chapter 11 - photosynthesis

Question 1

what is the site of photosynthesis

Answer 1

The site of photosynthesis is the leaf.

Question 2

What is the structure of a leaf that helps to maximise photosynthesis

Answer 2

1-Has a large surface area that absorbs as much sunlight as possible
2-an arrangement of leaves on the plants that minimises overlapping and avoids shadowing of one leaf by another
3-Thin, therefore the diffusion distance for gases is kept short
4-Long narrow upper mesophyll cels packed with chloroplasts that collect sunlight
5-Numerous stomata for gas exchange so there is a short diffusion pathway
6-may air spaces in the lower mesophyll layer to allow for rapid diffusion of CO2 and O2
7-A network of xylem that bring water to the leaf cells and a phloem that carries away the sugars and assimilate produced during photosynthesis.

Question 3

What is the outline of photosynthesis (overall equation)

Answer 3

6CO2+6H2O=(light)=C6H12O6+6O2

Carbon dioxide + water = Glucose + Oxygen

Question 4

What is the light dependent reaction overall

Answer 4

In the light dependent reaction some of the light energy absorbed is conserved in chemical bonds. During the process and electron flow is created by the effect of light on chlorophyll,Causing water to split (photolysis) into protons and electrons and oxygen. The products are reduced NADP, ATP, and oxygen.

Question 5

What is the light independent reaction overall

Answer 5

In the light independent reaction protons (hydrogen ions) are used to produce sugars and other organic molecules.

Question 6

what captures light energy

Answer 6

Chloroplast pigments such as chlorophyll

Question 7

What is another word for the light independent reaction

Answer 7

The Calvin cycle

Question 8

The main two purposes of the light dependent reaction

Answer 8

1-The splitting of water into protons electrons and oxygen (hydrogen ions, hydroxide ions)
2-To add an inorganic phosphate molecule to ADP therefore making ATP.

Question 9

What is a primary pigment

Answer 9

eg chlorophyll A
P680(680nm wavelength) PSII
P700(700nm wavelength) PSI

Primary pigments are also known as a reaction centre

Question 10

What is an accessory pigment

Answer 10

eg chlorophyll B
eg carotene
eg xanthophylls

Accessory pigments help the primary pigments. They absorb light and channel the energy absorbed to the reaction sentence (primary pigments).

Question 11

What is the difference between primary pigments and accessory pigments

Answer 11

Accessory pigments can absorb wavelengths of light that primary pigments cannot absorb. Accessory pigments also surround the reaction centre (primary pigment)

Question 12

What is a photosynthetic pigment

Answer 12

A photosynthetic pigment is a molecule that absorbs different wavelengths of light to provide enough energy for photosynthesis they can exist as either primary or accessory pigments. They have different lights absorbance properties and are involved in the light dependent reaction

Question 13

Describe in full the light dependent reaction of photosynthesis

Answer 13

1-Light energy is absorbed bye chlorophyll molecules, PSII & PSI.
2-Electrons from the chlorophyll molecules are emitted as light is absorbed from the photosystems and the electrons are passed to electron accepter is at higher energy.
3-These electrons are passed down a series of electron carriers at decreasing energy levels. As the electrons are emitted an inorganic phosphate is added to ADP to produce ATP.
4-The ETC involves pumping hydrogen ions (protons) across the thylakoids membrane into the thylakoids space. The hydrogen ions move via ATP synthase molecules embedded in the thylakoids membrane back into the stroma. It is the movement of hydrogen ions That provides energy for photophosphorylation and the synthesis of ATP.
5-electrons from the higher energy level (PSII) Are also emitted as light is absorbed in the same way.
6-Electrons from the higher energy level I’ll post through a series of electron carriers at decreasing energy levels onto NADP with H plus ions. To produce reduced NADP.
7-water molecules are also split via light energy to produce electrons hydrogen ions and oxygen. These electrons are used to replace those lost from the chlorophyll molecules in the lower energy photosystems and hydrogen ions are used to reduce NADP.

Question 14

What is this in detail stages of the light independent reaction

Answer 14

1-RuBP is a five carbon compound and a carbon dioxide acceptor molecule. This compound combines with a molecule of carbon dioxide [carbon fixation] to produce two molecules of a three carbon compound called GP. This reaction is catalyzed by an enzyme called RuBisCo.
2-GP is then converted into a three carbon sugar called triose phosphate [TP]. a hydrogen atom is added to GP to form TP. this requires reduced NADP and ATP from the light dependent reaction. NADP is produced. ATP becomes ADP.
3-Some of the TP is converted to useful organic substances for example glucose and the rest is converted back into RuBP. The glucose can be converted to sucrose, starch or cellulose in plants. TP can also be used to synthesize glycerol, fatty acids or amino acids.

Question 15

How many TP molecules out of 12 TP molecules are used to regenerate six molecules of RuBP

Answer 15

10

Question 16

Why is it called the light independent reactions

Answer 16

Although the Calvin cycle does not require light energy, it does depend on the products of the light dependent stage. Which are ATP and NADPH.

Therefore if there is no light, the products of the light dependent stage do not form that for the Calvin cycle cannot take place.

Question 17

What are the three factors affecting the rate of photosynthesis

Answer 17

Light intensity [and wave length]

Carbon dioxide concentration

Temperature

Question 18

How will light intensity affect the rate of photosynthesis

Answer 18

If there is a limited amount of light intensity ATP and reduced NADP levels will fall as the light dependent reactions will slow.

Question 19

How will carbon dioxide concentration affect the rate of photosynthesis

Answer 19

If carbon dioxide concentration is limited that will be less GP and TP. RuBP levels will rise

Question 20

how will the temperature affect the rate of photosynthesis

Answer 20

Low temperature reduces enzyme reactions in the light independent reaction. At high temperatures enzymes may start to denature, reducing the amount of carbon dioxide fixation.

Question 21

The effect of light intensity on photosynthesis [graph]

Answer 21

On the Y axis is the rate of photosynthesis, on the X axis is light intensity

From A to B light intensity is the limiting factor
From B to C the rate of photosynthesis is at a constant. This is called the light saturation point. This means that light intensity is no longer the limiting factor and either carbon dioxide concentration or temperature is the limiting factor.

Question 22

The effects of carbon dioxide concentration on photosynthesis [graph]

Answer 22

On the Y axis is the rate of photosynthesis and on the x-axis is the carbon dioxide concentration

From a to B carbon dioxide concentration is the limiting factor, the amount of carbon fixation increases. At the carbon dioxide concentration saturation point RuBisCO is fully saturated therefore an increase in the concentration of carbon dioxide will not increase the rate of photosynthesis any further. Therefore carbon dioxide is no longer the limiting factor

Question 23

The effect of temperature on photosynthesis [graph]

Answer 23

low temperatures inhibits the enzymes of photosynthesis doubling the rate every 10°C causes a rise in the temperature to the optimum. A small increase in the temperature has a large affect on the rate of photosynthesis. Until the optimum temperature for photosynthesis has been reached. After a certain temperature the enzymes of photosynthesis denature and there is irreversible damage to the enzymes active site as a confirmational change has occurred. And the rate of photosynthesis will fall to zero.

This graph looks like a backwards Maxwell Boltzmann distribution curve

Question 24

What happens to the concentration of GP and TP in the light then in the dark then in the light again.

Answer 24

1) in the light. In the daylight there’s plenty of light at a constant level. NADPH and ATP I’ll constantly being made. GP and TP are being constantly synthesized
2) in the dark. The concentration of GP increases (builds up) as there is no NADPH to reduce and no ATP to phosphorylate and produce TP. NADPH and ATP Are products of the light dependent reaction. The concentration of TP decreases as it is being converted into RuBP.
3) in the light. NADPH and ATP Can be produced again in the light dependent reaction so TP can be made again again. The concentration of GP decreases as GP is being converted into TP therefore the concentration of TP increases.