3.2 -photosynthesis Flashcards
What is the overall equation for photosynthesis?
Carbon dioxide + water —> glucose + oxygen
Define the term photophosphorylation
An endergonic reaction bonding a phosphate Ion to a molecules of ADP using energy from light making ATP
What are the two main stages of photosynthesis?
The light dependent stage
The light independent stage
Describe briefly what energy changes happen in the light dependent stage?
- The light dependent stage converts light energy into chemical energy via the photolysis of water which produces 2 protons and 2 electrons.
- the energy carried by electrons establishes a proton gradient across the thylakoid membrane
- the energy is used to phosphorylate ADP, which generates ATP
What happens in terms of energy change in the light independent stage of photosynthesis?
The ATP and reduced NADP reduce carbon dioxide and produce energy containing glucose
Where does photosynthesis take place?
In chloroplasts
Describe the structure of a chloroplast briefly
- chloroplasts are surrounded by a double membrane
- The inner membrane folds inwards to make a thylakoid lamellae
- these combine to form grana
- The stroma is the fluid filled interior bathing the thylakoids and grana
- starch grains
Where is the photosynthetic pigment stored in the chloroplast?
In the grana
Where did the reactions of the light dependent stage of photosynthesis take place?
In the grana
What do the light independent reactions of photosynthesis take place in a chloroplast?
In the stroma
Why do the starch grains in the chloroplast appear white in an electron micrograph?
Because the stain used for the electron micrograph (osmium tetroxide) binds to lipids and not carbohydrates.
What evidence do we have to indicate that chloroplasts are descended from cyanobacteria?
The base sequence of the small number of genes in chloroplasts indicate that they are descended from cyanobacteria
Where are chloroplasts found in a plant?
The leaves and the stem as they are exposed to light, especially in the palisade mesophyll, spongy mesophyll and guard cells.
What is the main organ of photosynthesis?
The leaf
What is the benefit of a leaf having a large surface area?
It can capture as much light as possible
What is the benefit of a leaf being thin?
Light penetrates right through the leaf
What is the benefit of a leaf having stomatal pores?
Allows carbon dioxide to diffuse into the leaf
What is the benefit of a leaf having air spaces in the spongy mesophyll?
Allows carbon dioxide to diffuse to the photosynthesising cells
What is the benefit of a leaf having space between palisade cells?
Allows carbon dioxide to diffuse to the photosynthesising cells
What is the benefit of cells having A transparent cuticle and epidermis and thin cellulose cell walls?
Light penetrates through to the mesophyll
What is the benefit of cells having Palisade cells with a large vacuole?
Chloroplasts form a single layer at the periphery of each cell so do not shade each other
What is the benefit of cells having palisade cells that are cylindrical, elongated and are right angels to the surface of the leaf?
- Can accommodate a large number of palisade cells
- Lights only has to penetrate through two epidermal cell walls and one Palisade cell wall before reaching chloroplasts (unlike if cells were stacked horizontally)
What is the benefit of chloroplasts having A large surface area?
Maximum absorption of light
What is the benefit of chloroplasts Being able to move within palisade cells?
- Chloroplasts can move towards the top of the cell on full days for maximum absorption of light
- If the light intensity is very high they move to the bottom of the cell protecting pigments from bleaching
What is the benefit of chloroplasts rotating within palisade cells?
Thylakoids maximise the absorption of light
What is the benefit of chloroplasts having pigments in the thylakoids forming a single layer at the surface of the thylakoid membrane?
Pigments maximise their absorption of light
What is the benefit of leafs having about five times as many chloroplasts in the palisade cells than spongy mesophyll cells?
Palisade cells are at the top of the leaf and they are more exposed to light than the spongy Mesophyll cells so chloroplasts can capture as much light as possible
List the structures in a leaf:
- cuticle
- upper epidermis
- palisade mesophyll
- spongy mesophyll
- lower epidermis
- stoma
- guard cells
What is a transducer?
It is something that changes energy from one form to another.
Why are biological transducers much more efficient than such artificial devices?
They waste less energy in the conversions that they make
How are chloroplasts transducers?
They turn energy in the photons of light into chemical energy made available through ATP and incorporated into molecules such as glucose.
What did Engelmanns experiment find?
He placed filamentous green alga in a suspension of evenly distributed motile aerobic bacteria and exposed them to a range of wavelengths of light.
He noticed that in blue and red light the bacteria clustered near the chloroplasts
He seduced that these wavelengths resulted in a high rate of photosynthesis which produced a lot of oxygen which attracted the bacteria.
Give some other examples of biological transducers
Conversion of heat, light and sound into electrical energy in sense organs.
The conversion of chemical energy into kinetic energy and heat in muscles.
What is a pigment?
It’s a molecule that absorbs specific wavelengths of light
Why is light energy and a chloroplast trapped by different photosynthetic pigments?
It allows a large range of wavelengths to be absorbed and is consequently more useful than if one pigment was used absorbing a small range of wavelengths
What are the two main classes of pigments in flowering plants?
1) chlorophylls
2) carotenoids
What are the main two forms of Pigment chlorophyll in plants?
1) Chlorophyll a
2) Chlorophyll b
What is the wavelength (peak) and pigment colour absorbed by pigment chlorophyll a?
Wavelength: 435, 670-680
Pigment colour: yellow-green
In what plants is chlorophyll a found?
All plants e.g misses, ferns, conifers, flowering plants
What is the wavelength (peak) and pigment colour absorbed by pigment chlorophyll b?
Peak wavelength: 480, 650
Pigment colour: blue-green
In what plants is chlorophyll b found?
Higher plants e.g conifers/flowering plants
What are the main two divisions of carotenoids found in plants?
1) beta-carotene
2) xanthophylls
What is the wavelength (peak) and pigment colour absorbed by pigment beta-carotene?
Peak wavelength: 425-480
Pigment colour: orange
What is the wavelength (peak) and pigment colour absorbed by pigment xanthophyll?
Peak wavelength: 400-500
Pigment colour: yellow
In what form of plants are beta-carotene and xanthophylls found?
Beta-carotene: all
Xanthophylls: most
What is phaeophytin?
It is a grey-blue breakdown product of chlorophyll which does not contain a magnesium ion.
It can absorb light but it’s role is transferring electrons in photo system 2 rather than light absorption.
Define the term absorption spectrum
A graph showing how much light is absorbed of different wavelengths.
Define the term action spectrum
A graph showing the rate of photosynthesis at different wavelengths.
In what regions do chlorophyll a and b absorb light in the absorption spectrum?
What wavelengths do they reflect?
Absorb light in the red and blue-violet regions of the absorption spectra.
Reflect light in green regions giving leaves their colour.