How are respiration and photosynthesis related?

During photosynthesis, a plant is able to convert solar energy into a chemical form. It does this by capturing light coming from the sun and, through a series of reactions, using its energy to help build a sugar molecule called glucose. Glucose is made of six carbon atoms, six oxygen atoms, and twelve hydrogen atoms. When the plant makes the glucose molecule, it gets the carbon and oxygen atoms it needs from carbon dioxide, which it takes from the air. Carbon dioxide doesn't have any hydrogen in it, though, so the plant must use another source for hydrogen. The source that it uses is water. There is a lot of water on the earth, and every water molecule is composed of two hydrogen atoms and one oxygen atom. In order to take the hydrogen it needs to build glucose molecules, the plant uses the energy from the sun to break the water molecule apart, taking electrons and hydrogen from it and releasing the oxygen into the air. The electrons it takes are put into an electron transport system, where they are used to produce energy molecules called ATP that are used to build the glucose molecule-- all made possible by the sun's energy. Thus, during photosynthesis a plant consumes water, carbon dioxide, and light energy, and produces glucose and oxygen.

The sugar glucose is important because it is necessary for cellular respiration. During cellular respiration, the chemical energy in the glucose molecule is converted into a form that the plant can use for growth and reproduction. In the first step of respiration, called glycolysis, the glucose molecule is broken down into two smaller molecules called pyruvate, and a little energy is released in the form of ATP. This step in respiration does not require any oxygen and is therefore called anaerobic respiration. In the second step of respiration, the pyruvate molecules are rearranged and combined and rearranged again in a cycle. While the molecules are being rearranged in this cycle, carbon dioxide is produced, and electrons are pulled off and passed into an electron transport system which, just as in photosynthesis, generates a lot of ATP for the plant to use for growth and reproduction. This last step requires oxygen, and therefore is called aerobic respiration. Thus, the final result of cellular respiration is that the plant consumes glucose and oxygen and produces carbon dioxide, water, and ATP energy molecules.

At first, this doesn't seem to make any sense! If the plant can use the energy from the sun to make ATP, why does it go through all the trouble of then using up the ATP to make glucose, just so it can get ATP again? There are two reasons why the plant does this. First, in addition to ATP, the plant needs materials to grow. Glucose is an important building block that is necessary to produce all of the proteins, DNA, cells, tissues, etc. that are important to life, growth, and reproduction. Second, one problem with the sun is that it goes away every night, and during winter it isn't very bright. The plant needs energy all of the time. So, by producing glucose, the plant can store this molecule and then use it to produce energy during the night and over winter when there isn't enough sun to provide good photosynthesis.

It is very interesting how photosynthesis and cellular respiration help each other. During photosynthesis, the plant needs carbon dioxide and water-- both of which are released into the air during respiration. And during respiration, the plant needs oxygen and glucose, which are both produced through photosynthesis! So in a way, the products of photosynthesis support respiration, and the products of respiration support photosynthesis forming a cycle.

While plants can complete this cycle by themselves, animals cannot, since animals aren't capable of photosynthesis! This means that animals have to survive solely through respiration. Also, since we animals can't produce glucose by ourselves, we have to get it from somewhere else-- from eating plants. We produce carbon dioxide that the plants need, and they produce the oxygen that we need, and then we eat them to get the glucose that we need. It seems that we need the plants a lot more than they need us!

Photosynthesis and respiration are complementary processes.

Let me briefly summarize what both processes do:

Photosynthesis

Is the chemical process where plants can capture and organically fix the energy of the sun. This chemical reaction can be described by the following simple equation:

CO₂ + H₂O + light energy = Sugars + O₂

the main product of photosynthesis is a carbohydrate, such as the sugar glucose, and oxygen which is released to the atmosphere (the earth's atmosphere presently contains 20% ofO₂)

Respiration is the typical process where mitochondria of cells of organisms release chemical energy from sugar and other organic molecules through chemical oxidation. This process occurs in both plants and animals. In most organisms, respiration releases the energy required for all metabolic processes. This chemical reaction can be described by the following simple equation:

Sugars + O₂ = CO₂ + H₂O + released energy

Through the process of photosynthesis, green plants absorb solar energy and remove carbon dioxide from the atmosphere to produce carbohydrates (sugars). Plants burn these carbohydrates (and other products derived from them) through the process of respiration, the reverse of photosynthesis. Respiration releases the energy contained in sugars for use in metabolism.

This process is not balanced because the oxygen used for respiration is much less than what is given off during the photosynthetic reaction and the carbon dioxide given off is much less than what is taken up during photosynthesis. This is because plants need the sugar molecules not only for energy but also for structural elements (plants are largely cellulose - which is a long sugar molecule).

I hope this helps you understand this complex process.

A lot of my college students still have trouble with this one. The reactions that happen in respiration and photosynthesis are different, but if we just look at what goes in and what comes out, they're opposites.

Here's photosynthesis:

Carbon dioxide (CO₂) and Water (H₂0) in, Oxygen and Sugar out.

Requires energy from the sun.

Here's cellular respiration:

Oxygen and Sugar in, CO₂ and H₂0 out. Releases energy from the sugar.

Plants can do both. When they have light, they use it as an energy source to put the pieces of CO₂ and H₂O to make sugar. They can put a bunch of sugars together to make starch (what foods are starchy?), cellulose (the stringy stuff you can't chew up), and wood.

When it's dark, they can do cellular respiration to break down the starch and sugar to release the energy they need.

Poor animals, we can only do cellular respiration. We need foods like starch, and oxygen, and we breathe out the CO₂ that's made. We don't get enough water from the process to take care of all of our needs so we have to drink more. Kangaroo rats don't have to drink water. They conserve water a lot better than we do.

How Nutrients, Fluids, and Sugars Move through Plants

Just like you have a circulatory system that moves food and oxygen throughout your body, plants have a system to move nutrients, fluids, and sugars throughout their bodies. (Even though plants make food in their leaves by photosynthesis, the entire plant needs some of that food and the nutrients it provides.) The following sections fill you in on the different nutrients plants must absorb to stay healthy as well as how they move sugars from their leaves and water from their roots (without losing too much of it).

Taking an inventory of the nutrients plants need to survive

All plants require carbohydrates, proteins, fats, and nucleic acids to function — the same as you do. They also need mineral elements to build their molecules and make sure their enzymes are working properly. Fortunately, plants can obtain all the nutrients they need to survive from their environment.

REMEMBER Plants get carbon, hydrogen, and oxygen by taking carbon dioxide from the atmosphere and water from the soil. With energy from the Sun, plants combine these molecules to form carbohydrates during the process of photosynthesis.

Plants obtain their necessary mineral elements from the soil as well. The mineral nutrients found in soil dissolve in water, so when plants absorb water through their roots, they obtain both macronutrients and micronutrients. Macronutrients help with molecule construction, andmicronutrients act as partners for enzymes and other proteins to help them function. Plants generally require large amounts of macronutrients and smaller amounts of micronutrients.

Other words, carbon, hydrogen, oxygen, phosphorous, potassium, nitrogen, sulfur, calcium, iron, and magnesium. All of these elements are macronutrients for plants, with the exception of iron, which is considered a micronutrient.

If plants don’t get enough of one of these important elements, they can’t function correctly. Without carbon, hydrogen, and oxygen (from carbon dioxide and water), plants can’t grow at all. And even though plants need smaller amounts of minerals, even one missing mineral can cause a specific problem.

Transporting water and other nutrients from the ground up

Several processes work together to transport water (as well as other nutrients) from where a plant absorbs it (the roots) upward through the rest of its body. To understand how these processes work, you first need to know one key feature of water: Water molecules tend to stick together, literally. Water molecules are attracted to each other by weak electrical attractions called hydrogen bonds. The stickiness of water helps keep the water molecules together when you drink water through a straw — a process that’s very similar to one of the methods plants use to move water through their bodies.

Water moves from the soil, into a plant’s roots, and then throughout the plant thanks to a combination of three processes:

· Osmosis: The method plants use to draw water from the soil into the xylem cells in their roots is called osmosis. Root cells have a higher concentration of minerals than the soil they’re in, so during osmosis, water flows toward the higher concentration of dissolved substances found in the root cells. This intake of water increases pressure in the root cells and pushes water into the plant’s xylem.

· Capillary action: This causes liquids to rise up through the tubes in the xylem of plants. This action results from adhesion (when two things stick together), which is caused by the attraction between water molecules and the walls of the narrow tube. The adhesion forces water to be pulled up the column of vessel elements in the xylem and in the tubules in the cell wall.

· Transpiration and cohesion: Transpiration is the technical term for the evaporation of water from plants. As water evaporates through the stomates in the leaves (or any part of the plant exposed to air), it creates a negative pressure (also called tension or suction) in the leaves and tissues of the xylem. The negative pressure in the leaves and xylem exerts a pulling force on the water in the plant’s xylem and draws the water upward. When water molecules stick to each other throughcohesion (where like — as opposed to different — substances stick together), they fill the column in the xylem and act as a huge single molecule of water. As water evaporates from the plant through transpiration, the rest of the water gets pulled up, causing the need for more water to be pulled into the plant.

REMEMBERThe back and forth of transpiration and cohesion is known as the cohesion-tension theory. It’s similar to what happens when you suck on a straw. The suction you apply to the straw is like the evaporation from the leaves of the plant. Just like you can pull up a column of liquid through your straw, a plant can pull up a column of liquid through its xylem.

Translocation sugars upward and downward through the phloem

Phloem moves sap, a sticky solution containing sugars, water, minerals, amino acids, and plant hormones throughout the plant via translocation, the transport of dissolved materials in a plant. Unlike xylem, which can only carry water upward, phloem carries sap upward and downward from sugar sources to sugar sinks.

· Sugar sources are plant organs such as leaves that produce sugars.

· Sugar sinks are plant organs, such as roots, tubers, or bulbs thatconsume or store sugars.

The specific way translocation works in a plant’s phloem is explained by the pressure-flow theory, which we outline step by step in the following list:

1. First, sugars are loaded into phloem cells called sieve tube elements within sugar sources, creating a high concentration of sugar at the source.

The concentration of sugars in sink organs is much lower.

2. Water enters the sieve tube elements by osmosis.

During osmosis, water moves into the areas with the highest concentration of solutes (in this case, sugars).

3. The inflow of water increases pressure at the source, causing the movement of water and carbohydrates toward the sieve tube elements at a sugar sink.

TIP You can think of this like turning on a water faucet that’s connected to a garden hose. As water flows from the tank into the hose, it pushes the water in front of it down the hose.

4. Sugars are removed from cells at the sugar sink, keeping the concentration of sugars low.

As a sugar sink receives water and carbohydrates, pressure builds. But before the sugar sink can turn into a sugar source, carbohydrates in a sink are actively transported out of the sink and into needy plant cells. As the carbohydrates are removed, the water then follows the solutes and diffuses out of the cell, relieving the pressure.

REMEMBER Sugar sinks that store carbohydrates can become sugar sources for plants when sugars are needed.Starch, a complex carbohydrate, is insoluble in water, so it acts as a carbohydrate storage molecule. Whenever a plant needs sugar, like at night or in the winter when photosynthesis doesn’t occur as well, the plant can break down its starches into simple sugars, allowing a tissue that would normally be a sugar sink to become a sugar source.

Because plant cells can act as both sinks and sources, and because phloem transport goes both upward and downward, plants are pretty good at spreading the wealth of carbohydrates and fluid to where they’re needed. As long as a plant has a continuous incoming source of minerals, water, carbon dioxide, and light, it can fend for itself.

Controlling water loss

Because water is essential to a plant’s functioning, it has built-in mechanisms that help prevent it from losing too much water: a cuticle and guard cells.

The cuticle is a layer of cells found on the top surfaces of a plant’s leaves light pass into the leaf but protects the leaf from losing water. Many plants have cuticles that contain waxes that resist the movement of water into and out of a leaf; much like wax on your car keeps water off the paint.

Guard cells are found on the bottom of a plant’s leaves, near a stomate, a tiny opening that you can’t see with your naked eye. (An individual opening is called a stomate, or stoma; several openings are called stomates, or stomata.) Plants need to keep their stomates, open in order to obtain carbon dioxide for photosynthesis and release oxygen. However, if the stomates are open too long or on a really hot day, the plant can lose too much water. To prevent such water loss from happening, each stoma has two guard cells surrounding it.

Guard cells can swell and contract in order to open and close the stomates. When the Sun is shining and photosynthesis is occurring, guard cells swell up with water like full balloons, which stretches them outward and opens the stomates. At night, when photosynthesis isn’t occurring, the guard cells release some water and collapse together, closing the stomates.

1. Water enters the sieve tube elements by osmosis.

During osmosis, water moves into the areas with the highest concentration of solutes (in this case, sugars).

2. The inflow of water increases pressure at the source, causing the movement of water and carbohydrates toward the sieve tube elements at a sugar sink.

TIPYou can think of this like turning on a water faucet that’s connected to a garden hose. As water flows from the tank into the hose, it pushes the water in front of it down the hose.

3. Sugars are removed from cells at the sugar sink, keeping the concentration of sugars low.

As a sugar sink receives water and carbohydrates, pressure builds. But before the sugar sink can turn into a sugar source, carbohydrates in a sink are actively transported out of the sink and into needy plant cells. As the carbohydrates are removed, the water then follows the solutes and diffuses out of the cell, relieving the pressure.

Sugar sinks that store carbohydrates can become sugar sources for plants when sugars are needed.Starch, a complex carbohydrate, is insoluble in water, so it acts as a carbohydrate storage molecule. Whenever a plant needs sugar, like at night or in the winter when photosynthesis doesn’t occur as well, the plant can break down its starches into simple sugars, allowing a tissue that would normally be a sugar sink to become a sugar source.

Because plant cells can act as both sinks and sources, and because phloem transport goes both upward and downward, plants are pretty good at spreading the wealth of carbohydrates and fluid to where they’re needed. As long as a plant has a continuous incoming source of minerals, water, carbon dioxide, and light, it can fend for itself.

Some plants that live in very hot, dry environments save water by opening their stomates at night and storing carbon dioxide in their leaves. Then, during the day when it’s hot and dry, they keep their stomates closed to conserve water, performing photosynthesis with the carbon dioxide they stored during the night.

Plant Nutrients

Sixteen chemical elements are known to be important to a plant's growth and survival. The sixteen chemical elements are divided into two main groups: non-mineral and minerals.

Mineral Nutrients

The 13 mineral nutrients, which come from the soil, are dissolved in water and absorbed through a plant's roots. There are not always enough of these nutrients in the soil for a plant to grow healthy. This is why many farmers and gardeners use fertilizers to add the nutrients to the soil.

The mineral nutrients are divided into two groups:

macronutrients and micronutrients.

Macronutrients

Macronutrients can be broken into two more groups:

primary and secondary nutrients.

The primary nutrients are nitrogen (N), phosphorus (P), andpotassium (K). These major nutrients usually are lacking from the soil first because plants use large amounts for their growth and survival.

The secondary nutrients are calcium (Ca), magnesium (Mg), andsulfur (S). There are usually enough of these nutrients in the soil so fertilization is not always needed. Also, large amounts of Calcium and Magnesium are added when lime is applied to acidic soils. Sulfur is usually found in sufficient amounts from the slow decomposition of soil organic matter, an important reason for not throwing out grass clippings and leaves.

Micronutrients

Micronutrients are those elements essential for plant growth which are needed in only very small (micro) quantities. These elements are sometimes called minor elements or trace elements, but use of the term micronutrient is encouraged by the American Society of Agronomy and the Soil Science Society of America. The micronutrients are boron (B), copper (Cu), iron(Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc(Zn). Recycling organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients (as well as macronutrients) to growing plants.

An ideal soil contains equivalent portions of sand, silt, clay, and organic matter. Soils across North Carolina vary in their texture and nutrient content, which makes some soils more productive than others. Sometimes, the nutrients that plants need occur naturally in the soil. Othertimes, they must be added to the soil as lime or fertilizer.

Soil pH (a measure of the acidity or alkalinity of the soil)Soil pH is one of the most important soil properties that affects the availability of nutrients.

• • Macronutrients tend to be less available in soils with low pH.

  • Micronutrients tend to be less available in soils with high pH.

Lime can be added to the soil to make it less sour (acid) and also supplies calcium and magnesium for plants to use. Lime also raises the pH to the desired range of 6.0 to 6.5.

In this pH range, nutrients are more readily available to plants, and microbial populations in the soil increase. Microbes convert nitrogen and sulfur to forms that plants can use. Lime also enhances the physical properties of the soil that promote water and air movement.

It is a good idea to have your soil tested. If you do, you will get a report that explains how much lime and fertilizer your crop needs.

Macronutrients

Nitrogen (N)

• Nitrogen is a part of all living cells and is a necessary part of all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy.

• Nitrogen is a part of chlorophyll, the green pigment of the plant that is responsible for photosynthesis.

• Helps plants with rapid growth, increasing seed and fruit production and improving the quality of leaf and forage crops.

• Nitrogen often comes from fertilizer application and from the air (legumes get their N from the atmosphere, water or rainfall contributes very little nitrogen)

Phosphorus (P)

• Like nitrogen, phosphorus (P) is an essential part of the process of photosynthesis.

• Involved in the formation of all oils, sugars, starches, etc.

• Helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress.

• Effects rapid growth.

• Encourages blooming and root growth.

• Phosphorus often comes from fertilizer, bone meal, and superphosphate.

Potassium (K)

• Potassium is absorbed by plants in larger amounts than any other mineral element except nitrogen and, in some cases, calcium.

• Helps in the building of protein, photosynthesis, fruit quality and reduction of diseases.

• Potassium is supplied to plants by soil minerals, organic materials, and fertilizer.

Calcium (Ca)

• Calcium, an essential part of plant cell wall structure, provides for normal transport and retention of other elements as well as strength in the plant. It is also thought to counteract the effect of alkali salts and organic acids within a plant.

• Sources of calcium are dolomitic lime, gypsum, and superphosphate.

Magnesium (Mg)

• Magnesium is part of the chlorophyll in all green plants and essential for photosynthesis. It also helps activate many plant enzymes needed for growth.

• Soil minerals, organic material, fertilizers, and dolomitic limestone are sources of magnesium for plants.

Sulfur (S)

• Essential plant food for production of protein.

• Promotes activity and development of enzymes and vitamins.

• Helps in chlorophyll formation.

• Improves root growth and seed production.

• Helps with vigorous plant growth and resistance to cold.

• Sulfur may be supplied to the soil from rainwater. It is also added in some fertilizers as an impurity, especially the lower grade fertilizers. The use of gypsum also increases soil sulfur levels.

Micronutrients

Boron (B)

• Helps in the use of nutrients and regulates other nutrients.

• Aids production of sugar and carbohydrates.

• Essential for seed and fruit development.

• Sources of boron are organic matter and borax

Copper (Cu)

• Important for reproductive growth.

• Aids in root metabolism and helps in the utilization of proteins

Chloride (Cl)

• Aids plant metabolism.

• Chloride is found in the soil.

Iron (Fe)

• Essential for formation of chlorophyll.

• Sources of iron are the soil, iron sulfate, iron chelate.

Manganese (Mn)

• Functions with enzyme systems involved in breakdown of carbohydrates, and nitrogen metabolism.

• Soil is a source of manganese.

Molybdenum (Mo)

• Helps in the use of nitrogen

• Soil is a source of molybdenum.

Zinc (Zn)