Plant Gas Exchange

Question 1

Autotroph

Answer 1

Something that converts inorganic molecules into organic molecules

Question 2

Example of an autotroph

Answer 2

Plants as photosynthesis creates glucose an organic molecule from carbon dioxide

Question 3

What is the equation for photosynthesis?

Answer 3

Water + carbon dioxide -> (light energy + chlorophyll) -> glucose + oxygen (+ATP)

Question 4

Where does photosynthesis occur

Answer 4

In the chloroplasts

Question 5

Where are the chloroplasts located

Answer 5

They are packed into the palisade mesophyll mostly and any other areas that are green

Question 6

Where does the water come from for photosynthesis?

Answer 6

The water comes from the soils, sourced by the roots

Question 7

Where does the CO2 come from for photosynthesis?

Answer 7

from the air, through the stomata

Question 8

What happens to the glucose?

Answer 8

1) transported around the plant as sucrose by the phloem and is used by the cells for aerobic respiration
2) stored as glucose energy in starch
3) to make cellulose for cell walls

Question 9

What happens to the oxygen?

Answer 9

1) Goes out through the stomata, into the air

2) used in aerobic respiration

Question 10

When does photosynthesis occur

Answer 10

Only daylight hours

Question 11

When does respiration occur in plants

Answer 11

All the time

Question 12

Waxy cuticle

Answer 12

Reduce water loss, transparent

Question 13

Palisade mesophyll layer

Answer 13

Main site of photosynthesis. Cells are deep, elongated and packed full of the chloroplasts which are able to move and arrange themselves in a position within the cell that gives maximum light absorption

Question 14

Spongy mesophyll layer

Answer 14

Cells contain few chloroplasts and are loosely packed Contains air spaces making it easier for gases to diffuse through the leaf. These cells in the spongy mesophyll are moist on their surfaces aiding in gas exchange surfaces of the spongy mesophyll cells provide a large surface area for gas exchange.

Question 15

What is the main gas exchange surface on a plant?

Answer 15

The leaf

Question 16

How do plants have a large surface area?

Answer 16

many air spaces as cells are not tightly packed

Question 17

How do leaves maintain a concentration gradient? For gas exchange

Answer 17

The palisade cells use carbon dioxide in photosynthesis and the oxygen diffuses down the the diffusion gradient into the air

Question 18

how are plants moist for gas exchange

Answer 18

There is a thin layer of water molecules that aid in the dissolving in diffusing of gases on the spongy mesophyll.

Question 19

Upper epidermis

Answer 19

Single layer of cells that’s transparent since no chloroplasts are present. There are not many stomata in the upper epidermis since the heat from direct sunlight would cause excessive evaporation.

Question 20

What are the gaps between cells called in a leaf?

Answer 20

Intercellular air spaces

Question 21

Lower epidermis

Answer 21

No waxy cuticle but large number of stomata which open to allow diffusion of gases. Water evaporates from the surfaces of the spongy mesophyll cells and leaves via stoma

Question 22

How can one identify the xylem compared to phloem?

Answer 22

Xylem is the top one and is darker with larger holes and and there is more inside it

Question 23

Guard cells

Answer 23

Control the opening and closing of stoma by surrounding the gap that is the stomata. Contains some chloroplasts.

Question 24

How do plants have a large surface area?

Answer 24

They have a large number of stomata and this maximises the area over which gases can diffuse and therefore the amount of the gases that diffuse

Question 25

What is the specific significance of a leaf being thin in regards to photosynthesis?

Answer 25

It means the light can penetrate through the leaf

Question 26

What is the specific significance of a leaf having a large surface area in regards to photosynthesis?

Answer 26

The maximum amount of light energy can be captured

Question 27

What is the specific significance of a leaf being transparent in the cuticle and upper dermis in regards to photosynthesis?

Answer 27

It means more light can be absorbed allowing a faster at photosynthesis

Question 28

What is the specific significance of palisade cells being elongated and packed full of moving chloroplasts in regards to photosynthesis?

Answer 28

There is an increased rate of photosynthesis as more light can be absorbed as chloroplasts can move to where there is most light.

Question 29

Describe a stomata

Answer 29

Found on the underside of the leaf, bordered by two guard cells

Question 30

Describe guard cells

Answer 30

Borders stomata. Contain chloroplast and found on Lower epidermis. Gases are exchanged between the air and the internal structures of the plant. 90% of water evaporation occur through the stomata

Question 31

What conditions does the opening of stoma depend on ?

Answer 31

Light intensity and water availability and other atmospheric conditions

Question 32

When do stoma open ?

Answer 32

Only in the day

Question 33

What are the guard cells like when the stoma are open vs closed?

Answer 33

They are turgid when open and otherwise plasmolysed

Question 34

Describe the closing of stoma

Answer 34

Potassium ions in the guard cells diffuse out passively into the epidermal cells, down their concentration gradient. Water moves out of the guard cells by osmosis. The guard cells are now plasmolysed and The stoma closes

Question 35

Describe the opening of stomata

Answer 35

The chloroplasts in the guard cells photosynthesise, producing ATP. This provides the energy for active transport of potassium ions into the guard cells from the surrounding epidermal cells. Stored starch is converted to malate which is negatively charged. the potassium ions and the mallate are soluble and therefore lower the water potential in the guard cells. As a result water enters the cells by osmosis and the guard cells expand. The thinner cell walls on the outside stretch, whereas the thicker walls on the inside stretch less causing a curved shape to be formed, creating a pore between two of these cells.

Question 36

Describe the stomata Peel method

Answer 36

Paint 1 cm squared of clear nail varnish on the underside of the leaf. Use a piece of Sellotape to remove the nail varnish with the imprint of stomata. Place the Sellotape on a slide and view under a microscope. Count the number of stoma in the field of view. Repeat three times in different fields of view and calculate a mean

Question 37

What should you do for reliability in experiments?

Answer 37

Do 3 repeats at least and calculate a mean

Question 38

What are the two ways to see how reliable your results are?

Answer 38

Using range bars and standard deviation

Question 39

When can you use range bars? What do large and small range bars Show?

Answer 39

When you have a small sample size of around 3. Large range bars show that there is a lot of variation around the mean. these results are therefore less reliable. This shows the repeats were not reproducible. Small range bars show there is little variation around the mean. These results are therefore more reliable and they show the repeats were reproducible

Question 40

When can you use standard deviation provide an indication of how reliable your results are?

Answer 40

When you have a large sample size

Question 41

What does standard deviation tell you?

Answer 41

It gives an indication of the spread of results around the mean. A large standard deviation means the results are less reliable. It allows you to identify anomalies

Question 42

How does standard deviation allow you to identify anomalies?

Answer 42

Your data should be within 2 standard deviations of the mean (or 95%….?) If it is outside this range it is regarded as anomalous.

Question 43

What are the limitations of comparing overlapping data?

Answer 43

As soon as you get overlapping data, you can’t significantly say that something has changed.