Limiting factors in photosynthesis

A limiting factor is a factor that controls a process. Light intensity, temperature and, CO2 concentration and availability of H2O are all factors which can control the rate of photosynthesis.










Usually, only one of these factors will be the limiting factor in a plant at a certain time. This is the factor which is the furthest from its optimum level at a particular point in time. If we change the limiting factor the rate of photosynthesis will change but changes to the other factors will have no effect on the rate.

If the levels of the limiting factor increase so that this factor is no longer the furthest from its optimum level, the limiting factor will change to the factor which is at that point in time, the furthest from its optimum level. For example, at night the limiting factor is likely to be the light intensity as this will be the furthest from its optimum level. During the day, the limiting factor is likely to switch to the temperature or the carbon dioxide concentration as the light intensity increases.

Effects of changes in light intensity, CO2, H2O and temperature on the rate of photosynthesis

1. Light intensity

• This affects the rate of the light-dependent reaction. The energy that drives this process is light energy.
• When the light intensity is poor, there is a shortage of ATP and NADPH, as these are products from the light dependent reactions. Without these products the light independent reactions can't occur as glycerate 3-phosphate cannot be reduced. Therefore a shortage of these products will limit the rate of photosynthesis. 

2. Temperature

• This affects the rate of the light-independent reaction. The energy that drives this process is heat energy. 
• At higher temperatures, molecules have more kinetic energy so collide more often and are more likely to react when they do collide. 
• Many enzymes are involved during the process of photosynthesis. At low temperatures these enzymes work slower. At high temperatures the enzymes no longer work effectively. This affects the rate of the reactions in the Calvin cycle and therefore the rate of photosynthesis will be affected.

3. CO2 concentration 

• CO2 is a reactant in photosynthesis. Normal air contains only about 0.04% CO2.
• When the CO2 concentration is low, the amount of glycerate 3-phosphate produced is limited as CO2 is needed for its production and therefore the rate of photosynthesis is affected. 

4. Availability of H2O

H2O is a reactant in photosynthesis, but there is usually far more H2O available than CO2, so even if water supplies are low this is not usually a problem. However, water supply can affect the rate of photosynthesis indirectly, because a plant that is short of water will close its stomata, preventing CO2 from diffusing into the leaf.

lf the level of anyone of these factors is too low, then the rate of photosynthesis will be reduced. The factor that has the greatest effect in reducing the rate is said to be the limiting factor.

Economics of greenhouses

Farmers can use their knowledge of factors limiting the rate of photosynthesis to increase crop yields. This is particularly true in greenhouses, where the conditions are more easily controlled than in the open air outside:

• The use of artificial light allows photosynthesis to continue beyond daylight hours. Bright lights also provide a higher-than-normal light intensity.
• The use of artificial heating allows photosynthesis to continue at an increased rate.
• The use of additional CO2 released into the atmosphere inside the greenhouse also allows photosynthesis to continue at an increased rate.

Artificial light in the green house. 

However, the additional cost of providing extra lighting, heat and CO2 has to be weighed against the increased crop yield and the extra income it will provide. The cost of should not exceed the additional income it generates for the farmer.

In practice, the farmer will need to find the optimum growing conditions for the crop, given the costs of providing extra lighting, heat and CO2. Paraffin lamps have traditionally been used in greenhouses. Their use increases the rate of photosynthesis because as well as the light generated from the lamps, the burning paraffin produces heat and CO2 too.

Investigating the effect of environmental factors on the rate of photosynthesis

One way to measure the rate of photosynthesis is to measure the rate at which oxygen is given off by an aquatic plant. There are various ways in which oxygen can be collected and measured. One method is shown in the diagram below.

Alternatively, you can make calcium alginate balls containing green algae and place them in hydrogencarbonate indicator solution. As the algae photosynthesise, they take in carbon dioxide which causes the pH around them to increase. The indicator changes from orange, through red to magenta.

Whichever technique is used, you should change one factor (your independent variable) while keeping all others constant (the control variables). The dependent variable will be the rate at which oxygen is given off (measured by the volume of oxygen collected per minute in the capillary tube) or
the rate at which carbon dioxide is used (measured by the rate of change of colour of the hydrogencarbonate indicator solution).

The independent variables you could investigate are:

• Light intensity. You can vary this by using a lamp to shine light onto the plant or algae. The closer the lamp. the higher the light intensity.
• Wavelength of light. You can vary this by placing coloured filters between the light source and the plant. Each filter will allow only light of certain wavelengths to pass through.
• CO2 concentration. You can vary this by adcting sodium hydrogencarbonate to the water around the aquatic plant. This contains hydrogencarbonate Ions, which are used as a source of carbon dioxide by aquatic plants.
• Temperature. The part of the apparatus containing the plant or algae can be placed in a water bath at a range of controlled temperatures.

Video: Limiting factors of photosynthesis

13.2  Investigation of limiting factors Environmental factors influence the rate  of photosynthesis. Investigating these shows how they can be managed in protected environments used in crop production. a)   explain the term  limiting factor in relation to photosynthesis b)   explain the effects of changes in light intensity, carbon  dioxide concentration and temperature on the rate  of photosynthesis c)   explain how an understanding of limiting factors is used to increase crop yields in protected environments, such  as glasshouses d)   carry out an investigation to determine the effect of light intensity or light wavelength on the rate  of photosynthesis using a redox indicator (e.g. DCPIP) and a suspension of chloroplasts (the Hill reaction) e)   carry out investigations on the effects of light intensity, carbon dioxide and temperature on the rate  of photosynthesis using whole  plants,  e.g. aquatic  plants  such  as Elodea and Cabomba

The light-independent reactions (Calvin cycle)

The light-independent reactions take place in the stroma of the chloroplast, where the enzyme ribulose bisphosphate carboxylase, usually known as rubisco, is found.

1. Carbon fixation

CO2 diffuses into the stroma from the air spaces within the leaf. It enters the active site of rubisco, which combines it with a 5-carbon compound called ribulose bisphosphate, RuBP. The reaction is called carbon fixation.

The products of this reaction are two 3-carbon molecules, glycerate 3-phosphate, GP.

2. Reduction 

Energy from ATP and hydrogen from reduced NADP are then used to convert the GP into triose phosphate, TP. Triose phosphate is the first carbohydrate produced in photosynthesis.

3. RuBP regeneration

Most of the triose phosphate is used to produce ribulose bisphosphate (RuBP), so that more carbon dioxide can be fixed.

The rest is used to make glucose or whatever other organic substances the plant cell requires. These include:

• polysaccharides such as starch for energy storage and cellulose for making cell walls,
• sucrose for transport, 
• amino acids for making proteins,
• lipids for energy storage 
• nucleotides for making DNA and RNA.

Syllabus:  13.1  Photosynthesis as an energy transfer process Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds. Chromatography is used to identify chloroplast pigments and was  also used to identify the intermediates in the Calvin cycle. a)   explain that  energy transferred as ATP and reduced NADP from the light dependent stage is used during the light independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules b)   state the sites of the light dependent and the light independent stages in the chloroplast c)   describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in the grana d)   interpret absorption and action spectra of chloroplast pigments  e)   use  chromatography to separate and identify chloroplast pigments and carry out an investigation to compare the chloroplast pigments in different plants  (reference should  be made to Rf  values  in identification) f) describe the light dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (cyclic and non-cyclic photophosphorylation should  be described in outline  only) g)   outline  the three main stages of the Calvin cycle: • fixation of carbon  dioxide by combination with ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of GP (PGA), a 3C compound •   the reduction of GP to triose  phosphate (TP) involving ATP and reduced NADP •   the regeneration of ribulose  bisphosphate (RuBP) using ATP h)   describe, in outline,  the conversion of Calvin cycle intermediates to carbohydrates, lipids and amino  acids  and their uses in the plant cell

Separating chlorophyll pigments by Thin layer chromatography (TLC)

Chromatography is a method of separation that relies on the different solubilities of different solutes in a solvent. A mixture of chlorophyll pigments is dissolved in a solvent, and then a small spot is placed onto chromatography paper. The solvent gradually moves up the paper, carrying the solutes with it. The more soluble the solvent, the further up the paper it is carried.




Paper chromatography is a useful technique in the separation and identification of different plant pigments.

• In this technique, the mixture containing the pigments to be separated is first applied as a spot or a line to the paper about 1.5 cm from the bottom edge of the paper. 
• The paper is then placed in a container with the tip of the paper touching the solvent. Solvent is absorbed by the paper and moves up the paper by capillary action.
• As the solvent crosses the area containing plant pigment extract, the pigments dissolve in and move with the solvent. 
• The solvent carries the dissolved pigments as it moves up the paper. The pigments are carried along at different rates because they are not equally soluble. Therefore, the less soluble pigments will move slower up the paper than the more soluble pigments. This is known as developing a chromatogram.

There are various methods. The one described here uses Thin layer chromatography (TLC) on specially prepared strips instead of paper. It is a chromatography technique for analyzing mixtures by separating the compounds in the mixture. TLC can be used to help determine the number of components in a mixture, the identity of compounds, and the purity of a compound. During chromatography, a mobile phase (eluent) distributes the compounds present in a mixture over a stationary phase (adsorbent).

The distance traveled by a particular compound can be used to identify the compound. The ratio of the distance traveled by a compound to that of the solvent front is known as the Rf value; unknown compounds may be identified by comparing their Rf's to the Rf's of known standards.

Rf equation:

Only an outline of the procedure is given here, so you cannot use these instructions to actually carry out the experiment.

Video TLC

Syllabus:  13.1  Photosynthesis as an energy transfer process Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds. Chromatography is used to identify chloroplast pigments and was  also used to identify the intermediates in the Calvin cycle. a)   explain that  energy transferred as ATP and reduced NADP from the light dependent stage is used during the light independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules b)   state the sites of the light dependent and the light independent stages in the chloroplast c)   describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in the grana d)   interpret absorption and action spectra of chloroplast pigments  e)   use  chromatography to separate and identify chloroplast pigments and carry out an investigation to compare the chloroplast pigments in different plants  (reference should  be made to Rf  values  in identification) f) describe the light dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (cyclic and non-cyclic photophosphorylation should  be described in outline  only) g)   outline  the three main stages of the Calvin cycle: • fixation of carbon  dioxide by combination with ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of GP (PGA), a 3C compound •   the reduction of GP to triose  phosphate (TP) involving ATP and reduced NADP •   the regeneration of ribulose  bisphosphate (RuBP) using ATP h)   describe, in outline,  the conversion of Calvin cycle intermediates to carbohydrates, lipids and amino  acids  and their uses in the plant cell

Health benefits of Sesame seeds

Sesame seeds are highly nutritive. Although some people are aware of sesame seeds, some people have probably never heard of them. Sesame seeds are an excellent source of copper, zinc, manganese, calcium, Vitamin B1 and dietary fiber. Sesame seeds contain two compounds, sesamin and sesamolin that are able to prevent high blood pressure and lower cholesterol levels. There are three different varieties of sesame seeds: the black, white and red. The black version has the best medicinal properties. Below are some of the health benefits of sesame seeds.

1 Sesame seeds relieve rheumatoid arthritis symptoms

Sesame seeds are a good source of copper. Copper helps in reducing some of the symptoms of rheumatoid arthritis such as pain and swelling.

2 Sesame seeds help relieve some respiratory disorders

The presence of magnesium in sesame seeds help improve the health of our respiratory system. Sesame seeds are able to relieve asthma by preventing airway spasms. Sesame seeds are also able to relieve chronic and acute bronchitis by acting as an expectorant.

• Mix one teaspoon of powdered sesame seeds with one table spoon of honey and consume.

3 Lowering high blood pressure                     

Sesame seeds are rich in magnesium and studies have supported magnesium’s usefulness in lowering high blood pressure. If one does not have high blood pressure, then the chances of having stroke, heart attack, and heart failure are low.

4 Preventing anaemia

Black sesame seeds contain iron which is able to prevent anaemia that results from deficiency of iron.

• Soak some black sesame seeds in warm water for about 6 hours.
• Grind the seeds until it becomes a paste. This paste can be added to a cup of milk and sweetened with honey.

5 Lowers cholesterol

Sesame seeds contain a compound called phytosterols that is similar in structure to cholesterol found in animals. Phytosterols are also found in soybean, corn and pumpkin seeds. When phytosterol is consumed by man, it is believed to bring down the levels of cholesterol in blood.

6 Strong and healthy bones

Sesame seeds contain zinc and calcium which are essential minerals for strong and healthy bones. A study published by the American Journal of Clinical Nutrition showed that those who had a low intake of zinc were more vulnerable to osteoporosis at the hip and spine. Calcium also helps in preventing bone loss that can occur as a result of ageing and menopause. 

7 Sesame seeds can help relieve menstrual cramps

The calcium found in sesame seeds help reduce the pain associated with menstrual cramps. A teaspoon of powdered sesame seeds should be taken with a cup of hot water.

8 Migraines

Sesame seeds can help prevent migraine headaches. 1 teaspoon of powdered sesame seeds should be taken with a cup of hot water to relieve migraine in those who suffer from them.

9 Prevention of colon cancer

Calcium has been shown to prevent colon cells from chemicals that cause colon cancer.

10 Causing abortion

Centuries ago in the African culture, sesame seeds were used traditionally to cause abortion when there was a need for it.

Sources:

http://www.whfoods.com/genpage.php?tname=foodspice&dbid=84

http://www.nutrition-and-you.com/sesame-seeds.html

http://www.greenmedinfo.com/blog/open-sesame-10-amazing-health-benefits-super-seed

H.K.Bakhru “Foods that heal” The natural way to good health.

light-dependent reactions, Photophosphorilation

Chlorophyll molecules in photosystern I (PSI) and photosystern II (PSII) absorb light energy. The energy excites electrons, raising their energy level so that they leave the chlorophyll. The chlorophyll is said to be photo-activated.







PSII contains an enzyme that splits water when activated by light. This reaction is called photolysis ('splitting by light'). The water molecules are split into oxygen and hydrogen atoms. Each hydrogen atom then loses its electron, to become a positively charged hydrogen ion (proton), H+.

The electrons are picked up by the chlorophyll in PSII, to replace the electrons they lost. The oxygen atoms join together to form oxygen molecules, which diffuse out of the chloroplast and into the air around the leaf.

The light- dependent reactions. Credit: Pears education. 

The electrons emitted from PSII are picked up by electron carriers in the membranes of the thylakoids. They are passed along a chain of these carriers, losing energy as they go. The energy they lose is used to make ADP combine with a phosphate group, producing ATP. This is called photophosphorylation. At the end of the electron carrier chain, the electron is picked up by PSI, to replace the electron the chlorophyll in PSI had lost.

The electrons from PSI are passed along a different chain of carriers to NADP. The NADP also picks up the hydrogen ions from the split water molecules. The NADP becomes reduced NADP.

We can show all of this in a diagram called the Z-scheme. The higher up the diagram, the higher the energy level. If you follow one electron from a water molecule, you can see how it
• is taken up by PSII
• has its energy raised as the chlorophyll in PSII absorbs light energy
• loses some of this energy as it passes along the electron carrier chain
• is taken up by PSI
• has its energy raised agaln as the chlorophyll in PSI absorbs light energy
• becomes part of a reduced NADP molecule

At the end of this process, two new substances have been made. These are ATP and reduced NADP. Both of them will now be used in the next stage of photosynthesis, the light-independent reactions.

Non-cyclic and cyclic photophosphorylation

The sequence of events just described and shown in the flow diagram above is known as non-cyclic photophosphorylation.

There is an alternative pathway for the electron that is emitted from PSI. It can simply be passed along the electron transport chain, then back to PSI again. ATP is produced as it moves along the electron transport chain (photophosphorylation). However, no reduced NADP is produced. This is called cyclic photophosphorylation.

Z- cheme.

Video: Photosynthesis

Syllabus:  13.1  Photosynthesis as an energy transfer process Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds. Chromatography is used to identify chloroplast pigments and was  also used to identify the intermediates in the Calvin cycle. a)   explain that  energy transferred as ATP and reduced NADP from the light dependent stage is used during the light independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules b)   state the sites of the light dependent and the light independent stages in the chloroplast c)   describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in the grana d)   interpret absorption and action spectra of chloroplast pigments  e)   use  chromatography to separate and identify chloroplast pigments and carry out an investigation to compare the chloroplast pigments in different plants  (reference should  be made to Rf  values  in identification) f) describe the light dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (cyclic and non-cyclic photophosphorylation should  be described in outline  only) g)   outline  the three main stages of the Calvin cycle: • fixation of carbon  dioxide by combination with ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of GP (PGA), a 3C compound •   the reduction of GP to triose  phosphate (TP) involving ATP and reduced NADP •   the regeneration of ribulose  bisphosphate (RuBP) using ATP h)   describe, in outline,  the conversion of Calvin cycle intermediates to carbohydrates, lipids and amino  acids  and their uses in the plant cell

Photosynthetic Pigments

Photosynthetic pigments are pigments presented in chloroplasts or photosynthetic bacteria. They capture light energy necessary for photosynthesis and convert it to chemical energy. 

Pigments

• A pigment is any substance that absorbs light.
• The color of the pigment comes from the wavelengths of light that are reflected (not absorbed). 
• If pigments absorb all wavelengths they will appear black.
• If pigments reflect most of the wavelengths they will appear white.
• The light absorption pattern of a pigment is called the absorption spectrum.

When pigments absorb light, electrons are temporarily boosted to a higher energy level. Energized electrons move further from the nucleus of the atom. When the e- returns to a lower energy level the energy may be:

• dissipated as heat
• re-emitted as a longer wavelength of light - fluorescence
• captured in a chemical bond (carbon gain!)

Photosynthetic pigments in chloroplast

Choloroplats contain several different pigments, which absorb different wavelengths of light. The photosynthetic pigments of higher plants form 2 groups: the cholophylls and the caroteinoids.

1. Chlorophylls absorb mainly red and blue-violet light, reflect green light - giving green leaves their colour.  

2. Carotenoids: orange pigments that protect chlorophyll from damage by the formation of single oxygen atoms (free radicals). They can also absorb wavelengths of light that chlorophyll cannot absorb, and pass on some of the energy from the light to chlorophyll. They absorb strongly in the blue-violet range. Carotenoids are usually masked by the green chlorophylls.

There are 2 types of carotenoid: 

• carotenes (β-carotene)
• xantophylls.

Main and accessory photosynthetic pigments

- Main pigment 

• Chlorophyll a is the most abundant pigment in most plants. Its absorption peaks are 430nm (blue) and 662nm (red). It emits an electron when it absorbs light. 

- Accessory pigments 

• Chlorophyll b is similar to chlorophyll a, but its absorption peaks are 453nm and 642nm. It has a similar role to chlorophyll a, but is not as abundant.
• Carotenoids : carotene and Xanthophylls.

The combination of all of the pigments increases the range of colors that plants can use in photosynthesis.

Chlorophill molecule.

Absorption spectrum and action spectrum of chloroplast pigments 

An absorption spectrum is a graph showing the percentage of light absorbed by pigments, for each wavelength of light.

An example is the absorption spectrum of chlorophyll a and b.

• The best absorption is seen with violet-blue light. 
• There is also good absorption with red-orange light. 
• Most of the green-yellow light is reflected and therefore not absorbed. This wavelength of light shows the least absorption. 

The action spectrum of photosynthesis is a graph showing the rate of photosynthesis for each wavelength of light. The rate of photosynthesis will not be the same for every wavelength of light.

• The rate of photosynthesis is the least with green-yellow light (525 nm-625 nm). 
• Red-orange light (625nm-700nm) shows a good rate of photosynthesis.
• The best rate of photosynthesis is seen with violet-blue light (400nm-525nm). 

The wavelengths that is does not absorb are reflected from it.
Chlorophyll Is the main pigment contained in chloroplasts. It looks green because it
reflects green light. Other wavelengths (colours) of light are absorbed.
llle diagram shows the wavelengths of light absorbed by the various pigments found
in chloroplasts. These graphs are called absorption spectra.
If we shine light of various wavelengths on chloroplasts containing different pigments, we can measure the rate at which they give off oxygen. These graphs are called action spectra.

Syllabus:  13.1  Photosynthesis as an energy transfer process Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds. Chromatography is used to identify chloroplast pigments and was  also used to identify the intermediates in the Calvin cycle. a)   explain that  energy transferred as ATP and reduced NADP from the light dependent stage is used during the light independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules b)   state the sites of the light dependent and the light independent stages in the chloroplast c)   describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in the grana d)   interpret absorption and action spectra of chloroplast pigments  e)   use  chromatography to separate and identify chloroplast pigments and carry out an investigation to compare the chloroplast pigments in different plants  (reference should  be made to Rf  values  in identification) f) describe the light dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (cyclic and non-cyclic photophosphorylation should  be described in outline  only) g)   outline  the three main stages of the Calvin cycle: • fixation of carbon  dioxide by combination with ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of GP (PGA), a 3C compound •   the reduction of GP to triose  phosphate (TP) involving ATP and reduced NADP •   the regeneration of ribulose  bisphosphate (RuBP) using ATP h)   describe, in outline,  the conversion of Calvin cycle intermediates to carbohydrates, lipids and amino  acids  and their uses in the plant cell

Chloroplasts

Photosynthesis takes place inside chloroplasts.










These are organelles surrounded by 2 membranes, called an envelope.




Chloroplasts are found in mesophyll cells in leaves:

- Palisade mesophyll cells contain most chloroplasts.
- Spongy mesophyll cells and Guard cells also contain chloroplasts.

Lamellae and light-dependent reactions 

The membranes inside a chloroplast are called lamellae, and it is here that the light-dependent
reactions take place. The membranes contain chlorophyl molecules, arranged in groups called photosystems. There are two kinds of photosysterns, PSI and PSII, each of which contains slightly different kinds of chlorophyll.

There are enclosed spaces between pairs of membranes, forming fluid-filled sacs called thylakoids. These are involved in photophosphorylation - the formation of ATP using energy from light. Thylakoids are often arranged in stacks called grana (singular: granum),

Stroma and light-independent reactions 

The 'background material' of the chloroplast is called the stroma, and this is where the light-independent reactions take place.

Chloroplasts often contain starch grains and lipid droplets. These are stores of energy-containing substances that have been made in the chloroplast but are not immediately needed by the cell or by other parts of the plant.

Syllabus:  13.1  Photosynthesis as an energy transfer process Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds. Chromatography is used to identify chloroplast pigments and was  also used to identify the intermediates in the Calvin cycle. a)   explain that  energy transferred as ATP and reduced NADP from the light dependent stage is used during the light independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules b)   state the sites of the light dependent and the light independent stages in the chloroplast c)   describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in the grana d)   interpret absorption and action spectra of chloroplast pigments  e)   use  chromatography to separate and identify chloroplast pigments and carry out an investigation to compare the chloroplast pigments in different plants  (reference should  be made to Rf  values  in identification) f) describe the light dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (cyclic and non-cyclic photophosphorylation should  be described in outline  only) g)   outline  the three main stages of the Calvin cycle: • fixation of carbon  dioxide by combination with ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of GP (PGA), a 3C compound •   the reduction of GP to triose  phosphate (TP) involving ATP and reduced NADP •   the regeneration of ribulose  bisphosphate (RuBP) using ATP h)   describe, in outline,  the conversion of Calvin cycle intermediates to carbohydrates, lipids and amino  acids  and their uses in the plant cell

9 home remedies for after shave bumps or razor burns

After shave bumps or razor burns are some unwanted effects that come as a result of shaving hair on our skin. It occurs after an area of the skin has been shaved and manifest as an irritation, inflammation, itching of the skin and bumps may result. It may sometimes swell and pain too. Men usually have razor burns on the chin while women get them on their armpits and at times on the legs and pubic area.

Some of the following will help relieve the symptoms of after shave bumps while some remedies will help heal after shave bumps.

1  Lemon juice

Lemon juice can help heal razor bumps. Its anti-bacterial properties help in preventing bacteria from invading aftershave bumps.

• Apply some lemon juice on the affected area and allow to get dry.
• Wash off the lemon juice after waiting for about 30 minutes.

2 Honey

Another home remedy that can be used to heal after shave bumps fast is honey. This is because honey has anti-bacterial properties and it will even prevent the after shave bumps from getting infected. Honey also reduces inflammation that is associated with after shave bumps.

• Apply some honey on the affected area and allow it to get dry. 
• Rinse off the honey after waiting for about 30 minutes.
• This can be done twice a day till the after shave bumps get healed.

3 cold compress

A cold compress is able to relieve the burning sensation that is caused by after shave bumps. 

• Wrap some ice in a piece of cloth and apply over the affected area. 
• Another option is to soak a face towel in ice cold water and apply over the affected area.

4 Aloe Vera

Aloe Vera helps in reducing pain and inflammation associated with aftershave bumps. Its anti-bacterial properties will aid in healing aftershave bumps especially if it gets infected.

• Extract the gel from aloe vera and rub on the affected spot. 
• Allow it to get dry and rinse with water. This can be done twice daily to get rid of after shave bumps

5 Tea tree oil

Tea tree oil naturally has anti-bacteria properties. It is used in most skin care products. It should be diluted with water before applying on the razor burns.

• Apply the tea tree oil on the affected area and allow to get dry. Rinse it off with water.

6 Apple cider vinegar

The anti-inflammatory properties of apple cider vinegar can relieve symptoms of inflammation associated with after shave bumps such as swelling and pain. Apple cider vinegar can also relieve itches that come as a result of after shave bumps

• Soak a cotton swab with apple cider vinegar and apply on the razor burn.
• Allow it to get dry and rinse off the apple cider vinegar with water.

7 Aspirin tablets

Aspirin can help relieve redness and pain associated with razor burns because it has anti-inflammatory properties. 

• Dissolve one aspirin tablet in a teaspoon of water and apply on the razor burns.
• Allow it to get dry and wash off the aspirin with water after about 10 minutes.

8 Baking soda

Baking soda helps in reducing inflammation that occur as a result of after shave bumps. It can also relieve the itching associated with after shave bumps.

• Make a paste using baking soda and warm water. 
• Apply on the skin and rinse after allowing it to sit for about 30 minutes.

9 corn starch

Get some cornstarch and mix with water to form a paste. Apply on the affected areas and allow it to get dry. Rinse off the corn starch with water after about 20 minutes.

After shave bumps can be prevented by using the right shaving cream and oil. The right shaving instrument that does not cut the skin during shaving should be used as well to prevent after shave bumps.

Sources:

https://getbevel.com/get-advice/other/what-home-remedies-work-best-to-get-rid-of-razor-bumps

http://www.top10homeremedies.com/how-to/get-rid-razor-burn-fast.html

http://www.rapidhomeremedies.com/how-to-get-rid-of-razor-burn-fast.html

http://www.howhunter.com/skin-care/get-rid-of-razor-bumps-fast/