Week 11 - Photosynthesis 1 Flashcards
What is a heterotroph?
An organism that cannot manufacture its own food and instead obtains its food and energy by taking in organic substances, usually plant or animal matter. All animals, protozoans, fungi, and most bacteria are heterotrophs.
What is photosynthesis?
The process by which plants, some bacteria and some protistans use the energy from sunlight to produce glucose from carbon dioxide and water. This glucose can be converted into pyruvate which releases adenosine triphosphate (ATP) by cellular respiration. Oxygen is also formed.
EXAM: What is the photosynthesis equation?
water + sunlight + carbon dioxide —> carbohydrates + oxygen.
What is special about photosynthetic bacteria eg. purple sulphur bacteria?
They can use alternative electron donors such as H2S, resulting in the equation 2H2S + hυ + CO2 —> (CH2O)n + 2S, where:
h = Planck’s constant (J/s); υ = frequency of light (cycles)
Photosynthesis provides carbohydrate
building blocks for what four things?
- biomass
- coal deposits
- crude oil
- gas deposits
What are the two main processes / reactions that occur during photosynthesis?
- Light-dependent reactions - Pigments absorb light energy and convert it to NADPH and ATP (and O2).
- Carbon-assimilation reactions - NADPH and ATP are used to reduce CO2 to form (CH2O)n.
Why is the palaside cell layer of the leaf so important?
They contain the majority of chloroplasts that will function in photosynthesis. Can contain up to a couple hundred chloroplasts, all conducting photosynthesis at the same time.
What is the main important component of chloroplasts, and why?
The thylakoid, and most importantly, its thylakoid membrane. It’s a lipid in nature, so it’s a bilipid-type membrane, and it’s very good for establishing gradients of ions across that membrane. This establishes electron flow, which then drives the production of ATP.
What’s the vascular bundle in plants?
They are the vascular system that allows the movement of things like water and other molecules around the plant. Sometimes visible to the naked eye.
What is the cuticle of the leaf?
The waxy covering, which does allow diffusion of oxygen and CO2 across it.
What is the role of chloroplasts?
The role of chloroplasts in plants is to capture light energy and convert it to chemical energy.
In which parts of the chloroplasts do the ‘light reactions’ and ‘dark reactions’ occur?
Light reactions - thylakoid membranes (lamellae)
Dark reactions - stroma (aqueous space)
Summary of light reactions (4 steps)?
- Light converts H2O to a good e- donor.
- Electron carriers pump H+ in as electrons flow to NADP+ (in the stroma).
- Energy of e- flow stored as electrochemical potential.
- ATP synthase uses electrochemical potential to synthesise ATP.
What are the three products of light synthesis?
ATP, NADPH, and oxygen.
What are the three protein complexes involved in the electron carrier chain of photosynthesis?
PSII, Cytochrome B, and PSI.
PS = Photosystems
Describe the path that the flow of electrons take in the electron carrier chain in photosynthesis?
- Split from water
- Through PSII via Mn4CaO5
- Into the ‘Q cycle’
- Through the intermediate Cytochrome B complex
- Onto Plastocyanin (a soluble molecule that carries electrons)
- Through PSI
- Onto ferredoxin
- Passed to NADP+ (final acceptor) to form NADPH
Describe the path that protons (or Hydrogen ions) take during the electron carrier chain process?
- Split from water
- Touches on PSII? Comes out as 2H+ and float around in the thylakoid lumen
- Two external protons (from the stroma) come in and enter into the ‘Q cycle’
- Pass through the Cytochrome B complex? and come out as 4H+ that float around in the thylakoid lumen
- H+ in the thylakoid lumen exit the thylakoid down their gradient through ATP synthase, generating ATP.
What is the main photoreceptor found in chloroplasts?
Chlorophyll.
What does chlorophyll’s structure allow it to do?
Allows it to absorb light and donate an electron to a nearby molecule, which is what’s important in this process, because basically those electrons are jumping between chlorophyll molecules and other pigments to a reaction centre, to establish that electron flow through those carrier proteins.
Secondary light absorbing pigments are called what? Which two are the most important?
Carotenoids.
• The two most important are:
– β-Carotene (absorb red-orange)
– Lutein (absorb yellow)
What is the secondary function of carotenoids?
They function as anti-oxidants - they can reduce oxidative stress within the plant, but also in animals etc that consume those plants.
What are photosystems?
- Light-absorbing pigments that are arranged in arrays, embedded in the thylakoid membrane.
- Plants have two types which act in tandem:
– Photosystem II (PSII) and Photosystem I (PSI). - Each have a unique photochemical reaction centre.
- Each is a multisubunit, transmembrane protein complex.
- Hundreds of each type per chloroplast.
- Each contains multiple antenna pigment molecules and a pair of reaction centre chlorophylls.
- Each contains a series of electron transfer molecules.
What are antenna chlorophyll? What do they do?
They are chlorophyll molecules bound to the proteins in the photosystems. They:
- Absorb light in the form of photons which leads to excitation, and
- They pass the electrons along from one molecule to another.
- Ultimately, they reach a specialised pair of chlorophyll molecules that sit in the photochemical reaction centre, and it’s those that transduce the light into the chemical energy and establish that electron flow.
What are light-harvesting complexes (LHCs)?
Arrangements of pigments that surround the reaction centre. The functional unit of these LHCs is a trimer, consisting of 36 molecules chlorophyll a (21 molecules) and chlorophyll b (15 molecules) and 6 lutein. In a monomer, we would have 7 chlorophyll a, 5 chlorophyll b, and two lutein, which kind of sit crossways structurally in the centre. These get excited by antenna chlorophyll that make up these LHCs - the antenna chlorophyll transfer energy directly to a neighbour, and this continues until it reaches that special chlorophyll pair that sits in the reaction centre.
