Plants And Food

Question 1

What is the equation for photosynthesis?

Answer 1

1. carbon dioxide + water -> glucose + oxygen (light and chlorophyll over and under arrow)
   6CO2 + 6H2O -> C6H12O6 + 6O2
2. Importance in converting light energy to chemical energy

Question 2

What is chlorophyll?

Answer 2

• A green pigment needed to absorb light energy

- Photosynthesis converts light energy into chemical energy

Question 3

How are leaves adapted for photosynthesis? 🍃🍃🍃🍃🍃🍃🍃🍃🍃🍃☀️☀️☀️☀️☀️☀️☀️☀️☀️☀️☀️☀️☀️☀️

Answer 3

1. LSF to absorb light efficiently.
2. Chloroplasts (containing chlorophyll).
3. Supply of water and carbon dioxide
4. Systems to carry away products of photosynthesis to other parts of the plant.
5. Thin flat structures supported by a lead stalk which can grow to allow the blade of the leaf to be angled to receive the maximum amount of sunlight.
6. Leaves are broad so there is a large surface area for diffusion

Question 4

How is the waxy cuticle adapted for its function?

Answer 4

• Reduces water loss by evaporation

- Prevents entry (barrier) to disease-causing microorganisms such as bacteria and fungi.

Question 5

How is the palisade layer adapted to its function? 🍃

Answer 5

-There are elongated palisade cells which are close to the source or light and filled with chloroplasts and so chlorophyll so main site of photosynthesis.

Question 6

How is the upper epidermis adapted for its function?

Answer 6

-Relatively transport and contains few chloroplasts to allow sunlight through easily to the photosynthetic cells.

Question 7

How is the spongy mesophyll layer adapted for its function?

Answer 7

• There a fewer chloroplasts (containing chlorophyll) to absorb any of the remaining sunlight
• This layer forms the main gas exchange surface by absorbing carbon dioxide and releasing oxygen and water vapour
• The air spaces increase the surface area for gas exchange allowing O2 and CO2 to diffuse in and out of cells in in and out of the mesophyll

Question 8

How is the lower epidermis adapted for its function?

Answer 8

-Contains may pores called stomata, these allow oxygen and water vapour to diffuse out of the leaf and allows carbon dioxide to diffuse into the leaf to reach the photosynthetic cells

Question 9

How are the guard cells adapted for its function?

Answer 9

1. The guard cells are highly specialised cells, which can alter their shape to open or close the stomata
2. At night the stomata close as there is no light, so no photosynthesis would be able to occur and so this prevent CO2 from entering and water from escaping and the plant drying out. Therefore as water is lost at night the guard cells move together closing the stomata
3. At day the guard cells become turgid, as they take up water by osmosis
4. In dry condition the stomata closes, this causes photosynthesis to stop (which is bad) but it prevents the plant from drying out and dying

Question 10

What are the limiting factors of photosynthesis?

Answer 10

• Light intensity
• Temperature
• Carbon dioxide concentration

Question 11

Why is light intensity a limiting factor?

Answer 11

• As light intensity increases, so does the rate of photosynthesis
• This is because light energy is needed to speed up the reaction
• However once the enzymatic reactions are carried out at a maximum velocity due to sufficient light, the rate plateaus

Question 12

Why is carbon dioxide a limiting factor?

Answer 12

• Carbon dioxide is needed as a substrate for photosynthesis
• This is why an increase in its concentration increases the rate of the reaction
• However once every enzyme is occupied with carbon dioxide a further increase fails to increase the rate
• Ans therefore the graph plateaus

Question 13

Why is temperature a limiting factor?

Answer 13

-As temperature increases so does the rate of the reaction until a certain temperature, after which a sudden drop is observed
-This is because initially the increase in temperature sped up the reaction as the particles were moving faster
-However beyond a certain temperature the enzymes become denatured which prevents further photosynthesis
(If there is cool temperature there is not enough kinetic energy for enzymes to carry out photosynthesis)

Question 14

What is the plant’s use for glucose?

Answer 14

• Respiration
• Sucrose: transport as main sugar carried in the phloem
• Starch: for storage
• Cellulose: another polymer which forms plant walls
• Lipids: membranes of all cells and energy store in many seeds and fruits e.g. in peanuts and olives
• Chlorophyll (and magnesium ions from the soil)
• Proteins and DNA (and mineral ions from the soil e.g. nitrates and phosphates)

Question 15

What is the use of magnesium ions for a plant and what is the deficiency?

Answer 15

Mg 2+

• Use: forms part of the chlorophyll molecule
• Deficiency: Chlorosis, leaves turn yellow

Question 16

What is the use of nitrate ions for a plant and what is the deficiency?

Answer 16

NO 3- / NH4 +

• Use: making amino acids, proteins, chlorophyll, DNA and many other compounds
• Deficiency: stunted growth, weak stem, older leaves turn yellow

Question 17

What is the use of potassium ions for a plant and what is the deficiency?

Answer 17

K+

• Use: needed for enzymes of respiration and photosynthesis to work
• Deficiency: leaves turn yellow with dead spots

Question 18

What is the use of phosphate ions for a plant and what is the deficiency?

Answer 18

PO4 3-

• Use: making DNA and many other compounds, part of cell membranes
• Deficiency: poor root growth and the younger leaves turn purple

Question 19

What is the result of a shortage of a particular mineral?

Answer 19

mineral deficiency disease

Question 20

How are minerals absorbed from the soil?

Answer 20

In the form of an ion

Question 21

How can you investigate if a particular plant is deficient?

Answer 21

• Plants can be grown in soil-free cultures (water cultures) as plants only take water and mineral ions from the soil for growth
• You could compare culture solution and so if you replace a mineral ion you would be deficient in that
• Hydroponics is growing plants in water culture solution
• Can determine by growing plants under selective conditions omitting single factors at a time and studying the plant’s growth characteristics

Question 22

How do you investigate photosynthesis?

Answer 22

1. Place a leaf in boiling water with forceps for 5-30 seconds, to arrest chemical reactions (i.e. as it denatures the enzymes) and to make the leaf permeable to iodine and ethanol
2. TURN the bunsen burner off as ethanol is highly flammable
3. Place the leaf in a boiling tube and boil it with ethanol and place it in a hot water bath for 5 minutes, the leaf should go pale yellow or colourless as the ethanol would have removed the green pigment, this allows the results of the iodine test to be seen more clearly
4. Wash the leaf off with cold water
5. Add iodine, and the areas where starch is present will go from brown iodine to bluey-black (dark)

Question 23

How do you destarch a leaf?

Answer 23

1. Place the plant in the dark for 2-3 days, and the plant will use up the starch stores in its leaves (since it was in the dark it would not have been able to photosynthesise and hence produce glucose and starch)
2. Add iodine and the leaf will NOT turn blue-black

Question 24

How do you test to see if a leaf needs carbon dioxide?

Answer 24

1. Place a plant in a close container which contains a chemical called soda lime which absorbs carbon dioxide from the air around the plant and in the jar
2. Add iodine to the leaf of the plant and it will not turn blue black as photosynthesis would not have been able to occur without carbon dioxide, so no starch produced even if there is a good light source, need CO2 for photosynthesis
   (Temperature would be a control variable)
   (The pot might be covered in a plastic bag because it stops bacteria and microorganisms from respiring)
   (If you had another pot with no soda lime it would be an experimental control)

Question 25

How do you test to see if a leaf needs chlorophyll?

Answer 25

1. Take a variegated leaf that has been exposed to light for a bit (record which areas are green and which are not)
2. Add iodine and only the areas that were green (i.e. areas that contain chlorophyll) will make the iodine turn form brown to blue-black as starch is present since photosynthesis occurred there, showing that chlorophyll is needed for photosynthesis

Question 26

How could you investigate the effect of light on net gas exchange from a leaf using hydrogen-carbonate indicator?

Answer 26

1. Place 10cm cubed of hydrocarbonate indicator solution at the bottom of each of the four boiling tubes.
2. Detach three large leaves from a suitable plant and placed in the tops of three of the tubes, each tube is sealed with a bung. Keep the fourth tube empty as a control
3. Place one tube in bright light, one tube in the dark (covered with silver foil), and the third covered with some translucent material to restrict the intensity of light reaching the leaf. The fourth tube without a leaf acts as a control
4. The four tubes are then left set up under a bright light for a few hours, and the colour of the indicator is recorded.
   5 Result: light (purple), dark (yellow), dim light (orange), control (orange)

Question 27

How does the hydrocarbonate indicator change with CO2?

Answer 27

• High concentration (more than 0.04%): yellow
• CO2 normal in air (0.04%): orange
• Low concentrations of CO2 (less than 0.04%): purple

Question 28

How are the stomata adapted for its function?

Answer 28

-They are laced on the lower epidermis, as if they were on the top the leaf would loose too much water, this would be because the stomata would be exposed to direct sunlight, which would produce a high rate of evaporation
-There is also less air movement on the underside of the leaves
This adaption that reduces water loss

Question 29

How do you measure the rate of photosynthesis?

Answer 29

1. Place a white light at a specific distance
2. Canadian pondweed is left to photosynthesise for a set amount of time (temperature, and time the pondweed was left to photosynthesise should be controlled)
3. Count the (oxygen) bubbles produced per minute
   OR let oxygen released collect in a capillary tube and the syringe used at the end of the experiment to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measure and this is proportional to the volume of O2 produced
4. The experiment above is repeated with the light source placed at different distances from the pondweed
   *This experiment can also be used to measure the effect of temperature (e.g. making the water a set temperature and then repeated but changing temperature) and CO2 on photosynthesis (bubbling CO2 into the test tube and then repeated by changing the concentration of CO2)

Question 30

Why do plants require mineral ions?

Answer 30

For growth

Question 31

How do plants exchange gases?

Answer 31

• By diffusion
  1. When plants photosynthesise they use up CO2 form the atmosphere and produce O2 as a waste product
  2. When plants respire they use up O2 and produce CO2 as a waste product. Therefore there are lost of gases mung to and fro in the plants and this movement happens by diffusion

Question 32

Explain, through an example, of how plants exchange goes by diffusion

Answer 32

1. When the plant is photosynthesising it uses up a lots of CO2 so there is hardly any inside the leaf. This makes more CO2 move into the leaf by diffusion (from an area of higher concentration to an area of lower concentration)
2. At the same time lots of O2 is being made as a waste product of photosynthesis. Some is used in respiration, and the rest diffuses out through the stomata (moving from an area of higher concentration to an area of lower concentration)

Question 33

How does the net exchange of gases depend of light intensity?

Answer 33

1. Photosynthesis only happens during the say (i.e. when there is light available). But plants must respire all the time day and night to get the energy they need to live
2. During the say (when light intensity is high) plants make more oxygen by photosynthesis than they use in respiration. So in daylight, they release oxygen. They also use up more carbon dioxide then they produce so they take in carbon dioxide
3. At night though (or when light intensity is low) plants only respire, there is not enough light for photosynthesis. This means they take in oxygen and release carbon dioxide