2.9 photosynthesis Flashcards
(13 cards)
how do you obtain water free of carbon dioxide?
boil and cool water
how to improve paper chromatography?
use thin layer chromatography for better results
what are autotrophs?
- organisms able to convert energy and derive nutrition from non-biotic sources to produce high energy molecules for biological use or storage
- plants who photosynthesise and chemotrophs who derive energy from deep sea volcanic vents
- autotrophs vs heterotrophs: dependent on other living organisms for energy and nutrition
explain the photosynthesis process
6CO2 + 6H2O –(SUNLIGHT)–> C6H12O6 + 6O2
- C: carbon is ‘fixed’ from CO2 and used to produce glucose
- H2: water is split; hydrogen used to help in production of glucose, O2 excreted as waste gas
- sunlight: light energy transferred to chemical energy stored in glucose molecule
- C6H12O6: used in respiration, stored as starch / used to build cell walls or cellulose
- metabolic pathways controlled by enzymes
2 phases
LIGHT DEPENDENT
- light energy used by chlorophyll to carry out photolysis (splitting) of water
- electrons released from photolysis become excited; gain energy converted from light energy
- energy from excited electrons used to produce high energy compounds (atp and reduced nadph)
LIGHT INDEPENDENT
- energy from high energy compounds used to reduce CO2 to produce C612O6
- carbon fixation: conversion of inorganic CO2 to organic molecules like glucose
how is oxygen produced in photosynthesis?
2H2O –(SUNLIGHT + CHLOROPHYLL)–> O2 + 4H+ +4e
- light energy used by chlorophyll (facilitator) to split water into oxygen, hydrogen ions (protons), electrons
how are carbohydrates and other compounds produced from carbon dioxide?
- ENERGY needed
- light dependent phase: light energy needed to generate high energy compounds (atp and reduced nadph)
- energy from these compounds used in calvin-benson cycle to convert CO2 –> g3p (glyceraldehyde 3 phosphate)
- g3p –> glucose –> other monosaccharides –> link together to form disaccharides and polysaccharides (in condensation reaction; form glycosidic bonds)
why do leaves and most plants appear green in colour?
- plant pigments like chlorophyll found on thylakoid membrane of chloroplasts in plant cells
- pigments absorb some light and reflect others
- chlorophyll absorbs red and blue light and reflects light in green wavelength
what is the absorption spectrum for and how does it work?
- specialised equipment can be used to shine light of different wavelength on leaf and determine absorption / reflection of light at different wavelength
- results can be plotted on a graph: absorption spectrum
what are the different pigments in leaves?
- photosynthetic pigments:
- 2 main types of chlorophyll: chlorophyll a & chlorophyll b - accessory pigments: absorb light at slightly different wavelength –> extend range of light absorption for photosynthesis
- chlorophyll is broken down first during senescence (deteriorating of plant w age) –> other pigments become more visible
- leaves turn yellow / reddish brown before shedding
how does carbon dioxide concentration / light intensity affect rate of photosynthesis?
- when carbon dioxide concentration / light intensity increases the rate of photosynthesis increases; at low levels it is the limiting factor
- at high levels of carbon dioxide concentration / light intensity further increases have no effect on rate of photosynthesis; another factor is limiting rate of photosynthesis (chloroplasts working at maximum efficiency, temp, enzymes)
- photosynthesis is enzyme-catalysed metabolic pathway
- CO2 is substrate for metabolic pathway; relationship is similar to how enzyme reactions are limited by substrate concentration
how does temperature affect rate of photosynthesis?
- photosynthesis is a metabolic pathway catalysed by enzymes; hence relationship is similar to how enzyme reactions are affected by temperature
- increase in temp gives molecules more kinetic energy –> substrates collide w active sites more frequently –> rate of photosynthesis increases
- as temp approaches optimum temp, enzymes begin to denature (active site changes to become non-functional) –> rate of photosynthesis increases more slowly and eventually peaks
- after optimum temp enzymes rapidly denature –> fast decrease in rate of photosynthesis as temp increases
how can you record rate of photosynthesis experimentally?
SHORT TERM:
- CO2 sensor –> determine changes in CO2 concentration in sealed chamber containing plant [can also use pH sensor as CO2 is slightly acidic in water]
- O2 probe –> measures concentration fo dissolved oxygen; use aquatic plant
LONG TERM:
- measure conc. of glucose / starch in leaf by measuring biomass
how did photosynthesis affect the earth over time?
- atmosphere, ocean, rock deposition
- primordial earth: highly reducing atmosphere w v. little oxygen
- prokaryotes w chlorophyll started photosynthesising; oxygen produced as by-product
- over time oxygen conc. in atmosphere slowly started to increase
- w evolution of plants, photosynthesis took place on larger scale and atmospheric oxygen levels started to increase until stabilised at 21%
- process of photosynthesis allows inorganic CO2 to enter ecosystem in organic forms
- organisms consume others –> derive carbon
- many marine organisms use carbon to form CaCO3, as seen in hard shells of molluscs and corals
- when they die, shells are deposited at bottom of ocean and over long periods of time are compressed to form limestone
