progressive gardens

Using Growth Materials Carbon Cycle Photosynthesis

Respiration Transpiration A Balancing Act…

Plant processes, through the operation of the food chain, is the fundamental source of energy for nearly all organisms. The fossil fuels (coal, petroleum, and natural gas) and the oxygen of the Earth's atmosphere are all derived from earlier activity of photosynthetic organisms. Creating an organic or indoor garden, in essence, is creating an isolated ecosystem

Ecosystem : A term used to describe a system of interactions between living organisms occupying the same environment.

. It is the responsibility of the grower to implement the correct growing components and conditions. This may sound like an enormous responsibility to the beginner, but it's actually an opportunity. By creating the conditions for ideal growth, the grower can reap the benefits of higher yields, healthier plants, and an overall more positive gardening experience. When growing plants, it's good practice to fully understand what the plant wants, not just what you want from the plant. Think of a plant as a building, and the components needed to make that plant grow (nutrients, CO2, light, water, etc.) as the building blocks. Plants take care of the hard part- the actual construction. All we have to do is supply themwith the correct materials- the

building blocks. This section is intended to address plant requirement issues by educating the grower about plant physiology and how plants utilize the materials you give them.

Physiology : The science of dealing with the functions and vital processes of living organisms.

How do plant use growth materials?
Plants "eat" ions

Ions : Atoms that carry an electric charge, either positive or negative. If an atom gains an electron it takes on a negative charge. If the atom loses an electron it takes on a positive charge. Ex. Table salt = NaCl, dissolved in water is Na+ and Cl-, hence ions. The same idea is applied to salts that break out into relavent nutrient spectrums for plant growth in synthetic fertilizers.

. Think table salt- Sodium Chloride (NaCl). When you whirl it around in water that NaCl turns into Na+ and Cl-, hence ions. Plants grown hydroponically or in soil utilize their food the same way, we are just not used to thinking about it. So a "nutrient" or "fertilizer" is a material that when broken down into its inorganic components is beneficial to plant growth. Whether that ion comes form an "organic" or synthetic source is irrelevant to the plant, but terribly relevant to our environment. They access this fertilizer via active transport

Active transport : Transport of molecules against a concentration gradient (from regions of low concentration to regions of high concentration) with the aid of proteins in the cell membrane and energy from ATP.

. They actually produce the energy they need to access food via photosynthesis, a truly remarkable and virtually unique phenomenon in living organisms.

Plants utilize water via osmosis

Osmosis : Water moves from a scenario of high concentration of dissolved solids to a low concentration and is the mechanism by which plants utilize water through their roots.

. By ensuring a higher concentration of ions inside the root relative to outside the root, water moves from a lower concentration to a higher concentration, respectively. That means water will travel INTO the root acting as a vehicle for nutrition. In comparison, if you present a nutrient concentration that represents a higher concentration of ions outside the root, by osmosis, water travels OUT of the root. This is termed water stress, and is noticeable when your plants begin to shrivel up and burn from the edges of leaves.

Water stress : Phenomenon whereby water leaves the plant by way of osmosis due to too high of a fertilizer or ion concentration outside the root. Normally inside the root is more concentrated resulting in the plants ability to uptake water by way of osmosis.

Each plant has its respective "threshold". That's why it's a good idea to be mindful about fertilizer levels and separate classes of plants that desire different concentrations of fertilizers, especially in an immediately available hydroponic scenario. This phenomenon is the reason that you can get faster growth with hydroponics. You're effectively pushing the plant to its "threshold" and maximizing its genetic potential.

Carbon Cycle

Plant processes are driven overall by the Carbon Cycle and specifically via photosynthesis, transpiration, and respiration. These

Photosythesis : The process by which carbon dioxide and water are combined in the presence of light energy and chlorophyll to form carbohydrates. Photosynthesis takes place in the plant cell's chloroplasts. Inside the chloroplasts, chlorophyll absorb light energy from the sun. The chloroplasts then use that energy to jumpstart the process of photosynthesis. The carbohydrates/ sugars are the plant's internal energy storehouse; they are used to build and maintain plant tissue.

Transpiration : Process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores. Plants (like the cacti) that evolved in arid climates have developed thick skins and have fewer surfaces (shorter stems and modified leaves) to protect against dehydration due to transpiration.

Respiration : The oxidative process occurring within living cells by which the chemical energy of organic molecules is released in a series of metabolic steps involving the consumption of oxygen and the liberation of carbon dioxide, water, and energy.

processes are the vehicles that move water through the plant, utilize CO2 to create O2, harness light energy for food, and all the other amazing processes we may be familiar with but may not understand logistically. This section is aimed at simplifying these logistics, in order to capitalize on them for maximizing plant potential and growth.

< - - - - - - - - - - - - The Carbon Cycle

Photosynthesis

Photosynthesis, through the operation of the food chain, is the ultimate source of energy for nearly all organisms. Furthermore, the fossil fuels (coal, petroleum, and natural gas) and the oxygen of the Earth's atmosphere are all derived from the earlier and current activity of photosynthetic organisms. Photosynthesis, literally, is the "synthesis" of molecules using "the energy of light" (photo-). Simply put, the reaction involves water and carbon dioxide converted into glucose and oxygen. Water is accessed through roots and CO2 is accessed via the underside of plant leaves through stomata, which permits and regulates the outflow of water vapor via transpiration

Stomata : An opening or pore on the upper (i.e. water lilies) and/or lower leaf surface through which gas exchange occurs (i.e. oxygen and carbon dioxide) and moisture vapor moves. The size of this opening of the stomate is controlled by `guard cells'. A similar gaseous exchange site (lenticle) exists on stems and roots.

and oxygen as a product of photosynthesis. The overall reaction can be stated as:

Carbon dioxide + Water + Sunlight = Sugar + Oxygen
or
6 CO₂ + 6 H₂0 + Energy => C₆H₁₂06 + 6 0₂

The process of photosynthesis essentially involves removing electrons from the oxygen in water and redistributing them around the carbons, which come from the CO2. This is a redox reaction

Redox reaction : (oxidation/reduction) A chemical reaction in which an atom or ion loses electrons to another atom or ion.

, or oxidative/reduction reaction.

Photosynthesis is actually a two-step process- a light-dependent reaction

Light reaction : The photosynthetic process in which solar energy is harvested and transferred into the chemical bonds of ATP; can occur only in light.

(oxidative), in which chemical energy is created, and a light-independent reaction or Calvin-Benson Cycle (dark reaction or reduction), in which carbon dioxide is used to make carbohydrate at the expense of the chemical energy created in the light reaction.

Photsythates : Food products (sugars and starches) created through photosynthesis.

After producing carbohydrates, a plant can use them as energy, store them in roots, or build them into complex energy compounds such as oils and proteins. All of these photosythetic products are called photosynthates. The plant uses them when light is limited, or transports them to its roots or developing fruits for assimilation.

Assimilation : To absorb and incorporate; digest.

Photosynthesis could not take place without the presence of chlorophyll. Chlorophyll is the green pigment found in plant cells that

Chlorophyll : The green pigment of plant cells necessary for photosynthesis that captures light energy and converts it into chemical energy. Found in the chloroplasts of plant cells. It is the pigment that makes plants green because it absorbs red and blue and reflects green. Chlorophyll is highly efficient at absorbing light energy, and is essential to photosynthesis.

captures light energy and converts it into plant usable chemical energy. Being the main pigment

Pigment : Any coloring matter in the tissues of plants or animals.

used in photosynthesis, it absorbs light in the violet and blue wavelengths as well as in the red, leaving green the color it reflects, and the plant color we see primarily. Chlorophyll is found in the chloroplasts of plant cells, and is highly efficient at absorbing light energy often arranging itself perpendicular to incoming light energy so that maximum light can be absorbed. The chloroplasts themselves are incredibly small. One square millimeter, about the size of a period on a page (·), would contain 400,000 chloroplasts.

Light Reaction

Plants have to break the bonds of two stable compounds, CO2 and H2O, rearrange electrons, and produce two compounds which are less stable relative to the first two, ATP

Adenosine Triphosphate (ATP) : A common form in which energy produced in the light reaction of photosynthesis stored in living systems; consists of a nucleotide (with ribose sugar) with three phosphate groups.

and NADPH

Nicotine adenine dinucleotide phosphate (NADP⁺): A substance to which electrons are transferred from photosystem I during photosynthesis; the addition of the electrons reduces NADP, which acquires a hydrogen ion to form NADPH, which is a storage form of energy that can be transferred to the Calvin Cycle for the production of carbohydrate.

. It would not be profitable for the plants to do this using their own energy. Instead plants use an energy source that is readily available to them- light.

In the light dependent processes (light reactions

Light reaction : The photosynthetic process in which solar energy is harvested and transferred into the chemical bonds of ATP; can occur only in light.

) light strikes chlorophyll in such a way as to excite electrons to a higher energy state. In a series of reactions, called a redox reaction, the energy is converted (by an electron transport process) into ATP and NADPH, or the energy components of plants. Water is split in

Electron transport : C oupled series of oxidation/reduction reactions during which ATP is generated by energy transfer as electrons move from high reducing state to lower reducing state.

the process, releasing oxygen as a by-product of the reaction. The ATP and NADPH are

Dark reaction : The photosynthetic process in which food (sugar/carbohydrate) molecules are formed from carbon dioxide from the atmosphere with the use of ATP and NADPH; can occur in the dark as long as energy source is present.

then used to make C-C bonds in the Light Independent Process (Dark Reactions).

The total process of the "light reactions" are the net result of two net reactions and result in the formation of ATP and NADPH, or plant energy components. One reaction involves the splitting of water. This process is an oxidative reaction that requires light, and may be written as:

12 H₂O -----------------------> 6 O₂ + 24 H⁺ + 24e^-
light or radiant energy

The oxidation

Oxidation reaction : The combination of a substance with oxygen; a reaction in which the atoms in an element lose electrons and the valence of the element is correspondingly increased. In photosynthesis this means that electrons are removed from oxygen by light energy in order to reconstitute them by way of a reduction reaction to produce ATP and NADPH.

of water is accompanied by a reduction reaction

Reduction reaction : A decrease in positive valence or an increase in negative valence by the gaining of electrons.

resulting in the formation of a compound, called nicotinamide adenine dinucleotide phosphate (NADPH). The total reaction is written here:

NADP⁺ + H_₂0 ------------> NADPH + H⁺ + O
(oxidized form) (reduced form) (oxygen)

The second reaction involved in the light reactions is yet another reaction resulting in the formation of a highly energetic compound, called adenosine triphosphate, (ATP). As this reaction involves the addition of a phosphate group (labeled, as Pi) to a compound called, adenosine diphosphate (ADP) during the light reaction, it is called photophosphorylation:

ADP + P_i ------------> ATP

Think of the light reaction, as a process by which organisms "capture and store" radiant energy as they produce oxygen gas. This energy is stored in the form of chemical bonds of the compounds NADPH and ATP.

Dark Reaction

In the light independent process (dark reaction), carbon dioxide from the atmosphere is captured and modified by the addition of hydrogen to form carbohydrates. Why is supplemental

Carbohydrate : Any of a group of organic compounds that includes sugars, starches, celluloses, and gums and serves as a major energy source in the diet of plants and animals. These compounds are produced by photosynthetic plants and contain only carbon, hydrogen, and oxygen, usually in the ratio 1:2:1. Glucose is the major plant carbohydrate and the end product of photosyntheis.

CO₂ not used at night when it is needed in the dark reactions? The answer is that the dark reaction takes place in the presence of usable (or already created by light reaction) energy, or available ATP and NADPH. It happens that the peak in available energy is during photosythetically active periods, i.e. when the lights are on. So the term "dark reactions" can be a little misleading. The incorporation of carbon dioxide into organic compounds is known as the Calvin Cycle (after Melvin Calvin for which he won a 1961 Nobel Prize in chemistry), or carbon fixation and is the major process involved in the dark reaction. The energy for this comes from the first phase of the photosynthetic process with the production of ATP and NADPH and takes place in the stroma

Stroma : The connective tissue framework of an organ, gland, or other structure, as distinguished from the tissues performing the special function of the organ or part. Site of the dark reaction of photosynthesis.

of plant leaves. Living systems cannot directly utilize light energy, but can, through a complicated series of reactions, convert it into C-C bond energy that can be released by glycolysis

Glycolysis : An ATP-generating metabolic process that occurs in nearly all living cells in which glucose is converted in a series of steps to pyruvic acid. The metabolic breakdown of glucose and other sugars that releases energy in the form of ATP.

and other metabolic processes.

The energy contained in both NADPH and ATP is used to reduce carbon dioxide to glucose, a type of sugar (C6H12O6). This reaction, shown below, does not require light, and it is often referred to as the "dark reaction". The 24 hydrogen ions and 24 electrons represent the energy obtained from ATP and NADPH of which the specifics will be skipped here for simplicity. A simple web search can garner this information if need be. The total dark reaction is as follows:

6 CO₂ + 24 H⁺ + 24 e^- ------> C₆H₁₂O₆ (glucose) + 6 H_₂O

The chemical bonds present in glucose

Glucose : A product of photosynthesis and an important source of physiological energy for plants and animals. Glucose is a sugar, or carbohydrate.

contain a considerable amount of potential energy. This stored energy is released whenever glucose is catabolized

Catabolism : The metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy.

to drive cellular processes. The carbon skeleton in glucose also serves as a source of carbon for the synthesis of other important biochemical compounds such as lipids, amino acids, and nucleic acids. A lot of glucose is transformed into cellulose

Cellulose : A polysaccharide made up of many glucose molecules chemically bonded together. The most abundant compound on earth. It comprises the bulk of cell walls of plants where it occurs as microfibrils.

, which comprises the bulk of

Lipids : Diverse class compounds, including fats, oils, fatty acids, triglycerides and steroids essential for membrane formation, energy stores, and fuel molecules.

cell

Amino acid : A ny one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins and enzymes. They are characterized by the presence of a carboxyl group (COOH) and an amino group (NH₂) attached to the same carbon at the end of the compound.

walls vital to plant structure.

In simplest terms, the process of photosynthesis can be viewed as one-half of the carbon cycle in plants. In this half, energy from the sun is captured and transformed into plant usable energy, which can be utilized by higher organisms in the food chain through ingestion or for plant energy. The release of energy during the metabolic re-conversion of glucose to water and carbon dioxide represents the second half of the carbon cycle and is termed cellular respiration.

Glycolysis

Before glucose (the product of photosynthesis) can be converted into ATP it has to be broken down into two pyruvate molecules (the ionized form of pyruvic acid). This process is known as glycolysis. Glycolysis takes place in the cytoplasm and can occur without the presence of oxygen and is the primary energy source for most organisms. This process consumes two ATP molecules, and produces four ATP molecules and two NADH2+ molecules. After the glucose molecule has been converted into pyruvate, it is then sent to the Kreb Cycle to be converted into more usable forms of energy.

Krebs Cycle

The pyruvate molecules produced during glycolysis contain a lot of energy in the bonds between their molecules. In order to use that energy, the cell must convert it into the form of ATP. To do so, pyruvate molecules are processed through the Kreb Cycle, also known as the citric acid cycle. Because glycolysis produces two pyruvate molecules from one glucose, each glucose is processed through the kreb cycle twice. For each molecule of glucose, six NADH2+, two FADH2, and two ATP are produced.

Electron Transport Chain

What happens to the NADH2+ and FADH2 produced during the Krebs cycle? The molecules have been reduced, receiving high energy electrons from the pyruvic acid molecules that were dismantled in the Krebs Cycle. These carrier molecules transport the high-energy electrons and their accompanying hydrogen protons from the Krebs Cycle to the electron transport chain in the inner mitochondrial membrane.

In a number of steps utilizing enzymes on the membrane, NADH2+ is oxidized to NAD+, and FADH2 to FAD. The electrons are then passed from molecule to molecule in the inner membrane of the mitochondron, losing some of their energy at each step. These electrons provide energy to "pump" hydrogen protons across the inner mitochondrial membrane to the outer compartment. This high concentration of hydrogen protons produces a free energy potential that can do work. That is, the hydrogen protons tend to move down the concentration

gradient from the outer compartment to the inner compartment. The free energy of the hydrogen protons is used to form ATP by phosphorylation, bonding phosphate to ADP in an enzymatically-mediated reaction. Since an electrochemical osmotic gradient supplies the energy, the entire process is referred to as chemiosmotic phosphorylation.

Once the electrons (originally from the Krebs Cycle) have yielded their energy, they combine with oxygen to form water. If the oxygen supply is cut off, the electrons and hydrogen protons cease to flow through the electron transport system. If this happens, the proton concentration gradient will not be sufficient to power the synthesis of ATP. We're not used to thinking of plants needing oxygen, but this is why they, and most living organisms, are not able to survive for long without it!

Respiration

Respiration

is an oxidative process that converts sugars and starches into energy using oxygen. Energy stored as chemical energy as a result of photosythesis (carbohydrates, proteins, etc.) is continually released in living cells during the process of respiration. Basica1ly, photosynthesis creates and stores energy and respiration releases it, allowing the plant to take up water, build new cells and grow, and basically run all other growth processes. Respiration uses oxygen, which is not something we are used to thinking. We are used to thinking that plants produce oxygen. The fact is all living organisms, with the exception of a few, use oxygen to some degree, plants simply create more than they use.

C₆H₁₂O₆ + 6 O₂ => 6 CO₂ + 6 H₂O + Energy

This equation is essentially the opposite of photosynthesis. Photosynthesis is a building process, while respiration is a breaking-down process.

Photosynthesis and Respiration
Photosynthesis	Respiration
produces food stores energy uses water uses carbon dioxide releases oxygen occurs in sunlight	uses food releases energy produces water produces carbon dioxide uses oxygen occurs in the dark as well as light

Unlike photosynthesis, respiration does not depend on light, so it occurs at night as well as during the day. Respiration occurs in all life forms and in all cells. An understanding of these processes elucidates the reasons not to provide your indoor garden with 24 hours of light. If a plant is provided light ALL day, it's energy is diverted from incorporating the energy produced through photosythesis into itself via respiration. Give your garden at least six hours of darkness a day.

Transpiration

During photosythesis, plants draw in carbon dioxide through their pores and water via their roots and give off oxygen and water vapor. Transpiration is the process by which water is absorbed through its roots and evaporated via plant surfaces. Energy from the sun evaporates water from the plant cell walls and stomata

release water vapor into the atmosphere. This results in water from the roots being "pulled" upwards, via xylem, acting as a vehicle for plant nutrients and

Xylem : The principal strengthening and water/nutrient conducting tissue of branches, stems and roots. Primarily, the water conducting tissue in plants, though it also carries dissolved nutrients. The xylem pumps the water from the roots into the stem and leaves of the plant. Compare with phloem. Xylem is dead at maturity.

ensuring turgidity. However, this energy is neither stored nor used to bring

Turgor : The normal distention or rigidity of plant cells, resulting from the pressure exerted from within against the cell walls by the cell contents.

about vital reactions involved in assimilation, growth, or reproduction, but simply as a vehicle for moving materials within the plant.

The stomata on the undersides of leaves are regulated by guard cells. When stomata are open,

Guard cells : The Guard cells control the stomatal openings in the epidermis of the leaf. Three environmental factors regulate these cells. These factors are light, CO₂ concentration and water availability. When the guard cells are activated, K⁺ pumps actively transport K+ into the guard cells, resulting in a high [K⁺] in the cells. As a result, water enters the cells by osmosis. This causes the guard cells to swell. The one side of the guard cells is thicker than the other and does not stretch. As the guard cells swell up they bend. When the stoma is open CO₂ can diffuse into the leaf and enter the Calvin Cycle. The oxygen produced in photolysis, diffuses out of the open stoma. Water vapor also escapes from the stoma by the process of transpiration. As water transpires, other water molecules are pulled up through the plant behind it.

transpiration occurs, sometimes at a very high rate. A corn plant may transpire 50 gallons of water per season, but a large tree may move 100 gallons per day! The amount and rate of water loss depends on factors such as temperature, humidity, and wind or air movement. Transpiration is greatest in hot, dry (low relative humidity), windy weather. Plants have problems if they lose too much water, so stomata close during hot, dry periods when transpiration is highest. However, CO₂, which is needed for photosynthesis, also enters the plant through open stomata. Thus, if stomata

stay closed a long time to stop water loss, not enough CO₂ will enter for photosynthesis. As a result, photosynthesis and respiration will slow down, in turn reducing plant growth. This is the main reason why controlling your environment can be such an advantage in comparison with outdoor environments. By ensuring ideal environmental conditions plant processes can be streamlined and maximized, resulting in higher yields and happier and healthier plants. When a leaf's guard cells shrink, its stomata open, and water is lost. The rate of transpiration is directly related to whether stomata are open or closed. Stomata account for only 1 percent of a leaf's surface but 90 percent of the water transpired. Transpiration is a necessary process and uses about 90 percent of the water that enters a plant's roots. The other 10 percent is used in chemical reactions and in plant tissues.

A balancing act…

In order for a plant to grow and develop properly, it must balance photosynthesis, respiration, and transpiration. Left to their own devices, plants do a good job of managing this intricate balance. In an indoor garden where the grower is creating an environment, this balance can be tipped without a fundamental understanding of the processes themselves. If a plant photosynthesizes at a high rate, but its respiration rate is not high enough to break down the photosynthates produced the plant

can have a burnout (i.e. light on 24 hours a day). On the other hand, if respiration is much more rapid than photosynthesis, the plant won't have adequate photosynthates to produce energy for growth. Hence, growth either will slow down or stop altogether (i.e. low or inadequate light levels or photoperiods).