Lecture 14: Gas Exchange in Plants

Question 1

Why do organisms need to exchange materials between their cells and the environments? what is the role of diffusion in this process?

Answer 1

Organisms must conduct gas exchange with their environments in order to perform the necessary metabolic functions for life (photosynthesis and cellular respiration).
Diffusion allows for gas exchange between cells and their environments.

Question 2

What is the relationship between the size of an organism, its surface area and the ability of its cells to exchange materials with its environment?

Answer 2

The smaller the size of the organism, the larger the SA will be in relation to its body size, so more cells will be exposed to the environment and more diffusion can occur.

Question 3

Define gas exchange

Answer 3

the process of plants taking up the gases they need for metabolic processes (CO2, H2O and O2)

and the process of releasing waste gases by exchange

Question 4

Define cellular respiration

Answer 4

A metabolic process that requires the intake of O2 to create ATP and waste products: CO2 and H2O.

Question 5

What is the relationship between gas exchange and cellular respiration in organisms?

Answer 5

it is complementary, the waste products of one are the reactants of the other.

Question 6

How are photosynthesis and cellular respiration complementary metabolic processes?

Answer 6

1. CO2 and H2O are reactions for photosynthesis
2. Photosynthesis produces organic molecules (sugar), and O2 as a waste product.
3. O2 is used as a reactant for CR
4. CR produces ATP, and CO2 and H2O as waste products
5. CO2 and H2O are used as reactants for photosynthesis

Question 7

Describe root hairs and how they function in gas exchange

Answer 7

root hairs are thin, hair-like, branching projections that grow off of plant roots to increase the plant’s surface area (and therefore gas exchange abilities). In good soils, there are air pockets with which root hairs and roots can exchange gases (O2) for cellular respiration.

Question 8

Describe Lenticels and how they function in gas exchange

Answer 8

lenticels are located on the bark of woody-stemmed plants (ex. tree trunk surface) and allow for the gas exchange in living cells of phloem tissues.

similar to stomata but are always open and only in woody plants.

Question 9

Describe stomata and how they function in gas exchange

Answer 9

stomata are located on the surface of the plant stems/leaves to regulate the passage of gases into and out of the leaves and green stems of plants.
Stomata open and close for gas exchange in order for the molecules to bypass the waxy cuticle that prevents molecules from moving in and out of the surface.
stomata are controlled by the guard cells of the dermal tissue system.

Question 10

Describe the structure and function of a stoma and how it is able to open and close

Answer 10

• Stomata are pores in the stem/leaf surface that are flanked by 2 specialized cells (guard cells).
• guard cells change shape when water moves into or out of them and cause a stoma to open or close

Question 11

What triggers a stoma to open?

Answer 11

water entering the guard cells will make them turgid and open the stoma

Question 12

What triggers a stoma to close?

Answer 12

water leaving the guard cells will make them flaccid and close the stoma

Question 13

T or F: if a stoma is open, the guard cells are turgid. Why/why not?

Answer 13

True. the cells are highly specialized and when water enters the guard cells they become turgid/pressurized and bow out to open.

Question 14

T or F: if a stoma is closed, the guard cells are flaccid. Why/why not?

Answer 14

TRUE. When water exits the guard cells, they will become flaccid and not have the support to stay open and droop closed.

Question 15

How does the structure of a leaf facilitate gas exchange? What are the 3 structures involved in gas exchange?

Answer 15

Plant leaves maximize surface area to facilitate gas exchange by having many air spaces to allow for contact between air and cells.

air spaces allow gas exchange to occur in parts of leaves that are not in direct contact with the atmosphere.

1. palisade mesophyll tissues
2. spongy mesophyll tissues
3. stomata

Question 16

T or F: gases are transported long distances in plants? why/why not?

Answer 16

FALSE. All living cells must conduct gas exchange.

Question 17

environmental conditions that will trigger a stoma to close?

Answer 17

• drought/dry soil
• high temperature (evapotranspiration is higher)
• lack of light

Question 18

environmental conditions that will trigger a stoma to open?

Answer 18

• moisture
• low temperatures
• light –> photosynthesis requires gas exchange (must be open)
• [CO2] too low or [O2] too high inside leaf

Question 19

What are the two mesophyll tissues in plant leaves that function in gas exchange? describe them

Answer 19

1. palisade mesophyll tissue:
   - composed of PARENCHYMA cells
   - chloroplasts concentrated tightly at the leaf surface for photosynthesis (and gas exchange)
2. spongy mesophyll tissue:
   - composed of PARENCHYMA cells
   - looser packed with more air pores
   - sponginess allows the air to move around the leaf to allow for more gas exchange across cell surfaces as these tissues are deeper in the leaf structure and are not exposed to the environment – air pores allow for gas exchange within the leaf.

Question 20

What are the two mesophyll tissues in plant leaves that function in gas exchange? describe them

Answer 20

1. palisade mesophyll tissue:
   - composed of PARENCHYMA cells
   - chloroplasts concentrated tightly at the leaf surface for photosynthesis (and gas exchange)
2. spongy mesophyll tissue:
   - composed of PARENCHYMA cells
   - looser packed with more air pores
   - sponginess allows the air to move around the leaf to allow for more gas exchange across cell surfaces as these tissues are deeper in the leaf structure and are not exposed to the environment – air pores allow for gas exchange within the leaf.

Question 21

How do veins/vascular bundles function in plant leaves?

Answer 21

• made up of xylem and phloem tissues

- carry materials across distances of the plants

Question 22

How do veins/vascular bundles function in plant leaves?

Answer 22

• made up of xylem and phloem tissues
• carry materials across distances of the plants
• every part of the leaf has veins in contact with it bc those are the vascular tissues that bring necessities for all cell life.

Question 23

How does gas exchange occur in the living cells of the woody stems, branches, and roots of trees?

Answer 23

Gas exchange occurs everywhere
but, in woody plants, xylem cells are in the middle of the tree trunk and are dead at maturity so don’t require gas exchange
phloem cells are alive but are only on the surface so they can perform gas exchange.

Question 24

How does gas exchange occur in the living cells of the woody stems, branches, and roots of trees?

Answer 24

Gas exchange occurs everywhere
but, in woody plants, xylem cells are in the middle of the tree trunk and are dead at maturity so don’t require gas exchange
phloem cells are alive but are only on the surface so they can perform gas exchange.

Question 25

New roots undergoing primary growth will have root hairs or lenticels?

Answer 25

Root hairs to maximize surface area

Question 26

T or F: older, woody roots have root hairs AND lenticels? why/why not?

Answer 26

TRUE. so they can exchange gases through the thicker, woodier bark.

Question 27

What is a challenge faced by plants growing in water-logged soils?

Answer 27

There will not be much pore space for air and they will not be able to take up O2 for cellular respiration.