M5 - Photosynthesis and Respiration Flashcards
(39 cards)
Photosynthesis involves a number of _______ that absorb _____ energy.
Only chlorophyll participates directly in photosynthesis. It mainly absorbs ____ and ____ light. It reflects ____ light.
________ pigments can absorb wavelengths of light that chlorophyll cannot.
pigments
light
red and blue
green
Accessory Pigments
What do accessory pigments do?
What may shade tolerant plants also contain?
They pass light energy (photons) to chlorphyll a, broadening the spectrum that allow photosynthesis to take place.
Shade tolerant plants may also contain ANTHOCYANINS (red or purple pigments) thought to protect chloroplasts from brief exposure to high light levels.
What is the link between photosynthesis and respiration?
PHOTOSYNTHESIS provides the O2 and carbohydrates, proteins and fats either directly or indirectly for cellular respiration.
Waste products of cellular respiration (CO2 + H2O) are used by chloroplasts as raw materials for photosynthesis.
Chemical elements to life are recycled but energy is not - it flows into an ecosystem as sunlight and back out as heat.
What is chlorophyll ionisation?
Light energy excites electrons which are released, leaving +ve ions.
Describe the process of the light-dependent reaction of photosynthesis.
Chlorophyll molecules in the thylakoid membranes absorb light energy and become excited.
- Excited electrons are emitted from the chlorophyll molecule, which becomes photoionised.
Describe the process of Non-cyclic Photophosphorylation.
1) Photolysis
2) Electrons in PS II are excited and are transferred along a chain of electron carriers to PS I (to replace emitted excited electrons).
3) As electrons are carried along the electron transport chain energy is lost and is used to pump H+ across the thylakoid membrane.
4) H+ ions diffuse down a concentration gradient back across the membrane through ATP synthase, synthesising ATP (chemiosmosis).
5) Excited electrons from PS I are accepted by an electron carrier and transferred to NADP. H+ from water are also transferred to NADP - forming reduced NADP (NADPH).
What is chemiosmosis?
The flow of H+ ions down a conc gradient through ATP synthase forming ATP from ADP + Pi.
What is photolysis?
The splitting of water using light energy.
- Electrons from water molecules replace those lost from PS II.
- H+ ions and O2 gas released (O2 diffused through membrane because small).
Describe photosystems.
They contain pigments arranged in a funnel-shaped light harvesting cluster.
Pigments are held in place by proteins in the membrane.
Accessory pigments absorb photons of light and transfer the energy to the primary pigment (Chlorophyll a) - also known as the reaction centre.
There are two main photosystems: PS II and PS I.
Describe Cyclic photophosphorylation
- Only PSI involved.
- The electrons emitted from PSI are passed to a higher energy level where they are received by a second electron acceptor.
- Electrons then pass along a chain of electron carriers and return to PSI.
- This releases energy to form ATP.
- No reduced NADPH is made in this process.
(Refer to notes on Z-scheme - do not need to know, but need to understand).
What does the Calvin cycle do? Where does it occur? What does it require?
Metabolic pathway - reducing CO2 to carbohydrates (gaining H).
Occurs in the stroma of chloroplast.
Required ATP and NADPH from the light dependent reactions.
Describe the steps involved in the Calvin Cycle (one cycle).
Rubisco fixes CO2 and combines it with Ribulose Bisphosphate (RuBP) 5C to form 2 x Glycerate-3-phosphate (GP). 2x3C
GP is reduced to form 2 x Triose phosphate (TP) 2x3C and converting ATP –> ADP + Pi and NADPH –> NADP.
1/6 of C of TP goes to form organic molecules (e.g. glucose - 6 turns of the cycle needed)
5/6 of C of TP goes on to regenerate ribulose bisphosphate using ATP.
How many Calvin cycle turns are required to from 1 glucose molecule?
6 turns
What organic molecules can be produced from Triose Phosphate?
Monosaccharides, Disaccharides, Polysaccharides
Lipids, Proteins
What are the 3 main limiting factors of photosynthesis?
- Light intensity
- Temperature
- CO2 Concentration
Describe the effect of increased CO2 concentration.
As CO2 conc increases, rate of photosynthesis increases.
Because… increased rate of L-I reactions providing no other factor is limiting (e.g. low light causing stomata to close).
CO2 is limiting factor initially and then other factors become limiting factor when graph plateaus.
Describe the effect of light intensity on photosynthesis.
Increasing light intensity increases the rate of photosynthesis.
increases light intensity increases photoionisation and photolysis and so increased production of ATP and NADPH for L-I reaction.
Light causes stomata to open so CO2 can enter the leaf.
Describe the effect of temperature on photosynthesis.
Increased movement of H+ ions and production of ATP and NADPH, affecting both LD and LI reactions.
Increasing temperature increases enzyme controlled reactions up to optimum temperature. Above optimum temp, rate falls due to enzymes working less efficiently/denaturing. (ATP synthase, Rubisco)
Higher temp increases rate of transpiration which may lead to the closure of the stomata and decrease uptake of CO2 (limiting LI reaction).
Describe how pigments are separated using chromotography.
- Chromatography paper suspended in a solvent - solvent level below line/origin (2cm).
- Solvent moves up paper, serparating out pigments into individual colours.
- Paper removed before solvent reaches the top (1cm).
- A line is drawn along the solvent front.
How do you measure the rate of photosynthesis? (experiment)
Photosynthometer set up. (capillary tube connected to a syringe and scale - immersed in test tube).
Test tube containing waterweed and potassium hydrogencarbonate solution (providing CO2) immersed in a water bath to maintain contant temperature.
Plant kept in dark for two hours before experiment.
Light source switched on and left for 30 mins to allow air spaces in leaves to fill with O2.
O2 released by plant during photosynthesis and collects iin funnel end of capillary tube above plant. After 30 mins O2 is gently drawn up the capillary tube by withdrawing syringe until volume can be measured on scale (mm^3). Gas produced is then measured in a set amount of time.
Experiment repeated with varying conditions.
What is a coenzyme? What are the examples in respiration?
An electron carrier - NAD, FAD and Coenzyme A
Name the stages of Respiration and where they take place.
Glycolysis - Cytoplasm of cell
Link Reaction - matrix
Krebs Cycle - Matrix
Oxidative Phosphorylation - on the cristae.
Describe Glycolysis. What are the overall products?
One molecule of Glucose (6C) is phosphorylated to Glucose (Bis)Phosphate (6C). Using 2xATP.
This is unstable so splits into 2 x Triose phosphate (3C)
TP is then oxidised to Pyruvate, reducing NAD and forming two ATP molecules each (4xATP)
Net gain of 2 ATP, 2 NADH and 2 Pyruvate.
What happens to Pyruvate after glycolysis?
It is actively transported into the mitochondrial matrix.
