Introduction to Photosynthesis (4.3.1)

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What organisms carry out photosynthesis?
Green plants, some bacteria, and algae.
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What does a plant do with the glucose molecules it produces?
They can either be respired to produce ATP which is needed for things like active transport. Or they can be built up into larger molecules and stored, or converted into structural molecules for plant growth.
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What are photoautotrophs?
They use light energy to make their own organic molecules.
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What is the compensation point?
The point where the amount of carbon dioxide released by respiration in a plant is completely reused in photosynthesis.
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What's the role of the stomata in PHS?
Can open and close using guard cells either side, allowing CO2 to diffuse in.
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What's the role of the upper epidermis in PHS?
Transparent, unspecialised cells allow light to pass through and reach the mesophyll cells.
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What is the role of palisade mesophyll in PHS?
Cells contain lots of chloroplasts for PHS. Cytoplasm is able to circulate around the cell, so light gets to all the chloroplasts.
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What is the role of spongy mesophyll in PHS?
Cells have many chloroplasts for photosynthesis. There are big air spaces between the cells to allow CO2 to diffuse quickly across the leaf.
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What is the role of the lower epidermis in PHS?
Contains the stomata and guard cells.
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What are the roles of the xylem and phloem in PHS?
Xylem carries water to the leaf cells for PHS. Phloem carries the sugars of PHS away from the leaf cells to those that need them.
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What are the main features of a chloroplast?
Double membrane, thylakoids, stroma, ribosomes, starch grains.
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What does the double membrane of the chloroplasts do?
The outer membrane is selectively permeable. The inner membrane is folded into an internal membrane network- lamellae.
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What are thylakoids?
Fluid-filling spaces enclosed by the lamellae. They can be stacked on top of each other to form grana. These provide a large surface area for the photosynthetic pigments to be located.
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What is stroma?
The background material of the chloroplast. All the necessary enzymes are found here. This is where the light-independent reactions occur.
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Why do chloroplasts usually contain starch grains?
They make glucose by photosynthesis and not all of it is needed for respiration, so it is converted into starch and stored.
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Why do chloroplasts contain their own DNA and ribosomes?
It is thought that chloroplasts once existed as single-celled organisms. They can still use these ribosomes to make some of the proteins (enzymes) for PHS using the genetic instructions from DNA.
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What are photosystems?
Different pigments that are arranged into funnel-shaped structures. They are held in place by proteins in the thylakoid membranes.
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What are the two types of photosystem?
Photosystem I- found mostly on the membranes between the grana. Photosystem II-found mostly on the granal lamellae.
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What type of chlorophyll-a is in photosystem II?
P680- absorbs light maximally at a wavelength of 680nm.
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What type of chlorophyll-a is in photosystem I?
P700- absorbs light maximally at a wavelength of 700nm.
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Where in the photosystem is the chlorophyll-a found?
The reaction centre.
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Give two accessory pigments.
Chlorophyll-b which absorbs light maximally at the blue end. Carotenoids, such as carotene.
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What do the accessory pigments do?
Pass on energy from the light they absorb to the chlorophyll-a at the reaction centre.
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Why is it useful for plants to have a range of pigments?
More types of light wave can be absorbed in total, so more energy available for PHS.
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How can an absorption spectrum graph be plotted?
The different pigments in PHS can be separated by chromatography. They can then be exposed to light of different wavelengths to see how much they absorb. This can then be plotted.
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How can an action spectrum graph be plotted?
Light of different wavelengths is projected onto aquatic green pondweed for a fixed time period. The oxygen produced by photosynthesis can be collected. The volume of oxygen collected is proportional to the rate of PHS. This can then be plotted.
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Card 2

Front

What does a plant do with the glucose molecules it produces?

Back

They can either be respired to produce ATP which is needed for things like active transport. Or they can be built up into larger molecules and stored, or converted into structural molecules for plant growth.

Card 3

Front

What are photoautotrophs?

Back

Preview of the front of card 3

Card 4

Front

What is the compensation point?

Back

Preview of the front of card 4

Card 5

Front

What's the role of the stomata in PHS?

Back

Preview of the front of card 5
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