A Basic Food ChainPlants absorb light from the sun, which is turned into energy to grow. We call these producers.

The vegetarian animals eat the plants, they are called primary consumers.

Secondary consumers prey on primary consumers.

DaurKarbon di alam

PHOTOSYNTHESIS

Photosynthesis is -

• conversion of light energy into chemical energy that is stored in organic compounds (carbohydrates > glucose)

• Used by autotrophs such as:– Plants– Algae– Some bacteria (prokaryotes)

MENGAPA FOTOSINTESIS PENTING BAGI KEHIDUPAN?

(1) karbohidrat sebagai hasil fotosintesis merupakan sumber energi bagi semua kehidupan;

(2) hasil fotosintesis merupakan bahan dasar sintesis berbagai senyawa organik yang diperlukan manusia, hewan dan kehidupan lainnya;

(3) pertumbuhan dan hasil tumbuhan sangat ditentukan oleh kecepatan dan efektivitas proses fotosintesis; dan

(4) dalam fotosintesis dihasilkan oksigen (O2) sebagai hasil samping yang sangat penting bagi kehidupan.

Why are plants green?

The electromagnetic spectrum

• A Red Object absorbs the blue and green wavelengths and reflects the red wavelengths

• pigment a compound that absorbs light– different pigments absorb different wavelengths of white light.

• chlorophyll is a pigment that absorbs red & blue light (photons) so green is reflected or transmitted.

• Chlorophyll is located in the thylakoid membranes

So, Plants are green because the green wavelength is reflected, not absorbed.

2 types of chlorophyll• Chlorophyll a – involved in light reactions

• Chlorophyll b – assists in capturing light energy – accessory pigment

• Carotenoids – accessory pigments – captures more light energy – Red, orange & yellow

Chlorophyll is the primary photosynthetic pigment

Accessory pigments

The electromagnetic wavelengths and the wavelengths that are absorbed by the chlorophyll

Where does photosynthesis

take place?

Plants

• Mainly occurs in the leaves:a.stoma - poresb.mesophyll cells

StomaMesophyllCell

Chloroplast

Stomata (stoma)Pores in a plant’s cuticle through

which water vapor and gases (CO2 & O2) are exchanged between the plant and the atmosphere.

Guard CellGuard CellCarbon Dioxide (CO2)

Oxygen (O2)

Found on the underside of Found on the underside of leavesleaves

StomStomaa

Mesophyll Cell of Leaf

Cell WallNucleusNucleus

Chloroplast

Central Vacuole

Photosynthesis occurs in these Photosynthesis occurs in these cells!cells!

Chloroplast

Organelle where photosynthesis takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected Thylakoid stacks are connected togethertogether

Partschloroplasts – double membrane organelle that absorbs

light energyThylakoids – flattened sacs contain pigment - chlorophyllGrana (pl: granum) – layered thylakoids (like pancakes)Stroma – solution around thylakoidsStomata – pore on underside of leaf where O2 is released

and CO2 enters

Thylakoid

Thylakoid Membrane

Thylakoid SpaceGranum

Grana make up the inner Grana make up the inner membranemembrane

energi sinar

6CO2 + 6H2O C6H12O6 + 6O2 Chlorophyll Chlorophyll in photosystems

absorb light energy andrelease electrons

Photosynthesis occurs in chloroplasts

Sintesis sukrosa dan pati

• Sintesis sukrosa di sitosol glukosa-1-fosfat+fruktosa-6-fosfat +ATP + 2H20

sukrosa + ADP + 3 Pi

• Sintesis pati di plastidaADPG +n(gluc) amilosa lebih besar +ADP

enzim sintetaseK+

Remember Redox Reaction

reduction/oxidation The transfer of one or more electrons from one reactant to another

Two types:1. Oxidation is the loss of e-

2. Reduction is the gain of e-

Oxidation Reaction

The loss of electrons from a substance or the gain of oxygen.

glucoseglucose

6CO2 + 6H2O C6H12O6 + 6O2

OxidationOxidation

Carbon Carbon dioxidedioxide WaterWater

OxygenOxygen

Reduction Reaction

The gain of electrons to a substance or the loss of oxygen.

glucoseglucose

6CO2 + 6H2O C6H12O6 + 6O2

ReductionReduction

The rate of photosynthesis would be the rate at which it can produce photosynthetic products (glucose). So it would mean the number of glucose molecules synthesised per unit of time, presumably seconds.

Methods to calculate the rate of photosynthesis: 1) Measuring the uptake of CO2

2) Measuring the production of O2

3) Measuring the production of carbohydrates4) Measuring the increase in dry mass

Factor affecting photosynthesis:Internal factors:

• Chlorophyll (amount)• leaves (age and anatomi), • demand of photosynthate

External factors (environmental): • temperature, • light, • carbondioxide, • water, • mineral elements.

Chlorophyll : The amount of chlorophyll present has a direct relationship witth the rate of photosynthesis because this pigment which is photoreceptive and is directly involved in trapping light energy .

Leaf age and anatomy : Newly expanding leaves show gradual increase in rate of photosynthesis and the maximum is reached when the leaves achieve full size. Chloroplast functions decline as the leaves age. Rate of photosynthesis is influenced by variation in (i) number , structure and distribution of stomata,(ii)size and distribution of intercellular spaces (iii)relative proportion of palisade and spongy tissues (iv)thickness of cuticle etc.

Demand for photo synthate : Rapidly growing plants show increased rate of photosynthesis in comparison to mature plants. When demand for photosynthesisis lowered by removal of meristem the photosynthetic rate declines.

• Light : The rate of photosynthesis increases with increase in rate of intensity oflight or rate of photosynthesis is directly proportional to light intensity. Except on a cloudy day light is never a limiting factor in nature.

• Temperature : Very high and very low temperature affect the rate of photosynthesis adversely. Rate of photosynthesis will rise with temperature from 5°-37°C beyond which there is a rapid fall, as the enzymes involved in the process in the dark reaction get inactive at the temperature. Between 5°-35°C, with every 10°C rise in temperature rate of photosynthesis doubles or Q10 is 2 (Q = quotient).

Carbon dioxide : Carbon dioxide being one of the raw materials for photosynthesis its concentration affects the rate of photosynthesis markedly. Because of its very low concentration (0.03%) in the atmosphere, it acts as limiting factor in natural photosynthesis. At optimum temperature and light intensity, if carbon dioxide supply is increased the rate of photosynthesis increases markedly.

• Water : Water has an indirect effect on the rate of photosynthesis. Loss of water in the soil is immediate the felt by the leaves which close down the stomata thus hampering the absorption of CO2 from the atmosphere. This causes decline in photosynthesis

Mineral elements : Some mineral elements like copper, manganese, chloride etc. which are components of photosynthetic enzymes or magnesium as a component of chlorophylls also affect the rate of photosynthesis indirectly by affecting the synthesis of photosynthetic enzyme and chlorophyll respectively.

Concept of limiting factors :

• This known as law of limiting factors or law of minimum shown by Blackman (1905): when a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of slowest factor

When light, carbon dioxide, and temperature are optimum, the rate of photosynthesis is maximum. if one of the factors become suboptimal and the other factors remain optimal, the rate of the process decline substantially.

ChemosynthesisWhen plants utilise light energy to reduce carbon dioxide to

carbohydrates photosynthetic autotrophs. When organisms utilise chemical energy released during

biological oxidation of certain inorganic substances to reduce carbon dioxide to carbohydrate chemosynthetic autotrophs.

Many colourless bacteria use chemical energy to reduce carbon dioxide for carbohydrate synthesis chemosynthesis.“the method of carbon assimilation when the reduction of CO2 is carried out in darkness, utilising the energy obtained from oxidations of inorganic substances.

(i) Nitrifying bacteria. Nitrosomonas oxidises NH3 to NO2(ii) Sulphur bacteria(iii) Iron bacteria(iv) Hydrogen and methane bacteria