2.9 Photosynthesis

Question 1

photosynthesis?

Answer 1

Photosynthesis is a metabolic pathway. Carbon dioxide and along with water is used to produce carbohydrates. Oxygen is released as a waste gas.

Question 2

photolysis

Answer 2

release of electrons needed in other stages

Question 3

Most of the oxygen is excreted as a waste product

Answer 3

H2O → 4e- + 4H+ + O2

Question 4

It converts light energy into…

Answer 4

chemical energy contained in carbon compounds.

Question 5

Light dependent reactions

Answer 5

use light energy to produce ATP and to split water (photolysis), making H+ ions (ATP and H+ used in next set of reactions)

Question 6

Light independent reactions

Answer 6

use ATP and H+ ions to “fix” CO2, making glucose. The enzyme rubisco catalyzes this reaction series (most abundant enzyme on Earth).

Question 7

Glucose can be used by,,,

Answer 7

cell respiration or stored as starch

Question 8

pigments

Answer 8

absorb useful wavelengths of light - those that contain energy appropriate for photolysis in the light dependent reactions.

Question 9

chlorophyll?

Answer 9

pigment stored in chloroplasts, changes color of reflected light

Question 10

why leafs look green

Answer 10

absorbs red and blue light from white light, reflecting only green light

Question 11

Accessory pigments

Answer 11

allow some plants to take advantage of the green wavelengths of light - a competitive advantage or an advantage in low-light conditions, such as underwater.

Question 12

Why do leaves turn colour in the autumn?

Answer 12

Some leaves have accessory pigments which cannot normally be seen when chlorophyll is active.
When temperature cools down, chlorophyll breaks down before the accessory pigments, leaving them to show through.

Question 13

light intensity factor

Answer 13

When light intensity is increased the rate of photosynthesis increases therefore it is the limiting factor at low levels.
- At high levels of light intensity further increases have no effect on the rate of photosynthesis.

Question 14

co2 factor

Answer 14

When carbon dioxide concentration is increased the rate of photosynthesis increases therefore it is the limiting factor at low concentrations.

↑[CO2] = ↑ rate of reaction due to increased amt. of substrate binding to rubisco

• All rubsico molecules are saturated with CO2, therefore, this is the maximum rate carbon fixation. An increase in concentration of CO2 has no effect.

Question 15

temperature factor

Answer 15

• Increases in temperature give molecules more kinetic energy causing substrates to collide with active sites more frequently, this increases the rate of photosynthesis
• After the optimum temperature enzymes denature rapidly causing a fast decrease in the rate of photosynthesis as temperature increases further.

Question 16

Iron compounds in the oceans were oxidized:

Answer 16

The insoluble iron oxides precipitated onto the seabed.
Time and further sedimentation has produced rocks with layers rich in iron ore called the banded iron formations.

Question 17

Oxygen generation also allowed the formation of an…

Answer 17

ozone layer (O3). Ozone shielded the Earth from damaging levels of UV radiation. This, in turn, lead to the evolution of a wider range of organisms.

Question 18

Oxygen in the atmosphere lead to the production of…

Answer 18

oxidised compounds (e.g. CO2) in the oceans