3.2 Photosynthesis (Part A) Flashcards
What are Autotrophs?
Organisms that are able to make their own food - using a source of energy to make complex organic molecules from inorganic raw materials.
What are the two main autotrophs?
Chemoautotrophs and Photoautotrophs
What are Chemoautotrophs?
Able to harness energy from exergonic reactions to synthesise their organic food.
An example of a Chemoautotroph?
Bacteria
What are Photoautotrophs?
Able to synthesise sugars from carbon dioxide and water, using sunlight as a source of energy
Which pigment traps the sunlight in Photoautotrophs?
Chlorophyll.
Examples of Photoautotrophs?
Green plants, algae
What is the definition of Photosynthesis?
The process by which green plants manufacture their carbohydrates in the chloroplasts from atmospheric carbon dioxide and water, in the presence of sunlight.
What is the Photosynthesis equation?
Carbon Dioxide + Water —–> Glucose + Oxygen
(light)
Where does Photosynthesis occur?
The ‘green parts’ of the plant that contain chlorophyll.
Where is chlorophyll found?
In chloroplasts.
Where are chloroplasts found?
In the mesophyll cells and guard cells of green leaves.
Which type of energy is trapped by chlorophyll in chloroplasts?
Sunlight energy.
What does ‘chloroplasts are transducers’ mean?
They contain chlorophyll, which absorbs light energy, and can convert it to chemical energy. This can then be made available as ATP, and then incorporated into molecules such as glucose.
How are leaves adapted for photosynthesis?
- The leaves have a large, flat surface, with chloroplasts located close to the top surface for maximum light absorption
- They allow gas exchange through surface pores called stomata - allow CO2 to diffuse into the leaf
- The leaf have a network of air spaces for gases to reach photosynthetic tissue
- The leaves have a thin structure, since light is only absorbed in the first mm of tissue.
How are palisade mesophyll cells adapted for photosynthesis?
- Have lots of chloroplasts - the sites of photosynthesis.
- Thin cellulose cell walls - light is absorbed into cell & absorbed more easily
- Chloroplasts can move around inside - maximum light.
- Elongated shape (in upright position) - allows larger numbers of cells to be packed in a leaf’s given area.
Structure of a chloroplast?
- Surrounded by a double membrane
- Inner membrane folds & forms thylakoids
- Thylakoids forms stacks called grana.
What is a photosynthetic pigment?
A molecule that absorbs a specific wavelength of light.
Why is it useful for different wavelengths of light to be absorbed by different photosynthetic pigments?
It allows for a large range of wavelengths to be absorbed.
What are the two main classes of photosynthetic pigments? (In flowering plants)
Chlorophylls & Carotenoids
What are the two different types of chlorophylls?
Chlorophyll a & Chlorophyll b
What are the two different types of carotenoids?
Beta Carotene & Xanthophylls
Which parts of the spectrum do Chlorophyll a & b absorb?
The light in the blue-violet and red parts.
Structure of chlorophylls?
- A complex ring structure
- A long hydrocarbon tail
- A magnesium atom at the centre of the ring
When do plants start to look yellow?
When there is a lack of magnesium in the soil - they can no longer make green chlorophylls.
What is the condition where plants produce insufficient chlorophyll?
Chlorosis - chlorotic leaves can be pale, yellow, or yellow-white
Which parts of the spectrum do carotenes and xanthophylls absorb?
The light in the blue-violet part.
What is an Absorption Spectrum?
A graph indicating how much light a particular pigment absorbs at each wavelength. (Does not indicate if they are actually used in photosynthesis.)
What is an Action Spectrum?
A graph showing the rate of photosynthesis at different wavelengths of light. - Can be produced by measuring the mass of carbohydrates produced at each wavelength.
What are the two main stages of Photosynthesis?
- The light dependent stage
- The light independent stage.
What are the particles in/on a thylakoid membrane called?
Photosystems
What do photosystems consist of?
- An antenna complex (a collection of accessory pigments)
- A reaction centre, containing 2 chlorophyll a molecules.
How many types of photosystems are there?
2 - Photosystem I and Photosystem II
Where does light harvesting take place?
On the thylakoid membranes
What does light harvesting involve?
- The absorption of various wavelengths of light by chlorophyll & associated pigments
- The energy transfer to reaction centres
What is in an antenna complex?
The pigment molecules in the thylakoid membranes, grouped in clusters of several hundred molecules.
What does the antenna complex do?
It harvests light energy & passes the excitation to the reaction centre.
