Photosynthesis 1 - Photosynthetic Organisms PDF

Prokaryotic Autotrophs Examples includes cyanobacteria, which is a blue-green algae Thrive on nitrogen and phosphate which can cause algal blooms which discolour water and may be toxic to other species Came into existence about 3.5 to 4 billion years ago and was first living thing t...

Prokaryotic Autotrophs Examples includes cyanobacteria, which is a blue-green algae Thrive on nitrogen and phosphate which can cause algal blooms which discolour water and may be toxic to other species Came into existence about 3.5 to 4 billion years ago and was first living thing to produce oxygen  Eukaryotic Autotrophs Examples include algae, plants, and photosynthetic protists These are organisms that have organelles called chloroplasts that contain chlorophyll Where is photosynthesis taking place in higher order plants? Leaves Mostly in spongy and palisade mesophyll Chloroplasts Thylakoids Chlorophyll molecules are the key Leaves  Transpiration The loss of water from leaves Pulls water up the plant from roots due to water cohesion Assists photosynthesis Moves substances (water, minerals, etc) to leaves where photosynthetic reactions occur Evaporative cooling effect – prevents inhibition or denaturation of photosynthetic enzymes  Control of Stomata Stomata are openings on surface of leaf Allow for the movement of gases (CO2 and water vapour) Controlled by sizes of guard cell  Control of Stomata a) Light activates specific receptors in guard cell membranes b) Results in stimulation of proton pumps that move protons out of the cell c) Creates electrochemical gradient that causes K+ ions to move into cell d) Water moves in by osmosis  Chloroplast Structure (Protein-rich fluid) (Attach grana) (A stack of thylakoids)  Location of Photosynthesis Occurs in the stroma, and the thylakoid membrane The thylakoid membrane contains: Light-gathering pigment molecules (chlorophyll) Electron transport chains Structure of thylakoid system greatly increases surface area and photosynthesis efficiency Plant Pigments Pigments are molecules that can absorb certain wavelengths of light while reflecting others Chlorophylls are easily excited by light and are the key to photosynthesis  Properties of Light Light (electromagnetic radiation) is a form of energy that travels in the form of wave packets called photons The amount of energy is inversely proportional to the wavelength (λ) E=1/λ The visible part of the electromagnetic spectrum ranges from 380 nm to 750 nm Electromagnetic Spectrum Effect of light on Atoms Light energy when directed on atoms can cause electrons to go to higher energy levels. Electrons at higher levels are unstable and will fall back down to their ground state  energy (in the form of light) given off as it falls  Chlorophyll Photosynthetic organisms contain the green- coloured pigment chlorophyll STRUCTURAL PARTS Head - Porphyrin ring Complex ring with carbon double bonds Ring contains a Mg atom Light excites electrons in the double bond orbitals Tail – Phytol Chain Hydrocarbon that helps to anchor and orient the molecule in the thylakoid membrane Chlorophyll a and b differ in the ‘R’ group that is attached at the head Chlorophyll Chlorophyll a and b Chlorophyll a – absorbs red light the best Chlorophyl b – absorbs violet-blue light the best Many of the green wavelengths are NOT absorbed and thus get reflected into our eyes  Prisms separate white light into different wavelengths (colours). Chlorophyll molecules absorb the red and blue ends of the spectrum but reflect the yellow and green parts. Caretenoid Pigments Beta carotene - specialized at absorbing particular wavelengths and reflect yellows red ranges Xanthophylls – absorb yellows, reflect oranges  Chlorophyll and accessory pigments Chlorophyll a is the only pigment that can transfer the energy of light to the carbon fixation reactions of photosynthesis – i.e. it’s electrons in the porphyrin head move to higher energy levels Chlorophyll b acts as an accessory pigment, absorbing photons that chlorophyll a absorbs poorly, or not at all Carotenoids, xanthophylls and anthocyanins act as accessory pigments Absorbance spectra Rate of oxygen production related to wavelengths of light absorbed Action Spectrum What causes “Autumn Leaves”? Synthesis of chlorophyll requires sunlight and warm temperatures Shortened daylight and cooler temperatures prevent nutrients from reaching leaves  chlorophyll production decreases Other pigments in the leaves will be left to reflect other colours of the spectrum In some leaves, concentration of sugars will increase  forms another pigment called anthocyanin  Anthocyanins Absorb blue-green, blue, and green light  reflect red light Not part of thylakoid membrane like other pigments are  they are dissolved in sap If the sap is more acidic then pigment appears bright red If the sap is less acidic then pigment appears more purple