Unit 5 - Energy transfers in and between organisms

what is the word equation for photosynthesis?

carbon dioxide + water —> glucose + oxygen

what is the balanced equation for photosynthesis?

6CO2 + 6H2O —> C6H12O6 + 6O2

what are the main stages of photosynthesis?

capturing of light energy by pigments such as chlorophyll
the light dependent reaction, where light energy is converted into chemical energy
the light independent reaction, where sugars and other organic molecules are produced

what is the role of ATP in organisms?

ATP is a molecule that temporarily stores and quickly releases energy for various cellular processes

what is the relationship between respiration and photosynthesis?

the products of photosynthesis, glucose and oxygen can be used as reactants in respiration to synthesise ATP
the products of respiration, carbon dioxide and water can then be used as reactants in photosynthesis

how are plant leaves adapted for photosynthesis?

large surface area to absorb sunlight
minimal overlapping to avoid shadowing
thin to keep diffusion distance short
transparent cuticle and epidermis to allow light to enter the leaves
chloroplasts packed into mesophyll cells to carry out photosynthesis
stomata for gas exchange taking in and out gases
xylem and phloem to transport reactants and products of photosynthesis between the leaves and the rest of the plant

what is the role of photosynthetic pigments?

absorb energy from certain wavelengths of light

what is the stroma?

is a fluid filled matrix in a chloroplast where the light-dependent stage of phtosynthesis takes place 

what are the grana, thylakoids and lamellae?

grana are stacks of flattened sacs called thylakoidsand they are jooined by membranes called lamellae

do chloroplasts have a single membrane or a double membrane?

a double membrane

what is the main function of chloroplasts and where are they usually found?

chloroplasts are the site of photosynthesis they are found in plant cells and they are mainly in the mesophyll tissues in leaves

what is the main pigment in photosynthesis?

chlorophyll

what is the site of the light dependent reaction and how is this region adapted for this function?

it takes place in the thylakoids

these are well adapted for light dependent reactions because 

1 they have a large surface area for chlorophyll and electron carriers in the electron transport chain 

2 they contain ATP synthase channels 

3 they are selectively permeable, allowing a proton gradients to be esablished for ATP production 

what are oxidation and reduction?

oxidation is when a substance loses electrons or gains oxygen

reduction is when a substance gains electrons or loses oxygen

what is the main reactants of the light dependent reaction?

water and light energy

what are the products of the light dependent reaction?

for non cyclic photophosphorylation are ATP, reduced NADP and oxygen

but in cyclic photophosphorylation is just ATP

what are the key stages of the light dependent reaction?

absorption of light by pigments
release of electrons from pigments
electron transfer along the electron transport chain
photolysis of water to provide protons and electrons
chemiosmosis 
production of ATP and reduced NADP

what is the role of chemiosmosis in photosynthesis?

is the diffusion of protons across the partially permeable thylahoid membrane down their gradient, through the ATP synthase channel

what is the role of the electron transport chain in the light dependent reaction?

it transfers the excited electrons from photosynthetic pigments to electron carriers, this transfer releases energy which is used to pump protons across the thylakoid membrane 

what is the equation for the photolysis of water?

2H2O + light energy —> 4H+ +4e- + O2

how is photolysis useful in photosynthesis?

photolysis produces electrons to replace these lost pigments, it produces that help set up the proton gradient that drives ATP synthesis, the protons and electrons are used to reduce NADP and produces oxygen

how is ATP produced in the light dependent reaction, including reference to ATP synthease and NADP?

ATP synthase catalyses the production of ATP from ADP and Pi this uses the energy from the flow of protons down their concentration gradient from the thylakoid space into the stroma through ATP synthase channels the protons are taken up by NADP in the stoma and along with the electrons produce reduced NADP

what are the products of the light dependent reaction?

ATP, reduced NADP and oxygen

where does the light dependent stage of photosynthesis take place?

in the stroma of chloroplasts

what are the reactants and products for the light independent stage of photosynthesis?

reactants are carbon dioxide, ATP and reduced NADP
products is glucose

what are the light independent reactions?

are a series of reactions in photosynthesis where carbon dioxide is fixed and glucose is produced

what enzyme catalyses the reaction between carbon dioxide and RuBP?

rubisco

what is the first step in the light dependent stage of photosynthesis?

carbon dioxide binds with a five carbon compound called RuBP to form an unstable six carbon compound but instantly breaks down into two three carbon GP

what is the second step in the light independent stage of photosynthesis?

energy from ATP and protons and electrons from reduced NADP are used to reduce GP to a phosphorylated three carbon TP

what is the role of TP in the light independent stage of photosynthesis?

most TP is used to regenerate RuBP using ATP from the light dependent reaction, the rest is used to produce organic molecules needed by the plant (glucose)

what are the three key steps in the light independent reactions?

fixation - carbon dioxide is fixed to from 3C GP
reduction - GP is reduced to TP using reduced NADP and ATP 
regeneration - RuBP is regenerated from TP and ATP

what happens to NADP after the light independent reaction?

NADP is reformed and goes back to the light dependent reaction to be reduced again

what are some of the organic molecules that TP can be converted to?

starch
sucrose
cellulose
glucose
lipids
amino acids
nucleotides

what are the five factors required for photosynthesis to occur?

presence of photosynthetic pigments
supply of carbon dioxide
supply of water
light energy
suitable temperature

what are the three main factors that affect the rate of photosynthesis?

light intensity
carbon dioxide concentration 
temperature

what is a limiting factor?

is a requirement for a physiological process that is in the shortest supply and increasing this factor allows the rate of this process to increase

describe how temperature affects the rate of photosynthesis

when temperature is a limiting factor the rate of photosynthesis initially increases as the temperature is increase until an optimum, at higher temperatures the rate of photosynthesis decreases

explain how temperature affects the light independent stage of photosynthesis specifically

as temperature increases initially enzyme and substrate molecules have more kinetic energy, increasing the reaction rates and GP, TP and RuBP concentrations, very high temperatures can denature enzymes preventing the light independent stage from proceeding

describe how light intensity affects the rate of photosynthesis

when light is a limiting factor the rate of photosynthesis increases as light intensity increases
but at higher light intensities, the rate of photosynthesis plateau and another factor becomes the limiting factor

explain the effect of light intensity on the rate of photosynthesis

increasing light intensity increases the rate of the light dependent stage, producing more ATP and reduced NADP this leads to more GP being converted to TP and increased RuBP regeneration

explain how carbon dioxide concentration affects the light independent stage and thus the rate of photosynthesis overall

low carbon dioxide concentrations reduce the amount of GP and TP due to less carbon dioxide being fixed this reduced the rate of photosynthesis overall

what is the light compensation point in photosynthesis?

is when the volume of oxygen produced and carbon dioxide absorbed in photosynthesis is balanced by the oxygen absorbed and the carbon dioxide produced by respiration