Chapter 6

Question 1

The process by which energy from the sun, in the form of shortwave radiation (PAR) is harnessed to drive a series of chemical reactions that result in the fixation of CO2 into simple sugars and the release of oxygen as a byproduct.

Answer 1

photosynthesis

Question 2

Where does C3 photosynthesis occur?

Answer 2

mesophyll cells

Question 3

What are the steps of C3 photosynthesis?

Answer 3

1. CO2 comes in and gets combined with RuBP, which is a 5 carbon molecule.
2. Catalyzed by rubisco, it gets split into 2 or 3 smaller molecules.
3. 3-PGA is made by this, but the plant uses ATP and NADPH from light reactions to turn it into G3P.
4. That’s used to make simple sugars for the plant.
5. Some more ATP is used to make new RuBP

Question 4

Total amount of energy made in photosynthesis:

Answer 4

gross photosynthesis

Question 5

This is the gross photosynthesis minus respiration.

Answer 5

Net photosynthesis

Question 6

The point where gross photosynthesis equals respiration, and net photosynthesis is zero.

Answer 6

light saturation point

Question 7

What’s the water potential for pure water?

Answer 7

0

Question 8

Water tends to move from areas of _____ water potential to _____.

Answer 8

higher; lower

Question 9

Why is water pulled into the root by the plant?

Answer 9

The water potential in the soil is highest, followed by the root, stem/leaf, and finally the atmosphere. So water wants to travel in that direction.

Question 10

What is the formula for water use efficiency?

Answer 10

carbon fixation/water loss in transpiration

Question 11

Plants in warmer environments generally use this type of photosynthesis.

Answer 11

C4

Question 12

Why can’t plants in warm environments just close their stomata during the day to prevent water loss?

Answer 12

The light reactions keep producing oxygen, but the oxygen has no way of escaping, so it binds to rubisco and breaks down RuBP.

Question 13

C4 leaves have this special type of cell to wrap around the xylem and phloem.

Answer 13

bundle sheath cell

Question 14

What are the steps to C4 photosynthesis?

Answer 14

1. CO2 comes in and binds to PEP (3 carbon).
2. Oxaloaceate (4 carbon) is formed.
3. Malate (4 carbon) is the end result.
4. The malate gets pulled into the bundle sheath cell, and a CO2 gets pulled off of it to go in the Calvin cycle.
5. Meanwhile, the naked 3 carbon molecule, pyruvate, heads back to the mesophyll.

Question 15

Where do dark reactions occur?

Answer 15

bundle sheath cells

Question 16

Why do dark reactions occur in the bundle sheath cells?

Answer 16

Because there’s no PEP for it to bind to, so oxygen buildup isn’t an issue.

Question 17

How does oxygen get to the dark reactions?

Answer 17

The malate kind of sneaks it in, and it gets pulled off as CO2.

Question 18

What’s different about CAM photosynthesis?

Answer 18

It occurs in plants like cacti, for starters. Also, it all happens in one cell, instead of two like in C4.

Question 19

Why don’t all plants use C4?

Answer 19

It’s not very efficient, and it has to happen across a narrower range of temperatures.