Photosynthesis• The discovery of

photosynthesis started when Jan Van Helmont began the research of this process in the mind-1640s.

• He had measured the mass of the soil used by a plant and the mass of the plant as it grew.

• After noticing that the soil mass was almost the same, he hypothesised that the mass or the growing plant must have come from the water, the only substance he added to the potted plant.

• In 1772, Joseph Priestley, then discovered that when he isolated a volume of air in an inverted jar and burn a candle in it, the candle would extinguish very quickly

• He further discovered that a mouse could similarly “injure” air. He then showed that the air that had been “injured” by the candle and also by the mouse could be restored by a plant.

• In 1778, Jan Ingenhousz, repeated Priestley’s experiments. He discovered that it was the influence of the sun and light on the plant that causes it to restore the air that saves the mouse.

• In 1780, Jean Senebier, showed that carbon dioxide was the “fixed” or “injured” air, and that it was taken up by plant in photosynthesis.

• Nicolas-Theodore de Saussure showed that the increase in mass of the plant as it grows is not only due to the carbon dioxide, but also to the intake of water. Thus the basic reaction by which photosynthesis is used to produce glucose was outlined.

• In 1845, Robert Mayer discovered that plants convert solar energy into chemical energy during photosynthesis.

• In 1905, Blackman discovered that photosynthesis involves two principal reactions- photochemical reaction (light-dependent) and biochemical reaction (light-independent)

• The first experiment to prove that the oxygen released during the photosynthesis of green plant comes from water performed by Robet Hill in 1937.

Leaf structure and function

• Cuticle – it prevents excessive water loss

• Palisade mesophyll– These cells are arranged

close together and located near the surface of the leaf.

– This is to receive maximum amount of light.

– It contains a lot of chloroplasts and are able to move about and arrange themselves to carry out maximum light absorption.

• Spongy mesophyll– Spongy mesophyll is made of

irregular shaped cells and contains fewer chloroplasts than palisade cells.

– They are arranged loosely and there are air spaces between them that connect the mesophyll with the stomata.

– These spaces allow water and carbon dioxide to diffuse through the leaf to the palisade cell.

– The irregular shape of the cells increase the internal surface area for gaseous exchange.

• Stomata– Carbon dioxide

diffuses into the leaf through the stomata. While oxygen diffuses out of the leaf via the same route.

– Each stomata has two guard cells which controls the size of the pore.

• Xylem– Water is

transported from the roots to the leaf through xylem.

• Phloem– Organic products

from the leaf are transported to the other parts of the plant through phloem.

Adaptation of plant

• Lamina or leaf blade– It is usually thin, flat and wide to allow the leaf

to absorb light.– It is also to allow more gas exchange involved

in photosynthesis• Vein

– It consists of vascular tissues, xylem and phloem

– Xylem transports mineral ions and water to leaf to be used during photosynthesis.

– Phloem transports products of photosynthesis to other parts of the plant.

• Petiole or leaf stalk– It makes sure that the leaf is held up to allow

maximum exposure to sunlight.

• Upper epidermis – it is thin and transparent, and is generally lack of

chloroplast.• Palisade mesophyll

– They are tightly packed cells and have a large number of chloroplasts.

– This is to trap as much light that comes through the epidermis.

• Spongy mesophyll– They are loosely packed cells and have large air

spaces between them.– This is to allow water and carbon dioxide to be

diffused easily into the cell.

• Lower epidermis– It contains guard cells to allow the opening and

closing of stomata. • Stomata

– Stomata can be found more in the lower epidermis than in the upper epidermis.

– This is where carbon dioxide move in and out of the leaf.

• Waxy cuticle– It is waterproof to ensure not much water is lost

during photosynthesis.– It is also transparent enough to let enough sunlight

in.

• The chloroplasts of the cactus are mostly found in the stems.

• This is because some of the cacti do not have leaves and some only grow small seasonal leaves that grow after it rains.

• Leaves with hairs help reduce water loss.

• Some plants such as Hakea sp. have sunken stomata in their leaves to reduce water loss during transpiration.

• For these kinds of plants, gaseous exchange occurs during night time.

• This is because it is hot during the day. This also helps in preventing too much water being lost during transpiration.

• The carbon dioxide is absorbed and stored during the night for these kinds of cacti. The carbon dioxide is used during the day when there is sunlight.

• Thorns on cactus reduce transpiration rate.

• The waxy coating on their stems and leaves help reduce water loss.

• Hibiscus is an example of plants living in this tropical weather.

• In order to allow maximum absorption of sunlight for the plants to carry out photosynthesis.

• A large number of chloroplasts are found on the palisade and spongy mesophyll cells.

• To allow maximum absorption of carbon dioxide, a large number of stomata are found in the lower epidermis of the leaf.

• Even so, not many stomata are found in the upper epidermis.

• This is because of its direct exposure to sunlight that can lead to too much water loss during transpiration.

• The duckweeds and water lilies are examples of floating aquatic plants.

• The leaves of duckweeds and water lilies are covered with thick and waxy cuticle.

• The function of cuticle is to repel water.• The thick and waxy cuticle also allows the

stomata to stay open.• Chloroplasts can only be found in the

upper epidermis to allow maximum absorption of sunlight.

The Mechanism of Photosynthesis

• The chloroplast consists of several structures which are related to photosynthesis.

• The structures are thylakoids, outer membranes, inner membranes and stroma.

• Thylakoid (grana) contains membranes that are important for photosynthesis.

• Thylakoid also contains chlorophyll which traps solar energy during photosynthesis.

• Thylakoid are arranged in stacks and they are called granum.

• Stroma is a gel-like matrix. The enzymes responsible for photosynthesis are found here.

• Photosynthesis happens in two stages.• The first stage is light reaction which

occurs only in the presence of light.• The next stage is dark reaction where light

is not needed but it can also occur in the presence of light.

• The light reaction takes place in the membrane of grana.

• During the light reaction, chlorophyll in the thylakoid captures light energy.

• Light energy, to split the water molecules into hydrogen ions (H+) and hydroxyl ions (OH-). The reaction is known as photolysis of water.

24H2O 24H+ + 24OH-

• The hydrogen ions then combine with the electrons released by chlorophyll to from hydrogen atom

• The energy released from the excited electrons is used to from energy-rice molecules of ATP.

24H+ + 24e- 24H

• The hydroxyl ion loses an electron to from a hydroxyl group.

• This electron is received by chlorophyll.

• The hydroxyl group then combine to from water and gaseous oxygen.

• Oxygen is released into the atmosphere and later used for cellular respiration.

24OH- 24OH + 24e-

24OH 12H2O + 6O2

• The ATP molecules and hydrogen atoms then move to the stroma to provide energy and reducing power.

• During the dark reaction, the hydrogen atoms are used to fix carbon dioxide in a series of reactions catalysed by photosynthetic enzymes.

• The overall reaction results in the reduction of carbon dioxide into glucose

6CO2 + 24H 6(CH2O) + 6H2O

6(CH2O) C6H12O6

• [CH2O] is the basic unit of glucose.

• Six units of [CH2O] combine to from one molecule of glucose.

• The glucose monomers then undergo condensation to from starch which is temporarily stored as starch granules in the chloroplasts.

6H2O + 6CO2 C6H12O6 + 6O2

Comparing and contrasting the lightreaction and dark reaction

The Factors Affecting Photosynthesis

• The rate of photosynthesis is affected by carbon dioxide, temperature, light intensity and water.

• Light intensity– Light intensity is the limiting factor at AB. – This is because between A and B, increasing

the light intensity increases the rate of photosynthesis.

– Between B and C, the rate of photosynthesis is constant (maximum).

– Between BC, either CO2 concentration or temperature is the limiting factor.

A

BC

• Concentration of carbon dioxide– Between DE, CO2 concentration is the the

limiting factor. – This is because between D and E, increasing

the CO2 concentration increases the rate of photosynthesis.

– Between EF, the rate of photosynthesis is constant (maximum rate).

– Between EF, either light intensity or temperature is the limiting factor.

D

EF

• Temperature– From 10oC to 35oC, the number of gas bubbles

released increases, but when the temperature increases from 35oC the number of bubbles released decreases until it became 0 at 50oC.

– Photosynthesis is catalysed by the photosynthetic enzymes and therefore changes in temperature will affect the rate of photosynthesis.

– The optimum temperature varies from the different species of plants, but most plants have an optimum temperature of between 25oC and 30oC.

– However, when the temperature is too high, the photosynthetic enzymes are destroyed and photosynthesis stops altogether.

A Caring Attitude towards Plants

• Plants are the primary producers that sustain all other life forms.

• Humans are in capable of making their own food.

• We depend directly or indirectly on plant for food supply.

• Through photosynthesis, plants absorb energy from the sun, carbon dioxide, water and minerals.

• They then give off water and oxygen.• Oxygen is the most important part of the air.

• Animals and other non-producers take part in this cycle through respiration.

• The cycles of photosynthesis and respiration help maintain the earth’s natural balance of oxygen, carbon dioxide and water.

• Latex, pigment and resin– Plant like Brazilian carnauba palm also

produce resin or wax that is an ingredient in car wax and candles so they look shiny.

– Colour pigment from parts of plants are used such as onion peel to get shade of light brown, tumeric to get shade of yellow and berries to get shade of pink and red.

• Oil palm– Palm oil comes from oil palm trees. Cooking

oil, soap and margarine are products that come from palm oil.

• Drug– Aspirin that is used in painkillers comes from the

bark of the white willow tree.– Quinine that comes from the quinine tree is used to

treat Malaria.– In Malaysia, there are lots of medicinal plants such

as Misai Kucing that is used traditionally to cure diabetes and Hempedu Bumi that can be used to cure high blood pressure.

• Fibre– Most of our clothes are made out of cotton.

Cotton fibre comes from the cotton plant. The fibre that comes from the jute plant is used to make ropes and sacks.

• Petroleum oil– Petroleum is formed from the decayed remains of

prehistoric marine animals and terrestrial plant.– It takes millions of years for petroleum to develop.– From petroleum, we can get gasoline, fuel, diesel

and tar.– Petroleum is also used to make plastic products

and synthetic rubber.

• Wood and wood products– Some furniture and wood products are made

out of wood that comes from trees.– Common trees that are used to make furniture

are Jati, Merbau and also rubber tree.

• Add aesthetic value– Plants make our surrounding more beautiful

with its flowers and green leaves.

• Reduce greenhouse effect– Plants control the quality of our air by

supplying oxygen. It lessens the greenhouse effect caused from the burning of fossil fuels.

• Prevent soil erosion– The plant’s roots help stabilise soil and

prevent erosion.– That’s why grass is often planted at the

slopes of hills.

• Water reservoirs– Forests act as water reservoirs and oxygen

tank, supplying water and oxygen to living things.

Technology Used in Food Production

• The rapid increase in Malaysia’s population imposes a greater demand on food supply.

• Because of this, greater supply of quality food needs to be provided.

• Although agriculture is an important sector in Malaysia, the production of certain foods is still not sufficient to support the greater demand.

• The government encourages consumption of food from diverse sources as well as developing new methods and techniques to improve the quantity and quality of food.

• Plant breeding– Plant breeding or cross breeding is a

technique which involves selective crossing of different varieties of plants to produce new varieties with beneficial characteristics.

– The new variety of plant inherits the beneficial characteristics of both parent plants.

– New plant varieties have increased nutritional value, higher yields and show greater resistance to diseases and climatic changes.

– For example, the most widely planted variety of oil palm is the Tenera hybrid variety

– It is bred by crossing the Dura variety with the Pisifera variety.

– Tenera hybrid variety produces fruits with thick mesocarp and more oil content.

• Animal breeding– Animal breeding is a method that involves the

cross-breeding of two different breeds of animals.

– Animals such as cows have been cross bred to enhance the yield of milk, meat and other products.

– The hybrid cattle called Mafriwal is a cross between Fresian cow and Sahiwal bull.

– Mafriwal produces more milk with low fat content.– Many breeds of goat, sheep, chicken and ducks

have also been crossbred in Malaysia.

• Biotechnology and tissue culture– Biotechnology has opened up new possibilities in

food production.– One of the branches of biotechnology is plant

tissue culture.– Plant tissue culture or micro propagation is an

important alternative to the more conventional method of plant propagation.

– It involves production of plants from very small plant parts.

– The propagated plants are exactly identical to their parent plant.

– In Malaysia, rubber, banana, oil palm, pineapple, papaya and orchid are also propagated by tissue culture.

• Soil management– Good soil will ensure continuous production of

crops well into the future.– In order to retain the nutrients in the soil, the crop

should be cultivated in a sustainable manner.– Sustainable soil management includes:

• Crop rotation to maintain and improve soil fertility• Ploughing to help increase aeration of the soil• Regular addition of fertilizers to return nutrients to the

soil• Adding organic matter to promote humus formation and

improves soil structure• Reducing soil erosion and leaching of nutrients from

the soil

• Direct seeding– Most farmers in Malaysia use the direct seeding

technique to plant paddy.– Using machines, seeds are sown directly into the

soil.– This technique is easier, faster to plant and it

requires less labour.– The product matures earlier by more than ten

days compared to the conventional transplanted paddy.

– Therefore, increasing the production of paddy.

• Biological control– Biological control is an approach of using natural

enemies of a pest or parasite to reduce its population.

– This programme is an alternative method to reduce and stop the use of chemicals such as pesticides, herbicides and insecticides.

– This method is safer to the environment.– Examples of successful biological control are

putting snakes and owls to control the rat population in oil palm plantation.

• Genetic engineering– Genetic engineering is a technique to enable the

characteristics of an organism to be altered by changing its genetic composition.

– This is a very useful and advanced way to increase the quantity and quality of food products.

– For example, beneficial genes from plant can be inserted into the DNA of animals and vice versa.

– The genetically modified organism otherwise known as GMO, is called a transgenic organism.

• Diverse protein sources– To diversify the sources of protein, the

consumption of rabbit meat, ostrich meat, quail meat, freshwater fish and prawns is encouraged.

– Rabbit meat is low in cholesterol and fat but high in protein.

– Freshwater fish like tilapia, jelawat and haruan are low in cholesterol.

– Fish protein are easy to digest and is important for growing child’s healthy development.

– Meanwhile, ostrich meat is very nutritious, low in fat and rich in protein.

• Different food sources– ‘Ulam’ is rich in vitamins, fibres and mineral ions.– Some of these ‘ulam’ are vital ingredients in

traditional and herbal medicines.– Examples of ‘ulam’ are pegaga, kacang botor and

petai– The efforts include the campaign of consuming

‘ulam’.– ‘Ulam’ is a vegetable salad that is eaten raw.– It consists of fresh leaves, fruits and other plant

parts.

• Hydroponics & aeroponics– Vegetables are important in our daily food intake/– An alternative method of planting vegetables is the

hydroponics method.– Hydroponics is a method of growing plants without

using soil.– First, the root of the plant is put in a solution.– This solution contains all the macronutrients and

micronutrients required for the plant to grow healthy.

– These plants are supported by a medium such as pebbles in a special container.

– The culture solution is aerated to provide enough oxygen for respiration.

– The water used in this method can be used again as it is less prone to evaporation.

Technological Development in Food Processing

• Food has to be processed so that it can last longer and safe for us to eat.

• The main purpose of food processing is to preserve food by overcoming the factors that cause food spoilage.

• There are a many things that can make good food turn bad, sometimes faster than usual.

• Among the two khown causes of food spoilage are:– Actions of microorganisms on food– The oxidation of food

• Actions of microorganisms– Decomposing bacteria and fungi act on

carbohydrates and proteins in food.– The actions will result in producing substances

like carbon dioxide, water, ammonia, hydrogen sulphide and other organic compounds.

– The presence of these substances subsequently spoils the food, making it toxic and poisonous for us to eat

• The oxidation– As for oily types of food, they become rancid

and start smelling and tasting differently as a result of oxidation.

– Spoiled food is harmful to the body and can cause food poisoning.

• Food is processed to diversify the uses of food substances.

• The production of food from raw materials can be diversified.

• Milk is a good example of how food processing has increased the various assortments of dairy products.

• Milk can be made into chocolate, cheese, yogurt and butter.

• Soya bean can be made into bean curd, tempe and soya souce.

• Cooking– Cooking is probably the easiest way to prevent

or delay food spoilage.– Heating food at high temperature can kill

microorganisms and denature the enzymes that cause the breakdown of food.

• Fermentation– Fermentation is the use of biological processes

to make food products, for instance, microorganisms are used to make yogurt and cheese.

– Fermentation of fruit juices produces ethanol which, at high concentrations, prevents the spoilage of juices.

– At the same time, the ethanol produces has a great commercial value.

– Traditional food such as tapai, is produces by the fermentation of glutinous rice or tapioca.

• Drying– Drying is one of the oldest methods of food

preservation.– This method involves removing enough moisture

from food to prevent its decay and spoilage.– Water content of properly dried food varies from

5 to 25 percent depending on the food.– Successful food drying depends on:

• Enough amount of heat to remove moisture, without cooking the food.

• Dry air to absorb the released moisture.• Adequate air circulation to remove the moisture.

• Pickling– Pickling vegetables and fruits with vinegar

prevents the growth of microorganisms.– This is because when food is kept in a low pH

solution, microorganisms cannot grow.

• Treating food with salt or sugar– Food is soaked in a concentrated salt solution or

boiled with sugar.– In this way, microorganisms lose water through

osmosis in a hypertonic solution and therefore, food is preserved.

• Pasteurisation is the process of killing most food-spoiling and pathogenic substances.

• This is done by heating the food to 63oC for 30 minutes or 72oC for 15 minutes, following by rapid cooling to below 10oC.

• Milk is preserved by pasteurisation to destroy bacteria such as Streptococcus lactis, which convert lactose in milk to lactic acid.

• This method of preservation retains the natural flavour of milk and nutrients like vitamin B.

• The pasteurized milk can then be refrigerated to last for a few days.

• Fruit juices and soups can also be preserved this way.

• Canning– Canning is an important, safe method for

preserving food by keeping foods in jars or similar containers.

– After that, they are heated to a temperature that destroys microorganisms that cause food spoilage.

– During the heating process of canning, air is driven out of the jar and as it cools off, a vacuum seal is formed.

– This vacuum seal prevents air from getting into the product, thus preventing the entry of the microorganisms.

• Refrigeration– Refrigeration is a common method employed at

home to keep food such as meat and fish from turning bad quickly.

– Food stored at the temperature below 0oC can remain fresh for a long period of time.

– The extremely low temperature prevents the growth of microorganisms such as bacteria, or germination of spores, thus preventing the food from spoilage.