Chapter 3: Photosynthesis

Question 0

How is the leaf adapted for photosynthesis?

Answer 0

• large surface area- collects as much light as possible.
• thin- short diffusion pathway.
• leaves arranged in such a way as to prevent overlapping and thus avoid shadowing.
• transparent cuticle and epidermis let light through to mesophyll cells.
• long, narrow upper mesophyll cells containing lots of chloroplasts.
• lots of stomata for gas exchange.
• stomata open and close in response to changes in light.
• lots of air spaces in lower mesophyll layer- allow diffusion of oxygen and carbon dioxide.
• xylem- brings water to leaf cells, phloem- carries sugars away.

Question 1

Where does photosynthesis take place?

Answer 1

• the leaf is the main photosynthetic structure.

* chloroplasts are the organelles in which photosynthesis takes place.

Question 2

What is the equation for photosynthesis?

Answer 2

6CO2 + 6H2O -> (light) C6H12O6 + 6O2

Question 3

What is photosynthesis?

Answer 3

Energy transformation in plants in which light energy is firstly transformed into electrical energy and then into chemical energy.

Question 4

Summarise the 3 stages of photosynthesis?

Answer 4

1. ) light energy is captured by chlorophyll pigments in the chloroplast.
2. ) light dependent reaction- light energy is converted into chemical energy. Electron flow is created from the effect of light on the chlorophyll and water is split to make electrons, protons and oxygen.
3. ) light dependent reaction- protons form light dependent reaction are used to reduce carbon dioxide into sugars and other organic molecules.

Question 5

What is oxidation?

Answer 5

Loss of electrons, loss of hydrogen and gain of oxygen.

Question 6

What is reduction?

Answer 6

Gain of electrons, gain of hydrogen and loss of oxygen.

Question 7

Explain the stages of making ATP in the light dependent reaction?

Answer 7

• light energy is absorbed by the chlorophyll molecule which excites a pair of electrons within it.
• electrons become so energetic that leave the chlorophyll molecule altogether and are taken up by an electron carrier.
• the chlorophyll molecule is not oxidised and the energy carrier is reduced.
• the electrons are now passed along a number of electron carriers that form a transfer chain the in thylakoid membrane.
• a series of oxidation-reduction reactions occur and the electrons lose some energy at each stage.
• this energy is combined with an ADP molecule and an inorganic phosphate to form ATP.