Theme C: C1 Molecules - C1.3 Photosynthesis Flashcards
(12 cards)
overall word equation of photosynthesis
CO2 + H20 —(light)—> C6H12O6 +O2
what is the by-product of photosynthesis? what is reduced and oxidised in the process?
during photosynthesis water is split to give hydrogen and oxugen. oxygen is a by-product of photosynthesis: it is not needed by the plant and is released into the atmosphere.
the hydrogens released during the splitting of water reduce carbon dioxide to form glucose. water becomes oxidised to form O2.
plants, algae and cyanobacteria all carry out photosynthesis, thus they all release oxygen as a by-product
consider the types of pigments
why are leafs green?
chloroplasts are the only structures in a leaf that are actually green. plants contain a variety of pignments in the chloroplasts. this photosynthetic pigment that dominates in most plant species is the molecule chlorophyll. there are several different types of chlorophyll, and these produce the characteristic green colour of most plants - chlorophyll a and chlorophyll b are the most common.
there is also a group of pigments called carotenoids, they usually include the specific pigments known as carotene and xanthophyll. each of the pigments and their concentration are unique to a plant species.
how can we determine the pigments present in chloroplasts?
chromatography allows us to determine the pigments present in chloroplasts. pigments with higher Rf values are more soluble in the solvent being used, and they are often smaller in size. higher Rf value pigments have a lower affinity for the paper used in the chromatography activity.
what part of the electromagnetic spectrum do plants use?
plants make use of the same part of the electromagnetic spectrum that our eyes can see. we call this the visible portion of the spectrum.
The visible light spectrum includes many colours but, for the purpose of considering how plant pigments absorbs light energy, we are going to consider three regions of the spectrum:
* the red end of the spectrum
* the green middle of the spectrum
* the blue end of the spectrum.
Substances can do 1 of 2 things when they are struck by a particular wavelength (colour) of light. They can:
* absorb that wavelength (if so, energy is being absorbed and may be used)
* reflect that wavelength (if so, the energy is not being absorbed and you will see that colour).
what determines the ability of photoautotrophs to absorb light energy, and what absorbs it?
The ability of photoautotrophs to absorb light energy is determined by the pigments present on the membranes of chloroplasts. It is the pigments that absorb the light.
What are the absorption spectrum and the action spectrum?
The amount of light absorbed plotted against the wavelength of light produces the absorption spectrum for that pigment.
The action spectrum indicates the rate of photosynthesis at different wavelengths of light.
How can the rate of photosynthesis be calculated?
The rate of photosynthesis can be calculated from either the rate of oxygen produced or the rate of carbon dioxide used up.
What are the similarities and differences between absorption and action spectra?
Absorption spectrum
* Varies depending on type of photosynthetic pigment present
* Represents the amount of light energy being absorbed by the photosynthetic pigment
* For the plant, this spectrum represents the light absorbed by all the pigments present
* Chlorophylls a and b have a high absorption of light energy in the violet-blue and red light wavelengths
* Pigments like carotenoids absorb light energy at different wavelengths compared to chlorophyll a and b
* Other pigments are not as efficient at absorbing light energy as chlorophylls a and b
Action spectrum
* Varies depending on type of photosynthetic pigment present
* Represents the rate of the photosynthetic process being carried out by the pigment
* For the plant, this spectrum represents the rate of photosynthesis as a result of all the pigments present
* Chlorophylls a and b create a relatively high efficiency rate of photosynthesis
* Pigments like carotenoids allow photosynthesis at different wavelengths
* Other pigments are not as effective at achieving high rates of photosynthesis as chlorophylls a and b
what is meant by the excitation of electrons?
When a pigment absorbs light, the energy is used to raise an electron in the pigment to a higher energy level. This is known as excitation of electrons. Raising an electron to a higher energy level requires a specific amount of energy (or specific photons of light).
This explains why different pigments absorb different wavelengths of light: they each need a different wavelength to excite electrons.
Once the electrons are excited to a higher energy level, this energy can then be used to make chemical bonds. The net result is that light energy is transformed into chemical energy.
photons
Light energy behaves as if it exists in discrete packets called photons. Shorter wavelengths of light have greater energy within their photons than longer wavelengths. Photons can transfer their energy upon interaction with other particles. This transfer of energy occurs many times during photosynthesis.
