiration;

able to live

Fermentation; able to live

When does resiration in plant occur?

Respiration is essential for all living organisms and this includes plants If

respiration stops in a plant it will die, so plants constantly respire during the day and through the night Respiration is a different process to photosynthesis, which depends on sunlight and therefore takes place only during the day

Plants absorb the energy they need through aerobic respiration, which is a chemical reaction that uses the oxygen in the air and glucose from within the plant to form carbon dioxide and water The plant derives the energy it needs to live from the

water and carbon dioxide formed by the respiration process To remain alive, the plant must respire at all times

Not only do plants respire at all times, the rate of respiration remains constant throughout the day and night In bright light, the rate of photosynthesis exceeds the respiration rate, while in dim light the rate is about the same In darkness,

photosynthesis stops but respiration continues at the same level

All plants continue to respire during winter months, even the plants that lose their leaves for the winter Respiration continues through all seasons, even though

photosynthesis dramatically slows down or stops altogether For respiration to carry on through the winter, plants use up stores of the food produced during the summer by photosynthesis

How do plants breath?

Every part of the plant is part of the respiration process Above the ground, the plant absorbs oxygen through pores on the surface of the entire plant called

stomata On woody trees, the pores on the branches are known as lenticles

According to The Open Door website, plants have on average 300 stomata on each leaf The roots take in oxygen from air spaces in the soil part of the reason why overwatering a plant is detrimental

Where does respiration occur?

Plant respiration is a rather diffuse process It occurs all over the plant Some of these functions are carried out in specific places and some are carried out by all portions of the plant

Stomata

• Plants are covered by pores, or "stomata," that open and close One of the functions of these stomata is to absorb oxygen from the air Oxygen is necessary for the chemical process of oxidation, or "burning." This is a chemical reaction that attaches oxygen atoms to other molecules, changing them and releasing energy as a side effect Oxidation is how the bodies of plants and animals literally burn their fuel It is the same process that makes brown spots on fruit, rusts metal and burns wood

• Plants do not get all of the oxygen they need for respiration from their

stomata They also absorb oxygen from their roots This is why plants need well-aerated soil to grow properly Waterlogged or compacted soil can kill plants by drowning or suffocating them

Mitochondria

• The rest of the respiration process occurs within the cells' mitochondria Mitochondria are small bodies, or organelles, that are about the same size as

bacteria They are somewhat like the cells' furnaces, creating energy out of the fuel that was produced in the cytosol These mitochondria absorb the pyruvic acids that were formed there and subject them to further chemical reactions These reactions produce adenosine triphosphate (ATP) molecules, which are what the plants use for energy They also produce water and carbon dioxide as a side effect

An Alternative

• Some plants, such a certain fungi, often grow in low-oxygen conditions This can seriously interfere with the plants' ability to breathe When this happens, plants will replace respiration with another set of chemical reactions, called

fermentation Fermentation is not as efficient at making energy as respiration is, but it does not require oxygen

Why do plants respire?

Respiration is a very important part of plant growth cycles and crop production For the home gardener, particularly one with a greenhouse, aiding respiration and photosynthesis will increase plant productivity and crop growth Increasing the carbon dioxide level in the photosynthesis stage will lead to more glucose for plants to utilize in respiration for growth One primary way to increase carbon dioxide levels is to fertilize with manure or compost, as the decaying of organic materials creates carbon dioxide Keeping the soil aerated helps increase root respiration Respiration, or breathing, is a function that plants and animals have in common Though plants do not have specialized organs to help them breathe, as

animals do, respiration is nonetheless critical for maintaining life and fueling growth in plants